Talk:Overscan

old version

Here is the big part I pulled, lets fix it here and restore it.

PC Video Capture

PC capture cards act as HD, with no overscan.

An image captured at 720x576 (with 4:3 content) generally looks like cropping to 658x540 when you account for what a CRT TV would remove from the edges. However, remember to scale this to 720x540 to restore 4:3 ratio (thanks to non-square pixels)

This is the rule of thumb to simulate CRT TV viewing, when using PC video capture:

	4:3		16:9
	crop to	then scale to	crop to	then scale to
NTSC 720x480	660x450	600x450	660x450	800x450
PAL 720x576	658x540	720x540	658x540	960x540
HDTV 1280x720	does not exist		no need to crop/scale
HDTV 1920x1080	does not exist		no need to crop/scale

(Other factors to consider are gamma reproduction, and 50fps / 60fps motion reproduction).

Tech Specs

There is no hard technical spec for overscan amounts. Some say 5%, some say 10%, and the figure can be doubled for title safe, which needs more margin compared to action safe.

The official BBC suggestions actually say 3.5% / 5% (see p21, p19). The following is a summary:

	Action Safe		Title Safe
	vertical	horizontal	vertical	horizontal
4:3 SD	3.5%	3.3%	5.0%	6.7%
16:9 SD	3.5%	3.5%	5.0%	10.0%
16:9 HD	0.0%	0.0%	1.5%	1.5%
14:9 SD on 16:9 HD	0.0%	10.0%	1.5%	12.5%
4:3 SD on 16:9 HD	3.5%	15.0%	5.0%	17.5%

As you can see, "14:9" provides a lot less wastage for 16:9 viewers — that extra 5% real-estate looks a lot better for corner logos, watermarks and scrolling news tickers.

4:3 viewers get an automatic 4.1% added to both vertical figures thanks to 14:9's thin black bars — this is why 0% and 1.5% safe areas are acceptable.

Terminology

Title safe or safe title is an area which is far enough in from the edges to neatly show text without distortion (in worst case).

Action safe or safe action is the area in which you can expect the customer to see action. However the transmitted image may extend to the edges of the MPEG frame 720x576. This presents a requirement unique to television, where an image with reasonable quality is expected to exist where (some) customers won't see it. This is the same concept as used in widescreen cropping.

TV safe is a generic term for the above two, and could mean either one.

720 or 702 or 704?

(PAL) 702 is the width of analogue, not digital; the definition of what is 4:3, and what is 16:9, derives from here (702 can be either).

(NTSC) 704 is the width of analogue, not digital; the definition of what is 4:3, and what is 16:9, derives from here (704 can be either).

720 is used to record analogue to digital safely, in case it shifts sideways, which it will.

It's also a highly composite number, useful for high-speed digital operations.

544x576 and 480x576 etc

(PAL) 540x576 and 480x576 are derived from 720x576, and defined as the same width as 720. 540 vs 544 is undefined (but divides into 16 neatly).

(NTSC) 540x480 and 480x480 are derived from 720x480, and defined as the same width as 720. 540 vs 544 is undefined (but divides into 16 neatly).

352x576 in MPEG-2 and 352x288 in MPEG-1 are derived from 704. This makes sense in NTSC land (704x480) but because PAL is 702, the difference is undefined. SDTV is messy.

625 / 525 or 576 / 480

In broadcasting, analogue systems count the lines not used for visible picture, whereas the digital systems only bother to encode (and compress) content that may contain something to see.

The 625 (PAL) and 525 (NTSC) line areas therefore contain even more to overscan, which can be seen when vertical hold is lost and the picture rolls.

A large part of the vertical overscan available in analogue only, known as the vertical blanking interval, can be used for datacasting.

Horizontally, the difference between 702/704 and 720 is referred to as nominal analogue blanking.

480 vs 486

The 525-line system originally contained 486 lines of picture, not 480.

Digital foundations to most storage and transmission systems since the early 1990s have meant that analogue NTSC has only been expected to have 480 lines of picture.

How this affects the interpretation of "the 4:3 ratio" as equal to 704x480 or 704x486 is unclear, but the VGA standard of 640x480 has had a large impact.

Nevertheless, expectations for wastage and bad quality of the overscan area were far lower before the era of digital subsystems.

217.162.118.129's rewrite

Sorry about the revert, 217.162.118.129, but I feel that you went much too technical with the article to be useful. "Overscan" is one of the basics of video, so anyone who could understand things like timebase, geometry, and linearity would already know what overscan is. People looking up overscan in wikipedia are probably hobbyists who can't figure out why their TV keeps cutting off the sides of the graphics they did on their computer, so that is the audience we should be writing for. Algr 15:22, 28 July 2006 (UTC)

Yeah, actually I think you're wrong. The whole point of technical material on Wikipedia is that the technical parts are linked. Anyone who doesn't understand something can either skip over it if it's not important to them, or they can look into it just by clicking. For this reason I think your reversion was a very poor decision. What's more, I don't think there was even anything particularly technical in the new version.

(later) I've just looked at it again; there really isn't anything technical in the new version. If you don't know what geometry or linearity are you need to take some English lessons. What's more, the old version you restored is actually wrong!

The latest version addresses my concern, so I'll go with it. Since you are new to wikipedia, here are some tips:

• Always sign your posts (on talk pages useing ~~~~ (four tildes). This will insert your name and timestamp. To insert just your name, type ~~~ (3 tildes). Otherwise it can get confusing where one comment stops and another starts.
• It's not useful to vaguely say something is wrong - you need to quote exactly what the problem is in the discussion.
• Read carefully. If the above refers to your edit note about CRTs, the article didn't site CRTs as the cause, it said vacuum tubes. This would include the tubes in the timing circuits. In the next section, CRT is shorthand for "TVs using CRTs". And even today they do drift - you can go into any store with TVs lined up and see variations.
• Be polite. The object of wikipedia is to get articles that everyone agrees on, so comments like "it sucks" aren't helpful for building consensus.
• The reader comes first. It is tempting to show off your technical or literary skills, but readers who get lost in the first few paragraphs won't skip further down or click on links - they'll go back to google and find something written for THEM. For articles with a wide range of possible readers, it is best to start simple and get into details further down in the article.

Algr 17:54, 29 July 2006 (UTC)

Spawned separate page

OK I've decided to 'be bold' and created a separate page at Overscan amounts. Feel free to delete the stuff off this page now, because everything on here was copied into that page, plus some tiny additions I made. But also feel free to reintegrate the two pages; I don't mind which way this goes, as long as the info is somewhere. Whophd 03:05, 18 September 2006 (UTC)

Looks like the page was reintegrated. --Trakon (talk) 20:31, 16 October 2012 (UTC)

Overscan in computers

"Analogue video signals such as VGA, however, are subject to timing variations and even when using an LCD panel do not have this exactness."

Actually, for all practical purposes, "auto-setup" will make a one-to-one correspondnace between software pixels and the real LCD screen pixels. Howver, a one-to-one correspondance is impossible if the video card pixel resolution setting does not match the native LCD pixel resolution. Scetpfe 20:40, 24 February 2007 (UTC)

One can get close to 1:1 mapping with an analogue signal where the panel supports it, but there will perhaps always exist some "bleeding" between adjacent horizontal pixels (ie. a neighbouring pixels on a scanline) but is this even relevant to an article specially on overscan? (I tend to think not myself).

Also, I feel that as many LCD panels designed to function as HDTV displays may be set to overscan even digital inputs like DVI (my Sanyo LCD set unfortunately won't even display its native resolution without scaling it so that it can overscan, and has no consumer available options to disable such; both which I am led to believe is rather common among cheaper panels). In light of this I find the section may be misleading and have added a citation needed tag to the preceding sentences.

Nat

Merger discussion

Don’t merge: There is no good reason to merge the two articles, non tech people can read safe area, and the more technical would prefer reading about overscan. — IncidentFlux (talk) 11:24, 27 February 2008 (UTC)

Don't merge: Agreed, topics are fundamentally different (although there is some confusion in both which shoudl be cleaned up). Both pages can be structured with "newbie overview", and "deep technical". --Uplinkguy (talk) 14:56, 23 July 2008 (UTC)

• Don't merge. Imagine how much more confusing it would be for someone to type "title safe" and be redirected to "overscan." Heck, I would even advocate splitting safe area into title safe and action safe. Cromulent Kwyjibo (talk) 21:38, 8 August 2008 (UTC)

How about creating a single comprehensive article on all topics eliminating redundancy while having multiple very short articles for all terms in question with links to the bigger one? —Preceding unsigned comment added by 91.94.14.1 (talk) 09:29, 24 February 2009 (UTC)

Meaning of the word "overscan"

When a display is set to "underscan", it displays the "overscan" area. When a display is set to "overscan", it doesn't display the "overscan" area. "Overscan" is therefore a fairly confusing word. [Martin] —Preceding unsigned comment added by Rvam1378 (talk • contribs) 22:32, 18 December 2008 (UTC)

Overscan means the edges of the image go outside the edges of the screen. The overscan area of the picture is the part that is gets overscanned, ie put out of the visible image. Ace of Sevens (talk) 04:32, 18 August 2009 (UTC

Technically, the vertical blanking interval (VBI) is independent of whether as display is overscanned or not. In CRT terms (which have considerable influence on current terms and thinking), overscanning occurs only after the beams are unblanked; the deflection system aims the beams beyond the visible edges of the screen. The VBI happens when the beams are blanked; it's during the vertical retrace interval. Therefore, any data (including Teletext) that's sent during the VBI cannot happen during overscan. I didn't want to change the text yet, however (even if Wikipedia speaks of "merciless editing"! So far, I'm too merciful.) Regards, Nikevich (talk) 00:59, 19 March 2010 (UTC)

That's not quite accurate. Horizontal deflections continue during vertical blanking. In fact, about 20 lines are traced out as the beam flies back to the top. The overscan in either direction is maintained, albeit with no visible image produced. 135.180.161.151 (talk) 19:36, 14 September 2020 (UTC)

Let's change the intro

The definition «Overscan is extra image area …» is what's confusing. Overscan is something done by the display! Everyone knows there is no «extra» in an image going into a computer display, and when swapping it with a TV results in chopped edges, that's obviously the TV's fault. Nikevich's explanation «… aims the beams beyond the visible edges» would be a better intro, and even hints at the origin of the word.Anordal (talk) 21:26, 3 June 2013 (UTC)

Modern Displays

This needs a rewrite. The citation doesn't support the claims at all. It only says HDTVs commonly had overscan back in 2002. CRT HDTVs were common at that point. It never says HDTVs are ideally supposed to be like this, much less gives figures as to how much overscan there should be. I've found plenty of tech review sites that imply zero overscan is correct. Can anyone find one that outright says it? Ace of Sevens (talk) 04:32, 18 August 2009 (UTC)

Zero overscan is ideal and correct. The section doesn't look that all confusing either; perhaps you need just a tiny bit of technical insight in order to understand? GraYoshi2x►^talk 20:54, 29 September 2009 (UTC)

The section has been changed since I wrote this. The current section seem to be talking about display of SD material on an HD set, but is confusing mainyl because it doesn't say this. Ace of Sevens (talk) 18:45, 8 October 2009 (UTC)

Yes,it needs a rewrite. Many modern TV's (my Pioneer and Panasonic for example) have a 'dot for dot' mode, ie no overscan. I use this all the time, for broadcast HD, and for BluRay and the edges are usually clean. The picture benefits by gaining resolution and avoiding the slight loss involved in resampling (it makes no sense to have a 1920x1080 'full HD' TV and then resample a section of the transmitted image). Overscan is a terrible waste of available resolution, and will surely disappear as analog TV disappears. To say that it is still necessary is misleading. --Memestream (talk) 13:45, 8 February 2010 (UTC)

Agreed. Please also see the next item. – ὁ οἶστρος (talk) 13:39, 7 June 2010 (UTC)

True that most (not all) modern LCD and plasma TVs optionally support a no overscan mode. But this is not the standard mode. HDTVs out of the box use overscan--the viewer is not seeing all 1920x1080 pixels of content. This is obvious the first time you plug a laptop into an HDTV. Samsung was criticized for selling HDTVs with glass less than the full HD size, figuring since they were using overscan anyway, save a few bucks by not having all the pixels physically there. Bottom line, HDTVs never were and are not now "ideally" overscan-free, the standards haven't changed. Overscan is not a 'terrible' waste, it allows sloppy conversion, various cruft around the edges like uncertain start and stop of program content, which happen at the source. 146.115.66.42 (talk) 06:23, 26 May 2013 (UTC)

reworking of the article and removal of disinformation

[post arbitrarily declared a Personal Attack and deleted by the Great King and Censor-in-Chief 62.188.122.162 on the 2010-08-15]

Exactly, it causes blurring. That is why all good HD displays use 1:1 pixel mapping. Actually if the stream is marked as "show overscan", overscan must not be used, when marked as "crop everscan" it signals that the display is allowed to (but does not have to) use overscan. [1]--90.179.235.249 (talk) 17:31, 8 June 2010 (UTC)

I'm sorry to disappoint you all, but sadly although you may intuitively expect a digital medium such as modern HD sources to display in 1:1 pixel mapping with modern digital displays, in reality it is not the case. The citation from the original version of the article covered the point adequately. 62.188.122.162 (talk) 18:05, 15 August 2010 (UTC)

blanking of lines regarding modern 1080p TV sets

So, what do you guys think of this blanking? – ὁ οἶστρος (talk) 22:51, 31 August 2010 (UTC)

The removed material has been flagged as requiring a citation for some while. No citation has been forthcoming (and probably never will as none is likely to exist as the contribution was totally incorect). Removal of uncited material is not blanking as you claim but a requirement of Wikipedia. However the removal of the original contribution is blanking as that was correctly cited. 62.188.120.5 (talk) 07:50, 2 September 2010 (UTC)

Datacasting

Correct me if I'm wrong, but are the VBI and overscan not completely separate things. VBI lines, are not part of the visible picture and therefore not part of the overscan.

As such the Datacasting section is somewhat misleading, as data is sent in the VBI, not parts of the visible picture usually obscured by overscan. -- Fursday 21:44, 7 December 2011 (UTC)

Underscan on CRT monitors

CRTs made for computer display are set to underscan with an adjustable border, usually colored black.

This is just the default configuration, all CRT monitors I used yet have controls to adjust the image size and all of them actually can also do overscan, because they all overscan when the image size is set to maximum (and they all underscan a lot when the image size is stet to minimum). Overscan is also a useful feature on CRT monitors, not only when they are used as TV replacement with a PC and a {{TV tuner card]]: I also use it in Windows (I have just a few lines and pixels outside the viewable are, because these don't contain any useful information anymore, just window borders (when using fullscreen windows) and the part of the taskbar which is below the taskbands and all icons) and in games (because the boarder of the image is impossible to get straight, so it looks more square when you use overscan and you don't loose much of the FOV and normally no menus or icons are placed at the outer edge of the screen in games). And it also reduces convergence problems, because many CRTs have unfixable convergence errors, which are worst at the far edge of the image and get much better just a few pixels or lines away, this doesn't depend on the actual position on the screen on the CRTs I used, only on how many pixels or lines it is away from the edge of the image. --MrBurns (talk) 17:47, 11 May 2012 (UTC)

More 480 vs 486

The 525-line system contains 485 lines of picture content. The picture content begins in the middle of the 20th line of the top field, and ends in the middle of the last line of the bottom field. The active picture area is 485 lines tall for D1 sampled analog. Thus 486 lines are sampled, because it's not practical to sample half a line. According to a presumably credible source the NTSC SD digital television standard (some SMPTE standard?) states 483 lines tall ( but I can't find justification or second source for this). Not aware of any broadcast standard ever calling it 480 lines. Clearly DVDs contain 480 lines, but that's not broadcast, that's consumer grade. Over-the-air NTSC may have content stored in cut-rate methods at 480 lines, but the SD 480i signal clearly can support the historical and documented 485 lines of active picture area, as can broadcast quality recording equipment.

It may not be obvious to consumers, but overscan is part of the HD standard, and HDTVs have overscan. In fact, it was considered mildly scandalous when Samsung was revealed to be making glass that is smaller than 1280 x 720 pixels because HDTVs, not just theirs, employ overscan and project less than the entire 1280x720 digitized frame to the viewer. They actually scale--this is very evident when driving an HDTV from a computer and the borders are missing--and some brands can turn off overscan so the entire 1280x720 frame appears to the viewer. (Are they putting 1280x720 pixels on a 1280x720 glass at that point, or downscaling slightly to fit 1280x720 content to a smaller than 1280x720 pixel glass?)

It is indeed uncertain regarding the 4:3 ratio and 480 line video. The NTSC analog picture area is defined as 52.6555 microseconds (710.85 pixels when sampled at 13.5 MHz) wide x 485 lines (858 pixels per total line for 525 lines, storing 720 pixels per line for 486 lines). If one scales this down to 480 lines, that is 703.52 pixels wide, comfortably close to the standard frame size of 704x480, which possibly suggests that 704x480 pixels might have the (nearly) exact display aspect ratio of 4:3 standard or 16:9 widescreen.

However, this scaling could simply be a misunderstanding. Just as active picture area is tossed out vertically when cropping from 485 lines to 480 lines, it could also be the case that the 704 pixel width was picked simply because it is the closest modulo 16 width to the picture width of 710.85 pixels, and thus that the picture area is being cropped horizontally as well as vertically. There is ample documentation about D1 video, and the active picture is 710.85x485 pixels in that format being exactly 4:3 aspect ratio, or 16:9 widescreen. However, there are other standards which may be contradictory. The 4CIF frame is defined as 704x480 at 4:3 aspect ratio, but this is a videoconferencing standard, not a broadcasting or consumer electronics standard.

Empirical tests using multiple brands of consumer grade DVD players demonstrate that DVDs encoded with frame sizes of either 720x480 or 704x480 both display the centered 704x480 element at the same aspect ratio.

Regarding whether the 8 pixels on either side of the 704 pixel wide picture area should be black rather than containing program material, ITU BT.601-7 depicts blanking to exist in the 138 samples other than the 720 samples of program information. The entire 720 pixels are an oversampling of the 710.85 pixel wide picture area. No standard requires the 8 pixels on either side of the 704 pixels to be blacked out vs containing actual captured program content.

It could be the case that obsessively-exact downscaling of HD content to widescreen SD (e.g. DVD) would resize the 1920x1080 source material to 710.85x485 and then crop height to 480, and crop to 704 width or pad to 720 width. Or alternatively just resize to 704x480 knowing it will be close enough for viewing enjoyment. Resizing to 720 width could cause visible distortion.

Both documentation of the DV codec and empirical tests demonstrate that the DV format creates a frame size of 720x480 (and not 704x480) pixels exactly 4:3 narrowscreen or 16:9 widescreen. When digitized, the pixel aspect ratio for NTSC 4:3 content is very nearly 10:11 for digital video--other than that recorded on a camcorder using the DV codec; the pixel aspect ratio for NTSC 4:3 content is 8:9 (640:720) for the DV codec. Video recorded on a camcorder in DV format should be resized from 720x480 to 704x480 when converting to DVD content, whether 4:3 narrowscreen or 16:9 widescreen.

The take-away from this is that SD, ED and HDTVs all employ overscan. The 1920x1080 and 1280x720 frames have exactly 16:9 aspect ratio. The 13.5 MHz sample rate digitized analog NTSC widescreen 710.85x485 frame has exactly 16:9 aspect ratio (and the narrowscreen, exactly 4:3). The 704x480 frame might be (nearly) exactly 4:3. The 720x480 frame definitely is not 4:3 or 16:9, unless it is from a source using the DV codec (such as a camcorder), then the 720x480 frame is indeed exactly 4:3 or 16:9. Most HDTVs whether CRT or LCD employ overscan so that less than the entire 1920x1080 is visible to the viewer. 146.115.66.42 (talk) 06:15, 26 May 2013 (UTC)