Quote Originally Posted by handrawn View Post
you cannot have pixels missing from a raster matrix they are always there, whatever their visible state at a given time, so a layer is homogeneous, there are no gaps as there are in xara
Umm.. bitmap software doesn't have to have a representation for every pixel on a layer internally, so I don't really accept that they are "always there"!

It may be convenient to have a representation for every pixel, but it doesn't have to be so. Software manipulating large, mostly empty datasets will use sparse arrays, or similar. In a bitmap editor a given pixel can be absent until the user decides otherwise, or the image is exported to a particular graphics format.