This effect applies a traditional darkroom technique, the so called unsharp mask to every video frame. With different parameter values, this can be used to soften or to sharpen the image. You can use sliders or, for maximum precision, you can use the input box. Its parameters are:

moving the slider to the right makes dark areas get darker and light areas get lighter.
this slider controls how much blurring is used in the edge-finding stage. The practical effect of this is to specify how large a region is darkened or lightened.
this slider controls how big a difference between a pixel in the blurred copy and the original copy is needed before any darkening or lightening will be applied.
to reset its slider to default without affecting others.

The CINELERRA-GG Community, 2021