
/* pngrtran.c - transforms the data in a row for PNG readers
 *
 * libpng 1.0.1
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
 * Copyright (c) 1996, 1997 Andreas Dilger
 * Copyright (c) 1998, Glenn Randers-Pehrson
 * March 15, 1998
 *
 * This file contains functions optionally called by an application 
 * in order to tell libpng how to handle data when reading a PNG.
 * Transformations which are used in both reading and writing are
 * in pngtrans.c.
 */

#define PNG_INTERNAL
#include "png.h"

#ifdef PNG_READ_COMPOSITE_NODIV_SUPPORTED
/* With these routines, we avoid an integer divide, which will be slower on
 * many machines.  However, it does take more operations than the corresponding
 * divide method, so it may be slower on some RISC systems.  There are two
 * shifts (by 8 or 16 bits) and an addition, versus a single integer divide.
 *
 * Note that the rounding factors are NOT supposed to be the same!  128 and
 * 32768 are correct for the NODIV code; 127 and 32767 are correct for the
 * standard method.
 *
 * [Optimized code by Greg Roelofs and Mark Adler...blame us for bugs. :-) ]
 */

   /* fg and bg should be in `gamma 1.0' space; alpha is the opacity */
#  define png_composite(composite, fg, alpha, bg) \
     { png_uint_16 temp = ((png_uint_16)(fg) * (png_uint_16)(alpha) + \
                        (png_uint_16)(bg)*(png_uint_16)(255 - \
                        (png_uint_16)(alpha)) + (png_uint_16)128); \
       (composite) = (png_byte)((temp + (temp >> 8)) >> 8); }
#  define png_composite_16(composite, fg, alpha, bg) \
     { png_uint_32 temp = ((png_uint_32)(fg) * (png_uint_32)(alpha) + \
                        (png_uint_32)(bg)*(png_uint_32)(65535L - \
                        (png_uint_32)(alpha)) + (png_uint_32)32768L); \
       (composite) = (png_uint_16)((temp + (temp >> 16)) >> 16); }

#else  /* standard method using integer division */

   /* fg and bg should be in `gamma 1.0' space; alpha is the opacity */
#  define png_composite(composite, fg, alpha, bg) \
     (composite) = (png_byte)(((png_uint_16)(fg) * (png_uint_16)(alpha) + \
       (png_uint_16)(bg) * (png_uint_16)(255 - (png_uint_16)(alpha)) + \
       (png_uint_16)127) / 255)
#  define png_composite_16(composite, fg, alpha, bg) \
     (composite) = (png_uint_16)(((png_uint_32)(fg) * (png_uint_32)(alpha) + \
       (png_uint_32)(bg)*(png_uint_32)(65535L - (png_uint_32)(alpha)) + \
       (png_uint_32)32767) / (png_uint_32)65535L)

#endif /* ?PNG_READ_COMPOSITE_NODIV_SUPPORTED */


/* Set the action on getting a CRC error for an ancillary or critical chunk. */
void
png_set_crc_action(png_structp png_ptr, int crit_action, int ancil_action)
{
   png_debug(1, "in png_set_crc_action\n");
   /* Tell libpng how we react to CRC errors in critical chunks */
   switch (crit_action)
   {
      case PNG_CRC_NO_CHANGE:                        /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                               /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
         break;
      case PNG_CRC_QUIET_USE:                             /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                           PNG_FLAG_CRC_CRITICAL_IGNORE;
         break;
      case PNG_CRC_WARN_DISCARD:    /* not a valid action for critical data */
         png_warning(png_ptr, "Can't discard critical data on CRC error.");
      case PNG_CRC_ERROR_QUIT:                                /* error/quit */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         break;
   }

   switch (ancil_action)
   {
      case PNG_CRC_NO_CHANGE:                       /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                              /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
         break;
      case PNG_CRC_QUIET_USE:                            /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                           PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_ERROR_QUIT:                               /* error/quit */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_WARN_DISCARD:                      /* warn/discard data */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         break;
   }
}

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
/* handle alpha and tRNS via a background color */
void
png_set_background(png_structp png_ptr,
   png_color_16p background_color, int background_gamma_code,
   int need_expand, double background_gamma)
{
   png_debug(1, "in png_set_background\n");
   if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
   {
      png_warning(png_ptr, "Application must supply a known background gamma");
      return;
   }

   png_ptr->transformations |= PNG_BACKGROUND;
   png_memcpy(&(png_ptr->background), background_color,
      sizeof(png_color_16));
   png_ptr->background_gamma = (float)background_gamma;
   png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
   png_ptr->transformations |= (need_expand ? PNG_BACKGROUND_EXPAND : 0);
}
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
/* strip 16 bit depth files to 8 bit depth */
void
png_set_strip_16(png_structp png_ptr)
{
   png_debug(1, "in png_set_strip_16\n");
   png_ptr->transformations |= PNG_16_TO_8;
}
#endif

#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
void
png_set_strip_alpha(png_structp png_ptr)
{
   png_debug(1, "in png_set_strip_alpha\n");
   png_ptr->transformations |= PNG_STRIP_ALPHA;
}
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
/* Dither file to 8 bit.  Supply a palette, the current number
 * of elements in the palette, the maximum number of elements
 * allowed, and a histogram if possible.  If the current number
 * of colors is greater then the maximum number, the palette will be
 * modified to fit in the maximum number.  "full_dither" indicates
 * whether we need a dithering cube set up for RGB images, or if we
 * simply are reducing the number of colors in a paletted image.
 */

typedef struct png_dsort_struct
{
   struct png_dsort_struct FAR * next;
   png_byte left;
   png_byte right;
} png_dsort;
typedef png_dsort FAR *       png_dsortp;
typedef png_dsort FAR * FAR * png_dsortpp;

void
png_set_dither(png_structp png_ptr, png_colorp palette,
   int num_palette, int maximum_colors, png_uint_16p histogram,
   int full_dither)
{
   png_debug(1, "in png_set_dither\n");
   png_ptr->transformations |= PNG_DITHER;

   if (!full_dither)
   {
      int i;

      png_ptr->dither_index = (png_bytep)png_malloc(png_ptr,
         (png_uint_32)(num_palette * sizeof (png_byte)));
      for (i = 0; i < num_palette; i++)
         png_ptr->dither_index[i] = (png_byte)i;
   }

   if (num_palette > maximum_colors)
   {
      if (histogram != NULL)
      {
         /* This is easy enough, just throw out the least used colors.
            Perhaps not the best solution, but good enough. */

         int i;
         png_bytep sort;

         /* initialize an array to sort colors */
         sort = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_palette
            * sizeof (png_byte)));

         /* initialize the sort array */
         for (i = 0; i < num_palette; i++)
            sort[i] = (png_byte)i;

         /* Find the least used palette entries by starting a
            bubble sort, and running it until we have sorted
            out enough colors.  Note that we don't care about
            sorting all the colors, just finding which are
            least used. */

         for (i = num_palette - 1; i >= maximum_colors; i--)
         {
            int done; /* to stop early if the list is pre-sorted */
            int j;

            done = 1;
            for (j = 0; j < i; j++)
            {
               if (histogram[sort[j]] < histogram[sort[j + 1]])
               {
                  png_byte t;

                  t = sort[j];
                  sort[j] = sort[j + 1];
                  sort[j + 1] = t;
                  done = 0;
               }
            }
            if (done)
               break;
         }

         /* swap the palette around, and set up a table, if necessary */
         if (full_dither)
         {
            int j;

            /* put all the useful colors within the max, but don't
               move the others */
            for (i = 0, j = num_palette; i < maximum_colors; i++)
            {
               if ((int)sort[i] >= maximum_colors)
               {
                  do
                     j--;
                  while ((int)sort[j] >= maximum_colors);
                  palette[i] = palette[j];
               }
            }
         }
         else
         {
            int j;

            /* move all the used colors inside the max limit, and
               develop a translation table */
            for (i = 0, j = num_palette; i < maximum_colors; i++)
            {
               /* only move the colors we need to */
               if ((int)sort[i] >= maximum_colors)
               {
                  png_color tmp_color;

                  do
                     j--;
                  while ((int)sort[j] >= maximum_colors);

                  tmp_color = palette[j];
                  palette[j] = palette[i];
                  palette[i] = tmp_color;
                  /* indicate where the color went */
                  png_ptr->dither_index[j] = (png_byte)i;
                  png_ptr->dither_index[i] = (png_byte)j;
               }
            }

            /* find closest color for those colors we are not using */
            for (i = 0; i < num_palette; i++)
            {
               if ((int)png_ptr->dither_index[i] >= maximum_colors)
               {
                  int min_d, k, min_k, d_index;

                  /* find the closest color to one we threw out */
                  d_index = png_ptr->dither_index[i];
                  min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                  for (k = 1, min_k = 0; k < maximum_colors; k++)
                  {
                     int d;

                     d = PNG_COLOR_DIST(palette[d_index], palette[k]);

                     if (d < min_d)
                     {
                        min_d = d;
                        min_k = k;
                     }
                  }
                  /* point to closest color */
                  png_ptr->dither_index[i] = (png_byte)min_k;
               }
            }
         }
         png_free(png_ptr, sort);
      }
      else
      {
         /* This is much harder to do simply (and quickly).  Perhaps
            we need to go through a median cut routine, but those
            don't always behave themselves with only a few colors
            as input.  So we will just find the closest two colors,
            and throw out one of them (chosen somewhat randomly).
            [I don't understand this at all, so if someone wants to
             work on improving it, be my guest - AED]
            */
         int i;
         int max_d;
         int num_new_palette;
         png_dsortpp hash;
         png_bytep index_to_palette;
            /* where the original index currently is in the palette */
         png_bytep palette_to_index;
            /* which original index points to this palette color */

         /* initialize palette index arrays */
         index_to_palette = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)(num_palette * sizeof (png_byte)));
         palette_to_index = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)(num_palette * sizeof (png_byte)));

         /* initialize the sort array */
         for (i = 0; i < num_palette; i++)
         {
            index_to_palette[i] = (png_byte)i;
            palette_to_index[i] = (png_byte)i;
         }

         hash = (png_dsortpp)png_malloc(png_ptr, (png_uint_32)(769 * 
            sizeof (png_dsortp)));
         for (i = 0; i < 769; i++)
            hash[i] = NULL;
/*         png_memset(hash, 0, 769 * sizeof (png_dsortp)); */

         num_new_palette = num_palette;

         /* initial wild guess at how far apart the farthest pixel
            pair we will be eliminating will be.  Larger
            numbers mean more areas will be allocated, Smaller
            numbers run the risk of not saving enough data, and
            having to do this all over again.

            I have not done extensive checking on this number.
            */
         max_d = 96;

         while (num_new_palette > maximum_colors)
         {
            for (i = 0; i < num_new_palette - 1; i++)
            {
               int j;

               for (j = i + 1; j < num_new_palette; j++)
               {
                  int d;

                  d = PNG_COLOR_DIST(palette[i], palette[j]);

                  if (d <= max_d)
                  {
                     png_dsortp t;

                     t = (png_dsortp)png_malloc(png_ptr, (png_uint_32)(sizeof
                         (png_dsort)));
                     t->next = hash[d];
                     t->left = (png_byte)i;
                     t->right = (png_byte)j;
                     hash[d] = t;
                  }
               }
            }

            for (i = 0; i <= max_d; i++)
            {
               if (hash[i] != NULL)
               {
                  png_dsortp p;

                  for (p = hash[i]; p; p = p->next)
                  {
                     if ((int)index_to_palette[p->left] < num_new_palette &&
                        (int)index_to_palette[p->right] < num_new_palette)
                     {
                        int j, next_j;

                        if (num_new_palette & 1)
                        {
                           j = p->left;
                           next_j = p->right;
                        }
                        else
                        {
                           j = p->right;
                           next_j = p->left;
                        }

                        num_new_palette--;
                        palette[index_to_palette[j]] = palette[num_new_palette];
                        if (!full_dither)
                        {
                           int k;

                           for (k = 0; k < num_palette; k++)
                           {
                              if (png_ptr->dither_index[k] ==
                                 index_to_palette[j])
                                 png_ptr->dither_index[k] =
                                    index_to_palette[next_j];
                              if ((int)png_ptr->dither_index[k] ==
                                 num_new_palette)
                                 png_ptr->dither_index[k] =
                                    index_to_palette[j];
                           }
                        }

                        index_to_palette[palette_to_index[num_new_palette]] =
                           index_to_palette[j];
                        palette_to_index[index_to_palette[j]] =
                           palette_to_index[num_new_palette];

                        index_to_palette[j] = (png_byte)num_new_palette;
                        palette_to_index[num_new_palette] = (png_byte)j;
                     }
                     if (num_new_palette <= maximum_colors)
                        break;
                  }
                  if (num_new_palette <= maximum_colors)
                     break;
               }
            }

            for (i = 0; i < 769; i++)
            {
               if (hash[i] != NULL)
               {
                  png_dsortp p;

                  p = hash[i];
                  while (p)
                  {
                     png_dsortp t;

                     t = p->next;
                     png_free(png_ptr, p);
                     p = t;
                  }
               }
               hash[i] = 0;
            }
            max_d += 96;
         }
         png_free(png_ptr, hash);
         png_free(png_ptr, palette_to_index);
         png_free(png_ptr, index_to_palette);
      }
      num_palette = maximum_colors;
   }
   if (png_ptr->palette == NULL)
   {
      png_ptr->palette = palette;
   }
   png_ptr->num_palette = (png_uint_16)num_palette;

   if (full_dither)
   {
      int i;
      int total_bits, num_red, num_green, num_blue;
      png_size_t num_entries;
      png_bytep distance;

      total_bits = PNG_DITHER_RED_BITS + PNG_DITHER_GREEN_BITS +
         PNG_DITHER_BLUE_BITS;

      num_red = (1 << PNG_DITHER_RED_BITS);
      num_green = (1 << PNG_DITHER_GREEN_BITS);
      num_blue = (1 << PNG_DITHER_BLUE_BITS);
      num_entries = ((png_size_t)1 << total_bits);

      png_ptr->palette_lookup = (png_bytep )png_malloc(png_ptr,
         (png_uint_32)(num_entries * sizeof (png_byte)));

      png_memset(png_ptr->palette_lookup, 0, num_entries * sizeof (png_byte));

      distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
         sizeof(png_byte)));

      png_memset(distance, 0xff, num_entries * sizeof(png_byte));

      for (i = 0; i < num_palette; i++)
      {
         int r, g, b, ir, ig, ib;

         r = (palette[i].red >> (8 - PNG_DITHER_RED_BITS));
         g = (palette[i].green >> (8 - PNG_DITHER_GREEN_BITS));
         b = (palette[i].blue >> (8 - PNG_DITHER_BLUE_BITS));

         for (ir = 0; ir < num_red; ir++)
         {
            int dr, index_r;

            dr = abs(ir - r);
            index_r = (ir << (PNG_DITHER_BLUE_BITS + PNG_DITHER_GREEN_BITS));
            for (ig = 0; ig < num_green; ig++)
            {
               int dg, dt, dm, index_g;

               dg = abs(ig - g);
               dt = dr + dg;
               dm = ((dr > dg) ? dr : dg);
               index_g = index_r | (ig << PNG_DITHER_BLUE_BITS);
               for (ib = 0; ib < num_blue; ib++)
               {
                  int d_index, db, dmax, d;

                  d_index = index_g | ib;
                  db = abs(ib - b);
                  dmax = ((dm > db) ? dm : db);
                  d = dmax + dt + db;

                  if (d < (int)distance[d_index])
                  {
                     distance[d_index] = (png_byte)d;
                     png_ptr->palette_lookup[d_index] = (png_byte)i;
                  }
               }
            }
         }
      }

      png_free(png_ptr, distance);
   }
}
#endif

#if defined(PNG_READ_GAMMA_SUPPORTED)
/* Transform the image from the file_gamma to the screen_gamma.  We
 * only do transformations on images where the file_gamma and screen_gamma
 * are not close reciprocals, otherwise it slows things down slightly, and
 * also needlessly introduces small errors.
 */
void
png_set_gamma(png_structp png_ptr, double scrn_gamma, double file_gamma)
{
   png_debug(1, "in png_set_gamma\n");
   if (fabs(scrn_gamma * file_gamma - 1.0) > PNG_GAMMA_THRESHOLD)
      png_ptr->transformations |= PNG_GAMMA;
   png_ptr->gamma = (float)file_gamma;
   png_ptr->screen_gamma = (float)scrn_gamma;
}
#endif

#if defined(PNG_READ_EXPAND_SUPPORTED)
/* Expand paletted images to rgb, expand grayscale images of
 * less then 8 bit depth to 8 bit depth, and expand tRNS chunks
 * to alpha channels.
 */
void
png_set_expand(png_structp png_ptr)
{
   png_debug(1, "in png_set_expand\n");
   png_ptr->transformations |= PNG_EXPAND;
}
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
void
png_set_gray_to_rgb(png_structp png_ptr)
{
   png_debug(1, "in png_set_gray_to_rgb\n");
   png_ptr->transformations |= PNG_GRAY_TO_RGB;
}
#endif

#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
/* Convert a RGB image to a grayscale of the given width.  This would
 * allow us, for example, to convert a 24 bpp RGB image into an 8 or
 * 16 bpp grayscale image. (Not yet implemented.)
 */
void
png_set_rgb_to_gray(png_structp png_ptr, int gray_bits)
{
   png_debug(1, "in png_set_rgb_to_gray\n");
   png_ptr->transformations |= PNG_RGB_TO_GRAY;
   /* Need to do something with gray_bits here. */
   png_warning(png_ptr, "RGB to GRAY transformation is not yet implemented.");
}
#endif

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
void
png_set_read_user_transform_fn(png_structp png_ptr, png_user_transform_ptr
   read_user_transform_fn)
{
   png_debug(1, "in png_set_read_user_transform_fn\n");
   png_ptr->transformations |= PNG_USER_TRANSFORM;
   png_ptr->read_user_transform_fn = read_user_transform_fn;
}
#endif

/* Initialize everything needed for the read.  This includes modifying
 * the palette.
 */
void
png_init_read_transformations(png_structp png_ptr)
{
   int color_type;

   png_debug(1, "in png_init_read_transformations\n");
   color_type = png_ptr->color_type;

#if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
   if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
   {
      if (color_type == PNG_COLOR_TYPE_GRAY)
      {
         /* expand background chunk. */
         switch (png_ptr->bit_depth)
         {
            case 1:
               png_ptr->background.gray *= (png_uint_16)0xff;
               png_ptr->background.red = png_ptr->background.green =
               png_ptr->background.blue = png_ptr->background.gray;
               break;
            case 2:
               png_ptr->background.gray *= (png_uint_16)0x55;
               png_ptr->background.red = png_ptr->background.green =
               png_ptr->background.blue = png_ptr->background.gray;
               break;
            case 4:
               png_ptr->background.gray *= (png_uint_16)0x11;
               png_ptr->background.red = png_ptr->background.green =
               png_ptr->background.blue = png_ptr->background.gray;
               break;
            case 8:
            case 16:
               png_ptr->background.red = png_ptr->background.green =
               png_ptr->background.blue = png_ptr->background.gray;
               break;
         }
      }
      else if (color_type == PNG_COLOR_TYPE_PALETTE)
      {
         png_ptr->background.red   =
            png_ptr->palette[png_ptr->background.index].red;
         png_ptr->background.green =
            png_ptr->palette[png_ptr->background.index].green;
         png_ptr->background.blue  =
            png_ptr->palette[png_ptr->background.index].blue;

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
        if (png_ptr->transformations & PNG_INVERT_ALPHA)
        {
#if defined(PNG_READ_EXPAND_SUPPORTED)
           if (!(png_ptr->transformations & PNG_EXPAND))
#endif
           {
           /* invert the alpha channel (in tRNS) unless the pixels are 
              going to be expanded, in which case leave it for later */
              int i;
              for (i=0; i<(int)png_ptr->num_trans; i++)
                 png_ptr->trans[i] = 255 - png_ptr->trans[i];
           }
        }
#endif

      }
   }
#endif

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   png_ptr->background_1 = png_ptr->background;
#endif
#if defined(PNG_READ_GAMMA_SUPPORTED)
   if (png_ptr->transformations & PNG_GAMMA)
   {
      png_build_gamma_table(png_ptr);
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
      if (png_ptr->transformations & PNG_BACKGROUND)
      {
         if (color_type == PNG_COLOR_TYPE_PALETTE)
         {
            int num_palette, i;
            png_color back, back_1;
            png_colorp palette;

            palette = png_ptr->palette;
            num_palette = png_ptr->num_palette;

            if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
            {
               back.red = png_ptr->gamma_table[png_ptr->background.red];
               back.green = png_ptr->gamma_table[png_ptr->background.green];
               back.blue = png_ptr->gamma_table[png_ptr->background.blue];

               back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
               back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
               back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
            }
            else
            {
               double g, gs;

               switch (png_ptr->background_gamma_type)
               {
                  case PNG_BACKGROUND_GAMMA_SCREEN:
                     g = (png_ptr->screen_gamma);
                     gs = 1.0;
                     break;
                  case PNG_BACKGROUND_GAMMA_FILE:
                     g = 1.0 / (png_ptr->gamma);
                     gs = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
                     break;
                  case PNG_BACKGROUND_GAMMA_UNIQUE:
                     g = 1.0 / (png_ptr->background_gamma);
                     gs = 1.0 / (png_ptr->background_gamma *
                                 png_ptr->screen_gamma);
                     break;
                  default:
                     g = 1.0;    /* back_1 */
                     gs = 1.0;   /* back */
               }

               if ( fabs(gs - 1.0) < PNG_GAMMA_THRESHOLD)
               {
                  back.red   = (png_byte)png_ptr->background.red;
                  back.green = (png_byte)png_ptr->background.green;
                  back.blue  = (png_byte)png_ptr->background.blue;
               }
               else
               {
                  back.red = (png_byte)(pow(
                     (double)png_ptr->background.red/255, gs) * 255.0 + .5);
                  back.green = (png_byte)(pow(
                     (double)png_ptr->background.green/255, gs) * 255.0 + .5);
                  back.blue = (png_byte)(pow(
                     (double)png_ptr->background.blue/255, gs) * 255.0 + .5);
               }

               back_1.red = (png_byte)(pow(
                  (double)png_ptr->background.red/255, g) * 255.0 + .5);
               back_1.green = (png_byte)(pow(
                  (double)png_ptr->background.green/255, g) * 255.0 + .5);
               back_1.blue = (png_byte)(pow(
                  (double)png_ptr->background.blue/255, g) * 255.0 + .5);
            }

            for (i = 0; i < num_palette; i++)
            {
               if (i < (int)png_ptr->num_trans && png_ptr->trans[i] != 0xff)
               {
                  if (png_ptr->trans[i] == 0)
                  {
                     palette[i] = back;
                  }
                  else /* if (png_ptr->trans[i] != 0xff) */
                  {
                     png_byte v, w;

                     v = png_ptr->gamma_to_1[palette[i].red];
                     png_composite(w, v, png_ptr->trans[i], back_1.red);
                     palette[i].red = png_ptr->gamma_from_1[w];

                     v = png_ptr->gamma_to_1[palette[i].green];
                     png_composite(w, v, png_ptr->trans[i], back_1.green);
                     palette[i].green = png_ptr->gamma_from_1[w];

                     v = png_ptr->gamma_to_1[palette[i].blue];
                     png_composite(w, v, png_ptr->trans[i], back_1.blue);
                     palette[i].blue = png_ptr->gamma_from_1[w];
                  }
               }
               else
               {
                  palette[i].red = png_ptr->gamma_table[palette[i].red];
                  palette[i].green = png_ptr->gamma_table[palette[i].green];
                  palette[i].blue = png_ptr->gamma_table[palette[i].blue];
               }
            }
         }
         /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN)*/
         else
         /* color_type != PNG_COLOR_TYPE_PALETTE */
         {
            double g, gs, m;

            m = (double)(((png_uint_32)1 << png_ptr->bit_depth) - 1);
            g = 1.0;
            gs = 1.0;

            switch (png_ptr->background_gamma_type)
            {
               case PNG_BACKGROUND_GAMMA_SCREEN:
                  g = (png_ptr->screen_gamma);
                  gs = 1.0;
                  break;
               case PNG_BACKGROUND_GAMMA_FILE:
                  g = 1.0 / (png_ptr->gamma);
                  gs = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);
                  break;
               case PNG_BACKGROUND_GAMMA_UNIQUE:
                  g = 1.0 / (png_ptr->background_gamma);
                  gs = 1.0 / (png_ptr->background_gamma *
                     png_ptr->screen_gamma);
                  break;
            }

            if (color_type & PNG_COLOR_MASK_COLOR)
            {
               /* RGB or RGBA */
               png_ptr->background_1.red = (png_uint_16)(pow(
                  (double)png_ptr->background.red / m, g) * m + .5);
               png_ptr->background_1.green = (png_uint_16)(pow(
                  (double)png_ptr->background.green / m, g) * m + .5);
               png_ptr->background_1.blue = (png_uint_16)(pow(
                  (double)png_ptr->background.blue / m, g) * m + .5);
               png_ptr->background.red = (png_uint_16)(pow(
                  (double)png_ptr->background.red / m, gs) * m + .5);
               png_ptr->background.green = (png_uint_16)(pow(
                  (double)png_ptr->background.green / m, gs) * m + .5);
               png_ptr->background.blue = (png_uint_16)(pow(
                  (double)png_ptr->background.blue / m, gs) * m + .5);
            }
            else
            {
               /* GRAY or GRAY ALPHA */
               png_ptr->background_1.gray = (png_uint_16)(pow(
                  (double)png_ptr->background.gray / m, g) * m + .5);
               png_ptr->background.gray = (png_uint_16)(pow(
                  (double)png_ptr->background.gray / m, gs) * m + .5);
            }
         }
      }
      else
      /* transformation does not include PNG_BACKGROUND */
#endif
      if (color_type == PNG_COLOR_TYPE_PALETTE)
      {
         int num_palette, i;
         png_colorp palette;

         palette = png_ptr->palette;
         num_palette = png_ptr->num_palette;

         for (i = 0; i < num_palette; i++)
         {
            palette[i].red = png_ptr->gamma_table[palette[i].red];
            palette[i].green = png_ptr->gamma_table[palette[i].green];
            palette[i].blue = png_ptr->gamma_table[palette[i].blue];
         }
      }
   }
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   else
#endif
#endif
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   /* No GAMMA transformation */
   if (png_ptr->transformations & PNG_BACKGROUND &&
       color_type == PNG_COLOR_TYPE_PALETTE)
   {
      int i;
      png_color back;
      png_colorp palette;

      palette = png_ptr->palette;
      back.red   = (png_byte)png_ptr->background.red;
      back.green = (png_byte)png_ptr->background.green;
      back.blue  = (png_byte)png_ptr->background.blue;

      for (i = 0; i < (int)png_ptr->num_trans; i++)
      {
         if (png_ptr->trans[i] == 0)
         {
            palette[i] = back;
         }
         else if (png_ptr->trans[i] != 0xff)
         {
            png_composite(palette[i].red, palette[i].red,
               png_ptr->trans[i], back.red);
            png_composite(palette[i].green, palette[i].green,
               png_ptr->trans[i], back.green);
            png_composite(palette[i].blue, palette[i].blue,
               png_ptr->trans[i], back.blue);
         }
      }
   }
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED)
   if ((png_ptr->transformations & PNG_SHIFT) &&
      color_type == PNG_COLOR_TYPE_PALETTE)
   {
      png_uint_16 i;
      int sr, sg, sb;

      sr = 8 - png_ptr->sig_bit.red;
      if (sr < 0 || sr > 8)
         sr = 0;
      sg = 8 - png_ptr->sig_bit.green;
      if (sg < 0 || sg > 8)
         sg = 0;
      sb = 8 - png_ptr->sig_bit.blue;
      if (sb < 0 || sb > 8)
         sb = 0;
      for (i = 0; i < png_ptr->num_palette; i++)
      {
         png_ptr->palette[i].red >>= sr;
         png_ptr->palette[i].green >>= sg;
         png_ptr->palette[i].blue >>= sb;
      }
   }
#endif
}

/* Modify the info structure to reflect the transformations.  The
 * info should be updated so a PNG file could be written with it,
 * assuming the transformations result in valid PNG data.
 */
void
png_read_transform_info(png_structp png_ptr, png_infop info_ptr)
{
   png_debug(1, "in png_read_transform_info\n");
#if defined(PNG_READ_EXPAND_SUPPORTED)
   if (png_ptr->transformations & PNG_EXPAND)
   {
      if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {
         if (png_ptr->num_trans)
            info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
         else
            info_ptr->color_type = PNG_COLOR_TYPE_RGB;
         info_ptr->bit_depth = 8;
         info_ptr->num_trans = 0;
      }
      else
      {
         if (png_ptr->num_trans)
            info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
         if (info_ptr->bit_depth < 8)
            info_ptr->bit_depth = 8;
         info_ptr->num_trans = 0;
      }
   }
#endif

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   if (png_ptr->transformations & PNG_BACKGROUND)
   {
      info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
      info_ptr->num_trans = 0;
      info_ptr->background = png_ptr->background;
   }
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
   if ((png_ptr->transformations & PNG_16_TO_8) && info_ptr->bit_depth == 16)
      info_ptr->bit_depth = 8;
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
   if (png_ptr->transformations & PNG_DITHER)
   {
      if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
         (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
         png_ptr->palette_lookup && info_ptr->bit_depth == 8)
      {
         info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
      }
   }
#endif

#if defined(PNG_READ_PACK_SUPPORTED)
   if ((png_ptr->transformations & PNG_PACK) && info_ptr->bit_depth < 8)
      info_ptr->bit_depth = 8;
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
      info_ptr->color_type |= PNG_COLOR_MASK_COLOR;
#endif

   if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      info_ptr->channels = 1;
   else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
      info_ptr->channels = 3;
   else
      info_ptr->channels = 1;

#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_STRIP_ALPHA)
      info_ptr->color_type &= ~PNG_COLOR_MASK_ALPHA;
#endif

#if defined(PNG_READ_FILLER_SUPPORTED)
   if ((png_ptr->transformations & PNG_FILLER) &&
       info_ptr->color_type & PNG_COLOR_TYPE_RGB &&
       info_ptr->channels == 3)
   {
      info_ptr->channels = 4;
   }
#endif

   if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
      info_ptr->channels++;
   info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
      info_ptr->bit_depth);

   info_ptr->rowbytes = ((info_ptr->width * info_ptr->pixel_depth + 7) >> 3);
}

/* Transform the row.  The order of transformations is significant,
 * and is very touchy.  If you add a transformation, take care to
 * decide how it fits in with the other transformations here.
 */
void
png_do_read_transformations(png_structp png_ptr)
{
   png_debug(1, "in png_do_read_transformations\n");
#if !defined(PNG_USELESS_TESTS_SUPPORTED)
   if (png_ptr->row_buf == NULL)
   {
#if !defined(PNG_NO_STDIO)
      char msg[50];

      sprintf(msg, "NULL row buffer for row %ld, pass %d", png_ptr->row_number,
         png_ptr->pass);
      png_error(png_ptr, msg);
#else
      png_error(png_ptr, "NULL row buffer");
#endif
   }
#endif

#if defined(PNG_READ_EXPAND_SUPPORTED)
   if (png_ptr->transformations & PNG_EXPAND)
   {
      if (png_ptr->row_info.color_type == PNG_COLOR_TYPE_PALETTE)
      {
         png_do_expand_palette(&(png_ptr->row_info), png_ptr->row_buf + 1,
            png_ptr->palette, png_ptr->trans, png_ptr->num_trans);
      }
      else if (png_ptr->transformations & PNG_EXPAND)
      {
         if (png_ptr->num_trans)
            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
               &(png_ptr->trans_values));
         else
            png_do_expand(&(png_ptr->row_info), png_ptr->row_buf + 1,
               NULL);
      }
   }
#endif

#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_STRIP_ALPHA)
      png_do_strip_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
         PNG_FLAG_FILLER_AFTER);
#endif

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   if ((png_ptr->transformations & PNG_BACKGROUND) &&
      ((png_ptr->num_trans != 0 ) ||
      (png_ptr->color_type & PNG_COLOR_MASK_ALPHA)))
      png_do_background(&(png_ptr->row_info), png_ptr->row_buf + 1,
         &(png_ptr->trans_values), &(png_ptr->background),
         &(png_ptr->background_1),
         png_ptr->gamma_table, png_ptr->gamma_from_1,
         png_ptr->gamma_to_1, png_ptr->gamma_16_table,
         png_ptr->gamma_16_from_1, png_ptr->gamma_16_to_1,
         png_ptr->gamma_shift);
#endif

#if defined(PNG_READ_GAMMA_SUPPORTED)
   if ((png_ptr->transformations & PNG_GAMMA) &&
      !(png_ptr->transformations & PNG_BACKGROUND) &&
      (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
      png_do_gamma(&(png_ptr->row_info), png_ptr->row_buf + 1,
         png_ptr->gamma_table, png_ptr->gamma_16_table,
         png_ptr->gamma_shift);
#endif

#if defined(PNG_READ_RGB_TO_GRAY_SUPPORTED)
   if (png_ptr->transformations & PNG_RGB_TO_GRAY)
      png_do_rgb_to_gray(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
   if (png_ptr->transformations & PNG_16_TO_8)
      png_do_chop(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
   if (png_ptr->transformations & PNG_DITHER)
   {
      png_do_dither((png_row_infop)&(png_ptr->row_info), png_ptr->row_buf + 1,
         png_ptr->palette_lookup, png_ptr->dither_index);
      if(png_ptr->row_info.rowbytes == (png_uint_32)0)
         png_error(png_ptr, "png_do_dither returned rowbytes=0");
   }
#endif

#if defined(PNG_READ_INVERT_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_MONO)
      png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED)
   if (png_ptr->transformations & PNG_SHIFT)
      png_do_unshift(&(png_ptr->row_info), png_ptr->row_buf + 1,
         &(png_ptr->shift));
#endif

#if defined(PNG_READ_PACK_SUPPORTED)
   if (png_ptr->transformations & PNG_PACK)
      png_do_unpack(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_BGR_SUPPORTED)
   if (png_ptr->transformations & PNG_BGR)
      png_do_bgr(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_PACKSWAP)
      png_do_packswap(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
   if (png_ptr->transformations & PNG_GRAY_TO_RGB)
      png_do_gray_to_rgb(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_FILLER_SUPPORTED)
   if (png_ptr->transformations & PNG_FILLER)
      png_do_read_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
         (png_uint_32)png_ptr->filler, png_ptr->flags);
#endif

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_ALPHA)
      png_do_read_invert_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_ALPHA)
      png_do_read_swap_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_SWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_BYTES)
      png_do_swap(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
   if (png_ptr->transformations & PNG_USER_TRANSFORM)
      if(png_ptr->read_user_transform_fn != NULL)
        (*(png_ptr->read_user_transform_fn)) /* user read transform function */
          (png_ptr,                    /* png_ptr */
           &(png_ptr->row_info),       /* row_info:     */
             /*  png_uint_32 width;          width of row */
             /*  png_uint_32 rowbytes;       number of bytes in row */
             /*  png_byte color_type;        color type of pixels */
             /*  png_byte bit_depth;         bit depth of samples */
             /*  png_byte channels;          number of channels (1-4) */
             /*  png_byte pixel_depth;       bits per pixel (depth*channels) */
           png_ptr->row_buf + 1);      /* start of pixel data for row */
#endif

}

#if defined(PNG_READ_PACK_SUPPORTED)
/* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
 * without changing the actual values.  Thus, if you had a row with
 * a bit depth of 1, you would end up with bytes that only contained
 * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
 * png_do_shift() after this.
 */
void
png_do_unpack(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_unpack\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL && row_info->bit_depth < 8)
#else
   if (row_info->bit_depth < 8)
#endif
   {
      png_uint_32 shift, i;
      png_bytep sp, dp;

      switch (row_info->bit_depth)
      {
         case 1:
         {
            sp = row + (png_size_t)((row_info->width - 1) >> 3);
            dp = row + (png_size_t)row_info->width - 1;
            shift = 7 - (int)((row_info->width + 7) & 7);
            for (i = 0; i < row_info->width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x1);
               if (shift == 7)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift++;

               dp--;
            }
            break;
         }
         case 2:
         {

            sp = row + (png_size_t)((row_info->width - 1) >> 2);
            dp = row + (png_size_t)row_info->width - 1;
            shift = (int)((3 - ((row_info->width + 3) & 3)) << 1);
            for (i = 0; i < row_info->width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0x3);
               if (shift == 6)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift += 2;

               dp--;
            }
            break;
         }
         case 4:
         {
            sp = row + (png_size_t)((row_info->width - 1) >> 1);
            dp = row + (png_size_t)row_info->width - 1;
            shift = (int)((1 - ((row_info->width + 1) & 1)) << 2);
            for (i = 0; i < row_info->width; i++)
            {
               *dp = (png_byte)((*sp >> shift) & 0xf);
               if (shift == 4)
               {
                  shift = 0;
                  sp--;
               }
               else
                  shift = 4;

               dp--;
            }
            break;
         }
      }
      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_info->width * row_info->channels;
   }
}
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED)
/* Reverse the effects of png_do_shift.  This routine merely shifts the
 * pixels back to their significant bits values.  Thus, if you have
 * a row of bit depth 8, but only 5 are significant, this will shift
 * the values back to 0 through 31.
 */
void
png_do_unshift(png_row_infop row_info, png_bytep row, png_color_8p sig_bits)
{
   png_debug(1, "in png_do_unshift\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL && sig_bits != NULL &&
#endif
       row_info->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      int shift[4];
      int channels, c;
      png_uint_16 value;

      channels = 0;
      if (row_info->color_type & PNG_COLOR_MASK_COLOR)
      {
         shift[channels++] = row_info->bit_depth - sig_bits->red;
         shift[channels++] = row_info->bit_depth - sig_bits->green;
         shift[channels++] = row_info->bit_depth - sig_bits->blue;
      }
      else
      {
         shift[channels++] = row_info->bit_depth - sig_bits->gray;
      }
      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
      {
         shift[channels++] = row_info->bit_depth - sig_bits->alpha;
      }

      value = 0;

      for (c = 0; c < channels; c++)
      {
         if (shift[c] <= 0)
            shift[c] = 0;
         else
            value = 1;
      }

      if (!value)
         return;

      switch (row_info->bit_depth)
      {
         case 2:
         {
            png_bytep bp;
            png_uint_32 i;

            for (bp = row, i = 0; i < row_info->rowbytes; i++, bp++)
            {
               *bp >>= 1;
               *bp &= 0x55;
            }
            break;
         }
         case 4:
         {
            png_bytep bp;
            png_byte mask;
            png_uint_32 i;

            mask = (png_byte)(((int)0xf0 >> shift[0]) & (int)0xf0) |
               (png_byte)((int)0xf >> shift[0]);
            for (bp = row, i = 0; i < row_info->rowbytes; i++, bp++)
            {
               *bp >>= shift[0];
               *bp &= mask;
            }
            break;
         }
         case 8:
         {
            png_bytep bp;
            png_uint_32 i;

            for (bp = row, i = 0; i < row_info->width; i++)
            {
               for (c = 0; c < (int)row_info->channels; c++, bp++)
               {
                  *bp >>= shift[c];
               }
            }
            break;
         }
         case 16:
         {
            png_bytep bp;
            png_size_t i;

            for (bp = row, i = 0; i < row_info->width; i++)
            {
               for (c = 0; c < (int)row_info->channels; c++, bp += 2)
               {
                  value = (png_uint_16)((*bp << 8) + *(bp + 1));
                  value >>= shift[c];
                  *bp = (png_byte)(value >> 8);
                  *(bp + 1) = (png_byte)(value & 0xff);
               }
            }
            break;
         }
      }
   }
}
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
/* chop rows of bit depth 16 down to 8 */
void
png_do_chop(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_chop\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL && row_info->bit_depth == 16)
#else
   if (row_info->bit_depth == 16)
#endif
   {
      png_bytep sp, dp;
      png_uint_32 i;

      sp = row;
      dp = row;
      for (i = 0; i < row_info->width * row_info->channels; i++, sp += 2, dp++)
      {
#if defined(PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED)
         /* This does a more accurate scaling of the 16-bit color
          * value, rather than a simple low-byte truncation.
          *
          * What the ideal calculation should be:
         *dp = (((((png_uint_32)(*sp) << 8) |
                   (png_uint_32)(*(sp + 1))) * 255 + 127) / (png_uint_32)65535L;


          * GRR: no, I think this is what it really should be:
         *dp = (((((png_uint_32)(*sp) << 8) |
                   (png_uint_32)(*(sp + 1))) + 128L) / (png_uint_32)257L;

          * GRR: here's the exact calculation with shifts:
         temp = (((png_uint_32)(*sp) << 8) | (png_uint_32)(*(sp + 1))) + 128L;
         *dp = (temp - (temp >> 8)) >> 8;


          * Approximate calculation with shift/add instead of multiply/divide:
         *dp = ((((png_uint_32)(*sp) << 8) |
                  (png_uint_32)((int)(*(sp + 1)) - *sp)) + 128) >> 8;

          * What we actually do to avoid extra shifting and conversion: */
         *dp = *sp + ((((int)(*(sp + 1)) - *sp) > 128) ? 1 : 0);
#else
         *dp = *sp;
#endif
      }
      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_info->width * row_info->channels;
   }
}
#endif

#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED)
void
png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_read_swap_alpha\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
      {
         /* This converts from RGBA to ARGB */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_byte save;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               save = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = save;
            }
         }
         /* This converts from RRGGBBAA to AARRGGBB */
         else
         {
            png_bytep sp, dp;
            png_byte save[2];
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               save[0] = *(--sp);
               save[1] = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = save[0];
               *(--dp) = save[1];
            }
         }
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      {
         /* This converts from GA to AG */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_byte save;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               save = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = save;
            }
         }
         /* This converts from GGAA to AAGG */
         else
         {
            png_bytep sp, dp;
            png_byte save[2];
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               save[0] = *(--sp);
               save[1] = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = save[0];
               *(--dp) = save[1];
            }
         }
      }
   }
}
#endif

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED)
void
png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_read_invert_alpha\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
      {
         /* This inverts the alpha channel in RGBA */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               *(--dp) = 255 - *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
         }
         /* This inverts the alpha channel in RRGGBBAA */
         else
         {
            png_bytep sp, dp;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               *(--dp) = 255 - *(--sp);
               *(--dp) = 255 - *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
         }
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      {
         /* This inverts the alpha channel in GA */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               *(--dp) = 255 - *(--sp);
               *(--dp) = *(--sp);
            }
         }
         /* This inverts the alpha channel in GGAA */
         else
         {
            png_bytep sp, dp;
            png_uint_32 i;

            for (i = 0, sp = dp = row + row_info->rowbytes;
               i < row_info->width; i++)
            {
               *(--dp) = 255 - *(--sp);
               *(--dp) = 255 - *(--sp);
               *(--dp) = *(--sp);
               *(--dp) = *(--sp);
            }
         }
      }
   }
}
#endif

#if defined(PNG_READ_FILLER_SUPPORTED)
/* Add filler channel if we have RGB color */
void
png_do_read_filler(png_row_infop row_info, png_bytep row,
   png_uint_32 filler, png_uint_32 flags)
{
   png_bytep sp, dp;
   png_uint_32 i;

   png_debug(1, "in png_do_read_filler\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL  && row_info != NULL &&
#endif
       row_info->color_type == PNG_COLOR_TYPE_RGB && row_info->bit_depth == 8)
   {
      /* This changes the data from RGB to RGBX */
      if (flags & PNG_FLAG_FILLER_AFTER)
      {
         for (i = 1, sp = row + (png_size_t)row_info->width * 3,
            dp = row + (png_size_t)row_info->width * 4;
            i < row_info->width;
            i++)
         {
            *(--dp) = (png_byte)filler;
            *(--dp) = *(--sp);
            *(--dp) = *(--sp);
            *(--dp) = *(--sp);
         }
         *(--dp) = (png_byte)filler;
         row_info->channels = 4;
         row_info->pixel_depth = 32;
         row_info->rowbytes = row_info->width * 4;
      }
      /* This changes the data from RGB to XRGB */
      else
      {
         for (i = 0, sp = row + (png_size_t)row_info->width * 3,
            dp = row + (png_size_t)row_info->width * 4;
            i < row_info->width;
            i++)
         {
            *(--dp) = *(--sp);
            *(--dp) = *(--sp);
            *(--dp) = *(--sp);
            *(--dp) = (png_byte)filler;
         }
         row_info->channels = 4;
         row_info->pixel_depth = 32;
         row_info->rowbytes = row_info->width * 4;
      }
   }
}
#endif

#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
/* expand grayscale files to RGB, with or without alpha */
void
png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
{
   png_bytep sp, dp;
   png_uint_32 i;

   png_debug(1, "in png_do_gray_to_rgb\n");
   if (row_info->bit_depth >= 8 &&
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
      !(row_info->color_type & PNG_COLOR_MASK_COLOR))
   {
      if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
      {
         if (row_info->bit_depth == 8)
         {
            for (i = 0, sp = row + (png_size_t)row_info->width - 1,
               dp = row + (png_size_t)row_info->width * 3 - 1;
               i < row_info->width;
               i++)
            {
               *(dp--) = *sp;
               *(dp--) = *sp;
               *(dp--) = *sp;
               sp--;
            }
         }
         else
         {
            for (i = 0, sp = row + (png_size_t)row_info->width * 2 - 1,
               dp = row + (png_size_t)row_info->width * 6 - 1;
               i < row_info->width;
               i++)
            {
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               sp--;
               sp--;
            }
         }
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      {
         if (row_info->bit_depth == 8)
         {
            for (i = 0, sp = row + (png_size_t)row_info->width * 2 - 1,
               dp = row + (png_size_t)row_info->width * 4 - 1;
               i < row_info->width;
               i++)
            {
               *(dp--) = *(sp--);
               *(dp--) = *sp;
               *(dp--) = *sp;
               *(dp--) = *sp;
               sp--;
            }
         }
         else
         {
            for (i = 0, sp = row + (png_size_t)row_info->width * 4 - 1,
               dp = row + (png_size_t)row_info->width * 8 - 1;
               i < row_info->width;
               i++)
            {
               *(dp--) = *(sp--);
               *(dp--) = *(sp--);
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               *(dp--) = *sp;
               *(dp--) = *(sp - 1);
               sp--;
               sp--;
            }
         }
      }
      row_info->channels += (png_byte)2;
      row_info->color_type |= PNG_COLOR_MASK_COLOR;
      row_info->pixel_depth = (png_byte)(row_info->channels *
         row_info->bit_depth);
      row_info->rowbytes = ((row_info->width *
         row_info->pixel_depth + 7) >> 3);
   }
}
#endif

/* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
 * large of png_color.  This lets grayscale images be treated as
 * paletted.  Most useful for gamma correction and simplification
 * of code.
 */
void
png_build_grayscale_palette(int bit_depth, png_colorp palette)
{
   int num_palette;
   int color_inc;
   int i;
   int v;

   png_debug(1, "in png_do_build_grayscale_palette\n");
   if (palette == NULL)
      return;

   switch (bit_depth)
   {
      case 1:
         num_palette = 2;
         color_inc = 0xff;
         break;
      case 2:
         num_palette = 4;
         color_inc = 0x55;
         break;
      case 4:
         num_palette = 16;
         color_inc = 0x11;
         break;
      case 8:
         num_palette = 256;
         color_inc = 1;
         break;
      default:
         num_palette = 0;
         color_inc = 0;
         break;
   }

   for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
   {
      palette[i].red = (png_byte)v;
      palette[i].green = (png_byte)v;
      palette[i].blue = (png_byte)v;
   }
}

/* This function is currently unused.  Do we really need it? */
#if defined(PNG_READ_DITHER_SUPPORTED) && defined(PNG_CORRECT_PALETTE_SUPPORTED)
void
png_correct_palette(png_structp png_ptr, png_colorp palette,
   int num_palette)
{
   png_debug(1, "in png_correct_palette\n");
#if defined(PNG_READ_BACKGROUND_SUPPORTED) && defined(PNG_READ_GAMMA_SUPPORTED)
   if ((png_ptr->transformations & (PNG_GAMMA)) &&
      (png_ptr->transformations & (PNG_BACKGROUND)))
   {
      png_color back, back_1;

      if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
      {
         back.red = png_ptr->gamma_table[png_ptr->background.red];
         back.green = png_ptr->gamma_table[png_ptr->background.green];
         back.blue = png_ptr->gamma_table[png_ptr->background.blue];

         back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
         back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
         back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
      }
      else
      {
         double g;

         g = 1.0 / (png_ptr->background_gamma * png_ptr->screen_gamma);

         if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_SCREEN ||
             fabs(g - 1.0) < PNG_GAMMA_THRESHOLD)
         {
            back.red = png_ptr->background.red;
            back.green = png_ptr->background.green;
            back.blue = png_ptr->background.blue;
         }
         else
         {
            back.red =
               (png_byte)(pow((double)png_ptr->background.red/255, g) *
                255.0 + 0.5);
            back.green =
               (png_byte)(pow((double)png_ptr->background.green/255, g) *
                255.0 + 0.5);
            back.blue =
               (png_byte)(pow((double)png_ptr->background.blue/255, g) *
                255.0 + 0.5);
         }

         g = 1.0 / png_ptr->background_gamma;

         back_1.red =
            (png_byte)(pow((double)png_ptr->background.red/255, g) *
             255.0 + 0.5);
         back_1.green =
            (png_byte)(pow((double)png_ptr->background.green/255, g) *
             255.0 + 0.5);
         back_1.blue =
            (png_byte)(pow((double)png_ptr->background.blue/255, g) *
             255.0 + 0.5);
      }

      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {
         png_uint_32 i;

         for (i = 0; i < (png_uint_32)num_palette; i++)
         {
            if (i < png_ptr->num_trans && png_ptr->trans[i] == 0)
            {
               palette[i] = back;
            }
            else if (i < png_ptr->num_trans && png_ptr->trans[i] != 0xff)
            {
               png_byte v, w;

               v = png_ptr->gamma_to_1[png_ptr->palette[i].red];
               png_composite(w, v, png_ptr->trans[i], back_1.red);
               palette[i].red = png_ptr->gamma_from_1[w];

               v = png_ptr->gamma_to_1[png_ptr->palette[i].green];
               png_composite(w, v, png_ptr->trans[i], back_1.green);
               palette[i].green = png_ptr->gamma_from_1[w];

               v = png_ptr->gamma_to_1[png_ptr->palette[i].blue];
               png_composite(w, v, png_ptr->trans[i], back_1.blue);
               palette[i].blue = png_ptr->gamma_from_1[w];
            }
            else
            {
               palette[i].red = png_ptr->gamma_table[palette[i].red];
               palette[i].green = png_ptr->gamma_table[palette[i].green];
               palette[i].blue = png_ptr->gamma_table[palette[i].blue];
            }
         }
      }
      else
      {
         int i;

         for (i = 0; i < num_palette; i++)
         {
            if (palette[i].red == (png_byte)png_ptr->trans_values.gray)
            {
               palette[i] = back;
            }
            else
            {
               palette[i].red = png_ptr->gamma_table[palette[i].red];
               palette[i].green = png_ptr->gamma_table[palette[i].green];
               palette[i].blue = png_ptr->gamma_table[palette[i].blue];
            }
         }
      }
   }
   else
#endif
#if defined(PNG_READ_GAMMA_SUPPORTED)
   if (png_ptr->transformations & PNG_GAMMA)
   {
      int i;

      for (i = 0; i < num_palette; i++)
      {
         palette[i].red = png_ptr->gamma_table[palette[i].red];
         palette[i].green = png_ptr->gamma_table[palette[i].green];
         palette[i].blue = png_ptr->gamma_table[palette[i].blue];
      }
   }
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   else
#endif
#endif
#if defined(PNG_READ_BACKGROUND_SUPPORTED)
   if (png_ptr->transformations & PNG_BACKGROUND)
   {
      if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      {
         png_color back;

         back.red   = (png_byte)png_ptr->background.red;
         back.green = (png_byte)png_ptr->background.green;
         back.blue  = (png_byte)png_ptr->background.blue;

         for (i = 0; i < (int)png_ptr->num_trans; i++)
         {
            if (png_ptr->trans[i] == 0)
            {
               palette[i].red = back.red;
               palette[i].green = back.green;
               palette[i].blue = back.blue;
            }
            else if (png_ptr->trans[i] != 0xff)
            {
               png_composite(palette[i].red, png_ptr->palette[i].red,
                  png_ptr->trans[i], back.red);
               png_composite(palette[i].green, png_ptr->palette[i].green,
                  png_ptr->trans[i], back.green);
               png_composite(palette[i].blue, png_ptr->palette[i].blue,
                  png_ptr->trans[i], back.blue);
            }
         }
      }
      else /* assume grayscale palette (what else could it be?) */
      {
         int i;

         for (i = 0; i < num_palette; i++)
         {
            if (i == (png_byte)png_ptr->trans_values.gray)
            {
               palette[i].red = (png_byte)png_ptr->background.red;
               palette[i].green = (png_byte)png_ptr->background.green;
               palette[i].blue = (png_byte)png_ptr->background.blue;
            }
         }
      }
   }
#endif
}
#endif

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
/* Replace any alpha or transparency with the supplied background color.
 * "background" is already in the screen gamma, while "background_1" is
 * at a gamma of 1.0.  Paletted files have already been taken care of.
 */
void
png_do_background(png_row_infop row_info, png_bytep row,
   png_color_16p trans_values, png_color_16p background,
   png_color_16p background_1,
   png_bytep gamma_table, png_bytep gamma_from_1, png_bytep gamma_to_1,
   png_uint_16pp gamma_16, png_uint_16pp gamma_16_from_1,
   png_uint_16pp gamma_16_to_1, int gamma_shift)
{
   png_bytep sp, dp;
   png_uint_32 i;
   int shift;

   png_debug(1, "in png_do_background\n");
   if (background != NULL &&
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
      (!(row_info->color_type & PNG_COLOR_MASK_ALPHA) ||
      (row_info->color_type != PNG_COLOR_TYPE_PALETTE && trans_values)))
   {
      switch (row_info->color_type)
      {
         case PNG_COLOR_TYPE_GRAY:
         {
            switch (row_info->bit_depth)
            {
               case 1:
               {
                  sp = row;
                  shift = 7;
                  for (i = 0; i < row_info->width; i++)
                  {
                     if ((png_uint_16)((*sp >> shift) & 0x1)
                        == trans_values->gray)
                     {
                        *sp &= (png_byte)((0x7f7f >> (7 - shift)) & 0xff);
                        *sp |= (png_byte)(background->gray << shift);
                     }
                     if (!shift)
                     {
                        shift = 7;
                        sp++;
                     }
                     else
                        shift--;
                  }
                  break;
               }
               case 2:
               {
                  sp = row;
                  shift = 6;
                  for (i = 0; i < row_info->width; i++)
                  {
                     if ((png_uint_16)((*sp >> shift) & 0x3)
                         == trans_values->gray)
                     {
                        *sp &= (png_byte)((0x3f3f >> (6 - shift)) & 0xff);
                        *sp |= (png_byte)(background->gray << shift);
                     }
                     if (!shift)
                     {
                        shift = 6;
                        sp++;
                     }
                     else
                        shift -= 2;
                  }
                  break;
               }
               case 4:
               {
                  sp = row;
                  shift = 4;
                  for (i = 0; i < row_info->width; i++)
                  {
                     if ((png_uint_16)((*sp >> shift) & 0xf)
                         == trans_values->gray)
                     {
                        *sp &= (png_byte)((0xf0f >> (4 - shift)) & 0xff);
                        *sp |= (png_byte)(background->gray << shift);
                     }
                     if (!shift)
                     {
                        shift = 4;
                        sp++;
                     }
                     else
                        shift -= 4;
                  }
                  break;
               }
               case 8:
               {
#if defined(PNG_READ_GAMMA_SUPPORTED)
                  if (gamma_table != NULL)
                  {
                     for (i = 0, sp = row; i < row_info->width; i++, sp++)
                     {
                        if (*sp == trans_values->gray)
                        {
                           *sp = (png_byte)background->gray;
                        }
                        else
                        {
                           *sp = gamma_table[*sp];
                        }
                     }
                  }
                  else
#endif
                  {
                     for (i = 0, sp = row; i < row_info->width; i++, sp++)
                     {
                        if (*sp == trans_values->gray)
                        {
                           *sp = (png_byte)background->gray;
                        }
                     }
                  }
                  break;
               }
               case 16:
               {
#if defined(PNG_READ_GAMMA_SUPPORTED)
                  if (gamma_16 != NULL)
                  {
                     for (i = 0, sp = row; i < row_info->width; i++, sp += 2)
                     {
                        png_uint_16 v;

                        v = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                        if (v == trans_values->gray)
                        {
                           /* background is already in screen gamma */
                           *sp = (png_byte)((background->gray >> 8) & 0xff);
                           *(sp + 1) = (png_byte)(background->gray & 0xff);
                        }
                        else
                        {
                           v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                           *sp = (png_byte)((v >> 8) & 0xff);
                           *(sp + 1) = (png_byte)(v & 0xff);
                        }
                     }
                  }
                  else
#endif
                  {
                     for (i = 0, sp = row; i < row_info->width; i++, sp += 2)
                     {
                        png_uint_16 v;

                        v = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                        if (v == trans_values->gray)
                        {
                           *sp = (png_byte)((background->gray >> 8) & 0xff);
                           *(sp + 1) = (png_byte)(background->gray & 0xff);
                        }
                     }
                  }
                  break;
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_RGB:
         {
            if (row_info->bit_depth == 8)
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_table != NULL)
               {
                  for (i = 0, sp = row; i < row_info->width; i++, sp += 3)
                  {
                     if (*sp == trans_values->red &&
                        *(sp + 1) == trans_values->green &&
                        *(sp + 2) == trans_values->blue)
                     {
                        *sp = (png_byte)background->red;
                        *(sp + 1) = (png_byte)background->green;
                        *(sp + 2) = (png_byte)background->blue;
                     }
                     else
                     {
                        *sp = gamma_table[*sp];
                        *(sp + 1) = gamma_table[*(sp + 1)];
                        *(sp + 2) = gamma_table[*(sp + 2)];
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row; i < row_info->width; i++, sp += 3)
                  {
                     if (*sp == trans_values->red &&
                        *(sp + 1) == trans_values->green &&
                        *(sp + 2) == trans_values->blue)
                     {
                        *sp = (png_byte)background->red;
                        *(sp + 1) = (png_byte)background->green;
                        *(sp + 2) = (png_byte)background->blue;
                     }
                  }
               }
            }
            else /* if (row_info->bit_depth == 16) */
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_16 != NULL)
               {
                  for (i = 0, sp = row; i < row_info->width; i++, sp += 6)
                  {
                     png_uint_16 r, g, b;

                     r = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                     g = ((png_uint_16)(*(sp + 2)) << 8) + *(sp + 3);
                     b = ((png_uint_16)(*(sp + 4)) << 8) + *(sp + 5);
                     if (r == trans_values->red && g == trans_values->green &&
                        b == trans_values->blue)
                     {
                        /* background is already in screen gamma */
                        *sp = (png_byte)((background->red >> 8) & 0xff);
                        *(sp + 1) = (png_byte)(background->red & 0xff);
                        *(sp + 2) = (png_byte)((background->green >> 8) & 0xff);
                        *(sp + 3) = (png_byte)(background->green & 0xff);
                        *(sp + 4) = (png_byte)((background->blue >> 8) & 0xff);
                        *(sp + 5) = (png_byte)(background->blue & 0xff);
                     }
                     else
                     {
                        png_uint_16 v;
                        v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                        *sp = (png_byte)((v >> 8) & 0xff);
                        *(sp + 1) = (png_byte)(v & 0xff);
                        v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                        *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                        *(sp + 3) = (png_byte)(v & 0xff);
                        v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                        *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                        *(sp + 5) = (png_byte)(v & 0xff);
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row; i < row_info->width; i++, sp += 6)
                  {
                     png_uint_16 r, g, b;

                     r = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                     g = ((png_uint_16)(*(sp + 2)) << 8) + *(sp + 3);
                     b = ((png_uint_16)(*(sp + 4)) << 8) + *(sp + 5);
                     if (r == trans_values->red && g == trans_values->green &&
                        b == trans_values->blue)
                     {
                        *sp = (png_byte)((background->red >> 8) & 0xff);
                        *(sp + 1) = (png_byte)(background->red & 0xff);
                        *(sp + 2) = (png_byte)((background->green >> 8) & 0xff);
                        *(sp + 3) = (png_byte)(background->green & 0xff);
                        *(sp + 4) = (png_byte)((background->blue >> 8) & 0xff);
                        *(sp + 5) = (png_byte)(background->blue & 0xff);
                     }
                  }
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_GRAY_ALPHA:
         {
            if (row_info->bit_depth == 8)
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                   gamma_table != NULL)
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 2, dp++)
                  {
                     png_uint_16 a;

                     a = *(sp + 1);
                     if (a == 0xff)
                     {
                        *dp = gamma_table[*sp];
                     }
                     else if (a == 0)
                     {
                        /* background is already in screen gamma */
                        *dp = (png_byte)background->gray;
                     }
                     else
                     {
                        png_byte v, w;

                        v = gamma_to_1[*sp];
                        png_composite(w, v, a, background_1->gray);
                        *dp = gamma_from_1[w];
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 2, dp++)
                  {
                     png_byte a;

                     a = *(sp + 1);
                     if (a == 0xff)
                     {
                        *dp = *sp;
                     }
                     else if (a == 0)
                     {
                        *dp = (png_byte)background->gray;
                     }
                     else
                     {
                        png_composite(*dp, *sp, a, background_1->gray);
                     }
                  }
               }
            }
            else /* if (png_ptr->bit_depth == 16) */
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                   gamma_16_to_1 != NULL)
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 4, dp += 2)
                  {
                     png_uint_16 a;

                     a = ((png_uint_16)(*(sp + 2)) << 8) + *(sp + 3);
                     if (a == (png_uint_16)0xffff)
                     {
                        png_uint_16 v;

                        v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                        *dp = (png_byte)((v >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(v & 0xff);
                     }
                     else if (a == 0)
                     {
                        /* background is already in screen gamma */
                        *dp = (png_byte)((background->gray >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(background->gray & 0xff);
                     }
                     else
                     {
                        png_uint_16 g, v, w;

                        g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                        png_composite_16(v, g, a, background_1->gray);
                        w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
                        *dp = (png_byte)((w >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(w & 0xff);
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 4, dp += 2)
                  {
                     png_uint_16 a;

                     a = ((png_uint_16)(*(sp + 2)) << 8) + *(sp + 3);
                     if (a == (png_uint_16)0xffff)
                     {
                        png_memcpy(dp, sp, 2);
                     }
                     else if (a == 0)
                     {
                        *dp = (png_byte)((background->gray >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(background->gray & 0xff);
                     }
                     else
                     {
                        png_uint_16 g, v;

                        g = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                        png_composite_16(v, g, a, background_1->gray);
                        *dp = (png_byte)((v >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(v & 0xff);
                     }
                  }
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_RGB_ALPHA:
         {
            if (row_info->bit_depth == 8)
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                   gamma_table != NULL)
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 4, dp += 3)
                  {
                     png_byte a;

                     a = *(sp + 3);
                     if (a == 0xff)
                     {
                        *dp = gamma_table[*sp];
                        *(dp + 1) = gamma_table[*(sp + 1)];
                        *(dp + 2) = gamma_table[*(sp + 2)];
                     }
                     else if (a == 0)
                     {
                        /* background is already in screen gamma */
                        *dp = (png_byte)background->red;
                        *(dp + 1) = (png_byte)background->green;
                        *(dp + 2) = (png_byte)background->blue;
                     }
                     else
                     {
                        png_byte v, w;

                        v = gamma_to_1[*sp];
                        png_composite(w, v, a, background_1->red);
                        *dp = gamma_from_1[w];
                        v = gamma_to_1[*(sp + 1)];
                        png_composite(w, v, a, background_1->green);
                        *(dp + 1) = gamma_from_1[w];
                        v = gamma_to_1[*(sp + 2)];
                        png_composite(w, v, a, background_1->blue);
                        *(dp + 2) = gamma_from_1[w];
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 4, dp += 3)
                  {
                     png_byte a;

                     a = *(sp + 3);
                     if (a == 0xff)
                     {
                        *dp = *sp;
                        *(dp + 1) = *(sp + 1);
                        *(dp + 2) = *(sp + 2);
                     }
                     else if (a == 0)
                     {
                        *dp = (png_byte)background->red;
                        *(dp + 1) = (png_byte)background->green;
                        *(dp + 2) = (png_byte)background->blue;
                     }
                     else
                     {
                        png_composite(*dp, *sp, a, background->red);
                        png_composite(*(dp + 1), *(sp + 1), a,
                           background->green);
                        png_composite(*(dp + 2), *(sp + 2), a,
                           background->blue);
                     }
                  }
               }
            }
            else /* if (row_info->bit_depth == 16) */
            {
#if defined(PNG_READ_GAMMA_SUPPORTED)
               if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                   gamma_16_to_1 != NULL)
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 8, dp += 6)
                  {
                     png_uint_16 a;

                     a = (png_uint_16)(((png_uint_16)(*(sp + 6)) << 8) +
                         (png_uint_16)(*(sp + 7)));
                     if (a == (png_uint_16)0xffff)
                     {
                        png_uint_16 v;

                        v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                        *dp = (png_byte)((v >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(v & 0xff);
                        v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                        *(dp + 2) = (png_byte)((v >> 8) & 0xff);
                        *(dp + 3) = (png_byte)(v & 0xff);
                        v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                        *(dp + 4) = (png_byte)((v >> 8) & 0xff);
                        *(dp + 5) = (png_byte)(v & 0xff);
                     }
                     else if (a == 0)
                     {
                        /* background is already in screen gamma */
                        *dp = (png_byte)((background->red >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(background->red & 0xff);
                        *(dp + 2) = (png_byte)((background->green >> 8) & 0xff);
                        *(dp + 3) = (png_byte)(background->green & 0xff);
                        *(dp + 4) = (png_byte)((background->blue >> 8) & 0xff);
                        *(dp + 5) = (png_byte)(background->blue & 0xff);
                     }
                     else
                     {
                        png_uint_16 v, w, x;

                        v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                        png_composite_16(w, v, a, background->red);
                        x = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
                        *dp = (png_byte)((x >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(x & 0xff);
                        v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
                        png_composite_16(w, v, a, background->green);
                        x = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >> 8];
                        *(dp + 2) = (png_byte)((x >> 8) & 0xff);
                        *(dp + 3) = (png_byte)(x & 0xff);
                        v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
                        png_composite_16(w, v, a, background->blue);
                        x = gamma_16_from_1[(w & 0xff) >> gamma_shift][w >> 8];
                        *(dp + 4) = (png_byte)((x >> 8) & 0xff);
                        *(dp + 5) = (png_byte)(x & 0xff);
                     }
                  }
               }
               else
#endif
               {
                  for (i = 0, sp = row, dp = row;
                     i < row_info->width; i++, sp += 8, dp += 6)
                  {
                     png_uint_16 a;

                     a = (png_uint_16)(((png_uint_16)(*(sp + 6)) << 8) +
                        (png_uint_16)(*(sp + 7)));
                     if (a == (png_uint_16)0xffff)
                     {
                        png_memcpy(dp, sp, 6);
                     }
                     else if (a == 0)
                     {
                        *dp = (png_byte)((background->red >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(background->red & 0xff);
                        *(dp + 2) = (png_byte)((background->green >> 8) & 0xff);
                        *(dp + 3) = (png_byte)(background->green & 0xff);
                        *(dp + 4) = (png_byte)((background->blue >> 8) & 0xff);
                        *(dp + 5) = (png_byte)(background->blue & 0xff);
                     }
                     else
                     {
                        png_uint_16 r, g, b, v;

                        r = ((png_uint_16)(*sp) << 8) + *(sp + 1);
                        g = ((png_uint_16)(*(sp + 2)) << 8) + *(sp + 3);
                        b = ((png_uint_16)(*(sp + 4)) << 8) + *(sp + 5);

                        png_composite_16(v, r, a, background->red);
                        *dp = (png_byte)((v >> 8) & 0xff);
                        *(dp + 1) = (png_byte)(v & 0xff);
                        png_composite_16(v, g, a, background->green);
                        *(dp + 2) = (png_byte)((v >> 8) & 0xff);
                        *(dp + 3) = (png_byte)(v & 0xff);
                        png_composite_16(v, b, a, background->blue);
                        *(dp + 4) = (png_byte)((v >> 8) & 0xff);
                        *(dp + 5) = (png_byte)(v & 0xff);
                     }
                  }
               }
            }
            break;
         }
      }

      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
      {
         row_info->color_type &= ~PNG_COLOR_MASK_ALPHA;
         row_info->channels--;
         row_info->pixel_depth = (png_byte)(row_info->channels *
            row_info->bit_depth);
         row_info->rowbytes = ((row_info->width *
            row_info->pixel_depth + 7) >> 3);
      }
   }
}
#endif

#if defined(PNG_READ_GAMMA_SUPPORTED)
/* Gamma correct the image, avoiding the alpha channel.  Make sure
 * you do this after you deal with the trasparency issue on grayscale
 * or rgb images. If your bit depth is 8, use gamma_table, if it
 * is 16, use gamma_16_table and gamma_shift.  Build these with
 * build_gamma_table().
 */
void
png_do_gamma(png_row_infop row_info, png_bytep row,
   png_bytep gamma_table, png_uint_16pp gamma_16_table,
   int gamma_shift)
{
   png_bytep sp;
   png_uint_32 i;

   png_debug(1, "in png_do_gamma\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
       ((row_info->bit_depth <= 8 && gamma_table != NULL) ||
        (row_info->bit_depth == 16 && gamma_16_table != NULL)))
   {
      switch (row_info->color_type)
      {
         case PNG_COLOR_TYPE_RGB:
         {
            if (row_info->bit_depth == 8)
            {
               for (i = 0, sp = row; i < row_info->width; i++)
               {
                  *sp = gamma_table[*sp];
                  sp++;
                  *sp = gamma_table[*sp];
                  sp++;
                  *sp = gamma_table[*sp];
                  sp++;
               }
            }
            else /* if (row_info->bit_depth == 16) */
            {
               for (i = 0, sp = row; i < row_info->width; i++)
               {
                  png_uint_16 v;

                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_RGB_ALPHA:
         {
            if (row_info->bit_depth == 8)
            {
               for (i = 0, sp = row;
                  i < row_info->width; i++)
               {
                  *sp = gamma_table[*sp];
                  sp++;
                  *sp = gamma_table[*sp];
                  sp++;
                  *sp = gamma_table[*sp];
                  sp++;
                  sp++;
               }
            }
            else /* if (row_info->bit_depth == 16) */
            {
               for (i = 0, sp = row;
                  i < row_info->width; i++)
               {
                  png_uint_16 v;

                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 4;
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_GRAY_ALPHA:
         {
            if (row_info->bit_depth == 8)
            {
               for (i = 0, sp = row;
                  i < row_info->width; i++)
               {
                  *sp = gamma_table[*sp];
                  sp += 2;
               }
            }
            else /* if (row_info->bit_depth == 16) */
            {
               for (i = 0, sp = row;
                  i < row_info->width; i++)
               {
                  png_uint_16 v;

                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 4;
               }
            }
            break;
         }
         case PNG_COLOR_TYPE_GRAY:
         {
            if (row_info->bit_depth == 2)
            {
               for (i = 0, sp = row; i < row_info->width; i += 4)
               {
                  int a = *sp & 0xc0;
                  int b = *sp & 0x30;
                  int c = *sp & 0x0c;
                  int d = *sp & 0x03;

                  *sp = ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
                        ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
                        ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
                        ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6)       );
                  sp++;
               }
            }
            if (row_info->bit_depth == 4)
            {
               for (i = 0, sp = row; i < row_info->width; i += 2)
               {
                  int msb = *sp & 0xf0;
                  int lsb = *sp & 0x0f;

                  *sp = (((int)gamma_table[msb | (msb >> 4)]) & 0xf0) |
                        (((int)gamma_table[(lsb << 4) | lsb]) >> 4);
                  sp++;
               }
            }
            else if (row_info->bit_depth == 8)
            {
               for (i = 0, sp = row; i < row_info->width; i++)
               {
                  *sp = gamma_table[*sp];
                  sp++;
               }
            }
            else if (row_info->bit_depth == 16)
            {
               for (i = 0, sp = row; i < row_info->width; i++)
               {
                  png_uint_16 v;

                  v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                  *sp = (png_byte)((v >> 8) & 0xff);
                  *(sp + 1) = (png_byte)(v & 0xff);
                  sp += 2;
               }
            }
            break;
         }
      }
   }
}
#endif

#if defined(PNG_READ_EXPAND_SUPPORTED)
/* Expands a palette row to an rgb or rgba row depending
 * upon whether you supply trans and num_trans.
 */
void
png_do_expand_palette(png_row_infop row_info, png_bytep row,
   png_colorp palette, png_bytep trans, int num_trans)
{
   int shift, value;
   png_bytep sp, dp;
   png_uint_32 i;

   png_debug(1, "in png_do_expand_palette\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
       row_info->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (row_info->bit_depth < 8)
      {
         switch (row_info->bit_depth)
         {
            case 1:
            {
               sp = row + (png_size_t)((row_info->width - 1) >> 3);
               dp = row + (png_size_t)row_info->width - 1;
               shift = 7 - (int)((row_info->width + 7) & 7);
               for (i = 0; i < row_info->width; i++)
               {
                  if ((*sp >> shift) & 0x1)
                     *dp = 1;
                  else
                     *dp = 0;
                  if (shift == 7)
                  {
                     shift = 0;
                     sp--;
                  }
                  else
                     shift++;

                  dp--;
               }
               break;
            }
            case 2:
            {
               sp = row + (png_size_t)((row_info->width - 1) >> 2);
               dp = row + (png_size_t)row_info->width - 1;
               shift = (int)((3 - ((row_info->width + 3) & 3)) << 1);
               for (i = 0; i < row_info->width; i++)
               {
                  value = (*sp >> shift) & 0x3;
                  *dp = (png_byte)value;
                  if (shift == 6)
                  {
                     shift = 0;
                     sp--;
                  }
                  else
                     shift += 2;

                  dp--;
               }
               break;
            }
            case 4:
            {
               sp = row + (png_size_t)((row_info->width - 1) >> 1);
               dp = row + (png_size_t)row_info->width - 1;
               shift = (int)((row_info->width & 1) << 2);
               for (i = 0; i < row_info->width; i++)
               {
                  value = (*sp >> shift) & 0xf;
                  *dp = (png_byte)value;
                  if (shift == 4)
                  {
                     shift = 0;
                     sp--;
                  }
                  else
                     shift += 4;

                  dp--;
               }
               break;
            }
         }
         row_info->bit_depth = 8;
         row_info->pixel_depth = 8;
         row_info->rowbytes = row_info->width;
      }
      switch (row_info->bit_depth)
      {
         case 8:
         {
            if (trans != NULL)
            {
               sp = row + (png_size_t)row_info->width - 1;
               dp = row + (png_size_t)(row_info->width << 2) - 1;

               for (i = 0; i < row_info->width; i++)
               {
                  if ((int)(*sp) >= num_trans)
                     *dp-- = 0xff;
                  else
                     *dp-- = trans[*sp];
                  *dp-- = palette[*sp].blue;
                  *dp-- = palette[*sp].green;
                  *dp-- = palette[*sp].red;
                  sp--;
               }
               row_info->bit_depth = 8;
               row_info->pixel_depth = 32;
               row_info->rowbytes = row_info->width * 4;
               row_info->color_type = 6;
               row_info->channels = 4;
            }
            else
            {
               sp = row + (png_size_t)row_info->width - 1;
               dp = row + (png_size_t)(row_info->width * 3) - 1;

               for (i = 0; i < row_info->width; i++)
               {
                  *dp-- = palette[*sp].blue;
                  *dp-- = palette[*sp].green;
                  *dp-- = palette[*sp].red;
                  sp--;
               }
               row_info->bit_depth = 8;
               row_info->pixel_depth = 24;
               row_info->rowbytes = row_info->width * 3;
               row_info->color_type = 2;
               row_info->channels = 3;
            }
            break;
         }
      }
   }
}

/* If the bit depth < 8, it is expanded to 8.  Also, if the
 * transparency value is supplied, an alpha channel is built.
 */
void
png_do_expand(png_row_infop row_info, png_bytep row,
   png_color_16p trans_value)
{
   int shift, value;
   png_bytep sp, dp;
   png_uint_32 i;

   png_debug(1, "in png_do_expand\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
      if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
      {
         png_uint_16 gray = trans_value ? trans_value->gray : 0;

         if (row_info->bit_depth < 8)
         {
            switch (row_info->bit_depth)
            {
               case 1:
               {
                  gray *= 0xff;
                  sp = row + (png_size_t)((row_info->width - 1) >> 3);
                  dp = row + (png_size_t)row_info->width - 1;
                  shift = 7 - (int)((row_info->width + 7) & 7);
                  for (i = 0; i < row_info->width; i++)
                  {
                     if ((*sp >> shift) & 0x1)
                        *dp = 0xff;
                     else
                        *dp = 0;
                     if (shift == 7)
                     {
                        shift = 0;
                        sp--;
                     }
                     else
                        shift++;

                     dp--;
                  }
                  break;
               }
               case 2:
               {
                  gray *= 0x55;
                  sp = row + (png_size_t)((row_info->width - 1) >> 2);
                  dp = row + (png_size_t)row_info->width - 1;
                  shift = (int)((3 - ((row_info->width + 3) & 3)) << 1);
                  for (i = 0; i < row_info->width; i++)
                  {
                     value = (*sp >> shift) & 0x3;
                     *dp = (png_byte)(value | (value << 2) | (value << 4) |
                        (value << 6));
                     if (shift == 6)
                     {
                        shift = 0;
                        sp--;
                     }
                     else
                        shift += 2;

                     dp--;
                  }
                  break;
               }
               case 4:
               {
                  gray *= 0x11;
                  sp = row + (png_size_t)((row_info->width - 1) >> 1);
                  dp = row + (png_size_t)row_info->width - 1;
                  shift = (int)((1 - ((row_info->width + 1) & 1)) << 2);
                  for (i = 0; i < row_info->width; i++)
                  {
                     value = (*sp >> shift) & 0xf;
                     *dp = (png_byte)(value | (value << 4));
                     if (shift == 4)
                     {
                        shift = 0;
                        sp--;
                     }
                     else
                        shift = 4;

                     dp--;
                  }
                  break;
               }
            }
            row_info->bit_depth = 8;
            row_info->pixel_depth = 8;
            row_info->rowbytes = row_info->width;
         }

         if (trans_value != NULL)
         {
            if (row_info->bit_depth == 8)
            {
               sp = row + (png_size_t)row_info->width - 1;
               dp = row + (png_size_t)(row_info->width << 1) - 1;
               for (i = 0; i < row_info->width; i++)
               {
                  if (*sp == gray)
                     *dp-- = 0;
                  else
                     *dp-- = 0xff;
                  *dp-- = *sp--;
               }
            }
            else if (row_info->bit_depth == 16)
            {
               sp = row + row_info->rowbytes - 1;
               dp = row + (row_info->rowbytes << 1) - 1;
               for (i = 0; i < row_info->width; i++)
               {
                  if (((png_uint_16)*(sp) |
                     ((png_uint_16)*(sp - 1) << 8)) == gray)
                  {
                     *dp-- = 0;
                     *dp-- = 0;
                  }
                  else
                  {
                     *dp-- = 0xff;
                     *dp-- = 0xff;
                  }
                  *dp-- = *sp--;
                  *dp-- = *sp--;
               }
            }
            row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
            row_info->channels = 2;
            row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
            row_info->rowbytes =
               ((row_info->width * row_info->pixel_depth) >> 3);
         }
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_value)
      {
         if (row_info->bit_depth == 8)
         {
            sp = row + (png_size_t)row_info->rowbytes - 1;
            dp = row + (png_size_t)(row_info->width << 2) - 1;
            for (i = 0; i < row_info->width; i++)
            {
               if (*(sp - 2) == trans_value->red &&
                  *(sp - 1) == trans_value->green &&
                  *(sp - 0) == trans_value->blue)
                  *dp-- = 0;
               else
                  *dp-- = 0xff;
               *dp-- = *sp--;
               *dp-- = *sp--;
               *dp-- = *sp--;
            }
         }
         else if (row_info->bit_depth == 16)
         {
            sp = row + row_info->rowbytes - 1;
            dp = row + (png_size_t)(row_info->width << 3) - 1;
            for (i = 0; i < row_info->width; i++)
            {
               if ((((png_uint_16)*(sp - 4) |
                  ((png_uint_16)*(sp - 5) << 8)) == trans_value->red) &&
                  (((png_uint_16)*(sp - 2) |
                  ((png_uint_16)*(sp - 3) << 8)) == trans_value->green) &&
                  (((png_uint_16)*(sp - 0) |
                  ((png_uint_16)*(sp - 1) << 8)) == trans_value->blue))
               {
                  *dp-- = 0;
                  *dp-- = 0;
               }
               else
               {
                  *dp-- = 0xff;
                  *dp-- = 0xff;
               }
               *dp-- = *sp--;
               *dp-- = *sp--;
               *dp-- = *sp--;
               *dp-- = *sp--;
               *dp-- = *sp--;
               *dp-- = *sp--;
            }
         }
         row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
         row_info->channels = 4;
         row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
         row_info->rowbytes =
            ((row_info->width * row_info->pixel_depth) >> 3);
      }
   }
}
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
void
png_do_dither(png_row_infop row_info, png_bytep row,
    png_bytep palette_lookup, png_bytep dither_lookup)
{
   png_bytep sp, dp;
   png_uint_32 i;

   png_debug(1, "in png_do_dither\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
      if (row_info->color_type == PNG_COLOR_TYPE_RGB &&
         palette_lookup && row_info->bit_depth == 8)
      {
         int r, g, b, p;
         sp = row;
         dp = row;
         for (i = 0; i < row_info->width; i++)
         {
            r = *sp++;
            g = *sp++;
            b = *sp++;

            /* this looks real messy, but the compiler will reduce
               it down to a reasonable formula.  For example, with
               5 bits per color, we get:
               p = (((r >> 3) & 0x1f) << 10) |
                  (((g >> 3) & 0x1f) << 5) |
                  ((b >> 3) & 0x1f);
               */
            p = (((r >> (8 - PNG_DITHER_RED_BITS)) &
               ((1 << PNG_DITHER_RED_BITS) - 1)) <<
               (PNG_DITHER_GREEN_BITS + PNG_DITHER_BLUE_BITS)) |
               (((g >> (8 - PNG_DITHER_GREEN_BITS)) &
               ((1 << PNG_DITHER_GREEN_BITS) - 1)) <<
               (PNG_DITHER_BLUE_BITS)) |
               ((b >> (8 - PNG_DITHER_BLUE_BITS)) &
               ((1 << PNG_DITHER_BLUE_BITS) - 1));

            *dp++ = palette_lookup[p];
         }
         row_info->color_type = PNG_COLOR_TYPE_PALETTE;
         row_info->channels = 1;
         row_info->pixel_depth = row_info->bit_depth;
         row_info->rowbytes =
             ((row_info->width * row_info->pixel_depth + 7) >> 3);
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
         palette_lookup != NULL && row_info->bit_depth == 8)
      {
         int r, g, b, p;
         sp = row;
         dp = row;
         for (i = 0; i < row_info->width; i++)
         {
            r = *sp++;
            g = *sp++;
            b = *sp++;
            sp++;

            p = (((r >> (8 - PNG_DITHER_RED_BITS)) &
               ((1 << PNG_DITHER_RED_BITS) - 1)) <<
               (PNG_DITHER_GREEN_BITS + PNG_DITHER_BLUE_BITS)) |
               (((g >> (8 - PNG_DITHER_GREEN_BITS)) &
               ((1 << PNG_DITHER_GREEN_BITS) - 1)) <<
               (PNG_DITHER_BLUE_BITS)) |
               ((b >> (8 - PNG_DITHER_BLUE_BITS)) &
               ((1 << PNG_DITHER_BLUE_BITS) - 1));

            *dp++ = palette_lookup[p];
         }
         row_info->color_type = PNG_COLOR_TYPE_PALETTE;
         row_info->channels = 1;
         row_info->pixel_depth = row_info->bit_depth;
         row_info->rowbytes =
            ((row_info->width * row_info->pixel_depth + 7) >> 3);
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
         dither_lookup && row_info->bit_depth == 8)
      {
         sp = row;
         for (i = 0; i < row_info->width; i++, sp++)
         {
            *sp = dither_lookup[*sp];
         }
      }
   }
}
#endif

#if defined(PNG_READ_GAMMA_SUPPORTED)
static int png_gamma_shift[] =
   {0x10, 0x21, 0x42, 0x84, 0x110, 0x248, 0x550, 0xff0};

/* We build the 8- or 16-bit gamma tables here.  Note that for 16-bit
 * tables, we don't make a full table if we are reducing to 8-bit in
 * the future.  Note also how the gamma_16 tables are segmented so that
 * we don't need to allocate > 64K chunks for a full 16-bit table.
 */
void
png_build_gamma_table(png_structp png_ptr)
{
   png_debug(1, "in png_build_gamma_table\n");
   if (png_ptr->bit_depth <= 8)
   {
      int i;
      double g;

      g = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);

      png_ptr->gamma_table = (png_bytep)png_malloc(png_ptr,
         (png_uint_32)256);

      for (i = 0; i < 256; i++)
      {
         png_ptr->gamma_table[i] = (png_byte)(pow((double)i / 255.0,
            g) * 255.0 + .5);
      }

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
      if (png_ptr->transformations & PNG_BACKGROUND)
      {
         g = 1.0 / (png_ptr->gamma);

         png_ptr->gamma_to_1 = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)256);

         for (i = 0; i < 256; i++)
         {
            png_ptr->gamma_to_1[i] = (png_byte)(pow((double)i / 255.0,
               g) * 255.0 + .5);
         }

         g = 1.0 / (png_ptr->screen_gamma);

         png_ptr->gamma_from_1 = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)256);

         for (i = 0; i < 256; i++)
         {
            png_ptr->gamma_from_1[i] = (png_byte)(pow((double)i / 255.0,
               g) * 255.0 + .5);
         }
      }
#endif /* PNG_BACKGROUND_SUPPORTED */
   }
   else
   {
      double g;
      int i, j, shift, num;
      int sig_bit;
      png_uint_32 ig;

      if (png_ptr->color_type & PNG_COLOR_MASK_COLOR)
      {
         sig_bit = (int)png_ptr->sig_bit.red;
         if ((int)png_ptr->sig_bit.green > sig_bit)
            sig_bit = png_ptr->sig_bit.green;
         if ((int)png_ptr->sig_bit.blue > sig_bit)
            sig_bit = png_ptr->sig_bit.blue;
      }
      else
      {
         sig_bit = (int)png_ptr->sig_bit.gray;
      }

      if (sig_bit > 0)
         shift = 16 - sig_bit;
      else
         shift = 0;

      if (png_ptr->transformations & PNG_16_TO_8)
      {
         if (shift < (16 - PNG_MAX_GAMMA_8))
            shift = (16 - PNG_MAX_GAMMA_8);
      }

      if (shift > 8)
         shift = 8;
      if (shift < 0)
         shift = 0;

      png_ptr->gamma_shift = (png_byte)shift;

      num = (1 << (8 - shift));

      g = 1.0 / (png_ptr->gamma * png_ptr->screen_gamma);

      png_ptr->gamma_16_table = (png_uint_16pp)png_malloc(png_ptr,
         (png_uint_32)(num * sizeof (png_uint_16p)));

      if ((png_ptr->transformations & PNG_16_TO_8) &&
         !(png_ptr->transformations & PNG_BACKGROUND))
      {
         double fin, fout;
         png_uint_32 last, max;

         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_table[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * sizeof (png_uint_16)));
         }

         g = 1.0 / g;
         last = 0;
         for (i = 0; i < 256; i++)
         {
            fout = ((double)i + 0.5) / 256.0;
            fin = pow(fout, g);
            max = (png_uint_32)(fin * (double)((png_uint_32)num << 8));
            while (last <= max)
            {
               png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
                  [(int)(last >> (8 - shift))] = (png_uint_16)(
                  (png_uint_16)i | ((png_uint_16)i << 8));
               last++;
            }
         }
         while (last < ((png_uint_32)num << 8))
         {
            png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
               [(int)(last >> (8 - shift))] = (png_uint_16)65535L;
            last++;
         }
      }
      else
      {
         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_table[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * sizeof (png_uint_16)));

            ig = (((png_uint_32)i * (png_uint_32)png_gamma_shift[shift]) >> 4);
            for (j = 0; j < 256; j++)
            {
               png_ptr->gamma_16_table[i][j] =
                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
                     65535.0, g) * 65535.0 + .5);
            }
         }
      }

#if defined(PNG_READ_BACKGROUND_SUPPORTED)
      if (png_ptr->transformations & PNG_BACKGROUND)
      {
         g = 1.0 / (png_ptr->gamma);

         png_ptr->gamma_16_to_1 = (png_uint_16pp)png_malloc(png_ptr,
            (png_uint_32)(num * sizeof (png_uint_16p )));

         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_to_1[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * sizeof (png_uint_16)));

            ig = (((png_uint_32)i *
               (png_uint_32)png_gamma_shift[shift]) >> 4);
            for (j = 0; j < 256; j++)
            {
               png_ptr->gamma_16_to_1[i][j] =
                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
                     65535.0, g) * 65535.0 + .5);
            }
         }
         g = 1.0 / (png_ptr->screen_gamma);

         png_ptr->gamma_16_from_1 = (png_uint_16pp)png_malloc(png_ptr,
            (png_uint_32)(num * sizeof (png_uint_16p)));

         for (i = 0; i < num; i++)
         {
            png_ptr->gamma_16_from_1[i] = (png_uint_16p)png_malloc(png_ptr,
               (png_uint_32)(256 * sizeof (png_uint_16)));

            ig = (((png_uint_32)i *
               (png_uint_32)png_gamma_shift[shift]) >> 4);
            for (j = 0; j < 256; j++)
            {
               png_ptr->gamma_16_from_1[i][j] =
                  (png_uint_16)(pow((double)(ig + ((png_uint_32)j << 8)) /
                     65535.0, g) * 65535.0 + .5);
            }
         }
      }
#endif /* PNG_BACKGROUND_SUPPORTED */
   }
}
#endif