Box Blur effect

Box Blur is similar to Fast Blur and Gaussian Blur, but Box Blur has the added advantage of an Iterations property, which allows you to control the quality of the blur.

Stu Maschwitz compares the Box Blur, Fast Blur, and Gaussian Blur effects in a post on his ProLost blog.

This effect works with 8-bpc, 16-bpc, and 32-bpc color.

Iterations

How many times the blur is sequentially applied to the image. A value around 3 gives a blur similar in quality to Fast Blur. A higher number of iterations creates smoother transitions between colors and increases the blur, but it also increases the render time. The default value creates boxy results.