Setting DPI of Monitor

Support Graphics & Display
1

Dear all,

I am struggling setting the dpi of my monitor.

It is an Eizo EV3285. The resolution is 3840 x 2160, The size of the screen is 697 mm x 392 mm. Thus, it has 140 dpi.

xdpyinfo | grep -B2 resolution returns:

screen #0:
dimensions: 3840x2160 pixels (677x381 millimeters)
resolution: 144x144 dots per inch

Size and resolution are wrong.

The relevant portion of xrandr -q is:

Screen 0: minimum 320 x 200, current 3840 x 2160, maximum 16384 x 16384
DisplayPort-0 connected primary 3840x2160+0+0 (normal left inverted right x axis y axis) 698mm x 393 mm

Here, only the size if off by 1 mm in each dimension.

I added a file /etc/X11/xorg.conf.d/90-monitor.conf to fix the dpi that reads:

Section “Monitor”
Identifier “DisplayPort-0”
DisplaySize 697 392 # In millimeters
EndSection

Why do xdpyinfo and xrandr return different dimensions?
Why does the added file have no effect?

Could you please help me fix the dpi issue?

Best regards,
Fabius

2

Because it needs (as I think) a Device and Screen Section aswell.

Example:

Section "Device"
    Identifier "radeon"
    Driver "radeon" #intel or radeon or amdgpu or nvidia ...
    BusID "PCI:0:1:0" #Choose the correct one
    # 00:01.0 -> PCI:0:1:0
EndSection

Section "Screen"
    Identifier "Screen0"
    Device "radeon" #Identifier of Device Section
    Monitor "DisplayPort-0" #Identifier of Monitor Section
EndSection

Section "Monitor"
    Identifier "DisplayPort-0"
    DisplaySize 697 392 # In millimeters
EndSection

Of course you need to adjust it to your needs.

3

Also … you usually, especially when the numbers are quite close, want to prefer steps of 25%

| 1.00x=96dpi | 1.25x=120dpi | 1.50x=144dpi | 1.75x=168dpi | 2.00x=192dpi |

So your 144 is exactly 1.5, and very close to 140 … up to you if it must change.

And some relevant links, such as impermanent config:
https://wiki.archlinux.org/title/HiDPI#Xorg

And the xrandr page, specifically the section on custom configs:
https://wiki.archlinux.org/title/Xrandr#Permanently_adding_undetected_resolutions

4