576i
Encyclopedia
576i is a standard-definition
video mode used in (former) PAL
and SECAM
countries. In digital applications it is usually referred to as "576i", in analogue contexts it is often quoted as "625 lines". Its NTSC
counterpart is 480i
; these are the two common forms of standard-definition television
.
The 576 identifies a vertical resolution of 576 lines, and the i identifies it as an interlaced resolution. The field rate
, which is 50 Hz
, is sometimes included when identifying the video mode, i.e. 576i50; another notation, endorsed by EBU/SMPTE, includes the frame rate
, as in 576i/25.
Its basic parameters common to both analogue and digital implementations are: 576 scan lines of picture content, 25 frames (giving 50 fields) per second. Also in analogue, 49 additional blank lines for the sync pulse are added, resulting in 625 lines. Analogue television signals have no pixels; they are rastered in scan lines, but along each line the signal is continuous.
In digital
applications, the number of pixels per line is an arbitrary choice as long as it fulfils the sampling theorem. Values above ca 500 columns are enough for conventional broadcast television; DVB-T, DVD and DV allow better values such as 704 or 720.
The video format can be transported by both major digital television
formats, ATSC and DVB, and on DVD
, and it supports aspect ratios
of standard 4:3 and anamorphic
16:9
.
When 576i video is transmitted via baseband (i.e., via consumer device cables, not via RF
), most of the differences between the "one-letter" systems
are no longer significant, other than vertical resolution and frame rate.
In this context, unqualified 576i invariably means
Full transponder mode (e.g., 72 MHz)
Half transponder mode (e.g., 36 MHz)
There is no longer any difference (in the digital domain) between PAL
and SECAM
. Digital video uses its own separate colour space, so even the minor colour space differences between PAL
and SECAM
become moot in the digital domain.
. Systems which recover progressive frames, or transcode video should ensure that this field order is obeyed, otherwise the recovered frame will consist of a field from one frame and a field from an adjacent frame, resulting in 'comb' interlacing artifacts.
d and played back at 576i25's standard of 25 frames per second, films run 4% faster. This also applies to most TV series that are shot on film or digital 24p. Unlike 480i30's telecine system, which uses 3:2 pulldown to convert the 24 frames per second to the 480i30 frame rate, 576i results in the telecined video running 4% shorter than the original film as well as the equivalent 480i30 telecined video.
Depending on the sound system in use, it also slightly increases the pitch of the soundtrack by 70.67 cents
(0.7067 of a semitone
). More recently, digital conversion methods have used algorithms which preserve the original pitch of the soundtrack, although the frame rate conversion still results in faster playback.
There also exist conversion methods that can convert 24 frames per second video to 25 frames per second with no speed increase, however image quality suffers when conversions of this type are used. This method is most commonly employed through conversions done digitally (i.e. using a computer and software like VirtualDub
), and is employed in situations where the importance of preserving the speed of the video outweighs the need for image quality.
Some movie enthusiasts prefer 576i speed-up over 480i30's 3:2 pulldown, because the latter results in telecine judder, a visual distortion not present in 576i speed-up video. This is not an issue on modern upconverting DVD players and PCs
, as they play back 23.97 frame/s–encoded video at its true frame rate, without 3:2 pulldown.
Software which corrects the speed-up is available for those viewing 576i DVD films on their computers, WinDVD's
"PAL TruSpeed" being the most ubiquitous. However, this method involves resampling the soundtrack(s), which results in a slight decrease in audio quality. The echo/audio balance issue can be resolved by re-adjusting the playback pitch (located in the Audio Effect tab) from normal to low and back to normal again.
Standard-definition television
Sorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
video mode used in (former) PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
countries. In digital applications it is usually referred to as "576i", in analogue contexts it is often quoted as "625 lines". Its NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
counterpart is 480i
480i
480i is the shorthand name for a video mode, namely the US NTSC television system or digital television systems with the same characteristics. The i, which is sometimes uppercase, stands for interlaced, the 480 for a vertical frame resolution of 480 lines containing picture information; while NTSC...
; these are the two common forms of standard-definition television
Standard-definition television
Sorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
.
The 576 identifies a vertical resolution of 576 lines, and the i identifies it as an interlaced resolution. The field rate
Field rate
The field rate of an interlaced video image is twice the effective frame rate, since interlacing draws only half of the image at a time. For example, a field rate of 60 Hertz will correspond to a 30 frames-per-second moving picture...
, which is 50 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, is sometimes included when identifying the video mode, i.e. 576i50; another notation, endorsed by EBU/SMPTE, includes the frame rate
Frame rate
Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems...
, as in 576i/25.
Its basic parameters common to both analogue and digital implementations are: 576 scan lines of picture content, 25 frames (giving 50 fields) per second. Also in analogue, 49 additional blank lines for the sync pulse are added, resulting in 625 lines. Analogue television signals have no pixels; they are rastered in scan lines, but along each line the signal is continuous.
In digital
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
applications, the number of pixels per line is an arbitrary choice as long as it fulfils the sampling theorem. Values above ca 500 columns are enough for conventional broadcast television; DVB-T, DVD and DV allow better values such as 704 or 720.
The video format can be transported by both major digital television
Digital television
Digital television is the transmission of audio and video by digital signals, in contrast to the analog signals used by analog TV...
formats, ATSC and DVB, and on DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
, and it supports aspect ratios
Aspect ratio (image)
The aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon. That is, for an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this...
of standard 4:3 and anamorphic
Anamorphic widescreen
Anamorphic widescreen, when applied to DVD manufacture, is a video process that horizontally squeezes a widescreen image so that it can be stored in a standard 4:3 aspect ratio DVD image frame. Compatible playback equipment can then re-expand the horizontal dimension to show the original widescreen...
16:9
16:9
16:9 is an aspect ratio with a width of 16 units and height of 9. Since 2009, it has become the most common aspect ratio for sold televisions and computer monitors and is also the international standard format of HDTV, Full HD, non-HD digital television and analog widescreen television ...
.
Baseband interoperability (analogue)
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
), most of the differences between the "one-letter" systems
Broadcast television system
Broadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television signals. There are three main analog television systems in current use around the world: NTSC, PAL, and SECAM...
are no longer significant, other than vertical resolution and frame rate.
In this context, unqualified 576i invariably means
- 625 lines per frame, of which 576 carry picture content
- 25 frames per second interlaced yielding 50 fields per second
- Two interlaced video fields per frame
- With PALPALPAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
or SECAMSECAMSECAM, also written SÉCAM , is an analog color television system first used in France....
colour (4.43 MHz or 3.58 MHz (576i-N & 576i-NC)) - Frequency modulated or amplitude modulated audio (mono)
- Mono or stereo audio, if sent via connector cables between devices
Modulation for TVRO transmission
576i when it is transmitted for TVRO viewing is transmitted substantially differently from terrestrial transmission.Full transponder mode (e.g., 72 MHz)
- Luma signal is FM modulated, but with a 50 Hz dithering signal to spread out energy over the transponder
- Chroma is phase modulated
- An FM subcarrier of 4,50, 5.50, 6.0, 6.50 or 6.65 MHz is added for mono sound
- Other FM subcarriers (usually 7.02, 7.20, 7.38, 7.56, 7.74 and 7.92 MHz) are added for a true stereo service and can also carry multi-lingual sound and radio services. These additional subcarriers are normally narrower bandwidth than the main mono subcarrier and are companded using Panda 1 or similar to preserve the signal to noise ratio
- Data subcarriers may also be added
Half transponder mode (e.g., 36 MHz)
- All of the above is done, but signal is bandwidth limited to 18 MHz
- The bandwidth limiting does not affect audio subcarriers
Baseband interoperability (digital)
In digital video applications, such as DVDs and digital broadcasting, colour encoding is no longer significant; in that context, 576i means only- 576 frame lines
- 25 frames or 50 fields per second
- Interlaced video
- PCM audio (baseband)
There is no longer any difference (in the digital domain) between PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
. Digital video uses its own separate colour space, so even the minor colour space differences between PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
and SECAM
SECAM
SECAM, also written SÉCAM , is an analog color television system first used in France....
become moot in the digital domain.
Use with progressive sources
When 576i is used to transmit content that was originally composed of 25 full progressive frames per second, the odd field of the frame is transmitted first. This is the opposite of NTSCNTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
. Systems which recover progressive frames, or transcode video should ensure that this field order is obeyed, otherwise the recovered frame will consist of a field from one frame and a field from an adjacent frame, resulting in 'comb' interlacing artifacts.
576i speed-up
Motion pictures are typically shot on film at 24 frames per second. When telecineTelecine
Telecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
d and played back at 576i25's standard of 25 frames per second, films run 4% faster. This also applies to most TV series that are shot on film or digital 24p. Unlike 480i30's telecine system, which uses 3:2 pulldown to convert the 24 frames per second to the 480i30 frame rate, 576i results in the telecined video running 4% shorter than the original film as well as the equivalent 480i30 telecined video.
Depending on the sound system in use, it also slightly increases the pitch of the soundtrack by 70.67 cents
Cent (music)
The cent is a logarithmic unit of measure used for musical intervals. Twelve-tone equal temperament divides the octave into 12 semitones of 100 cents each...
(0.7067 of a semitone
Semitone
A semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant when sounded harmonically....
). More recently, digital conversion methods have used algorithms which preserve the original pitch of the soundtrack, although the frame rate conversion still results in faster playback.
There also exist conversion methods that can convert 24 frames per second video to 25 frames per second with no speed increase, however image quality suffers when conversions of this type are used. This method is most commonly employed through conversions done digitally (i.e. using a computer and software like VirtualDub
VirtualDub
VirtualDub is a video capture and video processing utility for Microsoft Windows written by Avery Lee.It is designed to process linear video streams, including filtering and recompression...
), and is employed in situations where the importance of preserving the speed of the video outweighs the need for image quality.
Some movie enthusiasts prefer 576i speed-up over 480i30's 3:2 pulldown, because the latter results in telecine judder, a visual distortion not present in 576i speed-up video. This is not an issue on modern upconverting DVD players and PCs
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
, as they play back 23.97 frame/s–encoded video at its true frame rate, without 3:2 pulldown.
Software which corrects the speed-up is available for those viewing 576i DVD films on their computers, WinDVD's
WinDVD
WinDVD is a commercial video player and music player software for Microsoft Windows. It enables the viewing of DVD-Video movies on the user's PC. DVD-Video backups stored on hard disk can also be played...
"PAL TruSpeed" being the most ubiquitous. However, this method involves resampling the soundtrack(s), which results in a slight decrease in audio quality. The echo/audio balance issue can be resolved by re-adjusting the playback pitch (located in the Audio Effect tab) from normal to low and back to normal again.