Please help me to how should I treat alpha channnel in TouchDesigner

[horristic]

I am trying to use Over TOP to fade in my movie file using Channel Mix TOP.
But it looks weird to me when I make my alpha channel 0 over the banana image.
I expected the movie image is completely transparent and the banana shows up.
But it’s not.

On the other hand, when I try to make the banana over the other, it works as I expect. this makes me confused.

[malcolm]

The key with changing alpha is as you reduce alpha, the RGB needs to reduce with it. You should never have a RGB value that’s greater than your alpha value. The Channel Mix node isn’t great for this. Instead consider using a Level TOP to reduce the opacity if your image.