576i is a
standard-definition
Standard-definition television (SDTV, SD, often shortened to standard definition) is a television system which uses a resolution that is not considered to be either high or enhanced definition. "Standard" refers to it being the prevailing sp ...
digital video mode,
originally used for
digitizing analog television in most countries of the world where the
utility frequency for electric power distribution is 50 Hz. Because of its close association with the legacy color encoding systems, it is often referred to as
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
, PAL/
SECAM or
SECAM when compared to its 60 Hz (typically, see
PAL-M)
NTSC-colour-encoded counterpart,
480i.
The ''576'' identifies a vertical resolution of 576 lines, and the ''i'' identifies it as an
interlaced resolution.
The
field rate
The refresh rate (or "vertical refresh rate", "vertical scan rate", terminology originating with the cathode ray tubes) is the number of times per second that a Raster scan, raster-based display device displays a new image. This is independent fro ...
, which is 50
Hz, is sometimes included when identifying the video mode, i.e. 576i50; another notation, endorsed by both the
International Telecommunication Union in
BT.601 and SMPTE in
SMPTE 259M
SMPTE 259M is a standard published by SMPTE which "describes a 10-bit serial digital interface operating at 143/270/360 Mb/s."
The goal of SMPTE 259M is to define a serial digital interface (based on a coaxial cable), called SDI or SD-SDI.
There ...
, includes the
frame rate, as in 576i/25.
Operation
In analogue television, the full
raster uses 625 lines, with 49 lines having no image content to allow time for
cathode ray tube circuits to retrace for the next frame (see
Vertical blanking interval
In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...
),. These non-displayed lines can be used to transmit
teletext or other services. In the digital domain, only the visible 576 lines are considered.
Analogue television signals have no pixels; they are continuous along rastered scan lines, but limited by the available bandwidth. The maximal baseband bandwidth is around 6 MHz which, according to the
sampling theorem, translates to about 720 pixels. This value is enough to capture all the original information present. In
digital applications, the number of pixels per line is an arbitrary choice. Values above about 500 pixels per line are enough for a perceived quality equivalent to analog free-to-air television; DVB-T, DVD and DV allow better values such as 704 or 720 (matching the maximum theoretical resolution of the original analog system).
Color information is stored using the
YCbCr
YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-diff ...
color space (regardless of the original PAL or SECAM color system) with
4:2:2 sampling and following
Rec. 601 colorimetry.
Usage
Originally used for conversion of analog sources in TV studios, this resolution was adopted into digital broadcasting or home use.
In digital video applications, such as
DVD
The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
s and
digital broadcasting
Digital broadcasting is the practice of using digital signals rather than analogue signals for broadcasting over radio frequency bands. Digital television broadcasting (especially satellite television) is widespread. Digital audio broadcasting i ...
, 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)
The 576i video format can be transported by major
digital television formats,
ATSC,
DVB and
ISDB, and on
DVD
The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
, and it supports
aspect ratios of standard
4:3 and
anamorphic
Anamorphic format is the cinematography technique of shooting a widescreen picture on standard 35 mm film or other visual recording media with a non-widescreen native aspect ratio. It also refers to the projection format in which a distorted ...
16:9.
Progressive sources
When 576i is used to transmit content that was originally composed of 25 full progressive frames per second (576p25 or 576p/25), the odd field of the frame is transmitted first (this is the opposite to
480i). 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. Such progressive content can be marked using
encoding flags, for example in DVDs or other
MPEG2 based media.
PAL speed-up
Motion pictures are typically shot on film at 24 frames per second. When
telecine
Telecine ( or ) is the process of transferring 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.
Telecine enables a motion picture, captured originally on fi ...
d and played back at PAL's standard of 25 frames per second, films run about 4% faster. This also applies to most TV series that are shot on film or digital 24p.
Unlike NTSC's telecine system, which uses
3:2 pull down to convert the 24 frames per second to the 30 fps frame rate, PAL speed-up results in the telecined video running 4% shorter than the original film as well as the equivalent NTSC 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
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.
It is defined as the interval between two adjacent no ...
). More recently, digital conversion methods have used algorithms that preserve the original pitch of the soundtrack, although the frame rate conversion still results in faster playback.
Conversion methods exist 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 is a free and open-source 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. It uses AVI container format to ...
), and is employed in situations where the importance of preserving the speed of the video outweighs the need for image quality.
Many movie enthusiasts prefer PAL over NTSC despite the former's speed-up, because the latter results in
telecine judder, a visual distortion not present in PAL sped-up video.
DVDLard states ''"the majority of authorities on the subject favour PAL over NTSC for DVD playback quality"''.
Also DVD reviewers often make mention of this cause. For example, in his PAL vs. NTSC article,
the founder of MichaelDVD says: ''"Personally, I find
:2 pulldownall but intolerable and find it very hard to watch a movie on an NTSC DVD because of it."'' In the DVD review of
''Frequency'',
one of his reviewers mentions: ''"because of the 3:2 pull-down artefacts that are associated with the NTSC format (…) I prefer PAL pretty much any day of the week"''. This is not an issue on modern
upconverting DVD players and
personal computers, as they play back 23.97 frame/s–encoded video at its true frame rate, without 3:2 pulldown.
PAL speed-up does not occur on native 25 fps video, such as British or European TV-series or movies that are shot on video instead of film.
Software that 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, which results in a slight decrease in audio quality. There is also a DirectShow Filter for Windows called ReClock developed by RedFox (formerly SlySoft) that can be used in a custom DirectShow Graph to remap the reference audio timing clock to correct the clock timing skew using an accurate self-adaptive algorithm resulting in effective removal of judder during panning caused by Euro pulldown including audio pitch correction via time-stretching with WASAPI Exclusive Mode and SPDIF AC/3 Encoding output modes.
See also
*
List of common resolutions
This article lists computer monitor screen resolutions that are defined by standards or in common use. Most of them use certain preferred numbers.
Computer graphics
; Pixel aspect ratio (PAR): The horizontal to vertical ratio of each pixel.
; ...
*
4320p
8K resolution refers to an image or display resolution with a width of approximately 8,000 pixels. 8K UHD () is the highest resolution defined in the Rec. 2020 ( UHDTV) standard.
8K display resolution is the successor to 4K resolution. TV manuf ...
,
2160p
4K resolution refers to a horizontal display resolution of approximately 4,000 pixels. Digital television and digital cinematography commonly use several different 4K resolutions. In television and consumer media, 38402160 (4K UHD) is the dominan ...
,
1080p,
1080i,
720p,
576p,
480p
480p is the shorthand name for a family of video display resolutions. The p stands for progressive scan, i.e. non-interlaced. The ''480'' denotes a vertical resolution of 480 pixels, usually with a horizontal resolution of 640 pixels and 4:3 ...
,
480i,
360p,
240p
Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition TV systems. The term is usually used in reference to digital TV, in particular when broadcasting at the same (or similar) resolut ...
*
Standard-definition television
*
405-line television system
The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting. The number of television lines influences the image resolution, or quality of the picture.
It wa ...
References
{{Video formats
Video formats
Television technology