alpha channels

I meant the other way around, and Mask instead of Maskclip: clip3=Layer(clip, clip2, "add", 256) # clip2 is a black clip made with blankclip Maskclip(clip4, clip3) # clip4 gets the alpha channel of clip I guess it gives the same problem ?

Wilbert, My understanding is that Mask(clip,clip1) applies a greyscale version of the visible channels of clip1 as a mask to clip, ignoring the alpha channel of clip1. In your revised layer example, the output is always just the original clip isn't it, as all it does is add zero value pixels? It seems as if basing a BlankClip on a clip with an alpha channel does not make the BlankClip inherit the alpha channel. It is curious also that the Levels function should affect the alpha channel. I guess I am just too used to the way channels wotk in Photoshop, and expect AVISynth to work in roughly the same way.

Yes, I am discovering this. My original idea works if crudely, but whiting out the clip is problematic too. Using high values for RGBAdjust only works if none of the pixel values have a channel zero value. I tried layering on a white BlankClip, but for some reason this seems to be messing up the alpha channel of the original clip. In the same way that one can mess around with audio channels and the YUV channels of YV12 clips, it would be nice if one could manipulate R, G, B, and a channels.

More strangeness. Try this. vid00=ColorBars(352,288).ConvertToRGB32.ResetMask vid01=BlankClip(vid00,color=$FFFFFF).ResetMask Layer(vid00,vid01,"lighten",level=255,threshold=0) One would have thought that the output should be all white, but instead you get a mosaic of cyan!

lighten and darken seem to be ok only for YUY2. As the whole layer thing is written in assembler, I can't check anything :(