Using background color of bushes as "undercoating" on transparent pixels?

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1

Basically it works like this: When you draw with a brush on a transparent part of a layer the brush behaves as if it would draw on an opaque layer instead and the opaque color used is what is set as the brush’s background color. So when you would draw a semi transparent line over a transparent part of the canvas the foreground and the background color would mix as if it would draw on a opaque layer instead.

Krita has a fore- and background color that can be set for the brush (and other tools) but I couldn’t find a way to emulate this behavior. I think I first saw it in PaintShop Pro, many years ago when it still existed. Maybe it’s already in Krita, and I just didn’t find it in the pixel brush engine. Otherwise I would write a feature request for it when people think it’s a useful feature to have.

2

I think you can simulate this, in limited and restricted situations, by using Mix:

FG-BG Mix
FG-BG Mix301×459 25.5 KB

Is that the overall effect you mean?

3

That’s what I do now but it only works when the brush has no transparency and it would draw with the background color on already opaque pixels too.

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4

I managed to work around it with the following set up:

  1. Make a layer where you want to paint and use the background color (defined in step 4) for your strokes
  2. Clone the layer from step 1.
  3. Create a filter mask for the clone and “remove” the alpha like described here
  4. Put a Paint/Fill Layer with the desired background color (fully opaque of course) for the strokes over the clone from step 2, set it to inherit alpha.

background coloring on alpha
background coloring on alpha1221×685 384 KB

The Clone will basically act like self updating mask for the fully opaque paint layer with the “background” color.

Pro: Works with every Brush
Cons:

  • its quite a set up, every time
  • only works for that one layer that is cloned
  • you can not change the background color for the strokes without affecting the background color of all previous ones.
  • filter mask needs extra CPU
  • needs merging

perhaps there is a better way?

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