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* transupp.h
* Copyright (C) 1997, Thomas G. Lane.
* 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 */
/* Short forms of external names for systems with brain-damaged linkers. */
#define jtransform_request_workspace jTrRequest
#define jtransform_adjust_parameters jTrAdjust
#define jtransform_execute_transformation jTrExec
#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) */
* 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 "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.
typedef struct {
/* Options: set by caller */
JXFORM_CODE transform; /* image transform operator */
boolean trim; /* if TRUE, trim partial MCUs as needed */
boolean force_grayscale; /* if TRUE, convert color image to grayscale */
/* Internal workspace: caller should not touch these */
int num_components; /* # of components in workspace */
jvirt_barray_ptr * workspace_coef_arrays; /* workspace for transformations */
} jpeg_transform_info;
/* Request any required workspace */
EXTERN(void) 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_transformation
JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
jvirt_barray_ptr *src_coef_arrays,
jpeg_transform_info *info));
* 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));