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/* Copyright (c) 1992 Regents of the University of California */ |
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|
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#ifndef lint |
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static char SCCSid[] = "$SunId$ LBL"; |
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#endif |
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|
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/* |
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* Simple median-cut color quantization based on colortab.c |
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*/ |
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|
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#include "standard.h" |
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|
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#include "color.h" |
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/* histogram resolution */ |
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#define NRED 36 |
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#define NGRN 48 |
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#define NBLU 24 |
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#define HMAX NGRN |
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/* minimum box count for adaptive partition */ |
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#define MINSAMP 7 |
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/* color partition */ |
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#define set_branch(p,c) ((c)<<2|(p)) |
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#define part(cn) ((cn)>>2) |
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#define prim(cn) ((cn)&3) |
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/* our color table (global) */ |
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BYTE clrtab[256][3]; |
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/* histogram of colors / color assignments */ |
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static unsigned histo[NRED][NGRN][NBLU]; |
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#define cndx(c) histo[((c)[RED]*NRED)>>8][((c)[GRN]*NGRN)>>8][((c)[BLU]*NBLU)>>8] |
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/* initial color cube boundary */ |
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static int CLRCUBE[3][2] = {0,NRED,0,NGRN,0,NBLU}; |
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/* maximum propagated error during dithering */ |
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#define MAXERR 20 |
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|
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|
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new_histo() /* clear our histogram */ |
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{ |
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bzero((char *)histo, sizeof(histo)); |
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} |
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|
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|
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cnt_pixel(col) /* add pixel to our histogram */ |
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register BYTE col[]; |
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{ |
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cndx(col)++; |
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} |
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|
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|
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cnt_colrs(cs, n) /* add a scanline to our histogram */ |
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register COLR *cs; |
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register int n; |
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{ |
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while (n-- > 0) { |
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cndx(cs[0])++; |
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cs++; |
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} |
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} |
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|
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|
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new_clrtab(ncolors) /* make new color table using ncolors */ |
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int ncolors; |
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{ |
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if (ncolors < 1) |
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return(0); |
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if (ncolors > 256) |
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ncolors = 256; |
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/* partition color space */ |
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cut(CLRCUBE, 0, ncolors); |
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/* return new color table size */ |
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return(ncolors); |
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} |
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|
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|
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int |
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map_pixel(col) /* get pixel for color */ |
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register BYTE col[]; |
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{ |
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return(cndx(col)); |
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} |
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|
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|
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map_colrs(bs, cs, n) /* convert a scanline to color index values */ |
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register BYTE *bs; |
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register COLR *cs; |
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register int n; |
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{ |
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while (n-- > 0) { |
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*bs++ = cndx(cs[0]); |
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cs++; |
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} |
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} |
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|
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|
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dith_colrs(bs, cs, n) /* convert scanline to dithered index values */ |
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register BYTE *bs; |
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register COLR *cs; |
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int n; |
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{ |
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static short (*cerr)[3]; |
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static int N = 0; |
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int err[3], errp[3]; |
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register int x, i; |
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|
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if (n != N) { /* get error propogation array */ |
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if (N) |
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cerr = (short (*)[3])realloc((char *)cerr, |
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3*n*sizeof(short)); |
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else |
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cerr = (short (*)[3])malloc(3*n*sizeof(short)); |
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if (cerr == NULL) { |
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N = 0; |
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map_colrs(bs, cs, n); |
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return; |
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} |
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N = n; |
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bzero((char *)cerr, 3*N*sizeof(short)); |
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} |
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err[0] = err[1] = err[2] = 0; |
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for (x = 0; x < n; x++) { |
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for (i = 0; i < 3; i++) { /* dither value */ |
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errp[i] = err[i]; |
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err[i] += cerr[x][i]; |
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#ifdef MAXERR |
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if (err[i] > MAXERR) err[i] = MAXERR; |
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else if (err[i] < -MAXERR) err[i] = -MAXERR; |
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#endif |
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err[i] += cs[x][i]; |
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if (err[i] < 0) err[i] = 0; |
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else if (err[i] > 255) err[i] = 255; |
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} |
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bs[x] = cndx(err); |
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for (i = 0; i < 3; i++) { /* propagate error */ |
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err[i] -= clrtab[bs[x]][i]; |
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err[i] /= 3; |
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cerr[x][i] = err[i] + errp[i]; |
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} |
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} |
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} |
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|
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|
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static |
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cut(box, c0, c1) /* partition color space */ |
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register int box[3][2]; |
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int c0, c1; |
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{ |
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register int branch; |
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int kb[3][2]; |
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|
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if (c1-c0 <= 1) { /* assign pixel */ |
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mktabent(c0, box); |
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return; |
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} |
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/* split box */ |
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branch = split(box); |
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bcopy((char *)box, (char *)kb, sizeof(kb)); |
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/* do left (lesser) branch */ |
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kb[prim(branch)][1] = part(branch); |
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cut(kb, c0, (c0+c1)>>1); |
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/* do right branch */ |
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kb[prim(branch)][0] = part(branch); |
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kb[prim(branch)][1] = box[prim(branch)][1]; |
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cut(kb, (c0+c1)>>1, c1); |
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} |
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|
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|
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static int |
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split(box) /* find median cut for box */ |
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register int box[3][2]; |
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{ |
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#define c0 r |
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register int r, g, b; |
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int pri; |
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int t[HMAX], med; |
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/* find dominant axis */ |
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pri = RED; |
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if (box[GRN][1]-box[GRN][0] > box[pri][1]-box[pri][0]) |
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pri = GRN; |
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if (box[BLU][1]-box[BLU][0] > box[pri][1]-box[pri][0]) |
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pri = BLU; |
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/* sum histogram over box */ |
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med = 0; |
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switch (pri) { |
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case RED: |
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for (r = box[RED][0]; r < box[RED][1]; r++) { |
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t[r] = 0; |
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for (g = box[GRN][0]; g < box[GRN][1]; g++) |
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for (b = box[BLU][0]; b < box[BLU][1]; b++) |
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t[r] += histo[r][g][b]; |
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med += t[r]; |
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} |
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break; |
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case GRN: |
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for (g = box[GRN][0]; g < box[GRN][1]; g++) { |
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t[g] = 0; |
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for (b = box[BLU][0]; b < box[BLU][1]; b++) |
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for (r = box[RED][0]; r < box[RED][1]; r++) |
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t[g] += histo[r][g][b]; |
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med += t[g]; |
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} |
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break; |
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case BLU: |
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for (b = box[BLU][0]; b < box[BLU][1]; b++) { |
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t[b] = 0; |
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for (r = box[RED][0]; r < box[RED][1]; r++) |
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for (g = box[GRN][0]; g < box[GRN][1]; g++) |
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t[b] += histo[r][g][b]; |
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med += t[b]; |
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} |
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break; |
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} |
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if (med < MINSAMP) /* if too sparse, split at midpoint */ |
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return(set_branch(pri,(box[pri][0]+box[pri][1])>>1)); |
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/* find median position */ |
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med >>= 1; |
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for (c0 = box[pri][0]; med > 0; c0++) |
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med -= t[c0]; |
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if (c0 > (box[pri][0]+box[pri][1])>>1) /* if past the midpoint */ |
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c0--; /* part left of median */ |
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return(set_branch(pri,c0)); |
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#undef c0 |
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} |
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|
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|
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static |
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mktabent(p, box) /* compute average color for box and assign */ |
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int p; |
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register int box[3][2]; |
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{ |
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long sum[3]; |
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int r, g, n; |
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register int b, c; |
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/* sum pixels in box */ |
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n = 0; |
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sum[RED] = sum[GRN] = sum[BLU] = 0; |
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for (r = box[RED][0]; r < box[RED][1]; r++) |
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for (g = box[GRN][0]; g < box[GRN][1]; g++) |
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for (b = box[BLU][0]; b < box[BLU][1]; b++) { |
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if (c = histo[r][g][b]) { |
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n += c; |
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sum[RED] += (long)c*r; |
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sum[GRN] += (long)c*g; |
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sum[BLU] += (long)c*b; |
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} |
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histo[r][g][b] = p; /* assign pixel */ |
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} |
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if (n) { /* compute average */ |
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clrtab[p][RED] = sum[RED]*256/NRED/n; |
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clrtab[p][GRN] = sum[GRN]*256/NGRN/n; |
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clrtab[p][BLU] = sum[BLU]*256/NBLU/n; |
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} else { /* empty box -- use midpoint */ |
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clrtab[p][RED] = (box[RED][0]+box[RED][1])*256/NRED/2; |
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clrtab[p][GRN] = (box[GRN][0]+box[GRN][1])*256/NGRN/2; |
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clrtab[p][BLU] = (box[BLU][0]+box[BLU][1])*256/NBLU/2; |
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} |
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} |
