JPG thumbnails are proportionally darker than TIFF images

[lphilpot]

XnView MP Version 1.0 64bits (Apr 28 2022)
Windows 11

I've noticed something that I'm not sure is XnView or further upstream in the workflow. I have three sunset shots, all TIFFs (processed in RawTherapee) that were slightly cropped, scaled down, transparently watermarked (lower right corner only) and exported as quality-85 JPGs in GIMP.

When viewed each TIFF and JPG looks the same as its "partner", other than scale of course. But the JPG thumbnails are progressively darker than the TIFF thumbnails.

I've captured some screenshots to illustrate what I'm seeing.

Here are the images' thumbnails. Counted from left to right, the TIFFs are numbers 1, 3 and 5, and the JPGs are numbers 2, 4 and 6. You can see that #2 is very slightly darker than #1, #4 is relatively more dark than #3 and #6 is very much darker than #5.

Now, each pair is shown in Compare mode with the TIFF on left and JPG on right. I've zoomed in the JPG to make it approximately the same size on screen. You can see they look the same, not like the thumbnails. In fact you can see the same effect in the thumbnails at the bottom of Compare mode. In all other image viewers they look the same. What makes the JPG (only) thumbnails look progressively darker and darker?

I've not had time to see if this pattern is shown elsewhere, on other image sequences. Actually, I'm not sure if I have any other applicable images to test. But I have many TIFFs and JPGs from this basic workflow and have never noticed this before.

For comparison, here are the same thumbnails in another image viewer (same order plus a couple of other images, so ignore the first two) and they're all consistent:

FS_thumbs.png (177.72 KiB) Viewed 712 times

Thanks.

[xnview]

By default embedded thumbnail is used, try to rebuild thumbnail by disabling 'Settings>Thumbnail>Use embedded thumbnail'

[lphilpot]

I disabled embedded thumbnails, rebuilt them, optimized, etc. but there's no change.

[xnview]

could you send me a sample of each?

[lphilpot]

JPGs are attached. Not sending my (each) 120MB+ TIFFs...

Thanks.

[xnview]

i need a TIFF to compare

[lphilpot]

Sent you a PM.

[xnview]

The embedded thumbnail in the jpeg is darker. Uncheck 'Settings>Thumbnail>Use embedded', and select the file, 'View>Rebuild thumbnails'

[helmut]

The embedded thumbnail in the jpeg is darker. Uncheck 'Settings>Thumbnail>Use embedded', and select the file, 'View>Rebuild thumbnails'

"Settings > Thumbnails > Use embedded" should not be unchecked: FAIK, disabling usage of embedded thumbnails will slow down browsing and thumbnail generation in XnView significantly because complete image must be read to create a thumbnail the first time. "View > Rebuild thumbnails" should be sufficient to update thumbnails.