[Confirmed ok] ColorSync: GC correctly ignores RGB color profile embedded into grayscale image

[porg]

Original headline was
ColorSync: GC autoassigns sRGB to grayscale image then informs that it dropped sRGB as incompatible with grayscale


• Preferences > Open > Color Profiles > When opening a file which has no profile then [ Assign the default profile ▾ ] sRGB.icc
• I open "grayscale-image.png". This triggers the following dialog:
• The image "grayscale-image.png" contains a RGB color profile. But the image is in Grayscale color model. So, the profile will be dropped.

[ Okay ] [ ] Do not show this again


So what seemingly happens is that:

1) GC first autoassigns sRGB as the color profile (in memory only, not persisted to the file).
2) Then later comes the sanity check "Does the (embedded) profile (e.g. sRGB) contradict the color depth (grayscales)?" If yes through that dialog.

Please check whether the interplay of that sanity check plays well together when the color profile is assigned via user ad-hoc (dialog) or automatically (from preferences).

[forum_adm]

I rechecked it here. A do not auto assign a profile to a grayscale image. That is only be done for RGB images.

Does you PNG maybe already contain a profile?

Please forward the file.

[porg]

I sent you the file for inspection.

Please feel free to answer right here in the forum thread.

[forum_adm]

I checked the file with ExifTool.

The PNG is in grayscale mode (only one channel with 8 bit) - but it contains a RGB color profile.
So, the message is correct.

Screenshot 2022-11-19 at 19.22.46.jpg (295.43 KiB) Viewed 288 times

[porg]

Thanks for looking into this!

The file had this genesis:
1) Screenshot taken with macOS native screen capture or Snagit, exported as PNG.
2) PNG optimized with ImageOptim. If it detects that an RGB only contains grayscale colors then it converts it to grayscales to save data. But it does not correct the color profile accordingly. And it was also set to leave the metadata intact, so no profile stripping. Outcome: Grayscale image with an RGB color profile, a contradiction.

So GraphicConverter detected that anomaly correctly.