| MedianCut.java |
package ip.color;
import java.awt.*;
import java.awt.image.IndexColorModel;
import java.awt.image.MemoryImageSource;
/** Converts an RGB image to 8-bit index color using Heckbert's median-cut
color quantization algorithm. Based on median.c by Anton Kruger from the
September, 1994 issue of Dr. Dobbs Journal.
*/
// Thanks go to Wayne Rasband for his contribution
// of the MedianCut class.
// Also for putting his Image/J program,
// with source code, into the public domain
// (available at http://rsb.info.nih.gov/ij/).
public class MedianCut {
static final int MAXCOLORS = 256; // maximum # of output colors
static final int HSIZE = 32768; // size of image histogram
private int[] hist; // RGB histogram and reverse color lookup table
private int[] histPtr; // points to colors in "hist"
private MedianCube cubeList[]; // list of cubes
private int[] pixels32;
private int width, height;
private IndexColorModel cm;
public MedianCut(int pixels[], int width, int height) {
int color16;
pixels32 = pixels;
this.width = width;
this.height = height;
//build 32x32x32 RGB histogram
hist = new int[HSIZE];
for (int i = 0; i < width * height; i++) {
color16 = rgb(pixels32[i]);
hist[color16]++;
}
}
int getColorCount() {
int count = 0;
for (int i = 0; i < HSIZE; i++)
if (hist[i] > 0) count++;
return count;
}
Color getModalColor() {
int max = 0;
int c = 0;
for (int i = 0; i < HSIZE; i++)
if (hist[i] > max) {
max = hist[i];
c = i;
}
return new Color(red(c), green(c), blue(c));
}
// Convert from 24-bit to 15-bit color
private final int rgb(int c) {
int r = (c & 0xf80000) >> 19;
int g = (c & 0xf800) >> 6;
int b = (c & 0xf8) << 7;
return b | g | r;
}
// Get red component of a 15-bit color
private final int red(int x) {
return (x & 31) << 3;
}
// Get green component of a 15-bit color
private final int green(int x) {
return (x >> 2) & 0xf8;
}
// Get blue component of a 15-bit color
private final int blue(int x) {
return (x >> 7) & 0xf8;
}
public Image convert(int maxcubes) {
// Uses Heckbert's median-cut algorithm to divide the color space defined by
// "hist" into "maxcubes" cubes. The centroids (average value) of each cube
// are are used to create a color table. "hist" is then updated to function
// as an inverse color map that is used to generate an 8-bit image.
int lr, lg, lb;
int i, median, color;
int count;
int k, level, ncubes, splitpos;
int num, width;
int longdim = 0; //longest dimension of cube
MedianCube cube, cubeA, cubeB;
// Create initial cube
cubeList = new MedianCube[MAXCOLORS];
histPtr = new int[HSIZE];
ncubes = 0;
cube = new MedianCube();
for (i = 0, color = 0; i <= HSIZE - 1; i++) {
if (hist[i] != 0) {
histPtr[color++] = i;
cube.count = cube.count + hist[i];
}
}
cube.lower = 0;
cube.upper = color - 1;
cube.level = 0;
Shrink(cube);
cubeList[ncubes++] = cube;
//Main loop
while (ncubes < maxcubes) {
// Search the list of cubes for next cube to split,
// the lowest level cube
level = 255;
splitpos = -1;
for (k = 0; k <= ncubes - 1; k++) {
if (cubeList[k].lower == cubeList[k].upper)
; // single color; cannot be split
else if (cubeList[k].level < level) {
level = cubeList[k].level;
splitpos = k;
}
}
if (splitpos == -1) // no more cubes to split
break;
// Find longest dimension of this cube
cube = cubeList[splitpos];
lr = cube.rmax - cube.rmin;
lg = cube.gmax - cube.gmin;
lb = cube.bmax - cube.bmin;
if (lr >= lg && lr >= lb) longdim = 0;
if (lg >= lr && lg >= lb) longdim = 1;
if (lb >= lr && lb >= lg) longdim = 2;
// Sort along "longdim"
reorderColors(histPtr, cube.lower, cube.upper, longdim);
quickSort(histPtr, cube.lower, cube.upper);
restoreColorOrder(histPtr, cube.lower, cube.upper, longdim);
// Find median
count = 0;
for (i = cube.lower; i <= cube.upper - 1; i++) {
if (count >= cube.count / 2) break;
color = histPtr[i];
count = count + hist[color];
}
median = i;
// Now split "cube" at the median and add the two new
// cubes to the list of cubes.
cubeA = new MedianCube();
cubeA.lower = cube.lower;
cubeA.upper = median - 1;
cubeA.count = count;
cubeA.level = cube.level + 1;
Shrink(cubeA);
cubeList[splitpos] = cubeA; // add in old slot
cubeB = new MedianCube();
cubeB.lower = median;
cubeB.upper = cube.upper;
cubeB.count = cube.count - count;
cubeB.level = cube.level + 1;
Shrink(cubeB);
cubeList[ncubes++] = cubeB; // add in new slot */
}
// We have enough cubes, or we have split all we can. Now
// compute the color map, the inverse color map, and return
// an 8-bit image.
makeInverseMap(hist, ncubes);
return makeImage();
}
void Shrink(MedianCube cube) {
// Encloses "cube" with a tight-fitting cube by updating the
// (rmin,gmin,bmin) and (rmax,gmax,bmax) members of "cube".
int r, g, b;
int color;
int rmin, rmax, gmin, gmax, bmin, bmax;
rmin = 255;
rmax = 0;
gmin = 255;
gmax = 0;
bmin = 255;
bmax = 0;
for (int i = cube.lower; i <= cube.upper; i++) {
color = histPtr[i];
r = red(color);
g = green(color);
b = blue(color);
if (r > rmax) rmax = r;
if (r < rmin) rmin = r;
if (g > gmax) gmax = g;
if (g < gmin) gmin = g;
if (b > bmax) bmax = b;
if (b < bmin) bmin = b;
}
cube.rmin = rmin;
cube.rmax = rmax;
cube.gmin = gmin;
cube.gmax = gmax;
cube.gmin = gmin;
cube.gmax = gmax;
}
void makeInverseMap(int[] hist, int ncubes) {
// For each cube in the list of cubes, computes the centroid
// (average value) of the colors enclosed by that cube, and
// then loads the centroids in the color map. Next loads
// "hist" with indices into the color map
int r, g, b;
int color;
float rsum, gsum, bsum;
MedianCube cube;
byte rLUT[] = new byte[256];
byte gLUT[] = new byte[256];
byte bLUT[] = new byte[256];
for (int k = 0; k <= ncubes - 1; k++) {
cube = cubeList[k];
rsum = gsum = bsum = 0.0f;
for (int i = cube.lower; i <= cube.upper; i++) {
color = histPtr[i];
r = red(color);
rsum += (float) (r * hist[color]);
g = green(color);
gsum += (float) (g * hist[color]);
b = blue(color);
bsum += (float) (b * hist[color]);
}
// Update the color map
r = (int) (rsum / (float) cube.count);
g = (int) (gsum / (float) cube.count);
b = (int) (bsum / (float) cube.count);
// Now I have a cube centroid
if (r == 248 && g == 248 && b == 248)
r = g = b = 255; // Restore white (255,255,255)
rLUT[k] = (byte) (r & 0xff);
gLUT[k] = (byte) (g & 0xff);
bLUT[k] = (byte) (b & 0xff);
}
cm = new IndexColorModel(8, ncubes, rLUT, gLUT, bLUT);
// For each color in each cube, load the corre-
// sponding slot in "hist" with the centroid of the cube.
for (int k = 0; k <= ncubes - 1; k++) {
cube = cubeList[k];
for (int i = cube.lower; i <= cube.upper; i++) {
color = histPtr[i];
hist[color] = k;
}
}
}
// This method is never invoked.
// it is optimal,but slow...the search
// for the best map is exhaustive.. DL
void makeInverseTable(int[] hist, int ncubes,
byte[] rLUT, byte[] gLUT, byte[] bLUT) {
// For each color, find the entry in the color map
// that has the smallest Euclidian distance from that
// color. Record this information in "hist".
int r, g, b;
int index, color;
int dr, dg,db, d, dmin;
index = 0;
for (int i = 0; i < HSIZE; i++) {
if (hist[i] > 0) {
color = i;
r = red(color);
g = green(color);
b = blue(color);
dmin = 999999999;
for (int j = 0; j < ncubes; j++) {
dr = (rLUT[j] & 0xff) - r;
dg = (gLUT[j] & 0xff) - g;
db = (bLUT[j] & 0xff) - b;
d = dr * dr + dg * dg + db * db;
if (d == 0) {
index = j;
break;
} else if (d < dmin) {
dmin = d;
index = j;
}
}
hist[color] = index;
}
}
}
void reorderColors(int[] a, int lo, int hi, int longDim) {
// Change the ordering of the 5-bit colors in each word of int[]
// so we can sort on the 'longDim' color
int c, r, g, b;
switch (longDim) {
case 0: //red
for (int i = lo; i <= hi; i++) {
c = a[i];
r = c & 31;
a[i] = (r << 10) | (c >> 5);
}
break;
case 1: //green
for (int i = lo; i <= hi; i++) {
c = a[i];
r = c & 31;
g = (c >> 5) & 31;
b = c >> 10;
a[i] = (g << 10) | (b << 5) | r;
}
break;
case 2: //blue; already in the needed order
break;
}
}
void restoreColorOrder(int[] a, int lo, int hi, int longDim) {
// Restore the 5-bit colors to the original order
int c, r, g, b;
switch (longDim) {
case 0: //red
for (int i = lo; i <= hi; i++) {
c = a[i];
r = c >> 10;
a[i] = ((c & 1023) << 5) | r;
}
break;
case 1: //green
for (int i = lo; i <= hi; i++) {
c = a[i];
r = c & 31;
g = c >> 10;
b = (c >> 5) & 31;
a[i] = (b << 10) | (g << 5) | r;
}
break;
case 2: //blue
break;
}
}
void quickSort(int a[], int lo0, int hi0) {
// Based on the QuickSort method by James Gosling from Sun's SortDemo applet
int lo = lo0;
int hi = hi0;
int mid, t;
if (hi0 > lo0) {
mid = a[(lo0 + hi0) / 2];
while (lo <= hi) {
while ((lo < hi0) && (a[lo] < mid))
++lo;
while ((hi > lo0) && (a[hi] > mid))
--hi;
if (lo <= hi) {
t = a[lo];
a[lo] = a[hi];
a[hi] = t;
++lo;
--hi;
}
}
if (lo0 < hi)
quickSort(a, lo0, hi);
if (lo < hi0)
quickSort(a, lo, hi0);
}
}
Image makeImage() {
// Generate 8-bit image
Image img8;
byte[] pixels8;
int color16;
pixels8 = new byte[width * height];
for (int i = 0; i < width * height; i++) {
color16 = rgb(pixels32[i]);
pixels8[i] = (byte) (hist[color16] & 0xff);
}
img8 = Toolkit.getDefaultToolkit().createImage(
new MemoryImageSource(width, height, cm, pixels8, 0, width));
return img8;
}
} //class MedianCut
class MedianCube {
// structure for a cube in color space
int lower; // one corner's index in histogram
int upper; // another corner's index in histogram
int count; // cube's histogram count
int level; // cube's level
int rmin, rmax;
int gmin, gmax;
int bmin, bmax;
MedianCube() {
count = 0;
}
public String toString() {
String s = "lower=" + lower + " upper=" + upper;
s = s + " count=" + count + " level=" + level;
s = s + " rmin=" + rmin + " rmax=" + rmax;
s = s + " gmin=" + gmin + " gmax=" + gmax;
s = s + " bmin=" + bmin + " bmax=" + bmax;
return s;
}
}