# dlib C++ Library - transupp.h

    /*
     * transupp.h
     *
     * Copyright (C) 1997-2011, 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 */
    #ifndef TRANSFORMS_SUPPORTED
    #define TRANSFORMS_SUPPORTED 1		/* 0 disables transform code */
    #endif

    /*
     * 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.)
     * The adjustment of the region dimensions may be optionally disabled.
     *
     * 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. */

    #ifdef NEED_SHORT_EXTERNAL_NAMES
    #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
    #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;

    /*
     * Codes for crop parameters, which can individually be unspecified,
     * positive or negative for xoffset or yoffset,
     * positive or forced for width or height.
     */

    typedef enum {
            JCROP_UNSET,
            JCROP_POS,
            JCROP_NEG,
            JCROP_FORCE
    } JCROP_CODE;

    /*
     * 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;	/* (forced disables adjustment) */
      JDIMENSION crop_height;	/* Height of selected region */
      JCROP_CODE crop_height_set;	/* (forced disables adjustment) */
      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;

    #if TRANSFORMS_SUPPORTED

    /* 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

    #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));