Three-Way Blur

Three-Way Blur

After Effects offers quite a few blur effects, but
three are most common for general usage:
Gaussian Blur, Fast Blur (which at best quality is no
different), and Box Blur, which can match the other
two but offers more flexibility.
At the default Iterations setting (1), a Box Blur can
seem crude and, well, boxy, but it can approximate
the look of a defocused lens without all the more
complex polygons of Lens Blur; you can also hold it
out to the horizontal or vertical axis to create a nice
motion blur approximation (where Directional Blur
is actually too smooth and Gaussian).
Raising the Box Blur Iterations setting above 3 not
only amplifies the blur but refines the blur kernel
beyond anything the other two effects are capable
of producing. What actually occurs is that the blur
goes from a square appearance (suiting the name
box blur) to a softer, rounder look. You’re more
likely to notice the difference working with overrange
bright values in 32 bit HDR.
Fast Blur and Box Blur also each include a Repeat
Edge Pixels checkbox; enable this to avoid dark
borders when blurring a full frame image. The
same setting with these two effects will not, alas,
produce the same amount of blur even if Box Blur
is set to 3 iterations (to match Fast Blur).