Source code
Revision control
Copy as Markdown
Other Tools
/*
* jcdiffct.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1994-1997, Thomas G. Lane.
* Lossless JPEG Modifications:
* Copyright (C) 1999, Ken Murchison.
* libjpeg-turbo Modifications:
* Copyright (C) 2022, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains the difference buffer controller for compression.
* This controller is the top level of the lossless JPEG compressor proper.
* The difference buffer lies between the prediction/differencing and entropy
* encoding steps.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jlossls.h" /* Private declarations for lossless codec */
#ifdef C_LOSSLESS_SUPPORTED
/* We use a full-image sample buffer when doing Huffman optimization,
* and also for writing multiple-scan JPEG files. In all cases, the
* full-image buffer is filled during the first pass, and the scaling,
* prediction and differencing steps are run during subsequent passes.
*/
#ifdef ENTROPY_OPT_SUPPORTED
#define FULL_SAMP_BUFFER_SUPPORTED
#else
#ifdef C_MULTISCAN_FILES_SUPPORTED
#define FULL_SAMP_BUFFER_SUPPORTED
#endif
#endif
/* Private buffer controller object */
typedef struct {
struct jpeg_c_coef_controller pub; /* public fields */
JDIMENSION iMCU_row_num; /* iMCU row # within image */
JDIMENSION mcu_ctr; /* counts MCUs processed in current row */
int MCU_vert_offset; /* counts MCU rows within iMCU row */
int MCU_rows_per_iMCU_row; /* number of such rows needed */
_JSAMPROW cur_row[MAX_COMPONENTS]; /* row of point-transformed samples */
_JSAMPROW prev_row[MAX_COMPONENTS]; /* previous row of Pt'd samples */
JDIFFARRAY diff_buf[MAX_COMPONENTS]; /* iMCU row of differences */
/* In multi-pass modes, we need a virtual sample array for each component. */
jvirt_sarray_ptr whole_image[MAX_COMPONENTS];
} my_diff_controller;
typedef my_diff_controller *my_diff_ptr;
/* Forward declarations */
METHODDEF(boolean) compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf);
#ifdef FULL_SAMP_BUFFER_SUPPORTED
METHODDEF(boolean) compress_first_pass(j_compress_ptr cinfo,
_JSAMPIMAGE input_buf);
METHODDEF(boolean) compress_output(j_compress_ptr cinfo,
_JSAMPIMAGE input_buf);
#endif
LOCAL(void)
start_iMCU_row(j_compress_ptr cinfo)
/* Reset within-iMCU-row counters for a new row */
{
my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
/* In an interleaved scan, an MCU row is the same as an iMCU row.
* In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
* But at the bottom of the image, process only what's left.
*/
if (cinfo->comps_in_scan > 1) {
diff->MCU_rows_per_iMCU_row = 1;
} else {
if (diff->iMCU_row_num < (cinfo->total_iMCU_rows-1))
diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
else
diff->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
}
diff->mcu_ctr = 0;
diff->MCU_vert_offset = 0;
}
/*
* Initialize for a processing pass.
*/
METHODDEF(void)
start_pass_diff(j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
/* Because it is hitching a ride on the jpeg_forward_dct struct,
* start_pass_lossless() will be called at the start of the initial pass.
* This ensures that it will be called at the start of the Huffman
* optimization and output passes as well.
*/
if (pass_mode == JBUF_CRANK_DEST)
(*cinfo->fdct->start_pass) (cinfo);
diff->iMCU_row_num = 0;
start_iMCU_row(cinfo);
switch (pass_mode) {
case JBUF_PASS_THRU:
if (diff->whole_image[0] != NULL)
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
diff->pub._compress_data = compress_data;
break;
#ifdef FULL_SAMP_BUFFER_SUPPORTED
case JBUF_SAVE_AND_PASS:
if (diff->whole_image[0] == NULL)
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
diff->pub._compress_data = compress_first_pass;
break;
case JBUF_CRANK_DEST:
if (diff->whole_image[0] == NULL)
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
diff->pub._compress_data = compress_output;
break;
#endif
default:
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
break;
}
}
#define SWAP_ROWS(rowa, rowb) { \
_JSAMPROW temp = rowa; \
rowa = rowb; rowb = temp; \
}
/*
* Process some data in the single-pass case.
* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
* per call, ie, v_samp_factor rows for each component in the image.
* Returns TRUE if the iMCU row is completed, FALSE if suspended.
*
* NB: input_buf contains a plane for each component in image,
* which we index according to the component's SOF position.
*/
METHODDEF(boolean)
compress_data(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
{
my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
lossless_comp_ptr losslessc = (lossless_comp_ptr)cinfo->fdct;
JDIMENSION MCU_col_num; /* index of current MCU within row */
JDIMENSION MCU_count; /* number of MCUs encoded */
JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
int ci, compi, yoffset, samp_row, samp_rows, samps_across;
jpeg_component_info *compptr;
/* Loop to write as much as one whole iMCU row */
for (yoffset = diff->MCU_vert_offset; yoffset < diff->MCU_rows_per_iMCU_row;
yoffset++) {
MCU_col_num = diff->mcu_ctr;
/* Scale and predict each scanline of the MCU row separately.
*
* Note: We only do this if we are at the start of an MCU row, ie,
* we don't want to reprocess a row suspended by the output.
*/
if (MCU_col_num == 0) {
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
compi = compptr->component_index;
if (diff->iMCU_row_num < last_iMCU_row)
samp_rows = compptr->v_samp_factor;
else {
/* NB: can't use last_row_height here, since may not be set! */
samp_rows =
(int)(compptr->height_in_blocks % compptr->v_samp_factor);
if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
else {
/* Fill dummy difference rows at the bottom edge with zeros, which
* will encode to the smallest amount of data.
*/
for (samp_row = samp_rows; samp_row < compptr->v_samp_factor;
samp_row++)
memset(diff->diff_buf[compi][samp_row], 0,
jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor) * sizeof(JDIFF));
}
}
samps_across = compptr->width_in_blocks;
for (samp_row = 0; samp_row < samp_rows; samp_row++) {
(*losslessc->scaler_scale) (cinfo,
input_buf[compi][samp_row],
diff->cur_row[compi],
samps_across);
(*losslessc->predict_difference[compi])
(cinfo, compi, diff->cur_row[compi], diff->prev_row[compi],
diff->diff_buf[compi][samp_row], samps_across);
SWAP_ROWS(diff->cur_row[compi], diff->prev_row[compi]);
}
}
}
/* Try to write the MCU row (or remaining portion of suspended MCU row). */
MCU_count =
(*cinfo->entropy->encode_mcus) (cinfo,
diff->diff_buf, yoffset, MCU_col_num,
cinfo->MCUs_per_row - MCU_col_num);
if (MCU_count != cinfo->MCUs_per_row - MCU_col_num) {
/* Suspension forced; update state counters and exit */
diff->MCU_vert_offset = yoffset;
diff->mcu_ctr += MCU_col_num;
return FALSE;
}
/* Completed an MCU row, but perhaps not an iMCU row */
diff->mcu_ctr = 0;
}
/* Completed the iMCU row, advance counters for next one */
diff->iMCU_row_num++;
start_iMCU_row(cinfo);
return TRUE;
}
#ifdef FULL_SAMP_BUFFER_SUPPORTED
/*
* Process some data in the first pass of a multi-pass case.
* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
* per call, ie, v_samp_factor rows for each component in the image.
* This amount of data is read from the source buffer and saved into the
* virtual arrays.
*
* We must also emit the data to the compressor. This is conveniently
* done by calling compress_output() after we've loaded the current strip
* of the virtual arrays.
*
* NB: input_buf contains a plane for each component in image. All components
* are loaded into the virtual arrays in this pass. However, it may be that
* only a subset of the components are emitted to the compressor during
* this first pass; be careful about looking at the scan-dependent variables
* (MCU dimensions, etc).
*/
METHODDEF(boolean)
compress_first_pass(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
{
my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
JDIMENSION last_iMCU_row = cinfo->total_iMCU_rows - 1;
JDIMENSION samps_across;
int ci, samp_row, samp_rows;
_JSAMPARRAY buffer;
jpeg_component_info *compptr;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
/* Align the virtual buffer for this component. */
buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
((j_common_ptr)cinfo, diff->whole_image[ci],
diff->iMCU_row_num * compptr->v_samp_factor,
(JDIMENSION)compptr->v_samp_factor, TRUE);
/* Count non-dummy sample rows in this iMCU row. */
if (diff->iMCU_row_num < last_iMCU_row)
samp_rows = compptr->v_samp_factor;
else {
/* NB: can't use last_row_height here, since may not be set! */
samp_rows = (int)(compptr->height_in_blocks % compptr->v_samp_factor);
if (samp_rows == 0) samp_rows = compptr->v_samp_factor;
}
samps_across = compptr->width_in_blocks;
/* Perform point transform scaling and prediction/differencing for all
* non-dummy rows in this iMCU row. Each call on these functions
* processes a complete row of samples.
*/
for (samp_row = 0; samp_row < samp_rows; samp_row++) {
memcpy(buffer[samp_row], input_buf[ci][samp_row],
samps_across * sizeof(_JSAMPLE));
}
}
/* NB: compress_output will increment iMCU_row_num if successful.
* A suspension return will result in redoing all the work above next time.
*/
/* Emit data to the compressor, sharing code with subsequent passes */
return compress_output(cinfo, input_buf);
}
/*
* Process some data in subsequent passes of a multi-pass case.
* We process the equivalent of one fully interleaved MCU row ("iMCU" row)
* per call, ie, v_samp_factor rows for each component in the scan.
* The data is obtained from the virtual arrays and fed to the compressor.
* Returns TRUE if the iMCU row is completed, FALSE if suspended.
*
* NB: input_buf is ignored; it is likely to be a NULL pointer.
*/
METHODDEF(boolean)
compress_output(j_compress_ptr cinfo, _JSAMPIMAGE input_buf)
{
my_diff_ptr diff = (my_diff_ptr)cinfo->coef;
int ci, compi;
_JSAMPARRAY buffer[MAX_COMPS_IN_SCAN];
jpeg_component_info *compptr;
/* Align the virtual buffers for the components used in this scan.
* NB: during first pass, this is safe only because the buffers will
* already be aligned properly, so jmemmgr.c won't need to do any I/O.
*/
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
compi = compptr->component_index;
buffer[compi] = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
((j_common_ptr)cinfo, diff->whole_image[compi],
diff->iMCU_row_num * compptr->v_samp_factor,
(JDIMENSION)compptr->v_samp_factor, FALSE);
}
return compress_data(cinfo, buffer);
}
#endif /* FULL_SAMP_BUFFER_SUPPORTED */
/*
* Initialize difference buffer controller.
*/
GLOBAL(void)
_jinit_c_diff_controller(j_compress_ptr cinfo, boolean need_full_buffer)
{
my_diff_ptr diff;
int ci, row;
jpeg_component_info *compptr;
diff = (my_diff_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
sizeof(my_diff_controller));
cinfo->coef = (struct jpeg_c_coef_controller *)diff;
diff->pub.start_pass = start_pass_diff;
/* Create the prediction row buffers. */
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
diff->cur_row[ci] = *(_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
((j_common_ptr)cinfo, JPOOL_IMAGE,
(JDIMENSION)jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor),
(JDIMENSION)1);
diff->prev_row[ci] = *(_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
((j_common_ptr)cinfo, JPOOL_IMAGE,
(JDIMENSION)jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor),
(JDIMENSION)1);
}
/* Create the difference buffer. */
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
diff->diff_buf[ci] =
ALLOC_DARRAY(JPOOL_IMAGE,
(JDIMENSION)jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor),
(JDIMENSION)compptr->v_samp_factor);
/* Prefill difference rows with zeros. We do this because only actual
* data is placed in the buffers during prediction/differencing, leaving
* any dummy differences at the right edge as zeros, which will encode
* to the smallest amount of data.
*/
for (row = 0; row < compptr->v_samp_factor; row++)
memset(diff->diff_buf[ci][row], 0,
jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor) * sizeof(JDIFF));
}
/* Create the sample buffer. */
if (need_full_buffer) {
#ifdef FULL_SAMP_BUFFER_SUPPORTED
/* Allocate a full-image virtual array for each component, */
/* padded to a multiple of samp_factor differences in each direction. */
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
diff->whole_image[ci] = (*cinfo->mem->request_virt_sarray)
((j_common_ptr)cinfo, JPOOL_IMAGE, FALSE,
(JDIMENSION)jround_up((long)compptr->width_in_blocks,
(long)compptr->h_samp_factor),
(JDIMENSION)jround_up((long)compptr->height_in_blocks,
(long)compptr->v_samp_factor),
(JDIMENSION)compptr->v_samp_factor);
}
#else
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
#endif
} else
diff->whole_image[0] = NULL; /* flag for no virtual arrays */
}
#endif /* C_LOSSLESS_SUPPORTED */