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 numrows = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) / 177 cinfo->min_DCT_v_scaled_size; 178 expand_bottom_edge(output_buf[ci], 179 compptr->width_in_blocks * compptr->DCT_h_scaled_size, 180 (int) (*out_row_group_ctr * numrows), 181 (int) (out_row_groups_avail * numrows)); 182 } 183 *out_row_group_ctr = out_row_groups_avail; 184 break; /* can exit outer loop without test */ 185 } 186 } 187} 188 189 190#ifdef CONTEXT_ROWS_SUPPORTED 191 192/* 193 * Process some data in the context case. 194 */ 195 196METHODDEF(void) 197pre_process_context (j_compress_ptr cinfo, 198 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr, 199 JDIMENSION in_rows_avail, 200 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr, 201 JDIMENSION out_row_groups_avail) 202{ 203 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 204 int numrows, ci; 205 int buf_height = cinfo->max_v_samp_factor * 3; 206 JDIMENSION inrows; 207 208 while (*out_row_group_ctr < out_row_groups_avail) { 209 if (*in_row_ctr < in_rows_avail) { 210 /* Do color conversion to fill the conversion buffer. */ 211 inrows = in_rows_avail - *in_row_ctr; 212 numrows = prep->next_buf_stop - prep->next_buf_row; 213 numrows = (int) MIN((JDIMENSION) numrows, inrows); 214 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr, 215 prep->color_buf, 216 (JDIMENSION) prep->next_buf_row, 217 numrows); 218 /* Pad at top of image, if first time through */ 219 if (prep->rows_to_go == cinfo->image_height) { 220 for (ci = 0; ci < cinfo->num_components; ci++) { 221 int row; 222 for (row = 1; row <= cinfo->max_v_samp_factor; row++) { 223 jcopy_sample_rows(prep->color_buf[ci], 0, 224 prep->color_buf[ci], -row, 225 1, cinfo->image_width); 226 } 227 } 228 } 229 *in_row_ctr += numrows; 230 prep->next_buf_row += numrows; 231 prep->rows_to_go -= numrows; 232 } else { 233 /* Return for more data, unless we are at the bottom of the image. */ 234 if (prep->rows_to_go != 0) 235 break; 236 /* When at bottom of image, pad to fill the conversion buffer. */ 237 if (prep->next_buf_row < prep->next_buf_stop) { 238 for (ci = 0; ci < cinfo->num_components; ci++) { 239 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width, 240 prep->next_buf_row, prep->next_buf_stop); 241 } 242 prep->next_buf_row = prep->next_buf_stop; 243 } 244 } 245 /* If we've gotten enough data, downsample a row group. */ 246 if (prep->next_buf_row == prep->next_buf_stop) { 247 (*cinfo->downsample->downsample) (cinfo, 248 prep->color_buf, 249 (JDIMENSION) prep->this_row_group, 250 output_buf, *out_row_group_ctr); 251 (*out_row_group_ctr)++; 252 /* Advance pointers with wraparound as necessary. */ 253 prep->this_row_group += cinfo->max_v_samp_factor; 254 if (prep->this_row_group >= buf_height) 255 prep->this_row_group = 0; 256 if (prep->next_buf_row >= buf_height) 257 prep->next_buf_row = 0; 258 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor; 259 } 260 } 261} 262 263 264/* 265 * Create the wrapped-around downsampling input buffer needed for context mode. 266 */ 267 268LOCAL(void) 269create_context_buffer (j_compress_ptr cinfo) 270{ 271 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 272 int rgroup_height = cinfo->max_v_samp_factor; 273 int ci, i; 274 jpeg_component_info * compptr; 275 JSAMPARRAY true_buffer, fake_buffer; 276 277 /* Grab enough space for fake row pointers for all the components; 278 * we need five row groups' worth of pointers for each component. 279 */ 280 fake_buffer = (JSAMPARRAY) 281 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 282 (cinfo->num_components * 5 * rgroup_height) * 283 SIZEOF(JSAMPROW)); 284 285 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 286 ci++, compptr++) { 287 /* Allocate the actual buffer space (3 row groups) for this component. 288 * We make the buffer wide enough to allow the downsampler to edge-expand 289 * horizontally within the buffer, if it so chooses. 290 */ 291 true_buffer = (*cinfo->mem->alloc_sarray) 292 ((j_common_ptr) cinfo, JPOOL_IMAGE, 293 (JDIMENSION) (((long) compptr->width_in_blocks * 294 cinfo->min_DCT_h_scaled_size * 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]; 304 } 305 prep->color_buf[ci] = fake_buffer + rgroup_height; 306 fake_buffer += 5 * rgroup_height; /* point to space for next component */ 307 } 308} 309 310#endif /* CONTEXT_ROWS_SUPPORTED */ 311 312 313/* 314 * Initialize preprocessing controller. 315 */ 316 317GLOBAL(void) 318jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer) 319{ 320 my_prep_ptr prep; 321 int ci; 322 jpeg_component_info * compptr; 323 324 if (need_full_buffer) /* safety check */ 325 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 326 327 prep = (my_prep_ptr) 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; 332 333 /* 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. 336 */ 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); 342#else 343 ERREXIT(cinfo, JERR_NOT_COMPILED); 344#endif 345 } else { 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; 349 ci++, compptr++) { 350 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray) 351 ((j_common_ptr) cinfo, JPOOL_IMAGE, 352 (JDIMENSION) (((long) compptr->width_in_blocks * 353 cinfo->min_DCT_h_scaled_size * 354 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 355 (JDIMENSION) cinfo->max_v_samp_factor); 356 } 357 } 358} 359