bugMyPaint - Bugs: bug #14101, Discoloration when color picking

 
 
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bug #14101: Discoloration when color picking

Submitted by:  David Gowers <ion9>
Submitted on:  Mon 10 Aug 2009 07:39:36 AM UTC  
 
Severity: 3 - NormalPriority: 5 - Normal
Status: Need InfoPrivacy: Public
Assigned to: NoneOpen/Closed: Open
Release: Planned Release: None
Operating System: 

Mon 23 Jun 2014 06:35:04 PM UTC, comment #2:

Does this still happen with git master after 574af17a or f38b4b8a? I suspect it still does.

The code in the picker is fairly baroque now, with horrible performance issues when picking outside the window, and there are comments about deprecations in there post-Gtk3. It may well make more sense these days to replace it with a callback that looks only at the canvas.

This bug tracker will shortly be moving to github.
As part of this process, we're reviewing old bug reports on
gna.org.
Please respond so that we know this bug is still live.

Andrew Chadwick <achadwick>
Project Administrator
Wed 12 Aug 2009 07:41:07 PM UTC, comment #1:

I haven't had time to verify yet, but I guess your guess is correct ;-) Colors are picked from the screen by sampling screen pixels. This is for some part a feature, as it allows to pick also from other windows (eg. an image viewer).

It would be nice to fix this, though I don't know how. And for me it's low priority, so if anyone wants to pick this up, patch would be appreciated.

Martin Renold <martinxyz>
Project Administrator
Mon 10 Aug 2009 07:39:36 AM UTC, original submission:

steps to reproduce:
1. switch your display to 16bpp.
2. start mypaint, set brush opacity = 1. hardness = 1.. this makes sure that no other colors than exactly the ones you pick are used.
3. choose black
4. use the 'brighter' shortcut to draw a scale of shades black ->white; leave a fair amount of each shade
5. shrink the brush
6. eyedrop and fill in a few in-between shades.
7. save this image
8. open it in GIMP. eyedrop some of the colors you filled in; watch the hex field.

some of the colors will not be grayscale! for example, purplish-grey and greenish-gray have shown up for me.

I believe this is caused by sampling from the display pixels rather than the actual composited image. Thus, the non-dithered display discolors things most severely; sampling from a dithered display (ie 100% zoom, no rotation) reduces the color error greatly
(but it is still present)

This bug should be present only on 16bpp, not 15, due to the uneven component precision of 16bpp. unfortunately 16bpp is by far the more common.

David Gowers <ion9>
Project Member

 

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Items that depend on this one: None found

 

Carbon-Copy List
  • -unavailable- added by achadwick (Posted a comment)
  • -unavailable- added by martinxyz (Posted a comment)
  • -unavailable- added by ion9 (Submitted the item)
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    Follow 2 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Mon 23 Jun 2014 06:35:36 PM UTCachadwickStatusConfirmed=>Need Info
    Wed 12 Aug 2009 07:41:07 PM UTCmartinxyzStatusNone=>Confirmed
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