bugMyPaint - Bugs: bug #19648, Moving .ORA file between GIMP and...

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bug #19648: Moving .ORA file between GIMP and MyPaint destroys image

Submitted by:  Griatch <griatch>
Submitted on:  Sun Apr 15 18:49:48 2012  
Severity: 4 - ImportantPriority: 5 - Normal
Status: Ready For TestPrivacy: Public
Assigned to: Andrew Chadwick <achadwick>Open/Closed: Closed
Release: GITPlanned Release: None
Operating System: Linux Debian SID

Fri Jan 4 20:55:47 2013, comment #5:

This bug has been closed because it is marked ready-for-test and
no further comments have been added in a long while. Since we
have not heard otherwise, we assume that the fixes works as intended.

If there are problems with the implemented functionality, please
file a new issue.

Jon Nordby <jonnor>
Project Administrator
Mon Apr 16 22:33:21 2012, comment #4:

This bug should be fixed in MyPaint Git master.


That's what I get for not testing the really basic stuff properly. Thanks for the excellent test data - you should find it looks correct now; I've tested against pngsuite as well, and it all looks fine (like Firefox; unlike a lot of really dim image viewers out there). Specifically the "PNG-files" set at http://www.schaik.com/pngsuite/#gamma all look the same as each other like they should, with the caveat that the 0.4 sample image appears to posterize (however it's encoded at 8bpc: the posterization is actually there in the data. Firefox shows what MyPaint does.)

Andrew Chadwick <achadwick>
Project AdministratorIn charge of this item.
Mon Apr 16 18:00:19 2012, comment #3:

Including a gzipped tar file with a series of gradients saved as .ora in GIMP 2.6.11 along with jpg comparisons. They all result in a washed result when importing into MyPaint.

(file #15584)

Griatch <griatch>
Mon Apr 16 09:45:12 2012, comment #2:

griatch: please could you attach a small minimal "bad" .ora file and a .jpg of what it's supposed to look like saved from Gimp? I'll need the sample file it to fix this one. Thanks!

My gut feeling from looking at it is that MyPaint might be applying the file gamma incorrectly during processing (oops).

maxy: from your description, the file had no ICC profile embedded to say what its R,G,B[,A] samples mean, nor a chunk to indicate that they're sRGB values with standard gamma compression. Thus we fall back on treating it as a "generic" additive RGB colour space where the R, G and B primary colours the samples express degrees of are (maybe) defined in absolute XY[1] terms along with the white point[2], and (separately maybe) there's a gamma correction curve. lcms2 can handle all 3 cases, but probably only if we feed it the right data...

[1] http://en.wikipedia.org/wiki/CIE_XYZ
[2] http://search.cpan.org/search?query=Graphics%3A%3AColorObject&mode=module is a really good start point for how this sort of colour munging works.

Andrew Chadwick <achadwick>
Project AdministratorIn charge of this item.
Sun Apr 15 19:45:51 2012, comment #1:

Confirmed. The codepath taken when loading the PNG layer seems to be "cHRM and/or gAMA (generic RGB space)". The PNGs saved by GIMP inside the ORA have a gAMA chunk but no sRGB one (according to pngchunks), but I'm not sure yet what that means...

Martin Renold <martinxyz>
Project Administrator
Sun Apr 15 18:49:48 2012, original submission:

Saving an image in GIMP 2.6.11 using the latest ora-plugin works just fine. You can also re-load the file in GIMP without any problems. But when loading that .ora file into MyPaint-GIT, it gets a "white shade" applied to it that essentially destroys the image. Saving the file in MyPaint and importing it back into GIMP retains this white shade effect.

Below is a demonstration of what happens. To the left is the original .ora image, saved in GIMP. To the right is what comes back after having loaded and saved that image in MyPaint.

The image is a two-layer image, not different from any other I've used many times previously. I have tried this with single and multi-layer images too, getting the same result.

Griatch <griatch>


Attached Files
file #15584:  mypaint_bug_19648.tar.gz added by griatch (114kB - application/gzip)
file #15569:  error_screenshot.png added by griatch (460kB - image/png)


Depends on the following items: None found

Items that depend on this one: None found


Carbon-Copy List
  • -unavailable- added by jonnor (Posted a comment)
  • -unavailable- added by achadwick (Posted a comment)
  • -unavailable- added by martinxyz (Posted a comment)
  • -unavailable- added by martinxyz
  • -unavailable- added by griatch (Submitted the item)

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    Follow 7 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Fri Jan 4 20:55:47 2013jonnorOpen/ClosedOpen=>Closed
    Mon Apr 16 22:33:21 2012achadwickStatusConfirmed=>Ready For Test
    Mon Apr 16 18:00:19 2012griatchAttached File-=>Added mypaint_bug_19648.tar.gz, #15584
    Mon Apr 16 09:45:11 2012achadwickAssigned toNone=>achadwick
    Sun Apr 15 19:45:51 2012martinxyzStatusNone=>Confirmed
      Carbon-Copy-=>Added achadwick
    Sun Apr 15 18:49:48 2012griatchAttached File-=>Added error_screenshot.png, #15569
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