I want to create a transition using scanning effect (horizontal line going from a head to a toes of a character). Basically let's say I have two layers, one with green human, and second wth red human. Horizontal line while moving from up to bottom, switches layers, showing partially green/red human, then ending on showing only red one.
What should I do, in order to create an effect where this line, while going down, switching layer with the character to other layer. Also, is there any name for this kind of effect? Is it parallax?