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 file. 9 * 10 * This file contains the compression preprocessing controller. 11 * This controller manages the color conversion, downsampling, 12 * and edge expansion steps. 13 * 14 * Most of the complexity here is associated with buffering input rows 15 * as required by the downsampler. See the comments at the head of 16 * jcsample.c for the downsampler's needs. 17 */ 18 19 #define JPEG_INTERNALS 20 #include "jinclude.h" 21 #include "jpeglib.h" 22 23 24 /* At present, jcsample.c can request context rows only for smoothing. 25 * In the future, we might also need context rows for CCIR601 sampling 26 * or other more-complex downsampling procedures. The code to support 27 * context rows should be compiled only if needed. 28 */ 29 #ifdef INPUT_SMOOTHING_SUPPORTED 30 #define CONTEXT_ROWS_SUPPORTED 31 #endif 32 33 34 /* 35 * For the simple (no-context-row) case, we just need to buffer one 36 * row group's worth of pixels for the downsampling step. At the bottom of 37 * the image, we pad to a full row group by replicating the last pixel row. 38 * The downsampler's last output row is then replicated if needed to pad 39 * out to a full iMCU row. 40 * 41 * When providing context rows, we must buffer three row groups' worth of 42 * pixels. Three row groups are physically allocated, but the row pointer 43 * arrays are made five row groups high, with the extra pointers above and 44 * below "wrapping around" to point to the last and first real row groups. 45 * This allows the downsampler to access the proper context rows. 46 * At the top and bottom of the image, we create dummy context rows by 47 * copying the first or last real pixel row. This copying could be avoided 48 * by pointer hacking as is done in jdmainct.c, but it doesn't seem worth the 49 * trouble on the compression side. 50 */ 51 52 53 /* Private buffer controller object */ 54 55 typedef struct { 56 struct jpeg_c_prep_controller pub; /* public fields */ 57 58 /* Downsampling input buffer. This buffer holds color-converted data 59 * until we have enough to do a downsample step. 60 */ 61 JSAMPARRAY color_buf[MAX_COMPONENTS]; 62 63 JDIMENSION rows_to_go; /* counts rows remaining in source image */ 64 int next_buf_row; /* index of next row to store in color_buf */ 65 66 #ifdef CONTEXT_ROWS_SUPPORTED /* only needed for context case */ 67 int this_row_group; /* starting row index of group to process */ 68 int next_buf_stop; /* downsample when we reach this index */ 69 #endif 70 } my_prep_controller; 71 72 typedef my_prep_controller * my_prep_ptr; 73 74 75 /* 76 * Initialize for a processing pass. 77 */ 78 79 METHODDEF(void) 80 start_pass_prep (j_compress_ptr cinfo, J_BUF_MODE pass_mode) 81 { 82 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 83 84 if (pass_mode != JBUF_PASS_THRU) 85 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 86 87 /* Initialize total-height counter for detecting bottom of image */ 88 prep->rows_to_go = cinfo->image_height; 89 /* Mark the conversion buffer empty */ 90 prep->next_buf_row = 0; 91 #ifdef CONTEXT_ROWS_SUPPORTED 92 /* Preset additional state variables for context mode. 93 * These aren't used in non-context mode, so we needn't test which mode. 94 */ 95 prep->this_row_group = 0; 96 /* Set next_buf_stop to stop after two row groups have been read in. */ 97 prep->next_buf_stop = 2 * cinfo->max_v_samp_factor; 98 #endif 99 } 100 101 102 /* 103 * Expand an image vertically from height input_rows to height output_rows, 104 * by duplicating the bottom row. 105 */ 106 107 LOCAL(void) 108 expand_bottom_edge (JSAMPARRAY image_data, JDIMENSION num_cols, 109 int input_rows, int output_rows) 110 { 111 register int row; 112 113 for (row = input_rows; row < output_rows; row++) { 114 jcopy_sample_rows(image_data, input_rows-1, image_data, row, 115 1, num_cols); 116 } 117 } 118 119 120 /* 121 * Process some data in the simple no-context case. 122 * 123 * Preprocessor output data is counted in "row groups". A row group 124 * is defined to be v_samp_factor sample rows of each component. 125 * Downsampling will produce this much data from each max_v_samp_factor 126 * input rows. 127 */ 128 129 METHODDEF(void) 130 pre_process_data (j_compress_ptr cinfo, 131 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr, 132 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 && 175 *out_row_group_ctr < out_row_groups_avail) { 176 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 177 ci++, compptr++) { 178 expand_bottom_edge(output_buf[ci], 179 compptr->width_in_blocks * DCTSIZE, 180 (int) (*out_row_group_ctr * compptr->v_samp_factor), 181 (int) (out_row_groups_avail * compptr->v_samp_factor)); 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 */ 195 196 METHODDEF(void) 197 pre_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 */ 267 268 LOCAL(void) 269 create_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 * DCTSIZE * 294 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 295 (JDIMENSION) (3 * rgroup_height)); 296 /* Copy true buffer row pointers into the middle of the fake row array */ 297 MEMCOPY(fake_buffer + rgroup_height, true_buffer, 298 3 * rgroup_height * sizeof(JSAMPROW)); 299 /* Fill in the above and below wraparound pointers */ 300 for (i = 0; i < rgroup_height; i++) { 301 fake_buffer[i] = true_buffer[2 * rgroup_height + i]; 302 fake_buffer[4 * rgroup_height + i] = true_buffer[i]; 303 } 304 prep->color_buf[ci] = fake_buffer + rgroup_height; 305 fake_buffer += 5 * rgroup_height; /* point to space for next component */ 306 } 307 } 308 309 #endif /* CONTEXT_ROWS_SUPPORTED */ 310 311 312 /* 313 * Initialize preprocessing controller. 314 */ 315 316 GLOBAL(void) 317 jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer) 318 { 319 my_prep_ptr prep; 320 int ci; 321 jpeg_component_info * compptr; 322 323 if (need_full_buffer) /* safety check */ 324 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 325 326 prep = (my_prep_ptr) 327 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 328 sizeof(my_prep_controller)); 329 cinfo->prep = (struct jpeg_c_prep_controller *) prep; 330 prep->pub.start_pass = start_pass_prep; 331 332 /* Allocate the color conversion buffer. 333 * We make the buffer wide enough to allow the downsampler to edge-expand 334 * horizontally within the buffer, if it so chooses. 335 */ 336 if (cinfo->downsample->need_context_rows) { 337 /* Set up to provide context rows */ 338 #ifdef CONTEXT_ROWS_SUPPORTED 339 prep->pub.pre_process_data = pre_process_context; 340 create_context_buffer(cinfo); 341 #else 342 ERREXIT(cinfo, JERR_NOT_COMPILED); 343 #endif 344 } else { 345 /* No context, just make it tall enough for one row group */ 346 prep->pub.pre_process_data = pre_process_data; 347 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 348 ci++, compptr++) { 349 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray) 350 ((j_common_ptr) cinfo, JPOOL_IMAGE, 351 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE * 352 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 353 (JDIMENSION) cinfo->max_v_samp_factor); 354 } 355 } 356 } 357
