ec6e451d05
Referring to https://github.com/libjpeg-turbo/libjpeg-turbo/issues/402#issuecomment-768348440 and https://github.com/libjpeg-turbo/libjpeg-turbo/issues/402#issuecomment-770221584 Ken Murchison clarified that it was his intent to release the lossless JPEG patch under the IJG License and that adding his name to the copyright headers would be sufficient to acknowledge that any derivatives are based on his work.
121 lines
3.1 KiB
C
121 lines
3.1 KiB
C
/*
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* jdscale.c
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*
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* This file was part of the Independent JPEG Group's software:
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* Copyright (C) 1998, Thomas G. Lane.
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* Lossless JPEG Modifications:
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* Copyright (C) 1999, Ken Murchison.
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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 sample scaling for lossless JPEG. This is a
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* combination of upscaling the undifferenced sample by 2^Pt and downscaling
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* the sample to fit into JSAMPLE.
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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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#include "jlossls.h" /* Private declarations for lossless codec */
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#ifdef D_LOSSLESS_SUPPORTED
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/*
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* Private scaler object for lossless decoding.
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*/
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typedef struct {
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int scale_factor;
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} scaler;
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typedef scaler * scaler_ptr;
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/*
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* Scalers for packing sample differences into JSAMPLEs.
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*/
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METHODDEF(void)
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simple_upscale(j_decompress_ptr cinfo,
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JDIFFROW diff_buf, JSAMPROW output_buf,
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JDIMENSION width)
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{
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j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
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scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
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int scale_factor = scaler->scale_factor;
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int xindex;
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for (xindex = 0; xindex < width; xindex++)
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output_buf[xindex] = (JSAMPLE) (diff_buf[xindex] << scale_factor);
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}
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METHODDEF(void)
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simple_downscale(j_decompress_ptr cinfo,
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JDIFFROW diff_buf, JSAMPROW output_buf,
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JDIMENSION width)
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{
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j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
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scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
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int scale_factor = scaler->scale_factor;
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int xindex;
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for (xindex = 0; xindex < width; xindex++)
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output_buf[xindex] = (JSAMPLE) RIGHT_SHIFT(diff_buf[xindex], scale_factor);
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}
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METHODDEF(void)
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noscale(j_decompress_ptr cinfo,
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JDIFFROW diff_buf, JSAMPROW output_buf,
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JDIMENSION width)
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{
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int xindex;
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for (xindex = 0; xindex < width; xindex++)
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output_buf[xindex] = (JSAMPLE) diff_buf[xindex];
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}
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METHODDEF(void)
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scaler_start_pass (j_decompress_ptr cinfo)
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{
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j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
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scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
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int downscale;
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/*
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* Downscale by the difference in the input vs. output precision. If the
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* output precision >= input precision, then do not downscale.
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*/
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downscale = BITS_IN_JSAMPLE < cinfo->data_precision ?
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cinfo->data_precision - BITS_IN_JSAMPLE : 0;
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scaler->scale_factor = cinfo->Al - downscale;
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/* Set scaler functions based on scale_factor (positive = left shift) */
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if (scaler->scale_factor > 0)
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losslsd->scaler_scale = simple_upscale;
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else if (scaler->scale_factor < 0) {
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scaler->scale_factor = -scaler->scale_factor;
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losslsd->scaler_scale = simple_downscale;
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}
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else
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losslsd->scaler_scale = noscale;
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}
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GLOBAL(void)
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jinit_d_scaler (j_decompress_ptr cinfo)
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{
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j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
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scaler_ptr scaler;
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scaler = (scaler_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(scaler));
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losslsd->scaler_private = (void *) scaler;
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losslsd->scaler_start_pass = scaler_start_pass;
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}
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#endif /* D_LOSSLESS_SUPPORTED */
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