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Standard-definition television

From Wikipedia, the free encyclopedia

SDTV resolution by nation; due to historical reasons, different countries use either 480i or 576i as the standard-definition picture format.
SDTV resolution by nation; due to historical reasons, different countries use either 480i or 576i as the standard-definition picture format.

Standard-definition television (SDTV or SD) is a television system which uses a resolution that is not considered to be either high- or enhanced-definition. The two common SDTV signal types are 576i, with 576 interlaced lines of resolution, derived from the European-developed PAL and SECAM systems; and 480i based on the American NTSC system. SDTV and high definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions.

In North America, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals, with widescreen content being center cut.[1] However, in other parts of the world that used the PAL or SECAM color systems, standard-definition television is now usually shown with a 16:9 aspect ratio, with the transition occurring between the mid-1990s and mid-2000s depending on region. Older programs with a 4:3 aspect ratio are broadcast with a flag that switches the display to 4:3.[a]

Standards that support digital SDTV broadcast include DVB, ATSC, and ISDB. The last two were originally developed for HDTV, but are more often used for their ability to deliver multiple SD video and audio streams via multiplexing, than for using the entire bitstream for one HD channel.[clarification needed]

For SMPTE 259M-C compliance, a SDTV broadcast image is scaled to 720 pixels wide[b] for every 480 NTSC (or 576 PAL) lines of the image with the amount of non-proportional line scaling dependent on either the display or pixel aspect ratio. The display ratio for broadcast widescreen is commonly 16:9,[c] the display ratio for a traditional or letterboxed broadcast is 4:3.[d]

An SDTV image outside the constraints of the SMPTE standards requires no non-proportional scaling with 640 pixels[e] for every line of the image. The display and pixel aspect ratio is generally not required with the line height defining the aspect. For widescreen 16:9, 360 lines define a widescreen image and for traditional 4:3, 480 lines define an image.

SDTV refresh rates can be 24, 25, 30, 50 or 60 frames per second with a possible rate multiplier of 1000/1001 for NTSC. 50 and 60 rates are generally frame doubled versions of 25 and 30 rates for jitter issues when using non-interlaced lines.

Digital SDTV in 4:3 aspect ratio has the same appearance as regular analog TV (NTSC, PAL, SECAM) without the ghosting, snowy images and white noise. However, if the reception has interference or is poor, where the error correction cannot compensate one will encounter various other artifacts such as image freezing, stuttering or dropouts from missing intra-frames or blockiness from missing macroblocks. The audio encoding is the last to suffer loss due to the lower bandwidth requirements.

YouTube Encyclopedic

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  • High Definition Television (HDTV) : Converting Standard Definition DVDs
  • High Definition Television (HDTV) : Difference Between High & Standard Definition Video
  • Displaying HDTV on a standard definition TV

Transcription

Hi, I'm Brad Bear on behalf of Expert Village. In this title I want to talk a little bit about up conversion of DVDs and what that kind of is. With HD DVD players and Blu-ray players, they automatically take your standard definition disk or content, say a TV show or a movie that you've bought. Your older DVDs, your regular DVDs and they will take those and play those back just like they would their HD or Blu-ray disks that they were designed for. The only difference is they will take that signal and actually make the image larger in the disk. What they do is they double the amount of resolution or the amount of lines that that disk was made with to display optimally on your HD TV set. Now what happens is your standard definition content is at four hundred and eighty lines. And what the conversion does is it doubles those lines, or even triples those lines depending on if it's going to seven hundred and twenty or one thousand eighty lines of resolution for your set. Depending on the set that you've got. And it will up convert those images, send it up to the set so it can be displayed optimally. Your standard definition players, if you just hook a standard definition player, your regular DVD player up to your high definition set, what you might encounter is that the image kind of looks grainy. And the pixels, the little dots that make up the image kind of dance around and the edges are jagged and it doesn't look very good. It's like you bought this great TV and it looked great in the store, doesn't look good when you plug up your standard definition player. Well what happens is your standard definition player which is four hundred and eighty lines, when it sends a signal to your TV, your TV's trying to make it fit the TV itself. So it's just blowing images up. So if you have pixel information, it's just a little block, and it's blown up, you're going to start to see all the imperfections. It's kind of like taking a computer image and just zooming in as far as you can, and all you see are just big blocks of pixels. It's not quite that bad, but it's the same effect. You're just magnifying the image on a standard def player to a HD TV So if you get a HD TV you decide not to go HD DVD, or Blu-ray, you might want to consider the DVD sets that up convert the image for an HD set. You can buy a DVD player that will up convert it, and it's still just a standard def player. So those are some things to consider when also looking at HD DVD, Blu-ray, or if you just want to stick with all your regular DVDs and stick with a standard definition player. At least get one that does the up conversion for your HD DVD set.

Contents

Pixel aspect ratio

Television signals are transmitted in digitally encoded form, and the lines are scaled to fit SMPTE SDI bandwidth requirements, as opposed to unrestricted uses such as when lines are rendered or overlaid to a modern computer monitor and modern SMPTE implementations of HDTV. The table below summarizes pixel aspect ratios for the scaling of various kinds of SDTV video lines. Note that the actual image (be it 4:3 or 16:9) is always contained in the center 704 horizontal pixels of the digital frame, regardless of how many horizontal pixels (704 or 720) are used. In case of digital video line having 720 horizontal pixels, only the center 704 pixels contain actual 4:3 or 16:9 image, and the 8 pixel wide stripes from either side are called nominal analogue blanking for horizontal blanking and should be discarded before displaying the image. Nominal analogue blanking should not be confused with overscan, as overscan areas are part of the actual 4:3 or 16:9 image.

Video format Display aspect ratio (DAR) Resolution Pixel aspect ratio (PAR) After horizontal scaling
480i 4:3 704×480
(horizontal blanking cropped)
10:11 640×480
720×480 (full frame) 654×480
480i 16:9 704×480
(horizontal blanking cropped)
40:33 854×480
720×480 (full frame) 872×480
576i 4:3 704×576
(horizontal blanking cropped)
12:11 768×576
720×576 (full frame) 786×576
576i 16:9 704×576
(horizontal blanking cropped)
16:11 1024×576
720×576 (full frame) 1048×576

The pixel aspect ratio is always the same for corresponding 720 and 704 pixel resolutions because the center part of a 720 pixel wide image is equal to the corresponding 704 pixel wide image.

See also

Notes

  1. ^ Some broadcasters prefer to reduce the horizontal resolution by anamorphically scaling the video into a pillarbox.
  2. ^ Only 704 center pixels contain the image and 16 pixels are reserved for horizontal blanking. A number of broadcasters fill the whole 720 frame.
  3. ^ Pixel aspect ratio of 40:33 for anamorphic
  4. ^ Pixel aspect ratio of 10:11
  5. ^ Defined by the adopted IBM VGA standard

References

External links

This page was last edited on 9 October 2018, at 17:33
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