Color variations in output image thumbnails (only)

ART 1.20.2 on Windows 11

This (thumbnail color variations) just started with some images I shot today and processed in ART. It doesn’t happen on older images. Also, it’s happening on the thumbnails only, not when opened in ART nor any other program I’ve tried. All apps are color managed and otherwise all is OK. So it’s just sort of cosmetic at this point, but I’m wondering why it’s happening.

Here are the two raw files as seen in the ART file browser, post-edits (i.e., totally normal):
ART file browser - raw images

So as a test for each raw file I created four processed images, eight total:

  1. A TIFF via the queue
  2. A JPG via the “Save Current Image” button
    (restarted ART)
  3. Another TIFF via the queue
  4. Another JPG via the “Save Current Image” button

For comparison, here are the processed output files as seen in ART and a few other apps (filenames are self-explanatory):

ART file browser (images 4, 6 & 8 affected, numbered from left)

XnView MP file browser (all images affected)

FastStone Image Viewer file browser (all images affected)

RawTherapee 5.9 dev file browser (no images affected)

So why the variation between blue and purple in the sky and why did it just start? All output files used the same sidecars, no changes between them. There have been no configuration changes to any programs, including ART, nor to my camera, etc.

Again - This is affecting thumbnails ONLY so it’s not a functional problem (yet?), but very curious to me nonetheless. Here are the two raw files and their sidecars if anyone wants to test.

IMG_0197.CR3 (35.1 MB)
IMG_0197.CR3.arp (12.0 KB)

IMG_0198.CR3 (35.9 MB)
IMG_0198.CR3.arp (21.9 KB)


Thumbnails of non-raw images are not color managed and assumed to be in srgb. I guess they are in a different color space? I also don’t like this but my distaste has not been strong enough to fix it yet. But maybe I’ll reconsider…


They’re all in ROMM RGB (i.e., ProPhoto) as per my usual workflow.

That makes sense in a way but it’s curious it just started happening when it hasn’t before. Maybe there’s something about the hues and tones in the sky of these images that’s marginal in terms of rendering.