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 expand_bottom_edge(output_buf[ci], 177 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, 196 JSAMPARRAY input_buf, JDIMENSION *in_row_ctr, 197 JDIMENSION in_rows_avail, 198 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr, 199 JDIMENSION out_row_groups_avail) 200{ 201 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 202 int numrows, ci; 203 int buf_height = cinfo->max_v_samp_factor * 3; 204 JDIMENSION inrows; 205 206 while (*out_row_group_ctr < out_row_groups_avail) { 207 if (*in_row_ctr < in_rows_avail) { 208 /* Do color conversion to fill the conversion buffer. */ 209 inrows = in_rows_avail - *in_row_ctr; 210 numrows = prep->next_buf_stop - prep->next_buf_row; 211 numrows = (int) MIN((JDIMENSION) numrows, inrows); 212 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr, 213 prep->color_buf, 214 (JDIMENSION) prep->next_buf_row, 215 numrows); 216 /* Pad at top of image, if first time through */ 217 if (prep->rows_to_go == cinfo->image_height) { 218 for (ci = 0; ci < cinfo->num_components; ci++) { 219 int row; 220 for (row = 1; row <= cinfo->max_v_samp_factor; row++) { 221 jcopy_sample_rows(prep->color_buf[ci], 0, 222 prep->color_buf[ci], -row, 223 1, cinfo->image_width); 224 } 225 } 226 } 227 *in_row_ctr += numrows; 228 prep->next_buf_row += numrows; 229 prep->rows_to_go -= numrows; 230 } else { 231 /* Return for more data, unless we are at the bottom of the image. */ 232 if (prep->rows_to_go != 0) 233 break; 234 /* When at bottom of image, pad to fill the conversion buffer. */ 235 if (prep->next_buf_row < prep->next_buf_stop) { 236 for (ci = 0; ci < cinfo->num_components; ci++) { 237 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width, 238 prep->next_buf_row, prep->next_buf_stop); 239 } 240 prep->next_buf_row = prep->next_buf_stop; 241 } 242 } 243 /* If we've gotten enough data, downsample a row group. */ 244 if (prep->next_buf_row == prep->next_buf_stop) { 245 (*cinfo->downsample->downsample) (cinfo, 246 prep->color_buf, 247 (JDIMENSION) prep->this_row_group, 248 output_buf, *out_row_group_ctr); 249 (*out_row_group_ctr)++; 250 /* Advance pointers with wraparound as necessary. */ 251 prep->this_row_group += cinfo->max_v_samp_factor; 252 if (prep->this_row_group >= buf_height) 253 prep->this_row_group = 0; 254 if (prep->next_buf_row >= buf_height) 255 prep->next_buf_row = 0; 256 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor; 257 } 258 } 259} 260 261 262/* 263 * Create the wrapped-around downsampling input buffer needed for context mode. 264 */ 265 266LOCAL(void) 267create_context_buffer (j_compress_ptr cinfo) 268{ 269 my_prep_ptr prep = (my_prep_ptr) cinfo->prep; 270 int rgroup_height = cinfo->max_v_samp_factor; 271 int ci, i; 272 jpeg_component_info * compptr; 273 JSAMPARRAY true_buffer, fake_buffer; 274 275 /* Grab enough space for fake row pointers for all the components; 276 * we need five row groups' worth of pointers for each component. 277 */ 278 fake_buffer = (JSAMPARRAY) 279 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 280 (cinfo->num_components * 5 * rgroup_height) * 281 SIZEOF(JSAMPROW)); 282 283 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 284 ci++, compptr++) { 285 /* Allocate the actual buffer space (3 row groups) for this component. 286 * We make the buffer wide enough to allow the downsampler to edge-expand 287 * horizontally within the buffer, if it so chooses. 288 */ 289 true_buffer = (*cinfo->mem->alloc_sarray) 290 ((j_common_ptr) cinfo, JPOOL_IMAGE, 291 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE * 292 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 293 (JDIMENSION) (3 * rgroup_height)); 294 /* Copy true buffer row pointers into the middle of the fake row array */ 295 MEMCOPY(fake_buffer + rgroup_height, true_buffer, 296 3 * rgroup_height * SIZEOF(JSAMPROW)); 297 /* Fill in the above and below wraparound pointers */ 298 for (i = 0; i < rgroup_height; i++) { 299 fake_buffer[i] = true_buffer[2 * rgroup_height + i]; 300 fake_buffer[4 * rgroup_height + i] = true_buffer[i]; 301 } 302 prep->color_buf[ci] = fake_buffer + rgroup_height; 303 fake_buffer += 5 * rgroup_height; /* point to space for next component */ 304 } 305} 306 307#endif /* CONTEXT_ROWS_SUPPORTED */ 308 309 310/* 311 * Initialize preprocessing controller. 312 */ 313 314GLOBAL(void) 315jinit_c_prep_controller (j_compress_ptr cinfo, boolean need_full_buffer) 316{ 317 my_prep_ptr prep; 318 int ci; 319 jpeg_component_info * compptr; 320 321 if (need_full_buffer) /* safety check */ 322 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 323 324 prep = (my_prep_ptr) 325 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 326 SIZEOF(my_prep_controller)); 327 cinfo->prep = (struct jpeg_c_prep_controller *) prep; 328 prep->pub.start_pass = start_pass_prep; 329 330 /* Allocate the color conversion buffer. 331 * We make the buffer wide enough to allow the downsampler to edge-expand 332 * horizontally within the buffer, if it so chooses. 333 */ 334 if (cinfo->downsample->need_context_rows) { 335 /* Set up to provide context rows */ 336#ifdef CONTEXT_ROWS_SUPPORTED 337 prep->pub.pre_process_data = pre_process_context; 338 create_context_buffer(cinfo); 339#else 340 ERREXIT(cinfo, JERR_NOT_COMPILED); 341#endif 342 } else { 343 /* No context, just make it tall enough for one row group */ 344 prep->pub.pre_process_data = pre_process_data; 345 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 346 ci++, compptr++) { 347 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray) 348 ((j_common_ptr) cinfo, JPOOL_IMAGE, 349 (JDIMENSION) (((long) compptr->width_in_blocks * DCTSIZE * 350 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 351 (JDIMENSION) cinfo->max_v_samp_factor); 352 } 353 } 354} 355