Hi All - I have a client's logo that I would like to reveal as wine being poured into a glass rises to the top. I would rather not animate a mask to do it. It strikes me that I should be able to use the luma or alpha information in a track matte to do it, but I don't have much experience in this area. Any help is appreciated.
depending a lot on the wine glass footage, you may be able to either key the wine as it is filling, or create a luma matte by crushing the blacks and whites to create a high contrast image to use as a luma track matte.
if neither are possible, you could rotoscope out the wine as it fills the cut with a mask, or try rotobrush.
however you do it, to use that layer as a track matte, simply stack it above the logo layer in the timeline and then set the logo layer to use the layer above it as a track matte from the 'modes' options for the layer. you'll choose 'alpha' if the logo layer should use the matte layer's alpha (likely option if you roto'd the wine), use inverted alpha to take the transparent areas of the matt, rather than the opaque (likely option if you keyed the wine out), or use the luma options if you create a black and white matte.
if the wine fills up pretty quick, i.e., not too many frames to roto, or the wine is not red, shot over white or something high contrast, i think i might just draw a mask, it will likely be faster than tweaking setting to create a key or matte.