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 56 typedef 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 73 typedef my_prep_controller *my_prep_ptr; 74 75 76 /* 77 * Initialize for a processing pass. 78 */ 79 80 METHODDEF(void) 81 start_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 */ 107 108 LOCAL(void) 109 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols, 110 int input_rows, 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, 116 1, 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 */ 129 130 METHODDEF(void) 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) 136 { 137 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 138 int numrows, ci; 139 JDIMENSION inrows; 140 jpeg_component_info *compptr; 141 142 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, 149 prep->color_buf, 150 (JDIMENSION) prep->next_buf_row, 151 numrows); 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); 161 } 162 prep->next_buf_row = cinfo->max_v_samp_factor; 163 } 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)++; 171 } 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! 174 */ 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; 178 ci++, compptr++) { 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)); 183 } 184 *out_row_group_ctr = out_row_groups_avail; 185 break; /* can exit outer loop without test */ 186 } 187 } 188 } 189 190 191 #ifdef CONTEXT_ROWS_SUPPORTED 192 193 /* 194 * Process some data in the context case. 195 */ 196 197 METHODDEF(void) 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) 203 { 204 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 205 int numrows, ci; 206 int buf_height = cinfo->max_v_samp_factor * 3; 207 JDIMENSION inrows; 208 209 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, 216 prep->color_buf, 217 (JDIMENSION) prep->next_buf_row, 218 numrows); 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++) { 222 int row; 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); 227 } 228 } 229 } 230 *in_row_ctr += numrows; 231 prep->next_buf_row += numrows; 232 prep->rows_to_go -= numrows; 233 } else { 234 /* Return for more data, unless we are at the bottom of the image. */ 235 if (prep->rows_to_go != 0) 236 break; 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); 242 } 243 prep->next_buf_row = prep->next_buf_stop; 244 } 245 } 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, 249 prep->color_buf, 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; 260 } 261 } 262 } 263 264 265 /* 266 * Create the wrapped-around downsampling input buffer needed for context mode. 267 */ 268 269 LOCAL(void) 270 create_context_buffer (j_compress_ptr cinfo) 271 { 272 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 273 int rgroup_height = cinfo->max_v_samp_factor; 274 int ci, i; 275 jpeg_component_info *compptr; 276 JSAMPARRAY true_buffer, fake_buffer; 277 278 /* Grab enough space for fake row pointers for all the components; 279 * we need five row groups' worth of pointers for each component. 280 */ 281 fake_buffer = (JSAMPARRAY) 282 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 283 (cinfo->num_components * 5 * rgroup_height) * 284 sizeof(JSAMPROW)); 285 286 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 287 ci++, compptr++) { 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. 291 */ 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]; 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 */ 316 317 GLOBAL(void) 318 jinit_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 * DCTSIZE * 353 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 354 (JDIMENSION) cinfo->max_v_samp_factor); 355 } 356 } 357 } 358
