Slide 30 of 42
Now the second stage, where the user sets the boundary emphasis
function. So here the user set it to be a simple peak centered around
zero, and here is the semi-automatically generated opacity function-
two peaks, one for each boundary, and here is the resulting rendering,
so you can see the two spheres, one inside the other. Next the user
is saying, "keep the boundaries the same, but move them slightly
towards the interior of the objects", and so the peak in b(x) has been
moved up, and, in the resulting opacity function, the two peaks in
alpha(v) have also moved up. In the resulting rendering, the
boundaries look the same, but if you look carefully you can tell that
the two spheres got smaller in the second rendering. The important
thing to notice in this slide is that the user never had to set the
locations of the peaks in the opacity function here- that was done
automatically, based on the position function, calculated from the
histogram volume. But, as we saw here, the user was able to influence
the location of the peaks in alpha(v) by moving the peak in b(x).
