Distance transform, need to look at how labelling works next.
Made a video with this transform.
http://www.youtube.com/watch?v=WRzYljmyfW4
Flood fill, can generate some interesting patterns when operating on gradients from interpolations.

TBD make optional mask mode to output only the fill pattern.
Have masked output node.
Looking at labels from distance transform.  It looks like the way to recover the labels is just count left to right top to bottom?  In the attached image the labels in the same rows look the same... but probably this is an artifact of scaling the image down to 8-bit, the rows would have gradations but they are too fine for 256 values.