Lighttable previews rendered at low resolution on 4K screen

[bastibe]

Describe the bug
In 3.2.1, previews in the lighttable render at a non-native resolution, as can be seen in the screenshot below.

This applies to all preview sizes, including the full-screen sticky preview, and makes judging focus very difficult. The previous release of Darktable (3.0.1) did render at the correct resolution.

The issue appears only in the lighttable, darkroom rendering is unaffected.

To Reproduce
Import images into Darktable, look at them in the lighttable.
On a 4K screen.

Expected behavior
Image previews should render in the screen's native resolution, just like the rest of the UI, and in the darktable.

Screenshots

Platform (please complete the following information):

• Darktable Version: 3.2.1
• OS: Ubuntu 20.04
• OpenCL active (disabling does not fix the issue)
• AMD Vega M with RocM 2.9

[cryptomilk]

What did you set settings -> lighttable -> high quality thumbs processing form size to?

[bastibe]

I tried several, including "always" and "never", but it does not seem to make a difference. I restarted Darktable in between changes to "high quality thumb processing from size" as well.

[bastibe]

The issue also persists in a pristine copy of Darktable right from the OBS latest release debian repo with my previous ~/.config/darktable removed.

Here is at least one more user affected by this on a thread in discuss.pixls.us

[cryptomilk]

Hmm, I don't have that issue.

[bastibe]

Is there anything I can do to help to debug this issue?

[A-Herold]

Had the same problem, but rolled back to 3.0.2 due to #5945. I experienced another related problem. For the same screen settings (3 images in row on a a MacBook Pro Retina 13’’, 2560 x 1600) now cached previews of size 5 are required, before it was 4.

[konig12]

I am seeing the same issue. I have high quality thumbs processing set to "Always". I have not touched this setting in months. The effect applies to images imported before and after the upgrade.

I'm happy to help with any debugging or diagnostics that would be helpful as well.

Darktable 3.2.1
Arch Linux with i3 window manager
Nvidia GTX 1050Ti
4k display

[edit: typo]

[hahihohehe]

I am having the same issue. For me the thumbnails are rendered better if I change system screen scaling of the monitor to 100% (I use 200% normally). But even then it is not nearly as smooth and detailed as in darkroom.

Darktable 3.2.1
Manjaro Gnome
4k display

[bastibe]

Setting "GUI thumbs and DPI scaling factor" to "1,0" gets rid of the pixeliness, but does not increase resolution:

(The crooked tower roof is straight in reality. This is an artifact of the faulty scaling.)

[bastibe]

Setting "GUI thumbs and DPI scaling factor" to "1,0" gets rid of the pixeliness, but does not increase resolution:

Never mind. This also decreases darktable resolution by a factor of two.

[esm7]

I suffer from this too following the upgrade to 3.2.1. I don't have a 4K monitor, using just the Dell XPS 15 laptop monitor. Running Linux Manjaro.

[XAndrey]

I have this bug too with ordinary FULL HD monitor: 1920*1080. In v3.2.1 on Windows 7 thumbs AND full screen previews looks like low quality - pixelated. On same PC and same photos but in Linux Mint 20 with v3.0.1 of Darktable there is no such problem. And in Windows 7 before upgrade from 3.0.2 to 3.2.1 all looked good. But there is a bug in 3.2.1 version.

[gadolf66]

I confirm this behavior on a 1366 x 768 laptop monitor, in Ubuntu 20.04.
Thumbnails are cached in disk for all resolutions, but darktable seems to be picking a lower one.
Attached is a debugging log.
dt.txt
As a side note, there's a message where screen resolution seems to be calculated:

setting the screen resolution to 81,599609 dpi

However, the correct screen resolution should be 111,94, according to https://www.sven.de/dpi/, since the screen diagonal is 14". Screen diagonal can be calculated using screen dimensions:

xrandr | grep -w connected
LVDS-1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 309mm x 173mm