Wavelet artifacts

While tinkering around with g’mics wavelet decompose in gimp 2.9.5, I noticed some strange artifacts and a little shift in brightness in the image, the shift and the artifacts stayed after combining the layers.
The image which I used is Mairi_Troisieme.ORF from [PlayRaw?] Mairi Troisieme converted to a 16bit prophoto tiff with Raw Therapee.

I tested some other pictures and it seems, that those artifacts mostly appear in the darker parts of the images.

I am thankful for every reply, thanks.

Yes, @patdavid already mentioned this issue, and all I can tell now is that it seems to be a bug in the way the grain merge blending mode is implemented in GIMP 2.9. This luminosity change effects does not occur when using GIMP 2.8, as far as I know.

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I’m wondering if we can produce a clear example of the problem to report as a bug?

I’ve done one once, but apparently it’s gone… :slight_smile:
What I did is I created a .xcf file with several layers in ‘grain merge’ mode that had a different rendering on GIMP 2.8 and 2.9.
If you run G’MIC Wavelet decompose and save the result as a .xcf, this should do the trick.

Thanks, I’ll run a set later and file a bug report with the team. :slight_smile: