My attempt at translating an image and... 2 hard 2 explain

translate.js

var a, b, brightness, checked, e, g, getBrightnessOf, icanvas, ictx, j, l, margin, pixels, r, ref, ref1, ref2, rx, ry, threshold, weight, x, y;
try
{
    icanvas = document.createElement('canvas');
    icanvas.width = img.naturalWidth;
    icanvas.height = img.naturalHeight;
    chunkSize *= renderer.canvas.height / 1000;
    ictx = icanvas.getContext('2d');
    ictx.drawImage(img, 0, 0, Math.floor(renderer.canvas.height * icanvas.width / icanvas.height / chunkSize), Math.floor(renderer.canvas.height / chunkSize));
    map.clearResize(Math.floor(renderer.canvas.width / chunkSize), Math.floor(renderer.canvas.height / chunkSize));
    getBrightnessOf = function(r, g, b, a)
    {
        return (0.299 * r + 0.587 * g + 0.114 * b) * a - a + 1;
    };
    margin = Math.floor((renderer.canvas.width - (renderer.canvas.height * icanvas.width / icanvas.height)) / chunkSize / 2);
    console.log(margin, (Math.floor(renderer.canvas.width / chunkSize)) + "x" + (Math.floor(renderer.canvas.height / chunkSize)), (Math.floor(renderer.canvas.height * icanvas.width / icanvas.height / chunkSize)) + "x" + (Math.floor(renderer.canvas.height / chunkSize)));
    for (rx = j = 0, ref = Math.floor(renderer.canvas.width / chunkSize); 0 <= ref ? j < ref : j > ref; rx = 0 <= ref ? ++j : --j)
    {
        for (ry = l = 0, ref1 = Math.floor(renderer.canvas.height / chunkSize); 0 <= ref1 ? l < ref1 : l > ref1; ry = 0 <= ref1 ? ++l : --l)
        {
            if (margin > rx || rx >= Math.floor(renderer.canvas.width / chunkSize) - margin)
            {
                map.setDataAttr(rx, ry, 'weight', 4);
                continue;
            }
            x = Math.floor((rx - margin) * chunkSize * icanvas.width / (renderer.canvas.width - margin * 2 * chunkSize));
            y = Math.floor(ry * chunkSize * icanvas.height / renderer.canvas.height);
            pixels = ictx.getImageData(x, y, 1, 1).data;
            ref2 = pixels.map(function(c)
            {
                return c / 255.0;
            }), r = ref2[0], g = ref2[1], b = ref2[2], a = ref2[3];
            brightness = getBrightnessOf(r, g, b, a);
            threshold = +(document.getElementById('threshold').value) / 100;
            map.setDataAttr(rx, ry, 'obstacle', brightness < threshold);
            if (brightness >= threshold)
            {
                checked = document.getElementById('weightmap').checked;
                if (checked)
                {
                    weight = Math.floor(((threshold - brightness) / threshold) * 24);
                    map.setDataAttr(rx, ry, 'weight', weight);
                }
            }
        }
    }
    console.log(rx, Math.floor(renderer.canvas.width / chunkSize), "|", x, icanvas.width);
}
catch (error)
{
    e = error;
    setStatus('<span style="color:red;">Error importing map from image!</span>');
    setTimeout((function()
    {
        return setStatus(lastStatus);
    }), 5000);
    throw e;
}