[Nexus]

Не так давно писал подобный helper:

var imageWidth = canvas.width, 
    imageHeight = canvas.height,
    ctx = canvas.getContext('2d');

var getPixelDataByCoordinates = (function () {
    var imageData = ctx.getImageData(0, 0, imageWidth, imageHeight).data;

    return function (x, y) {
        var pixelIndex = ((y * (imageWidth * 4)) + (x * 4));
        if (!(pixelIndex in imageData)) {
            return undefined;
        }

        var result = {
            r: imageData[pixelIndex],
            g: imageData[pixelIndex + 1],
            b: imageData[pixelIndex + 2],
            a: imageData[pixelIndex + 3]
        };

        result.weight = result.r + result.g + result.b + result.a;

        return result.weight > 0 ? result : undefined;
    };
})();

console.log(
    getPixelDataByCoordinates(0, 0)
);