tmeng@sfu.ca, May 26, 2003

A .tf file is organized as follows:

- number of components (must be 3, for RGB)
this line can be removed; 3 is the default.

- a set of nodes for opacity. format: (intensity, opacity)

- a set of nodes for colours. format: (intensity, R, G, B, ?)
I am not quite sure what ? means, probably a place holder for Alpha,
but it is not useful since opacity info is already specified.
Note: ? can be safely removed (see default.tf vs hipiph.tf)

- All three sections mentionned above are optional

- More specifically, each opacity line denotes a node, for example:

opacity(0, 0)
opacity(255, 1)

will be a linear interpolation between 0 and 1 from intensity 0 to
255.

- each colour line denotes a node, for example:

colour(5, 0, 0, 0, 1)
colour(255, 1, 1, 1, 1)

There is no interpolation by default, so, from intensities 0 to 5
(inclusive) the color is black, and from 6 to 255 the color is white. 
If there is interpolation then colours will simply be
interpolated. Just remember that each node governs every value
to its LEFT (smaller values) until the previous node on its left.

- by default, the first node is 0 (black or transparent) in both
  opacity and colour