Alpha is also multiplicative, not just transmissivity. You just pick the right operation to think about it. https://en.wikipedia.org/wiki/Alpha_compositing htt

Alpha is also multiplicative, not just transmissivity. You just pick the right operation to think about it. https://en.wikipedia.org/wiki/Alpha_compositing https://en.wikipedia.org/wiki/Alpha_compositing If your compositing operation is A over B, then transmissivity is multiplicative for the A&B region. If your compositing mode is A in B, then opacity (alpha) is multiplicative. This has the same structure, mathematically, as thinking about logical operations like AND and OR, which are complementary to each other. If you think of AND as multiplication, well, you can think of OR as multiplication as well, just with the values flipped around.