The Gaussian Blur filter blurs an image or selection.
The radius affects the strength of the blur. Besides for creating a fuzzy image, the Gaussian Blur has a few other uses. If you are working on an image with edges which one deems to be overly rough, one could use a blur radius of 1 to soften the image slightly, yet less dramatically than using a larger radius or the standard Blur filter. It is also very useful for a variety of image effects, such as shadows.
IIR vs. RLE
The filter supports two methods of Gaussian Blur: IIR and RLE. They both produce the same results, but each one can be faster in some cases.
IIR (Infinite Impulse Response) works best for large radius values or for images which are not computer generated, such as photographs.
RLE (run-length encoding) works best for computer-generated images or those with large areas of constant intensity, such as logos.
Selective Gaussian Blur
The Selective Gaussian Blur filter will selectively apply a Gaussian Blur to areas of a picture with less detail, leaving the areas with detail untouched. This can be used for cleaning up noise in a picture.