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