MP 7,1 underscan is greyed out when scaling display

[RyanFlynn]

Hey friends,

I have a Mac Pro LG CX 48" coming out of a Pro Vega ii duo via HDMI. When I'm in default for display, but when I scale the image, the underscan is grey out, I'm just missing some of my task bar on the screen. I've tried holding option for more choices, but underscan just isn't an option.

A little help?

Ryan

 

[joevt]

Shouldn't underscan be unnecessary on a flat panel display? Such displays should have a 1:1 pixel mode for PCs such that one pixel output = one pixel on the display and a test pattern of alternating horizontal and vertical pixels should appear perfectly.
https://www.nies.ch/doc/it/hori-vert.en.html
https://www.walvisions.com/FullFields.html

Maybe try the Custom Resolutions feature of SwitchResX? Then see if the Quick change buttons can change the border.
So first create the 3840x2160 HDMI timing if it doesn't already exist (it probably does, select it to make it the current resolution, then when you create a custom resolution, the values for the current resolution will be the default for the new custom resolution).

You can use the edid-decode --list-vics command to get a list of modes.
Then for the particular mode you want (3840x2180 120Hz in this example), use the edid-decode --vics 120 command to get all the numbers.
Then enter the numbers into SwitchResX. Test it (Save and Activate Immediately or Save and Disconnect and Reconnect the display).
If you need to adjust the border than try using the Quick change buttons (but maybe these are only for CRT displays - I'm not sure they'll have the right effect in your case).

 

[RyanFlynn]

On the LG c9 and CX there is a setting for underscan in the aspect ratio tv menu. Changing it from Auto to on solved my issue