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colortab.c
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Wed, Apr 2, 11:35

colortab.c
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#ifndef lint
static const char RCSid[] = "$Id: colortab.c,v 2.12 2016/03/18 22:52:05 schorsch Exp $";
#endif
/*
* colortab.c - allocate and control dynamic color table.
*
* We start off with a uniform partition of color space.
* As pixels are sent to the frame buffer, a histogram is built.
* When a new color table is requested, the histogram is used
* to make a pseudo-optimal partition, after which the
* histogram is cleared. This algorithm
* performs only as well as the next drawing's color
* distribution is correlated to the last.
*
* External symbols declared in drvier.h
*/
#include "copyright.h"
#include <string.h>
#include "standard.h"
#include "color.h"
#include "driver.h"
/* histogram resolution */
#define NRED 24
#define NGRN 32
#define NBLU 16
#define HMAX NGRN
/* minimum box count for adaptive partition */
#define MINSAMP 7
/* maximum distance^2 before color reassign */
#define MAXDST2 12
/* map a color */
#define map_col(c,p) clrmap[p][ colval(c,p)<1. ? \
(int)(colval(c,p)*256.) : 255 ]
/* color partition tree */
#define CNODE short
#define set_branch(p,c) ((c)<<2|(p))
#define set_pval(pv) ((pv)<<2|3)
#define is_branch(cn) (((cn)&3)!=3)
#define is_pval(cn) (((cn)&3)==3)
#define part(cn) ((cn)>>2)
#define prim(cn) ((cn)&3)
#define pval(cn) ((cn)>>2)
/* our color table */
static struct tabent {
long sum[3]; /* sum of colors using this entry */
int n; /* number of colors */
uby8 ent[3]; /* current table value */
} *clrtab = NULL;
/* color cube partition */
static CNODE *ctree = NULL;
/* our color correction map */
static uby8 clrmap[3][256];
/* histogram of colors used */
static unsigned short histo[NRED][NGRN][NBLU];
/* initial color cube boundary */
static int CLRCUBE[3][2] = {{0,NRED},{0,NGRN},{0,NBLU}};
static int split();
static void cut();
int
new_ctab(ncolors) /* start new color table with max ncolors */
int ncolors;
{
int treesize;
if (ncolors < 1)
return(0);
/* free old tables */
if (clrtab != NULL)
free((void *)clrtab);
if (ctree != NULL)
free((void *)ctree);
/* get new tables */
for (treesize = 1; treesize < ncolors; treesize <<= 1)
;
treesize <<= 1;
clrtab = (struct tabent *)calloc(ncolors, sizeof(struct tabent));
ctree = (CNODE *)malloc(treesize*sizeof(CNODE));
if (clrtab == NULL || ctree == NULL)
return(0);
/* partition color space */
cut(ctree, 0, CLRCUBE, 0, ncolors);
/* clear histogram */
memset((void *)histo, '\0', sizeof(histo));
/* return number of colors used */
return(ncolors);
}
int
get_pixel( /* get pixel for color */
COLOR col,
dr_newcolrf_t *newcolr
)
{
int r, g, b;
int cv[3];
CNODE *tp;
int h;
/* map color */
r = map_col(col,RED);
g = map_col(col,GRN);
b = map_col(col,BLU);
/* reduce resolution */
cv[RED] = (r*NRED)>>8;
cv[GRN] = (g*NGRN)>>8;
cv[BLU] = (b*NBLU)>>8;
/* add to histogram */
histo[cv[RED]][cv[GRN]][cv[BLU]]++;
/* find pixel in tree */
for (tp = ctree, h = 0; is_branch(*tp); h++)
if (cv[prim(*tp)] < part(*tp))
tp += (size_t)1<<h; /* left branch */
else
tp += (size_t)1<<(h+1); /* right branch */
h = pval(*tp);
/* add to color table */
clrtab[h].sum[RED] += r;
clrtab[h].sum[GRN] += g;
clrtab[h].sum[BLU] += b;
clrtab[h].n++;
/* recompute average */
r = clrtab[h].sum[RED] / clrtab[h].n;
g = clrtab[h].sum[GRN] / clrtab[h].n;
b = clrtab[h].sum[BLU] / clrtab[h].n;
/* check for movement */
if (clrtab[h].n == 1 ||
(r-clrtab[h].ent[RED])*(r-clrtab[h].ent[RED]) +
(g-clrtab[h].ent[GRN])*(g-clrtab[h].ent[GRN]) +
(b-clrtab[h].ent[BLU])*(b-clrtab[h].ent[BLU]) > MAXDST2) {
clrtab[h].ent[RED] = r;
clrtab[h].ent[GRN] = g; /* reassign pixel */
clrtab[h].ent[BLU] = b;
#ifdef DEBUG
sprintf(errmsg, "pixel %d = (%d,%d,%d) (%d refs)\n",
h, r, g, b, clrtab[h].n);
eputs(errmsg);
#endif
(*newcolr)(h, r, g, b);
}
return(h); /* return pixel value */
}
void
make_gmap(gam) /* make gamma correction map */
double gam;
{
int i;
for (i = 0; i < 256; i++)
clrmap[RED][i] =
clrmap[GRN][i] =
clrmap[BLU][i] = 256.0 * pow((i+0.5)/256.0, 1.0/gam);
}
void
set_cmap(rmap, gmap, bmap) /* set custom color correction map */
uby8 *rmap, *gmap, *bmap;
{
memcpy((void *)clrmap[RED], (void *)rmap, 256);
memcpy((void *)clrmap[GRN], (void *)gmap, 256);
memcpy((void *)clrmap[BLU], (void *)bmap, 256);
}
void
map_color(rgb, col) /* map a color to a byte triplet */
uby8 rgb[3];
COLOR col;
{
rgb[RED] = map_col(col,RED);
rgb[GRN] = map_col(col,GRN);
rgb[BLU] = map_col(col,BLU);
}
static void
cut(tree, level, box, c0, c1) /* partition color space */
CNODE *tree;
int level;
int box[3][2];
int c0, c1;
{
int kb[3][2];
if (c1-c0 <= 1) { /* assign pixel */
*tree = set_pval(c0);
return;
}
/* split box */
*tree = split(box);
memcpy((void *)kb, (void *)box, sizeof(kb));
/* do left (lesser) branch */
kb[prim(*tree)][1] = part(*tree);
cut(tree+((size_t)1<<level), level+1, kb, c0, (c0+c1)>>1);
/* do right branch */
kb[prim(*tree)][0] = part(*tree);
kb[prim(*tree)][1] = box[prim(*tree)][1];
cut(tree+((size_t)1<<(level+1)), level+1, kb, (c0+c1)>>1, c1);
}
static int
split(box) /* find median cut for box */
int box[3][2];
{
#define c0 r
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
}

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