similar image search not always working as expected

[Maik Qualmann]

Hi Daniel,

Thanks for the sample images, I can reproduce the problem with them.
The cause is still unclear. If I save the PNG file with digiKam as a TIFF or 
again as a PNG file, it works as expected.
After debugging, I currently see no difference in the 128x128 thumbnails that 
are created before they are processed into signatures.
Surprisingly, removing the metadata leads to different results. To be 
continued...

Maik

Am Dienstag, 6. Mai 2025, 12:27:16 Mitteleuropäische Sommerzeit schrieben Sie:
> I think we have a similar bug report; I'll have to look for it this evening.
> In that image set, one image was slightly cropped from the edges and the
> colors were modified. They were also barely recognized as similar. If you
> don't mind, send me an image set.
> 
> Maik
> 
> Am Dienstag, 6. Mai 2025, 11:52:43 Mitteleuropäische Sommerzeit schrieb
> Daniel
> Bauer:
> > Hello,
> > 
> > Sometimes similar image search does not show all possible results, even
> > though I use similarity 55 - 100%. It does find it though with
> > similarity set to 40%, but then of course it also finds a lot of false
> > positives.
> > 
> > Besides of file format and size the two images are identical, actually
> > the image used for the search is just a smaller .jpg-version made from
> > the .png original with a small added watermark.
> > 
> > Over this night I let digikam rebuild all "fingerprints", but even after
> > a restart of dk if doesn't find those images when set to 50 or 55%.
> > 
> > Is there a problem with .png files? (although it happens only with few
> > images, other .png's of other images are found)
> > Can I better the results with any trick?
> > 
> > I can provide access to sample images in private, but those are nudes...
> > 
> > Kind regards
> > 
> > Daniel
> > 
> > (I often use this function to find the original file or a published
> > version without having to go through the albums with countless photos,
> > even more when I forgot the name of a model :-) )