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e8b40f3c2ba187ba95c13c3e8ce21c8534256df7
mozjpeg/jcsample.c
DRC e8b40f3c2b Vastly improve 12-bit JPEG integration 
The Gordian knot that 7fec5074f9 attempted
to unravel was caused by the fact that there are several
data-precision-dependent (JSAMPLE-dependent) fields and methods in the
exposed libjpeg API structures, and if you change the exposed libjpeg
API structures, then you have to change the whole API.  If you change
the whole API, then you have to provide a whole new library to support
the new API, and that makes it difficult to support multiple data
precisions in the same application.  (It is not impossible, as example.c
demonstrated, but using data-precision-dependent libjpeg API structures
would have made the cjpeg, djpeg, and jpegtran source code hard to read,
so it made more sense to build, install, and package 12-bit-specific
versions of those applications.)

Unfortunately, the result of that initial integration effort was an
unreadable and unmaintainable mess, which is a problem for a library
that is an ISO/ITU-T reference implementation.  Also, as I dug into the
problem of lossless JPEG support, I realized that 16-bit lossless JPEG
images are a thing, and supporting yet another version of the libjpeg
API just for those images is untenable.

In fact, however, the touch points for JSAMPLE in the exposed libjpeg
API structures are minimal:

  - The colormap and sample_range_limit fields in jpeg_decompress_struct
  - The alloc_sarray() and access_virt_sarray() methods in
    jpeg_memory_mgr
  - jpeg_write_scanlines() and jpeg_write_raw_data()
  - jpeg_read_scanlines() and jpeg_read_raw_data()
  - jpeg_skip_scanlines() and jpeg_crop_scanline()
    (This is subtle, but both of those functions use JSAMPLE-dependent
    opaque structures behind the scenes.)

It is much more readable and maintainable to provide 12-bit-specific
versions of those six top-level API functions and to document that the
aforementioned methods and fields must be type-cast when using 12-bit
samples.  Since that eliminates the need to provide a 12-bit-specific
version of the exposed libjpeg API structures, we can:

  - Compile only the precision-dependent libjpeg modules (the
    coefficient buffer controllers, the colorspace converters, the
    DCT/IDCT managers, the main buffer controllers, the preprocessing
    and postprocessing controller, the downsampler and upsamplers, the
    quantizers, the integer DCT methods, and the IDCT methods) for
    multiple data precisions.
  - Introduce 12-bit-specific methods into the various internal
    structures defined in jpegint.h.
  - Create precision-independent data type, macro, method, field, and
    function names that are prefixed by an underscore, and use an
    internal header to convert those into precision-dependent data
    type, macro, method, field, and function names, based on the value
    of BITS_IN_JSAMPLE, when compiling the precision-dependent libjpeg
    modules.
  - Expose precision-dependent jinit*() functions for each of the
    precision-dependent libjpeg modules.
  - Abstract the precision-dependent libjpeg modules by calling the
    appropriate precision-dependent jinit*() function, based on the
    value of cinfo->data_precision, from top-level libjpeg API
    functions.
2022-11-04 12:30:33 -05:00

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/*
* jcsample.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1991-1996, Thomas G. Lane.
* libjpeg-turbo Modifications:
* Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
* Copyright (C) 2014, MIPS Technologies, Inc., California.
* Copyright (C) 2015, 2019, 2022, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains downsampling routines.
*
* Downsampling input data is counted in "row groups". A row group
* is defined to be max_v_samp_factor pixel rows of each component,
* from which the downsampler produces v_samp_factor sample rows.
* A single row group is processed in each call to the downsampler module.
*
* The downsampler is responsible for edge-expansion of its output data
* to fill an integral number of DCT blocks horizontally. The source buffer
* may be modified if it is helpful for this purpose (the source buffer is
* allocated wide enough to correspond to the desired output width).
* The caller (the prep controller) is responsible for vertical padding.
*
* The downsampler may request "context rows" by setting need_context_rows
* during startup. In this case, the input arrays will contain at least
* one row group's worth of pixels above and below the passed-in data;
* the caller will create dummy rows at image top and bottom by replicating
* the first or last real pixel row.
*
* 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.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jsimd.h"
#include "jsamplecomp.h"
/* Pointer to routine to downsample a single component */
typedef void (*downsample1_ptr) (j_compress_ptr cinfo,
jpeg_component_info *compptr,
_JSAMPARRAY input_data,
_JSAMPARRAY output_data);
/* Private subobject */
typedef struct {
struct jpeg_downsampler pub; /* public fields */
/* Downsampling method pointers, one per component */
downsample1_ptr methods[MAX_COMPONENTS];
} my_downsampler;
typedef my_downsampler *my_downsample_ptr;
/*
* Initialize for a downsampling pass.
*/
METHODDEF(void)
start_pass_downsample(j_compress_ptr cinfo)
{
/* no work for now */
}
/*
* Expand a component horizontally from width input_cols to width output_cols,
* by duplicating the rightmost samples.
*/
LOCAL(void)
expand_right_edge(_JSAMPARRAY image_data, int num_rows, JDIMENSION input_cols,
JDIMENSION output_cols)
{
register _JSAMPROW ptr;
register _JSAMPLE pixval;
register int count;
int row;
int numcols = (int)(output_cols - input_cols);
if (numcols > 0) {
for (row = 0; row < num_rows; row++) {
ptr = image_data[row] + input_cols;
pixval = ptr[-1];
for (count = numcols; count > 0; count--)
*ptr++ = pixval;
}
}
}
/*
* Do downsampling for a whole row group (all components).
*
* In this version we simply downsample each component independently.
*/
METHODDEF(void)
sep_downsample(j_compress_ptr cinfo, _JSAMPIMAGE input_buf,
JDIMENSION in_row_index, _JSAMPIMAGE output_buf,
JDIMENSION out_row_group_index)
{
my_downsample_ptr downsample = (my_downsample_ptr)cinfo->downsample;
int ci;
jpeg_component_info *compptr;
_JSAMPARRAY in_ptr, out_ptr;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
in_ptr = input_buf[ci] + in_row_index;
out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
(*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
}
}
/*
* Downsample pixel values of a single component.
* One row group is processed per call.
* 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(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
_JSAMPROW inptr, outptr;
JLONG outvalue;
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;
/* Expand input data enough to let all the output samples be generated
* by the standard loop. Special-casing padded output would be more
* efficient.
*/
expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
output_cols * h_expand);
inrow = 0;
for (outrow = 0; outrow < compptr->v_samp_factor; 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 += (JLONG)(*inptr++);
}
}
*outptr++ = (_JSAMPLE)((outvalue + numpix2) / numpix);
}
inrow += v_expand;
}
}
/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* without smoothing.
*/
METHODDEF(void)
fullsize_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
/* Copy the data */
_jcopy_sample_rows(input_data, 0, output_data, 0, cinfo->max_v_samp_factor,
cinfo->image_width);
/* Edge-expand */
expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
compptr->width_in_blocks * DCTSIZE);
}
/*
* Downsample pixel values of a single component.
* This version handles the common case of 2:1 horizontal and 1:1 vertical,
* without smoothing.
*
* A note about the "bias" calculations: when rounding fractional values to
* integer, we do not want to always round 0.5 up to the next integer.
* If we did that, we'd introduce a noticeable bias towards larger values.
* Instead, this code is arranged so that 0.5 will be rounded up or down at
* alternate pixel locations (a simple ordered dither pattern).
*/
METHODDEF(void)
h2v1_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
int outrow;
JDIMENSION outcol;
JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
register _JSAMPROW inptr, outptr;
register int bias;
/* Expand input data enough to let all the output samples be generated
* by the standard loop. Special-casing padded output would be more
* efficient.
*/
expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
output_cols * 2);
for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
outptr = output_data[outrow];
inptr = input_data[outrow];
bias = 0; /* bias = 0,1,0,1,... for successive samples */
for (outcol = 0; outcol < output_cols; outcol++) {
*outptr++ = (_JSAMPLE)((inptr[0] + inptr[1] + bias) >> 1);
bias ^= 1; /* 0=>1, 1=>0 */
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(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
int inrow, outrow;
JDIMENSION outcol;
JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
register _JSAMPROW inptr0, inptr1, outptr;
register int bias;
/* Expand input data enough to let all the output samples be generated
* by the standard loop. Special-casing padded output would be more
* efficient.
*/
expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
output_cols * 2);
inrow = 0;
for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
outptr = output_data[outrow];
inptr0 = input_data[inrow];
inptr1 = input_data[inrow + 1];
bias = 1; /* bias = 1,2,1,2,... for successive samples */
for (outcol = 0; outcol < output_cols; outcol++) {
*outptr++ = (_JSAMPLE)
((inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1] + bias) >> 2);
bias ^= 3; /* 1=>2, 2=>1 */
inptr0 += 2; inptr1 += 2;
}
inrow += 2;
}
}
#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. One row of context is required.
*/
METHODDEF(void)
h2v2_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
int inrow, outrow;
JDIMENSION colctr;
JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
register _JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
JLONG membersum, neighsum, memberscale, neighscale;
/* Expand input data enough to let all the output samples be generated
* by the standard loop. Special-casing padded output would be more
* efficient.
*/
expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
cinfo->image_width, output_cols * 2);
/* 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 < compptr->v_samp_factor; outrow++) {
outptr = output_data[outrow];
inptr0 = input_data[inrow];
inptr1 = input_data[inrow + 1];
above_ptr = input_data[inrow - 1];
below_ptr = input_data[inrow + 2];
/* Special case for first column: pretend column -1 is same as column 0 */
membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
inptr0[0] + inptr0[2] + inptr1[0] + inptr1[2];
neighsum += neighsum;
neighsum += above_ptr[0] + above_ptr[2] + below_ptr[0] + below_ptr[2];
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (_JSAMPLE)((membersum + 32768) >> 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 = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
/* sum of edge-neighbor pixels */
neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
inptr0[-1] + inptr0[2] + inptr1[-1] + inptr1[2];
/* The edge-neighbors count twice as much as corner-neighbors */
neighsum += neighsum;
/* Add in the corner-neighbors */
neighsum += above_ptr[-1] + above_ptr[2] + below_ptr[-1] + below_ptr[2];
/* form final output scaled up by 2^16 */
membersum = membersum * memberscale + neighsum * neighscale;
/* round, descale and output it */
*outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
}
/* Special case for last column */
membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
inptr0[-1] + inptr0[1] + inptr1[-1] + inptr1[1];
neighsum += neighsum;
neighsum += above_ptr[-1] + above_ptr[1] + below_ptr[-1] + below_ptr[1];
membersum = membersum * memberscale + neighsum * neighscale;
*outptr = (_JSAMPLE)((membersum + 32768) >> 16);
inrow += 2;
}
}
/*
* Downsample pixel values of a single component.
* This version handles the special case of a full-size component,
* with smoothing. One row of context is required.
*/
METHODDEF(void)
fullsize_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
_JSAMPARRAY input_data, _JSAMPARRAY output_data)
{
int outrow;
JDIMENSION colctr;
JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
register _JSAMPROW inptr, above_ptr, below_ptr, outptr;
JLONG membersum, neighsum, memberscale, neighscale;
int colsum, lastcolsum, nextcolsum;
/* Expand input data enough to let all the output samples be generated
* by the standard loop. Special-casing padded output would be more
* efficient.
*/
expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
cinfo->image_width, output_cols);
/* 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 < compptr->v_samp_factor; outrow++) {
outptr = output_data[outrow];
inptr = input_data[outrow];
above_ptr = input_data[outrow - 1];
below_ptr = input_data[outrow + 1];
/* Special case for first column */
colsum = (*above_ptr++) + (*below_ptr++) + inptr[0];
membersum = *inptr++;
nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
neighsum = colsum + (colsum - membersum) + nextcolsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
lastcolsum = colsum; colsum = nextcolsum;
for (colctr = output_cols - 2; colctr > 0; colctr--) {
membersum = *inptr++;
above_ptr++; below_ptr++;
nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr++ = (_JSAMPLE)((membersum + 32768) >> 16);
lastcolsum = colsum; colsum = nextcolsum;
}
/* Special case for last column */
membersum = *inptr;
neighsum = lastcolsum + (colsum - membersum) + colsum;
membersum = membersum * memberscale + neighsum * neighscale;
*outptr = (_JSAMPLE)((membersum + 32768) >> 16);
}
}
#endif /* INPUT_SMOOTHING_SUPPORTED */
/*
* Module initialization routine for downsampling.
* Note that we must select a routine for each component.
*/
GLOBAL(void)
_jinit_downsampler(j_compress_ptr cinfo)
{
my_downsample_ptr downsample;
int ci;
jpeg_component_info *compptr;
boolean smoothok = TRUE;
if (cinfo->data_precision != BITS_IN_JSAMPLE)
ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
downsample = (my_downsample_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
sizeof(my_downsampler));
cinfo->downsample = (struct jpeg_downsampler *)downsample;
downsample->pub.start_pass = start_pass_downsample;
downsample->pub._downsample = sep_downsample;
downsample->pub.need_context_rows = FALSE;
if (cinfo->CCIR601_sampling)
ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
/* Verify we can handle the sampling factors, and set up method pointers */
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
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) {
downsample->methods[ci] = fullsize_smooth_downsample;
downsample->pub.need_context_rows = TRUE;
} else
#endif
downsample->methods[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;
#ifdef WITH_SIMD
if (jsimd_can_h2v1_downsample())
downsample->methods[ci] = jsimd_h2v1_downsample;
else
#endif
downsample->methods[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) {
#if defined(WITH_SIMD) && defined(__mips__)
if (jsimd_can_h2v2_smooth_downsample())
downsample->methods[ci] = jsimd_h2v2_smooth_downsample;
else
#endif
downsample->methods[ci] = h2v2_smooth_downsample;
downsample->pub.need_context_rows = TRUE;
} else
#endif
{
#ifdef WITH_SIMD
if (jsimd_can_h2v2_downsample())
downsample->methods[ci] = jsimd_h2v2_downsample;
else
#endif
downsample->methods[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;
downsample->methods[ci] = int_downsample;
} else
ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
}
#ifdef INPUT_SMOOTHING_SUPPORTED
if (cinfo->smoothing_factor && !smoothok)
TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
#endif
}
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