Here’s something you may not know: that HDTV that you love so much probably doesn’t show the whole picture on its screen. In fact, up to five percent of the picture can get cut off around the edges—this is called overscan. It’s old technology that’s left over from the CRT (cathode ray tube) televisions of yesteryear. Here’s why it existed in the first place, why it’s still used today, and how to (hopefully) turn it off on your TV.
If you have ever tried to connect a computer to a HDTV set via a HDMI port, you may have found that portions of the top and bottom of the screen were cut off, possibly including an entire top or bottom menu bar (this issue seems especially acute on systems that use a “skinny” top menu bar, such as Ubuntu Linux). This is because many, if not all HDTV manufacturers apply “Overscan”.
This is a holdover from the old analog TV days, when certain information (such as closed captions and timing information) was transmitted in the first few lines of the video, so sets were deliberately set up to not display those lines. Digital TV, for the most part, does not transmit data of any kind as part of the picture area (at least not in the U.S.A.), although occasionally you might still see it on an up-converted standard definition video. Usually, the only time we have every really noticed it since the digital conversion is when older commercials are played by a local TV station.
Nevertheless, most TV manufacturers enable overscan by default, even if it means that you lose a portion of the picture area most of the time. That also implies that the picture is degraded – think about it, if the station is sending a full 1920×1080 picture, but the TV discards some of that information, then it has to try to stretch the remaining picture to fill the 1920×1080 screen. So, you are losing resolution on those sets that don’t give you a way to disable overscan.
Some TVs do give you an easy way to turn overscan off, but the setting is called something different by different manufacturers. Terms we have seen used are “Dot by Dot”, “Exact Fit”, “Just Scan”, or simply “Overscan” (if you know of others feel free to add them in the comments), but there are many TV’s that don’t appear to have this setting at all. The problem is that if you are thinking about ordering a TV from an online retailer, it is often difficult to determine if the TV has a way to disable overscan or not.
Sometimes you can download a manual from a manufacturer’s site, but even it it mentions such a setting, you need to read carefully to determine if it can be used regardless of the signal source, and in particular, whether it can be used with the HDMI inputs. It seems a some TV manufacturers are still stuck in 2005, and think that there is no other way to connect a computer to a TV other than via an old school VGA or DVI input, so they only offer the ability to disable overscan on that one port. Perhaps they think those HDMI output ports on modern laptops are just for decoration?
If you were buying a TV in a store, and IF they happen to actually have the remote next to the TV, you could try looking through the various options before making a purchase, but if buying online you can’t.
We just wish that the TV manufacturers would disable overscan by default – for the most part it’s not needed anymore, and degrades the picture. Also, we wish they’d all provide an easily accessible and clearly labeled control to enable or disable it that applies to ALL the inputs, not just the VGA or DVI input. We suppose it might be too much to ask that they agree on a common name for the setting, though that would certainly make things easier on consumers. So far, only some of the Sharp TV’s actually have a control labelled “Overscan”, which is described in the manual this way:
- Overscan—Extends text and images past the screen edges to hide edge artifacts. You can select On or Off.
If only all HDTV manufacturers would do that! Even Sharp isn’t consistent – on some of their TV’s the setting is called “Dot by Dot”, and on some of their older models it can’t be enabled for anything other than the VGA input (unless maybe you use a hack to make the option appear, but you can only do that if the source is a Linux-based computer that utilizes an xorg.conf file, or you have some other way to set “CVT reduced blank” on the sending computer or device).
If you are lucky enough to have such a setting, you might want to make sure it’s turned off for display of the full picture area, and less distortion of the picture. And if you are considering the purchase of a TV, make sure it has this setting! Unless, of course, you like the idea of deliberately introducing distortion into your video, and you don’t mind not seeing top and/or bottom menus when you connect a computer.