src/px/clrtab.c

#ifndef lint
static const char       RCSid[] = "$Id: clrtab.c,v 2.15 2003/06/30 14:59:12 schorsch Exp $";
#endif
/*
 * Simple median-cut color quantization based on colortab.c
 */

#include "copyright.h"

#include <string.h>

#include "standard.h"
#include "color.h"

                                /* histogram resolution */
#define NRED            36
#define NGRN            48
#define NBLU            24
#define HMAX            NGRN
                                /* minimum box count for adaptive partition */
#define MINSAMP         7
                                /* color partition */
#define set_branch(p,c) ((c)<<2|(p))
#define part(cn)        ((cn)>>2)
#define prim(cn)        ((cn)&3)
                                /* our color table (global) */
extern BYTE     clrtab[256][3];
                                /* histogram of colors / color assignments */
static unsigned histo[NRED][NGRN][NBLU];
#define cndx(c)         histo[((c)[RED]*NRED)>>8][((c)[GRN]*NGRN)>>8][((c)[BLU]*NBLU)>>8]
                                /* initial color cube boundary */
static int      CLRCUBE[3][2] = {0,NRED,0,NGRN,0,NBLU};
                                /* maximum propagated error during dithering */
#define MAXERR          20
                                /* define CLOSEST to get closest colors */
#ifndef CLOSEST
#ifdef SPEED
#if  SPEED > 8
#define CLOSEST         1       /* this step takes a little longer */
#endif
#endif
#endif

static  cut(), mktabent(), closest(), addneigh(), setclosest();
static int      split();
static unsigned dist();


new_histo(n)            /* clear our histogram */
int     n;
{
        memset((void *)histo, '\0', sizeof(histo));
        return(0);
}


cnt_pixel(col)          /* add pixel to our histogram */
register BYTE   col[];
{
        cndx(col)++;
}


cnt_colrs(cs, n)                /* add a scanline to our histogram */
register COLR   *cs;
register int    n;
{
        while (n-- > 0) {
                cndx(cs[0])++;
                cs++;
        }
}


new_clrtab(ncolors)             /* make new color table using ncolors */
int     ncolors;
{
        if (ncolors < 1)
                return(0);
        if (ncolors > 256)
                ncolors = 256;
                                /* partition color space */
        cut(CLRCUBE, 0, ncolors);
#ifdef CLOSEST
        closest(ncolors);       /* ensure colors picked are closest */
#endif
                                /* reset dithering function */
        dith_colrs((BYTE *)NULL, (COLR *)NULL, 0);
                                /* return new color table size */
        return(ncolors);
}


int
map_pixel(col)                  /* get pixel for color */
register BYTE   col[];
{
    return(cndx(col));
}


map_colrs(bs, cs, n)            /* convert a scanline to color index values */
register BYTE   *bs;
register COLR   *cs;
register int    n;
{
        while (n-- > 0) {
                *bs++ = cndx(cs[0]);
                cs++;
        }
}


dith_colrs(bs, cs, n)           /* convert scanline to dithered index values */
register BYTE   *bs;
register COLR   *cs;
int     n;
{
        static short    (*cerr)[3] = NULL;
        static int      N = 0;
        int     err[3], errp[3];
        register int    x, i;

        if (n != N) {           /* get error propogation array */
                if (N) {
                        free((void *)cerr);
                        cerr = NULL;
                }
                if (n)
                        cerr = (short (*)[3])malloc(3*n*sizeof(short));
                if (cerr == NULL) {
                        N = 0;
                        map_colrs(bs, cs, n);
                        return;
                }
                N = n;
                memset((void *)cerr, '\0', 3*N*sizeof(short));
        }
        err[0] = err[1] = err[2] = 0;
        for (x = 0; x < n; x++) {
                for (i = 0; i < 3; i++) {       /* dither value */
                        errp[i] = err[i];
                        err[i] += cerr[x][i];
#ifdef MAXERR
                        if (err[i] > MAXERR) err[i] = MAXERR;
                        else if (err[i] < -MAXERR) err[i] = -MAXERR;
#endif
                        err[i] += cs[x][i];
                        if (err[i] < 0) err[i] = 0;
                        else if (err[i] > 255) err[i] = 255;
                }
                bs[x] = cndx(err);
                for (i = 0; i < 3; i++) {       /* propagate error */
                        err[i] -= clrtab[bs[x]][i];
                        err[i] /= 3;
                        cerr[x][i] = err[i] + errp[i];
                }
        }
}


static
cut(box, c0, c1)                        /* partition color space */
register int    box[3][2];
int     c0, c1;
{
        register int    branch;
        int     kb[3][2];
        
        if (c1-c0 <= 1) {               /* assign pixel */
                mktabent(c0, box);
                return;
        }
                                        /* split box */
        branch = split(box);
        memcpy((void *)kb, (void *)box, sizeof(kb));
                                                /* do left (lesser) branch */
        kb[prim(branch)][1] = part(branch);
        cut(kb, c0, (c0+c1)>>1);
                                                /* do right branch */
        kb[prim(branch)][0] = part(branch);
        kb[prim(branch)][1] = box[prim(branch)][1];
        cut(kb, (c0+c1)>>1, c1);
}


static int
split(box)                              /* find median cut for box */
register int    box[3][2];
{
#define c0      r
        register int    r, g, b;
        int     pri;
        long    t[HMAX], med;
                                        /* find dominant axis */
        pri = RED;
        if (box[GRN][1]-box[GRN][0] > box[pri][1]-box[pri][0])
                pri = GRN;
        if (box[BLU][1]-box[BLU][0] > box[pri][1]-box[pri][0])
                pri = BLU;
                                        /* sum histogram over box */
        med = 0;
        switch (pri) {
        case RED:
                for (r = box[RED][0]; r < box[RED][1]; r++) {
                        t[r] = 0;
                        for (g = box[GRN][0]; g < box[GRN][1]; g++)
                                for (b = box[BLU][0]; b < box[BLU][1]; b++)
                                        t[r] += histo[r][g][b];
                        med += t[r];
                }
                break;
        case GRN:
                for (g = box[GRN][0]; g < box[GRN][1]; g++) {
                        t[g] = 0;
                        for (b = box[BLU][0]; b < box[BLU][1]; b++)
                                for (r = box[RED][0]; r < box[RED][1]; r++)
                                        t[g] += histo[r][g][b];
                        med += t[g];
                }
                break;
        case BLU:
                for (b = box[BLU][0]; b < box[BLU][1]; b++) {
                        t[b] = 0;
                        for (r = box[RED][0]; r < box[RED][1]; r++)
                                for (g = box[GRN][0]; g < box[GRN][1]; g++)
                                        t[b] += histo[r][g][b];
                        med += t[b];
                }
                break;
        }
        if (med < MINSAMP)              /* if too sparse, split at midpoint */
                return(set_branch(pri,(box[pri][0]+box[pri][1])>>1));
                                        /* find median position */
        med >>= 1;
        for (c0 = box[pri][0]; med > 0; c0++)
                med -= t[c0];
        if (c0 > (box[pri][0]+box[pri][1])>>1)  /* if past the midpoint */
                c0--;                           /* part left of median */
        return(set_branch(pri,c0));
#undef c0
}


static
mktabent(p, box)        /* compute average color for box and assign */
int     p;
register int    box[3][2];
{
        unsigned long   sum[3];
        unsigned        r, g;
        unsigned long   n;
        register unsigned       b, c;
                                                /* sum pixels in box */
        n = 0;
        sum[RED] = sum[GRN] = sum[BLU] = 0;
        for (r = box[RED][0]; r < box[RED][1]; r++)
            for (g = box[GRN][0]; g < box[GRN][1]; g++)
                for (b = box[BLU][0]; b < box[BLU][1]; b++) {
                    if ( (c = histo[r][g][b]) ) {
                        n += c;
                        sum[RED] += (long)c*r;
                        sum[GRN] += (long)c*g;
                        sum[BLU] += (long)c*b;
                    }
                    histo[r][g][b] = p;         /* assign pixel */
                }
        if (n >= (1L<<23)/HMAX) {               /* avoid overflow */
                sum[RED] /= n;
                sum[GRN] /= n;
                sum[BLU] /= n;
                n = 1;
        }
        if (n) {                                /* compute average */
                clrtab[p][RED] = sum[RED]*256/NRED/n;
                clrtab[p][GRN] = sum[GRN]*256/NGRN/n;
                clrtab[p][BLU] = sum[BLU]*256/NBLU/n;
        } else {                                /* empty box -- use midpoint */
                clrtab[p][RED] = (box[RED][0]+box[RED][1])*256/NRED/2;
                clrtab[p][GRN] = (box[GRN][0]+box[GRN][1])*256/NGRN/2;
                clrtab[p][BLU] = (box[BLU][0]+box[BLU][1])*256/NBLU/2;
        }
}


#ifdef CLOSEST
#define NBSIZ           32
static
closest(n)                      /* make sure we have the closest colors */
int     n;
{
        BYTE    *neigh[256];
        register int    r, g, b;
#define i r
                                        /* get space for neighbor lists */
        for (i = 0; i < n; i++) {
                if ((neigh[i] = (BYTE *)malloc(NBSIZ)) == NULL) {
                        while (i--)
                                free(neigh[i]);
                        return;                 /* ENOMEM -- abandon effort */
                }
                neigh[i][0] = i;                /* identity is terminator */
        }
                                        /* make neighbor lists */
        for (r = 0; r < NRED; r++)
            for (g = 0; g < NGRN; g++)
                for (b = 0; b < NBLU; b++) {
                    if (r < NRED-1 && histo[r][g][b] != histo[r+1][g][b])
                        addneigh(neigh, histo[r][g][b], histo[r+1][g][b]);
                    if (g < NGRN-1 && histo[r][g][b] != histo[r][g+1][b])
                        addneigh(neigh, histo[r][g][b], histo[r][g+1][b]);
                    if (b < NBLU-1 && histo[r][g][b] != histo[r][g][b+1])
                        addneigh(neigh, histo[r][g][b], histo[r][g][b+1]);
                }
                                        /* assign closest values */
        for (r = 0; r < NRED; r++)
            for (g = 0; g < NGRN; g++)
                for (b = 0; b < NBLU; b++)
                    setclosest(neigh, r, g, b);
                                        /* free neighbor lists */
        for (i = 0; i < n; i++)
                free(neigh[i]);
#undef i
}


static
addneigh(nl, i, j)              /* i and j are neighbors; add them to list */
register BYTE   *nl[];
register int    i;
int     j;
{
        int     nc;
        char    *nnl;
        register int    t;
        
        for (nc = 0; nc < 2; nc++) {            /* do both neighbors */
                for (t = 0; nl[i][t] != i; t++)
                        if (nl[i][t] == j)
                                break;          /* in list already */
                if (nl[i][t] == i) {            /* add to list */
                        nl[i][t++] = j;
                        if (t % NBSIZ == 0) {   /* enlarge list */
                                if ((nnl = realloc((void *)nl[i],
                                                t+NBSIZ)) == NULL)
                                        t--;
                                else
                                        nl[i] = (BYTE *)nnl;
                        }
                        nl[i][t] = i;           /* terminator */
                }
                t = i; i = j; j = t;            /* swap and do it again */
        }
}


static unsigned
dist(col, r, g, b)              /* find distance from clrtab entry to r,g,b */
register BYTE   col[3];
int     r, g, b;
{
        register int    tmp;
        register unsigned       sum;
        
        tmp = col[RED]*NRED/256 - r;
        sum = tmp*tmp;
        tmp = col[GRN]*NGRN/256 - g;
        sum += tmp*tmp;
        tmp = col[BLU]*NBLU/256 - b;
        sum += tmp*tmp;
        return(sum);
}


static
setclosest(nl, r, g, b)         /* find index closest to color and assign */
BYTE    *nl[];
int     r, g, b;
{
        int     ident;
        unsigned        min;
        register unsigned       d;
        register BYTE   *p;
                                        /* get starting value */
        min = dist(clrtab[ident=histo[r][g][b]], r, g, b);
                                        /* find minimum */
        for (p = nl[ident]; *p != ident; p++)
                if ((d = dist(clrtab[*p], r, g, b)) < min) {
                        min = d;
                        histo[r][g][b] = *p;
                }
}
#endif
Revision:	2.16
Committed:	Sun Jul 27 22:12:03 2003 UTC (20 years, 9 months ago) by schorsch
Content type:	text/plain
Branch:	MAIN
Changes since 2.15:	+2 -2 lines
Log Message:	Added grouping parens to reduce ambiguity warnings.
#	User	Rev	Content
1	greg	2.1	#ifndef lint
2	schorsch	2.16	static const char RCSid[] = "$Id: clrtab.c,v 2.15 2003/06/30 14:59:12 schorsch Exp $";
3	greg	2.1	#endif
4			/*
5			* Simple median-cut color quantization based on colortab.c
6			*/
7
8	schorsch	2.15	#include "copyright.h"
9
10			#include <string.h>
11
12	greg	2.1	#include "standard.h"
13	schorsch	2.15	#include "color.h"
14	greg	2.1
15			/* histogram resolution */
16			#define NRED 36
17			#define NGRN 48
18			#define NBLU 24
19			#define HMAX NGRN
20			/* minimum box count for adaptive partition */
21			#define MINSAMP 7
22			/* color partition */
23			#define set_branch(p,c) ((c)<<2\|(p))
24			#define part(cn) ((cn)>>2)
25			#define prim(cn) ((cn)&3)
26			/* our color table (global) */
27	greg	2.10	extern BYTE clrtab[256][3];
28	greg	2.1	/* histogram of colors / color assignments */
29			static unsigned histo[NRED][NGRN][NBLU];
30			#define cndx(c) histo[((c)[RED]NRED)>>8][((c)[GRN]NGRN)>>8][((c)[BLU]*NBLU)>>8]
31			/* initial color cube boundary */
32			static int CLRCUBE[3][2] = {0,NRED,0,NGRN,0,NBLU};
33			/* maximum propagated error during dithering */
34			#define MAXERR 20
35	greg	2.2	/* define CLOSEST to get closest colors */
36	greg	2.4	#ifndef CLOSEST
37			#ifdef SPEED
38			#if SPEED > 8
39			#define CLOSEST 1 /* this step takes a little longer */
40			#endif
41			#endif
42			#endif
43	greg	2.1
44	greg	2.11	static cut(), mktabent(), closest(), addneigh(), setclosest();
45			static int split();
46			static unsigned dist();
47
48	greg	2.1
49	greg	2.10	new_histo(n) /* clear our histogram */
50			int n;
51	greg	2.1	{
52	schorsch	2.15	memset((void *)histo, '\0', sizeof(histo));
53	greg	2.10	return(0);
54	greg	2.1	}
55
56
57			cnt_pixel(col) /* add pixel to our histogram */
58			register BYTE col[];
59			{
60			cndx(col)++;
61			}
62
63
64			cnt_colrs(cs, n) /* add a scanline to our histogram */
65			register COLR *cs;
66			register int n;
67			{
68			while (n-- > 0) {
69			cndx(cs[0])++;
70			cs++;
71			}
72			}
73
74
75			new_clrtab(ncolors) /* make new color table using ncolors */
76			int ncolors;
77			{
78			if (ncolors < 1)
79			return(0);
80			if (ncolors > 256)
81			ncolors = 256;
82			/* partition color space */
83			cut(CLRCUBE, 0, ncolors);
84	greg	2.2	#ifdef CLOSEST
85			closest(ncolors); /* ensure colors picked are closest */
86			#endif
87	greg	2.9	/* reset dithering function */
88			dith_colrs((BYTE )NULL, (COLR )NULL, 0);
89	greg	2.1	/* return new color table size */
90			return(ncolors);
91			}
92
93
94			int
95			map_pixel(col) /* get pixel for color */
96			register BYTE col[];
97			{
98			return(cndx(col));
99			}
100
101
102			map_colrs(bs, cs, n) /* convert a scanline to color index values */
103			register BYTE *bs;
104			register COLR *cs;
105			register int n;
106			{
107			while (n-- > 0) {
108			*bs++ = cndx(cs[0]);
109			cs++;
110			}
111			}
112
113
114			dith_colrs(bs, cs, n) /* convert scanline to dithered index values */
115			register BYTE *bs;
116			register COLR *cs;
117			int n;
118			{
119	greg	2.8	static short (*cerr)[3] = NULL;
120	greg	2.1	static int N = 0;
121			int err[3], errp[3];
122			register int x, i;
123
124			if (n != N) { /* get error propogation array */
125	greg	2.8	if (N) {
126	greg	2.12	free((void *)cerr);
127	greg	2.8	cerr = NULL;
128			}
129			if (n)
130	greg	2.1	cerr = (short ()[3])malloc(3n*sizeof(short));
131			if (cerr == NULL) {
132			N = 0;
133			map_colrs(bs, cs, n);
134			return;
135			}
136			N = n;
137	schorsch	2.15	memset((void )cerr, '\0', 3N*sizeof(short));
138	greg	2.1	}
139			err[0] = err[1] = err[2] = 0;
140			for (x = 0; x < n; x++) {
141			for (i = 0; i < 3; i++) { /* dither value */
142			errp[i] = err[i];
143			err[i] += cerr[x][i];
144			#ifdef MAXERR
145			if (err[i] > MAXERR) err[i] = MAXERR;
146			else if (err[i] < -MAXERR) err[i] = -MAXERR;
147			#endif
148			err[i] += cs[x][i];
149			if (err[i] < 0) err[i] = 0;
150			else if (err[i] > 255) err[i] = 255;
151			}
152			bs[x] = cndx(err);
153			for (i = 0; i < 3; i++) { /* propagate error */
154			err[i] -= clrtab[bs[x]][i];
155			err[i] /= 3;
156			cerr[x][i] = err[i] + errp[i];
157			}
158			}
159			}
160
161
162			static
163			cut(box, c0, c1) /* partition color space */
164			register int box[3][2];
165			int c0, c1;
166			{
167			register int branch;
168			int kb[3][2];
169
170			if (c1-c0 <= 1) { /* assign pixel */
171			mktabent(c0, box);
172			return;
173			}
174			/* split box */
175			branch = split(box);
176	schorsch	2.15	memcpy((void )kb, (void )box, sizeof(kb));
177	greg	2.1	/* do left (lesser) branch */
178			kb[prim(branch)][1] = part(branch);
179			cut(kb, c0, (c0+c1)>>1);
180			/* do right branch */
181			kb[prim(branch)][0] = part(branch);
182			kb[prim(branch)][1] = box[prim(branch)][1];
183			cut(kb, (c0+c1)>>1, c1);
184			}
185
186
187			static int
188			split(box) /* find median cut for box */
189			register int box[3][2];
190			{
191			#define c0 r
192			register int r, g, b;
193			int pri;
194	greg	2.6	long t[HMAX], med;
195	greg	2.1	/* find dominant axis */
196			pri = RED;
197			if (box[GRN][1]-box[GRN][0] > box[pri][1]-box[pri][0])
198			pri = GRN;
199			if (box[BLU][1]-box[BLU][0] > box[pri][1]-box[pri][0])
200			pri = BLU;
201			/* sum histogram over box */
202			med = 0;
203			switch (pri) {
204			case RED:
205			for (r = box[RED][0]; r < box[RED][1]; r++) {
206			t[r] = 0;
207			for (g = box[GRN][0]; g < box[GRN][1]; g++)
208			for (b = box[BLU][0]; b < box[BLU][1]; b++)
209			t[r] += histo[r][g][b];
210			med += t[r];
211			}
212			break;
213			case GRN:
214			for (g = box[GRN][0]; g < box[GRN][1]; g++) {
215			t[g] = 0;
216			for (b = box[BLU][0]; b < box[BLU][1]; b++)
217			for (r = box[RED][0]; r < box[RED][1]; r++)
218			t[g] += histo[r][g][b];
219			med += t[g];
220			}
221			break;
222			case BLU:
223			for (b = box[BLU][0]; b < box[BLU][1]; b++) {
224			t[b] = 0;
225			for (r = box[RED][0]; r < box[RED][1]; r++)
226			for (g = box[GRN][0]; g < box[GRN][1]; g++)
227			t[b] += histo[r][g][b];
228			med += t[b];
229			}
230			break;
231			}
232			if (med < MINSAMP) /* if too sparse, split at midpoint */
233			return(set_branch(pri,(box[pri][0]+box[pri][1])>>1));
234			/* find median position */
235			med >>= 1;
236			for (c0 = box[pri][0]; med > 0; c0++)
237			med -= t[c0];
238			if (c0 > (box[pri][0]+box[pri][1])>>1) /* if past the midpoint */
239			c0--; /* part left of median */
240			return(set_branch(pri,c0));
241			#undef c0
242			}
243
244
245			static
246			mktabent(p, box) /* compute average color for box and assign */
247			int p;
248			register int box[3][2];
249			{
250	greg	2.5	unsigned long sum[3];
251	greg	2.7	unsigned r, g;
252			unsigned long n;
253	greg	2.5	register unsigned b, c;
254	greg	2.1	/* sum pixels in box */
255			n = 0;
256			sum[RED] = sum[GRN] = sum[BLU] = 0;
257			for (r = box[RED][0]; r < box[RED][1]; r++)
258			for (g = box[GRN][0]; g < box[GRN][1]; g++)
259			for (b = box[BLU][0]; b < box[BLU][1]; b++) {
260	schorsch	2.16	if ( (c = histo[r][g][b]) ) {
261	greg	2.1	n += c;
262			sum[RED] += (long)c*r;
263			sum[GRN] += (long)c*g;
264			sum[BLU] += (long)c*b;
265			}
266			histo[r][g][b] = p; /* assign pixel */
267			}
268	greg	2.7	if (n >= (1L<<23)/HMAX) { /* avoid overflow */
269	greg	2.5	sum[RED] /= n;
270			sum[GRN] /= n;
271			sum[BLU] /= n;
272			n = 1;
273			}
274	greg	2.1	if (n) { /* compute average */
275			clrtab[p][RED] = sum[RED]*256/NRED/n;
276			clrtab[p][GRN] = sum[GRN]*256/NGRN/n;
277			clrtab[p][BLU] = sum[BLU]*256/NBLU/n;
278			} else { /* empty box -- use midpoint */
279			clrtab[p][RED] = (box[RED][0]+box[RED][1])*256/NRED/2;
280			clrtab[p][GRN] = (box[GRN][0]+box[GRN][1])*256/NGRN/2;
281			clrtab[p][BLU] = (box[BLU][0]+box[BLU][1])*256/NBLU/2;
282			}
283			}
284	greg	2.2
285
286			#ifdef CLOSEST
287			#define NBSIZ 32
288			static
289			closest(n) /* make sure we have the closest colors */
290			int n;
291			{
292			BYTE *neigh[256];
293			register int r, g, b;
294			#define i r
295			/* get space for neighbor lists */
296			for (i = 0; i < n; i++) {
297			if ((neigh[i] = (BYTE *)malloc(NBSIZ)) == NULL) {
298			while (i--)
299			free(neigh[i]);
300			return; /* ENOMEM -- abandon effort */
301			}
302			neigh[i][0] = i; /* identity is terminator */
303			}
304			/* make neighbor lists */
305	greg	2.3	for (r = 0; r < NRED; r++)
306			for (g = 0; g < NGRN; g++)
307			for (b = 0; b < NBLU; b++) {
308			if (r < NRED-1 && histo[r][g][b] != histo[r+1][g][b])
309	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r+1][g][b]);
310	greg	2.3	if (g < NGRN-1 && histo[r][g][b] != histo[r][g+1][b])
311	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r][g+1][b]);
312	greg	2.3	if (b < NBLU-1 && histo[r][g][b] != histo[r][g][b+1])
313	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r][g][b+1]);
314			}
315			/* assign closest values */
316			for (r = 0; r < NRED; r++)
317			for (g = 0; g < NGRN; g++)
318			for (b = 0; b < NBLU; b++)
319			setclosest(neigh, r, g, b);
320			/* free neighbor lists */
321			for (i = 0; i < n; i++)
322			free(neigh[i]);
323			#undef i
324			}
325
326
327			static
328			addneigh(nl, i, j) /* i and j are neighbors; add them to list */
329			register BYTE *nl[];
330			register int i;
331			int j;
332			{
333			int nc;
334			char *nnl;
335			register int t;
336
337			for (nc = 0; nc < 2; nc++) { /* do both neighbors */
338			for (t = 0; nl[i][t] != i; t++)
339			if (nl[i][t] == j)
340			break; /* in list already */
341			if (nl[i][t] == i) { /* add to list */
342			nl[i][t++] = j;
343			if (t % NBSIZ == 0) { /* enlarge list */
344	greg	2.13	if ((nnl = realloc((void *)nl[i],
345			t+NBSIZ)) == NULL)
346	greg	2.2	t--;
347			else
348			nl[i] = (BYTE *)nnl;
349			}
350			nl[i][t] = i; /* terminator */
351			}
352			t = i; i = j; j = t; /* swap and do it again */
353			}
354			}
355
356
357			static unsigned
358			dist(col, r, g, b) /* find distance from clrtab entry to r,g,b */
359			register BYTE col[3];
360			int r, g, b;
361			{
362	greg	2.4	register int tmp;
363	greg	2.2	register unsigned sum;
364
365			tmp = col[RED]*NRED/256 - r;
366			sum = tmp*tmp;
367			tmp = col[GRN]*NGRN/256 - g;
368			sum += tmp*tmp;
369			tmp = col[BLU]*NBLU/256 - b;
370			sum += tmp*tmp;
371			return(sum);
372			}
373
374
375			static
376			setclosest(nl, r, g, b) /* find index closest to color and assign */
377			BYTE *nl[];
378			int r, g, b;
379			{
380			int ident;
381			unsigned min;
382			register unsigned d;
383			register BYTE *p;
384			/* get starting value */
385			min = dist(clrtab[ident=histo[r][g][b]], r, g, b);
386			/* find minimum */
387			for (p = nl[ident]; *p != ident; p++)
388			if ((d = dist(clrtab[*p], r, g, b)) < min) {
389			min = d;
390			histo[r][g][b] = *p;
391			}
392			}
393			#endif