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'''576i''', bir [[standart çözünürlüklü televizyon|standart çözünürlüklü]] video modu. Aslen elektrik dağıtımı için [[şebeke frekansı]]nın 50 Hz olduğu, dünyanın birçok ülkesinde [[televizyonu yayını]] için kullanılır. Renk kodlama sistemi ile yakın ilişkisi yüzünden 60 Hz temelli [[NTSC]] karşılığı [[480i]] ile karşılaştırıldığında sıklıkla '''[[PAL]]''' veya PAL/[[SECAM]] olarak ifade edilir. Dijital uygulamalarda genellikle "576i" olarak ifade edilir; analog bağlamlarda sıklıkla "'''625 lines'''" olarak adlandırılır<ref>[http://www.afterdawn.com/glossary/terms/576i.cfm afterdawn.com - 576i]</ref> ve çerçeve oranı genellikle analog iletimde 4:3, [[Digital Video Broadcasting|dijital iletimde]] ise 16:9'dur.
''576'', 576 dikey çözünürlük çizgisini ifade eder, ''i'' ise [[interlacing|geçmeli]] bir çözünürlük olduğunu ifade eder. The [[field rate]], which is 50 [[Hertz|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]], includes the [[frame rate]], as in '''576i/25'''.
Its basic parameters common to both analogue and digital implementations are: 576 scan lines or vertical pixels of picture content, 25 frames (giving 50 fields) per second.
In analogue [[Vertical blanking interval|49 additional lines without image content]] are added to the displayed frame of 576 lines to allow time for older [[cathode ray tube]] circuits to retrace for the next frame,<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> giving 625 lines per frame. Digital information not to be displayed as part of the image can be transmitted in the non-displayed lines; [[teletext]] and other services and test signals are often implemented.
Analogue television signals have no pixels; they are rastered in scan lines, but along each line the signal is continuous. In [[digital television|digital]] applications, the number of pixels per line is an arbitrary choice as long as it fulfils the [[sampling theorem]]. Values above about 500 pixels per line 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 major [[digital television]] formats, [[ATSC Standards|ATSC]], [[Digital Video Broadcasting|DVB]] and [[Integrated Services Digital Broadcasting|ISDB]], and on [[DVD]], and it supports [[aspect ratio (image)|aspect ratios]] of standard 4:3 and [[anamorphic widescreen|anamorphic]] [[16:9]].
== Taban bantı birlikte çalışabilirliği (analog)==
[[Dosya:Pal channel.svg|thumb|400px|right|Spectrum of a System I (bands IV and V) television channel with PAL or SECAM colour]]
576i videosu tabanbandı (yani tüketici aygıt kabloları, [[radyo frekansı]] değil) ile iletildiğinde, [[televizyon yayın sistemi|"tek harfli" sistemler]] arasındaki çoğu fark, dikey çözünürlük ve kare hızı dışında, önemini yitirmektedir.
Bu bağlamda, vasıfsız '''576i''' değişmeksizin
* Çerçeve başına 625 çizgi (576'sı resim içeriğini taşır)
* 25 frames per second interlaced yielding 50 fields per second
* Two interlaced video fields per frame
* With [[PAL]] or [[SECAM]] colour (4.43 MHz or 3.58 MHz (576i-N & 576i-NC))
* [[Frequency modulated|frequency-modulated]] or [[amplitude modulated|amplitude-modulated]] audio (mono)
* Mono or stereo audio, if sent via connector cables between devices
anlamına gelir.
==Modulation for TVRO transmission==
576i when it is transmitted over [[Television receive-only|free-to-air satellite]] signals is transmitted substantially differently from terrestrial transmission.
Full transponder mode (e.g., 72 MHz)
* Luma signal is frequency-modulated (FM), but with a 50 Hz [[dithering]] signal to spread out energy over the transponder
* Chroma is phase-modulated (PM)
* 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 [[DVD]]s and [[Digital Video Broadcasting|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 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.
==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 [[NTSC]]. 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.
==PAL speed-up==<!-- This section is linked from [[NTSC]] -->
[[Motion picture]]s are typically shot on film at 24 frames per second. When [[telecine]]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.<ref>[http://www.michaeldvd.com.au/Articles/PALvsNTSC/PALvsNTSC.asp PAL speedup]</ref> Unlike NTSC's telecine system, which uses [[Telecine#2:3 pulldown|3:2 pulldown]] 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 [[cent (music)|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.
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]]), 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#Telecine judder|telecine judder]], a visual distortion not present in PAL sped-up video.<ref name="Enthusiasts">[http://www.dvdlard.co.uk/Content.aspx?ContentID=109 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 [http://www.michaeldvd.com.au/Articles/PALvsNTSC/PALvsNTSC.asp PAL vs. NTSC article], the founder of [http://www.michaeldvd.com.au MichaelDVD] says ''"Personally, I find [3:2 pulldown] all but intolerable and find it very hard to watch a movie on an NTSC DVD because of it."'' In the [http://www.michaeldvd.com.au/Reviews/Reviews.asp?ID=3999 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"''.</ref> This is not an issue on modern [[upconverting]] DVD players and [[personal computer|PCs]], as they play back 23.97 frame/s–encoded video at its true frame rate, without 3:2 pulldown.
Naturally, 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 which corrects the speed-up is available for those viewing 576i DVD films on their computers, [[WinDVD|WinDVD's]] "PAL TruSpeed" being the most ubiquitous{{Citation needed|reason=Statements like this need some data to support them|date=April 2014}}. 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.
==582i==
The original implementation of the version of the analogue 625 line standard used in Ireland, the United Kingdom and South Africa ([[Broadcast television systems|System I]]) specified 582 active lines rather than the 576 used in all other implementations of the 625 line system.<ref>Report 308-2 of the XIIth Pleniary Assembly of the CCIR - Characteristics of Monochrome Television Systems</ref> However most present day analogue broadcasting (and all non-HD digital broadcasting) in these countries is based on 576i exclusively.
== Ayrıca bakınız ==
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