public
Last active

Javascript module for color quantization, based on Leptonica

  • Download Gist
quantize.js
JavaScript
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471
/*!
* quantize.js Copyright 2008 Nick Rabinowitz.
* Licensed under the MIT license: http://www.opensource.org/licenses/mit-license.php
*/
 
// fill out a couple protovis dependencies
/*!
* Block below copied from Protovis: http://mbostock.github.com/protovis/
* Copyright 2010 Stanford Visualization Group
* Licensed under the BSD License: http://www.opensource.org/licenses/bsd-license.php
*/
if (!pv) {
var pv = {
map: function(array, f) {
var o = {};
return f
? array.map(function(d, i) { o.index = i; return f.call(o, d); })
: array.slice();
},
naturalOrder: function(a, b) {
return (a < b) ? -1 : ((a > b) ? 1 : 0);
},
sum: function(array, f) {
var o = {};
return array.reduce(f
? function(p, d, i) { o.index = i; return p + f.call(o, d); }
: function(p, d) { return p + d; }, 0);
},
max: function(array, f) {
return Math.max.apply(null, f ? pv.map(array, f) : array);
}
}
}
/**
* Basic Javascript port of the MMCQ (modified median cut quantization)
* algorithm from the Leptonica library (http://www.leptonica.com/).
* Returns a color map you can use to map original pixels to the reduced
* palette. Still a work in progress.
*
* @author Nick Rabinowitz
* @example
 
// array of pixels as [R,G,B] arrays
var myPixels = [[190,197,190], [202,204,200], [207,214,210], [211,214,211], [205,207,207]
// etc
];
var maxColors = 4;
 
var cmap = MMCQ.quantize(myPixels, maxColors);
var newPalette = cmap.palette();
var newPixels = myPixels.map(function(p) {
return cmap.map(p);
});
*/
var MMCQ = (function() {
// private constants
var sigbits = 5,
rshift = 8 - sigbits,
maxIterations = 1000,
fractByPopulations = 0.75;
// get reduced-space color index for a pixel
function getColorIndex(r, g, b) {
return (r << (2 * sigbits)) + (g << sigbits) + b;
}
// Simple priority queue
function PQueue(comparator) {
var contents = [],
sorted = false;
function sort() {
contents.sort(comparator);
sorted = true;
}
return {
push: function(o) {
contents.push(o);
sorted = false;
},
peek: function(index) {
if (!sorted) sort();
if (index===undefined) index = contents.length - 1;
return contents[index];
},
pop: function() {
if (!sorted) sort();
return contents.pop();
},
size: function() {
return contents.length;
},
map: function(f) {
return contents.map(f);
},
debug: function() {
if (!sorted) sort();
return contents;
}
};
}
// 3d color space box
function VBox(r1, r2, g1, g2, b1, b2, histo) {
var vbox = this;
vbox.r1 = r1;
vbox.r2 = r2;
vbox.g1 = g1;
vbox.g2 = g2;
vbox.b1 = b1;
vbox.b2 = b2;
vbox.histo = histo;
}
VBox.prototype = {
volume: function(force) {
var vbox = this;
if (!vbox._volume || force) {
vbox._volume = ((vbox.r2 - vbox.r1 + 1) * (vbox.g2 - vbox.g1 + 1) * (vbox.b2 - vbox.b1 + 1));
}
return vbox._volume;
},
count: function(force) {
var vbox = this,
histo = vbox.histo;
if (!vbox._count_set || force) {
var npix = 0,
i, j, k;
for (i = vbox.r1; i <= vbox.r2; i++) {
for (j = vbox.g1; j <= vbox.g2; j++) {
for (k = vbox.b1; k <= vbox.b2; k++) {
index = getColorIndex(i,j,k);
npix += (histo[index] || 0);
}
}
}
vbox._count = npix;
vbox._count_set = true;
}
return vbox._count;
},
copy: function() {
var vbox = this;
return new VBox(vbox.r1, vbox.r2, vbox.g1, vbox.g2, vbox.b1, vbox.b2, vbox.histo);
},
avg: function(force) {
var vbox = this,
histo = vbox.histo;
if (!vbox._avg || force) {
var ntot = 0,
mult = 1 << (8 - sigbits),
rsum = 0,
gsum = 0,
bsum = 0,
hval,
i, j, k, histoindex;
for (i = vbox.r1; i <= vbox.r2; i++) {
for (j = vbox.g1; j <= vbox.g2; j++) {
for (k = vbox.b1; k <= vbox.b2; k++) {
histoindex = getColorIndex(i,j,k);
hval = histo[histoindex] || 0;
ntot += hval;
rsum += (hval * (i + 0.5) * mult);
gsum += (hval * (j + 0.5) * mult);
bsum += (hval * (k + 0.5) * mult);
}
}
}
if (ntot) {
vbox._avg = [~~(rsum/ntot), ~~(gsum/ntot), ~~(bsum/ntot)];
} else {
console.log('empty box');
vbox._avg = [
~~(mult * (vbox.r1 + vbox.r2 + 1) / 2),
~~(mult * (vbox.g1 + vbox.g2 + 1) / 2),
~~(mult * (vbox.b1 + vbox.b2 + 1) / 2)
];
}
}
return vbox._avg;
},
contains: function(pixel) {
var vbox = this,
rval = pixel[0] >> rshift;
gval = pixel[1] >> rshift;
bval = pixel[2] >> rshift;
return (rval >= vbox.r1 && rval <= vbox.r2 &&
gval >= vbox.g1 && rval <= vbox.g2 &&
bval >= vbox.b1 && rval <= vbox.b2);
}
};
// Color map
function CMap() {
this.vboxes = new PQueue(function(a,b) {
return pv.naturalOrder(
a.vbox.count()*a.vbox.volume(),
b.vbox.count()*b.vbox.volume()
)
});;
}
CMap.prototype = {
push: function(vbox) {
this.vboxes.push({
vbox: vbox,
color: vbox.avg()
});
},
palette: function() {
return this.vboxes.map(function(vb) { return vb.color });
},
size: function() {
return this.vboxes.size();
},
map: function(color) {
var vboxes = this.vboxes;
for (var i=0; i<vboxes.size(); i++) {
if (vboxes.peek(i).vbox.contains(color)) {
return vboxes.peek(i).color;
}
}
return this.nearest(color);
},
nearest: function(color) {
var vboxes = this.vboxes,
d1, d2, pColor;
for (var i=0; i<vboxes.size(); i++) {
d2 = Math.sqrt(
Math.pow(color[0] - vboxes.peek(i).color[0], 2) +
Math.pow(color[1] - vboxes.peek(i).color[1], 2) +
Math.pow(color[1] - vboxes.peek(i).color[1], 2)
);
if (d2 < d1 || d1 === undefined) {
d1 = d2;
pColor = vboxes.peek(i).color;
}
}
return pColor;
},
forcebw: function() {
// XXX: won't work yet
var vboxes = this.vboxes;
vboxes.sort(function(a,b) { return pv.naturalOrder(pv.sum(a.color), pv.sum(b.color) )});
// force darkest color to black if everything < 5
var lowest = vboxes[0].color;
if (lowest[0] < 5 && lowest[1] < 5 && lowest[2] < 5)
vboxes[0].color = [0,0,0];
// force lightest color to white if everything > 251
var idx = vboxes.length-1,
highest = vboxes[idx].color;
if (highest[0] > 251 && highest[1] > 251 && highest[2] > 251)
vboxes[idx].color = [255,255,255];
}
};
// histo (1-d array, giving the number of pixels in
// each quantized region of color space), or null on error
function getHisto(pixels) {
var histosize = 1 << (3 * sigbits),
histo = new Array(histosize),
index, rval, gval, bval;
pixels.forEach(function(pixel) {
rval = pixel[0] >> rshift;
gval = pixel[1] >> rshift;
bval = pixel[2] >> rshift;
index = getColorIndex(rval, gval, bval);
histo[index] = (histo[index] || 0) + 1;
});
return histo;
}
function vboxFromPixels(pixels, histo) {
var rmin=1000000, rmax=0,
gmin=1000000, gmax=0,
bmin=1000000, bmax=0,
rval, gval, bval;
// find min/max
pixels.forEach(function(pixel) {
rval = pixel[0] >> rshift;
gval = pixel[1] >> rshift;
bval = pixel[2] >> rshift;
if (rval < rmin) rmin = rval;
else if (rval > rmax) rmax = rval;
if (gval < gmin) gmin = gval;
else if (gval > gmax) gmax = gval;
if (bval < bmin) bmin = bval;
else if (bval > bmax) bmax = bval;
});
return new VBox(rmin, rmax, gmin, gmax, bmin, bmax, histo);
}
function medianCutApply(histo, vbox) {
if (!vbox.count()) return;
var rw = vbox.r2 - vbox.r1 + 1,
gw = vbox.g2 - vbox.g1 + 1,
bw = vbox.b2 - vbox.b1 + 1,
maxw = pv.max([rw, gw, bw]);
// only one pixel, no split
if (vbox.count() == 1) {
return [vbox.copy()]
}
/* Find the partial sum arrays along the selected axis. */
var total = 0,
partialsum = [],
lookaheadsum = [],
i, j, k, sum, index;
if (maxw == rw) {
for (i = vbox.r1; i <= vbox.r2; i++) {
sum = 0;
for (j = vbox.g1; j <= vbox.g2; j++) {
for (k = vbox.b1; k <= vbox.b2; k++) {
index = getColorIndex(i,j,k);
sum += (histo[index] || 0);
}
}
total += sum;
partialsum[i] = total;
}
}
else if (maxw == gw) {
for (i = vbox.g1; i <= vbox.g2; i++) {
sum = 0;
for (j = vbox.r1; j <= vbox.r2; j++) {
for (k = vbox.b1; k <= vbox.b2; k++) {
index = getColorIndex(j,i,k);
sum += (histo[index] || 0);
}
}
total += sum;
partialsum[i] = total;
}
}
else { /* maxw == bw */
for (i = vbox.b1; i <= vbox.b2; i++) {
sum = 0;
for (j = vbox.r1; j <= vbox.r2; j++) {
for (k = vbox.g1; k <= vbox.g2; k++) {
index = getColorIndex(j,k,i);
sum += (histo[index] || 0);
}
}
total += sum;
partialsum[i] = total;
}
}
partialsum.forEach(function(d,i) {
lookaheadsum[i] = total-d
});
function doCut(color) {
var dim1 = color + '1',
dim2 = color + '2',
left, right, vbox1, vbox2, d2, count2=0;
for (i = vbox[dim1]; i <= vbox[dim2]; i++) {
if (partialsum[i] > total / 2) {
vbox1 = vbox.copy();
vbox2 = vbox.copy();
left = i - vbox[dim1];
right = vbox[dim2] - i;
if (left <= right)
d2 = Math.min(vbox[dim2] - 1, ~~(i + right / 2));
else d2 = Math.max(vbox[dim1], ~~(i - 1 - left / 2));
// avoid 0-count boxes
while (!partialsum[d2]) d2++;
count2 = lookaheadsum[d2];
while (!count2 && partialsum[d2-1]) count2 = lookaheadsum[--d2];
// set dimensions
vbox1[dim2] = d2;
vbox2[dim1] = vbox1[dim2] + 1;
console.log('vbox counts:', vbox.count(), vbox1.count(), vbox2.count());
return [vbox1, vbox2];
}
}
}
// determine the cut planes
return maxw == rw ? doCut('r') :
maxw == gw ? doCut('g') :
doCut('b');
}
 
function quantize(pixels, maxcolors) {
// short-circuit
if (!pixels.length || maxcolors < 2 || maxcolors > 256) {
console.log('wrong number of maxcolors');
return false;
}
// XXX: check color content and convert to grayscale if insufficient
var histo = getHisto(pixels),
histosize = 1 << (3 * sigbits);
// check that we aren't below maxcolors already
var nColors = 0;
histo.forEach(function() { nColors++ });
if (nColors <= maxcolors) {
// XXX: generate the new colors from the histo and return
}
// get the beginning vbox from the colors
var vbox = vboxFromPixels(pixels, histo),
pq = new PQueue(function(a,b) { return pv.naturalOrder(a.count(), b.count()) });
pq.push(vbox);
// inner function to do the iteration
function iter(lh, target) {
var ncolors = 1,
niters = 0,
vbox;
while (niters < maxIterations) {
vbox = lh.pop();
if (!vbox.count()) { /* just put it back */
lh.push(vbox);
niters++;
continue;
}
// do the cut
var vboxes = medianCutApply(histo, vbox),
vbox1 = vboxes[0],
vbox2 = vboxes[1];
if (!vbox1) {
console.log("vbox1 not defined; shouldn't happen!");
return;
}
lh.push(vbox1);
if (vbox2) { /* vbox2 can be null */
lh.push(vbox2);
ncolors++;
}
if (ncolors >= target) return;
if (niters++ > maxIterations) {
console.log("infinite loop; perhaps too few pixels!");
return;
}
}
}
// first set of colors, sorted by population
iter(pq, fractByPopulations * maxcolors);
// console.log(pq.size(), pq.debug().length, pq.debug().slice());
// Re-sort by the product of pixel occupancy times the size in color space.
var pq2 = new PQueue(function(a,b) {
return pv.naturalOrder(a.count()*a.volume(), b.count()*b.volume())
});
while (pq.size()) {
pq2.push(pq.pop());
}
// next set - generate the median cuts using the (npix * vol) sorting.
iter(pq2, maxcolors - pq2.size());
// calculate the actual colors
var cmap = new CMap();
while (pq2.size()) {
cmap.push(pq2.pop());
}
return cmap;
}
return {
quantize: quantize
}
})();

Projects that use this:

Color thief: http://lokeshdhakar.com/projects/color-thief/

Meemoo: http://meemoo.org/iframework/#gist/5233740 (Select an image from your computer or use your webcam. View source to see color codes.)

https://gist.github.com/nrabinowitz/1104622#file-quantize-js-L233

green is being used again here instead of blue? shouldn't it be this:

Math.pow(color[2] - vboxes.peek(i).color[2], 2)

you can see the difference here

full color:
full-color

before correction:
2x green

after correction:
2x green

Is this correct (rval 3 times) ?

       return (rval >= vbox.r1 && rval <= vbox.r2 &&
                gval >= vbox.g1 && rval <= vbox.g2 &&
                bval >= vbox.b1 && rval <= vbox.b2);

Shouldn't it be (rval, gval, bval):

       return (rval >= vbox.r1 && rval <= vbox.r2 &&
                gval >= vbox.g1 && gval <= vbox.g2 &&
                bval >= vbox.b1 && bval <= vbox.b2); 

Cheers,
Brett

@iOSBrett, yes! looks like a similar mistake.

after fixes:
better

@nrabinowitz, can you please correct these issues? this broken port is used in many projects :(

i suspect there are more bugs hiding somewhere because other Median Cut implementations don't yield the edge artifacts or hue shifts (black->red) that appear here.

I forked the code and fixed the two issues found by leeoniya and iOSBrett.
https://gist.github.com/cwey/6200071
Any other bug found by anyone?

Hi nrabinowitz,

I am learning how to use your quantitize.js
I uncomment line 45, and from line 47 to 53 and run it with chrome.
It return an error in console of chrome:
"Uncaught TypeError: Cannot call method 'quantize' of undefined "

Please help! Thanks a lot.

if anyone's interested, i wrote my own quantization lib. feel free to use it.

repo: https://github.com/leeoniya/RgbQuant.js
demo: http://o-0.me/RgbQuant/

full color:
full color

256 colors:
full color

Please sign in to comment on this gist.

Something went wrong with that request. Please try again.