How to effectively fill your Mac's display when screen sharing

Reader Earl Andrews is interested in getting the full picture—at least when screen sharing with his Mac mini. He writes:

I have a Mac mini connected to my 720p HDTV via HDMI that I use as a media server. I don’t always want to turn the TV on to configure that Mac. I prefer instead to screen share with it from my iMac. The problem is that I can’t seem to get it to fill my iMac’s display. The screen sharing window is small and even when I switch to Full Screen it won’t fill the screen. What can I do to make this work?

The main issue you have is the HDMI connection and the limitations it imposes on your iMac’s display. Let’s walk through it.

While screen sharing from your iMac launch System Preferences on the Mac mini and select the Displays system preference. In the Display tab click on Scaled if it’s not already selected. My guess is that 720p is currently selected (as it should be as that’s the resolution that’s going to look best on your HDTV). If you’d like to enlarge the window, choose 1080p instead. This will make the window much bigger, but in Full Screen mode you’ll still find bars above and below the window.

You could try choosing one of the other resolutions in the list below but you’ll find that none of them fill the screen from side to side as well as top to bottom. And they don’t because the native resolution of your iMac’s display isn’t offered.

You could, of course, put up with it as it is. After all, at the 1080p resolution that window will take up much of your display. However, if you won’t be happy until that shared screen fits your iMac’s display perfectly, I’m more than willing to help.

That help comes in the form of Stéphane Madrau’s $18 SwitchRezX. This is a preference pane that, once installed on the Mac you’re sharing, allows you to choose screen resolutions not natively supported by that Mac.

Let’s suppose, for example, that your monitor is happiest at a resolution of 1920 by 1200 pixels. You won’t find this resolution in the Mac mini’s Displays preferences. But you can add it after installing SwitchResX on the mini.

Launch SwitchResX from the mini’s System Preference window and select the mini’s display in the resulting SwitchResX Preferences window. Click the Custom Resolutions tab and then click the small Plus (+) button near the bottom of the window. In the sheet that appears enter 1920 in the Active Horizontal field, 1200 in the Active Vertical field, and click OK. Choose File > Save and, when prompted, enter your mini’s user name and password and click OK. Then restart your mini from within the Screen Sharing window. That window will show Reconnecting as the mini restarts.

Configure SwitchRezX with the unsupported screen resolution.

Once you’re restarted the mini, launch its System Preferences application, click the Displays preference, and utter joyous noises when you discover that 1920 by 1200 now appears when you choose Scaled in this preference. Select it and the mini’s screen will fill your iMac’s display when you choose Full Screen mode.

After restart choose the desired resolution to fill your display.

Now, the word of caution. If you leave your Mac mini set up this way and flip on the TV, the mini’s display will not appear on the TV’s screen. And it won’t for good reason: The TV doesn’t natively support the 1920 by 1200 resolution and so just shows a black screen. Therefore, before attempting to use your mini with your TV, screen share into it and choose 720p in the Displays system preference. All will then be right with the world (or at least with your HDTV).

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