Learn about overscan and underscan

You might see the terms "overscan" or "underscan" used in OS X, Apple TV, or your favorite app. This article explains what these terms mean, and how selecting or changing related settings affect output to a television. 

Some televisions draw the borders of an image beyond the normally visible area. Some TVs also have bezels that cover a small percentage of their physical screen. Either of these conditions result in a slight cropping of the visible image on the TV screen. This is known as "overscan". 

When an image is sent from your Apple TV, Mac or iOS device to a TV or HDTV, you might see an option to adjust overscan or underscan. For example, if you don't see the OS X menu bar or Dock when mirroring your Mac to Apple TV, try adjusting the overscan or underscan setting in the Displays pane of System Preferences.

When you change the overscan or underscan setting, the video signal sent from the Apple device compensates by slightly changing the size of the displayed image. On some TVs, changing this setting might create a black border around the image (underscan). This is expected behavior.

Some HDTVs have built-in settings you can also use to adjust overscan or underscan. Check the documentation that came with your HDTV for more information.

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