Blurred & darkened wallpaper on the 3.36 lockscreen has dithering / color banding
I wish I had a way to screenshot this, but GNOME Shell 3.36's blurred and darkened lockscreen exhibits a lot of color banding on big wide screens (in my case, a dual screen setup comprised of a portrait 1080x1920 screen and a 25" landscape 2560x1080 ultrawide screen, equivalent to the width of a 27" 16:9 screen). With https://img.wallpapersafari.com/desktop/1680/1050/39/35/7uVpQ4.jpg as a wallpaper (or even the official time-based tesselated GNOME wallpaper in Fedora 31), both in Xorg or Wayland GNOME session, I get some very noticeable color bands on the lock screen.
This is much more pronounced on physically bigger (and higher-resolution) screens like my ultrawide IPS monitor, vs my ThinkPad X220's old 13" TN display where the problem is less apparent.
If trying to reproduce this and experiment a bit by taking the wallpaper and applying a 100px gaussian blur in GIMP or Krita, and I can see that:
- the stronger the blur,
- the higher the image displayed resolution/zoom level,
- the darker the image (if you use the levels tool to darken it, for example)
...the more noticeable the color banding is.
So, maybe I'm wishing for a pony here, but I'm wondering if there's something GNOME Shell's new blurred lockscreen implementation can do to mitigate that.