Kate's Comment

Thoughts on British ICT, energy & environment, cloud computing and security from Memset's MD

Using TV screens as monitors (how to fix overscan/zoom)

I have a fairly cheap and generic 32″ LG 1080p screen connected to my media computer (a Mac Mini) as a backup to the projector which doesn’t work well during the day time. We mainly use that machine for watching stuff from Netflix (astonishing quality by the way!).

In my office I also have three 27″ Samsung SyncMaster TA550/T27A550 LED screens which I’ve recently used for a very successful little Xbox Halo: Reach LAN party (see left). 🙂 They appear to be perfectly adequate for gaming despite a 5ms response time. Accepted wisdom is that you need a 2ms response time for gaming, but I think that’s rubbish – humans cannot detect delays of less than about 20ms! I also selected the T27A550 because I wanted 27″ LED screens with VESA mounts on the back – not that many wall-mountable options it turns out!

I also intend to use the three screens in my office for work. In fact I’m typing on one now rigged up as the second screen for my Mac Air; it seems quite happy driving the screen at 1920×1080 via a moshi adapter, while also driving its built in screen. I’ve yet to decide how to drive the other two. I may use a DisplayLink device and my ‘Air or I might get another machine to drive them. I intend to use them as monitoring boards (network ops on one, sales/marketing stats on the other) rather than additional workspace, though it would be nice to have Tweetdeck/whatever open on one too. I have standardised around HDMI as the interface (see below for why I don’t use expensive cables though!).

However, when I first started using the screens there was “overscan” – the edges of the picture did not quite fit. See the picture on the right for what I mean. On the media PC it was mildly irritating and I tried fixing it with the “underscan” setting in the Mac’s system preferences.

This was far from ideal since it lost some of the crispiness. In the end I just accepted that I could not see the status bar on that computer if using that screen – I normally contolled it remotely from my laptop via VNC anyway.

But with the new office screens that was not acceptable. This weekend I invested a bit of time rummaging in the monitors’ options and found the answer: by default they all are programmed to “zoom” slightly. Not sure why that’s the case but it is possible to tell them to just display what they are getting on their HDMI imputs pixel-for-pixel. The image on the left shows the LG with the status bar now visible (ie. no overscan / zoom), without using the computer’s “underscan” facility. I must have navigated around the menus several times before stumbling across the necessary setting, confusingly masked by a picture size/aspect ratio setting of 16:9. Apparently in screen manufacturer land, 16:9 actually means “chop off the edges”. Who knew!

Anyway, on the LG you press menu then go into “Picture Mode” then “Aspect ratio” and change from “16:9” to “Just scan”. See below:

On the Samsungs it was Menu -> Picture -> Screen adjustment -> Picture Size, then change from “16:9” to “Screen Fit”. See below:

HDMI cables

As an aside, no I do not pay lots of money for HDMI cables. HDMI is a digital signal, not analogue like with VGA cables, so it makes no difference. It will either work or not work. I have seen one edge case with a cable that was too long, but it would lose sync every few seconds briefly – not some gradual degredation of quality as the morons in shops would have you believe. See this article from CNET on why all HDMI cables are the same for more info!