am I missing something? In 2.77, in the Video Sequence Editor in the ‘Edit Strip’ panel, I have the option to Blend a strip. There are several options like “alpha over”, “add”, “multiply”, etc. but I did not find “Screen”. Isn’t this implemented or does it hide behind some unconventional name?
Using the formula f(a,b)=1-(1-a)(1-b), I found a workaround by adding white strips, having strips a and b subtract from them, multiply them and have the result subtracted from 1 again. This seems very tedious and slow, though…
Thanks and best regards