-
-
Save bert/1192520 to your computer and use it in GitHub Desktop.
Wu's Color Quantizer
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Having received many constructive comments and bug reports about my previous | |
C implementation of my color quantizer (Graphics Gems vol. II, p. 126-133), | |
I am posting the following second version of my program (hopefully 100% | |
healthy) as a reply to all those who are interested in the problem. | |
/********************************************************************** | |
C Implementation of Wu's Color Quantizer (v. 2) | |
(see Graphics Gems vol. II, pp. 126-133) | |
Author: Xiaolin Wu | |
Dept. of Computer Science | |
Univ. of Western Ontario | |
London, Ontario N6A 5B7 | |
wu@csd.uwo.ca | |
Algorithm: Greedy orthogonal bipartition of RGB space for variance | |
minimization aided by inclusion-exclusion tricks. | |
For speed no nearest neighbor search is done. Slightly | |
better performance can be expected by more sophisticated | |
but more expensive versions. | |
The author thanks Tom Lane at Tom_Lane@G.GP.CS.CMU.EDU for much of | |
additional documentation and a cure to a previous bug. | |
Free to distribute, comments and suggestions are appreciated. | |
**********************************************************************/ | |
#include<stdio.h> | |
#define MAXCOLOR 256 | |
#define RED 2 | |
#define GREEN 1 | |
#define BLUE 0 | |
struct box { | |
int r0; /* min value, exclusive */ | |
int r1; /* max value, inclusive */ | |
int g0; | |
int g1; | |
int b0; | |
int b1; | |
int vol; | |
}; | |
/* Histogram is in elements 1..HISTSIZE along each axis, | |
* element 0 is for base or marginal value | |
* NB: these must start out 0! | |
*/ | |
float m2[33][33][33]; | |
long int wt[33][33][33], mr[33][33][33], mg[33][33][33], mb[33][33][33]; | |
unsigned char *Ir, *Ig, *Ib; | |
int size; /*image size*/ | |
int K; /*color look-up table size*/ | |
unsigned short int *Qadd; | |
void | |
Hist3d(vwt, vmr, vmg, vmb, m2) | |
/* build 3-D color histogram of counts, r/g/b, c^2 */ | |
long int *vwt, *vmr, *vmg, *vmb; | |
float *m2; | |
{ | |
register int ind, r, g, b; | |
int inr, ing, inb, table[256]; | |
register long int i; | |
for(i=0; i<256; ++i) table[i]=i*i; | |
Qadd = (unsigned short int *)malloc(sizeof(short int)*size); | |
if (Qadd==NULL) {printf("Not enough space\n"); exit(1);} | |
for(i=0; i<size; ++i){ | |
r = Ir[i]; g = Ig[i]; b = Ib[i]; | |
inr=(r>>3)+1; | |
ing=(g>>3)+1; | |
inb=(b>>3)+1; | |
Qadd[i]=ind=(inr<<10)+(inr<<6)+inr+(ing<<5)+ing+inb; | |
/*[inr][ing][inb]*/ | |
++vwt[ind]; | |
vmr[ind] += r; | |
vmg[ind] += g; | |
vmb[ind] += b; | |
m2[ind] += (float)(table[r]+table[g]+table[b]); | |
} | |
} | |
/* At conclusion of the histogram step, we can interpret | |
* wt[r][g][b] = sum over voxel of P(c) | |
* mr[r][g][b] = sum over voxel of r*P(c) , similarly for mg, mb | |
* m2[r][g][b] = sum over voxel of c^2*P(c) | |
* Actually each of these should be divided by 'size' to give the usual | |
* interpretation of P() as ranging from 0 to 1, but we needn't do that here. | |
*/ | |
/* We now convert histogram into moments so that we can rapidly calculate | |
* the sums of the above quantities over any desired box. | |
*/ | |
void | |
M3d(vwt, vmr, vmg, vmb, m2) /* compute cumulative moments. */ | |
long int *vwt, *vmr, *vmg, *vmb; | |
float *m2; | |
{ | |
register unsigned short int ind1, ind2; | |
register unsigned char i, r, g, b; | |
long int line, line_r, line_g, line_b, | |
area[33], area_r[33], area_g[33], area_b[33]; | |
float line2, area2[33]; | |
for(r=1; r<=32; ++r){ | |
for(i=0; i<=32; ++i) | |
area2[i]=area[i]=area_r[i]=area_g[i]=area_b[i]=0; | |
for(g=1; g<=32; ++g){ | |
line2 = line = line_r = line_g = line_b = 0; | |
for(b=1; b<=32; ++b){ | |
ind1 = (r<<10) + (r<<6) + r + (g<<5) + g + b; /* [r][g][b] */ | |
line += vwt[ind1]; | |
line_r += vmr[ind1]; | |
line_g += vmg[ind1]; | |
line_b += vmb[ind1]; | |
line2 += m2[ind1]; | |
area[b] += line; | |
area_r[b] += line_r; | |
area_g[b] += line_g; | |
area_b[b] += line_b; | |
area2[b] += line2; | |
ind2 = ind1 - 1089; /* [r-1][g][b] */ | |
vwt[ind1] = vwt[ind2] + area[b]; | |
vmr[ind1] = vmr[ind2] + area_r[b]; | |
vmg[ind1] = vmg[ind2] + area_g[b]; | |
vmb[ind1] = vmb[ind2] + area_b[b]; | |
m2[ind1] = m2[ind2] + area2[b]; | |
} | |
} | |
} | |
} | |
long int Vol(cube, mmt) | |
/* Compute sum over a box of any given statistic */ | |
struct box *cube; | |
long int mmt[33][33][33]; | |
{ | |
return( mmt[cube->r1][cube->g1][cube->b1] | |
-mmt[cube->r1][cube->g1][cube->b0] | |
-mmt[cube->r1][cube->g0][cube->b1] | |
+mmt[cube->r1][cube->g0][cube->b0] | |
-mmt[cube->r0][cube->g1][cube->b1] | |
+mmt[cube->r0][cube->g1][cube->b0] | |
+mmt[cube->r0][cube->g0][cube->b1] | |
-mmt[cube->r0][cube->g0][cube->b0] ); | |
} | |
/* The next two routines allow a slightly more efficient calculation | |
* of Vol() for a proposed subbox of a given box. The sum of Top() | |
* and Bottom() is the Vol() of a subbox split in the given direction | |
* and with the specified new upper bound. | |
*/ | |
long int Bottom(cube, dir, mmt) | |
/* Compute part of Vol(cube, mmt) that doesn't depend on r1, g1, or b1 */ | |
/* (depending on dir) */ | |
struct box *cube; | |
unsigned char dir; | |
long int mmt[33][33][33]; | |
{ | |
switch(dir){ | |
case RED: | |
return( -mmt[cube->r0][cube->g1][cube->b1] | |
+mmt[cube->r0][cube->g1][cube->b0] | |
+mmt[cube->r0][cube->g0][cube->b1] | |
-mmt[cube->r0][cube->g0][cube->b0] ); | |
break; | |
case GREEN: | |
return( -mmt[cube->r1][cube->g0][cube->b1] | |
+mmt[cube->r1][cube->g0][cube->b0] | |
+mmt[cube->r0][cube->g0][cube->b1] | |
-mmt[cube->r0][cube->g0][cube->b0] ); | |
break; | |
case BLUE: | |
return( -mmt[cube->r1][cube->g1][cube->b0] | |
+mmt[cube->r1][cube->g0][cube->b0] | |
+mmt[cube->r0][cube->g1][cube->b0] | |
-mmt[cube->r0][cube->g0][cube->b0] ); | |
break; | |
} | |
} | |
long int Top(cube, dir, pos, mmt) | |
/* Compute remainder of Vol(cube, mmt), substituting pos for */ | |
/* r1, g1, or b1 (depending on dir) */ | |
struct box *cube; | |
unsigned char dir; | |
int pos; | |
long int mmt[33][33][33]; | |
{ | |
switch(dir){ | |
case RED: | |
return( mmt[pos][cube->g1][cube->b1] | |
-mmt[pos][cube->g1][cube->b0] | |
-mmt[pos][cube->g0][cube->b1] | |
+mmt[pos][cube->g0][cube->b0] ); | |
break; | |
case GREEN: | |
return( mmt[cube->r1][pos][cube->b1] | |
-mmt[cube->r1][pos][cube->b0] | |
-mmt[cube->r0][pos][cube->b1] | |
+mmt[cube->r0][pos][cube->b0] ); | |
break; | |
case BLUE: | |
return( mmt[cube->r1][cube->g1][pos] | |
-mmt[cube->r1][cube->g0][pos] | |
-mmt[cube->r0][cube->g1][pos] | |
+mmt[cube->r0][cube->g0][pos] ); | |
break; | |
} | |
} | |
float Var(cube) | |
/* Compute the weighted variance of a box */ | |
/* NB: as with the raw statistics, this is really the variance * size */ | |
struct box *cube; | |
{ | |
float dr, dg, db, xx; | |
dr = Vol(cube, mr); | |
dg = Vol(cube, mg); | |
db = Vol(cube, mb); | |
xx = m2[cube->r1][cube->g1][cube->b1] | |
-m2[cube->r1][cube->g1][cube->b0] | |
-m2[cube->r1][cube->g0][cube->b1] | |
+m2[cube->r1][cube->g0][cube->b0] | |
-m2[cube->r0][cube->g1][cube->b1] | |
+m2[cube->r0][cube->g1][cube->b0] | |
+m2[cube->r0][cube->g0][cube->b1] | |
-m2[cube->r0][cube->g0][cube->b0]; | |
return( xx - (dr*dr+dg*dg+db*db)/(float)Vol(cube,wt) ); | |
} | |
/* We want to minimize the sum of the variances of two subboxes. | |
* The sum(c^2) terms can be ignored since their sum over both subboxes | |
* is the same (the sum for the whole box) no matter where we split. | |
* The remaining terms have a minus sign in the variance formula, | |
* so we drop the minus sign and MAXIMIZE the sum of the two terms. | |
*/ | |
float Maximize(cube, dir, first, last, cut, | |
whole_r, whole_g, whole_b, whole_w) | |
struct box *cube; | |
unsigned char dir; | |
int first, last, *cut; | |
long int whole_r, whole_g, whole_b, whole_w; | |
{ | |
register long int half_r, half_g, half_b, half_w; | |
long int base_r, base_g, base_b, base_w; | |
register int i; | |
register float temp, max; | |
base_r = Bottom(cube, dir, mr); | |
base_g = Bottom(cube, dir, mg); | |
base_b = Bottom(cube, dir, mb); | |
base_w = Bottom(cube, dir, wt); | |
max = 0.0; | |
*cut = -1; | |
for(i=first; i<last; ++i){ | |
half_r = base_r + Top(cube, dir, i, mr); | |
half_g = base_g + Top(cube, dir, i, mg); | |
half_b = base_b + Top(cube, dir, i, mb); | |
half_w = base_w + Top(cube, dir, i, wt); | |
/* now half_x is sum over lower half of box, if split at i */ | |
if (half_w == 0) { /* subbox could be empty of pixels! */ | |
continue; /* never split into an empty box */ | |
} else | |
temp = ((float)half_r*half_r + (float)half_g*half_g + | |
(float)half_b*half_b)/half_w; | |
half_r = whole_r - half_r; | |
half_g = whole_g - half_g; | |
half_b = whole_b - half_b; | |
half_w = whole_w - half_w; | |
if (half_w == 0) { /* subbox could be empty of pixels! */ | |
continue; /* never split into an empty box */ | |
} else | |
temp += ((float)half_r*half_r + (float)half_g*half_g + | |
(float)half_b*half_b)/half_w; | |
if (temp > max) {max=temp; *cut=i;} | |
} | |
return(max); | |
} | |
int | |
Cut(set1, set2) | |
struct box *set1, *set2; | |
{ | |
unsigned char dir; | |
int cutr, cutg, cutb; | |
float maxr, maxg, maxb; | |
long int whole_r, whole_g, whole_b, whole_w; | |
whole_r = Vol(set1, mr); | |
whole_g = Vol(set1, mg); | |
whole_b = Vol(set1, mb); | |
whole_w = Vol(set1, wt); | |
maxr = Maximize(set1, RED, set1->r0+1, set1->r1, &cutr, | |
whole_r, whole_g, whole_b, whole_w); | |
maxg = Maximize(set1, GREEN, set1->g0+1, set1->g1, &cutg, | |
whole_r, whole_g, whole_b, whole_w); | |
maxb = Maximize(set1, BLUE, set1->b0+1, set1->b1, &cutb, | |
whole_r, whole_g, whole_b, whole_w); | |
if( (maxr>=maxg)&&(maxr>=maxb) ) { | |
dir = RED; | |
if (cutr < 0) return 0; /* can't split the box */ | |
} | |
else | |
if( (maxg>=maxr)&&(maxg>=maxb) ) | |
dir = GREEN; | |
else | |
dir = BLUE; | |
set2->r1 = set1->r1; | |
set2->g1 = set1->g1; | |
set2->b1 = set1->b1; | |
switch (dir){ | |
case RED: | |
set2->r0 = set1->r1 = cutr; | |
set2->g0 = set1->g0; | |
set2->b0 = set1->b0; | |
break; | |
case GREEN: | |
set2->g0 = set1->g1 = cutg; | |
set2->r0 = set1->r0; | |
set2->b0 = set1->b0; | |
break; | |
case BLUE: | |
set2->b0 = set1->b1 = cutb; | |
set2->r0 = set1->r0; | |
set2->g0 = set1->g0; | |
break; | |
} | |
set1->vol=(set1->r1-set1->r0)*(set1->g1-set1->g0)*(set1->b1-set1->b0); | |
set2->vol=(set2->r1-set2->r0)*(set2->g1-set2->g0)*(set2->b1-set2->b0); | |
return 1; | |
} | |
Mark(cube, label, tag) | |
struct box *cube; | |
int label; | |
unsigned char *tag; | |
{ | |
register int r, g, b; | |
for(r=cube->r0+1; r<=cube->r1; ++r) | |
for(g=cube->g0+1; g<=cube->g1; ++g) | |
for(b=cube->b0+1; b<=cube->b1; ++b) | |
tag[(r<<10) + (r<<6) + r + (g<<5) + g + b] = label; | |
} | |
int | |
main () | |
{ | |
struct box cube[MAXCOLOR]; | |
unsigned char *tag; | |
unsigned char lut_r[MAXCOLOR], lut_g[MAXCOLOR], lut_b[MAXCOLOR]; | |
int next; | |
register long int i, weight; | |
register int k; | |
float vv[MAXCOLOR], temp; | |
/* input R,G,B components into Ir, Ig, Ib; | |
set size to width*height */ | |
printf("no. of colors:\n"); | |
scanf("%d", &K); | |
Hist3d(wt, mr, mg, mb, m2); printf("Histogram done\n"); | |
free(Ig); free(Ib); free(Ir); | |
M3d(wt, mr, mg, mb, m2); printf("Moments done\n"); | |
cube[0].r0 = cube[0].g0 = cube[0].b0 = 0; | |
cube[0].r1 = cube[0].g1 = cube[0].b1 = 32; | |
next = 0; | |
for(i=1; i<K; ++i){ | |
if (Cut(&cube[next], &cube[i])) { | |
/* volume test ensures we won't try to cut one-cell box */ | |
vv[next] = (cube[next].vol>1) ? Var(&cube[next]) : 0.0; | |
vv[i] = (cube[i].vol>1) ? Var(&cube[i]) : 0.0; | |
} else { | |
vv[next] = 0.0; /* don't try to split this box again */ | |
i--; /* didn't create box i */ | |
} | |
next = 0; temp = vv[0]; | |
for(k=1; k<=i; ++k) | |
if (vv[k] > temp) { | |
temp = vv[k]; next = k; | |
} | |
if (temp <= 0.0) { | |
K = i+1; | |
fprintf(stderr, "Only got %d boxes\n", K); | |
break; | |
} | |
} | |
printf("Partition done\n"); | |
/* the space for array m2 can be freed now */ | |
tag = (unsigned char *)malloc(33*33*33); | |
if (tag==NULL) {printf("Not enough space\n"); exit(1);} | |
for(k=0; k<K; ++k){ | |
Mark(&cube[k], k, tag); | |
weight = Vol(&cube[k], wt); | |
if (weight) { | |
lut_r[k] = Vol(&cube[k], mr) / weight; | |
lut_g[k] = Vol(&cube[k], mg) / weight; | |
lut_b[k] = Vol(&cube[k], mb) / weight; | |
} | |
else{ | |
fprintf(stderr, "bogus box %d\n", k); | |
lut_r[k] = lut_g[k] = lut_b[k] = 0; | |
} | |
} | |
for(i=0; i<size; ++i) Qadd[i] = tag[Qadd[i]]; | |
/* output lut_r, lut_g, lut_b as color look-up table contents, | |
Qadd as the quantized image (array of table addresses). */ | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Code works well... got it working in .Net with visual studio 2015 in ~ hour.
Had to change a few things (ie K & R style header)... and made main a function.
ifndef DWORD
endif
DWORD x_wu_main(DWORD update, DWORD *p_Idata, DWORD *p_IDest, DWORD p_size, DWORD pal_colors, DWORD *pal);
include "stdafx.h"
include "LCD Maker Support.h"
include <memory.h>
include <malloc.h>
/**********************************************************************
C Implementation of Wu's Color Quantizer (v. 2)
(see Graphics Gems vol. II, pp. 126-133)
Author: Xiaolin Wu
Dept. of Computer Science
Univ. of Western Ontario
London, Ontario N6A 5B7
wu@csd.uwo.ca
Algorithm: Greedy orthogonal bipartition of RGB space for variance
minimization aided by inclusion-exclusion tricks.
For speed no nearest neighbor search is done. Slightly
better performance can be expected by more sophisticated
but more expensive versions.
The author thanks Tom Lane at Tom_Lane@G.GP.CS.CMU.EDU for much of
additional documentation and a cure to a previous bug.
Free to distribute, comments and suggestions are appreciated.
**********************************************************************/
include <stdio.h>
define MAXCOLOR 256
define RED 2
define GREEN 1
define BLUE 0
struct box
{
int r0;
int r1;
int g0;
int g1;
int b0;
int b1;
int vol;
};
typedef struct box _BOX;
/* Histogram is in elements 1..HISTSIZE along each axis,
*/
float m2[33][33][33];
int wt[33][33][33];
int mr[33][33][33];
int mg[33][33][33];
int mb[33][33][33];
// These items set from main
DWORD _Idata; // 32 bit pointer to ARGB
int size; // how many ARGB items
int K; /_color look-up table size*/
USHORT *Qadd;
bool Hist3d(int *vwt, int *vmr, int *vmg, int *vmb, float *m2)
{
int ind, r, g, b;
int inr, ing, inb, table[256];
int i;
}
/* At conclusion of the histogram step, we can interpret
*/
/* We now convert histogram into moments so that we can rapidly calculate
*/
void M3d(int vwt, int *vmr, int *vmg, int *vmb, float *m2) / compute cumulative moments. */
{
unsigned short int ind1, ind2;
unsigned char i, r, g, b;
int line, line_r, line_g, line_b, area[33], area_r[33], area_g[33], area_b[33];
float line2, area2[33];
}
int Vol(_BOX cube, int mmt[33][33][33]) / Compute sum over a box of any given statistic */
{
return (mmt[cube->r1][cube->g1][cube->b1]
- mmt[cube->r1][cube->g1][cube->b0]
- mmt[cube->r1][cube->g0][cube->b1]
+ mmt[cube->r1][cube->g0][cube->b0]
- mmt[cube->r0][cube->g1][cube->b1]
+ mmt[cube->r0][cube->g1][cube->b0]
+ mmt[cube->r0][cube->g0][cube->b1]
- mmt[cube->r0][cube->g0][cube->b0]);
}
/* The next two routines allow a slightly more efficient calculation
of Vol() for a proposed subbox of a given box. The sum of Top()
and Bottom() is the Vol() of a subbox split in the given direction
and with the specified new upper bound.
*/
int Bottom(_BOX cube, unsigned char dir, int mmt[33][33][33]) / Compute part of Vol(cube, mmt) that doesn't depend on r1, g1, or b1 (depending on dir) */
{
if (dir == RED)
{
return -mmt[cube->r0][cube->g1][cube->b1] + mmt[cube->r0][cube->g1][cube->b0] + mmt[cube->r0][cube->g0][cube->b1] - mmt[cube->r0][cube->g0][cube->b0];
}
else if (dir == GREEN)
{
return -mmt[cube->r1][cube->g0][cube->b1] + mmt[cube->r1][cube->g0][cube->b0] + mmt[cube->r0][cube->g0][cube->b1] - mmt[cube->r0][cube->g0][cube->b0];
}
else
{
return -mmt[cube->r1][cube->g1][cube->b0] + mmt[cube->r1][cube->g0][cube->b0] + mmt[cube->r0][cube->g1][cube->b0] - mmt[cube->r0][cube->g0][cube->b0];
}
}
int Top(_BOX cube, BYTE dir, int pos, int mmt[33][33][33]) / Compute remainder of Vol(cube, mmt), substituting pos for r1, g1, or b1 (depending on dir) */
{
if (dir == RED)
{
return mmt[pos][cube->g1][cube->b1] - mmt[pos][cube->g1][cube->b0] - mmt[pos][cube->g0][cube->b1] + mmt[pos][cube->g0][cube->b0];
}
else if (dir == GREEN)
{
return mmt[cube->r1][pos][cube->b1] - mmt[cube->r1][pos][cube->b0] - mmt[cube->r0][pos][cube->b1] + mmt[cube->r0][pos][cube->b0];
}
else
{
return mmt[cube->r1][cube->g1][pos] - mmt[cube->r1][cube->g0][pos] - mmt[cube->r0][cube->g1][pos] + mmt[cube->r0][cube->g0][pos];
}
}
float Var(_BOX cube) / Compute the weighted variance of a box - NB: as with the raw statistics, this is really the variance * size */
{
int dr = Vol(cube, mr);
int dg = Vol(cube, mg);
int db = Vol(cube, mb);
}
/* We want to minimize the sum of the variances of two subboxes.
*/
float Maximize(_BOX *cube, unsigned char dir, int first, int last, int *cut, int whole_r, int whole_g, int whole_b, int whole_w)
{
int base_r = Bottom(cube, dir, mr);
int base_g = Bottom(cube, dir, mg);
int base_b = Bottom(cube, dir, mb);
int base_w = Bottom(cube, dir, wt);
}
int Cut(_BOX *set1, _BOX *set2)
{
BYTE dir;
int cutr, cutg, cutb;
}
void Mark(_BOX *cube, int label, BYTE *tag)
{
for (int r = cube->r0 + 1; r <= cube->r1; r++)
{
for (int g = cube->g0 + 1; g <= cube->g1; g++)
{
for (int b = cube->b0 + 1; b <= cube->b1; b++)
{
tag[(r << 10) + (r << 6) + r + (g << 5) + g + b] = label;
}
}
}
}
DWORD x_wu_main(DWORD update_bmp, DWORD *p_Idata, DWORD *p_IDest, DWORD p_size, DWORD pal_colors, DWORD *pal)
{
_BOX cube[MAXCOLOR];
BYTE *tag;
BYTE lut_r[MAXCOLOR], lut_g[MAXCOLOR], lut_b[MAXCOLOR];
}