writefile fn img writes the image img to the file fn. This function guesses the desired format using the extension. Raises Corrupted_image if it encounters a problem. If the file extension is unknown to imagelib, this will first write out a png and then convert that to the desired format using the "convert" command from imagemagick.

size fn reads the image from the file fn. It returns the pixel dimensions of the image as the tuple width, heigth.

openfile fn reads the image from the file fn. This function guesses the file format using the extension. Raises Corrupted_image if it encounters a problem. If the file extension is unknown to imagelib, this will attempt to convert to png using imagemagick and then read in the png file.