Read barcodes from an image

Image.prototype.barcode.js

// Image.prototype.barcode
(function () {
	'use strict';

	var UPC_SET = {
		'3211': '0',
		'2221': '1',
		'2122': '2',
		'1411': '3',
		'1132': '4',
		'1231': '5',
		'1114': '6',
		'1312': '7',
		'1213': '8',
		'3112': '9'
	};


	Image.prototype.barcode = function barcode() {
		var
		image = this,
		canvas = document.createElement('canvas'),
		context = canvas.getContext('2d'),
		width = image.width,
		height = image.height,
		spoints = [1, 9, 2, 8, 3, 7, 4, 6, 5],
		numLines = spoints.length,
		slineStep = height / (numLines + 1);

		canvas.width = width;
		canvas.height = height;

		context.drawImage(image, 0, 0);

		while (numLines--) {
			var pxLine = context.getImageData(0, slineStep * spoints[numLines], width, 2).data,
				sum = [],
				min = 0,
				max = 0;

			for (var row = 0; row < 2; ++row) {
				for (var col = 0; col < width; ++col) {
					var i = ((row * width) + col) * 4,
						g = ((pxLine[i] * 3) + (pxLine[i + 1] * 4) + (pxLine[i + 2] * 2)) / 9,
						s = sum[col];

					pxLine[i] = pxLine[i + 1] = pxLine[i + 2] = g;

					sum[col] = g + (s === undefined ? 0 : s);
				}
			}

			for (var i = 0; i < width; ++i) {
				var s = sum[i] = sum[i] / 2;

				if (s < min) {
					min = s;
				}

				if (s > max) {
					max = s;
				}
			}

			var pivot = min + ((max - min) / 2), bmp = [];

			for (var col = 0; col < width; ++col) {
				var matches = 0;

				for (var row = 0; row < 2; ++row) {
					if (pxLine[((row * width) + col) * 4] > pivot) {
						++matches;
					}
				}

				bmp.push(matches > 1);
			}

			var curr = bmp[0], count = 1, lines = [];

			for (var col = 0; col < width; ++col) {
				if (bmp[col] == curr) {
					++count;
				} else {
					lines.push(count);
					count = 1;
					curr = bmp[col];
				}
			}

			var code = '', bar = ~~ ((lines[1] + lines[2] + lines[3]) / 3), u = UPC_SET;

			for (var i = 1, l = lines.length; i < l; ++i) {
				if (code.length < 6) {
					var group = lines.slice(i * 4, (i * 4) + 4);
				} else {
					var group = lines.slice((i * 4) + 5, (i * 4) + 9);
				}

				var digits = [
					Math.round(group[0] / bar),
					Math.round(group[1] / bar),
					Math.round(group[2] / bar),
					Math.round(group[3] / bar)
				];

				code += u[digits.join('')] || u[digits.reverse().join('')] || 'X';

				if (12 == code.length) {
					return code;
				}
			}

			if (-1 == code.indexOf('X')) {
				return code || false;
			}
		}

		return false;
	};
})();