1/* 2 * reserved comment block 3 * DO NOT REMOVE OR ALTER! 4 */ 5/* 6 * jcsample.c 7 * 8 * Copyright (C) 1991-1996, Thomas G. Lane. 9 * This file is part of the Independent JPEG Group's software. 10 * For conditions of distribution and use, see the accompanying README file. 11 * 12 * This file contains downsampling routines. 13 * 14 * Downsampling input data is counted in "row groups". A row group 15 * is defined to be max_v_samp_factor pixel rows of each component, 16 * from which the downsampler produces v_samp_factor sample rows. 17 * A single row group is processed in each call to the downsampler module. 18 * 19 * The downsampler is responsible for edge-expansion of its output data 20 * to fill an integral number of DCT blocks horizontally. The source buffer 21 * may be modified if it is helpful for this purpose (the source buffer is 22 * allocated wide enough to correspond to the desired output width). 23 * The caller (the prep controller) is responsible for vertical padding. 24 * 25 * The downsampler may request "context rows" by setting need_context_rows 26 * during startup. In this case, the input arrays will contain at least 27 * one row group's worth of pixels above and below the passed-in data; 28 * the caller will create dummy rows at image top and bottom by replicating 29 * the first or last real pixel row. 30 * 31 * An excellent reference for image resampling is 32 * Digital Image Warping, George Wolberg, 1990. 33 * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7. 34 * 35 * The downsampling algorithm used here is a simple average of the source 36 * pixels covered by the output pixel. The hi-falutin sampling literature 37 * refers to this as a "box filter". In general the characteristics of a box 38 * filter are not very good, but for the specific cases we normally use (1:1 39 * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not 40 * nearly so bad. If you intend to use other sampling ratios, you'd be well 41 * advised to improve this code. 42 * 43 * A simple input-smoothing capability is provided. This is mainly intended 44 * for cleaning up color-dithered GIF input files (if you find it inadequate, 45 * we suggest using an external filtering program such as pnmconvol). When 46 * enabled, each input pixel P is replaced by a weighted sum of itself and its 47 * eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF, 48 * where SF = (smoothing_factor / 1024). 49 * Currently, smoothing is only supported for 2h2v sampling factors. 50 */ 51 52#define JPEG_INTERNALS 53#include "jinclude.h" 54#include "jpeglib.h" 55 56 57/* Pointer to routine to downsample a single component */ 58typedef JMETHOD(void, downsample1_ptr, 59 (j_compress_ptr cinfo, jpeg_component_info * compptr, 60 JSAMPARRAY input_data, JSAMPARRAY output_data)); 61 62/* Private subobject */ 63 64typedef struct { 65 struct jpeg_downsampler pub; /* public fields */ 66 67 /* Downsampling method pointers, one per component */ 68 downsample1_ptr methods[MAX_COMPONENTS]; 69} my_downsampler; 70 71typedef my_downsampler * my_downsample_ptr; 72 73 74/* 75 * Initialize for a downsampling pass. 76 */ 77 78METHODDEF(void) 79start_pass_downsample (j_compress_ptr cinfo) 80{ 81 /* no work for now */ 82} 83 84 85/* 86 * Expand a component horizontally from width input_cols to width output_cols, 87 * by duplicating the rightmost samples. 88 */ 89 90LOCAL(void) 91expand_right_edge (JSAMPARRAY image_data, int num_rows, 92 JDIMENSION input_cols, JDIMENSION output_cols) 93{ 94 register JSAMPROW ptr; 95 register JSAMPLE pixval; 96 register int count; 97 int row; 98 int numcols = (int) (output_cols - input_cols); 99 100 if (numcols > 0) { 101 for (row = 0; row < num_rows; row++) { 102 ptr = image_data[row] + input_cols; 103 pixval = ptr[-1]; /* don't need GETJSAMPLE() here */ 104 for (count = numcols; count > 0; count--) 105 *ptr++ = pixval; 106 } 107 } 108} 109 110 111/* 112 * Do downsampling for a whole row group (all components). 113 * 114 * In this version we simply downsample each component independently. 115 */ 116 117METHODDEF(void) 118sep_downsample (j_compress_ptr cinfo, 119 JSAMPIMAGE input_buf, JDIMENSION in_row_index, 120 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index) 121{ 122 my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample; 123 int ci; 124 jpeg_component_info * compptr; 125 JSAMPARRAY in_ptr, out_ptr; 126 127 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 128 ci++, compptr++) { 129 in_ptr = input_buf[ci] + in_row_index; 130 out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor); 131 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr); 132 } 133} 134 135 136/* 137 * Downsample pixel values of a single component. 138 * One row group is processed per call. 139 * This version handles arbitrary integral sampling ratios, without smoothing. 140 * Note that this version is not actually used for customary sampling ratios. 141 */ 142 143METHODDEF(void) 144int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr, 145 JSAMPARRAY input_data, JSAMPARRAY output_data) 146{ 147 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v; 148 JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */ 149 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE; 150 JSAMPROW inptr, outptr; 151 INT32 outvalue; 152 153 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor; 154 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor; 155 numpix = h_expand * v_expand; 156 numpix2 = numpix/2; 157 158 /* Expand input data enough to let all the output samples be generated 159 * by the standard loop. Special-casing padded output would be more 160 * efficient. 161 */ 162 expand_right_edge(input_data, cinfo->max_v_samp_factor, 163 cinfo->image_width, output_cols * h_expand); 164 165 inrow = 0; 166 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) { 167 outptr = output_data[outrow]; 168 for (outcol = 0, outcol_h = 0; outcol < output_cols; 169 outcol++, outcol_h += h_expand) { 170 outvalue = 0; 171 for (v = 0; v < v_expand; v++) { 172 inptr = input_data[inrow+v] + outcol_h; 173 for (h = 0; h < h_expand; h++) { 174 outvalue += (INT32) GETJSAMPLE(*inptr++); 175 } 176 } 177 *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix); 178 } 179 inrow += v_expand; 180 } 181} 182 183 184/* 185 * Downsample pixel values of a single component. 186 * This version handles the special case of a full-size component, 187 * without smoothing. 188 */ 189 190METHODDEF(void) 191fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr, 192 JSAMPARRAY input_data, JSAMPARRAY output_data) 193{ 194 /* Copy the data */ 195 jcopy_sample_rows(input_data, 0, output_data, 0, 196 cinfo->max_v_samp_factor, cinfo->image_width); 197 /* Edge-expand */ 198 expand_right_edge(output_data, cinfo->max_v_samp_factor, 199 cinfo->image_width, compptr->width_in_blocks * DCTSIZE); 200} 201 202 203/* 204 * Downsample pixel values of a single component. 205 * This version handles the common case of 2:1 horizontal and 1:1 vertical, 206 * without smoothing. 207 * 208 * A note about the "bias" calculations: when rounding fractional values to 209 * integer, we do not want to always round 0.5 up to the next integer. 210 * If we did that, we'd introduce a noticeable bias towards larger values. 211 * Instead, this code is arranged so that 0.5 will be rounded up or down at 212 * alternate pixel locations (a simple ordered dither pattern). 213 */ 214 215METHODDEF(void) 216h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr, 217 JSAMPARRAY input_data, JSAMPARRAY output_data) 218{ 219 int outrow; 220 JDIMENSION outcol; 221 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE; 222 register JSAMPROW inptr, outptr; 223 register int bias; 224 225 /* Expand input data enough to let all the output samples be generated 226 * by the standard loop. Special-casing padded output would be more 227 * efficient. 228 */ 229 expand_right_edge(input_data, cinfo->max_v_samp_factor, 230 cinfo->image_width, output_cols * 2); 231 232 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) { 233 outptr = output_data[outrow]; 234 inptr = input_data[outrow]; 235 bias = 0; /* bias = 0,1,0,1,... for successive samples */ 236 for (outcol = 0; outcol < output_cols; outcol++) { 237 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1]) 238 + bias) >> 1); 239 bias ^= 1; /* 0=>1, 1=>0 */ 240 inptr += 2; 241 } 242 } 243} 244 245 246/* 247 * Downsample pixel values of a single component. 248 * This version handles the standard case of 2:1 horizontal and 2:1 vertical, 249 * without smoothing. 250 */ 251 252METHODDEF(void) 253h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr, 254 JSAMPARRAY input_data, JSAMPARRAY output_data) 255{ 256 int inrow, outrow; 257 JDIMENSION outcol; 258 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE; 259 register JSAMPROW inptr0, inptr1, outptr; 260 register int bias; 261 262 /* Expand input data enough to let all the output samples be generated 263 * by the standard loop. Special-casing padded output would be more 264 * efficient. 265 */ 266 expand_right_edge(input_data, cinfo->max_v_samp_factor, 267 cinfo->image_width, output_cols * 2); 268 269 inrow = 0; 270 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) { 271 outptr = output_data[outrow]; 272 inptr0 = input_data[inrow]; 273 inptr1 = input_data[inrow+1]; 274 bias = 1; /* bias = 1,2,1,2,... for successive samples */ 275 for (outcol = 0; outcol < output_cols; outcol++) { 276 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) + 277 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]) 278 + bias) >> 2); 279 bias ^= 3; /* 1=>2, 2=>1 */ 280 inptr0 += 2; inptr1 += 2; 281 } 282 inrow += 2; 283 } 284} 285 286 287#ifdef INPUT_SMOOTHING_SUPPORTED 288 289/* 290 * Downsample pixel values of a single component. 291 * This version handles the standard case of 2:1 horizontal and 2:1 vertical, 292 * with smoothing. One row of context is required. 293 */ 294 295METHODDEF(void) 296h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr, 297 JSAMPARRAY input_data, JSAMPARRAY output_data) 298{ 299 int inrow, outrow; 300 JDIMENSION colctr; 301 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE; 302 register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr; 303 INT32 membersum, neighsum, memberscale, neighscale; 304 305 /* Expand input data enough to let all the output samples be generated 306 * by the standard loop. Special-casing padded output would be more 307 * efficient. 308 */ 309 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2, 310 cinfo->image_width, output_cols * 2); 311 312 /* We don't bother to form the individual "smoothed" input pixel values; 313 * we can directly compute the output which is the average of the four 314 * smoothed values. Each of the four member pixels contributes a fraction 315 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three 316 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final 317 * output. The four corner-adjacent neighbor pixels contribute a fraction 318 * SF to just one smoothed pixel, or SF/4 to the final output; while the 319 * eight edge-adjacent neighbors contribute SF to each of two smoothed 320 * pixels, or SF/2 overall. In order to use integer arithmetic, these 321 * factors are scaled by 2^16 = 65536. 322 * Also recall that SF = smoothing_factor / 1024. 323 */ 324 325 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */ 326 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */ 327 328 inrow = 0; 329 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) { 330 outptr = output_data[outrow]; 331 inptr0 = input_data[inrow]; 332 inptr1 = input_data[inrow+1]; 333 above_ptr = input_data[inrow-1]; 334 below_ptr = input_data[inrow+2]; 335 336 /* Special case for first column: pretend column -1 is same as column 0 */ 337 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) + 338 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]); 339 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) + 340 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) + 341 GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) + 342 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]); 343 neighsum += neighsum; 344 neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) + 345 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]); 346 membersum = membersum * memberscale + neighsum * neighscale; 347 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16); 348 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2; 349 350 for (colctr = output_cols - 2; colctr > 0; colctr--) { 351 /* sum of pixels directly mapped to this output element */ 352 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) + 353 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]); 354 /* sum of edge-neighbor pixels */ 355 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) + 356 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) + 357 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) + 358 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]); 359 /* The edge-neighbors count twice as much as corner-neighbors */ 360 neighsum += neighsum; 361 /* Add in the corner-neighbors */ 362 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) + 363 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]); 364 /* form final output scaled up by 2^16 */ 365 membersum = membersum * memberscale + neighsum * neighscale; 366 /* round, descale and output it */ 367 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16); 368 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2; 369 } 370 371 /* Special case for last column */ 372 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) + 373 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]); 374 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) + 375 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) + 376 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) + 377 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]); 378 neighsum += neighsum; 379 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) + 380 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]); 381 membersum = membersum * memberscale + neighsum * neighscale; 382 *outptr = (JSAMPLE) ((membersum + 32768) >> 16); 383 384 inrow += 2; 385 } 386} 387 388 389/* 390 * Downsample pixel values of a single component. 391 * This version handles the special case of a full-size component, 392 * with smoothing. One row of context is required. 393 */ 394 395METHODDEF(void) 396fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr, 397 JSAMPARRAY input_data, JSAMPARRAY output_data) 398{ 399 int outrow; 400 JDIMENSION colctr; 401 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE; 402 register JSAMPROW inptr, above_ptr, below_ptr, outptr; 403 INT32 membersum, neighsum, memberscale, neighscale; 404 int colsum, lastcolsum, nextcolsum; 405 406 /* Expand input data enough to let all the output samples be generated 407 * by the standard loop. Special-casing padded output would be more 408 * efficient. 409 */ 410 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2, 411 cinfo->image_width, output_cols); 412 413 /* Each of the eight neighbor pixels contributes a fraction SF to the 414 * smoothed pixel, while the main pixel contributes (1-8*SF). In order 415 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536. 416 * Also recall that SF = smoothing_factor / 1024. 417 */ 418 419 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */ 420 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */ 421 422 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) { 423 outptr = output_data[outrow]; 424 inptr = input_data[outrow]; 425 above_ptr = input_data[outrow-1]; 426 below_ptr = input_data[outrow+1]; 427 428 /* Special case for first column */ 429 colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) + 430 GETJSAMPLE(*inptr); 431 membersum = GETJSAMPLE(*inptr++); 432 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) + 433 GETJSAMPLE(*inptr); 434 neighsum = colsum + (colsum - membersum) + nextcolsum; 435 membersum = membersum * memberscale + neighsum * neighscale; 436 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16); 437 lastcolsum = colsum; colsum = nextcolsum; 438 439 for (colctr = output_cols - 2; colctr > 0; colctr--) { 440 membersum = GETJSAMPLE(*inptr++); 441 above_ptr++; below_ptr++; 442 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) + 443 GETJSAMPLE(*inptr); 444 neighsum = lastcolsum + (colsum - membersum) + nextcolsum; 445 membersum = membersum * memberscale + neighsum * neighscale; 446 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16); 447 lastcolsum = colsum; colsum = nextcolsum; 448 } 449 450 /* Special case for last column */ 451 membersum = GETJSAMPLE(*inptr); 452 neighsum = lastcolsum + (colsum - membersum) + colsum; 453 membersum = membersum * memberscale + neighsum * neighscale; 454 *outptr = (JSAMPLE) ((membersum + 32768) >> 16); 455 456 } 457} 458 459#endif /* INPUT_SMOOTHING_SUPPORTED */ 460 461 462/* 463 * Module initialization routine for downsampling. 464 * Note that we must select a routine for each component. 465 */ 466 467GLOBAL(void) 468jinit_downsampler (j_compress_ptr cinfo) 469{ 470 my_downsample_ptr downsample; 471 int ci; 472 jpeg_component_info * compptr; 473 boolean smoothok = TRUE; 474 475 downsample = (my_downsample_ptr) 476 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 477 SIZEOF(my_downsampler)); 478 cinfo->downsample = (struct jpeg_downsampler *) downsample; 479 downsample->pub.start_pass = start_pass_downsample; 480 downsample->pub.downsample = sep_downsample; 481 downsample->pub.need_context_rows = FALSE; 482 483 if (cinfo->CCIR601_sampling) 484 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL); 485 486 /* Verify we can handle the sampling factors, and set up method pointers */ 487 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; 488 ci++, compptr++) { 489 if (compptr->h_samp_factor == cinfo->max_h_samp_factor && 490 compptr->v_samp_factor == cinfo->max_v_samp_factor) { 491#ifdef INPUT_SMOOTHING_SUPPORTED 492 if (cinfo->smoothing_factor) { 493 downsample->methods[ci] = fullsize_smooth_downsample; 494 downsample->pub.need_context_rows = TRUE; 495 } else 496#endif 497 downsample->methods[ci] = fullsize_downsample; 498 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor && 499 compptr->v_samp_factor == cinfo->max_v_samp_factor) { 500 smoothok = FALSE; 501 downsample->methods[ci] = h2v1_downsample; 502 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor && 503 compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) { 504#ifdef INPUT_SMOOTHING_SUPPORTED 505 if (cinfo->smoothing_factor) { 506 downsample->methods[ci] = h2v2_smooth_downsample; 507 downsample->pub.need_context_rows = TRUE; 508 } else 509#endif 510 downsample->methods[ci] = h2v2_downsample; 511 } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 && 512 (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) { 513 smoothok = FALSE; 514 downsample->methods[ci] = int_downsample; 515 } else 516 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL); 517 } 518 519#ifdef INPUT_SMOOTHING_SUPPORTED 520 if (cinfo->smoothing_factor && !smoothok) 521 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL); 522#endif 523} 524