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