Game Development Reference
Figure 19.6 With the Time Offset
value changed to 0.2, we can
compare the current frame with
the frame 2/10 of a second ahead.
with the current layer. It defaults to the layer the effect was applied
to, but it can be any layer, and the layer doesn't even have to be
visible to be used as a Target.
The Time Offset value is the amount, in seconds, that the
Target layer is offset from the current time. To compare the same
frame, keep this at zero. Contrast increases the intensity of the
The Alpha Channel value is very interesting. It allows you to
change the Alpha Channel of the result, which opens up a lot of
doors. Here's the gist of what each option does:
Original: no change to the alpha.
Target: uses the alpha channel of the layer chosen with the
Blend: blends the alpha channels of both the target layer,
and the layer the effect is applied to.
Max: uses whichever alpha channel is more opaque
between the target layer and the effect layer.
Full On: forces the alpha channel to be completely opaque.
Lightness of Result: this is where it starts getting interest-
ing. Lightness of Result will create a new alpha channel
that is based on the difference result only. This option cre-
ates an alpha based on the lightness of the result.
Max of Result: this is similar to Lightness of Result, but the
result is usually brighter.
Alpha Difference: uses the difference between the alphas
of the target layer and the effect layer.
Alpha Difference Only: this returns the same alpha chan-
nel as Alpha Difference, except that the entire RGB result