NodeJS script to extract the color palette of a PNG

png_colors.js

// usage: node png_colors.js | sort | uniq
//
// ignores alpha
var PNG = require('png-js');

var myimage = PNG.load('my_image.png');

myimage.decodePixels(function (pixels) {
    for( var ii = 0; ii < pixels.length; ii = ii + 4){
        console.log( pixels.readUInt32BE(ii).toString(16).substring(0,6));
    }
});