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* transupp.h
* Copyright (C) 1997-2009, Thomas G. Lane, Guido Vollbeding.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
* This file contains declarations for image transformation routines and
* other utility code used by the jpegtran sample application. These are
* NOT part of the core JPEG library. But we keep these routines separate
* from jpegtran.c to ease the task of maintaining jpegtran-like programs
* that have other user interfaces.
* NOTE: all the routines declared here have very specific requirements
* about when they are to be executed during the reading and writing of the
* source and destination files. See the comments in transupp.c, or see
* jpegtran.c for an example of correct usage.
/* If you happen not to want the image transform support, disable it here */
#define TRANSFORMS_SUPPORTED 1 /* 0 disables transform code */
* Although rotating and flipping data expressed as DCT coefficients is not
* hard, there is an asymmetry in the JPEG format specification for images
* whose dimensions aren't multiples of the iMCU size. The right and bottom
* image edges are padded out to the next iMCU boundary with junk data; but
* no padding is possible at the top and left edges. If we were to flip
* the whole image including the pad data, then pad garbage would become
* visible at the top and/or left, and real pixels would disappear into the
* pad margins --- perhaps permanently, since encoders & decoders may not
* bother to preserve DCT blocks that appear to be completely outside the
* nominal image area. So, we have to exclude any partial iMCUs from the
* basic transformation.
* Transpose is the only transformation that can handle partial iMCUs at the
* right and bottom edges completely cleanly. flip_h can flip partial iMCUs
* at the bottom, but leaves any partial iMCUs at the right edge untouched.
* Similarly flip_v leaves any partial iMCUs at the bottom edge untouched.
* The other transforms are defined as combinations of these basic transforms
* and process edge blocks in a way that preserves the equivalence.
* The "trim" option causes untransformable partial iMCUs to be dropped;
* this is not strictly lossless, but it usually gives the best-looking
* result for odd-size images. Note that when this option is active,
* the expected mathematical equivalences between the transforms may not hold.
* (For example, -rot 270 -trim trims only the bottom edge, but -rot 90 -trim
* followed by -rot 180 -trim trims both edges.)
* We also offer a lossless-crop option, which discards data outside a given
* image region but losslessly preserves what is inside. Like the rotate and
* flip transforms, lossless crop is restricted by the JPEG format: the upper
* left corner of the selected region must fall on an iMCU boundary. If this
* does not hold for the given crop parameters, we silently move the upper left
* corner up and/or left to make it so, simultaneously increasing the region
* dimensions to keep the lower right crop corner unchanged. (Thus, the
* output image covers at least the requested region, but may cover more.)
* We also provide a lossless-resize option, which is kind of a lossless-crop
* operation in the DCT coefficient block domain - it discards higher-order
* coefficients and losslessly preserves lower-order coefficients of a
* sub-block.
* Rotate/flip transform, resize, and crop can be requested together in a
* single invocation. The crop is applied last --- that is, the crop region
* is specified in terms of the destination image after transform/resize.
* We also offer a "force to grayscale" option, which simply discards the
* chrominance channels of a YCbCr image. This is lossless in the sense that
* the luminance channel is preserved exactly. It's not the same kind of
* thing as the rotate/flip transformations, but it's convenient to handle it
* as part of this package, mainly because the transformation routines have to
* be aware of the option to know how many components to work on.
/* Short forms of external names for systems with brain-damaged linkers. */
#define jtransform_parse_crop_spec jTrParCrop
#define jtransform_request_workspace jTrRequest
#define jtransform_adjust_parameters jTrAdjust
#define jtransform_execute_transform jTrExec
#define jtransform_perfect_transform jTrPerfect
#define jcopy_markers_setup jCMrkSetup
#define jcopy_markers_execute jCMrkExec
* Codes for supported types of image transformations.
typedef enum {
JXFORM_NONE, /* no transformation */
JXFORM_FLIP_H, /* horizontal flip */
JXFORM_FLIP_V, /* vertical flip */
JXFORM_TRANSPOSE, /* transpose across UL-to-LR axis */
JXFORM_TRANSVERSE, /* transpose across UR-to-LL axis */
JXFORM_ROT_90, /* 90-degree clockwise rotation */
JXFORM_ROT_180, /* 180-degree rotation */
JXFORM_ROT_270 /* 270-degree clockwise (or 90 ccw) */
* Codes for crop parameters, which can individually be unspecified,
* positive, or negative. (Negative width or height makes no sense, though.)
typedef enum {
* Transform parameters struct.
* NB: application must not change any elements of this struct after
* calling jtransform_request_workspace.
typedef struct {
/* Options: set by caller */
JXFORM_CODE transform; /* image transform operator */
boolean perfect; /* if TRUE, fail if partial MCUs are requested */
boolean trim; /* if TRUE, trim partial MCUs as needed */
boolean force_grayscale; /* if TRUE, convert color image to grayscale */
boolean crop; /* if TRUE, crop source image */
/* Crop parameters: application need not set these unless crop is TRUE.
* These can be filled in by jtransform_parse_crop_spec().
JDIMENSION crop_width; /* Width of selected region */
JCROP_CODE crop_width_set;
JDIMENSION crop_height; /* Height of selected region */
JCROP_CODE crop_height_set;
JDIMENSION crop_xoffset; /* X offset of selected region */
JCROP_CODE crop_xoffset_set; /* (negative measures from right edge) */
JDIMENSION crop_yoffset; /* Y offset of selected region */
JCROP_CODE crop_yoffset_set; /* (negative measures from bottom edge) */
/* Internal workspace: caller should not touch these */
int num_components; /* # of components in workspace */
jvirt_barray_ptr * workspace_coef_arrays; /* workspace for transformations */
JDIMENSION output_width; /* cropped destination dimensions */
JDIMENSION output_height;
JDIMENSION x_crop_offset; /* destination crop offsets measured in iMCUs */
JDIMENSION y_crop_offset;
int iMCU_sample_width; /* destination iMCU size */
int iMCU_sample_height;
} jpeg_transform_info;
/* Parse a crop specification (written in X11 geometry style) */
EXTERN(boolean) jtransform_parse_crop_spec
JPP((jpeg_transform_info *info, const char *spec));
/* Request any required workspace */
EXTERN(boolean) jtransform_request_workspace
JPP((j_decompress_ptr srcinfo, jpeg_transform_info *info));
/* Adjust output image parameters */
EXTERN(jvirt_barray_ptr *) jtransform_adjust_parameters
JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
jvirt_barray_ptr *src_coef_arrays,
jpeg_transform_info *info));
/* Execute the actual transformation, if any */
EXTERN(void) jtransform_execute_transform
JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
jvirt_barray_ptr *src_coef_arrays,
jpeg_transform_info *info));
/* Determine whether lossless transformation is perfectly
* possible for a specified image and transformation.
EXTERN(boolean) jtransform_perfect_transform
JPP((JDIMENSION image_width, JDIMENSION image_height,
int MCU_width, int MCU_height,
JXFORM_CODE transform));
/* jtransform_execute_transform used to be called
* jtransform_execute_transformation, but some compilers complain about
* routine names that long. This macro is here to avoid breaking any
* old source code that uses the original name...
#define jtransform_execute_transformation jtransform_execute_transform
* Support for copying optional markers from source to destination file.
typedef enum {
JCOPYOPT_NONE, /* copy no optional markers */
JCOPYOPT_COMMENTS, /* copy only comment (COM) markers */
JCOPYOPT_ALL /* copy all optional markers */
#define JCOPYOPT_DEFAULT JCOPYOPT_COMMENTS /* recommended default */
/* Setup decompression object to save desired markers in memory */
EXTERN(void) jcopy_markers_setup
JPP((j_decompress_ptr srcinfo, JCOPY_OPTION option));
/* Copy markers saved in the given source object to the destination object */
EXTERN(void) jcopy_markers_execute
JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
JCOPY_OPTION option));