The Gaussian Blend filter blurs an image and blends the result with the original. Blending is a very powerfull technique and there is a lot of tutorials how to get soft, film and other interesting looks by blending blurred image with the original. With other blending modes you can get glow, fog and many other effects. Parameters: Size Controls the blur power. Value of 1.0 sets the maximum blur, but you can enter in edit field values up to 4.0 and get  more blur, but with a slightly reduced quality. Blend Mode Select blend mode. Almost all known blending modes are realized here. Opacity Controls the blend opacity. Value of 0.0 is equal to 0% opacity (base image) 1.0 is equal to 100% opacity (blended image). But while most effects stop here in Gaussian Blend you can get mix between blended and blurred image (values in range 1.0-2.0). Plus - you can enter in edit field values from -20.0 to 20.0 and get other unusial effects. The power of color blending modes - you can blur only the colors or some color channel. With entering in opacity edit field values out of 0.0-2.0 range you actually get new, never seen before blending modes and sometimes very unusual effects. See also Blur variations: Gaussian Blur - Blur an image. Variable size - control the blur power within the frame with a Radial Mask, or Linear Mask.