Still obsessing over the "Add Sub" blend mode...I thought I was closer, but when I tried to work through some cases, it fell apart again.
Restating the rule more verbosely, this is what I
thought I'd figured out...
- If the Foreground is above 50%, it will be added to the Background.
- If the Foreground is below 50%, it will be subtracted from the Background.
Results above 1 or below 0 are capped in the 0-to-1 range, as usual
I'm left with some puzzles:
- If both the Foreground and Background are near 50%, shouldn't the result be either near-black or near-white?
- I am having trouble explaining the resulting middle row of results.
- Every time I do the math "manually" I seem to run into an issue. For example, when you transition from under to over 50%, why don't you get a sudden transition from black to white?
I used a color-picker and, assuming a linear scale, I decided my "0.2" value in my previous post should be close to 0.3.
Also, to further illustrate my problems, I used some "mid-gray" examples slightly above and slightly below the 50% level.
In this example, I am listing Background first:
1: 0.7 + 0.7 = 1.4 = "1" = White
2: 0.5 + 0.7 = 0.8 = Bright Gray
3: 0.3 + 0.7 = 0.6 = Light Gray
4a: 0.7 + 0.51 = 1.21 = "1" = White ---> But it's gray
4b: 0.7 - 0.49 = 0.31 = Gray... Should we have darkish-gray right next to white (4a)?
5a: 0.5 + 0.5 = 1.0 Why is the center gray instead of either black or white?5a: 0.5 - 0.5 = 0.0 Why is the center gray instead of either black or white?6a: 0.3 + 0.51 = 0.81 = gray... Should we have darkish-gray right next to black (6b)?
6a: 0.3 - 0.49 = -0.19 = "0" = Black ---> But it's rather dark
7: 0.7 - 0.3 => 0.4 = Gray
8: 0.5 - 0.3 => 0.2 = Dark Gray
9: 0.3 - 0.3 => 0.0 = Black