compiler/libjpeg/main/jdscale.c

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * jdscale.c
   7  *
   8  * Copyright (C) 1998, Thomas G. Lane.
   9  * This file is part of the Independent JPEG Group's software.
  10  * For conditions of distribution and use, see the accompanying README file.
  11  *
  12  * This file contains sample scaling for lossless JPEG.  This is a
  13  * combination of upscaling the undifferenced sample by 2^Pt and downscaling
  14  * the sample to fit into JSAMPLE.
  15  */
  16
  17 #define JPEG_INTERNALS
  18 #include "jinclude.h"
  19 #include "jpeglib.h"
  20 #include "jlossls.h"            /* Private declarations for lossless codec */
  21
  22
  23 #ifdef D_LOSSLESS_SUPPORTED
  24
  25 /*
  26  * Private scaler object for lossless decoding.
  27  */
  28
  29 typedef struct {
  30   int scale_factor;
  31 } scaler;
  32
  33 typedef scaler * scaler_ptr;
  34
  35
  36 /*
  37  * Scalers for packing sample differences into JSAMPLEs.
  38  */
  39
  40 METHODDEF(void)
  41 simple_upscale(j_decompress_ptr cinfo,
  42                JDIFFROW diff_buf, JSAMPROW output_buf,
  43                JDIMENSION width)
  44 {
  45   j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
  46   scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
  47   int scale_factor = scaler->scale_factor;
  48   int xindex;
  49
  50   for (xindex = 0; xindex < width; xindex++)
  51     output_buf[xindex] = (JSAMPLE) (diff_buf[xindex] << scale_factor);
  52 }
  53
  54 METHODDEF(void)
  55 simple_downscale(j_decompress_ptr cinfo,
  56                  JDIFFROW diff_buf, JSAMPROW output_buf,
  57                  JDIMENSION width)
  58 {
  59   j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
  60   scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
  61   int scale_factor = scaler->scale_factor;
  62   int xindex;
  63
  64   for (xindex = 0; xindex < width; xindex++)
  65     output_buf[xindex] = (JSAMPLE) RIGHT_SHIFT(diff_buf[xindex], scale_factor);
  66 }
  67
  68 METHODDEF(void)
  69 noscale(j_decompress_ptr cinfo,
  70         JDIFFROW diff_buf, JSAMPROW output_buf,
  71         JDIMENSION width)
  72 {
  73   int xindex;
  74
  75   for (xindex = 0; xindex < width; xindex++)
  76     output_buf[xindex] = (JSAMPLE) diff_buf[xindex];
  77 }
  78
  79
  80 METHODDEF(void)
  81 scaler_start_pass (j_decompress_ptr cinfo)
  82 {
  83   j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
  84   scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
  85   int downscale;
  86
  87   /*
  88    * Downscale by the difference in the input vs. output precision.  If the
  89    * output precision >= input precision, then do not downscale.
  90    */
  91   downscale = BITS_IN_JSAMPLE < cinfo->data_precision ?
  92     cinfo->data_precision - BITS_IN_JSAMPLE : 0;
  93
  94   scaler->scale_factor = cinfo->Al - downscale;
  95
  96   /* Set scaler functions based on scale_factor (positive = left shift) */
  97   if (scaler->scale_factor > 0)
  98     losslsd->scaler_scale = simple_upscale;
  99   else if (scaler->scale_factor < 0) {
 100     scaler->scale_factor = -scaler->scale_factor;
 101     losslsd->scaler_scale = simple_downscale;
 102   }
 103   else
 104     losslsd->scaler_scale = noscale;
 105 }
 106
 107
 108 JGLOBAL(void)
 109 jinit_d_scaler (j_decompress_ptr cinfo)
 110 {
 111   j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
 112   scaler_ptr scaler;
 113
 114   scaler = (scaler_ptr)
 115     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 116                                 SIZEOF(scaler));
 117   losslsd->scaler_private = (void *) scaler;
 118   losslsd->scaler_start_pass = scaler_start_pass;
 119 }
 120
 121 #endif /* D_LOSSLESS_SUPPORTED */
 122