ec6e451d05
Referring to https://github.com/libjpeg-turbo/libjpeg-turbo/issues/402#issuecomment-768348440 and https://github.com/libjpeg-turbo/libjpeg-turbo/issues/402#issuecomment-770221584 Ken Murchison clarified that it was his intent to release the lossless JPEG patch under the IJG License and that adding his name to the copyright headers would be sufficient to acknowledge that any derivatives are based on his work.
300 lines
8.1 KiB
C
300 lines
8.1 KiB
C
/*
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* jcpred.c
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*
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* This file was part of the Independent JPEG Group's software:
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* Copyright (C) 1998, Thomas G. Lane.
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* Lossless JPEG Modifications:
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* Copyright (C) 1999, Ken Murchison.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains sample differencing for lossless JPEG.
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*
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* In order to avoid paying the performance penalty of having to check the
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* predictor being used and the row being processed for each call of the
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* undifferencer, and to promote optimization, we have separate differencing
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* functions for each case.
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*
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* We are able to avoid duplicating source code by implementing the predictors
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* and differencers as macros. Each of the differencing functions are
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* simply wrappers around a DIFFERENCE macro with the appropriate PREDICTOR
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* macro passed as an argument.
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*/
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jlossls.h" /* Private declarations for lossless codec */
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#ifdef C_LOSSLESS_SUPPORTED
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/* Private predictor object */
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typedef struct {
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/* MCU-rows left in the restart interval for each component */
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unsigned int restart_rows_to_go[MAX_COMPONENTS];
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} c_predictor;
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typedef c_predictor * c_pred_ptr;
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/* Forward declarations */
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LOCAL(void) reset_predictor
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JPP((j_compress_ptr cinfo, int ci));
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METHODDEF(void) start_pass
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JPP((j_compress_ptr cinfo));
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/* Predictor for the first column of the first row: 2^(P-Pt-1) */
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#define INITIAL_PREDICTORx (1 << (cinfo->data_precision - cinfo->Al - 1))
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/* Predictor for the first column of the remaining rows: Rb */
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#define INITIAL_PREDICTOR2 GETJSAMPLE(prev_row[0])
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/*
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* 1-Dimensional differencer routine.
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*
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* This macro implements the 1-D horizontal predictor (1). INITIAL_PREDICTOR
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* is used as the special case predictor for the first column, which must be
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* either INITIAL_PREDICTOR2 or INITIAL_PREDICTORx. The remaining samples
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* use PREDICTOR1.
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*/
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#define DIFFERENCE_1D(INITIAL_PREDICTOR) \
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j_lossless_c_ptr losslsc = (j_lossless_c_ptr) cinfo->codec; \
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c_pred_ptr pred = (c_pred_ptr) losslsc->pred_private; \
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boolean restart = FALSE; \
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int xindex; \
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int samp, Ra; \
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\
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samp = GETJSAMPLE(input_buf[0]); \
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diff_buf[0] = samp - INITIAL_PREDICTOR; \
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\
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for (xindex = 1; xindex < width; xindex++) { \
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Ra = samp; \
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samp = GETJSAMPLE(input_buf[xindex]); \
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diff_buf[xindex] = samp - PREDICTOR1; \
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} \
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\
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/* Account for restart interval (no-op if not using restarts) */ \
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if (cinfo->restart_interval) { \
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if (--(pred->restart_rows_to_go[ci]) == 0) { \
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reset_predictor(cinfo, ci); \
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restart = TRUE; \
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} \
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}
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/*
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* 2-Dimensional differencer routine.
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*
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* This macro implements the 2-D horizontal predictors (#2-7). PREDICTOR2 is
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* used as the special case predictor for the first column. The remaining
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* samples use PREDICTOR, which is a function of Ra, Rb, Rc.
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*
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* Because prev_row and output_buf may point to the same storage area (in an
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* interleaved image with Vi=1, for example), we must take care to buffer Rb/Rc
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* before writing the current reconstructed sample value into output_buf.
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*/
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#define DIFFERENCE_2D(PREDICTOR) \
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j_lossless_c_ptr losslsc = (j_lossless_c_ptr) cinfo->codec; \
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c_pred_ptr pred = (c_pred_ptr) losslsc->pred_private; \
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int xindex; \
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int samp, Ra, Rb, Rc; \
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\
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Rb = GETJSAMPLE(prev_row[0]); \
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samp = GETJSAMPLE(input_buf[0]); \
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diff_buf[0] = samp - PREDICTOR2; \
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\
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for (xindex = 1; xindex < width; xindex++) { \
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Rc = Rb; \
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Rb = GETJSAMPLE(prev_row[xindex]); \
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Ra = samp; \
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samp = GETJSAMPLE(input_buf[xindex]); \
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diff_buf[xindex] = samp - PREDICTOR; \
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} \
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\
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/* Account for restart interval (no-op if not using restarts) */ \
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if (cinfo->restart_interval) { \
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if (--pred->restart_rows_to_go[ci] == 0) \
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reset_predictor(cinfo, ci); \
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}
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/*
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* Differencers for the all rows but the first in a scan or restart interval.
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* The first sample in the row is differenced using the vertical
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* predictor (2). The rest of the samples are differenced using the
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* predictor specified in the scan header.
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*/
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METHODDEF(void)
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jpeg_difference1(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_1D(INITIAL_PREDICTOR2);
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}
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METHODDEF(void)
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jpeg_difference2(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR2);
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}
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METHODDEF(void)
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jpeg_difference3(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR3);
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}
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METHODDEF(void)
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jpeg_difference4(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR4);
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}
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METHODDEF(void)
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jpeg_difference5(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR5);
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}
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METHODDEF(void)
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jpeg_difference6(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR6);
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}
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METHODDEF(void)
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jpeg_difference7(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_2D(PREDICTOR7);
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}
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/*
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* Differencer for the first row in a scan or restart interval. The first
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* sample in the row is differenced using the special predictor constant
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* x=2^(P-Pt-1). The rest of the samples are differenced using the
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* 1-D horizontal predictor (1).
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*/
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METHODDEF(void)
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jpeg_difference_first_row(j_compress_ptr cinfo, int ci,
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JSAMPROW input_buf, JSAMPROW prev_row,
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JDIFFROW diff_buf, JDIMENSION width)
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{
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DIFFERENCE_1D(INITIAL_PREDICTORx);
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/*
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* Now that we have differenced the first row, we want to use the
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* differencer which corresponds to the predictor specified in the
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* scan header.
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*
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* Note that we don't to do this if we have just reset the predictor
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* for a new restart interval.
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*/
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if (!restart) {
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switch (cinfo->Ss) {
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case 1:
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losslsc->predict_difference[ci] = jpeg_difference1;
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break;
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case 2:
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losslsc->predict_difference[ci] = jpeg_difference2;
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break;
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case 3:
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losslsc->predict_difference[ci] = jpeg_difference3;
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break;
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case 4:
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losslsc->predict_difference[ci] = jpeg_difference4;
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break;
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case 5:
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losslsc->predict_difference[ci] = jpeg_difference5;
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break;
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case 6:
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losslsc->predict_difference[ci] = jpeg_difference6;
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break;
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case 7:
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losslsc->predict_difference[ci] = jpeg_difference7;
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break;
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}
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}
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}
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/*
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* Reset predictor at the start of a pass or restart interval.
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*/
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LOCAL(void)
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reset_predictor (j_compress_ptr cinfo, int ci)
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{
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j_lossless_c_ptr losslsc = (j_lossless_c_ptr) cinfo->codec;
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c_pred_ptr pred = (c_pred_ptr) losslsc->pred_private;
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/* Initialize restart counter */
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pred->restart_rows_to_go[ci] =
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cinfo->restart_interval / cinfo->MCUs_per_row;
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/* Set difference function to first row function */
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losslsc->predict_difference[ci] = jpeg_difference_first_row;
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}
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/*
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* Initialize for an input processing pass.
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*/
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METHODDEF(void)
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start_pass (j_compress_ptr cinfo)
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{
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j_lossless_c_ptr losslsc = (j_lossless_c_ptr) cinfo->codec;
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c_pred_ptr pred = (c_pred_ptr) losslsc->pred_private;
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int ci;
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/* Check that the restart interval is an integer multiple of the number
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* of MCU in an MCU-row.
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*/
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if (cinfo->restart_interval % cinfo->MCUs_per_row != 0)
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ERREXIT2(cinfo, JERR_BAD_RESTART,
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cinfo->restart_interval, cinfo->MCUs_per_row);
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/* Set predictors for start of pass */
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for (ci = 0; ci < cinfo->num_components; ci++)
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reset_predictor(cinfo, ci);
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}
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/*
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* Module initialization routine for the differencer.
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*/
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GLOBAL(void)
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jinit_differencer (j_compress_ptr cinfo)
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{
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j_lossless_c_ptr losslsc = (j_lossless_c_ptr) cinfo->codec;
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c_pred_ptr pred;
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pred = (c_pred_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(c_predictor));
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losslsc->pred_private = (void *) pred;
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losslsc->predict_start_pass = start_pass;
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}
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#endif /* C_LOSSLESS_SUPPORTED */
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