1/*
2 * jcprepct.c
3 *
4 * Copyright (C) 1994-1996, 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 the compression preprocessing controller.
9 * This controller manages the color conversion, downsampling,
10 * and edge expansion steps.
11 *
12 * Most of the complexity here is associated with buffering input rows
13 * as required by the downsampler. See the comments at the head of
14 * jcsample.c for the downsampler's needs.
15 */
16
17#define JPEG_INTERNALS
18#include "jinclude.h"
19#include "jpeglib.h"
20
21
22/* At present, jcsample.c can request context rows only for smoothing.
23 * In the future, we might also need context rows for CCIR601 sampling
24 * or other more-complex downsampling procedures. The code to support
25 * context rows should be compiled only if needed.
26 */
27#ifdef INPUT_SMOOTHING_SUPPORTED
28#define CONTEXT_ROWS_SUPPORTED
29#endif
30
31
32/*
33 * For the simple (no-context-row) case, we just need to buffer one
34 * row group's worth of pixels for the downsampling step. At the bottom of
35 * the image, we pad to a full row group by replicating the last pixel row.
36 * The downsampler's last output row is then replicated if needed to pad
37 * out to a full iMCU row.
38 *
39 * When providing context rows, we must buffer three row groups' worth of
40 * pixels. Three row groups are physically allocated, but the row pointer
41 * arrays are made five row groups high, with the extra pointers above and
42 * below "wrapping around" to point to the last and first real row groups.
43 * This allows the downsampler to access the proper context rows.
44 * At the top and bottom of the image, we create dummy context rows by
45 * copying the first or last real pixel row. This copying could be avoided
46 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
47 * trouble on the compression side.
48 */
49
50
51/* Private buffer controller object */
52
53typedef struct {
54 struct jpeg_c_prep_controller pub; /* public fields */
55
56 /* Downsampling input buffer. This buffer holds color-converted data
57 * until we have enough to do a downsample step.
58 */
59 JSAMPARRAY color_buf[MAX_COMPONENTS];
60
61 JDIMENSION rows_to_go; /* counts rows remaining in source image */
62 int next_buf_row; /* index of next row to store in color_buf */
63
64#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
65 int this_row_group; /* starting row index of group to process */
66 int next_buf_stop; /* downsample when we reach this index */
67#endif
68} my_prep_controller;
69
70typedef my_prep_controller * my_prep_ptr;
71
72
73/*
74 * Initialize for a processing pass.
75 */
76
77METHODDEF(void)
78start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
79{
80 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
81
82 if (pass_mode != JBUF_PASS_THRU)
83 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
84
85 /* Initialize total-height counter for detecting bottom of image */
86 prep->rows_to_go = cinfo->image_height;
87 /* Mark the conversion buffer empty */
88 prep->next_buf_row = 0;
89#ifdef CONTEXT_ROWS_SUPPORTED
90 /* Preset additional state variables for context mode.
91 * These aren't used in non-context mode, so we needn't test which mode.
92 */
93 prep->this_row_group = 0;
94 /* Set next_buf_stop to stop after two row groups have been read in. */
95 prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
96#endif
97}
98
99
100/*
101 * Expand an image vertically from height input_rows to height output_rows,
102 * by duplicating the bottom row.
103 */
104
105LOCAL(void)
106expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
107 int input_rows, int output_rows)
108{
109 register int row;
110
111 for (row = input_rows; row < output_rows; row++) {
112 jcopy_sample_rows(image_data, input_rows-1, image_data, row,
113 1, num_cols);
114 }
115}
116
117
118/*
119 * Process some data in the simple no-context case.
120 *
121 * Preprocessor output data is counted in "row groups". A row group
122 * is defined to be v_samp_factor sample rows of each component.
123 * Downsampling will produce this much data from each max_v_samp_factor
124 * input rows.
125 */
126
127METHODDEF(void)
128pre_process_data (j_compress_ptr cinfo,
129 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
130 JDIMENSION in_rows_avail,
131 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
132 JDIMENSION out_row_groups_avail)
133{
134 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
135 int numrows, ci;
136 JDIMENSION inrows;
137 jpeg_component_info * compptr;
138
139 while (*in_row_ctr < in_rows_avail &&
140 *out_row_group_ctr < out_row_groups_avail) {
141 /* Do color conversion to fill the conversion buffer. */
142 inrows = in_rows_avail - *in_row_ctr;
143 numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
144 numrows = (int) MIN((JDIMENSION) numrows, inrows);
145 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
146 prep->color_buf,
147 (JDIMENSION) prep->next_buf_row,
148 numrows);
149 *in_row_ctr += numrows;
150 prep->next_buf_row += numrows;
151 prep->rows_to_go -= numrows;
152 /* If at bottom of image, pad to fill the conversion buffer. */
153 if (prep->rows_to_go == 0 &&
154 prep->next_buf_row < cinfo->max_v_samp_factor) {
155 for (ci = 0; ci < cinfo->num_components; ci++) {
156 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
157 prep->next_buf_row, cinfo->max_v_samp_factor);
158 }
159 prep->next_buf_row = cinfo->max_v_samp_factor;
160 }
161 /* If we've filled the conversion buffer, empty it. */
162 if (prep->next_buf_row == cinfo->max_v_samp_factor) {
163 (*cinfo->downsample->downsample) (cinfo,
164 prep->color_buf, (JDIMENSION) 0,
165 output_buf, *out_row_group_ctr);
166 prep->next_buf_row = 0;
167 (*out_row_group_ctr)++;
168 }
169 /* If at bottom of image, pad the output to a full iMCU height.
170 * Note we assume the caller is providing a one-iMCU-height output buffer!
171 */
172 if (prep->rows_to_go == 0 &&
173 *out_row_group_ctr < out_row_groups_avail) {
174 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
175 ci++, compptr++) {
176 expand_bottom_edge(output_buf[ci],
177 compptr->width_in_blocks * DCTSIZE,
178 (int) (*out_row_group_ctr * compptr->v_samp_factor),
179 (int) (out_row_groups_avail * compptr->v_samp_factor));
180 }
181 *out_row_group_ctr = out_row_groups_avail;
182 break; /* can exit outer loop without test */
183 }
184 }
185}
186
187
188#ifdef CONTEXT_ROWS_SUPPORTED
189
190/*
191 * Process some data in the context case.
192 */
193
194METHODDEF(void)
195pre_process_context (j_compress_ptr cinfo,
196 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
197 JDIMENSION in_rows_avail,
198 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
199 JDIMENSION out_row_groups_avail)
200{
201 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
202 int numrows, ci;
203 int buf_height = cinfo->max_v_samp_factor * 3;
204 JDIMENSION inrows;
205
206 while (*out_row_group_ctr < out_row_groups_avail) {
207 if (*in_row_ctr < in_rows_avail) {
208 /* Do color conversion to fill the conversion buffer. */
209 inrows = in_rows_avail - *in_row_ctr;
210 numrows = prep->next_buf_stop - prep->next_buf_row;
211 numrows = (int) MIN((JDIMENSION) numrows, inrows);
212 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
213 prep->color_buf,
214 (JDIMENSION) prep->next_buf_row,
215 numrows);
216 /* Pad at top of image, if first time through */
217 if (prep->rows_to_go == cinfo->image_height) {
218 for (ci = 0; ci < cinfo->num_components; ci++) {
219 int row;
220 for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
221 jcopy_sample_rows(prep->color_buf[ci], 0,
222 prep->color_buf[ci], -row,
223 1, cinfo->image_width);
224 }
225 }
226 }
227 *in_row_ctr += numrows;
228 prep->next_buf_row += numrows;
229 prep->rows_to_go -= numrows;
230 } else {
231 /* Return for more data, unless we are at the bottom of the image. */
232 if (prep->rows_to_go != 0)
233 break;
234 /* When at bottom of image, pad to fill the conversion buffer. */
235 if (prep->next_buf_row < prep->next_buf_stop) {
236 for (ci = 0; ci < cinfo->num_components; ci++) {
237 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
238 prep->next_buf_row, prep->next_buf_stop);
239 }
240 prep->next_buf_row = prep->next_buf_stop;
241 }
242 }
243 /* If we've gotten enough data, downsample a row group. */
244 if (prep->next_buf_row == prep->next_buf_stop) {
245 (*cinfo->downsample->downsample) (cinfo,
246 prep->color_buf,
247 (JDIMENSION) prep->this_row_group,
248 output_buf, *out_row_group_ctr);
249 (*out_row_group_ctr)++;
250 /* Advance pointers with wraparound as necessary. */
251 prep->this_row_group += cinfo->max_v_samp_factor;
252 if (prep->this_row_group >= buf_height)
253 prep->this_row_group = 0;
254 if (prep->next_buf_row >= buf_height)
255 prep->next_buf_row = 0;
256 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
257 }
258 }
259}
260
261
262/*
263 * Create the wrapped-around downsampling input buffer needed for context mode.
264 */
265
266LOCAL(void)
267create_context_buffer (j_compress_ptr cinfo)
268{
269 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
270 int rgroup_height = cinfo->max_v_samp_factor;
271 int ci, i;
272 jpeg_component_info * compptr;
273 JSAMPARRAY true_buffer, fake_buffer;
274
275 /* Grab enough space for fake row pointers for all the components;
276 * we need five row groups' worth of pointers for each component.
277 */
278 fake_buffer = (JSAMPARRAY)
279 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
280 (cinfo->num_components * 5 * rgroup_height) *
281 SIZEOF(JSAMPROW));
282
283 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
284 ci++, compptr++) {
285 /* Allocate the actual buffer space (3 row groups) for this component.
286 * We make the buffer wide enough to allow the downsampler to edge-expand
287 * horizontally within the buffer, if it so chooses.
288 */
289 true_buffer = (*cinfo->mem->alloc_sarray)
290 ((j_common_ptr) cinfo, JPOOL_IMAGE,
291 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
292 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
293 (JDIMENSION) (3 * rgroup_height));
294 /* Copy true buffer row pointers into the middle of the fake row array */
295 MEMCOPY(fake_buffer + rgroup_height, true_buffer,
296 3 * rgroup_height * SIZEOF(JSAMPROW));
297 /* Fill in the above and below wraparound pointers */
298 for (i = 0; i < rgroup_height; i++) {
299 fake_buffer[i] = true_buffer[2 * rgroup_height + i];
300 fake_buffer[4 * rgroup_height + i] = true_buffer[i];
301 }
302 prep->color_buf[ci] = fake_buffer + rgroup_height;
303 fake_buffer += 5 * rgroup_height; /* point to space for next component */
304 }
305}
306
307#endif /* CONTEXT_ROWS_SUPPORTED */
308
309
310/*
311 * Initialize preprocessing controller.
312 */
313
314GLOBAL(void)
315jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
316{
317 my_prep_ptr prep;
318 int ci;
319 jpeg_component_info * compptr;
320
321 if (need_full_buffer) /* safety check */
322 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
323
324 prep = (my_prep_ptr)
325 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
326 SIZEOF(my_prep_controller));
327 cinfo->prep = (struct jpeg_c_prep_controller *) prep;
328 prep->pub.start_pass = start_pass_prep;
329
330 /* Allocate the color conversion buffer.
331 * We make the buffer wide enough to allow the downsampler to edge-expand
332 * horizontally within the buffer, if it so chooses.
333 */
334 if (cinfo->downsample->need_context_rows) {
335 /* Set up to provide context rows */
336#ifdef CONTEXT_ROWS_SUPPORTED
337 prep->pub.pre_process_data = pre_process_context;
338 create_context_buffer(cinfo);
339#else
340 ERREXIT(cinfo, JERR_NOT_COMPILED);
341#endif
342 } else {
343 /* No context, just make it tall enough for one row group */
344 prep->pub.pre_process_data = pre_process_data;
345 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
346 ci++, compptr++) {
347 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
348 ((j_common_ptr) cinfo, JPOOL_IMAGE,
349 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
350 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
351 (JDIMENSION) cinfo->max_v_samp_factor);
352 }
353 }
354}
355