HD 101: Overscan and why all TVs do it
By Ben Drawbaugh 
posted May 27th 2010 2:43PM
posted May 27th 2010 2:43PM
Other HD 101 goodness:
What is ATSC, PSIP, QAM, and 8-VSB?
How to use Dolby TrueHD and DTS-HD with your PS3
Why there are black bars on HDTVs
A test pattern with overscan markers on the four edges.
The easiest way to wrap your head around overscan is to forget about the word for a second and think of cropping an image. If you take a picture and cut off an inch from each edge and blow it up to the original size, then you'd effectively be overscanning. The term comes from the days of CRTs when the scan lines that drew the image literally scanned over the edge of the viewable part of the tube -- PC users were all too familiar with the small print that a 21-inch CRT PC display proclaiming that it was actually 20-inch viewable. The problem with CRTs was that a limitation of the technology was its inability to accurately reproduce images along the edges of the tube. So instead the image was overscanned which resulted in some loss of picture but maintained quality for the center of the image -- the part that matters most.
So if CRTs are dead then why do we still have overscan? This is where the bad news comes in, but the short answer is because it used to be there. The source of the problem is that broadcasters expect the TV to crop the image so they don't mind putting garbage on the edge -- like a misc yellow line on the left or black and white dots show in the images below.
Notice the zoomed part contains white and black dots that are used for the 1st and 10 marker.
Sometimes this garbage serves a purpose. Like in the image above or an analog broadcasts that's converted to digital. Since analog doesn't have a way to send metadata, like rating and closed captions, the data is encoded in the vertical blanking interval and shows up as flashing pixels when the signal is converted to digital and displayed without overscan.
In this zoomed section you can see a faint yellow line on the left hand side. Luckily NBC finally fixed this particular problem.
It isn't just broadcasters who are to blame, the TV manufactures play their part too. You see because some broadcasters don't ensure a clean picture on the edge, the TV manufactures err on the side of caution and crop it just in case. They know that a yellow line on the left side of a brand new HDTV is a great way to get a return. On top of that, talking heads on an HDTV with overscan appear larger, so consumers see this and think, "oh that TV looks better to me." It's really crazy to think that consumers would rather see a zoomed, fuzzy image than a yellow line on the edge, but that's most people for ya.
These are the same screen shot, one is presented with overscan, one isn't. See how much bigger McCain's head is?
It's not all bad
In a perfect world broadcasters would mind their signal and ensure every pixel was worth watching, then TV manufacturers wouldn't feel the need for overscan -- or at least we hope. In the meantime we're just happy that most TVs have a way to turn it off. When an image is displayed properly, it's sometimes referred as 1:1 pixel mapping. This simply means that every pixel in the signal is displayed by a single pixel on the display. Of course each manufacture has its own name for this mode; like Samsung who sometimes calls it Screen Fit, and Pioneer called it Dot by Dot. No matter what it's called, it's rarely on by default -- even when watching 1080p24 from Blu-ray which never has garbage on the edges! -- so you'll have to find the button on the remote called something like format or P.size, depending on the brand. Your best bet is to read the manual -- shocker.
But even if you don't ever find the button or just like it on, modern video processors aren't half bad at scaling the image. Sure it'll never be as good displaying it properly, but to some the occasional garbage on the edge is far worse then the lack of detail -- which they're less likely to notice. But, there are some HDTVs that don't let you turn it off, which is really lame. Some sources like Vudu and HTPCs will let you adjust the overscan at the source, but this only solves half the problem, as seeing the edges of the image is better than nothing, but the image is still being scaled twice.
Vudu overscan adjustment that is on by default.
nVidia overscan and centering adjustment.
Another issue we've seen, although less frequently, is where the HDTV will display the image without overscan, but it still shifts by a line or two and scales the image -- although we admit that we only learned of this by running the Pixel Phase test on Digital Video Essentials HD Basic calibration disc. This is the type of thing that most will never know and unless you test it with a pattern or read it in a review, you'll never be the wiser.
I sell/install HT systems, and often have to turn ON overscan because customers are distracted by the 'junk' on the very outside of the picture area. Glad the function is still there, but wish broadcasters would master for 100% viewable area.
@(Unverified)
Well they sort of are determining what that 100% is...
@bravokiloromeo
true but 10% is a lot of information at 1920.
Worse if you are making content for playback on HDTV and say a projector or a computer then either you make two versions or the non HDTV viewers end up with titles etc looking strange sitting a long way in
and from experience it is a LONG way in on HDTV. Back in SD days it wasn't so bad.
@Cy Starkman
Sure it's a lot of information, but it's not a lot of actual screenspace.
Interesting & I have just set my Pioneer Kuro to 'dot by dot' - thanks!
However I did have a chuckle at the statement "Notice the zoomed part contains white and black dots that are used for the 1st and 10 marker". If I'm not very much mistaken those dots are a camera's 16:9 flag in the vertical blanking interval - nothing to do with football! Displays can read this and adjust their scans accordingly! I know this as I often have to mask them out when editing broadcast programmes. It could also be Vertical Interval Timecode (VITC) but this bar code like real time clock usually extends across the whole frame. Subtitlers read this 'gash' so they know where they are in the programme (for one).
Cheers
D Evans
My Samsung (Series 5) has the Screen Fit option greyed out - it's unselectable, and no it's not already applied.
Any ideas if theres a custom firmware I can load or something, it is up to date with the official ones..
@FORDY my Samsung does the same thing but only on certain inputs. Are you using HDMI?
@FORDY
it's greyed out if the current signal doesn't support it. (e.g. non digital signals).
it can't map pixels 1:1 if it's not getting a digital signal.
try something that feeds the TV digital 1080p or i, i.e. a 360 over HDMI, a bluray player or anything like that. Shouldn't be greyed out then.
@Fliesen There is another trick that might work, I have an older Samsung DLP TV and when hooked up through HDMI 1 I was unable to alter the P.size to fix overscan, However if you change the "Label" of the input (ie. change HDMI to PC) it will enable a whole new set of options. In my case, it allowed me to Wide Fit and Wide TV P.size modes which fixed the overscan.
TLDR: Try changing the input label of your HDMI connection to something other than HDMI 1/2. For me, setting it to "PC" opened up the greyed out picture options.
@Fliesen
But wouldn't non-digital sources be the only ones that actually need it? Digital sources should be able to provide metadata without encoding it in the video itself.
If the display is smart enough to disable it for certain inputs, I would think that the digital signals would be the ones that don't use it, and the analog (which is crappy SD or ED at best) would be the only inputs that do use it. But then I don't know anything about it, I don't have a fancy TV.
@FORDY
I had a similar issue on my panasonic TH-50PZ700U. It turns out that I could only change the setting if I use a 1080i/p signal. Since the TV's native res is 1080p, I can't turn off overscan if I am sending a 720p signal to the TV. I found this out with my DirecTV receiver. I had it set to output the native res of each channel. Once I changed the box to only send 1080i signal's, I could turn off overscan on channels like ESPN HD. Since ESPN is really 720p, my DirecTV box was sending 720p until I made the change. It's something to try on a display that is greying out the overscan option.
@Fliesen
Thanks all, I was testing it out on the builtin analogue tuner..
@FORDY
Some sets won't allow a 1:1 mode for 720p images, depending on the input source.
@FORDY On my Samsung (Series 4, 450), the option to turn off overscan is called "Just Scan". Does yours have a "Just Scan" option? Try that.
My Pani 42 inch 720P (getting a little grey in the beard TV) has no way to turn off the overscan. I need to use the video drivers on my HTPC in order to see the edge of the image. Thanksfully, I will soon be replacing this TV.
@glennS
I've got a 56 inch Samsung DLP that I had to do the exact same thing to. Was driving me nuts until I updated my HTPC drivers and was able to scale it.
@glennS
Yes, Panasonic is known to be particularly sucky sucky when it comes to this. At least that was when I decided on a TV, which was why (despite looking better and being cheaper) I decided on a more expensive Acer. That was a while ago though, when no TV could display PC input without overscan. Amusingly it is usually the VGA input that works flawlessly, while DVI employs overscan. I hope that has changed by now...
@kadajawi I just set my Panasonic G35 to "HD size: Size 2" and overscan is gone.
"Ultimately overscan is really just one of those things that videophiles obsess about while most are content not knowing."
well...Engadget HD readers = 99.5% Videophiles and .5% lost Engadget classic readers.
So thanks for the article! I'd always wondered why I was seeing junk on the top and had to have my projector crop it out.
@tkuhl87 as a lost engadget classic reader i had to lol ;)
@fokka same boat, i think i took a wrong turn somewhere between steve balmer and rock band 3...
@tkuhl87 Same here. We'd have the occasional channel that had random dots and crap up there... now at least i know why.
I'd still like it to go away though!! That way i can actually see the whole image... maybe in another 2 TV generations or so?
@tkuhl87
I'm not lost, I just don't know where I am. :)
The worst part now are Blu-Ray movies that pad the overscan area with a black border. So if you disable scaling you get a pseudo-black border (and video black is never truly black).
My TV is this one:
http://www.plasmatvbuyingguide.com/plasmatv/pioneer-pdp43a5hd.html
That write-up says it offers "Dot by Dot" for PC, but it does not give me the same option using the HDMI connection. So, I imagine it only works with the VGA port, which isn't really an option... :(
Any ideas?
@palehorse
Set your device's output resolution to force 1080i or 1080p. Some TVs, including Pioneers since it sounds like that's what you're using if it's called Dot by Dot, only allow that selection on 1080i or 1080p signals.
@palehorse
Actually, check that. According to the specs of your panel, its panel resolution is 1024x768, which is why you can do dot by dot on your PC input but not anything else -- because none of the "normal" HD resolutions that other devices would output have pixel layouts that correspond directly to your TV's panel.
What's even stranger is that 1024x768 isn't a widescreen resolution but rather a 4:3 resolution. The only way that 1024x768 is fitted onto a widescreen display is if the pixels themselves have a 4:3 aspect ratio rather than being square, which if you do the math does indeed give a 4:3 resolution a 16:9 aspect ratio. That means that either 4:3 resolutions are being stretched out, or widescreen resolutions are being displayed in their proper aspect ratio but with a lot of pixel information dropped out.
@John H
Actually, I believe the resolution specs for my TV are consistently wrong on the web... I almost positive about that.
This TV model is unique. It was actually only made for Tweeter's Black Friday Event back in 2005. The TV uses the same panel and internals as the Elite PRO-930HD of that same year -- which itself is 1366x768. The only real difference between mine and that Elite is the lack of an external media box for all connections.
When connected directly to the TV, my HTPC's current output resolution, using Nvidia's overscan correction tool in the Nvidia control panel, is set for 1218x688. 720p mode is detected by the TV and then up/down/sideways converted to 768p by the set.... right?
So, my HTPC is fine. The problem is that I can't correct the overscan from the STB or Bluray player sources since normal HDMI input does not allow for "Dot by Dot," and neither of those sources has a tool/mechanism of its own... right?
If I'm wrong, PLEASE let me know!
I've set up my Panasonic TC-P42G10 to use overscan mode for cable TV and 1:1 pixel mapping for everything else. I'm happy with that arrangement. Though I do wish broadcasters would quit putting junk at the edges of the picture so I could use 1:1 pixel mapping on cable TV, too.
@UnnDunn On your Panny, is 1:1 called "Just" as indicated in the above article? Because on my Panny "Just" is not 1:1. It stretches the image (for viewing 4:3 content).
@Jimi 1:1 pixel mapping is activated from the "Advanced Picture" menu. There is an option called "HD Size" and I can select "HD Size 1" which gives me 3% overscan or "HD Size 2" which gives me 1:1 pixel mapping.
My set has a THX mode, which forces 1:1 pixel mapping (ie. while in THX mode, "HD Size 2" is set and cannot be changed.)
seeing that first picture brings me back to a sad time as a Pats fan.
i have always wondered what 'overscan' was and why it matters
@cwalters74
18 wins, 1 GIANT loss! We sent Tom Brady running home to mommy. What a glorious Sunday that was. :)
I have it turned off for ALL content. I'm not bothered at all when the garbage on the top/side rarely appears.
@migmanson you make me proud. I have friends that use stretch mode on 4:3 content on their HDTV, so depressing. "But I paid for those pixels!"
Wouldnt care so much about a little bit of overscan if it didn't crop the taskbar on my htpc. On the upside, both nvidia's and ATI's systems make this a relatively easy fix.
My Samsung Plasma that I bought last November has a working "screen fit". The same goes for my Epson 1080p projector.
@erh: is it at the left and right edges? Top and bottom can be explained with the slight mismatch in aspect ratios, fitting 1.85:1 in 1.77:1 nets thin letterboxing bars if you don't crop the sides.
I notice the edge garbage (Top of image) when I record in SD on my TiVo and then convert it to play on my WMC. Not too distracting now because I am so used to it.
> So if CRTs are dead then why do we still have overscan?
Hold on there, cowboy. I'm still sitting in front of an HD CRT, and love it. Keeping my Sony KV-34XBR910 @ 7' until it dies.
The overscan on it can be quite annoying, I will admit. And i celebrate games that support overscan adjustments/tuning. I just can't calibrate all of the overscan out, it's a CRT after all. ;)
@Jamescb
Me too! I've just bought a new (to me) telly - sony KD-28DL10, I call it. £10. 28 inch screen, flat as a pancake at the front. Size of a washing machine at the back. Great picture (trumps any lcd I've seen), beautiful sound.
Roll on, world cup, tour de france, wimbledon. I figure lcd technology is moving faster than £10 a year so if I get a year from it, I'm up.
@Jamescb You have to because you can't lift that thing ! You're stuck with it forever ! :-)
I sold mine and it took 3 guys to lift it
One of our channels has junk on the top of the screen (horizontal lines) and I have to set that area hidden because of the distraction.
The ideal approach to handle a pixel or two of "garbage" around the border is to crop but not scale. That is, the TV should be configurable to allow one or more rows/columns of pixels on each side of the image to be blacked out.
As an alternative, if there is garbage only on a single side of the image, you can just shift the image just enough to move it off of the screen. For instance, if the top row is garbage, just bump the image up by a pixel.
@mcg
,,The ideal approach to handle a pixel or two of "garbage" around the border is to crop but not scale. That is, the TV should be configurable to allow one or more rows/columns of pixels on each side of the image to be blacked out,,
NO. THE IDEAL IS AND ALWAYS WILL BE FOR BROADCASTERS TO FIX THE PROBLEM AT THE SOURCE.
BUT YOUR "BLACKED OUT IDEA" IS ONE THAT IS WAS GOING TO MENTION:
MANUFACTURERS SHOULD HAVE A BLANKING OPTION SO THAT PEOPLE LIKE ME CAN TURN OFF THE 'OVERSCAN' AND THEN BLANK OUT THE OUTER EDGES TO HIDE THE 'GARBAGE'.
THIS WAY YOU KEEP THE CORRECT RESOLUTION, BUT SIMPLY MAKE THE BEZEL LOOK A LITTLE WIDER THAN IT REALLY IS...
Wait, are we sure that nearly ALL HDTV's still do this? Because mine doesn't and I've had it for years.
And yes, I get the random junk on top and sides of the screen sometimes - I deal with it.
@badasscat
I've heard of some Westinghouse TVs that don't have overscan, but it is the exception and not the rule.
I have a Westinghouse (W4207) and after reading this article, I went through all the settings looking for something that sounded like an overscan toggle, but couldn't find anything. And the manual is pretty basic (the on-line one at least) and didn't have any more info.
Good to know.
Interesting... I've got a question about overscan and maybe someone here can answer it:
I recently bought a mini-displayport to hdmi adapter. Hooking it up to my macbook pro running Snow leopard and plugging it into the tv I get options in OS X for adjusting overscan (and putting sound out through hdmi). Hooking up my mac mini which doesn't have snow leopard, I can turn overscan on/off but not adjust it and have no option to pipe sound out through the hdmi. Turning overscan on cuts off the desktop at the edges, turning it off leaves black bars around everything.
Is this purely hardware related? or will upgrading to snow leopard on my mac mini allow me to better adjust the overscan? I'm doubtful the sound through the hdmi can be helped but that would be nice.