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.
8 * This file contains sample undifferencing (reconstruction) for lossless JPEG.
10 * In order to avoid paying the performance penalty of having to check the
11 * predictor being used and the row being processed for each call of the
12 * undifferencer, and to promote optimization, we have separate undifferencing
13 * functions for each case.
15 * We are able to avoid duplicating source code by implementing the predictors
16 * and undifferencers as macros. Each of the undifferencing functions are
17 * simply wrappers around an UNDIFFERENCE macro with the appropriate PREDICTOR
18 * macro passed as an argument.
21 #define JPEG_INTERNALS
24 #include "jlossls.h" /* Private declarations for lossless codec */
27 #ifdef D_LOSSLESS_SUPPORTED
29 /* Predictor for the first column of the first row: 2^(P-Pt-1) */
30 #define INITIAL_PREDICTORx (1 << (cinfo->data_precision - cinfo->Al - 1))
32 /* Predictor for the first column of the remaining rows: Rb */
33 #define INITIAL_PREDICTOR2 GETJSAMPLE(prev_row[0])
37 * 1-Dimensional undifferencer routine.
39 * This macro implements the 1-D horizontal predictor (1). INITIAL_PREDICTOR
40 * is used as the special case predictor for the first column, which must be
41 * either INITIAL_PREDICTOR2 or INITIAL_PREDICTORx. The remaining samples
44 * The reconstructed sample is supposed to be calculated modulo 2^16, so we
45 * logically AND the result with 0xFFFF.
48 #define UNDIFFERENCE_1D(INITIAL_PREDICTOR) \
49 unsigned int xindex; \
52 Ra = (diff_buf[0] + INITIAL_PREDICTOR) & 0xFFFF; \
55 for (xindex = 1; xindex < width; xindex++) { \
56 Ra = (diff_buf[xindex] + PREDICTOR1) & 0xFFFF; \
57 undiff_buf[xindex] = Ra; \
61 * 2-Dimensional undifferencer routine.
63 * This macro implements the 2-D horizontal predictors (#2-7). PREDICTOR2 is
64 * used as the special case predictor for the first column. The remaining
65 * samples use PREDICTOR, which is a function of Ra, Rb, Rc.
67 * Because prev_row and output_buf may point to the same storage area (in an
68 * interleaved image with Vi=1, for example), we must take care to buffer Rb/Rc
69 * before writing the current reconstructed sample value into output_buf.
71 * The reconstructed sample is supposed to be calculated modulo 2^16, so we
72 * logically AND the result with 0xFFFF.
75 #define UNDIFFERENCE_2D(PREDICTOR) \
76 unsigned int xindex; \
79 Rb = GETJSAMPLE(prev_row[0]); \
80 Ra = (diff_buf[0] + PREDICTOR2) & 0xFFFF; \
83 for (xindex = 1; xindex < width; xindex++) { \
85 Rb = GETJSAMPLE(prev_row[xindex]); \
86 Ra = (diff_buf[xindex] + PREDICTOR) & 0xFFFF; \
87 undiff_buf[xindex] = Ra; \
92 * Undifferencers for the all rows but the first in a scan or restart interval.
93 * The first sample in the row is undifferenced using the vertical
94 * predictor (2). The rest of the samples are undifferenced using the
95 * predictor specified in the scan header.
99 jpeg_undifference1(j_decompress_ptr cinfo, int comp_index,
100 JDIFFROW diff_buf, JDIFFROW prev_row,
101 JDIFFROW undiff_buf, JDIMENSION width)
103 UNDIFFERENCE_1D(INITIAL_PREDICTOR2);
107 jpeg_undifference2(j_decompress_ptr cinfo, int comp_index,
108 JDIFFROW diff_buf, JDIFFROW prev_row,
109 JDIFFROW undiff_buf, JDIMENSION width)
111 UNDIFFERENCE_2D(PREDICTOR2);
115 jpeg_undifference3(j_decompress_ptr cinfo, int comp_index,
116 JDIFFROW diff_buf, JDIFFROW prev_row,
117 JDIFFROW undiff_buf, JDIMENSION width)
119 UNDIFFERENCE_2D(PREDICTOR3);
123 jpeg_undifference4(j_decompress_ptr cinfo, int comp_index,
124 JDIFFROW diff_buf, JDIFFROW prev_row,
125 JDIFFROW undiff_buf, JDIMENSION width)
127 UNDIFFERENCE_2D(PREDICTOR4);
131 jpeg_undifference5(j_decompress_ptr cinfo, int comp_index,
132 JDIFFROW diff_buf, JDIFFROW prev_row,
133 JDIFFROW undiff_buf, JDIMENSION width)
136 UNDIFFERENCE_2D(PREDICTOR5);
140 jpeg_undifference6(j_decompress_ptr cinfo, int comp_index,
141 JDIFFROW diff_buf, JDIFFROW prev_row,
142 JDIFFROW undiff_buf, JDIMENSION width)
145 UNDIFFERENCE_2D(PREDICTOR6);
149 jpeg_undifference7(j_decompress_ptr cinfo, int comp_index,
150 JDIFFROW diff_buf, JDIFFROW prev_row,
151 JDIFFROW undiff_buf, JDIMENSION width)
154 UNDIFFERENCE_2D(PREDICTOR7);
159 * Undifferencer for the first row in a scan or restart interval. The first
160 * sample in the row is undifferenced using the special predictor constant
161 * x=2^(P-Pt-1). The rest of the samples are undifferenced using the
162 * 1-D horizontal predictor (1).
166 jpeg_undifference_first_row(j_decompress_ptr cinfo, int comp_index,
167 JDIFFROW diff_buf, JDIFFROW prev_row,
168 JDIFFROW undiff_buf, JDIMENSION width)
170 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
172 UNDIFFERENCE_1D(INITIAL_PREDICTORx);
175 * Now that we have undifferenced the first row, we want to use the
176 * undifferencer which corresponds to the predictor specified in the
181 losslsd->predict_undifference[comp_index] = jpeg_undifference1;
184 losslsd->predict_undifference[comp_index] = jpeg_undifference2;
187 losslsd->predict_undifference[comp_index] = jpeg_undifference3;
190 losslsd->predict_undifference[comp_index] = jpeg_undifference4;
193 losslsd->predict_undifference[comp_index] = jpeg_undifference5;
196 losslsd->predict_undifference[comp_index] = jpeg_undifference6;
199 losslsd->predict_undifference[comp_index] = jpeg_undifference7;
206 * Initialize for an input processing pass.
210 predict_start_pass (j_decompress_ptr cinfo)
212 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
215 /* Check that the scan parameters Ss, Se, Ah, Al are OK for lossless JPEG.
217 * Ss is the predictor selection value (psv). Legal values for sequential
218 * lossless JPEG are: 1 <= psv <= 7.
220 * Se and Ah are not used and should be zero.
222 * Al specifies the point transform (Pt). Legal values are: 0 <= Pt <= 15.
224 if (cinfo->Ss < 1 || cinfo->Ss > 7 ||
225 cinfo->Se != 0 || cinfo->Ah != 0 ||
226 cinfo->Al > 15) /* need not check for < 0 */
227 ERREXIT4(cinfo, JERR_BAD_LOSSLESS,
228 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
230 /* Set undifference functions to first row function */
231 for (ci = 0; ci < cinfo->num_components; ci++)
232 losslsd->predict_undifference[ci] = jpeg_undifference_first_row;
237 * Module initialization routine for the undifferencer.
241 jinit_undifferencer (j_decompress_ptr cinfo)
243 j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
245 losslsd->predict_start_pass = predict_start_pass;
246 losslsd->predict_process_restart = predict_start_pass;
249 #endif /* D_LOSSLESS_SUPPORTED */