[Javascript] Neopets OCR

[sim0n]

Another implementation of the "darkest pixel" OCR method for Neopets autobuyers. Wrote this one for a Greasemonkey autobuyer I've been working on.

Requires the Canvas tag (HTML 5) however since this will be ran through Greasemonkey, I would assume that you all keep your browsers up to date and the Canvas tag is implemented in the latest versions of Firefox, Opera, Safari, and Konqueror.

function getDarkestPixel(src, c) {
    if (c == undefined) {
        c = document.createElement("canvas");
        document.appendChild(c);
    }
    var img = new Image()
    img.src = src;
    img.onload = function() {

        c.width = img.width;
        c.height = img.height;
        var cvx = c.getContext("2d");
        cvx.drawImage(img, 0, 0);
        var imgd = cvx.getImageData(0, 0, img.width, img.height);
        
        var intDarkest = 765;
        var ptDarkest = new Array(2);

        for (y = 0; y < imgd.height; y++) {
            for (x = 0; x < imgd.width; x++) {
                var i = (y * 4) * imgd.width + (x * 4);
                var intColour = imgd.data[i] + imgd.data[i+1] + imgd.data[i+2];

                if(intColour < intDarkest) {
                    intDarkest = intColour;
                    ptDarkest[0] = x;
                    ptDarkest[1] = y;
                }
            }
        }
        
        i = (ptDarkest[1] * 4) * imgd.width + (ptDarkest[0] * 4);
        
        imgd.data[i]=255;
        imgd.data[i+1]=255;
        imgd.data[i+2]=255;
        imgd.data[i+3]=255; 
        cvx.putImageData(imgd,0,0,0,0, imgd.width, imgd.height);
    }
}

usage:

            var c = document.createElement("canvas");
            c.id = "canvas"
            document.body.appendChild(c)
            getDarkestPixel("http://www.neopets.com/captcha_show.phtml?_x_pwned...", c)