Thanks for your contribution, @fleg

To check the content of the image, you'll need to retrieve the canvas Image data.
You'll get back an ImageData object with a data property representing a one-dimensional array containing the data in the RGBA order, with integer values between 0 and 255 (included).

getImageData throws error in browser (because of file:/// protocol), but if perfectly working in phantomjs, and now test failing

I fix scale, but it hard to properly test this feature with single colored image

Thanks, I think your test is sufficient.

Just one note regarding your fix:
Instead of introducing another variable (cropped), please simply add the following two lines after the first loadImage.renderImageToCanvas call in the downsampling loop:

          sourceX = 0
          sourceY = 0

After this change, please squash your commits into one (or two if you want to add the test separately).
Then I'll merge your changes gladly. :)

done

Perfect, thanks!