Composite Modes

[Bester]

Every paint program has a layer compositing mode called "overlay". I would like to
apply this in avisynth, but I don't know how to get there.

aka from here
http://img373.imageshack.us/img373/812/comporig3oh.jpg

to there
http://img373.imageshack.us/img373/4...laymode2sa.jpg

I found this on the net:
"Overlay mode applies two different techniques. If the pixel color value is lighter than middle gray, 128 value, then Screen mode is applied. Where the pixel color value is darker then middle gray, 128, Multiply mode is applied which makes the dark parts darker."

"Multiply compares the color values of the pixels in both clips and multiplies them together. Dark areas of the clips will remain dark, lighter areas will be darkened as a result. px = (pxlayer1 * pxlayer2) / 255"

"Screen compares the color values of the pixels in both clips and multiplies the inverse values of the pixels. Lighter parts of the image will remain the same. Darker parts of the image will be lightened by this process.
Wert=255-((255-pxlayer1)*(255-pxlayer2)/255)"

Any ideas how to achieve this??