Talk:Overscan

message: 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)
replies: text: Looks like the page was reintegrated. --Trakon (talk) 20:31, 16 October 2012 (UTC)
thread_title:  Spawned separate page 

message: "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)
thread_title:  Overscan in computers 

message: 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)
thread_title:  Merger discussion   

message: 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)
replies: text: 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)

text: 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)
thread_title:  Meaning of the word "overscan" 

message: 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)
thread_title:  Let's change the intro 

message: 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)
replies: text: 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)
replies: text: 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)
replies: text: 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)
replies: text: Agreed. Please also see the next item. – ὁ οἶστρος (talk) 13:39, 7 June 2010 (UTC)
replies: text: 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)
thread_title:  Modern Displays 

message: [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. --90.179.235.249 (talk) 17:31, 8 June 2010 (UTC)
replies: text: 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)
thread_title: reworking of the article and removal of disinformation

message: So, what do you guys think of this blanking? – ὁ οἶστρος (talk) 22:51, 31 August 2010 (UTC)
replies: text: 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)
thread_title: blanking of lines regarding modern 1080p TV sets

message: 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)
thread_title:  Datacasting 

message: 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)
thread_title:  Underscan on CRT monitors 

message: 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)
thread_title:  More 480 vs 486 

message: I happen to have an LG TV but the word LG is not a link and it's not clear where I can find information on what to do about an overscan problem.
68.109.194.172 (talk) 22:01, 31 August 2019 (UTC)
replies: text: This isn't a technical support forum TurboSonic (talk) 14:19, 7 September 2019 (UTC)
thread_title:  Resolution issues when connecting a PC to televisions via HDMI