Bacckround picture is really dark

I tried out OpenOS and switched back to the normal one (with Updater). Now when I change my homescreen background the picture gets much darker when it apperars on the homescreen than it was in the preview. How can I fix this?

Please don’t open a new topic if you already found the right topic for it:

https://forum.fairphone.com/t/homescreen-background-is-really-dark/14860/5?source_topic_id=17892