constructor(width /*int*/, height /*int*/) {
			this.width = width;
			this.height = height;
		}
The purpose of this class hierarchy is to abstract different bitmap implementations across
platforms into a standard interface for requesting greyscale luminance values. The interface
only provides immutable methods; therefore crop and rotation create copies. This is to ensure
that one Reader does not modify the original luminance source and leave it in an unknown state
for other Readers in the chain.

@author dswitkin@google.com (Daniel Switkin)