Picking resolutions on a Raspberry Pi

Dig through your Raspberry Pi’s boot configuration, and you’ll find the hdmi_group and hdmi_mode variables that control the screen resolution. Setting these to a value your TV doesn’t support causes your Pi to revert to a default VGA resolution. So short of trying every possible combination, how do you figure out which values work for your TV?

Fire up a GUI with startx and you find the “Monitor Settings” tool under “Preferences” on the menu. If all you get back is an “Unable to find monitor information!” error message, you’ll have to resort to the command line.

Running tvservice with the “-d” flag will spit out a binary file with information about your TV. You can pipe that file through the edidparser to get something human readable.

/opt/vc/bin/tvservice -d edid.dat
/opt/vc/bin/edidparser edid.dat > edid.txt

There’s a lot of information there about your TV. The interesting lines contain the word “score”, and describe the mode, resolution, refresh rate, and pixel clock rates your TV supports. You can grep the output to figure out if your TV supports a particular resolution, like 1080p.

cat edid.txt | grep score | grep 1080p

CEA mode (32) 1920x1080p @ 24 Hz...
CEA mode (34) 1920x1080p @ 30 Hz...

Pick the CEA mode by setting the hdmi_mode variable to “1” in your Pi’s /boot/config.txt file. Setting it to “2” will pick the DMT mode. The hdmi_group variable can be set to the number in parenthesis that matches the resolution you want. In CEA mode, 32 and 34 are both 1080p resolutions.

Once you’ve mode the changes, reboot your Pi to see if they work. Don’t worry if you mess things up. Your Pi will default back to a 640x480 VGA resolution if you pick values your TV doesn’t support.