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I've tried various settings, and get different results, but I don't understand how flow percentage affects the outcome. It seems to affect how "fast" I get to the maximum opacity set for the brush in an uninterrupted stroke, yet if I set it to, say, 25% with opacity of 50%, even the first movement of the brush gives me a much thicker layer of colour than 25% of the 50%. Looks more like 75 or 80. And it also seems to depend on brush spacing.

Can someone explain in a simple way what flow is and how it works together with opacity, please?

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up vote 2 down vote accepted

there are two main differences between flow and opacity.

  1. flow affects how smoothly your 'paint' is applied: a hard brush with a flow of 20% will leave a kind of strobed paint application effect.
  2. it also differs in the way the 'paint' is laid down. while a brush with 20% opacity lays down a smooth layer of paint from mouse click to mouse release (i.e it doesn't get darker even if you cross over your own brush stroke), flow with the same value actually lays down 20% of your opacity value. if your cross your stroke again, and again it continues to darken until it matches your specified opacity.

there is a full description of the effect here:

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Thanks for the answer, though, after reading the article and trying again, I think I understand why I couldn't reproduce the effect that I was expecting (and which you explain in pt.2). This depends on brush spacing setting! So the strobed effect that you see in pt.1 is actually a side effect of brush copies applying over each other! It is clear to me now, VERY useful, thank you very much :D – NPC Dec 13 '10 at 13:29
great! I learnt something too. thanks – JamesHenare Dec 15 '10 at 2:03

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