Low-definition television

Low-definition television (LDTV) refers to television systems that have a lower screen resolution than standard-definition television systems. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as low-definition analog TV systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan TV systems.

Sources

The most common source of LDTV programming is the Internet, where mass distribution of higher-resolution video files could overwhelm computer servers and take too long to download. Many mobile phones and portable devices such as Apple’s iPod Nano, or Sony’s PlayStation Portable use LDTV video, as higher-resolution files would be excessive to the needs of their small screens (320×240 and 480×272 pixels respectively). The most recent generation of iPod Nanos have LDTV screens, as do the first three generations of iPod Touch and iPhone (480×320).

For the first years of its existence, YouTube offered only one, low-definition resolution of 320x240p at 30fps or less, only extending - first to widescreen 426×240, then to gradually higher resolutions - once the video service had become well established, it could afford radically improved storage space and transmission bandwidth, and could rely on a good proportion of its users having high-speed internet connections. More recently, YouTube has also extended further into the LDTV realm by adding an even lower 256×144p resolution with a halved framerate - giving an overall effect reminiscent of early online video streaming attempts using RealVideo or similar, where 160×120p at single-figure fps was deemed acceptable - to cater to those whose network connections could not even widthstand the rigors of "240p".

A VHS videotape can be considered SDTV due to its resolution (approximately 360 × 480i/576i), but using VHS for professional production will yield results subjectively comparable to LDTV because of VHS's low bandwidth, particularly in the field of color reproduction, which can be as little as a few hundred kHz, translating to a few dozen color clocks per line. VHS does, however, still provide high motion and a relatively high vertical resolution via interlacing, which is a feature uncommon in true LDTV material, and reasonable luma resolution.

In comparison, professional-level Betacam SP tape produces approx 440×486i/576i, and some college TV studios use Super VHS at ~560×486i/576i, along with an increased colour carrier bandwidth. Both of these systems, whilst showing a marked improvement over VHS, ultimately offer lower resolution images than DVD, but are still comparable to (and thus remain useful for) lower-bandwidth broadcast television, which is compromised in the analogue domain by a narrower available frequency range for each individual channel, and in the digital by a literally lower horizontal pixel count (often 480 or 544, versus the 720 of DVD and full-rate SDTV broadcasts). Again, both systems offer high motion and a high vertical resolution by way of interlacing, and are more justifiably counted as SD rather than LD.

Older video game consoles and home computers often generated a technically-compliant NTSC or PAL signal, but only sent one field type rather than alternating between the two. This created a 240- or 288-line progressive signal, which in theory can be decoded on any receiver that can decode normal, interlaced signals.[1][2][3] Since the shadow mask and beam width of standard cathode ray tube televisions were designed for interlaced signals, these systems produced a distinctive fixed pattern of alternating bright and dark scan lines; many emulators for older systems offer to recreate this effect. The horizontal resolution ranged from 160 pixels to 720 pixels, depending on the video chip's capabilities (and the skill of the programmer).

The Video CD format was introduced on such a console (CD-i), and it likewise originally used a progressive LDTV signal (352×240 or 352×288), which is half the vertical and horizontal resolution of full-bandwidth SDTV. However, most DVD and SVCD players, as well as VCD 2.0 players (which can display still images at 704×480/576i and offer limited DVD menu-esque functions), will internally upscale VCD material to 704x480/576i (or 480/576p for progressive-scan players) for playback, as this is both more widely compatible and gives a better overall appearance. No motion information is lost due to this process, as, unlike the single-field output of classic computers and consoles, VCD video is not high-motion and only plays back at 25 or 30 frames per second. A similar recording standard (quarter-resolution and half framerate) is also used for super-long-play home DVD recording, although it does not typically adhere to the same bitrate or encoding specifications, and could therefore be considered LDTV. (Regular "LP" DVD recording is closest in spec to a high grade VHS or Betamax recording, having half the normal horizontal resolution and a lower bitrate, but otherwise being identical to a full-rate "SP" recording, including high-motion interlace, and thus still qualifies as SDTV)

With the late 1980s introduction of 16 and 32-bit computers/game consoles, such as Atari ST, Commodore Amiga, Super Nintendo[3], and Sega Genesis, outputs up to 486i/576i were supported for the first time, but rarely used due to heavy demands on processing power and memory. Standard resolutions also had a tendency to produce annoying flicker at horizontal edges unless employed quite carefully, such as using anti-aliasing, which was either not available or computationally exorbitant. Thus, 240/288p remained the primary format on most games of the fourth and fifth generation consoles (Sega Saturn, PlayStation and Nintendo 64). With the advent of sixth generation consoles and the launch of the Dreamcast, 480/576i use became more common, and 240/288p usage declined.

More recent game systems tend to use only properly interlaced NTSC or PAL in addition to higher resolution modes, except when running games designed for older, compatible systems in their native modes. The PlayStation 2 generates 240p/288p if a PlayStation game calls for this mode, as do many Virtual Console emulated games on Wii. Nintendo's official software development kit documentation refers to 240p as 'non-interlaced mode' or 'double-strike'.[4][5]

Shortly after the launch of the Wii Virtual Console service many users with component video cables experienced problems displaying some Virtual Console games due to certain TV models/manufacturers not supporting 240p over a component video connection. Nintendo's solution was to implement 'Wii Component Cable Interlace Mode' which forces the emulator to output 480i instead of 240p,[6] however many games released prior have still not been updated.[7]

Teleconferencing LDTV

Upcoming sources of LDTV using standard broadcasting techniques include mobile TV services powered by DVB-H, 1seg, DMB, or ATSC-M/H. However, this kind of LDTV transmission technology is based on existent LDTV teleconferencing standards that have been in place for a decade or more.

Resolutions

Standard Class Resolution Aspect Ratio Notes
MMS-Small 96p 128×96 4:3 Lowest size recommended for use with 3GPP video transmitted by MMS to/from cellular phones, matching resolution of smallest generally used color cellphone screen.
QQVGA 120p 160×120 4:3 Used with some webcams and early colour-screen cellular phones, commonly used in early desktop computer and online video applications. Lowest commonly used video resolution.
QnHD 180p 320×180 16:9
QCIF Webcam 144p 176×144 11:9 Approximately one-sixth analogue PAL resolution (one-half horizontal, one-third vertical). Also the size recommended for "medium" quality MMS videos.
YouTube 144p 144p 256×144 16:9 One tenth of 1440p. The lowest resolution on YouTube.
NTSC square pixel 240p 320×240 4:3 Comparable to "low resolution" output of many popular home computers and games consoles, including VGA "Mode X". Used in some webcams and for video recordings in early/budget digital cameras and cameraphones, and low-end smartphone screens. Original YouTube resolution. Maximum recommended size for "large" MMS videos.
SIF (525) 240p 352×240 4:3 NTSC-standard VCD / super-long-play DVD. Narrow/tall pixels.
NTSC widescreen 240p 426×240 16:9 Same as current YouTube "240p" mode; screen resolution of some budget portable DVD players. Roughly one-third full NTSC resolution (half vertical, two thirds horizontal).
CIF, SIF (625) 288p 4:3 PAL-standard VCD / super-long-play DVD. Wide/short pixels. Also a common resolution in early webcam / video conferencing, and in advanced featurephones and smartphones of mid-2000s (ca 2006).
PSP 288p 480×272 30:17 Notionally 16:9 with slight left/right edge cropping. Used in many portable DVD player screens and other small-format devices besides.
360p 360p 480×360 4:3 Uncommon, used in some lower-mid-market smartphone screens and as an intermediate screen resolution for some 1990s videogames.
Wide 360p 360p 640×360 16:9 Current base resolution in YouTube, labelled as "360p".
  • The lowest and least computationally demanding resolution supported by hardware able to run mainstream desktop operating systems; the lowest interruption-free resolution with low-end broadband connections.
  • Typically used as the base "SD" standard by VoD services due to subjective similarity (and similar pixel counts) to a mid-grade free-to-air broadcast picture.
  • Effectively, the resolution offered by any higher-definition 16:9 video scaled down for a standard 640×480 (VGA) computer screen. Offers 75% of the pixel count of a true anamorphic NTSC DVD image, or 89% of a letterboxed 16:9 image.
  • Historically used as an ad-hoc standard for intermediate-quality / CD-R-sized MPEG4 conversions on P2P file sharing networks.

See also

References

  1. ^ "Scanlines Demystified". Retrieved 2010-06-03.
  2. ^ "Connecting your old videogames to your new flatpanel TV set". Retrieved 2010-06-03.
  3. ^ a b SNES Development Manual. Nintendo of America. 1993. p. 2-1-2. Retrieved 2017-08-28. The picture display on the Super Nintendo Entertainment System (Super NES) has two modes. One is an interlace mode, based on the television system. The other is a non-interlace mode, in which one frame takes 1/60th of a second. In the non-interlace mode the same position is scanned every field. Each frame consists of only 262 lines, half that of the interlace mode. There appears to be no flickering compared to the interlace mode, since each point on the screen is radiated every 1/60th of a second.
  4. ^ "N64 Functions Reference Manual - Video Interface (VI) Management". Retrieved 2011-06-27.
  5. ^ "GameCube SDK - Video Interface Library (VI)" (PDF). p. 6. Retrieved 2011-06-27.
  6. ^ "Nintendo Support - Display problems while playing Virtual Console games". Retrieved 2011-06-27.
  7. ^ "Wii Component cable Interlace Mode". Retrieved 2011-06-27.
720p

720p (1280×720 px; also called HD Ready or standard HD) is a progressive HDTV signal format with 720 horizontal lines and an aspect ratio (AR) of 16:9, normally known as widescreen HDTV (1.78:1). All major HDTV broadcasting standards (such as SMPTE 292M) include a 720p format, which has a resolution of 1280×720; however, there are other formats, including HDV Playback and AVCHD for camcorders, that use 720p images with the standard HDTV resolution. The frame rate is standards-dependent, and for conventional broadcasting appears in 50 progressive frames per second in former PAL/SECAM countries (Europe, Australia, others), and 59.94 frames per second in former NTSC countries (North America, Japan, Brazil, others).

The number 720 stands for the 720 horizontal scan lines of image display resolution (also known as 720 pixels of vertical resolution). The p stands for progressive scan, i.e. non-interlaced. When broadcast at 60.00 frames/s frames per second, 720p features the highest temporal resolution possible under the ATSC and DVB standards. The term assumes a widescreen aspect ratio of 16:9, thus implying a resolution of 1280×720 px (0.9 megapixels).

720i (720 lines interlaced) is an erroneous term found in numerous sources and publications. Typically, it is a typographical error in which the author is referring to the 720p HDTV format. However, in some cases it is incorrectly presented as an actual alternative format to 720p. No proposed or existing broadcast standard permits 720 interlaced lines in a video frame at any frame rate.

TVU Music Television

TVU Music Television (or simply TVU) is a commercial-free, Christian rock television network which broadcasts through the Internet, Sky Angel and KTV. TVU began in 2001, and is owned and operated by Spirit Communications Incorporated, and is a fully non-profit, listener-supported station. A fund-raiser, called Unleash the Music, is held twice a year to raise the funds of TVU and its radio extension, RadioU.

TVU's target audience is people from ages 12–24 and is known for its Christian message, as well as anti-drugs, anti-violence and anti-drunk driving messages.

Television

Television (TV), sometimes shortened to tele or telly, is a telecommunication medium used for transmitting moving images in monochrome (black and white), or in colour, and in two or three dimensions and sound. The term can refer to a television set, a television program ("TV show"), or the medium of television transmission. Television is a mass medium for advertising, entertainment and news.

Television became available in crude experimental forms in the late 1920s, but it would still be several years before the new technology would be marketed to consumers. After World War II, an improved form of black-and-white TV broadcasting became popular in the United States and Britain, and television sets became commonplace in homes, businesses, and institutions. During the 1950s, television was the primary medium for influencing public opinion. In the mid-1960s, color broadcasting was introduced in the US and most other developed countries. The availability of multiple types of archival storage media such as Betamax, VHS tape, local disks, DVDs, flash drives, high-definition Blu-ray Discs, and cloud digital video recorders has enabled viewers to watch pre-recorded material—such as movies—at home on their own time schedule. For many reasons, especially the convenience of remote retrieval, the storage of television and video programming now occurs on the cloud. At the end of the first decade of the 2000s, digital television transmissions greatly increased in popularity. Another development was the move from standard-definition television (SDTV) (576i, with 576 interlaced lines of resolution and 480i) to high-definition television (HDTV), which provides a resolution that is substantially higher. HDTV may be transmitted in various formats: 1080p, 1080i and 720p. Since 2010, with the invention of smart television, Internet television has increased the availability of television programs and movies via the Internet through streaming video services such as Netflix, Amazon Video, iPlayer, Hulu and Roku.

In 2013, 79% of the world's households owned a television set. The replacement of early bulky, high-voltage cathode ray tube (CRT) screen displays with compact, energy-efficient, flat-panel alternative technologies such as LCDs (both fluorescent-backlit and LED), OLED displays, and plasma displays was a hardware revolution that began with computer monitors in the late 1990s. Most TV sets sold in the 2000s were flat-panel, mainly LEDs. Major manufacturers announced the discontinuation of CRT, DLP, plasma, and even fluorescent-backlit LCDs by the mid-2010s. In the near future, LEDs are expected to be gradually replaced by OLEDs. Also, major manufacturers have announced that they will increasingly produce smart TVs in the mid-2010s. Smart TVs with integrated Internet and Web 2.0 functions became the dominant form of television by the late 2010s.Television signals were initially distributed only as terrestrial television using high-powered radio-frequency transmitters to broadcast the signal to individual television receivers. Alternatively television signals are distributed by coaxial cable or optical fiber, satellite systems and, since the 2000s via the Internet. Until the early 2000s, these were transmitted as analog signals, but a transition to digital television is expected to be completed worldwide by the late 2010s. A standard television set is composed of multiple internal electronic circuits, including a tuner for receiving and decoding broadcast signals. A visual display device which lacks a tuner is correctly called a video monitor rather than a television.

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