Is there a mod to reverse engineer merged colors?

[Hiddena0]

I wouldn't need this if I was merging two colors with 255 opacity but in this case I am pretty sure one of the colors had an opacity of half or 100 or something. If a(background) + b (light effect on top, with lower opacity) = c, I have a and c, and I just need to find b at different opacity levels (they don't need to be too precise, can be 3 intervals like 70, 123, 180 or something)

[Ego Eram Reputo]

There are two identically named Unblend plugins which should do this. The latest one is this >> Unblend

[MJW]

If I understand the question correctly, my Color Clearer plugin performs the desired operation. Just set the "Color to Make Transparent" to the background color (i.e, color a).

 

It should be noted that there isn't a unique solution to the problem. A simple example is when colors a and b have the same RGB values. In that case, color c will be the same color, no matter what the opacity of color b. Basically for all cases, any amount of color a can be blended (from below) into color b without changing color c. Color Clearer always minimizes the opacity of color b.