1 /*
2 * jdscale.c
3 *
4 * Copyright (C) 1998, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
7 *
8 * This file contains sample scaling for lossless JPEG. This is a
9 * combination of upscaling the undifferenced sample by 2^Pt and downscaling
10 * the sample to fit into JSAMPLE.
11 */
12
13 #define JPEG_INTERNALS
14 #include "jinclude16.h"
15 #include "jpeglib16.h"
16 #include "jlossls16.h" /* Private declarations for lossless codec */
17
18
19 #ifdef D_LOSSLESS_SUPPORTED
20
21 /*
22 * Private scaler object for lossless decoding.
23 */
24
25 typedef struct {
26 int scale_factor;
27 } scaler;
28
29 typedef scaler * scaler_ptr;
30
31
32 /*
33 * Scalers for packing sample differences into JSAMPLEs.
34 */
35
36 METHODDEF(void)
simple_upscale(j_decompress_ptr cinfo,const JDIFFROW diff_buf,JSAMPROW output_buf,JDIMENSION width)37 simple_upscale(j_decompress_ptr cinfo,
38 const JDIFFROW diff_buf, JSAMPROW output_buf,
39 JDIMENSION width)
40 {
41 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
42 scaler_ptr scale = (scaler_ptr) losslsd->scaler_private;
43 int scale_factor = scale->scale_factor;
44 unsigned int xindex;
45
46 for (xindex = 0; xindex < width; xindex++)
47 output_buf[xindex] = (JSAMPLE) (diff_buf[xindex] << scale_factor);
48 }
49
50 METHODDEF(void)
simple_downscale(j_decompress_ptr cinfo,const JDIFFROW diff_buf,JSAMPROW output_buf,JDIMENSION width)51 simple_downscale(j_decompress_ptr cinfo,
52 const JDIFFROW diff_buf, JSAMPROW output_buf,
53 JDIMENSION width)
54 {
55 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
56 scaler_ptr scale = (scaler_ptr) losslsd->scaler_private;
57 int scale_factor = scale->scale_factor;
58 unsigned int xindex;
59 SHIFT_TEMPS
60
61 for (xindex = 0; xindex < width; xindex++)
62 output_buf[xindex] = (JSAMPLE) RIGHT_SHIFT(diff_buf[xindex], scale_factor);
63 }
64
65 METHODDEF(void)
noscale(j_decompress_ptr cinfo,const JDIFFROW diff_buf,JSAMPROW output_buf,JDIMENSION width)66 noscale(j_decompress_ptr cinfo,
67 const JDIFFROW diff_buf, JSAMPROW output_buf,
68 JDIMENSION width)
69 {
70 unsigned int xindex;
71
72 for (xindex = 0; xindex < width; xindex++)
73 output_buf[xindex] = (JSAMPLE) diff_buf[xindex];
74 }
75
76
77 METHODDEF(void)
scaler_start_pass(j_decompress_ptr cinfo)78 scaler_start_pass (j_decompress_ptr cinfo)
79 {
80 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
81 scaler_ptr scale = (scaler_ptr) losslsd->scaler_private;
82 int downscale;
83
84 /*
85 * Downscale by the difference in the input vs. output precision. If the
86 * output precision >= input precision, then do not downscale.
87 */
88 downscale = BITS_IN_JSAMPLE < cinfo->data_precision ?
89 cinfo->data_precision - BITS_IN_JSAMPLE : 0;
90
91 scale->scale_factor = cinfo->Al - downscale;
92
93 /* Set scaler functions based on scale_factor (positive = left shift) */
94 if (scale->scale_factor > 0)
95 losslsd->scaler_scale = simple_upscale;
96 else if (scale->scale_factor < 0) {
97 scale->scale_factor = -scale->scale_factor;
98 losslsd->scaler_scale = simple_downscale;
99 }
100 else
101 losslsd->scaler_scale = noscale;
102 }
103
104
105 GLOBAL(void)
jinit_d_scaler(j_decompress_ptr cinfo)106 jinit_d_scaler (j_decompress_ptr cinfo)
107 {
108 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
109 scaler_ptr scale;
110
111 scale = (scaler_ptr)
112 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
113 SIZEOF(scaler));
114 losslsd->scaler_private = (void *) scale;
115 losslsd->scaler_start_pass = scaler_start_pass;
116 }
117
118 #endif /* D_LOSSLESS_SUPPORTED */
119
120