: Why does a brush with 50% opacity and 100% flow take 8 individual strokes to reach 100% opacity? I have a simple round brush with 100% hardness, 50% opacity and 100% flow. All other brush

@Margaret771

I suspect this has to do with the limits of transparency layers. You say that it took 8 x 50% transparency to get 0% transparency.

If you have 50% transparency, then 50% of the background colour should be visible through the top layer. If you apply 50% transparency again, then 50% of that NEW background layer should be visible = 50% x 50% = 25% original background.

Repeating 8 times, we get (0.5)^8 = 1/256. Oh, that's a pretty suspicious number!

So my guess is that you have an effective 8-bit limit - you get grades of transparency from 0/255 (0%) to 255/255 (100%), and 1/256 gets rounded down to 0/255 = 0% transparency.

Hence, it takes 8 applications of 50% to reach 0% because:


Transparency is multiplicative, not additive
It takes 8 applications to reach the lower limit of colour/transparency resolution (which appears to be based on some sort of 8-bit limit)

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@Gretchen549

Each stroke is moving 50% from the current color towards the brush color. The formula would be 100% * (1 - (brush opacity ^ number of strokes)). So going from white to black, you will have:


50% gray
75% gray
87,5% gray
93,75% gray
96,875% gray
98,4375% gray


...etc, slowly moving towards black.

I.e, you'll never actually truly reach full opacity, but at some point it will round off to 100% anyway.

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@Si6392903

Basically it blocks 50% of what is left behind, as opposed to being a pure 50% opacity in a additive way. Therefore working in an inverse exponential way towards 99.999...% opacity.

So laid on top of each other:


1st stroke: 50%
2nd stroke: 75% (50% + 50% of 50%)
3rd stroke: 87.5% (75% + 50% of 25%)
4th stroke: 93.75% (87.5 + 50% of 12.5%)
5th stroke: 96.875% (93.75% + 50% of 6.25%)
6th stroke: 98.4375% (96.875% + 50% of 3.125%)
7th stroke: 99.21875% (98.4375% + 50% of 1.5625%)
8th stroke: 99.609375% (99.21875% + 50% of 0.78125%)


etc...

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