/* * transupp.h * * This file was part of the Independent JPEG Group's software: * Copyright (C) 1997-2019, Thomas G. Lane, Guido Vollbeding. * libjpeg-turbo Modifications: * Copyright (C) 2017, 2021, D. R. Commander. * For conditions of distribution and use, see the accompanying README.ijg * 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 … #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. * * A complementary lossless wipe option is provided to discard (gray out) data * inside a given image region while losslessly preserving what is outside. * A lossless drop option is also provided, which allows another JPEG image to * be inserted ("dropped") into the source image data at a given position, * replacing the existing image data at that position. Both the source image * and the drop image must have the same subsampling level. It is best if they * also have the same quantization (quality.) Otherwise, the quantization of * the output image will be adapted to accommodate the higher of the source * image quality and the drop image quality. The trim option can be used with * the drop option to requantize the drop image to match the source image. * * 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. */ /* * Codes for supported types of image transformations. */ JXFORM_CODE; /* * Codes for crop parameters, which can individually be unspecified, * positive or negative for xoffset or yoffset, * positive or force or reflect for width or height. */ JCROP_CODE; /* * Transform parameters struct. * NB: application must not change any elements of this struct after * calling jtransform_request_workspace. */ jpeg_transform_info; #if TRANSFORMS_SUPPORTED /* Parse a crop specification (written in X11 geometry style) */ EXTERN(boolean) jtransform_parse_crop_spec(jpeg_transform_info *info, const char *spec); /* Request any required workspace */ EXTERN(boolean) jtransform_request_workspace(j_decompress_ptr srcinfo, jpeg_transform_info *info); /* Adjust output image parameters */ EXTERN(jvirt_barray_ptr *) jtransform_adjust_parameters (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(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(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 … #endif /* TRANSFORMS_SUPPORTED */ /* * Support for copying optional markers from source to destination file. */ JCOPY_OPTION; #define JCOPYOPT_DEFAULT … /* Setup decompression object to save desired markers in memory */ EXTERN(void) jcopy_markers_setup(j_decompress_ptr srcinfo, JCOPY_OPTION option); /* Copy markers saved in the given source object to the destination object */ EXTERN(void) jcopy_markers_execute(j_decompress_ptr srcinfo, j_compress_ptr dstinfo, JCOPY_OPTION option);
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