Custom Bitmap Effects allow you to alter the brightness of each pixel in a bitmap depending on the brightness of adjacent pixels using a method known as convolution. The matrix on the right of the Bitmap Effects dialog box controls the process. Type values into the matrix such that the sum of all the values is 1. For more information see Applying special effects to bitmaps.

For example:

-2 -1 0

-1 1 1

0 1 2