520 lines
18 KiB
C
520 lines
18 KiB
C
/*
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* jcsample.c
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*
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* Copyright (C) 1991-1996, 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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*/
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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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/*
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* Initialize for a downsampling pass.
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*/
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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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/*
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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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*/
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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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/*
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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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*/
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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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/*
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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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*/
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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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*/
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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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/*
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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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*/
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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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/*
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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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*/
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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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*/
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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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/*
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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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*/
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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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*/
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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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/*
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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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*/
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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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*/
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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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*/
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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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/*
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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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*/
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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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*/
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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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*/
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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 */
|
|
membersum = GETJSAMPLE(*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;
|
|
|
|
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;
|
|
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) {
|
|
downsample->methods[ci] = h2v2_smooth_downsample;
|
|
downsample->pub.need_context_rows = TRUE;
|
|
} 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
|
|
}
|