/* * jquant1.c * * Copyright (C) 1991-1995, Thomas G. Lane. * This file is part of the Independent JPEG Group's software. * For conditions of distribution and use, see the accompanying README file. * * This file contains 1-pass color quantization (color mapping) routines. * These routines provide mapping to a fixed color map using equally spaced * color values. Optional Floyd-Steinberg or ordered dithering is available. */ #define JPEG_INTERNALS #include "jinclude.h" #include "jpeglib.h" #ifdef QUANT_1PASS_SUPPORTED /* * The main purpose of 1-pass quantization is to provide a fast, if not very * high quality, colormapped output capability. A 2-pass quantizer usually * gives better visual quality; however, for quantized grayscale output this * quantizer is perfectly adequate. Dithering is highly recommended with this * quantizer, though you can turn it off if you really want to. * * In 1-pass quantization the colormap must be chosen in advance of seeing the * image. We use a map consisting of all combinations of Ncolors[i] color * values for the i'th component. The Ncolors[] values are chosen so that * their product, the total number of colors, is no more than that requested. * (In most cases, the product will be somewhat less.) * * Since the colormap is orthogonal, the representative value for each color * component can be determined without considering the other components; * then these indexes can be combined into a colormap index by a standard * N-dimensional-array-subscript calculation. Most of the arithmetic involved * can be precalculated and stored in the lookup table colorindex[]. * colorindex[i][j] maps pixel value j in component i to the nearest * representative value (grid plane) for that component; this index is * multiplied by the array stride for component i, so that the * index of the colormap entry closest to a given pixel value is just * sum( colorindex[component-number][pixel-component-value] ) * Aside from being fast, this scheme allows for variable spacing between * representative values with no additional lookup cost. * * If gamma correction has been applied in color conversion, it might be wise * to adjust the color grid spacing so that the representative colors are * equidistant in linear space. At this writing, gamma correction is not * implemented by jdcolor, so nothing is done here. */ /* Declarations for ordered dithering. * * We use a standard 16x16 ordered dither array. The basic concept of ordered * dithering is described in many references, for instance Dale Schumacher's * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991). * In place of Schumacher's comparisons against a "threshold" value, we add a * "dither" value to the input pixel and then round the result to the nearest * output value. The dither value is equivalent to (0.5 - threshold) times * the distance between output values. For ordered dithering, we assume that * the output colors are equally spaced; if not, results will probably be * worse, since the dither may be too much or too little at a given point. * * The normal calculation would be to form pixel value + dither, range-limit * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual. * We can skip the separate range-limiting step by extending the colorindex * table in both directions. */ #define ODITHER_SIZE 16 /* dimension of dither matrix */ /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */ #define ODITHER_CELLS ( ODITHER_SIZE * ODITHER_SIZE ) /* # cells in matrix */ #define ODITHER_MASK ( ODITHER_SIZE - 1 ) /* mask for wrapping around counters */ typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE]; typedef int ( *ODITHER_MATRIX_PTR )[ODITHER_SIZE]; static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = { /* Bayer's order-4 dither array. Generated by the code given in * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I. * The values in this array must range from 0 to ODITHER_CELLS-1. */ { 0, 192, 48, 240, 12, 204, 60, 252, 3, 195, 51, 243, 15, 207, 63, 255 }, { 128, 64, 176, 112, 140, 76, 188, 124, 131, 67, 179, 115, 143, 79, 191, 127 }, { 32, 224, 16, 208, 44, 236, 28, 220, 35, 227, 19, 211, 47, 239, 31, 223 }, { 160, 96, 144, 80, 172, 108, 156, 92, 163, 99, 147, 83, 175, 111, 159, 95 }, { 8, 200, 56, 248, 4, 196, 52, 244, 11, 203, 59, 251, 7, 199, 55, 247 }, { 136, 72, 184, 120, 132, 68, 180, 116, 139, 75, 187, 123, 135, 71, 183, 119 }, { 40, 232, 24, 216, 36, 228, 20, 212, 43, 235, 27, 219, 39, 231, 23, 215 }, { 168, 104, 152, 88, 164, 100, 148, 84, 171, 107, 155, 91, 167, 103, 151, 87 }, { 2, 194, 50, 242, 14, 206, 62, 254, 1, 193, 49, 241, 13, 205, 61, 253 }, { 130, 66, 178, 114, 142, 78, 190, 126, 129, 65, 177, 113, 141, 77, 189, 125 }, { 34, 226, 18, 210, 46, 238, 30, 222, 33, 225, 17, 209, 45, 237, 29, 221 }, { 162, 98, 146, 82, 174, 110, 158, 94, 161, 97, 145, 81, 173, 109, 157, 93 }, { 10, 202, 58, 250, 6, 198, 54, 246, 9, 201, 57, 249, 5, 197, 53, 245 }, { 138, 74, 186, 122, 134, 70, 182, 118, 137, 73, 185, 121, 133, 69, 181, 117 }, { 42, 234, 26, 218, 38, 230, 22, 214, 41, 233, 25, 217, 37, 229, 21, 213 }, { 170, 106, 154, 90, 166, 102, 150, 86, 169, 105, 153, 89, 165, 101, 149, 85 } }; /* Declarations for Floyd-Steinberg dithering. * * Errors are accumulated into the array fserrors[], at a resolution of * 1/16th of a pixel count. The error at a given pixel is propagated * to its not-yet-processed neighbors using the standard F-S fractions, * ... (here) 7/16 * 3/16 5/16 1/16 * We work left-to-right on even rows, right-to-left on odd rows. * * We can get away with a single array (holding one row's worth of errors) * by using it to store the current row's errors at pixel columns not yet * processed, but the next row's errors at columns already processed. We * need only a few extra variables to hold the errors immediately around the * current column. (If we are lucky, those variables are in registers, but * even if not, they're probably cheaper to access than array elements are.) * * The fserrors[] array is indexed [component#][position]. * We provide (#columns + 2) entries per component; the extra entry at each * end saves us from special-casing the first and last pixels. * * Note: on a wide image, we might not have enough room in a PC's near data * segment to hold the error array; so it is allocated with alloc_large. */ #if BITS_IN_JSAMPLE == 8 typedef INT16 FSERROR; /* 16 bits should be enough */ typedef int LOCFSERROR; /* use 'int' for calculation temps */ #else typedef INT32 FSERROR; /* may need more than 16 bits */ typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */ #endif typedef FSERROR FAR * FSERRPTR; /* pointer to error array (in FAR storage!) */ /* Private subobject */ #define MAX_Q_COMPS 4 /* max components I can handle */ typedef struct { struct jpeg_color_quantizer pub;/* public fields */ /* Initially allocated colormap is saved here */ JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */ int sv_actual; /* number of entries in use */ JSAMPARRAY colorindex; /* Precomputed mapping for speed */ /* colorindex[i][j] = index of color closest to pixel value j in component i, * premultiplied as described above. Since colormap indexes must fit into * JSAMPLEs, the entries of this array will too. */ boolean is_padded; /* is the colorindex padded for odither? */ int Ncolors[MAX_Q_COMPS];/* # of values alloced to each component */ /* Variables for ordered dithering */ int row_index; /* cur row's vertical index in dither matrix */ ODITHER_MATRIX_PTR odither[MAX_Q_COMPS];/* one dither array per component */ /* Variables for Floyd-Steinberg dithering */ FSERRPTR fserrors[MAX_Q_COMPS];/* accumulated errors */ boolean on_odd_row; /* flag to remember which row we are on */ } my_cquantizer; typedef my_cquantizer * my_cquantize_ptr; /* * Policy-making subroutines for create_colormap and create_colorindex. * These routines determine the colormap to be used. The rest of the module * only assumes that the colormap is orthogonal. * * * select_ncolors decides how to divvy up the available colors * among the components. * * output_value defines the set of representative values for a component. * * largest_input_value defines the mapping from input values to * representative values for a component. * Note that the latter two routines may impose different policies for * different components, though this is not currently done. */ LOCAL int select_ncolors( j_decompress_ptr cinfo, int Ncolors[] ) { /* Determine allocation of desired colors to components, */ /* and fill in Ncolors[] array to indicate choice. */ /* Return value is total number of colors (product of Ncolors[] values). */ int nc = cinfo->out_color_components;/* number of color components */ int max_colors = cinfo->desired_number_of_colors; int total_colors, iroot, i, j; boolean changed; long temp; static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE }; /* We can allocate at least the nc'th root of max_colors per component. */ /* Compute floor(nc'th root of max_colors). */ iroot = 1; do { iroot++; temp = iroot; /* set temp = iroot ** nc */ for ( i = 1; i < nc; i++ ) { temp *= iroot; } } while ( temp <= (long) max_colors );/* repeat till iroot exceeds root */ iroot--; /* now iroot = floor(root) */ /* Must have at least 2 color values per component */ if ( iroot < 2 ) { ERREXIT1( cinfo, JERR_QUANT_FEW_COLORS, (int) temp ); } /* Initialize to iroot color values for each component */ total_colors = 1; for ( i = 0; i < nc; i++ ) { Ncolors[i] = iroot; total_colors *= iroot; } /* We may be able to increment the count for one or more components without * exceeding max_colors, though we know not all can be incremented. * Sometimes, the first component can be incremented more than once! * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.) * In RGB colorspace, try to increment G first, then R, then B. */ do { changed = FALSE; for ( i = 0; i < nc; i++ ) { j = ( cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i ); /* calculate new total_colors if Ncolors[j] is incremented */ temp = total_colors / Ncolors[j]; temp *= Ncolors[j] + 1;/* done in long arith to avoid oflo */ if ( temp > (long) max_colors ) { break; } /* won't fit, done with this pass */ Ncolors[j]++; /* OK, apply the increment */ total_colors = (int) temp; changed = TRUE; } } while ( changed ); return total_colors; } LOCAL int output_value( j_decompress_ptr cinfo, int ci, int j, int maxj ) { /* Return j'th output value, where j will range from 0 to maxj */ /* The output values must fall in 0..MAXJSAMPLE in increasing order */ /* We always provide values 0 and MAXJSAMPLE for each component; * any additional values are equally spaced between these limits. * (Forcing the upper and lower values to the limits ensures that * dithering can't produce a color outside the selected gamut.) */ return (int) ( ( (INT32) j * MAXJSAMPLE + maxj / 2 ) / maxj ); } LOCAL int largest_input_value( j_decompress_ptr cinfo, int ci, int j, int maxj ) { /* Return largest input value that should map to j'th output value */ /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */ /* Breakpoints are halfway between values returned by output_value */ return (int) ( ( (INT32) ( 2 * j + 1 ) * MAXJSAMPLE + maxj ) / ( 2 * maxj ) ); } /* * Create the colormap. */ LOCAL void create_colormap( j_decompress_ptr cinfo ) { my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; JSAMPARRAY colormap; /* Created colormap */ int total_colors; /* Number of distinct output colors */ int i, j, k, nci, blksize, blkdist, ptr, val; /* Select number of colors for each component */ total_colors = select_ncolors( cinfo, cquantize->Ncolors ); /* Report selected color counts */ if ( cinfo->out_color_components == 3 ) { TRACEMS4( cinfo, 1, JTRC_QUANT_3_NCOLORS, total_colors, cquantize->Ncolors[0], cquantize->Ncolors[1], cquantize->Ncolors[2] ); } else { TRACEMS1( cinfo, 1, JTRC_QUANT_NCOLORS, total_colors ); } /* Allocate and fill in the colormap. */ /* The colors are ordered in the map in standard row-major order, */ /* i.e. rightmost (highest-indexed) color changes most rapidly. */ colormap = ( *cinfo->mem->alloc_sarray ) ( (j_common_ptr) cinfo, JPOOL_IMAGE, (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components ); /* blksize is number of adjacent repeated entries for a component */ /* blkdist is distance between groups of identical entries for a component */ blkdist = total_colors; for ( i = 0; i < cinfo->out_color_components; i++ ) { /* fill in colormap entries for i'th color component */ nci = cquantize->Ncolors[i];/* # of distinct values for this color */ blksize = blkdist / nci; for ( j = 0; j < nci; j++ ) { /* Compute j'th output value (out of nci) for component */ val = output_value( cinfo, i, j, nci - 1 ); /* Fill in all colormap entries that have this value of this component */ for ( ptr = j * blksize; ptr < total_colors; ptr += blkdist ) { /* fill in blksize entries beginning at ptr */ for ( k = 0; k < blksize; k++ ) { colormap[i][ptr + k] = (JSAMPLE) val; } } } blkdist = blksize; /* blksize of this color is blkdist of next */ } /* Save the colormap in private storage, * where it will survive color quantization mode changes. */ cquantize->sv_colormap = colormap; cquantize->sv_actual = total_colors; } /* * Create the color index table. */ LOCAL void create_colorindex( j_decompress_ptr cinfo ) { my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; JSAMPROW indexptr; int i, j, k, nci, blksize, val, pad; /* For ordered dither, we pad the color index tables by MAXJSAMPLE in * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE). * This is not necessary in the other dithering modes. However, we * flag whether it was done in case user changes dithering mode. */ if ( cinfo->dither_mode == JDITHER_ORDERED ) { pad = MAXJSAMPLE * 2; cquantize->is_padded = TRUE; } else { pad = 0; cquantize->is_padded = FALSE; } cquantize->colorindex = ( *cinfo->mem->alloc_sarray ) ( (j_common_ptr) cinfo, JPOOL_IMAGE, (JDIMENSION) ( MAXJSAMPLE + 1 + pad ), (JDIMENSION) cinfo->out_color_components ); /* blksize is number of adjacent repeated entries for a component */ blksize = cquantize->sv_actual; for ( i = 0; i < cinfo->out_color_components; i++ ) { /* fill in colorindex entries for i'th color component */ nci = cquantize->Ncolors[i];/* # of distinct values for this color */ blksize = blksize / nci; /* adjust colorindex pointers to provide padding at negative indexes. */ if ( pad ) { cquantize->colorindex[i] += MAXJSAMPLE; } /* in loop, val = index of current output value, */ /* and k = largest j that maps to current val */ indexptr = cquantize->colorindex[i]; val = 0; k = largest_input_value( cinfo, i, 0, nci - 1 ); for ( j = 0; j <= MAXJSAMPLE; j++ ) { while ( j > k ) {/* advance val if past boundary */ k = largest_input_value( cinfo, i, ++val, nci - 1 ); } /* premultiply so that no multiplication needed in main processing */ indexptr[j] = (JSAMPLE) ( val * blksize ); } /* Pad at both ends if necessary */ if ( pad ) { for ( j = 1; j <= MAXJSAMPLE; j++ ) { indexptr[-j] = indexptr[0]; indexptr[MAXJSAMPLE + j] = indexptr[MAXJSAMPLE]; } } } } /* * Create an ordered-dither array for a component having ncolors * distinct output values. */ LOCAL ODITHER_MATRIX_PTR make_odither_array( j_decompress_ptr cinfo, int ncolors ) { ODITHER_MATRIX_PTR odither; int j, k; INT32 num, den; odither = (ODITHER_MATRIX_PTR) ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF( ODITHER_MATRIX ) ); /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1). * Hence the dither value for the matrix cell with fill order f * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1). * On 16-bit-int machine, be careful to avoid overflow. */ den = 2 * ODITHER_CELLS * ( (INT32) ( ncolors - 1 ) ); for ( j = 0; j < ODITHER_SIZE; j++ ) { for ( k = 0; k < ODITHER_SIZE; k++ ) { num = ( (INT32) ( ODITHER_CELLS - 1 - 2 * ( (int)base_dither_matrix[j][k] ) ) ) * MAXJSAMPLE; /* Ensure round towards zero despite C's lack of consistency * about rounding negative values in integer division... */ odither[j][k] = (int) ( num < 0 ? -( ( -num ) / den ) : num / den ); } } return odither; } /* * Create the ordered-dither tables. * Components having the same number of representative colors may * share a dither table. */ LOCAL void create_odither_tables( j_decompress_ptr cinfo ) { my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; ODITHER_MATRIX_PTR odither; int i, j, nci; for ( i = 0; i < cinfo->out_color_components; i++ ) { nci = cquantize->Ncolors[i];/* # of distinct values for this color */ odither = NULL; /* search for matching prior component */ for ( j = 0; j < i; j++ ) { if ( nci == cquantize->Ncolors[j] ) { odither = cquantize->odither[j]; break; } } if ( odither == NULL ) {/* need a new table? */ odither = make_odither_array( cinfo, nci ); } cquantize->odither[i] = odither; } } /* * Map some rows of pixels to the output colormapped representation. */ METHODDEF void color_quantize( j_decompress_ptr cinfo, JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows ) { /* General case, no dithering */ my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; JSAMPARRAY colorindex = cquantize->colorindex; register int pixcode, ci; register JSAMPROW ptrin, ptrout; int row; JDIMENSION col; JDIMENSION width = cinfo->output_width; register int nc = cinfo->out_color_components; for ( row = 0; row < num_rows; row++ ) { ptrin = input_buf[row]; ptrout = output_buf[row]; for ( col = width; col > 0; col-- ) { pixcode = 0; for ( ci = 0; ci < nc; ci++ ) { pixcode += GETJSAMPLE( colorindex[ci][GETJSAMPLE( *ptrin++ )] ); } *ptrout++ = (JSAMPLE) pixcode; } } } METHODDEF void color_quantize3( j_decompress_ptr cinfo, JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows ) { /* Fast path for out_color_components==3, no dithering */ my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; register int pixcode; register JSAMPROW ptrin, ptrout; JSAMPROW colorindex0 = cquantize->colorindex[0]; JSAMPROW colorindex1 = cquantize->colorindex[1]; JSAMPROW colorindex2 = cquantize->colorindex[2]; int row; JDIMENSION col; JDIMENSION width = cinfo->output_width; for ( row = 0; row < num_rows; row++ ) { ptrin = input_buf[row]; ptrout = output_buf[row]; for ( col = width; col > 0; col-- ) { pixcode = GETJSAMPLE( colorindex0[GETJSAMPLE( *ptrin++ )] ); pixcode += GETJSAMPLE( colorindex1[GETJSAMPLE( *ptrin++ )] ); pixcode += GETJSAMPLE( colorindex2[GETJSAMPLE( *ptrin++ )] ); *ptrout++ = (JSAMPLE) pixcode; } } } METHODDEF void quantize_ord_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows ) { /* General case, with ordered dithering */ my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; register JSAMPROW input_ptr; register JSAMPROW output_ptr; JSAMPROW colorindex_ci; int * dither; /* points to active row of dither matrix */ int row_index, col_index;/* current indexes into dither matrix */ int nc = cinfo->out_color_components; int ci; int row; JDIMENSION col; JDIMENSION width = cinfo->output_width; for ( row = 0; row < num_rows; row++ ) { /* Initialize output values to 0 so can process components separately */ jzero_far( (void FAR *) output_buf[row], (size_t) ( width * SIZEOF( JSAMPLE ) ) ); row_index = cquantize->row_index; for ( ci = 0; ci < nc; ci++ ) { input_ptr = input_buf[row] + ci; output_ptr = output_buf[row]; colorindex_ci = cquantize->colorindex[ci]; dither = cquantize->odither[ci][row_index]; col_index = 0; for ( col = width; col > 0; col-- ) { /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE, * select output value, accumulate into output code for this pixel. * Range-limiting need not be done explicitly, as we have extended * the colorindex table to produce the right answers for out-of-range * inputs. The maximum dither is +- MAXJSAMPLE; this sets the * required amount of padding. */ *output_ptr += colorindex_ci[GETJSAMPLE( *input_ptr ) + dither[col_index]]; input_ptr += nc; output_ptr++; col_index = ( col_index + 1 ) & ODITHER_MASK; } } /* Advance row index for next row */ row_index = ( row_index + 1 ) & ODITHER_MASK; cquantize->row_index = row_index; } } METHODDEF void quantize3_ord_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows ) { /* Fast path for out_color_components==3, with ordered dithering */ my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; register int pixcode; register JSAMPROW input_ptr; register JSAMPROW output_ptr; JSAMPROW colorindex0 = cquantize->colorindex[0]; JSAMPROW colorindex1 = cquantize->colorindex[1]; JSAMPROW colorindex2 = cquantize->colorindex[2]; int * dither0; /* points to active row of dither matrix */ int * dither1; int * dither2; int row_index, col_index;/* current indexes into dither matrix */ int row; JDIMENSION col; JDIMENSION width = cinfo->output_width; for ( row = 0; row < num_rows; row++ ) { row_index = cquantize->row_index; input_ptr = input_buf[row]; output_ptr = output_buf[row]; dither0 = cquantize->odither[0][row_index]; dither1 = cquantize->odither[1][row_index]; dither2 = cquantize->odither[2][row_index]; col_index = 0; for ( col = width; col > 0; col-- ) { pixcode = GETJSAMPLE( colorindex0[GETJSAMPLE( *input_ptr++ ) + dither0[col_index]] ); pixcode += GETJSAMPLE( colorindex1[GETJSAMPLE( *input_ptr++ ) + dither1[col_index]] ); pixcode += GETJSAMPLE( colorindex2[GETJSAMPLE( *input_ptr++ ) + dither2[col_index]] ); *output_ptr++ = (JSAMPLE) pixcode; col_index = ( col_index + 1 ) & ODITHER_MASK; } row_index = ( row_index + 1 ) & ODITHER_MASK; cquantize->row_index = row_index; } } METHODDEF void quantize_fs_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf, JSAMPARRAY output_buf, int num_rows ) { /* General case, with Floyd-Steinberg dithering */ my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; register LOCFSERROR cur;/* current error or pixel value */ LOCFSERROR belowerr; /* error for pixel below cur */ LOCFSERROR bpreverr; /* error for below/prev col */ LOCFSERROR bnexterr; /* error for below/next col */ LOCFSERROR delta; register FSERRPTR errorptr; /* => fserrors[] at column before current */ register JSAMPROW input_ptr; register JSAMPROW output_ptr; JSAMPROW colorindex_ci; JSAMPROW colormap_ci; int pixcode; int nc = cinfo->out_color_components; int dir; /* 1 for left-to-right, -1 for right-to-left */ int dirnc; /* dir * nc */ int ci; int row; JDIMENSION col; JDIMENSION width = cinfo->output_width; JSAMPLE * range_limit = cinfo->sample_range_limit; SHIFT_TEMPS for ( row = 0; row < num_rows; row++ ) { /* Initialize output values to 0 so can process components separately */ jzero_far( (void FAR *) output_buf[row], (size_t) ( width * SIZEOF( JSAMPLE ) ) ); for ( ci = 0; ci < nc; ci++ ) { input_ptr = input_buf[row] + ci; output_ptr = output_buf[row]; if ( cquantize->on_odd_row ) { /* work right to left in this row */ input_ptr += ( width - 1 ) * nc;/* so point to rightmost pixel */ output_ptr += width - 1; dir = -1; dirnc = -nc; errorptr = cquantize->fserrors[ci] + ( width + 1 );/* => entry after last column */ } else { /* work left to right in this row */ dir = 1; dirnc = nc; errorptr = cquantize->fserrors[ci];/* => entry before first column */ } colorindex_ci = cquantize->colorindex[ci]; colormap_ci = cquantize->sv_colormap[ci]; /* Preset error values: no error propagated to first pixel from left */ cur = 0; /* and no error propagated to row below yet */ belowerr = bpreverr = 0; for ( col = width; col > 0; col-- ) { /* cur holds the error propagated from the previous pixel on the * current line. Add the error propagated from the previous line * to form the complete error correction term for this pixel, and * round the error term (which is expressed * 16) to an integer. * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct * for either sign of the error value. * Note: errorptr points to *previous* column's array entry. */ cur = RIGHT_SHIFT( cur + errorptr[dir] + 8, 4 ); /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE. * The maximum error is +- MAXJSAMPLE; this sets the required size * of the range_limit array. */ cur += GETJSAMPLE( *input_ptr ); cur = GETJSAMPLE( range_limit[cur] ); /* Select output value, accumulate into output code for this pixel */ pixcode = GETJSAMPLE( colorindex_ci[cur] ); *output_ptr += (JSAMPLE) pixcode; /* Compute actual representation error at this pixel */ /* Note: we can do this even though we don't have the final */ /* pixel code, because the colormap is orthogonal. */ cur -= GETJSAMPLE( colormap_ci[pixcode] ); /* Compute error fractions to be propagated to adjacent pixels. * Add these into the running sums, and simultaneously shift the * next-line error sums left by 1 column. */ bnexterr = cur; delta = cur * 2; cur += delta;/* form error * 3 */ errorptr[0] = (FSERROR) ( bpreverr + cur ); cur += delta;/* form error * 5 */ bpreverr = belowerr + cur; belowerr = bnexterr; cur += delta;/* form error * 7 */ /* At this point cur contains the 7/16 error value to be propagated * to the next pixel on the current line, and all the errors for the * next line have been shifted over. We are therefore ready to move on. */ input_ptr += dirnc;/* advance input ptr to next column */ output_ptr += dir;/* advance output ptr to next column */ errorptr += dir;/* advance errorptr to current column */ } /* Post-loop cleanup: we must unload the final error value into the * final fserrors[] entry. Note we need not unload belowerr because * it is for the dummy column before or after the actual array. */ errorptr[0] = (FSERROR) bpreverr;/* unload prev err into array */ } cquantize->on_odd_row = ( cquantize->on_odd_row ? FALSE : TRUE ); } } /* * Allocate workspace for Floyd-Steinberg errors. */ LOCAL void alloc_fs_workspace( j_decompress_ptr cinfo ) { my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; size_t arraysize; int i; arraysize = (size_t) ( ( cinfo->output_width + 2 ) * SIZEOF( FSERROR ) ); for ( i = 0; i < cinfo->out_color_components; i++ ) { cquantize->fserrors[i] = (FSERRPTR) ( *cinfo->mem->alloc_large )( (j_common_ptr) cinfo, JPOOL_IMAGE, arraysize ); } } /* * Initialize for one-pass color quantization. */ METHODDEF void start_pass_1_quant( j_decompress_ptr cinfo, boolean is_pre_scan ) { my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize; size_t arraysize; int i; /* Install my colormap. */ cinfo->colormap = cquantize->sv_colormap; cinfo->actual_number_of_colors = cquantize->sv_actual; /* Initialize for desired dithering mode. */ switch ( cinfo->dither_mode ) { case JDITHER_NONE: if ( cinfo->out_color_components == 3 ) { cquantize->pub.color_quantize = color_quantize3; } else { cquantize->pub.color_quantize = color_quantize; } break; case JDITHER_ORDERED: if ( cinfo->out_color_components == 3 ) { cquantize->pub.color_quantize = quantize3_ord_dither; } else { cquantize->pub.color_quantize = quantize_ord_dither; } cquantize->row_index = 0;/* initialize state for ordered dither */ /* If user changed to ordered dither from another mode, * we must recreate the color index table with padding. * This will cost extra space, but probably isn't very likely. */ if ( !cquantize->is_padded ) { create_colorindex( cinfo ); } /* Create ordered-dither tables if we didn't already. */ if ( cquantize->odither[0] == NULL ) { create_odither_tables( cinfo ); } break; case JDITHER_FS: cquantize->pub.color_quantize = quantize_fs_dither; cquantize->on_odd_row = FALSE;/* initialize state for F-S dither */ /* Allocate Floyd-Steinberg workspace if didn't already. */ if ( cquantize->fserrors[0] == NULL ) { alloc_fs_workspace( cinfo ); } /* Initialize the propagated errors to zero. */ arraysize = (size_t) ( ( cinfo->output_width + 2 ) * SIZEOF( FSERROR ) ); for ( i = 0; i < cinfo->out_color_components; i++ ) { jzero_far( (void FAR *) cquantize->fserrors[i], arraysize ); } break; default: ERREXIT( cinfo, JERR_NOT_COMPILED ); break; } } /* * Finish up at the end of the pass. */ METHODDEF void finish_pass_1_quant( j_decompress_ptr cinfo ) { /* no work in 1-pass case */ } /* * Switch to a new external colormap between output passes. * Shouldn't get to this module! */ METHODDEF void new_color_map_1_quant( j_decompress_ptr cinfo ) { ERREXIT( cinfo, JERR_MODE_CHANGE ); } /* * Module initialization routine for 1-pass color quantization. */ GLOBAL void jinit_1pass_quantizer( j_decompress_ptr cinfo ) { my_cquantize_ptr cquantize; cquantize = (my_cquantize_ptr) ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF( my_cquantizer ) ); cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize; cquantize->pub.start_pass = start_pass_1_quant; cquantize->pub.finish_pass = finish_pass_1_quant; cquantize->pub.new_color_map = new_color_map_1_quant; cquantize->fserrors[0] = NULL;/* Flag FS workspace not allocated */ cquantize->odither[0] = NULL;/* Also flag odither arrays not allocated */ /* Make sure my internal arrays won't overflow */ if ( cinfo->out_color_components > MAX_Q_COMPS ) { ERREXIT1( cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS ); } /* Make sure colormap indexes can be represented by JSAMPLEs */ if ( cinfo->desired_number_of_colors > ( MAXJSAMPLE + 1 ) ) { ERREXIT1( cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE + 1 ); } /* Create the colormap and color index table. */ create_colormap( cinfo ); create_colorindex( cinfo ); /* Allocate Floyd-Steinberg workspace now if requested. * We do this now since it is FAR storage and may affect the memory * manager's space calculations. If the user changes to FS dither * mode in a later pass, we will allocate the space then, and will * possibly overrun the max_memory_to_use setting. */ if ( cinfo->dither_mode == JDITHER_FS ) { alloc_fs_workspace( cinfo ); } } #endif /* QUANT_1PASS_SUPPORTED */