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/*
* jdscale.c
*
* Copyright (C) 1998, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains sample scaling for lossless JPEG. This is a
* combination of upscaling the undifferenced sample by 2^Pt and downscaling
* the sample to fit into JSAMPLE.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jlossls.h" /* Private declarations for lossless codec */
#ifdef D_LOSSLESS_SUPPORTED
/*
* Private scaler object for lossless decoding.
*/
typedef struct {
int scale_factor;
} scaler;
typedef scaler * scaler_ptr;
/*
* Scalers for packing sample differences into JSAMPLEs.
*/
METHODDEF(void)
simple_upscale(j_decompress_ptr cinfo,
JDIFFROW diff_buf, JSAMPROW output_buf,
JDIMENSION width)
{
j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
scaler_ptr scalerv = (scaler_ptr) losslsd->scaler_private;
int scale_factor = scalerv->scale_factor;
unsigned int xindex;
for (xindex = 0; xindex < width; xindex++)
output_buf[xindex] = (JSAMPLE) (diff_buf[xindex] << scale_factor);
}
METHODDEF(void)
simple_downscale(j_decompress_ptr cinfo,
JDIFFROW diff_buf, JSAMPROW output_buf,
JDIMENSION width)
{
j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
scaler_ptr scalerv = (scaler_ptr) losslsd->scaler_private;
int scale_factor = scalerv->scale_factor;
unsigned int xindex;
SHIFT_TEMPS
for (xindex = 0; xindex < width; xindex++)
output_buf[xindex] = (JSAMPLE) RIGHT_SHIFT(diff_buf[xindex], scale_factor);
}
METHODDEF(void)
noscale(j_decompress_ptr cinfo,
JDIFFROW diff_buf, JSAMPROW output_buf,
JDIMENSION width)
{
unsigned int xindex;
(void)cinfo;
for (xindex = 0; xindex < width; xindex++)
output_buf[xindex] = (JSAMPLE) diff_buf[xindex];
}
METHODDEF(void)
scaler_start_pass (j_decompress_ptr cinfo)
{
j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
scaler_ptr scalerv = (scaler_ptr) losslsd->scaler_private;
int downscale;
/*
* Downscale by the difference in the input vs. output precision. If the
* output precision >= input precision, then do not downscale.
*/
downscale = BITS_IN_JSAMPLE < cinfo->data_precision ?
cinfo->data_precision - BITS_IN_JSAMPLE : 0;
scalerv->scale_factor = cinfo->Al - downscale;
/* Set scaler functions based on scale_factor (positive = left shift) */
if (scalerv->scale_factor > 0)
losslsd->scaler_scale = simple_upscale;
else if (scalerv->scale_factor < 0) {
scalerv->scale_factor = -scalerv->scale_factor;
losslsd->scaler_scale = simple_downscale;
}
else
losslsd->scaler_scale = noscale;
}
GLOBAL(void)
jinit_d_scaler (j_decompress_ptr cinfo)
{
j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
scaler_ptr scalerv;
scalerv = (scaler_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(scalerv));
losslsd->scaler_private = (void *) scalerv;
losslsd->scaler_start_pass = scaler_start_pass;
}
#endif /* D_LOSSLESS_SUPPORTED */
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