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I have an Ubuntu 18.04 on my PC, and I would like to use my external monitor with it. It's a LG UltraFine 27UL850-W that supports 4K display. However, when I plug it, it seems to be zoomed out compared to the main laptop screen.

Here is the output from xrandr : eDP-1-1 is my laptop sceen and DP-1-1 is my external monitor.

Screen 0: minimum 8 x 8, current 5760 x 2160, maximum 16384 x 16384
eDP-1-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 381mm x 214mm
   1920x1080     60.01*+  60.01    59.97    59.96    59.93    40.00  
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      59.99    59.94    59.95    59.82  
   1280x1024     60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1440x810      60.00    59.97  
   1368x768      59.88    59.85  
   1360x768      59.80    59.96  
   1280x800      59.99    59.97    59.81    59.91  
   1152x864      60.00  
   1280x720      60.00    59.99    59.86    59.74  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   1024x576      59.95    59.96    59.90    59.82  
   960x600       59.93    60.00  
   960x540       59.96    59.99    59.63    59.82  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   864x486       59.92    59.57  
   800x512       60.17  
   700x525       59.98  
   800x450       59.95    59.82  
   640x512       60.02  
   720x450       59.89  
   700x450       59.96    59.88  
   640x480       60.00    59.94  
   720x405       59.51    58.99  
   684x384       59.88    59.85  
   680x384       59.80    59.96  
   640x400       59.88    59.98  
   576x432       60.06  
   640x360       59.86    59.83    59.84    59.32  
   512x384       60.00  
   512x288       60.00    59.92  
   480x270       59.63    59.82  
   400x300       60.32    56.34  
   432x243       59.92    59.57  
   320x240       60.05  
   360x202       59.51    59.13  
   320x180       59.84    59.32  
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-1 connected primary 3840x2160+1920+0 (normal left inverted right x axis y axis) 600mm x 340mm
   3840x2160     60.00*+  30.00  
   2560x1440     59.95  
   1920x1080     60.00    59.94  
   1600x900      60.00  
   1280x1024     60.02  
   1280x800      59.81  
   1152x864      59.97  
   1280x720      60.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
HDMI-1-2 disconnected (normal left inverted right x axis y axis)

How could I scale it to a decent resolution without bluriness ? I think I need a scale of 150% on my external monitor so that everything looks good.

1 Answer 1

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If I understand correctly, everything looks and works OK: you just want a higher scale factor on your 4K monitor presumably because the physical pixels are smaller.

The basic way to do this is with xrandr itself:

xrandr --output DP-1-1 --scale 1.5x1.5

You can obviously adjust the scaling factors to suit by tweaking the 1.5 above (looking at the physical sizes reported by xrandr, you'd probably have better luck with 1.25x1.25, though this might introduce more blur/visual artefacts). You can't scale in this way without some blurriness - that's just how it works. (By way of contrast, MacOS scales in a much less blurry way by pre-rendering the desktop at high resolution, and at significant cost to graphical performance).

Personally I find that font scaling makes for a better result than xrandr in many cases, and avoids blurring, but that is a higher level operation which varies according to application / desktop environement. You'd need to consult the manual for your desktop environment (e.g. GNOME).

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    Font scaling definitely helped ! I hadn't think about it before, thank you much ! Commented Jan 21, 2021 at 16:50

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