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