I recently had two of my monitors die on the same day, and as a replacement I bought a new Samsung Syncmaster S23A350H monitor to gain back some of the desktop real estate that I had lost.

While generally happy with the monitor (cheap and cheerful!), it doesn’t have great connectivity options, being limited to VGA and HDMI. I decided to use the HDMI option since I didn’t want to go back to the bad old days of analogue.

I connected up the monitor to my Raedon HD5700 graphics card using a HDMI cable, and found that the image was not filling the screen. I got a image in the centre surrounded by black pixels.

It turns out that the fix is actually quite easy, though it can be a bit of a pain to find if you don’t know where to look. By default the HDMI output from RAEDON cards is scaled down by 15%, and to get the image showing full screen you need to disable this using the following steps:

1. Right click on the Desktop and select the Catalyst Control Centre
2. Select My Digital Flat-Panels from the left hand menu
3. Select Scaling options (Digital Flat-Panel) from the sub menu
4. Select the monitor attached to the HDMI cable from the drop down menu
5. Change the Underscan-Overscan option to the value that will make the image appear full screen – 0% in my case

There you go – you should have now have full screen HDMI output using your ATI graphics card!