Hi I have a posterized black/grey/white mosaic layer, set to 7 on posterize (so there are 7 grey values) It is made with a base of fractal noise, so the 7 different greys flicker aound the comp. Examples from different points on the timeline:
I also have 7 layers with a different image grid on each (these match the squares in the mosaic grid) Examples: Layer 1 Dollar
Layer 2 Money Layer 3 Skull
I want to have, for example 100% black squares from the mosaic to reveal Layer 1 Dollar 75% black (dark grey) to reveal Layer 2 Money 25% black (light grey) to reveal Layer 3 Skull (and so on) The result being a comp with multiple symbols flickering in different positions based on the black value in the Mosaic layer.
Apply a levels effect on your grid, adjust the lower and upper limits to clip out the range you need, apply the Shift Channels effect to e.g. convert the luminance into transparency or apply a white fill to get a clean luma matte. Rinse-repeat for every level until you have your 7 pre-comps with the individual mattes based on the same noise grid source comp. Tweak away!