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transupp.h

/*
 * 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 */
#ifndef TRANSFORMS_SUPPORTED
#define TRANSFORMS_SUPPORTED 1            /* 0 disables transform code */
#endif

/* Short forms of external names for systems with brain-damaged linkers. */

#ifdef NEED_SHORT_EXTERNAL_NAMES
#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
#endif /* NEED_SHORT_EXTERNAL_NAMES */


/*
 * 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) */
} JXFORM_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 "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;


#if TRANSFORMS_SUPPORTED

/* 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));

#endif /* TRANSFORMS_SUPPORTED */


/*
 * 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 */
} JCOPY_OPTION;

#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));

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