image.load(string filename,string type,number depth) loads an image file of type type, and converts to an m x n x p Tensor, where m is the width of the image and n is the height, and p is the depth.

If depth is not supplied or depth = 1 then the image is converted to grey-scale. If depth = 3 the image is converted to RGB. If depth = 4 the image is converted to RGBA.

type can be currently only be set to 'PNG'.

image.load(string filename) loads a PNG with depth 4.