src/px/clrtab.c

#ifndef lint
static const char       RCSid[] = "$Id: clrtab.c,v 2.16 2003/07/27 22:12:03 schorsch Exp $";
#endif
/*
 * Simple median-cut color quantization based on colortab.c
 */

#include "copyright.h"

#include <string.h>

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


#ifdef CLOSEST
static void closest(int n);
static void setclosest(BYTE *nl[], int r, int g, int b);
static void addneigh(BYTE *nl[], int i, int j);
static unsigned int dist(BYTE col[3], int r, int g, int b);
#endif
static void cut(int box[3][2], int c0, int c1);
static int split(int box[3][2]);
static void mktabent(int p, int box[3][2]);


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


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


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


extern int
new_clrtab(             /* 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);
}


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


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


extern void
dith_colrs(             /* 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 void
cut(                    /* partition color space */
        register int    box[3][2],
        int     c0,
        int     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(                          /* 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 void
mktabent(       /* 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 void
closest(                        /* 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 void
addneigh(               /* 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 int
dist(           /* find distance from clrtab entry to r,g,b */
        register BYTE   col[3],
        int     r,
        int     g,
        int     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 void
setclosest(             /* find index closest to color and assign */
        BYTE    *nl[],
        int     r,
        int     g,
        int     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:	2.17
Committed:	Sun Mar 28 20:33:13 2004 UTC (20 years, 1 month ago) by schorsch
Content type:	text/plain
Branch:	MAIN
CVS Tags:	rad3R7P2, rad3R7P1, rad3R6, rad3R6P1
Changes since 2.16:	+84 -51 lines
Log Message:	Continued ANSIfication, and other fixes and clarifications.
#	User	Rev	Content
1	greg	2.1	#ifndef lint
2	schorsch	2.17	static const char RCSid[] = "$Id: clrtab.c,v 2.16 2003/07/27 22:12:03 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	schorsch	2.17	#include "clrtab.h"
15	greg	2.1
16			/* histogram resolution */
17			#define NRED 36
18			#define NGRN 48
19			#define NBLU 24
20			#define HMAX NGRN
21			/* minimum box count for adaptive partition */
22			#define MINSAMP 7
23			/* color partition */
24			#define set_branch(p,c) ((c)<<2\|(p))
25			#define part(cn) ((cn)>>2)
26			#define prim(cn) ((cn)&3)
27			/* our color table (global) */
28	greg	2.10	extern BYTE clrtab[256][3];
29	greg	2.1	/* histogram of colors / color assignments */
30			static unsigned histo[NRED][NGRN][NBLU];
31			#define cndx(c) histo[((c)[RED]NRED)>>8][((c)[GRN]NGRN)>>8][((c)[BLU]*NBLU)>>8]
32			/* initial color cube boundary */
33	schorsch	2.17	static int CLRCUBE[3][2] = {{0,NRED},{0,NGRN},{0,NBLU}};
34	greg	2.1	/* maximum propagated error during dithering */
35			#define MAXERR 20
36	greg	2.2	/* define CLOSEST to get closest colors */
37	greg	2.4	#ifndef CLOSEST
38			#ifdef SPEED
39			#if SPEED > 8
40			#define CLOSEST 1 /* this step takes a little longer */
41			#endif
42			#endif
43			#endif
44	greg	2.1
45	schorsch	2.17
46			#ifdef CLOSEST
47			static void closest(int n);
48			static void setclosest(BYTE *nl[], int r, int g, int b);
49			static void addneigh(BYTE *nl[], int i, int j);
50			static unsigned int dist(BYTE col[3], int r, int g, int b);
51			#endif
52			static void cut(int box[3][2], int c0, int c1);
53			static int split(int box[3][2]);
54			static void mktabent(int p, int box[3][2]);
55	greg	2.11
56	greg	2.1
57	schorsch	2.17	extern int
58			new_histo( /* clear our histogram */
59			int n
60			)
61	greg	2.1	{
62	schorsch	2.15	memset((void *)histo, '\0', sizeof(histo));
63	greg	2.10	return(0);
64	greg	2.1	}
65
66
67	schorsch	2.17	extern void
68			cnt_pixel( /* add pixel to our histogram */
69			register BYTE col[]
70			)
71	greg	2.1	{
72			cndx(col)++;
73			}
74
75
76	schorsch	2.17	extern void
77			cnt_colrs( /* add a scanline to our histogram */
78			register COLR *cs,
79			register int n
80			)
81	greg	2.1	{
82			while (n-- > 0) {
83			cndx(cs[0])++;
84			cs++;
85			}
86			}
87
88
89	schorsch	2.17	extern int
90			new_clrtab( /* make new color table using ncolors */
91			int ncolors
92			)
93	greg	2.1	{
94			if (ncolors < 1)
95			return(0);
96			if (ncolors > 256)
97			ncolors = 256;
98			/* partition color space */
99			cut(CLRCUBE, 0, ncolors);
100	greg	2.2	#ifdef CLOSEST
101			closest(ncolors); /* ensure colors picked are closest */
102			#endif
103	greg	2.9	/* reset dithering function */
104			dith_colrs((BYTE )NULL, (COLR )NULL, 0);
105	greg	2.1	/* return new color table size */
106			return(ncolors);
107			}
108
109
110	schorsch	2.17	extern int
111			map_pixel( /* get pixel for color */
112			register BYTE col[]
113			)
114	greg	2.1	{
115			return(cndx(col));
116			}
117
118
119	schorsch	2.17	extern void
120			map_colrs( /* convert a scanline to color index values */
121			register BYTE *bs,
122			register COLR *cs,
123			register int n
124			)
125	greg	2.1	{
126			while (n-- > 0) {
127			*bs++ = cndx(cs[0]);
128			cs++;
129			}
130			}
131
132
133	schorsch	2.17	extern void
134			dith_colrs( /* convert scanline to dithered index values */
135			register BYTE *bs,
136			register COLR *cs,
137			int n
138			)
139	greg	2.1	{
140	greg	2.8	static short (*cerr)[3] = NULL;
141	greg	2.1	static int N = 0;
142			int err[3], errp[3];
143			register int x, i;
144
145			if (n != N) { /* get error propogation array */
146	greg	2.8	if (N) {
147	greg	2.12	free((void *)cerr);
148	greg	2.8	cerr = NULL;
149			}
150			if (n)
151	greg	2.1	cerr = (short ()[3])malloc(3n*sizeof(short));
152			if (cerr == NULL) {
153			N = 0;
154			map_colrs(bs, cs, n);
155			return;
156			}
157			N = n;
158	schorsch	2.15	memset((void )cerr, '\0', 3N*sizeof(short));
159	greg	2.1	}
160			err[0] = err[1] = err[2] = 0;
161			for (x = 0; x < n; x++) {
162			for (i = 0; i < 3; i++) { /* dither value */
163			errp[i] = err[i];
164			err[i] += cerr[x][i];
165			#ifdef MAXERR
166			if (err[i] > MAXERR) err[i] = MAXERR;
167			else if (err[i] < -MAXERR) err[i] = -MAXERR;
168			#endif
169			err[i] += cs[x][i];
170			if (err[i] < 0) err[i] = 0;
171			else if (err[i] > 255) err[i] = 255;
172			}
173			bs[x] = cndx(err);
174			for (i = 0; i < 3; i++) { /* propagate error */
175			err[i] -= clrtab[bs[x]][i];
176			err[i] /= 3;
177			cerr[x][i] = err[i] + errp[i];
178			}
179			}
180			}
181
182
183	schorsch	2.17	static void
184			cut( /* partition color space */
185			register int box[3][2],
186			int c0,
187			int c1
188			)
189	greg	2.1	{
190			register int branch;
191			int kb[3][2];
192
193			if (c1-c0 <= 1) { /* assign pixel */
194			mktabent(c0, box);
195			return;
196			}
197			/* split box */
198			branch = split(box);
199	schorsch	2.15	memcpy((void )kb, (void )box, sizeof(kb));
200	greg	2.1	/* do left (lesser) branch */
201			kb[prim(branch)][1] = part(branch);
202			cut(kb, c0, (c0+c1)>>1);
203			/* do right branch */
204			kb[prim(branch)][0] = part(branch);
205			kb[prim(branch)][1] = box[prim(branch)][1];
206			cut(kb, (c0+c1)>>1, c1);
207			}
208
209
210			static int
211	schorsch	2.17	split( /* find median cut for box */
212			register int box[3][2]
213			)
214	greg	2.1	{
215			#define c0 r
216			register int r, g, b;
217			int pri;
218	greg	2.6	long t[HMAX], med;
219	greg	2.1	/* find dominant axis */
220			pri = RED;
221			if (box[GRN][1]-box[GRN][0] > box[pri][1]-box[pri][0])
222			pri = GRN;
223			if (box[BLU][1]-box[BLU][0] > box[pri][1]-box[pri][0])
224			pri = BLU;
225			/* sum histogram over box */
226			med = 0;
227			switch (pri) {
228			case RED:
229			for (r = box[RED][0]; r < box[RED][1]; r++) {
230			t[r] = 0;
231			for (g = box[GRN][0]; g < box[GRN][1]; g++)
232			for (b = box[BLU][0]; b < box[BLU][1]; b++)
233			t[r] += histo[r][g][b];
234			med += t[r];
235			}
236			break;
237			case GRN:
238			for (g = box[GRN][0]; g < box[GRN][1]; g++) {
239			t[g] = 0;
240			for (b = box[BLU][0]; b < box[BLU][1]; b++)
241			for (r = box[RED][0]; r < box[RED][1]; r++)
242			t[g] += histo[r][g][b];
243			med += t[g];
244			}
245			break;
246			case BLU:
247			for (b = box[BLU][0]; b < box[BLU][1]; b++) {
248			t[b] = 0;
249			for (r = box[RED][0]; r < box[RED][1]; r++)
250			for (g = box[GRN][0]; g < box[GRN][1]; g++)
251			t[b] += histo[r][g][b];
252			med += t[b];
253			}
254			break;
255			}
256			if (med < MINSAMP) /* if too sparse, split at midpoint */
257			return(set_branch(pri,(box[pri][0]+box[pri][1])>>1));
258			/* find median position */
259			med >>= 1;
260			for (c0 = box[pri][0]; med > 0; c0++)
261			med -= t[c0];
262			if (c0 > (box[pri][0]+box[pri][1])>>1) /* if past the midpoint */
263			c0--; /* part left of median */
264			return(set_branch(pri,c0));
265			#undef c0
266			}
267
268
269	schorsch	2.17	static void
270			mktabent( /* compute average color for box and assign */
271			int p,
272			register int box[3][2]
273			)
274	greg	2.1	{
275	greg	2.5	unsigned long sum[3];
276	greg	2.7	unsigned r, g;
277			unsigned long n;
278	greg	2.5	register unsigned b, c;
279	greg	2.1	/* sum pixels in box */
280			n = 0;
281			sum[RED] = sum[GRN] = sum[BLU] = 0;
282			for (r = box[RED][0]; r < box[RED][1]; r++)
283			for (g = box[GRN][0]; g < box[GRN][1]; g++)
284			for (b = box[BLU][0]; b < box[BLU][1]; b++) {
285	schorsch	2.16	if ( (c = histo[r][g][b]) ) {
286	greg	2.1	n += c;
287			sum[RED] += (long)c*r;
288			sum[GRN] += (long)c*g;
289			sum[BLU] += (long)c*b;
290			}
291			histo[r][g][b] = p; /* assign pixel */
292			}
293	greg	2.7	if (n >= (1L<<23)/HMAX) { /* avoid overflow */
294	greg	2.5	sum[RED] /= n;
295			sum[GRN] /= n;
296			sum[BLU] /= n;
297			n = 1;
298			}
299	greg	2.1	if (n) { /* compute average */
300			clrtab[p][RED] = sum[RED]*256/NRED/n;
301			clrtab[p][GRN] = sum[GRN]*256/NGRN/n;
302			clrtab[p][BLU] = sum[BLU]*256/NBLU/n;
303			} else { /* empty box -- use midpoint */
304			clrtab[p][RED] = (box[RED][0]+box[RED][1])*256/NRED/2;
305			clrtab[p][GRN] = (box[GRN][0]+box[GRN][1])*256/NGRN/2;
306			clrtab[p][BLU] = (box[BLU][0]+box[BLU][1])*256/NBLU/2;
307			}
308			}
309	greg	2.2
310
311			#ifdef CLOSEST
312			#define NBSIZ 32
313	schorsch	2.17	static void
314			closest( /* make sure we have the closest colors */
315			int n
316			)
317	greg	2.2	{
318			BYTE *neigh[256];
319			register int r, g, b;
320			#define i r
321			/* get space for neighbor lists */
322			for (i = 0; i < n; i++) {
323			if ((neigh[i] = (BYTE *)malloc(NBSIZ)) == NULL) {
324			while (i--)
325			free(neigh[i]);
326			return; /* ENOMEM -- abandon effort */
327			}
328			neigh[i][0] = i; /* identity is terminator */
329			}
330			/* make neighbor lists */
331	greg	2.3	for (r = 0; r < NRED; r++)
332			for (g = 0; g < NGRN; g++)
333			for (b = 0; b < NBLU; b++) {
334			if (r < NRED-1 && histo[r][g][b] != histo[r+1][g][b])
335	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r+1][g][b]);
336	greg	2.3	if (g < NGRN-1 && histo[r][g][b] != histo[r][g+1][b])
337	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r][g+1][b]);
338	greg	2.3	if (b < NBLU-1 && histo[r][g][b] != histo[r][g][b+1])
339	greg	2.2	addneigh(neigh, histo[r][g][b], histo[r][g][b+1]);
340			}
341			/* assign closest values */
342			for (r = 0; r < NRED; r++)
343			for (g = 0; g < NGRN; g++)
344			for (b = 0; b < NBLU; b++)
345			setclosest(neigh, r, g, b);
346			/* free neighbor lists */
347			for (i = 0; i < n; i++)
348			free(neigh[i]);
349			#undef i
350			}
351
352
353	schorsch	2.17	static void
354			addneigh( /* i and j are neighbors; add them to list */
355			register BYTE *nl[],
356			register int i,
357			int j
358			)
359	greg	2.2	{
360			int nc;
361			char *nnl;
362			register int t;
363
364			for (nc = 0; nc < 2; nc++) { /* do both neighbors */
365			for (t = 0; nl[i][t] != i; t++)
366			if (nl[i][t] == j)
367			break; /* in list already */
368			if (nl[i][t] == i) { /* add to list */
369			nl[i][t++] = j;
370			if (t % NBSIZ == 0) { /* enlarge list */
371	greg	2.13	if ((nnl = realloc((void *)nl[i],
372			t+NBSIZ)) == NULL)
373	greg	2.2	t--;
374			else
375			nl[i] = (BYTE *)nnl;
376			}
377			nl[i][t] = i; /* terminator */
378			}
379			t = i; i = j; j = t; /* swap and do it again */
380			}
381			}
382
383
384	schorsch	2.17	static unsigned int
385			dist( /* find distance from clrtab entry to r,g,b */
386			register BYTE col[3],
387			int r,
388			int g,
389			int b
390			)
391	greg	2.2	{
392	greg	2.4	register int tmp;
393	greg	2.2	register unsigned sum;
394
395			tmp = col[RED]*NRED/256 - r;
396			sum = tmp*tmp;
397			tmp = col[GRN]*NGRN/256 - g;
398			sum += tmp*tmp;
399			tmp = col[BLU]*NBLU/256 - b;
400			sum += tmp*tmp;
401			return(sum);
402			}
403
404
405	schorsch	2.17	static void
406			setclosest( /* find index closest to color and assign */
407			BYTE *nl[],
408			int r,
409			int g,
410			int b
411			)
412	greg	2.2	{
413			int ident;
414			unsigned min;
415			register unsigned d;
416			register BYTE *p;
417			/* get starting value */
418			min = dist(clrtab[ident=histo[r][g][b]], r, g, b);
419			/* find minimum */
420			for (p = nl[ident]; *p != ident; p++)
421			if ((d = dist(clrtab[*p], r, g, b)) < min) {
422			min = d;
423			histo[r][g][b] = *p;
424			}
425			}
426			#endif