A Good HDTV Shows You Everything
If you purchased a gallon of gas and it measured 5% short, would you still call it a gallon? When it comes to viewing high definition (HD) video on a high definition television (HDTV), many HDTVs have a nasty habit of hiding (destroying) visual information along the border of the video image reducing the detail and clarity of the remaining visible picture that fills the screen. The excessive scaling of video beyond the edge of a TV’s screen is referred to as overscan and it is often expressed as a percentage of the sacrificed video picture – a TV that exhibits 5% overscan fails to display the outermost 5% of the video’s border.
The following pictures show the lower right corner of a 1080p flat panel HDTV’s screen including a bit of its black bezel. This HDTV has a default overscan of about 6% as well as an underscan display mode that shows every pixel the video signal has to offer. The left half of each picture shows the TV screen using its default overscan setting, and the right half of each picture shows the exact same portion of the TV’s screen and the same frame of video but with overscan disabled – an underscanned picture. In each picture I’ve highlighted the details concealed by TV’s overscan in yellow.
For this particular HDTV, pressing a button on the remote returned the missing video pixels and improved the overall clarity of the picture. Unfortunately, most older HDTVs and many new HDTVs lack these desirable underscanning abilities. I’ve yet to see a new rear-projection television (RPTV) provide an underscan picture mode for video signals – some RPTVs can be configured to display an underscanned picture with PC video signals, but the effective screen resolution is usually less than advertised.
The relatively small percentages of video overscan I’ve mentioned may not sound like much, but the losses incurred scale with screen size. A 65 inch 1080p RPTV with 6% overscan (a typical amount) is missing 1.7 inches of video from the left and right sides of an HD image – a total of 3.4 inches of lost visual information along the horizontal axis. With full-frame 1080p video, a 6% overscan equals a loss of over 124,000 video pixels – regardless of screen size.
It doesn’t matter if the video source is a favorite HD channel, a next-generation game console, Blu-ray or HD DVD movies, or even DVDs, a good HDTV doesn’t waste a single pixel and it allows the viewer to see more. Of course a HDTV can degrade image quality in a number of other ways, but video overscan shouldn’t be one of them.
Robert Heron
I agree that over-scan stinks. The concern I have is content that has artifacts on the bottom of the screen. Unfortunately this even includes many Revision 3 programs that have an out of place line at the bottom of the image that doesn’t match up with the rest of the image. While hardware is ready for a full image, a lot of non blu-ray content doesn’t seem to be.
I agree with both the article and the previous comment to a certain extent. There are a fair amount of television stations that display their information a little funny. For example, ESPN’s ubiquitous bottom bar floats high in the screen with a lot of unused space at the bottom if overscan isn’t on. Discovery uses a bizarre aspect ratio in most of its content and is window-boxed unless overscan is on. In other words, overscan is used as a subtler form of zoom to make the screen look correct since the zoom on our tele isn’t very subtle. Just to be clear, I am talking about HD content. We do prefer not to overscan (and don’t with computer or dvd content) but we’re waiting for stations to fix their formatting.
I should expand on the “detail destroying” comment I made in the article. Overscan ruins the potential 1:1 overlay of the video bitmap to the display’s pixels. At best, the loss of detail results in only a slight blur of the video image. This discussion gives me ideas for a few interesting picture detail tests.
Robert good article on HDTV overscan. My Rear projection 3LCD HDTV Sony WEGA does not do it as much as some older rear projection HDTV’s. I don’t like overscan and I agree when your shopping for a new HDTV turn off overscan.
This must be what my Panasonic TV calls Size 1 and Size 2. However, when turning overscan off, some channels show a little white line on top of the screen which is met with much frustration and annoyance.
Robert,
Do you have an update on 40 – 42 inch TV in 700 – 800$ range?
I am asking because the last recommended blog post on this is six months old.
Thx
Actually, gas with ethanol made from corn is about 5% less effective…