View source for 576i

{{Short description|Standard-definition video mode}}
{{About|the digital resolution|the SECAM analogue colour system|SECAM|the PAL analogue colour system|PAL|the 625-line analogue system|625 lines}}
{{More citations needed|date=April 2023}}
{{Use British English|date=July 2021}}
[[File:TV-line-count-world.svg|thumb|500px|SDTV resolution by nation: countries using 576i are in blue.]]

'''576i''' is a [[standard-definition television|standard-definition]] digital video mode,<ref name="auto">{{cite web |title=What means 576i? |url=http://www.afterdawn.com/glossary/terms/576i.cfm |website=Afterdawn.com}}</ref> originally used for [[Digitization|digitizing]] [[625 lines|625 line]] [[Analog television|analogue television]] in most countries of the world where the [[utility frequency]] for electric power distribution is 50&nbsp;Hz. Because of its close association with the legacy colour encoding systems, it is often referred to as [[PAL#PAL region|PAL]], PAL/[[SECAM]] or [[SECAM]] when compared to its 60&nbsp;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 video|interlaced]] resolution.<ref name="auto"/> The [[Refresh rate|field rate]], which is 50&nbsp;[[Hertz|Hz]], is sometimes included when identifying the video mode, i.e. '''576i50'''; another notation, endorsed by both the [[International Telecommunication Union]] in [[Rec. 601|BT.601]]<ref>{{cite web |date=March 2011 |title=Recommendation ITU-R BT.601-7: Studio encoding parameters of digital television for standard 4:3 and wide-screen 16:9 aspect ratios |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-7-201102-I!!PDF-E.pdf |access-date=2 March 2022 |website=Itu.int}}</ref> and SMPTE in [[SMPTE 259M]], includes the [[frame rate]], as in '''576i/25'''.

== Operation ==
[[File:Balayage entrelace affichage trames.svg|alt=Interlaced scanning: display of the odd and even frames, and line returns|thumb|300px|Interlaced scanning: display of odd (green) and even (red) scanlines, and line return blanking periods (dotted)]]
In analogue television, the full [[Raster scan|raster]] uses 625 lines, with 49 lines having no image content to allow time for [[Cathode-ray tube|cathode ray tube]] circuits to retrace for the next frame (see [[Vertical blanking interval]]).<ref>The 625-line television standard was introduced in the early 1950s. After tracing a frame on a CRT, the electron beam has to be moved from the bottom right to the top left of the screen ready for the next frame. The beam is blanked, no information is transmitted for the duration of 49 lines, and circuitry relatively slow by modern standards executes the retrace.</ref> 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&nbsp;MHz which, according to the [[Nyquist–Shannon sampling theorem|sampling theorem]], translates to about 720 pixels. This value is enough to capture all the original information present. In [[digital television|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 analogue 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 analogue system).

Colour information is stored using the [[YCbCr]] [[Color space|colour space]] (regardless of the original PAL or SECAM colour system) with [[Chroma subsampling#4:2:2|4:2:2]] sampling and following [[Rec. 601]] colourimetry.

== Usage ==
Originally used for conversion of analogue sources in TV studios, this resolution was adopted into digital broadcasting or home use.
In digital video applications, such as [[DVD]]s and [[DVB|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]])

The 576i video format can be transported by major [[digital television]] formats, [[ATSC standards|ATSC]], [[DVB]] and [[ISDB]], and on [[DVD]], and it supports [[aspect ratio (image)|aspect ratios]] of standard [[Fullscreen (aspect ratio)|4:3]] and [[anamorphic widescreen|anamorphic]] [[16:9 aspect ratio|16:9]].

== Progressive sources ==
When 576i is used to transmit content that was originally composed of 25&nbsp;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 [[DVD-Video#Video data|encoding flags]], for example in DVDs or other [[MPEG-2|MPEG2]] based media.<ref>{{cite web |last1=Munsil |first1=Don |last2=Florian |first2=Brian |date=September 30, 2000 |title=DVD Benchmark - Part 5 - Progressive Scan DVD |url=https://hometheaterhifi.com/technical/technical-reviews/dvd-benchmark-part-5-progressive-scan-dvd/ |website=HomeTheaterHifi}}</ref><ref>{{cite web |date=15 December 2021 |title=MPEG and Progressive Content - Windows drivers |url=https://docs.microsoft.com/en-us/windows-hardware/drivers/display/mpeg-and-progressive-content |website=docs.microsoft.com}}</ref>

== PAL speed-up ==<!-- This section is linked from [[NTSC]] -->
{{anchor|576i speed-up}}

[[Film|Motion pictures shot on film]] are typically intended to be played back at 24&nbsp;frames per second. When [[telecine]]d and played back at the PAL standard 25&nbsp;frames per second, films run 4.1{{overline|6}}% faster than the original, and 4.2708{{overline|3}}% faster than the NTSC film standard{{efn|For NTSC playback, 24&nbsp;fps sources are generally slowed down to 23.{{overline|976023976}}&nbsp;fps, to be able to fit into a 29.{{overline|97002997}}&nbsp;fps timebase with a [[3:2 pulldown]].}} 23.{{overline|976023976}}&nbsp;frames per second. This increase in speed also increases the pitch of the audio by about 70.672&nbsp;[[Cent (music)|cents]].<ref name="On PAL speedup">{{cite web|url=http://www.robert-bresson.com/Words/On_PALspeedup.html|title=PAL Speedup — Case Study: A Man Escaped (New Yorker DVD)|first=Trond S.|last=Trondsen|work=Masters of Cinema|via=Robert Bresson|date=2004-05-29|access-date=2025-01-28}}</ref>{{bsn|date=January 2025}} Digital conversion methods can correct for this increased speed and play the video back at its correct speed and pitch, at the expense of a decreased audio sample rate.{{efn|This method reduces the typical DVD sample rate of {{val|48000}}&nbsp;Hz to {{val|46080}}&nbsp;Hz.}}

Some movie enthusiasts may prefer PAL over NTSC despite this increased speed, because the&nbsp;latter results in [[Telecine#Telecine judder|stutter]], a visual distortion not present in sped-up PAL video, where different frames last for uneven amounts of time.<ref name="Enthusiasts">{{cite web |last=Ogg |first=Allan |date=2003-09-22 |title=The Art of Buying DVDs |url=http://www.dvdlard.co.uk/Content.aspx?ContentID=109 |archiveurl=https://web.archive.org/web/20060114015926/http://www.dvdlard.co.uk/Content.aspx?ContentID=109 |archive-date=2006-01-14 |website=DVDLard}}</ref><ref name="Taran framerate guide">{{cite AV media |url=https://www.youtube.com/watch?v=p3Jb3UPAw-w&t=3m34s |chapter=What causes stuttering?|first=Taran |last=van&nbsp;Hemert |via=YouTube |time=3:34 |date=2022-11-19 |title=Mixing Different Framerates - The Ultimate Guide<!--The video has had multiple different titles on YouTube. This is the title as it has always appeared on Nebula.-->}}</ref> This is generally not an issue on modern [[Video scaler|upconverting]] DVD players and [[personal computer]]s, as they play back 23.{{overline|976023976}}&nbsp;fps video at its native frame rate.

Another method of converting 24&nbsp;fps footage to 25&nbsp;fps is the [[Telecine#Euro pulldown|Euro pulldown]], where every frame of the original footage is distributed into two fields, except every 12th frame which lasts for three fields. This preserves the pitch and sample rate of the audio, and the higher resolution of PAL video compared to NTSC, at the expense of more stuttery motion.<ref name="Taran framerate guide"/><ref name="DVD-Video Bible">{{cite web |url=https://gist.github.com/rlaphoenix/eaa987f7fd365fcd6803576746471b8d#pulldown-222222222223-12-cycle-pulldown |title=The DVD-Video Bible |author=PHOENiX |via=GitHub |date=2020-02-23 |access-date=2025-01-28}}</ref>

Yet another method is [[Inbetweening#Digital animation|frame blending]], which preserves smooth motion but leaves [[Ghosting (television)|ghosting artifacts]], although it has been criticized by some as looking amateurish.<ref name="Taran blended frames">{{cite AV media |url=https://www.youtube.com/watch?v=p3Jb3UPAw-w&t=34m14s |chapter=Never use frame blending to convert 24 to 30, or 30 to 24. (Or 25.) |first=Taran |last=van&nbsp;Hemert |via=YouTube |time=34:14 |date=2022-11-19 |title=Mixing Different Framerates - The Ultimate Guide<!--The video has had multiple different titles on YouTube. This is the title as it has always appeared on Nebula.-->}}</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=DyqjTZHRdRs&t=2m14s |first=Alan |last=Melikdjanian |work=Captain Disillusion |via=YouTube |time=2:14 |date=2019-04-09 |title=CD / Frame Rate}}</ref>

PAL speed-up does not occur on footage intended for playback at 25&nbsp;frames per second.

{{notelist}}

== See also ==
{{Portal|Television}}
* [[List of common display resolutions]]
* [[Ultra-high-definition television|4320p]], [[4K resolution#2160p resolution|2160p]], [[1080p]], [[1080i]], [[720p]], [[576p]], [[480p]], [[480i]], [[Low-definition television|360p]], [[240p]]
* [[Standard-definition television]]
* [[405-line television system]]

== References ==
{{reflist}}

{{TV resolution}}
{{Video formats}}

[[Category:Television terminology]]
[[Category:Video formats]]