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An example: I have a Windows 7 desktop connected to a monitor with a native resolution of 1600x900 and support for several lower resolutions. I also connect a projector with a native resolution of 1024x768 and support for several higher resolutions (up to 1920x1200). I use the Windows + P key and select "Duplicate". This causes both the monitor and the projector to change to the same resolution, usually 1024x768, but sometimes 1600x900. Either displays a picture, but with different scaling/cropping.
I've confirmed that EDID is working because if I select "Computer only" or "Projector only" it uses the native resolution of each one automatically. I've also checked in Display Settings that the monitor is always display 1 and the projector is display 2.
How does Windows choose what resolution to use? How can I change this behavior before duplicate is selected?
If you choose "duplicate", then they will be set to the same resolution, which will be the highest that is seen as supported on both displays. – Ƭᴇcʜιᴇ007 – 2017-02-07T17:17:44.790
@Ƭᴇcʜιᴇ007 In my example, that would be 1600x900, but it's not what happens in my experience. – Jason – 2017-02-07T17:31:46.453