Slide 26 of 42
... map the histogram volume to an opacity function. There are probably
ways of doing that which are completely automatic, but I think that
would be rather difficult, if not somewhat presumptious. So, we've
chosen to break the mapping from data value to opacity into two steps,
one of which is automatic, one of which is controlled by the user.
The domain in between is an abstract spatial domain which we can
sensibly call "position". Each of the two stages are done by seperate
functions which I will describe in the next two slides, but I'm going
to name them here for context. The position function p(v) maps from
data value to position, and the boundary emphasis function b(x) maps
from position to opacity. Then, the semi-automatically generated
opacity function alpha(v) is just the composition of these two:
b(p(v)).
