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jcprepct.c
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/*
* jcprepct.c
*
* Copyright (C) 1994-1996, Thomas G. Lane.
* 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 the compression preprocessing controller.
* This controller manages the color conversion, downsampling,
* and edge expansion steps.
*
* Most of the complexity here is associated with buffering input rows
* as required by the downsampler. See the comments at the head of
* jcsample.c for the downsampler's needs.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/* At present, jcsample.c can request context rows only for smoothing.
* In the future, we might also need context rows for CCIR601 sampling
* or other more-complex downsampling procedures. The code to support
* context rows should be compiled only if needed.
*/
#ifdef INPUT_SMOOTHING_SUPPORTED
#define CONTEXT_ROWS_SUPPORTED
#endif
/*
* For the simple (no-context-row) case, we just need to buffer one
* row group's worth of pixels for the downsampling step. At the bottom of
* the image, we pad to a full row group by replicating the last pixel row.
* The downsampler's last output row is then replicated if needed to pad
* out to a full iMCU row.
*
* When providing context rows, we must buffer three row groups' worth of
* pixels. Three row groups are physically allocated, but the row pointer
* arrays are made five row groups high, with the extra pointers above and
* below "wrapping around" to point to the last and first real row groups.
* This allows the downsampler to access the proper context rows.
* At the top and bottom of the image, we create dummy context rows by
* copying the first or last real pixel row. This copying could be avoided
* by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
* trouble on the compression side.
*/
/* Private buffer controller object */
typedef struct {
struct jpeg_c_prep_controller pub; /* public fields */
/* Downsampling input buffer. This buffer holds color-converted data
* until we have enough to do a downsample step.
*/
JSAMPARRAY color_buf[MAX_COMPONENTS];
JDIMENSION rows_to_go; /* counts rows remaining in source image */
int next_buf_row; /* index of next row to store in color_buf */
#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
int this_row_group; /* starting row index of group to process */
int next_buf_stop; /* downsample when we reach this index */
#endif
} my_prep_controller;
typedef my_prep_controller * my_prep_ptr;
/*
* Initialize for a processing pass.
*/
METHODDEF(void)
start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
{
my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
if (pass_mode != JBUF_PASS_THRU)
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
/* Initialize total-height counter for detecting bottom of image */
prep->rows_to_go = cinfo->image_height;
/* Mark the conversion buffer empty */
prep->next_buf_row = 0;
#ifdef CONTEXT_ROWS_SUPPORTED
/* Preset additional state variables for context mode.
* These aren't used in non-context mode, so we needn't test which mode.
*/
prep->this_row_group = 0;
/* Set next_buf_stop to stop after two row groups have been read in. */
prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
#endif
}
/*
* Expand an image vertically from height input_rows to height output_rows,
* by duplicating the bottom row.
*/
LOCAL(void)
expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
int input_rows, int output_rows)
{
register int row;
for (row = input_rows; row < output_rows; row++) {
jcopy_sample_rows(image_data, input_rows-1, image_data, row,
1, num_cols);
}
}
/*
* Process some data in the simple no-context case.
*
* Preprocessor output data is counted in "row groups". A row group
* is defined to be v_samp_factor sample rows of each component.
* Downsampling will produce this much data from each max_v_samp_factor
* input rows.
*/
METHODDEF(void)
pre_process_data (j_compress_ptr cinfo,
JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
JDIMENSION in_rows_avail,
JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
JDIMENSION out_row_groups_avail)
{
my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
int numrows, ci;
JDIMENSION inrows;
jpeg_component_info * compptr;
while (*in_row_ctr < in_rows_avail &&
*out_row_group_ctr < out_row_groups_avail) {
/* Do color conversion to fill the conversion buffer. */
inrows = in_rows_avail - *in_row_ctr;
numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
numrows = (int) MIN((JDIMENSION) numrows, inrows);
(*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
prep->color_buf,
(JDIMENSION) prep->next_buf_row,
numrows);
*in_row_ctr += numrows;
prep->next_buf_row += numrows;
prep->rows_to_go -= numrows;
/* If at bottom of image, pad to fill the conversion buffer. */
if (prep->rows_to_go == 0 &&
prep->next_buf_row < cinfo->max_v_samp_factor) {
for (ci = 0; ci < cinfo->num_components; ci++) {
expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
prep->next_buf_row, cinfo->max_v_samp_factor);
}
prep->next_buf_row = cinfo->max_v_samp_factor;
}
/* If we've filled the conversion buffer, empty it. */
if (prep->next_buf_row == cinfo->max_v_samp_factor) {
(*cinfo->downsample->downsample) (cinfo,
prep->color_buf, (JDIMENSION) 0,
output_buf, *out_row_group_ctr);
prep->next_buf_row = 0;
(*out_row_group_ctr)++;
}
/* If at bottom of image, pad the output to a full iMCU height.
* Note we assume the caller is providing a one-iMCU-height output buffer!
*/
if (prep->rows_to_go == 0 &&
*out_row_group_ctr < out_row_groups_avail) {
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
expand_bottom_edge(output_buf[ci],
compptr->width_in_blocks * DCTSIZE,
(int) (*out_row_group_ctr * compptr->v_samp_factor),
(int) (out_row_groups_avail * compptr->v_samp_factor));
}
*out_row_group_ctr = out_row_groups_avail;
break; /* can exit outer loop without test */
}
}
}
#ifdef CONTEXT_ROWS_SUPPORTED
/*
* Process some data in the context case.
*/
METHODDEF(void)
pre_process_context (j_compress_ptr cinfo,
JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
JDIMENSION in_rows_avail,
JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
JDIMENSION out_row_groups_avail)
{
my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
int numrows, ci;
int buf_height = cinfo->max_v_samp_factor * 3;
JDIMENSION inrows;
while (*out_row_group_ctr < out_row_groups_avail) {
if (*in_row_ctr < in_rows_avail) {
/* Do color conversion to fill the conversion buffer. */
inrows = in_rows_avail - *in_row_ctr;
numrows = prep->next_buf_stop - prep->next_buf_row;
numrows = (int) MIN((JDIMENSION) numrows, inrows);
(*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
prep->color_buf,
(JDIMENSION) prep->next_buf_row,
numrows);
/* Pad at top of image, if first time through */
if (prep->rows_to_go == cinfo->image_height) {
for (ci = 0; ci < cinfo->num_components; ci++) {
int row;
for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
jcopy_sample_rows(prep->color_buf[ci], 0,
prep->color_buf[ci], -row,
1, cinfo->image_width);
}
}
}
*in_row_ctr += numrows;
prep->next_buf_row += numrows;
prep->rows_to_go -= numrows;
} else {
/* Return for more data, unless we are at the bottom of the image. */
if (prep->rows_to_go != 0)
break;
/* When at bottom of image, pad to fill the conversion buffer. */
if (prep->next_buf_row < prep->next_buf_stop) {
for (ci = 0; ci < cinfo->num_components; ci++) {
expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
prep->next_buf_row, prep->next_buf_stop);
}
prep->next_buf_row = prep->next_buf_stop;
}
}
/* If we've gotten enough data, downsample a row group. */
if (prep->next_buf_row == prep->next_buf_stop) {
(*cinfo->downsample->downsample) (cinfo,
prep->color_buf,
(JDIMENSION) prep->this_row_group,
output_buf, *out_row_group_ctr);
(*out_row_group_ctr)++;
/* Advance pointers with wraparound as necessary. */
prep->this_row_group += cinfo->max_v_samp_factor;
if (prep->this_row_group >= buf_height)
prep->this_row_group = 0;
if (prep->next_buf_row >= buf_height)
prep->next_buf_row = 0;
prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
}
}
}
/*
* Create the wrapped-around downsampling input buffer needed for context mode.
*/
LOCAL(void)
create_context_buffer (j_compress_ptr cinfo)
{
my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
int rgroup_height = cinfo->max_v_samp_factor;
int ci, i;
jpeg_component_info * compptr;
JSAMPARRAY true_buffer, fake_buffer;
/* Grab enough space for fake row pointers for all the components;
* we need five row groups' worth of pointers for each component.
*/
fake_buffer = (JSAMPARRAY)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
(cinfo->num_components * 5 * rgroup_height) *
SIZEOF(JSAMPROW));
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
/* Allocate the actual buffer space (3 row groups) for this component.
* We make the buffer wide enough to allow the downsampler to edge-expand
* horizontally within the buffer, if it so chooses.
*/
true_buffer = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE,
(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
cinfo->max_h_samp_factor) / compptr->h_samp_factor),
(JDIMENSION) (3 * rgroup_height));
/* Copy true buffer row pointers into the middle of the fake row array */
MEMCOPY(fake_buffer + rgroup_height, true_buffer,
3 * rgroup_height * SIZEOF(JSAMPROW));
/* Fill in the above and below wraparound pointers */
for (i = 0; i < rgroup_height; i++) {
fake_buffer[i] = true_buffer[2 * rgroup_height + i];
fake_buffer[4 * rgroup_height + i] = true_buffer[i];
}
prep->color_buf[ci] = fake_buffer + rgroup_height;
fake_buffer += 5 * rgroup_height; /* point to space for next component */
}
}
#endif /* CONTEXT_ROWS_SUPPORTED */
/*
* Initialize preprocessing controller.
*/
GLOBAL(void)
jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
{
my_prep_ptr prep;
int ci;
jpeg_component_info * compptr;
if (need_full_buffer) /* safety check */
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
prep = (my_prep_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(my_prep_controller));
cinfo->prep = (struct jpeg_c_prep_controller *) prep;
prep->pub.start_pass = start_pass_prep;
/* Allocate the color conversion buffer.
* We make the buffer wide enough to allow the downsampler to edge-expand
* horizontally within the buffer, if it so chooses.
*/
if (cinfo->downsample->need_context_rows) {
/* Set up to provide context rows */
#ifdef CONTEXT_ROWS_SUPPORTED
prep->pub.pre_process_data = pre_process_context;
create_context_buffer(cinfo);
#else
ERREXIT(cinfo, JERR_NOT_COMPILED);
#endif
} else {
/* No context, just make it tall enough for one row group */
prep->pub.pre_process_data = pre_process_data;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE,
(JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
cinfo->max_h_samp_factor) / compptr->h_samp_factor),
(JDIMENSION) cinfo->max_v_samp_factor);
}
}
}

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