[libpng16] Avoid the double gamma correction warning in the simplified API.
This allows the --strict option to pass in the pngstest checks
diff --git a/ANNOUNCE b/ANNOUNCE
index 62d76fc..f2e652f 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -336,6 +336,8 @@
Added application error reporting and added chunk names to read
benign errors; also added --strict to pngstest - not enabled
yet because a warning is produced.
+ Avoid the double gamma correction warning in the simplified API.
+ This allows the --strict option to pass in the pngstest checks
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diff --git a/CHANGES b/CHANGES
index e378d3c..6191cda 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4087,6 +4087,8 @@
Added application error reporting and added chunk names to read
benign errors; also added --strict to pngstest - not enabled
yet because a warning is produced.
+ Avoid the double gamma correction warning in the simplified API.
+ This allows the --strict option to pass in the pngstest checks
Send comments/corrections/commendations to png-mng-implement at lists.sf.net
(subscription required; visit
diff --git a/contrib/libtests/pngstest.c b/contrib/libtests/pngstest.c
index d826713..c16de96 100644
--- a/contrib/libtests/pngstest.c
+++ b/contrib/libtests/pngstest.c
@@ -299,7 +299,7 @@
#define READ_FILE 1 /* else memory */
#define USE_STDIO 2 /* else use file name */
-/* 4: unused */
+#define STRICT 4 /* fail on warnings too */
#define VERBOSE 8
#define KEEP_TMPFILES 16 /* else delete temporary files */
#define KEEP_GOING 32
@@ -313,6 +313,8 @@
printf(" --file");
if (opts & USE_STDIO)
printf(" --stdio");
+ if (opts & STRICT)
+ printf(" --strict");
if (opts & VERBOSE)
printf(" --verbose");
if (opts & KEEP_TMPFILES)
@@ -321,6 +323,8 @@
printf(" --keep-going");
if (opts & ACCUMULATE)
printf(" --accumulate");
+ if (!(opts & FAST_WRITE)) /* --fast is currently the default */
+ printf(" --slow");
}
#define FORMAT_NO_CHANGE 0x80000000 /* additional flag */
@@ -715,6 +719,9 @@
return logerror(image, image->file_name, ": opaque not NULL", "");
}
+ else if (image->image.warning_or_error != 0 && (image->opts & STRICT) != 0)
+ return logerror(image, image->file_name, " --strict", "");
+
else
return 1;
}
@@ -3454,6 +3461,8 @@
redundant = 1;
else if (strcmp(arg, "--stop") == 0)
opts &= ~KEEP_GOING;
+ else if (strcmp(arg, "--strict") == 0)
+ opts |= STRICT;
else if (strcmp(arg, "--touch") == 0)
{
if (c+1 < argc)
diff --git a/pngread.c b/pngread.c
index e9cd59c..78285b5 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1839,6 +1839,17 @@
}
static int
+make_gray_file_colormap(png_image_read_control *display)
+{
+ unsigned int i;
+
+ for (i=0; i<256; ++i)
+ png_create_colormap_entry(display, i, i, i, i, 255, E_FILE);
+
+ return i;
+}
+
+static int
make_gray_colormap(png_image_read_control *display)
{
unsigned int i;
@@ -2368,7 +2379,23 @@
if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
png_error(png_ptr, "rgb[gray] color-map: too few entries");
- cmap_entries = make_gray_colormap(display);
+ /* Ideally this code would use libpng to do the gamma correction,
+ * but if an input alpha channel is to be removed we will hit the
+ * libpng bug in gamma+compose+rgb-to-gray (the double gamma
+ * correction bug). Fix this by dropping the gamma correction in
+ * this case and doing it in the palette; this will result in
+ * duplicate palette entries, but that's better than the
+ * alternative of double gamma correction.
+ */
+ if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
+ png_ptr->num_trans > 0) && png_gamma_not_sRGB(png_ptr->gamma))
+ {
+ cmap_entries = make_gray_file_colormap(display);
+ data_encoding = E_FILE;
+ }
+
+ else
+ cmap_entries = make_gray_colormap(display);
/* But if the input has alpha or transparency it must be removed
*/
@@ -2383,18 +2410,38 @@
* it. Achieve this simply by ensuring that the entry
* selected for the background really is the background color.
*/
- if (output_encoding == E_LINEAR)
+ if (data_encoding == E_FILE) /* from the fixup above */
+ {
+ /* The app supplied a gray which is in output_encoding, we
+ * need to convert it to a value of the input (E_FILE)
+ * encoding then set this palette entry to the required
+ * output encoding.
+ */
+ if (output_encoding == E_sRGB)
+ gray = png_sRGB_table[gray]; /* now E_LINEAR */
+
+ gray = PNG_DIV257(png_gamma_16bit_correct(gray,
+ png_ptr->gamma)); /* now E_FILE */
+
+ /* And make sure the corresponding palette entry contains
+ * exactly the required sRGB value.
+ */
+ png_create_colormap_entry(display, gray, back_g, back_g,
+ back_g, 0/*unused*/, output_encoding);
+ }
+
+ else if (output_encoding == E_LINEAR)
{
gray = PNG_sRGB_FROM_LINEAR(gray * 255);
/* And make sure the corresponding palette entry matches.
*/
png_create_colormap_entry(display, gray, back_g, back_g,
- back_g, 65535, E_LINEAR);
+ back_g, 0/*unused*/, E_LINEAR);
}
- /* The background passed to libpng, however, must be the sRGB
- * value.
+ /* The background passed to libpng, however, must be the
+ * output (normally sRGB) value.
*/
c.index = 0; /*unused*/
c.gray = c.red = c.green = c.blue = (png_uint_16)gray;
@@ -2657,13 +2704,12 @@
png_error(png_ptr, "bad data option (internal error)");
break;
- case E_FILE:
- /* Make no changes */
- break;
-
case E_sRGB:
/* Change to 8-bit sRGB */
png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
+ /* FALL THROUGH */
+
+ case E_FILE:
if (png_ptr->bit_depth > 8)
png_set_scale_16(png_ptr);
break;
diff --git a/test-pngstest.sh b/test-pngstest.sh
index c9da532..e977a5b 100755
--- a/test-pngstest.sh
+++ b/test-pngstest.sh
@@ -11,7 +11,7 @@
do
for opts in ""
do
- if ./pngstest --log "$@" $opts $image >>pngtest-log.txt 2>&1
+ if ./pngstest --strict --log "$@" $opts $image >>pngtest-log.txt 2>&1
then
echo " PASS: pngstest $opts $image"
else
