NxM image support

[ransnir]

Hi,
Great work! I work with it a bit and found that you are not supporting NxM images.
I think that you have a small logic error in the intensities function (pricessing.js file). The inner loop working on the "imagedata.height", as well the outer loop. Moreover the calculation of "i" seems to be different from the other functions.

I suggest this fix, it worked well on NxM images.

intensities: function(imagedata) {
if (!imagedata.data) {
// it's a canvas, extract the imagedata
var canvas = imagedata;
var context = canvas.getContext("2d");
imagedata = context.getImageData(0, 0, canvas.width, canvas.height);
}

var lumas = new Array(imagedata.height);

for (var y = 0; y < imagedata.height; y++) {
  lumas[y] = new Array(imagedata.width);

  for (var x = 0; x < imagedata.width; x++) {
    //var i = x * 4 + y * 4 * imagedata.width;
    var i = (y * 4) * imagedata.width + x * 4;
    var r = imagedata.data[i],
        g = imagedata.data[i + 1],
        b = imagedata.data[i + 2],
        a = imagedata.data[i + 3];

    var luma = a == 0 ? 1 : (r * 299/1000 + g * 587/1000
      + b * 114/1000) / 255;

    lumas[y][x] = luma;
  }
}

return lumas;

}