[Solved] Full Screen Preview Brightening

[GwentLarry]

iMac Retina 4K, 21.5-inch, 2019
macOS Sequoia 15.7.1 (24G231)
GC 12.4.2 (6956)

When I use many tools which bring up a subsidiary window (Highlights & Shadows …, Levels …, Gamma Correction …, Luminance …) the main image brightens - at least, it appears to brighten. When I close the tool window, it darkens. It doesn't seem to actually change the image but it makes adjusting the image as desired difficult.

This happens whether Full Screen Preview is selected or not.

This issue has only appeared within the last few weeks.

[forum_adm]

Do you display the image with color profile? Is the color wheel in the footer active?

[GwentLarry]

Color Wheel is not active.

Normally, I display images with the sRGB Color Profile.

However, it seems the images causing problems have no color profile and are displayed with the default profile … and I am unable to display with the sRGB profile.

The problem images have all been scanned relatively recently, since 17/09/25 with VueScan. Images scanned with VueScan before 17/09/25 do have a color profile.

Although, I'm fairly sure when I initially scanned and edited images from 17/09 onwards, they did have a color profile, the problem only appearing more recently. macOS, VueScan and GC have all been updated since 17/09/25.

If I do a Metadata Rebuild, it seems the problem is fixed.

1. Is there a better way to fix the problem than Metadata Rebuild?

2. Do you know if this an issue with GC or VueScan?

3. I see in GC Settings -> Open -> Color Profiles an option for assigning profiles when opening RGB images with no color profile. Currently set to "Always Ignore." I suppose setting this to "Assign default profile" and choosing the sRGB Profile.icc will stop the problem happening again?

Thanks

[forum_adm]

Please email one image file zipped to support@lemkesoft.de for testing.

[GwentLarry]

Just done so.

[forum_adm]

Thanks for sending the file.

The problem is the missing embedded color profile for a working workflow.

Please check your VueScan settings. Normally VueScan adds the correct color profile to any scanned image.

[forum_adm]

You can select "Assign default profile" in the Settings > Open > Color Profiles as workaround.

[GwentLarry]

Thanks Thorsten,

Looks like is it a bug in VueScan - I have checked the settings and it should be adding a sRGB profile.