1/ Load in portable pixmaps (PPM). Set an arbitrary paint attribute
map for each different colour. Otherwise load in a paint attribute
map definition file.
2/ Input from "brush". Incremental development of brush input.
First simple mixing then
empty brush moving paint
paint on top of paint
attribute application.
3/ Animation 
1000000 = 1 fps
500000  = 2 fps
250000  = 4 fps
125000  = 8 fps
62500   = 16 fps
41660   = 24 fps

4/ NK times    178.9 real        49.4 user        13.3 sys
   Orig times  636.6 real       111.1 user        43.6 sys

5/ Cross section through volume 

6/ Separate Colour scale window

7/ Transparency
