492 lines
18 KiB
C++
492 lines
18 KiB
C++
// * jcsample.c
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// *
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// * Copyright (C) 1991-1994, Thomas G. Lane.
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// * This file is part of the Independent JPEG Group's software.
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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 downsampling routines.
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// *
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// * Downsampling input data is counted in "row groups". A row group
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// * is defined to be max_v_samp_factor pixel rows of each component,
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// * from which the downsampler produces v_samp_factor sample rows.
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// * A single row group is processed in each call to the downsampler module.
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// *
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// * The downsampler is responsible for edge-expansion of its output data
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// * to fill an integral number of DCT blocks horizontally. The source buffer
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// * may be modified if it is helpful for this purpose (the source buffer is
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// * allocated wide enough to correspond to the desired output width).
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// * The caller (the prep controller) is responsible for vertical padding.
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// *
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// * The downsampler may request "context rows" by setting need_context_rows
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// * during startup. In this case, the input arrays will contain at least
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// * one row group's worth of pixels above and below the passed-in data;
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// * the caller will create dummy rows at image top and bottom by replicating
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// * the first or last real pixel row.
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// *
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// * An excellent reference for image resampling is
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// * Digital Image Warping, George Wolberg, 1990.
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// * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
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// *
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// * The downsampling algorithm used here is a simple average of the source
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// * pixels covered by the output pixel. The hi-falutin sampling literature
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// * refers to this as a "box filter". In general the characteristics of a box
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// * filter are not very good, but for the specific cases we normally use (1:1
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// * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
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// * nearly so bad. If you intend to use other sampling ratios, you'd be well
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// * advised to improve this code.
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// *
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// * A simple input-smoothing capability is provided. This is mainly intended
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// * for cleaning up color-dithered GIF input files (if you find it inadequate,
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// * we suggest using an external filtering program such as pnmconvol). When
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// * enabled, each input pixel P is replaced by a weighted sum of itself and its
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// * eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
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// * where SF = (smoothing_factor / 1024).
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// * Currently, smoothing is only supported for 2h2v sampling factors.
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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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// Pointer to routine to downsample a single component
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typedef JMETHOD(void, downsample1_ptr,
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(j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data));
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// Private subobject
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typedef struct {
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struct jpeg_downsampler pub; // public fields
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// Downsampling method pointers, one per component
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downsample1_ptr methods[MAX_COMPONENTS];
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} my_downsampler;
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typedef my_downsampler * my_downsample_ptr;
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// * Initialize for a downsampling pass.
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METHODDEF void
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start_pass_downsample (j_compress_ptr cinfo)
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{
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// no work for now
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}
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// * Expand a component horizontally from width input_cols to width output_cols,
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// * by duplicating the rightmost samples.
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LOCAL void
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expand_right_edge (JSAMPARRAY image_data, int num_rows,
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JDIMENSION input_cols, JDIMENSION output_cols)
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{
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register JSAMPROW ptr;
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register JSAMPLE pixval;
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register int count;
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int row;
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int numcols = (int) (output_cols - input_cols);
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if (numcols > 0) {
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for (row = 0; row < num_rows; row++) {
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ptr = image_data[row] + input_cols;
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pixval = ptr[-1]; // don't need GETJSAMPLE() here
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for (count = numcols; count > 0; count--)
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*ptr++ = pixval;
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}
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}
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}
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// * Do downsampling for a whole row group (all components).
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// *
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// * In this version we simply downsample each component independently.
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METHODDEF void
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sep_downsample (j_compress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION in_row_index,
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JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
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{
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my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
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int ci;
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jpeg_component_info * compptr;
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JSAMPARRAY in_ptr, out_ptr;
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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ci++, compptr++) {
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in_ptr = input_buf[ci] + in_row_index;
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out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
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(*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
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}
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}
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// * Downsample pixel values of a single component.
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// * One row group is processed per call.
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// * This version handles arbitrary integral sampling ratios, without smoothing.
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// * Note that this version is not actually used for customary sampling ratios.
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METHODDEF void
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int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
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JDIMENSION outcol, outcol_h; // outcol_h == outcol*h_expand
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JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
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JSAMPROW inptr, outptr;
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INT32 outvalue;
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h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
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v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
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numpix = h_expand * v_expand;
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numpix2 = numpix/2;
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// Expand input data enough to let all the output samples be generated
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// * by the standard loop. Special-casing padded output would be more
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// * efficient.
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expand_right_edge(input_data, cinfo->max_v_samp_factor,
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cinfo->image_width, output_cols * h_expand);
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inrow = 0;
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for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
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outptr = output_data[outrow];
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for (outcol = 0, outcol_h = 0; outcol < output_cols;
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outcol++, outcol_h += h_expand) {
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outvalue = 0;
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for (v = 0; v < v_expand; v++) {
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inptr = input_data[inrow+v] + outcol_h;
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for (h = 0; h < h_expand; h++) {
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outvalue += (INT32) GETJSAMPLE(*inptr++);
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}
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}
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*outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
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}
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inrow += v_expand;
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}
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}
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// * Downsample pixel values of a single component.
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// * This version handles the special case of a full-size component,
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// * without smoothing.
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METHODDEF void
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fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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// Copy the data
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jcopy_sample_rows(input_data, 0, output_data, 0,
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cinfo->max_v_samp_factor, cinfo->image_width);
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// Edge-expand
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expand_right_edge(output_data, cinfo->max_v_samp_factor,
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cinfo->image_width, compptr->width_in_blocks * DCTSIZE);
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}
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// * Downsample pixel values of a single component.
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// * This version handles the common case of 2:1 horizontal and 1:1 vertical,
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// * without smoothing.
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// *
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// * A note about the "bias" calculations: when rounding fractional values to
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// * integer, we do not want to always round 0.5 up to the next integer.
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// * If we did that, we'd introduce a noticeable bias towards larger values.
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// * Instead, this code is arranged so that 0.5 will be rounded up or down at
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// * alternate pixel locations (a simple ordered dither pattern).
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METHODDEF void
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h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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int outrow;
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JDIMENSION outcol;
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JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
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register JSAMPROW inptr, outptr;
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register int bias;
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// Expand input data enough to let all the output samples be generated
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// * by the standard loop. Special-casing padded output would be more
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// * efficient.
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expand_right_edge(input_data, cinfo->max_v_samp_factor,
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cinfo->image_width, output_cols * 2);
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for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
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outptr = output_data[outrow];
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inptr = input_data[outrow];
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bias = 0; // bias = 0,1,0,1,... for successive samples
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for (outcol = 0; outcol < output_cols; outcol++) {
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*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
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+ bias) >> 1);
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bias ^= 1; // 0=>1, 1=>0
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inptr += 2;
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}
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}
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}
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// * Downsample pixel values of a single component.
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// * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
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// * without smoothing.
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METHODDEF void
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h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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int inrow, outrow;
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JDIMENSION outcol;
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JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
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register JSAMPROW inptr0, inptr1, outptr;
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register int bias;
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// Expand input data enough to let all the output samples be generated
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// * by the standard loop. Special-casing padded output would be more
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// * efficient.
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expand_right_edge(input_data, cinfo->max_v_samp_factor,
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cinfo->image_width, output_cols * 2);
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inrow = 0;
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for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
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outptr = output_data[outrow];
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inptr0 = input_data[inrow];
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inptr1 = input_data[inrow+1];
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bias = 1; // bias = 1,2,1,2,... for successive samples
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for (outcol = 0; outcol < output_cols; outcol++) {
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*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
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+ bias) >> 2);
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bias ^= 3; // 1=>2, 2=>1
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inptr0 += 2; inptr1 += 2;
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}
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inrow += 2;
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}
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}
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#ifdef INPUT_SMOOTHING_SUPPORTED
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// * Downsample pixel values of a single component.
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// * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
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// * with smoothing. One row of context is required.
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METHODDEF void
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h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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int inrow, outrow;
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JDIMENSION colctr;
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JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
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register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
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INT32 membersum, neighsum, memberscale, neighscale;
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// Expand input data enough to let all the output samples be generated
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// * by the standard loop. Special-casing padded output would be more
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// * efficient.
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expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
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cinfo->image_width, output_cols * 2);
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// We don't bother to form the individual "smoothed" input pixel values;
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// * we can directly compute the output which is the average of the four
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// * smoothed values. Each of the four member pixels contributes a fraction
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// * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
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// * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
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// * output. The four corner-adjacent neighbor pixels contribute a fraction
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// * SF to just one smoothed pixel, or SF/4 to the final output; while the
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// * eight edge-adjacent neighbors contribute SF to each of two smoothed
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// * pixels, or SF/2 overall. In order to use integer arithmetic, these
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// * factors are scaled by 2^16 = 65536.
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// * Also recall that SF = smoothing_factor / 1024.
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memberscale = 16384 - cinfo->smoothing_factor * 80; // scaled (1-5*SF)/4
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neighscale = cinfo->smoothing_factor * 16; // scaled SF/4
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inrow = 0;
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for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
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outptr = output_data[outrow];
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inptr0 = input_data[inrow];
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inptr1 = input_data[inrow+1];
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above_ptr = input_data[inrow-1];
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below_ptr = input_data[inrow+2];
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// Special case for first column: pretend column -1 is same as column 0
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membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
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neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
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GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
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GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
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neighsum += neighsum;
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neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
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GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
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membersum = membersum * memberscale + neighsum * neighscale;
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*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
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inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
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for (colctr = output_cols - 2; colctr > 0; colctr--) {
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// sum of pixels directly mapped to this output element
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membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
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// sum of edge-neighbor pixels
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neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
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GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
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GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
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GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
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// The edge-neighbors count twice as much as corner-neighbors
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neighsum += neighsum;
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// Add in the corner-neighbors
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neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
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GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
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// form final output scaled up by 2^16
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membersum = membersum * memberscale + neighsum * neighscale;
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// round, descale and output it
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*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
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inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
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}
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// Special case for last column
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membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
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neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
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GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
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GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
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neighsum += neighsum;
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neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
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GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
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membersum = membersum * memberscale + neighsum * neighscale;
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*outptr = (JSAMPLE) ((membersum + 32768) >> 16);
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inrow += 2;
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}
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}
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// * Downsample pixel values of a single component.
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// * This version handles the special case of a full-size component,
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// * with smoothing. One row of context is required.
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METHODDEF void
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fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
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JSAMPARRAY input_data, JSAMPARRAY output_data)
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{
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int outrow;
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JDIMENSION colctr;
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JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
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register JSAMPROW inptr, above_ptr, below_ptr, outptr;
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INT32 membersum, neighsum, memberscale, neighscale;
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int colsum, lastcolsum, nextcolsum;
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// Expand input data enough to let all the output samples be generated
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// * by the standard loop. Special-casing padded output would be more
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// * efficient.
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expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
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cinfo->image_width, output_cols);
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// Each of the eight neighbor pixels contributes a fraction SF to the
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// * smoothed pixel, while the main pixel contributes (1-8*SF). In order
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// * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
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// * Also recall that SF = smoothing_factor / 1024.
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memberscale = 65536L - cinfo->smoothing_factor * 512L; // scaled 1-8*SF
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neighscale = cinfo->smoothing_factor * 64; // scaled SF
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for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
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outptr = output_data[outrow];
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inptr = input_data[outrow];
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above_ptr = input_data[outrow-1];
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below_ptr = input_data[outrow+1];
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// Special case for first column
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colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
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GETJSAMPLE(*inptr);
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membersum = GETJSAMPLE(*inptr++);
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nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
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GETJSAMPLE(*inptr);
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neighsum = colsum + (colsum - membersum) + nextcolsum;
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membersum = membersum * memberscale + neighsum * neighscale;
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*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
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lastcolsum = colsum; colsum = nextcolsum;
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for (colctr = output_cols - 2; colctr > 0; colctr--) {
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membersum = GETJSAMPLE(*inptr++);
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above_ptr++; below_ptr++;
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nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
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GETJSAMPLE(*inptr);
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neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
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membersum = membersum * memberscale + neighsum * neighscale;
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*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
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lastcolsum = colsum; colsum = nextcolsum;
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}
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// Special case for last column
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membersum = GETJSAMPLE(*inptr);
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neighsum = lastcolsum + (colsum - membersum) + colsum;
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membersum = membersum * memberscale + neighsum * neighscale;
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*outptr = (JSAMPLE) ((membersum + 32768) >> 16);
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}
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}
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#endif // INPUT_SMOOTHING_SUPPORTED
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// * Module initialization routine for downsampling.
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// * Note that we must select a routine for each component.
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GLOBAL void
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jinit_downsampler (j_compress_ptr cinfo)
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{
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my_downsample_ptr downsample;
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int ci;
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jpeg_component_info * compptr;
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boolean smoothok = TRUE;
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downsample = (my_downsample_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(my_downsampler));
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cinfo->downsample = (struct jpeg_downsampler *) downsample;
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downsample->pub.start_pass = start_pass_downsample;
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downsample->pub.downsample = sep_downsample;
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downsample->pub.need_context_rows = FALSE;
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if (cinfo->CCIR601_sampling)
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ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
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// Verify we can handle the sampling factors, and set up method pointers
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for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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ci++, compptr++) {
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if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
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compptr->v_samp_factor == cinfo->max_v_samp_factor) {
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#ifdef INPUT_SMOOTHING_SUPPORTED
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if (cinfo->smoothing_factor) {
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downsample->methods[ci] = fullsize_smooth_downsample;
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downsample->pub.need_context_rows = TRUE;
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} else
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#endif
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downsample->methods[ci] = fullsize_downsample;
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} else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
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compptr->v_samp_factor == cinfo->max_v_samp_factor) {
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smoothok = FALSE;
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downsample->methods[ci] = h2v1_downsample;
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} else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
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compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
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#ifdef INPUT_SMOOTHING_SUPPORTED
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if (cinfo->smoothing_factor) {
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downsample->methods[ci] = h2v2_smooth_downsample;
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downsample->pub.need_context_rows = TRUE;
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} else
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#endif
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downsample->methods[ci] = h2v2_downsample;
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} else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
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(cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
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smoothok = FALSE;
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downsample->methods[ci] = int_downsample;
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} else
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ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
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}
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#ifdef INPUT_SMOOTHING_SUPPORTED
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if (cinfo->smoothing_factor && !smoothok)
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TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
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#endif
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}
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