Bug 401712 - Blur brush mixes colour with white when near the edge of image
Summary: Blur brush mixes colour with white when near the edge of image
Status: RESOLVED INTENTIONAL
Alias: None
Product: krita
Classification: Applications
Component: Brush engines (show other bugs)
Version: 4.4.0
Platform: Microsoft Windows Microsoft Windows
: NOR normal
Target Milestone: ---
Assignee: Dmitry Kazakov
URL:
Keywords: triaged
Depends on:
Blocks:
 
Reported: 2018-12-03 19:33 UTC by kalia24
Modified: 2021-10-01 11:43 UTC (History)
4 users (show)

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Latest Commit:
Version Fixed In:


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Description kalia24 2018-12-03 19:33:14 UTC
SUMMARY
So I'm using a predefined brush k)_Blender_Blur (though any Blender Brush causes the issue) - whenever I'm near the border of the picture, it starts mixing white into the colours I'm blending - this causes it impossible to bled colours near the picture edge.

STEPS TO REPRODUCE
1. Create a file with any-but-white colour layer (so the issue is visible).
2. Use any blur brush near the picture edge.

OBSERVED RESULT
Krita blends white (apparently there's "infinite white space" beyond the visible canvas) into the colour when blending near the picture edge.

EXPECTED RESULT
Only pixels on the visible canvas are taken into account when calculating blend outcome (if needed - edge pixels are repeated to "fill" the required blur brush shape).

SOFTWARE/OS VERSIONS
Windows 7 x64
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Comment 1 wolthera 2019-04-08 16:01:59 UTC
Hi, thanks for the report.

It's the default pixel, actually, but I think this is a very complex bug to resolve either how.
Comment 2 kalia24 2019-04-12 10:49:12 UTC
Just as note - using Blur effect on a non-white layer also causes blurred white borders to appear and I'm kinda sure it wasn't always like this. If there was some update that changed blur algorithm(s), maybe the answer to the problem is somewhere there?
Comment 3 vanyossi 2019-04-13 04:21:11 UTC
The way krita works when you paint in the offcanvas area is to paint "behind" the gray area. you can see how this is a problem working on background layers and Blending.

1. Create new image and delete the top layer
2. Fill background with a non color white
3. Use move tool and reveal white.
4. to avoid white. Select Rectangular tool and use an eraser brush to fillover the gray area near the edge.
5 Now blend and you should get alpha not white as blended color.

What to do now? generate some content in that border.

When painting just paint outside in the gray area so you put pixel data outside the border. If a complex image is already done: Mirror your edge contents or grow a copy of your image to fill those edges.

1. Duplicate current layer
2. Scale duplicated to grow over the edge a little.
3. Set dublipated layer below
4. Merge both layers.
Comment 4 Dmitry Kazakov 2021-01-11 08:02:07 UTC
Well, it is not actually white that is blended into the layer. It is **transparency**, which is dragged from the outer area of the image. That is, you just start seeing the background layer through the blended area.

To fix the issue you should uncheck this option:

Brush Editor -> Smudge Length -> Smear Alpha

With this option unchecked the brush works as expected in the report.

Question for all:

Do we want to change the default brush preset to fix that in 5.0, or we'd better just write about that in the manual?
Comment 5 kalia24 2021-01-11 08:31:21 UTC
I see, but then no alpha is smeared at all - when smearing the image content is what I'd like to be able to do (especially when blending background blur on the egdes). So I still find it a bug - with "alpha" instead of "white" then.
Comment 6 Dmitry Kazakov 2021-07-20 08:09:50 UTC
Hi, kalia24!

> To fix the issue you should uncheck this option:
> Brush Editor -> Smudge Length -> Smear Alpha

Could you please check this solution? It should fix the issue for you (I've just checked)

Or you want to have both things at the same time, smear alpha channel and not having blends on the border of the image?
Comment 7 kalia24 2021-08-02 19:01:29 UTC
Nope, it doesn't. It's not alpha that causes the issue - I can smear the white into the visible canvas with the "Smear Alpha" inactive and paint on it while the layer has alpha locked. So it's a solid white colour, no alpha in question.
Comment 8 kalia24 2021-08-02 19:06:21 UTC
Update - it concerns only the "Background" layer, other layers have "pure alpha" beyond the visible canvas.
Comment 9 Bug Janitor Service 2021-08-03 04:33:41 UTC
Thanks for your comment!

Automatically switching the status of this bug to REPORTED so that the KDE team
knows that the bug is ready to get confirmed.

In the future you may also do this yourself when providing needed information.
Comment 10 Dmitry Kazakov 2021-08-10 10:17:25 UTC
Hi, kalia24!

> Update - it concerns only the "Background" layer

Perhaps you just shouldn't use background layer for painting then? When creating the image you can choose whether to pre-fill the layer with the default color or set the canvas color. I mean, the brush works in a way how we expected it to work and there is a way how to overcome the issue very easily (create a new layer and deactivate "smear alpha" in the brush). I don't think I can do any more about that.
Comment 11 Dmitry Kazakov 2021-10-01 11:43:28 UTC
Okay, I will close this bug as "intentional". There is a quick fix for it: just don't use background layer for painting with transparency. Create a new layer and paint on it.