Reduced bit depth / dithering pattern on monitor?

There are weird streaks that seems to be dithering pattern on the (GNOME) desktop background image. It’s very pronounced on the monitor[1] that I connected to the laptop [2] through DP and much more subtle on the laptop screen. The monitor didn’t have this issue when connected to my old laptop (through HDMI).

Is there a way to check what bit depth the system thinks the monitor has?


  1. AOC 24G2 ↩︎

  2. Framework 13, Radeon 780M ↩︎

I’m not currently at my Framework 13 but I have the same specs as yours- what kind of monitor is that?

Ah, an AOC monitor. I would ask for a dmidecode -t something output but it’s been a while since I’ve troubleshot monitors. What’s the xrandr output?

What you are seeing are Moiré pattern - Wikipedia effects I’m guessing.

This can happen if the resolution of the monitor is not 1 to 1 with the pixels on the display.

Are you scaling the monitor? Is its resolution the recommended setting?

xrandr, dmidecode, xwininfo
$ xrandr --verbose
Screen 0: minimum 16 x 16, current 4176 x 1504, maximum 32767 x 32767
DP-4 connected 1920x1080+2256+0 (0x25) normal (normal left inverted right x axis y axis) 530mm x 300mm
        Identifier: 0x21
        Timestamp:  673519
        Subpixel:   unknown
        Gamma:      1.0:1.0:1.0
        Brightness: 0.0
        Clones:    
        CRTC:       0
        CRTCs:      0
        Transform:  1.000000 0.000000 0.000000
                    0.000000 1.000000 0.000000
                    0.000000 0.000000 1.000000
                   filter: 
        RANDR Emulation: 1 
        non-desktop: 0 
                supported: 0, 1
  1920x1080 (0x25) 452.500MHz -HSync +VSync *current +preferred
        h: width  1920 start 2088 end 2296 total 2672 skew    0 clock 169.35KHz
        v: height 1080 start 1083 end 1088 total 1177           clock 143.88Hz

...

eDP-1 connected 2256x1504+0+0 (0x41) normal (normal left inverted right x axis y axis) 280mm x 190mm
        Identifier: 0x23
        Timestamp:  673519
        Subpixel:   unknown
        Gamma:      1.0:1.0:1.0
        Brightness: 0.0
        Clones:    
        CRTC:       1
        CRTCs:      1
        Transform:  1.000000 0.000000 0.000000
                    0.000000 1.000000 0.000000
                    0.000000 0.000000 1.000000
                   filter: 
        RANDR Emulation: 1 
        non-desktop: 0 
                supported: 0, 1
  2256x1504 (0x41) 287.000MHz -HSync +VSync *current +preferred
        h: width  2256 start 2424 end 2664 total 3072 skew    0 clock  93.42KHz
        v: height 1504 start 1507 end 1517 total 1559           clock  59.93Hz


$ sudo dmidecode -t 8
# dmidecode 3.4
Getting SMBIOS data from sysfs.
SMBIOS 3.5.0 present.

Handle 0x0008, DMI type 8, 9 bytes
Port Connector Information
        Internal Reference Designator: JTYPEC0
        Internal Connector Type: None
        External Reference Designator: USB
        External Connector Type: Access Bus (USB)
        Port Type: USB

...

$ xwininfo -root

xwininfo: Window id: 0x3f2 (the root window) (has no name)

  Absolute upper-left X:  0
  Absolute upper-left Y:  0
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 4176
  Height: 1504
  Depth: 24
  Visual: 0x63
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x62 (installed)
  Bit Gravity State: ForgetGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +0+0  -0+0  -0-0  +0-0
  -geometry 4176x1504+0+0

dmidecode shows just 4 USB slots as Framework uses USB-C expansion cards.

:sweat_smile: The pattern is on the thumbnail because I selected 50% on the images. It’s not in the full-sized images.

p.s. Checking and setting bit depth may be impossible on Wayland[1].


  1. ↩︎

I think this might be a bug.

  1. It is noticeable even when comparing the desktop background with the image (opened by Loupe) on the same screen.
    Screenshot from 2023-12-27 12-13-29Screenshot from 2023-12-27 12-13-21
    (The above 2 are again 50% scaled.)
    Screenshot from 2023-12-27 12-16-46
    Screenshot from 2023-12-27 12-18-02

  2. It seems to be caused by having 2 screens of different resolution / dimension.
    It goes away if I set the laptop screen to 1920x1080 then log out & log in. (My old laptop is 1080p, same as the screen.)
    It affects the laptop screen as well.

How have you configure the external monitor?
Is it mirroring the laptop screen or extending the desktop?
I often use different sized screen with laptops without issue, but I do not mirror.

“Join”. It’s just configured in GNOME settings, made it my primary display, changed to 144Hz, nothing else.

I use kde, i do not know what join does, sorry,

Join is just extend. Sorry for the rushed reply.
I think this might be a GNOME problem. Imma just leave this since it doesn’t seem to affect applications.