1/*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5/*
6 * jcprepct.c
7 *
8 * Copyright (C) 1994-1996, 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 the compression preprocessing controller.
13 * This controller manages the color conversion, downsampling,
14 * and edge expansion steps.
15 *
16 * Most of the complexity here is associated with buffering input rows
17 * as required by the downsampler. See the comments at the head of
18 * jcsample.c for the downsampler's needs.
19 */
20
21#define JPEG_INTERNALS
22#include "jinclude.h"
23#include "jpeglib.h"
24
25
26/* At present, jcsample.c can request context rows only for smoothing.
27 * In the future, we might also need context rows for CCIR601 sampling
28 * or other more-complex downsampling procedures. The code to support
29 * context rows should be compiled only if needed.
30 */
31#ifdef INPUT_SMOOTHING_SUPPORTED
32#define CONTEXT_ROWS_SUPPORTED
33#endif
34
35
36/*
37 * For the simple (no-context-row) case, we just need to buffer one
38 * row group's worth of pixels for the downsampling step. At the bottom of
39 * the image, we pad to a full row group by replicating the last pixel row.
40 * The downsampler's last output row is then replicated if needed to pad
41 * out to a full iMCU row.
42 *
43 * When providing context rows, we must buffer three row groups' worth of
44 * pixels. Three row groups are physically allocated, but the row pointer
45 * arrays are made five row groups high, with the extra pointers above and
46 * below "wrapping around" to point to the last and first real row groups.
47 * This allows the downsampler to access the proper context rows.
48 * At the top and bottom of the image, we create dummy context rows by
49 * copying the first or last real pixel row. This copying could be avoided
50 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the
51 * trouble on the compression side.
52 */
53
54
55/* Private buffer controller object */
56
57typedef struct {
58 struct jpeg_c_prep_controller pub; /* public fields */
59
60 /* Downsampling input buffer. This buffer holds color-converted data
61 * until we have enough to do a downsample step.
62 */
63 JSAMPARRAY color_buf[MAX_COMPONENTS];
64
65 JDIMENSION rows_to_go; /* counts rows remaining in source image */
66 int next_buf_row; /* index of next row to store in color_buf */
67
68#ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */
69 int this_row_group; /* starting row index of group to process */
70 int next_buf_stop; /* downsample when we reach this index */
71#endif
72} my_prep_controller;
73
74typedef my_prep_controller * my_prep_ptr;
75
76
77/*
78 * Initialize for a processing pass.
79 */
80
81METHODDEF(void)
82start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
83{
84 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
85
86 if (pass_mode != JBUF_PASS_THRU)
87 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
88
89 /* Initialize total-height counter for detecting bottom of image */
90 prep->rows_to_go = cinfo->image_height;
91 /* Mark the conversion buffer empty */
92 prep->next_buf_row = 0;
93#ifdef CONTEXT_ROWS_SUPPORTED
94 /* Preset additional state variables for context mode.
95 * These aren't used in non-context mode, so we needn't test which mode.
96 */
97 prep->this_row_group = 0;
98 /* Set next_buf_stop to stop after two row groups have been read in. */
99 prep->next_buf_stop = 2 * cinfo->max_v_samp_factor;
100#endif
101}
102
103
104/*
105 * Expand an image vertically from height input_rows to height output_rows,
106 * by duplicating the bottom row.
107 */
108
109LOCAL(void)
110expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
111 int input_rows, int output_rows)
112{
113 register int row;
114
115 for (row = input_rows; row < output_rows; row++) {
116 jcopy_sample_rows(image_data, input_rows-1, image_data, row,
117 1, num_cols);
118 }
119}
120
121
122/*
123 * Process some data in the simple no-context case.
124 *
125 * Preprocessor output data is counted in "row groups". A row group
126 * is defined to be v_samp_factor sample rows of each component.
127 * Downsampling will produce this much data from each max_v_samp_factor
128 * input rows.
129 */
130
131METHODDEF(void)
132pre_process_data (j_compress_ptr cinfo,
133 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
134 JDIMENSION in_rows_avail,
135 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
136 JDIMENSION out_row_groups_avail)
137{
138 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
139 int numrows, ci;
140 JDIMENSION inrows;
141 jpeg_component_info * compptr;
142
143 while (*in_row_ctr < in_rows_avail &&
144 *out_row_group_ctr < out_row_groups_avail) {
145 /* Do color conversion to fill the conversion buffer. */
146 inrows = in_rows_avail - *in_row_ctr;
147 numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
148 numrows = (int) MIN((JDIMENSION) numrows, inrows);
149 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
150 prep->color_buf,
151 (JDIMENSION) prep->next_buf_row,
152 numrows);
153 *in_row_ctr += numrows;
154 prep->next_buf_row += numrows;
155 prep->rows_to_go -= numrows;
156 /* If at bottom of image, pad to fill the conversion buffer. */
157 if (prep->rows_to_go == 0 &&
158 prep->next_buf_row < cinfo->max_v_samp_factor) {
159 for (ci = 0; ci < cinfo->num_components; ci++) {
160 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
161 prep->next_buf_row, cinfo->max_v_samp_factor);
162 }
163 prep->next_buf_row = cinfo->max_v_samp_factor;
164 }
165 /* If we've filled the conversion buffer, empty it. */
166 if (prep->next_buf_row == cinfo->max_v_samp_factor) {
167 (*cinfo->downsample->downsample) (cinfo,
168 prep->color_buf, (JDIMENSION) 0,
169 output_buf, *out_row_group_ctr);
170 prep->next_buf_row = 0;
171 (*out_row_group_ctr)++;
172 }
173 /* If at bottom of image, pad the output to a full iMCU height.
174 * Note we assume the caller is providing a one-iMCU-height output buffer!
175 */
176 if (prep->rows_to_go == 0 &&
177 *out_row_group_ctr < out_row_groups_avail) {
178 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
179 ci++, compptr++) {
180 expand_bottom_edge(output_buf[ci],
181 compptr->width_in_blocks * DCTSIZE,
182 (int) (*out_row_group_ctr * compptr->v_samp_factor),
183 (int) (out_row_groups_avail * compptr->v_samp_factor));
184 }
185 *out_row_group_ctr = out_row_groups_avail;
186 break; /* can exit outer loop without test */
187 }
188 }
189}
190
191
192#ifdef CONTEXT_ROWS_SUPPORTED
193
194/*
195 * Process some data in the context case.
196 */
197
198METHODDEF(void)
199pre_process_context (j_compress_ptr cinfo,
200 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
201 JDIMENSION in_rows_avail,
202 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
203 JDIMENSION out_row_groups_avail)
204{
205 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
206 int numrows, ci;
207 int buf_height = cinfo->max_v_samp_factor * 3;
208 JDIMENSION inrows;
209
210 while (*out_row_group_ctr < out_row_groups_avail) {
211 if (*in_row_ctr < in_rows_avail) {
212 /* Do color conversion to fill the conversion buffer. */
213 inrows = in_rows_avail - *in_row_ctr;
214 numrows = prep->next_buf_stop - prep->next_buf_row;
215 numrows = (int) MIN((JDIMENSION) numrows, inrows);
216 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
217 prep->color_buf,
218 (JDIMENSION) prep->next_buf_row,
219 numrows);
220 /* Pad at top of image, if first time through */
221 if (prep->rows_to_go == cinfo->image_height) {
222 for (ci = 0; ci < cinfo->num_components; ci++) {
223 int row;
224 for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
225 jcopy_sample_rows(prep->color_buf[ci], 0,
226 prep->color_buf[ci], -row,
227 1, cinfo->image_width);
228 }
229 }
230 }
231 *in_row_ctr += numrows;
232 prep->next_buf_row += numrows;
233 prep->rows_to_go -= numrows;
234 } else {
235 /* Return for more data, unless we are at the bottom of the image. */
236 if (prep->rows_to_go != 0)
237 break;
238 /* When at bottom of image, pad to fill the conversion buffer. */
239 if (prep->next_buf_row < prep->next_buf_stop) {
240 for (ci = 0; ci < cinfo->num_components; ci++) {
241 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
242 prep->next_buf_row, prep->next_buf_stop);
243 }
244 prep->next_buf_row = prep->next_buf_stop;
245 }
246 }
247 /* If we've gotten enough data, downsample a row group. */
248 if (prep->next_buf_row == prep->next_buf_stop) {
249 (*cinfo->downsample->downsample) (cinfo,
250 prep->color_buf,
251 (JDIMENSION) prep->this_row_group,
252 output_buf, *out_row_group_ctr);
253 (*out_row_group_ctr)++;
254 /* Advance pointers with wraparound as necessary. */
255 prep->this_row_group += cinfo->max_v_samp_factor;
256 if (prep->this_row_group >= buf_height)
257 prep->this_row_group = 0;
258 if (prep->next_buf_row >= buf_height)
259 prep->next_buf_row = 0;
260 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
261 }
262 }
263}
264
265
266/*
267 * Create the wrapped-around downsampling input buffer needed for context mode.
268 */
269
270LOCAL(void)
271create_context_buffer (j_compress_ptr cinfo)
272{
273 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
274 int rgroup_height = cinfo->max_v_samp_factor;
275 int ci, i;
276 jpeg_component_info * compptr;
277 JSAMPARRAY true_buffer, fake_buffer;
278
279 /* Grab enough space for fake row pointers for all the components;
280 * we need five row groups' worth of pointers for each component.
281 */
282 fake_buffer = (JSAMPARRAY)
283 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
284 (cinfo->num_components * 5 * rgroup_height) *
285 SIZEOF(JSAMPROW));
286
287 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
288 ci++, compptr++) {
289 /* Allocate the actual buffer space (3 row groups) for this component.
290 * We make the buffer wide enough to allow the downsampler to edge-expand
291 * horizontally within the buffer, if it so chooses.
292 */
293 true_buffer = (*cinfo->mem->alloc_sarray)
294 ((j_common_ptr) cinfo, JPOOL_IMAGE,
295 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
296 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
297 (JDIMENSION) (3 * rgroup_height));
298 /* Copy true buffer row pointers into the middle of the fake row array */
299 MEMCOPY(fake_buffer + rgroup_height, true_buffer,
300 3 * rgroup_height * SIZEOF(JSAMPROW));
301 /* Fill in the above and below wraparound pointers */
302 for (i = 0; i < rgroup_height; i++) {
303 fake_buffer[i] = true_buffer[2 * rgroup_height + i];
304 fake_buffer[4 * rgroup_height + i] = true_buffer[i];
305 }
306 prep->color_buf[ci] = fake_buffer + rgroup_height;
307 fake_buffer += 5 * rgroup_height; /* point to space for next component */
308 }
309}
310
311#endif /* CONTEXT_ROWS_SUPPORTED */
312
313
314/*
315 * Initialize preprocessing controller.
316 */
317
318GLOBAL(void)
319jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
320{
321 my_prep_ptr prep;
322 int ci;
323 jpeg_component_info * compptr;
324
325 if (need_full_buffer) /* safety check */
326 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
327
328 prep = (my_prep_ptr)
329 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
330 SIZEOF(my_prep_controller));
331 cinfo->prep = (struct jpeg_c_prep_controller *) prep;
332 prep->pub.start_pass = start_pass_prep;
333
334 /* Allocate the color conversion buffer.
335 * We make the buffer wide enough to allow the downsampler to edge-expand
336 * horizontally within the buffer, if it so chooses.
337 */
338 if (cinfo->downsample->need_context_rows) {
339 /* Set up to provide context rows */
340#ifdef CONTEXT_ROWS_SUPPORTED
341 prep->pub.pre_process_data = pre_process_context;
342 create_context_buffer(cinfo);
343#else
344 ERREXIT(cinfo, JERR_NOT_COMPILED);
345#endif
346 } else {
347 /* No context, just make it tall enough for one row group */
348 prep->pub.pre_process_data = pre_process_data;
349 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
350 ci++, compptr++) {
351 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
352 ((j_common_ptr) cinfo, JPOOL_IMAGE,
353 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
354 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
355 (JDIMENSION) cinfo->max_v_samp_factor);
356 }
357 }
358}
359