Game Development Reference
So what can you do with this wackiness? One of the great
purposes of this effect is to compare color adjusted frames and
instantly see their differences.
Another great purpose is to use the end result for visual
effects. Let's use this example, and say I wanted to create some
fi re around my hands a la that guy in Fantastic Four. I could roto-
scope my hands as they move around. But it would be much eas-
ier to simply use Time Difference to create a layer with an alpha
channel that was roughly my moving hands, as in Fig. 19.7.
Figure 19.7 Because my
hands are the only thing moving
much here, we can use Time
Difference to create a layer with
just my hands, complete with
In this example, I set Time Offset to a small 0.07, enabled
Absolute Difference, and took the Alpha Channel result to Max
of Result. There's some extra pixels around the edge of me, but
we could easily mask that out. The point is that we've isolated
the hands for the most part, with a modicum of effort. We can
then add an effect like Particle Playground and use the Layer
Exploder to create the illusion that my hands are on fi re. What
else can be done with Time Difference? The potential is pretty
big with this one.
The Time Displacement Effect
As we saw back in Chapter 7 when we looked at the
Displacement Map effect, you can use the lightness values
in an image as a controller to shift pixels. Similarly, we can use
the lightness values in a map as a controller with the Time
Displacement effect, only the map will not shift pixels spatially.
The map will shift pixels in time .