jpeg/transupp.h

   1 /*
   2  * transupp.h
   3  *
   4  * Copyright (C) 1997-2009, Thomas G. Lane, Guido Vollbeding.
   5  * This file is part of the Independent JPEG Group's software.
   6  * For conditions of distribution and use, see the accompanying README file.
   7  *
   8  * This file contains declarations for image transformation routines and
   9  * other utility code used by the jpegtran sample application.  These are
  10  * NOT part of the core JPEG library.  But we keep these routines separate
  11  * from jpegtran.c to ease the task of maintaining jpegtran-like programs
  12  * that have other user interfaces.
  13  *
  14  * NOTE: all the routines declared here have very specific requirements
  15  * about when they are to be executed during the reading and writing of the
  16  * source and destination files.  See the comments in transupp.c, or see
  17  * jpegtran.c for an example of correct usage.
  18  */
  19
  20 /* If you happen not to want the image transform support, disable it here */
  21 #ifndef TRANSFORMS_SUPPORTED
  22 #define TRANSFORMS_SUPPORTED 1          /* 0 disables transform code */
  23 #endif
  24
  25 /*
  26  * Although rotating and flipping data expressed as DCT coefficients is not
  27  * hard, there is an asymmetry in the JPEG format specification for images
  28  * whose dimensions aren't multiples of the iMCU size.  The right and bottom
  29  * image edges are padded out to the next iMCU boundary with junk data; but
  30  * no padding is possible at the top and left edges.  If we were to flip
  31  * the whole image including the pad data, then pad garbage would become
  32  * visible at the top and/or left, and real pixels would disappear into the
  33  * pad margins --- perhaps permanently, since encoders & decoders may not
  34  * bother to preserve DCT blocks that appear to be completely outside the
  35  * nominal image area.  So, we have to exclude any partial iMCUs from the
  36  * basic transformation.
  37  *
  38  * Transpose is the only transformation that can handle partial iMCUs at the
  39  * right and bottom edges completely cleanly.  flip_h can flip partial iMCUs
  40  * at the bottom, but leaves any partial iMCUs at the right edge untouched.
  41  * Similarly flip_v leaves any partial iMCUs at the bottom edge untouched.
  42  * The other transforms are defined as combinations of these basic transforms
  43  * and process edge blocks in a way that preserves the equivalence.
  44  *
  45  * The "trim" option causes untransformable partial iMCUs to be dropped;
  46  * this is not strictly lossless, but it usually gives the best-looking
  47  * result for odd-size images.  Note that when this option is active,
  48  * the expected mathematical equivalences between the transforms may not hold.
  49  * (For example, -rot 270 -trim trims only the bottom edge, but -rot 90 -trim
  50  * followed by -rot 180 -trim trims both edges.)
  51  *
  52  * We also offer a lossless-crop option, which discards data outside a given
  53  * image region but losslessly preserves what is inside.  Like the rotate and
  54  * flip transforms, lossless crop is restricted by the JPEG format: the upper
  55  * left corner of the selected region must fall on an iMCU boundary.  If this
  56  * does not hold for the given crop parameters, we silently move the upper left
  57  * corner up and/or left to make it so, simultaneously increasing the region
  58  * dimensions to keep the lower right crop corner unchanged.  (Thus, the
  59  * output image covers at least the requested region, but may cover more.)
  60  *
  61  * We also provide a lossless-resize option, which is kind of a lossless-crop
  62  * operation in the DCT coefficient block domain - it discards higher-order
  63  * coefficients and losslessly preserves lower-order coefficients of a
  64  * sub-block.
  65  *
  66  * Rotate/flip transform, resize, and crop can be requested together in a
  67  * single invocation.  The crop is applied last --- that is, the crop region
  68  * is specified in terms of the destination image after transform/resize.
  69  *
  70  * We also offer a "force to grayscale" option, which simply discards the
  71  * chrominance channels of a YCbCr image.  This is lossless in the sense that
  72  * the luminance channel is preserved exactly.  It's not the same kind of
  73  * thing as the rotate/flip transformations, but it's convenient to handle it
  74  * as part of this package, mainly because the transformation routines have to
  75  * be aware of the option to know how many components to work on.
  76  */
  77
  78
  79 /* Short forms of external names for systems with brain-damaged linkers. */
  80
  81 #ifdef NEED_SHORT_EXTERNAL_NAMES
  82 #define jtransform_parse_crop_spec      jTrParCrop
  83 #define jtransform_request_workspace    jTrRequest
  84 #define jtransform_adjust_parameters    jTrAdjust
  85 #define jtransform_execute_transform    jTrExec
  86 #define jtransform_perfect_transform    jTrPerfect
  87 #define jcopy_markers_setup             jCMrkSetup
  88 #define jcopy_markers_execute           jCMrkExec
  89 #endif /* NEED_SHORT_EXTERNAL_NAMES */
  90
  91
  92 /*
  93  * Codes for supported types of image transformations.
  94  */
  95
  96 typedef enum {
  97         JXFORM_NONE,            /* no transformation */
  98         JXFORM_FLIP_H,          /* horizontal flip */
  99         JXFORM_FLIP_V,          /* vertical flip */
 100         JXFORM_TRANSPOSE,       /* transpose across UL-to-LR axis */
 101         JXFORM_TRANSVERSE,      /* transpose across UR-to-LL axis */
 102         JXFORM_ROT_90,          /* 90-degree clockwise rotation */
 103         JXFORM_ROT_180,         /* 180-degree rotation */
 104         JXFORM_ROT_270          /* 270-degree clockwise (or 90 ccw) */
 105 } JXFORM_CODE;
 106
 107 /*
 108  * Codes for crop parameters, which can individually be unspecified,
 109  * positive, or negative.  (Negative width or height makes no sense, though.)
 110  */
 111
 112 typedef enum {
 113         JCROP_UNSET,
 114         JCROP_POS,
 115         JCROP_NEG
 116 } JCROP_CODE;
 117
 118 /*
 119  * Transform parameters struct.
 120  * NB: application must not change any elements of this struct after
 121  * calling jtransform_request_workspace.
 122  */
 123
 124 typedef struct {
 125   /* Options: set by caller */
 126   JXFORM_CODE transform;        /* image transform operator */
 127   boolean perfect;              /* if TRUE, fail if partial MCUs are requested */
 128   boolean trim;                 /* if TRUE, trim partial MCUs as needed */
 129   boolean force_grayscale;      /* if TRUE, convert color image to grayscale */
 130   boolean crop;                 /* if TRUE, crop source image */
 131
 132   /* Crop parameters: application need not set these unless crop is TRUE.
 133    * These can be filled in by jtransform_parse_crop_spec().
 134    */
 135   JDIMENSION crop_width;        /* Width of selected region */
 136   JCROP_CODE crop_width_set;
 137   JDIMENSION crop_height;       /* Height of selected region */
 138   JCROP_CODE crop_height_set;
 139   JDIMENSION crop_xoffset;      /* X offset of selected region */
 140   JCROP_CODE crop_xoffset_set;  /* (negative measures from right edge) */
 141   JDIMENSION crop_yoffset;      /* Y offset of selected region */
 142   JCROP_CODE crop_yoffset_set;  /* (negative measures from bottom edge) */
 143
 144   /* Internal workspace: caller should not touch these */
 145   int num_components;           /* # of components in workspace */
 146   jvirt_barray_ptr * workspace_coef_arrays; /* workspace for transformations */
 147   JDIMENSION output_width;      /* cropped destination dimensions */
 148   JDIMENSION output_height;
 149   JDIMENSION x_crop_offset;     /* destination crop offsets measured in iMCUs */
 150   JDIMENSION y_crop_offset;
 151   int iMCU_sample_width;        /* destination iMCU size */
 152   int iMCU_sample_height;
 153 } jpeg_transform_info;
 154
 155
 156 #if TRANSFORMS_SUPPORTED
 157
 158 /* Parse a crop specification (written in X11 geometry style) */
 159 EXTERN(boolean) jtransform_parse_crop_spec
 160         JPP((jpeg_transform_info *info, const char *spec));
 161 /* Request any required workspace */
 162 EXTERN(boolean) jtransform_request_workspace
 163         JPP((j_decompress_ptr srcinfo, jpeg_transform_info *info));
 164 /* Adjust output image parameters */
 165 EXTERN(jvirt_barray_ptr *) jtransform_adjust_parameters
 166         JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
 167              jvirt_barray_ptr *src_coef_arrays,
 168              jpeg_transform_info *info));
 169 /* Execute the actual transformation, if any */
 170 EXTERN(void) jtransform_execute_transform
 171         JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
 172              jvirt_barray_ptr *src_coef_arrays,
 173              jpeg_transform_info *info));
 174 /* Determine whether lossless transformation is perfectly
 175  * possible for a specified image and transformation.
 176  */
 177 EXTERN(boolean) jtransform_perfect_transform
 178         JPP((JDIMENSION image_width, JDIMENSION image_height,
 179              int MCU_width, int MCU_height,
 180              JXFORM_CODE transform));
 181
 182 /* jtransform_execute_transform used to be called
 183  * jtransform_execute_transformation, but some compilers complain about
 184  * routine names that long.  This macro is here to avoid breaking any
 185  * old source code that uses the original name...
 186  */
 187 #define jtransform_execute_transformation       jtransform_execute_transform
 188
 189 #endif /* TRANSFORMS_SUPPORTED */
 190
 191
 192 /*
 193  * Support for copying optional markers from source to destination file.
 194  */
 195
 196 typedef enum {
 197         JCOPYOPT_NONE,          /* copy no optional markers */
 198         JCOPYOPT_COMMENTS,      /* copy only comment (COM) markers */
 199         JCOPYOPT_ALL            /* copy all optional markers */
 200 } JCOPY_OPTION;
 201
 202 #define JCOPYOPT_DEFAULT  JCOPYOPT_COMMENTS     /* recommended default */
 203
 204 /* Setup decompression object to save desired markers in memory */
 205 EXTERN(void) jcopy_markers_setup
 206         JPP((j_decompress_ptr srcinfo, JCOPY_OPTION option));
 207 /* Copy markers saved in the given source object to the destination object */
 208 EXTERN(void) jcopy_markers_execute
 209         JPP((j_decompress_ptr srcinfo, j_compress_ptr dstinfo,
 210              JCOPY_OPTION option));