I'm sure I've done this in the past but can't seem to remember the easiest method.
I've got a precomp that has different levels of transparency along with some text and other elements.
I want to use this precomp as a matte for another layer in my main comp, but without the transparency, so I need the alpha channel to be fully white.
I know I could duplicate the precomp to make one without transparency, but I'm looking for a solution that can use this same precomp as I'm working with many different precomps and I'd like to not have double the number.
Shift channels and set channels effects don't seem to help in this case, and using a fill effect, or a layer style fill on the precomped layer aren't working either because they take into account the transparency.
Maybe I'm not understanding the goal here but wouldn't you just put a white solid on the bottom to remove the transparency for the matte? Are you trying to maintain the semi transparent areas or make the whole alpha channel white? Are you using an alpha matte or luma matte for the main comp?