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
8 * For conditions of distribution and use, see the accompanying README.ijg
11 * This file contains the compression preprocessing controller.
12 * This controller manages the color conversion, downsampling,
13 * and edge expansion steps.
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.
20 #define JPEG_INTERNALS
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.
30 #ifdef INPUT_SMOOTHING_SUPPORTED
31 #define CONTEXT_ROWS_SUPPORTED
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.
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.
54 /* Private buffer controller object */
57 struct jpeg_c_prep_controller pub; /* public fields */
59 /* Downsampling input buffer. This buffer holds color-converted data
60 * until we have enough to do a downsample step.
62 JSAMPARRAY color_buf[MAX_COMPONENTS];
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 */
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 */
73 typedef my_prep_controller *my_prep_ptr;
77 * Initialize for a processing pass.
81 start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode)
83 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
85 if (pass_mode != JBUF_PASS_THRU)
86 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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.
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;
104 * Expand an image vertically from height input_rows to height output_rows,
105 * by duplicating the bottom row.
109 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols,
110 int input_rows, int output_rows)
114 for (row = input_rows; row < output_rows; row++) {
115 jcopy_sample_rows(image_data, input_rows-1, image_data, row,
122 * Process some data in the simple no-context case.
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
131 pre_process_data (j_compress_ptr cinfo,
132 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
133 JDIMENSION in_rows_avail,
134 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
135 JDIMENSION out_row_groups_avail)
137 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
140 jpeg_component_info *compptr;
142 while (*in_row_ctr < in_rows_avail &&
143 *out_row_group_ctr < out_row_groups_avail) {
144 /* Do color conversion to fill the conversion buffer. */
145 inrows = in_rows_avail - *in_row_ctr;
146 numrows = cinfo->max_v_samp_factor - prep->next_buf_row;
147 numrows = (int) MIN((JDIMENSION) numrows, inrows);
148 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
150 (JDIMENSION) prep->next_buf_row,
152 *in_row_ctr += numrows;
153 prep->next_buf_row += numrows;
154 prep->rows_to_go -= numrows;
155 /* If at bottom of image, pad to fill the conversion buffer. */
156 if (prep->rows_to_go == 0 &&
157 prep->next_buf_row < cinfo->max_v_samp_factor) {
158 for (ci = 0; ci < cinfo->num_components; ci++) {
159 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
160 prep->next_buf_row, cinfo->max_v_samp_factor);
162 prep->next_buf_row = cinfo->max_v_samp_factor;
164 /* If we've filled the conversion buffer, empty it. */
165 if (prep->next_buf_row == cinfo->max_v_samp_factor) {
166 (*cinfo->downsample->downsample) (cinfo,
167 prep->color_buf, (JDIMENSION) 0,
168 output_buf, *out_row_group_ctr);
169 prep->next_buf_row = 0;
170 (*out_row_group_ctr)++;
172 /* If at bottom of image, pad the output to a full iMCU height.
173 * Note we assume the caller is providing a one-iMCU-height output buffer!
175 if (prep->rows_to_go == 0 &&
176 *out_row_group_ctr < out_row_groups_avail) {
177 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
179 expand_bottom_edge(output_buf[ci],
180 compptr->width_in_blocks * DCTSIZE,
181 (int) (*out_row_group_ctr * compptr->v_samp_factor),
182 (int) (out_row_groups_avail * compptr->v_samp_factor));
184 *out_row_group_ctr = out_row_groups_avail;
185 break; /* can exit outer loop without test */
191 #ifdef CONTEXT_ROWS_SUPPORTED
194 * Process some data in the context case.
198 pre_process_context (j_compress_ptr cinfo,
199 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr,
200 JDIMENSION in_rows_avail,
201 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr,
202 JDIMENSION out_row_groups_avail)
204 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
206 int buf_height = cinfo->max_v_samp_factor * 3;
209 while (*out_row_group_ctr < out_row_groups_avail) {
210 if (*in_row_ctr < in_rows_avail) {
211 /* Do color conversion to fill the conversion buffer. */
212 inrows = in_rows_avail - *in_row_ctr;
213 numrows = prep->next_buf_stop - prep->next_buf_row;
214 numrows = (int) MIN((JDIMENSION) numrows, inrows);
215 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr,
217 (JDIMENSION) prep->next_buf_row,
219 /* Pad at top of image, if first time through */
220 if (prep->rows_to_go == cinfo->image_height) {
221 for (ci = 0; ci < cinfo->num_components; ci++) {
223 for (row = 1; row <= cinfo->max_v_samp_factor; row++) {
224 jcopy_sample_rows(prep->color_buf[ci], 0,
225 prep->color_buf[ci], -row,
226 1, cinfo->image_width);
230 *in_row_ctr += numrows;
231 prep->next_buf_row += numrows;
232 prep->rows_to_go -= numrows;
234 /* Return for more data, unless we are at the bottom of the image. */
235 if (prep->rows_to_go != 0)
237 /* When at bottom of image, pad to fill the conversion buffer. */
238 if (prep->next_buf_row < prep->next_buf_stop) {
239 for (ci = 0; ci < cinfo->num_components; ci++) {
240 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width,
241 prep->next_buf_row, prep->next_buf_stop);
243 prep->next_buf_row = prep->next_buf_stop;
246 /* If we've gotten enough data, downsample a row group. */
247 if (prep->next_buf_row == prep->next_buf_stop) {
248 (*cinfo->downsample->downsample) (cinfo,
250 (JDIMENSION) prep->this_row_group,
251 output_buf, *out_row_group_ctr);
252 (*out_row_group_ctr)++;
253 /* Advance pointers with wraparound as necessary. */
254 prep->this_row_group += cinfo->max_v_samp_factor;
255 if (prep->this_row_group >= buf_height)
256 prep->this_row_group = 0;
257 if (prep->next_buf_row >= buf_height)
258 prep->next_buf_row = 0;
259 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor;
266 * Create the wrapped-around downsampling input buffer needed for context mode.
270 create_context_buffer (j_compress_ptr cinfo)
272 my_prep_ptr prep = (my_prep_ptr) cinfo->prep;
273 int rgroup_height = cinfo->max_v_samp_factor;
275 jpeg_component_info *compptr;
276 JSAMPARRAY true_buffer, fake_buffer;
278 /* Grab enough space for fake row pointers for all the components;
279 * we need five row groups' worth of pointers for each component.
281 fake_buffer = (JSAMPARRAY)
282 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
283 (cinfo->num_components * 5 * rgroup_height) *
286 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
288 /* Allocate the actual buffer space (3 row groups) for this component.
289 * We make the buffer wide enough to allow the downsampler to edge-expand
290 * horizontally within the buffer, if it so chooses.
292 true_buffer = (*cinfo->mem->alloc_sarray)
293 ((j_common_ptr) cinfo, JPOOL_IMAGE,
294 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
295 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
296 (JDIMENSION) (3 * rgroup_height));
297 /* Copy true buffer row pointers into the middle of the fake row array */
298 MEMCOPY(fake_buffer + rgroup_height, true_buffer,
299 3 * rgroup_height * sizeof(JSAMPROW));
300 /* Fill in the above and below wraparound pointers */
301 for (i = 0; i < rgroup_height; i++) {
302 fake_buffer[i] = true_buffer[2 * rgroup_height + i];
303 fake_buffer[4 * rgroup_height + i] = true_buffer[i];
305 prep->color_buf[ci] = fake_buffer + rgroup_height;
306 fake_buffer += 5 * rgroup_height; /* point to space for next component */
310 #endif /* CONTEXT_ROWS_SUPPORTED */
314 * Initialize preprocessing controller.
318 jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer)
322 jpeg_component_info *compptr;
324 if (need_full_buffer) /* safety check */
325 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
328 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
329 sizeof(my_prep_controller));
330 cinfo->prep = (struct jpeg_c_prep_controller *) prep;
331 prep->pub.start_pass = start_pass_prep;
333 /* Allocate the color conversion buffer.
334 * We make the buffer wide enough to allow the downsampler to edge-expand
335 * horizontally within the buffer, if it so chooses.
337 if (cinfo->downsample->need_context_rows) {
338 /* Set up to provide context rows */
339 #ifdef CONTEXT_ROWS_SUPPORTED
340 prep->pub.pre_process_data = pre_process_context;
341 create_context_buffer(cinfo);
343 ERREXIT(cinfo, JERR_NOT_COMPILED);
346 /* No context, just make it tall enough for one row group */
347 prep->pub.pre_process_data = pre_process_data;
348 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
350 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray)
351 ((j_common_ptr) cinfo, JPOOL_IMAGE,
352 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE *
353 cinfo->max_h_samp_factor) / compptr->h_samp_factor),
354 (JDIMENSION) cinfo->max_v_samp_factor);