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/*
* jcsample.c
*
* Copyright (C) 1991, 1992, 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 downsampling routines.
* These routines are invoked via the downsample and
* downsample_init/term methods.
*
* An excellent reference for image resampling is
* Digital Image Warping, George Wolberg, 1990.
* Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
*
* The downsampling algorithm used here is a simple average of the source
* pixels covered by the output pixel. The hi-falutin sampling literature
* refers to this as a "box filter". In general the characteristics of a box
* filter are not very good, but for the specific cases we normally use (1:1
* and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
* nearly so bad. If you intend to use other sampling ratios, you'd be well
* advised to improve this code.
*
* A simple input-smoothing capability is provided. This is mainly intended
* for cleaning up color-dithered GIF input files (if you find it inadequate,
* we suggest using an external filtering program such as pnmconvol). When
* enabled, each input pixel P is replaced by a weighted sum of itself and its
* eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
* where SF = (smoothing_factor / 1024).
* Currently, smoothing is only supported for 2h2v sampling factors.
*/
#include "jinclude.h"
/*
* Initialize for downsampling a scan.
*/
METHODDEF void
downsample_init (compress_info_ptr cinfo)
{
/* no work for now */
}
/*
* Downsample pixel values of a single component.
* This version handles arbitrary integral sampling ratios, without smoothing.
* Note that this version is not actually used for customary sampling ratios.
*/
METHODDEF void
int_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
long outcol, outcol_h; /* outcol_h == outcol*h_expand */
JSAMPROW inptr, outptr;
INT32 outvalue;
#ifdef DEBUG /* for debugging pipeline controller */
if (output_rows != compptr->v_samp_factor ||
input_rows != cinfo->max_v_samp_factor ||
(output_cols % compptr->h_samp_factor) != 0 ||
(input_cols % cinfo->max_h_samp_factor) != 0 ||
input_cols*compptr->h_samp_factor != output_cols*cinfo->max_h_samp_factor)
ERREXIT(cinfo->emethods, "Bogus downsample parameters");
#endif
h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
numpix = h_expand * v_expand;
numpix2 = numpix/2;
inrow = 0;
for (outrow = 0; outrow < output_rows; outrow++) {
outptr = output_data[outrow];
for (outcol = 0, outcol_h = 0; outcol < output_cols;
outcol++, outcol_h += h_expand) {
outvalue = 0;
for (v = 0; v < v_expand; v++) {
inptr = input_data[inrow+v] + outcol_h;
for (h = 0; h < h_expand; h++) {
outvalue += (INT32) GETJSAMPLE(*inptr++);
}
}
*outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
}
inrow += v_expand;
}
}
/*
* Downsample pixel values of a single component.
* This version handles the common case of 2:1 horizontal and 1:1 vertical,
* without smoothing.
*/
METHODDEF void
h2v1_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
int outrow;
long outcol;
register JSAMPROW inptr, outptr;
#ifdef DEBUG /* for debugging pipeline controller */
jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
if (output_rows != compptr->v_samp_factor ||
input_rows != cinfo->max_v_samp_factor ||
(output_cols % compptr->h_samp_factor) != 0 ||
(input_cols % cinfo->max_h_samp_factor) != 0 ||
input_cols*compptr->h_samp_factor != output_cols*cinfo->max_h_samp_factor)
ERREXIT(cinfo->emethods, "Bogus downsample parameters");
#endif
for (outrow = 0; outrow < output_rows; outrow++) {
outptr = output_data[outrow];
inptr = input_data[outrow];
for (outcol = 0; outcol < output_cols; outcol++) {
*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
+ 1) >> 1);
inptr += 2;
}
}
}
/*
* Downsample pixel values of a single component.
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
* without smoothing.
*/
METHODDEF void
h2v2_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
int inrow, outrow;
long outcol;
register JSAMPROW inptr0, inptr1, outptr;
#ifdef DEBUG /* for debugging pipeline controller */
jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
if (output_rows != compptr->v_samp_factor ||
input_rows != cinfo->max_v_samp_factor ||
(output_cols % compptr->h_samp_factor) != 0 ||
(input_cols % cinfo->max_h_samp_factor) != 0 ||
input_cols*compptr->h_samp_factor != output_cols*cinfo->max_h_samp_factor)
ERREXIT(cinfo->emethods, "Bogus downsample parameters");
#endif
inrow = 0;
for (outrow = 0; outrow < output_rows; outrow++) {
outptr = output_data[outrow];
inptr0 = input_data[inrow];
inptr1 = input_data[inrow+1];
for (outcol = 0; outcol < output_cols; outcol++) {
*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
+ 2) >> 2);
inptr0 += 2; inptr1 += 2;
}
inrow += 2;
}
}
/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* without smoothing.
*/
METHODDEF void
fullsize_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
#ifdef DEBUG /* for debugging pipeline controller */
if (input_cols != output_cols || input_rows != output_rows)
ERREXIT(cinfo->emethods, "Pipeline controller messed up");
#endif
jcopy_sample_rows(input_data, 0, output_data, 0, output_rows, output_cols);
}
#ifdef INPUT_SMOOTHING_SUPPORTED
/*
* Downsample pixel values of a single component.
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
* with smoothing.
*/
METHODDEF void
h2v2_smooth_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
int inrow, outrow;
long colctr;
register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
INT32 membersum, neighsum, memberscale, neighscale;
#ifdef DEBUG /* for debugging pipeline controller */
jpeg_component_info * compptr = cinfo->cur_comp_info[which_component];
if (output_rows != compptr->v_samp_factor ||
input_rows != cinfo->max_v_samp_factor ||
(output_cols % compptr->h_samp_factor) != 0 ||
(input_cols % cinfo->max_h_samp_factor) != 0 ||
input_cols*compptr->h_samp_factor != output_cols*cinfo->max_h_samp_factor)
ERREXIT(cinfo->emethods, "Bogus downsample parameters");
#endif
/* We don't bother to form the individual "smoothed" input pixel values;
* we can directly compute the output which is the average of the four
* smoothed values. Each of the four member pixels contributes a fraction
* (1-8*SF) to its own smoothed image and a fraction SF to each of the three
* other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
* output. The four corner-adjacent neighbor pixels contribute a fraction
* SF to just one smoothed pixel, or SF/4 to the final output; while the
* eight edge-adjacent neighbors contribute SF to each of two smoothed
* pixels, or SF/2 overall. In order to use integer arithmetic, these
* factors are scaled by 2^16 = 65536.
* Also recall that SF = smoothing_factor / 1024.
*/
memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
inrow = 0;
for (outrow = 0; outrow < output_rows; outrow++) {
outptr = output_data[outrow];
inptr0 = input_data[inrow];
inptr1 = input_data[inrow+1];
if (inrow == 0)
above_ptr = above[input_rows-1];
else
above_ptr = input_data[inrow-1];
if (inrow >= input_rows-2)
below_ptr = below[0];
else
below_ptr = input_data[inrow+2];
/* Special case for first column: pretend column -1 is same as column 0 */
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
neighsum += neighsum;
neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (JSAMPLE) ((membersum + 32768L) >> 16);
inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
for (colctr = output_cols - 2; colctr > 0; colctr--) {
/* sum of pixels directly mapped to this output element */
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
/* sum of edge-neighbor pixels */
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
/* The edge-neighbors count twice as much as corner-neighbors */
neighsum += neighsum;
/* Add in the corner-neighbors */
neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
/* form final output scaled up by 2^16 */
membersum = membersum * memberscale + neighsum * neighscale;
/* round, descale and output it */
*outptr++ = (JSAMPLE) ((membersum + 32768L) >> 16);
inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
}
/* Special case for last column */
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
neighsum += neighsum;
neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
membersum = membersum * memberscale + neighsum * neighscale;
*outptr = (JSAMPLE) ((membersum + 32768L) >> 16);
inrow += 2;
}
}
/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* with smoothing.
*/
METHODDEF void
fullsize_smooth_downsample (compress_info_ptr cinfo, int which_component,
long input_cols, int input_rows,
long output_cols, int output_rows,
JSAMPARRAY above, JSAMPARRAY input_data, JSAMPARRAY below,
JSAMPARRAY output_data)
{
int outrow;
long colctr;
register JSAMPROW inptr, above_ptr, below_ptr, outptr;
INT32 membersum, neighsum, memberscale, neighscale;
int colsum, lastcolsum, nextcolsum;
#ifdef DEBUG /* for debugging pipeline controller */
if (input_cols != output_cols || input_rows != output_rows)
ERREXIT(cinfo->emethods, "Pipeline controller messed up");
#endif
/* Each of the eight neighbor pixels contributes a fraction SF to the
* smoothed pixel, while the main pixel contributes (1-8*SF). In order
* to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
* Also recall that SF = smoothing_factor / 1024.
*/
memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
for (outrow = 0; outrow < output_rows; outrow++) {
outptr = output_data[outrow];
inptr = input_data[outrow];
if (outrow == 0)
above_ptr = above[input_rows-1];
else
above_ptr = input_data[outrow-1];
if (outrow >= input_rows-1)
below_ptr = below[0];
else
below_ptr = input_data[outrow+1];
/* Special case for first column */
colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
GETJSAMPLE(*inptr);
membersum = GETJSAMPLE(*inptr++);
nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
GETJSAMPLE(*inptr);
neighsum = colsum + (colsum - membersum) + nextcolsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (JSAMPLE) ((membersum + 32768L) >> 16);
lastcolsum = colsum; colsum = nextcolsum;
for (colctr = output_cols - 2; colctr > 0; colctr--) {
membersum = GETJSAMPLE(*inptr++);
above_ptr++; below_ptr++;
nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
GETJSAMPLE(*inptr);
neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (JSAMPLE) ((membersum + 32768L) >> 16);
lastcolsum = colsum; colsum = nextcolsum;
}
/* Special case for last column */
membersum = GETJSAMPLE(*inptr);
neighsum = lastcolsum + (colsum - membersum) + colsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr = (JSAMPLE) ((membersum + 32768L) >> 16);
}
}
#endif /* INPUT_SMOOTHING_SUPPORTED */
/*
* Clean up after a scan.
*/
METHODDEF void
downsample_term (compress_info_ptr cinfo)
{
/* no work for now */
}
/*
* The method selection routine for downsampling.
* Note that we must select a routine for each component.
*/
GLOBAL void
jseldownsample (compress_info_ptr cinfo)
{
short ci;
jpeg_component_info * compptr;
boolean smoothok = TRUE;
if (cinfo->CCIR601_sampling)
ERREXIT(cinfo->emethods, "CCIR601 downsampling not implemented yet");
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
compptr = cinfo->cur_comp_info[ci];
if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
compptr->v_samp_factor == cinfo->max_v_samp_factor) {
#ifdef INPUT_SMOOTHING_SUPPORTED
if (cinfo->smoothing_factor)
cinfo->methods->downsample[ci] = fullsize_smooth_downsample;
else
#endif
cinfo->methods->downsample[ci] = fullsize_downsample;
} else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
compptr->v_samp_factor == cinfo->max_v_samp_factor) {
smoothok = FALSE;
cinfo->methods->downsample[ci] = h2v1_downsample;
} else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
#ifdef INPUT_SMOOTHING_SUPPORTED
if (cinfo->smoothing_factor)
cinfo->methods->downsample[ci] = h2v2_smooth_downsample;
else
#endif
cinfo->methods->downsample[ci] = h2v2_downsample;
} else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
(cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
smoothok = FALSE;
cinfo->methods->downsample[ci] = int_downsample;
} else
ERREXIT(cinfo->emethods, "Fractional downsampling not implemented yet");
}
#ifdef INPUT_SMOOTHING_SUPPORTED
if (cinfo->smoothing_factor && !smoothok)
TRACEMS(cinfo->emethods, 0,
"Smoothing not supported with nonstandard sampling ratios");
#endif
cinfo->methods->downsample_init = downsample_init;
cinfo->methods->downsample_term = downsample_term;
}
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