Rick6Star wrote: ↑
Sun May 13, 2018 9:11 am
When I started using VNC on Raspberry without a monitor connected the resolution dropped to 720x480. I changed de resolution with "Raspberry Pi Configuration" tool from the preference menu without any problems.
By default VNC uses the resolution of the connected HDMI monitor. When no monitor is connected the RPi automatically switches to Composite mode NTSC or PAL.
In that case VNC uses the very low resolution of the Composite.
As you found you can use the GUI config utility or sudo raspi-config to set a specific resolution.
The config tool does 2 things.....1) enables hdmi_force_hotplug=1 so that HDMI is always on without the monitor and 2), sets the resolution of your choice (mode and group) in /boot/config.txt
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.