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, int input_rows, 110 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, 1, 116 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, JSAMPARRAY input_buf, 132 JDIMENSION *in_row_ctr, 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 && *out_row_group_ctr < out_row_groups_avail) { 175 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 176 ci++, compptr++) { 177 expand_bottom_edge(output_buf[ci], 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 */ 193 194 METHODDEF(void) 195 pre_process_context(j_compress_ptr cinfo, JSAMPARRAY input_buf, 196 JDIMENSION *in_row_ctr, JDIMENSION in_rows_avail, 197 JSAMPIMAGE output_buf, JDIMENSION *out_row_group_ctr, 198 JDIMENSION out_row_groups_avail) 199 { 200 my_prep_ptr prep = (my_prep_ptr)cinfo->prep; 201 int numrows, ci; 202 int buf_height = cinfo->max_v_samp_factor * 3; 203 JDIMENSION inrows; 204 205 while (*out_row_group_ctr < out_row_groups_avail) { 206 if (*in_row_ctr < in_rows_avail) { 207 /* Do color conversion to fill the conversion buffer. */ 208 inrows = in_rows_avail - *in_row_ctr; 209 numrows = prep->next_buf_stop - prep->next_buf_row; 210 numrows = (int)MIN((JDIMENSION)numrows, inrows); 211 (*cinfo->cconvert->color_convert) (cinfo, input_buf + *in_row_ctr, 212 prep->color_buf, 213 (JDIMENSION)prep->next_buf_row, 214 numrows); 215 /* Pad at top of image, if first time through */ 216 if (prep->rows_to_go == cinfo->image_height) { 217 for (ci = 0; ci < cinfo->num_components; ci++) { 218 int row; 219 for (row = 1; row <= cinfo->max_v_samp_factor; row++) { 220 jcopy_sample_rows(prep->color_buf[ci], 0, prep->color_buf[ci], 221 -row, 1, cinfo->image_width); 222 } 223 } 224 } 225 *in_row_ctr += numrows; 226 prep->next_buf_row += numrows; 227 prep->rows_to_go -= numrows; 228 } else { 229 /* Return for more data, unless we are at the bottom of the image. */ 230 if (prep->rows_to_go != 0) 231 break; 232 /* When at bottom of image, pad to fill the conversion buffer. */ 233 if (prep->next_buf_row < prep->next_buf_stop) { 234 for (ci = 0; ci < cinfo->num_components; ci++) { 235 expand_bottom_edge(prep->color_buf[ci], cinfo->image_width, 236 prep->next_buf_row, prep->next_buf_stop); 237 } 238 prep->next_buf_row = prep->next_buf_stop; 239 } 240 } 241 /* If we've gotten enough data, downsample a row group. */ 242 if (prep->next_buf_row == prep->next_buf_stop) { 243 (*cinfo->downsample->downsample) (cinfo, prep->color_buf, 244 (JDIMENSION)prep->this_row_group, 245 output_buf, *out_row_group_ctr); 246 (*out_row_group_ctr)++; 247 /* Advance pointers with wraparound as necessary. */ 248 prep->this_row_group += cinfo->max_v_samp_factor; 249 if (prep->this_row_group >= buf_height) 250 prep->this_row_group = 0; 251 if (prep->next_buf_row >= buf_height) 252 prep->next_buf_row = 0; 253 prep->next_buf_stop = prep->next_buf_row + cinfo->max_v_samp_factor; 254 } 255 } 256 } 257 258 259 /* 260 * Create the wrapped-around downsampling input buffer needed for context mode. 261 */ 262 263 LOCAL(void) 264 create_context_buffer(j_compress_ptr cinfo) 265 { 266 my_prep_ptr prep = (my_prep_ptr)cinfo->prep; 267 int rgroup_height = cinfo->max_v_samp_factor; 268 int ci, i; 269 jpeg_component_info *compptr; 270 JSAMPARRAY true_buffer, fake_buffer; 271 272 /* Grab enough space for fake row pointers for all the components; 273 * we need five row groups' worth of pointers for each component. 274 */ 275 fake_buffer = (JSAMPARRAY) 276 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 277 (cinfo->num_components * 5 * rgroup_height) * 278 sizeof(JSAMPROW)); 279 280 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 281 ci++, compptr++) { 282 /* Allocate the actual buffer space (3 row groups) for this component. 283 * We make the buffer wide enough to allow the downsampler to edge-expand 284 * horizontally within the buffer, if it so chooses. 285 */ 286 true_buffer = (*cinfo->mem->alloc_sarray) 287 ((j_common_ptr)cinfo, JPOOL_IMAGE, 288 (JDIMENSION)(((long)compptr->width_in_blocks * DCTSIZE * 289 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 290 (JDIMENSION)(3 * rgroup_height)); 291 /* Copy true buffer row pointers into the middle of the fake row array */ 292 MEMCOPY(fake_buffer + rgroup_height, true_buffer, 293 3 * rgroup_height * sizeof(JSAMPROW)); 294 /* Fill in the above and below wraparound pointers */ 295 for (i = 0; i < rgroup_height; i++) { 296 fake_buffer[i] = true_buffer[2 * rgroup_height + i]; 297 fake_buffer[4 * rgroup_height + i] = true_buffer[i]; 298 } 299 prep->color_buf[ci] = fake_buffer + rgroup_height; 300 fake_buffer += 5 * rgroup_height; /* point to space for next component */ 301 } 302 } 303 304 #endif /* CONTEXT_ROWS_SUPPORTED */ 305 306 307 /* 308 * Initialize preprocessing controller. 309 */ 310 311 GLOBAL(void) 312 jinit_c_prep_controller(j_compress_ptr cinfo, boolean need_full_buffer) 313 { 314 my_prep_ptr prep; 315 int ci; 316 jpeg_component_info *compptr; 317 318 if (need_full_buffer) /* safety check */ 319 ERREXIT(cinfo, JERR_BAD_BUFFER_MODE); 320 321 prep = (my_prep_ptr) 322 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 323 sizeof(my_prep_controller)); 324 cinfo->prep = (struct jpeg_c_prep_controller *)prep; 325 prep->pub.start_pass = start_pass_prep; 326 327 /* Allocate the color conversion buffer. 328 * We make the buffer wide enough to allow the downsampler to edge-expand 329 * horizontally within the buffer, if it so chooses. 330 */ 331 if (cinfo->downsample->need_context_rows) { 332 /* Set up to provide context rows */ 333 #ifdef CONTEXT_ROWS_SUPPORTED 334 prep->pub.pre_process_data = pre_process_context; 335 create_context_buffer(cinfo); 336 #else 337 ERREXIT(cinfo, JERR_NOT_COMPILED); 338 #endif 339 } else { 340 /* No context, just make it tall enough for one row group */ 341 prep->pub.pre_process_data = pre_process_data; 342 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 343 ci++, compptr++) { 344 prep->color_buf[ci] = (*cinfo->mem->alloc_sarray) 345 ((j_common_ptr)cinfo, JPOOL_IMAGE, 346 (JDIMENSION)(((long)compptr->width_in_blocks * DCTSIZE * 347 cinfo->max_h_samp_factor) / compptr->h_samp_factor), 348 (JDIMENSION)cinfo->max_v_samp_factor); 349 } 350 } 351 } 352
