1 /* 2 * jquant1.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1991-1996, Thomas G. Lane. 6 * libjpeg-turbo Modifications: 7 * Copyright (C) 2009, D. R. Commander 8 * For conditions of distribution and use, see the accompanying README file. 9 * 10 * This file contains 1-pass color quantization (color mapping) routines. 11 * These routines provide mapping to a fixed color map using equally spaced 12 * color values. Optional Floyd-Steinberg or ordered dithering is available. 13 */ 14 15 #define JPEG_INTERNALS 16 #include "jinclude.h" 17 #include "jpeglib.h" 18 19 #ifdef QUANT_1PASS_SUPPORTED 20 21 22 /* 23 * The main purpose of 1-pass quantization is to provide a fast, if not very 24 * high quality, colormapped output capability. A 2-pass quantizer usually 25 * gives better visual quality; however, for quantized grayscale output this 26 * quantizer is perfectly adequate. Dithering is highly recommended with this 27 * quantizer, though you can turn it off if you really want to. 28 * 29 * In 1-pass quantization the colormap must be chosen in advance of seeing the 30 * image. We use a map consisting of all combinations of Ncolors[i] color 31 * values for the i'th component. The Ncolors[] values are chosen so that 32 * their product, the total number of colors, is no more than that requested. 33 * (In most cases, the product will be somewhat less.) 34 * 35 * Since the colormap is orthogonal, the representative value for each color 36 * component can be determined without considering the other components; 37 * then these indexes can be combined into a colormap index by a standard 38 * N-dimensional-array-subscript calculation. Most of the arithmetic involved 39 * can be precalculated and stored in the lookup table colorindex[]. 40 * colorindex[i][j] maps pixel value j in component i to the nearest 41 * representative value (grid plane) for that component; this index is 42 * multiplied by the array stride for component i, so that the 43 * index of the colormap entry closest to a given pixel value is just 44 * sum( colorindex[component-number][pixel-component-value] ) 45 * Aside from being fast, this scheme allows for variable spacing between 46 * representative values with no additional lookup cost. 47 * 48 * If gamma correction has been applied in color conversion, it might be wise 49 * to adjust the color grid spacing so that the representative colors are 50 * equidistant in linear space. At this writing, gamma correction is not 51 * implemented by jdcolor, so nothing is done here. 52 */ 53 54 55 /* Declarations for ordered dithering. 56 * 57 * We use a standard 16x16 ordered dither array. The basic concept of ordered 58 * dithering is described in many references, for instance Dale Schumacher's 59 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991). 60 * In place of Schumacher's comparisons against a "threshold" value, we add a 61 * "dither" value to the input pixel and then round the result to the nearest 62 * output value. The dither value is equivalent to (0.5 - threshold) times 63 * the distance between output values. For ordered dithering, we assume that 64 * the output colors are equally spaced; if not, results will probably be 65 * worse, since the dither may be too much or too little at a given point. 66 * 67 * The normal calculation would be to form pixel value + dither, range-limit 68 * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual. 69 * We can skip the separate range-limiting step by extending the colorindex 70 * table in both directions. 71 */ 72 73 #define ODITHER_SIZE 16 /* dimension of dither matrix */ 74 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */ 75 #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE) /* # cells in matrix */ 76 #define ODITHER_MASK (ODITHER_SIZE-1) /* mask for wrapping around counters */ 77 78 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE]; 79 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE]; 80 81 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = { 82 /* Bayer's order-4 dither array. Generated by the code given in 83 * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I. 84 * The values in this array must range from 0 to ODITHER_CELLS-1. 85 */ 86 { 0,192, 48,240, 12,204, 60,252, 3,195, 51,243, 15,207, 63,255 }, 87 { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 }, 88 { 32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 }, 89 { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 }, 90 { 8,200, 56,248, 4,196, 52,244, 11,203, 59,251, 7,199, 55,247 }, 91 { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 }, 92 { 40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 }, 93 { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 }, 94 { 2,194, 50,242, 14,206, 62,254, 1,193, 49,241, 13,205, 61,253 }, 95 { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 }, 96 { 34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 }, 97 { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 }, 98 { 10,202, 58,250, 6,198, 54,246, 9,201, 57,249, 5,197, 53,245 }, 99 { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 }, 100 { 42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 }, 101 { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 } 102 }; 103 104 105 /* Declarations for Floyd-Steinberg dithering. 106 * 107 * Errors are accumulated into the array fserrors[], at a resolution of 108 * 1/16th of a pixel count. The error at a given pixel is propagated 109 * to its not-yet-processed neighbors using the standard F-S fractions, 110 * ... (here) 7/16 111 * 3/16 5/16 1/16 112 * We work left-to-right on even rows, right-to-left on odd rows. 113 * 114 * We can get away with a single array (holding one row's worth of errors) 115 * by using it to store the current row's errors at pixel columns not yet 116 * processed, but the next row's errors at columns already processed. We 117 * need only a few extra variables to hold the errors immediately around the 118 * current column. (If we are lucky, those variables are in registers, but 119 * even if not, they're probably cheaper to access than array elements are.) 120 * 121 * The fserrors[] array is indexed [component#][position]. 122 * We provide (#columns + 2) entries per component; the extra entry at each 123 * end saves us from special-casing the first and last pixels. 124 */ 125 126 #if BITS_IN_JSAMPLE == 8 127 typedef INT16 FSERROR; /* 16 bits should be enough */ 128 typedef int LOCFSERROR; /* use 'int' for calculation temps */ 129 #else 130 typedef INT32 FSERROR; /* may need more than 16 bits */ 131 typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */ 132 #endif 133 134 typedef FSERROR *FSERRPTR; /* pointer to error array */ 135 136 137 /* Private subobject */ 138 139 #define MAX_Q_COMPS 4 /* max components I can handle */ 140 141 typedef struct { 142 struct jpeg_color_quantizer pub; /* public fields */ 143 144 /* Initially allocated colormap is saved here */ 145 JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */ 146 int sv_actual; /* number of entries in use */ 147 148 JSAMPARRAY colorindex; /* Precomputed mapping for speed */ 149 /* colorindex[i][j] = index of color closest to pixel value j in component i, 150 * premultiplied as described above. Since colormap indexes must fit into 151 * JSAMPLEs, the entries of this array will too. 152 */ 153 boolean is_padded; /* is the colorindex padded for odither? */ 154 155 int Ncolors[MAX_Q_COMPS]; /* # of values alloced to each component */ 156 157 /* Variables for ordered dithering */ 158 int row_index; /* cur row's vertical index in dither matrix */ 159 ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */ 160 161 /* Variables for Floyd-Steinberg dithering */ 162 FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */ 163 boolean on_odd_row; /* flag to remember which row we are on */ 164 } my_cquantizer; 165 166 typedef my_cquantizer * my_cquantize_ptr; 167 168 169 /* 170 * Policy-making subroutines for create_colormap and create_colorindex. 171 * These routines determine the colormap to be used. The rest of the module 172 * only assumes that the colormap is orthogonal. 173 * 174 * * select_ncolors decides how to divvy up the available colors 175 * among the components. 176 * * output_value defines the set of representative values for a component. 177 * * largest_input_value defines the mapping from input values to 178 * representative values for a component. 179 * Note that the latter two routines may impose different policies for 180 * different components, though this is not currently done. 181 */ 182 183 184 LOCAL(int) 185 select_ncolors (j_decompress_ptr cinfo, int Ncolors[]) 186 /* Determine allocation of desired colors to components, */ 187 /* and fill in Ncolors[] array to indicate choice. */ 188 /* Return value is total number of colors (product of Ncolors[] values). */ 189 { 190 int nc = cinfo->out_color_components; /* number of color components */ 191 int max_colors = cinfo->desired_number_of_colors; 192 int total_colors, iroot, i, j; 193 boolean changed; 194 long temp; 195 int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE }; 196 RGB_order[0] = rgb_green[cinfo->out_color_space]; 197 RGB_order[1] = rgb_red[cinfo->out_color_space]; 198 RGB_order[2] = rgb_blue[cinfo->out_color_space]; 199 200 /* We can allocate at least the nc'th root of max_colors per component. */ 201 /* Compute floor(nc'th root of max_colors). */ 202 iroot = 1; 203 do { 204 iroot++; 205 temp = iroot; /* set temp = iroot ** nc */ 206 for (i = 1; i < nc; i++) 207 temp *= iroot; 208 } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */ 209 iroot--; /* now iroot = floor(root) */ 210 211 /* Must have at least 2 color values per component */ 212 if (iroot < 2) 213 ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp); 214 215 /* Initialize to iroot color values for each component */ 216 total_colors = 1; 217 for (i = 0; i < nc; i++) { 218 Ncolors[i] = iroot; 219 total_colors *= iroot; 220 } 221 /* We may be able to increment the count for one or more components without 222 * exceeding max_colors, though we know not all can be incremented. 223 * Sometimes, the first component can be incremented more than once! 224 * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.) 225 * In RGB colorspace, try to increment G first, then R, then B. 226 */ 227 do { 228 changed = FALSE; 229 for (i = 0; i < nc; i++) { 230 j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i); 231 /* calculate new total_colors if Ncolors[j] is incremented */ 232 temp = total_colors / Ncolors[j]; 233 temp *= Ncolors[j]+1; /* done in long arith to avoid oflo */ 234 if (temp > (long) max_colors) 235 break; /* won't fit, done with this pass */ 236 Ncolors[j]++; /* OK, apply the increment */ 237 total_colors = (int) temp; 238 changed = TRUE; 239 } 240 } while (changed); 241 242 return total_colors; 243 } 244 245 246 LOCAL(int) 247 output_value (j_decompress_ptr cinfo, int ci, int j, int maxj) 248 /* Return j'th output value, where j will range from 0 to maxj */ 249 /* The output values must fall in 0..MAXJSAMPLE in increasing order */ 250 { 251 /* We always provide values 0 and MAXJSAMPLE for each component; 252 * any additional values are equally spaced between these limits. 253 * (Forcing the upper and lower values to the limits ensures that 254 * dithering can't produce a color outside the selected gamut.) 255 */ 256 return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj); 257 } 258 259 260 LOCAL(int) 261 largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj) 262 /* Return largest input value that should map to j'th output value */ 263 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */ 264 { 265 /* Breakpoints are halfway between values returned by output_value */ 266 return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj)); 267 } 268 269 270 /* 271 * Create the colormap. 272 */ 273 274 LOCAL(void) 275 create_colormap (j_decompress_ptr cinfo) 276 { 277 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 278 JSAMPARRAY colormap; /* Created colormap */ 279 int total_colors; /* Number of distinct output colors */ 280 int i,j,k, nci, blksize, blkdist, ptr, val; 281 282 /* Select number of colors for each component */ 283 total_colors = select_ncolors(cinfo, cquantize->Ncolors); 284 285 /* Report selected color counts */ 286 if (cinfo->out_color_components == 3) 287 TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS, 288 total_colors, cquantize->Ncolors[0], 289 cquantize->Ncolors[1], cquantize->Ncolors[2]); 290 else 291 TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors); 292 293 /* Allocate and fill in the colormap. */ 294 /* The colors are ordered in the map in standard row-major order, */ 295 /* i.e. rightmost (highest-indexed) color changes most rapidly. */ 296 297 colormap = (*cinfo->mem->alloc_sarray) 298 ((j_common_ptr) cinfo, JPOOL_IMAGE, 299 (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components); 300 301 /* blksize is number of adjacent repeated entries for a component */ 302 /* blkdist is distance between groups of identical entries for a component */ 303 blkdist = total_colors; 304 305 for (i = 0; i < cinfo->out_color_components; i++) { 306 /* fill in colormap entries for i'th color component */ 307 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 308 blksize = blkdist / nci; 309 for (j = 0; j < nci; j++) { 310 /* Compute j'th output value (out of nci) for component */ 311 val = output_value(cinfo, i, j, nci-1); 312 /* Fill in all colormap entries that have this value of this component */ 313 for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) { 314 /* fill in blksize entries beginning at ptr */ 315 for (k = 0; k < blksize; k++) 316 colormap[i][ptr+k] = (JSAMPLE) val; 317 } 318 } 319 blkdist = blksize; /* blksize of this color is blkdist of next */ 320 } 321 322 /* Save the colormap in private storage, 323 * where it will survive color quantization mode changes. 324 */ 325 cquantize->sv_colormap = colormap; 326 cquantize->sv_actual = total_colors; 327 } 328 329 330 /* 331 * Create the color index table. 332 */ 333 334 LOCAL(void) 335 create_colorindex (j_decompress_ptr cinfo) 336 { 337 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 338 JSAMPROW indexptr; 339 int i,j,k, nci, blksize, val, pad; 340 341 /* For ordered dither, we pad the color index tables by MAXJSAMPLE in 342 * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE). 343 * This is not necessary in the other dithering modes. However, we 344 * flag whether it was done in case user changes dithering mode. 345 */ 346 if (cinfo->dither_mode == JDITHER_ORDERED) { 347 pad = MAXJSAMPLE*2; 348 cquantize->is_padded = TRUE; 349 } else { 350 pad = 0; 351 cquantize->is_padded = FALSE; 352 } 353 354 cquantize->colorindex = (*cinfo->mem->alloc_sarray) 355 ((j_common_ptr) cinfo, JPOOL_IMAGE, 356 (JDIMENSION) (MAXJSAMPLE+1 + pad), 357 (JDIMENSION) cinfo->out_color_components); 358 359 /* blksize is number of adjacent repeated entries for a component */ 360 blksize = cquantize->sv_actual; 361 362 for (i = 0; i < cinfo->out_color_components; i++) { 363 /* fill in colorindex entries for i'th color component */ 364 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 365 blksize = blksize / nci; 366 367 /* adjust colorindex pointers to provide padding at negative indexes. */ 368 if (pad) 369 cquantize->colorindex[i] += MAXJSAMPLE; 370 371 /* in loop, val = index of current output value, */ 372 /* and k = largest j that maps to current val */ 373 indexptr = cquantize->colorindex[i]; 374 val = 0; 375 k = largest_input_value(cinfo, i, 0, nci-1); 376 for (j = 0; j <= MAXJSAMPLE; j++) { 377 while (j > k) /* advance val if past boundary */ 378 k = largest_input_value(cinfo, i, ++val, nci-1); 379 /* premultiply so that no multiplication needed in main processing */ 380 indexptr[j] = (JSAMPLE) (val * blksize); 381 } 382 /* Pad at both ends if necessary */ 383 if (pad) 384 for (j = 1; j <= MAXJSAMPLE; j++) { 385 indexptr[-j] = indexptr[0]; 386 indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE]; 387 } 388 } 389 } 390 391 392 /* 393 * Create an ordered-dither array for a component having ncolors 394 * distinct output values. 395 */ 396 397 LOCAL(ODITHER_MATRIX_PTR) 398 make_odither_array (j_decompress_ptr cinfo, int ncolors) 399 { 400 ODITHER_MATRIX_PTR odither; 401 int j,k; 402 INT32 num,den; 403 404 odither = (ODITHER_MATRIX_PTR) 405 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 406 sizeof(ODITHER_MATRIX)); 407 /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1). 408 * Hence the dither value for the matrix cell with fill order f 409 * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1). 410 * On 16-bit-int machine, be careful to avoid overflow. 411 */ 412 den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1)); 413 for (j = 0; j < ODITHER_SIZE; j++) { 414 for (k = 0; k < ODITHER_SIZE; k++) { 415 num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k]))) 416 * MAXJSAMPLE; 417 /* Ensure round towards zero despite C's lack of consistency 418 * about rounding negative values in integer division... 419 */ 420 odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den); 421 } 422 } 423 return odither; 424 } 425 426 427 /* 428 * Create the ordered-dither tables. 429 * Components having the same number of representative colors may 430 * share a dither table. 431 */ 432 433 LOCAL(void) 434 create_odither_tables (j_decompress_ptr cinfo) 435 { 436 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 437 ODITHER_MATRIX_PTR odither; 438 int i, j, nci; 439 440 for (i = 0; i < cinfo->out_color_components; i++) { 441 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */ 442 odither = NULL; /* search for matching prior component */ 443 for (j = 0; j < i; j++) { 444 if (nci == cquantize->Ncolors[j]) { 445 odither = cquantize->odither[j]; 446 break; 447 } 448 } 449 if (odither == NULL) /* need a new table? */ 450 odither = make_odither_array(cinfo, nci); 451 cquantize->odither[i] = odither; 452 } 453 } 454 455 456 /* 457 * Map some rows of pixels to the output colormapped representation. 458 */ 459 460 METHODDEF(void) 461 color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 462 JSAMPARRAY output_buf, int num_rows) 463 /* General case, no dithering */ 464 { 465 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 466 JSAMPARRAY colorindex = cquantize->colorindex; 467 register int pixcode, ci; 468 register JSAMPROW ptrin, ptrout; 469 int row; 470 JDIMENSION col; 471 JDIMENSION width = cinfo->output_width; 472 register int nc = cinfo->out_color_components; 473 474 for (row = 0; row < num_rows; row++) { 475 ptrin = input_buf[row]; 476 ptrout = output_buf[row]; 477 for (col = width; col > 0; col--) { 478 pixcode = 0; 479 for (ci = 0; ci < nc; ci++) { 480 pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]); 481 } 482 *ptrout++ = (JSAMPLE) pixcode; 483 } 484 } 485 } 486 487 488 METHODDEF(void) 489 color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 490 JSAMPARRAY output_buf, int num_rows) 491 /* Fast path for out_color_components==3, no dithering */ 492 { 493 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 494 register int pixcode; 495 register JSAMPROW ptrin, ptrout; 496 JSAMPROW colorindex0 = cquantize->colorindex[0]; 497 JSAMPROW colorindex1 = cquantize->colorindex[1]; 498 JSAMPROW colorindex2 = cquantize->colorindex[2]; 499 int row; 500 JDIMENSION col; 501 JDIMENSION width = cinfo->output_width; 502 503 for (row = 0; row < num_rows; row++) { 504 ptrin = input_buf[row]; 505 ptrout = output_buf[row]; 506 for (col = width; col > 0; col--) { 507 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]); 508 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]); 509 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]); 510 *ptrout++ = (JSAMPLE) pixcode; 511 } 512 } 513 } 514 515 516 METHODDEF(void) 517 quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 518 JSAMPARRAY output_buf, int num_rows) 519 /* General case, with ordered dithering */ 520 { 521 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 522 register JSAMPROW input_ptr; 523 register JSAMPROW output_ptr; 524 JSAMPROW colorindex_ci; 525 int * dither; /* points to active row of dither matrix */ 526 int row_index, col_index; /* current indexes into dither matrix */ 527 int nc = cinfo->out_color_components; 528 int ci; 529 int row; 530 JDIMENSION col; 531 JDIMENSION width = cinfo->output_width; 532 533 for (row = 0; row < num_rows; row++) { 534 /* Initialize output values to 0 so can process components separately */ 535 jzero_far((void *) output_buf[row], (size_t) (width * sizeof(JSAMPLE))); 536 row_index = cquantize->row_index; 537 for (ci = 0; ci < nc; ci++) { 538 input_ptr = input_buf[row] + ci; 539 output_ptr = output_buf[row]; 540 colorindex_ci = cquantize->colorindex[ci]; 541 dither = cquantize->odither[ci][row_index]; 542 col_index = 0; 543 544 for (col = width; col > 0; col--) { 545 /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE, 546 * select output value, accumulate into output code for this pixel. 547 * Range-limiting need not be done explicitly, as we have extended 548 * the colorindex table to produce the right answers for out-of-range 549 * inputs. The maximum dither is +- MAXJSAMPLE; this sets the 550 * required amount of padding. 551 */ 552 *output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]]; 553 input_ptr += nc; 554 output_ptr++; 555 col_index = (col_index + 1) & ODITHER_MASK; 556 } 557 } 558 /* Advance row index for next row */ 559 row_index = (row_index + 1) & ODITHER_MASK; 560 cquantize->row_index = row_index; 561 } 562 } 563 564 565 METHODDEF(void) 566 quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 567 JSAMPARRAY output_buf, int num_rows) 568 /* Fast path for out_color_components==3, with ordered dithering */ 569 { 570 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 571 register int pixcode; 572 register JSAMPROW input_ptr; 573 register JSAMPROW output_ptr; 574 JSAMPROW colorindex0 = cquantize->colorindex[0]; 575 JSAMPROW colorindex1 = cquantize->colorindex[1]; 576 JSAMPROW colorindex2 = cquantize->colorindex[2]; 577 int * dither0; /* points to active row of dither matrix */ 578 int * dither1; 579 int * dither2; 580 int row_index, col_index; /* current indexes into dither matrix */ 581 int row; 582 JDIMENSION col; 583 JDIMENSION width = cinfo->output_width; 584 585 for (row = 0; row < num_rows; row++) { 586 row_index = cquantize->row_index; 587 input_ptr = input_buf[row]; 588 output_ptr = output_buf[row]; 589 dither0 = cquantize->odither[0][row_index]; 590 dither1 = cquantize->odither[1][row_index]; 591 dither2 = cquantize->odither[2][row_index]; 592 col_index = 0; 593 594 for (col = width; col > 0; col--) { 595 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) + 596 dither0[col_index]]); 597 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) + 598 dither1[col_index]]); 599 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) + 600 dither2[col_index]]); 601 *output_ptr++ = (JSAMPLE) pixcode; 602 col_index = (col_index + 1) & ODITHER_MASK; 603 } 604 row_index = (row_index + 1) & ODITHER_MASK; 605 cquantize->row_index = row_index; 606 } 607 } 608 609 610 METHODDEF(void) 611 quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf, 612 JSAMPARRAY output_buf, int num_rows) 613 /* General case, with Floyd-Steinberg dithering */ 614 { 615 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 616 register LOCFSERROR cur; /* current error or pixel value */ 617 LOCFSERROR belowerr; /* error for pixel below cur */ 618 LOCFSERROR bpreverr; /* error for below/prev col */ 619 LOCFSERROR bnexterr; /* error for below/next col */ 620 LOCFSERROR delta; 621 register FSERRPTR errorptr; /* => fserrors[] at column before current */ 622 register JSAMPROW input_ptr; 623 register JSAMPROW output_ptr; 624 JSAMPROW colorindex_ci; 625 JSAMPROW colormap_ci; 626 int pixcode; 627 int nc = cinfo->out_color_components; 628 int dir; /* 1 for left-to-right, -1 for right-to-left */ 629 int dirnc; /* dir * nc */ 630 int ci; 631 int row; 632 JDIMENSION col; 633 JDIMENSION width = cinfo->output_width; 634 JSAMPLE *range_limit = cinfo->sample_range_limit; 635 SHIFT_TEMPS 636 637 for (row = 0; row < num_rows; row++) { 638 /* Initialize output values to 0 so can process components separately */ 639 jzero_far((void *) output_buf[row], (size_t) (width * sizeof(JSAMPLE))); 640 for (ci = 0; ci < nc; ci++) { 641 input_ptr = input_buf[row] + ci; 642 output_ptr = output_buf[row]; 643 if (cquantize->on_odd_row) { 644 /* work right to left in this row */ 645 input_ptr += (width-1) * nc; /* so point to rightmost pixel */ 646 output_ptr += width-1; 647 dir = -1; 648 dirnc = -nc; 649 errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */ 650 } else { 651 /* work left to right in this row */ 652 dir = 1; 653 dirnc = nc; 654 errorptr = cquantize->fserrors[ci]; /* => entry before first column */ 655 } 656 colorindex_ci = cquantize->colorindex[ci]; 657 colormap_ci = cquantize->sv_colormap[ci]; 658 /* Preset error values: no error propagated to first pixel from left */ 659 cur = 0; 660 /* and no error propagated to row below yet */ 661 belowerr = bpreverr = 0; 662 663 for (col = width; col > 0; col--) { 664 /* cur holds the error propagated from the previous pixel on the 665 * current line. Add the error propagated from the previous line 666 * to form the complete error correction term for this pixel, and 667 * round the error term (which is expressed * 16) to an integer. 668 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct 669 * for either sign of the error value. 670 * Note: errorptr points to *previous* column's array entry. 671 */ 672 cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4); 673 /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE. 674 * The maximum error is +- MAXJSAMPLE; this sets the required size 675 * of the range_limit array. 676 */ 677 cur += GETJSAMPLE(*input_ptr); 678 cur = GETJSAMPLE(range_limit[cur]); 679 /* Select output value, accumulate into output code for this pixel */ 680 pixcode = GETJSAMPLE(colorindex_ci[cur]); 681 *output_ptr += (JSAMPLE) pixcode; 682 /* Compute actual representation error at this pixel */ 683 /* Note: we can do this even though we don't have the final */ 684 /* pixel code, because the colormap is orthogonal. */ 685 cur -= GETJSAMPLE(colormap_ci[pixcode]); 686 /* Compute error fractions to be propagated to adjacent pixels. 687 * Add these into the running sums, and simultaneously shift the 688 * next-line error sums left by 1 column. 689 */ 690 bnexterr = cur; 691 delta = cur * 2; 692 cur += delta; /* form error * 3 */ 693 errorptr[0] = (FSERROR) (bpreverr + cur); 694 cur += delta; /* form error * 5 */ 695 bpreverr = belowerr + cur; 696 belowerr = bnexterr; 697 cur += delta; /* form error * 7 */ 698 /* At this point cur contains the 7/16 error value to be propagated 699 * to the next pixel on the current line, and all the errors for the 700 * next line have been shifted over. We are therefore ready to move on. 701 */ 702 input_ptr += dirnc; /* advance input ptr to next column */ 703 output_ptr += dir; /* advance output ptr to next column */ 704 errorptr += dir; /* advance errorptr to current column */ 705 } 706 /* Post-loop cleanup: we must unload the final error value into the 707 * final fserrors[] entry. Note we need not unload belowerr because 708 * it is for the dummy column before or after the actual array. 709 */ 710 errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */ 711 } 712 cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE); 713 } 714 } 715 716 717 /* 718 * Allocate workspace for Floyd-Steinberg errors. 719 */ 720 721 LOCAL(void) 722 alloc_fs_workspace (j_decompress_ptr cinfo) 723 { 724 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 725 size_t arraysize; 726 int i; 727 728 arraysize = (size_t) ((cinfo->output_width + 2) * sizeof(FSERROR)); 729 for (i = 0; i < cinfo->out_color_components; i++) { 730 cquantize->fserrors[i] = (FSERRPTR) 731 (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize); 732 } 733 } 734 735 736 /* 737 * Initialize for one-pass color quantization. 738 */ 739 740 METHODDEF(void) 741 start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan) 742 { 743 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; 744 size_t arraysize; 745 int i; 746 747 /* Install my colormap. */ 748 cinfo->colormap = cquantize->sv_colormap; 749 cinfo->actual_number_of_colors = cquantize->sv_actual; 750 751 /* Initialize for desired dithering mode. */ 752 switch (cinfo->dither_mode) { 753 case JDITHER_NONE: 754 if (cinfo->out_color_components == 3) 755 cquantize->pub.color_quantize = color_quantize3; 756 else 757 cquantize->pub.color_quantize = color_quantize; 758 break; 759 case JDITHER_ORDERED: 760 if (cinfo->out_color_components == 3) 761 cquantize->pub.color_quantize = quantize3_ord_dither; 762 else 763 cquantize->pub.color_quantize = quantize_ord_dither; 764 cquantize->row_index = 0; /* initialize state for ordered dither */ 765 /* If user changed to ordered dither from another mode, 766 * we must recreate the color index table with padding. 767 * This will cost extra space, but probably isn't very likely. 768 */ 769 if (! cquantize->is_padded) 770 create_colorindex(cinfo); 771 /* Create ordered-dither tables if we didn't already. */ 772 if (cquantize->odither[0] == NULL) 773 create_odither_tables(cinfo); 774 break; 775 case JDITHER_FS: 776 cquantize->pub.color_quantize = quantize_fs_dither; 777 cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */ 778 /* Allocate Floyd-Steinberg workspace if didn't already. */ 779 if (cquantize->fserrors[0] == NULL) 780 alloc_fs_workspace(cinfo); 781 /* Initialize the propagated errors to zero. */ 782 arraysize = (size_t) ((cinfo->output_width + 2) * sizeof(FSERROR)); 783 for (i = 0; i < cinfo->out_color_components; i++) 784 jzero_far((void *) cquantize->fserrors[i], arraysize); 785 break; 786 default: 787 ERREXIT(cinfo, JERR_NOT_COMPILED); 788 break; 789 } 790 } 791 792 793 /* 794 * Finish up at the end of the pass. 795 */ 796 797 METHODDEF(void) 798 finish_pass_1_quant (j_decompress_ptr cinfo) 799 { 800 /* no work in 1-pass case */ 801 } 802 803 804 /* 805 * Switch to a new external colormap between output passes. 806 * Shouldn't get to this module! 807 */ 808 809 METHODDEF(void) 810 new_color_map_1_quant (j_decompress_ptr cinfo) 811 { 812 ERREXIT(cinfo, JERR_MODE_CHANGE); 813 } 814 815 816 /* 817 * Module initialization routine for 1-pass color quantization. 818 */ 819 820 GLOBAL(void) 821 jinit_1pass_quantizer (j_decompress_ptr cinfo) 822 { 823 my_cquantize_ptr cquantize; 824 825 cquantize = (my_cquantize_ptr) 826 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 827 sizeof(my_cquantizer)); 828 cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize; 829 cquantize->pub.start_pass = start_pass_1_quant; 830 cquantize->pub.finish_pass = finish_pass_1_quant; 831 cquantize->pub.new_color_map = new_color_map_1_quant; 832 cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */ 833 cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */ 834 835 /* Make sure my internal arrays won't overflow */ 836 if (cinfo->out_color_components > MAX_Q_COMPS) 837 ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS); 838 /* Make sure colormap indexes can be represented by JSAMPLEs */ 839 if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1)) 840 ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1); 841 842 /* Create the colormap and color index table. */ 843 create_colormap(cinfo); 844 create_colorindex(cinfo); 845 846 /* Allocate Floyd-Steinberg workspace now if requested. 847 * We do this now since it may affect the memory manager's space 848 * calculations. If the user changes to FS dither mode in a later pass, we 849 * will allocate the space then, and will possibly overrun the 850 * max_memory_to_use setting. 851 */ 852 if (cinfo->dither_mode == JDITHER_FS) 853 alloc_fs_workspace(cinfo); 854 } 855 856 #endif /* QUANT_1PASS_SUPPORTED */ 857
