# 576i
**576i** is a standard-definition digital video mode with 576 active scan lines in interlaced scanning, operating at 25 full frames per second made up of 50 fields (half-frames) per second[1](https://tech.ebu.ch/docs/techreports/tr005.pdf). It is the digital descendant of the 625-line analog television systems used in countries whose electricity supply runs at 50 Hz, and it is commonly, though imprecisely, called PAL or PAL/SECAM[2](https://www.afterdawn.com/glossary/term.cfm/576i). Its 60 Hz counterpart, with 480 active lines, is 480i.
| Key fact | Detail |
|---|---|
| Scanning | 576 active lines, interlaced; 25 frames per second from 50 fields per second[1](https://tech.ebu.ch/docs/techreports/tr005.pdf) |
| Digital sampling | ITU-R BT.601 production aperture of 720 pixels × 576 lines for 625-line systems; luminance sampled at 13.5 MHz[3](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1683-0-200406-I%21%21PDF-E.pdf) • [4](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-5-199510-S%21%21PDF-E.pdf) |
| Aspect ratios | 4:3 standard and anamorphic 16:9; 720×576 PAL footage uses a D1/DV pixel aspect ratio of 1.094[5](https://helpx.adobe.com/premiere/desktop/edit-projects/intro-to-editing/aspect-ratio-preservation.html) |
| Delivery | Carried by digital television systems including DVB, and on DVD at 720×576, 25 frames per second[6](https://broadcast.nbtc.go.th/data/tv_standard/Technical-Standard-for-Transmission-revised-Final-Postweb.pdf) |
| Regulatory example | Thailand's DVB-T2 standard defines SD as 720×576 interlaced at 25 frames/sec in 16:9 and 4:3; Australia defined SDTV as 576 lines × 720 pixels at 50 Hz interlaced[6](https://broadcast.nbtc.go.th/data/tv_standard/Technical-Standard-for-Transmission-revised-Final-Postweb.pdf) • [7](https://www.aph.gov.au/%20Parliamentary_Business/Committees/House_of_Representatives_Committees?url=cita%2Fdigitaltv%2Freport%2Fchapter2.pdf) |
## Meaning of the name
The EBU nomenclature places the number of active lines first (576), then the scanning format (i for interlaced, p for progressive, psf for progressive segmented frames), then the full frame rate, as in 576i/25[1](https://tech.ebu.ch/docs/techreports/tr005.pdf).
The 576 figure counts active (picture-carrying) lines only. Under BT.601 sampling the full digital luminance frame for a 625-line system is 720 pixels by 576 lines, the production aperture representing the maximum image extent before blanking[3](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1683-0-200406-I%21%21PDF-E.pdf).
## Relationship to PAL and SECAM
576i is sometimes used as a synonym for PAL, but the two are not the same thing. PAL and SECAM are analog color-encoding systems; 576i describes a line-and-field scanning structure. A digitized PAL signal, such as a captured analog broadcast conforming to the 576-line standard of ITU-R BT.601, is a 576i signal[2](https://www.afterdawn.com/glossary/term.cfm/576i).
The 576i and 576p family spans several signal types: analog composite video, interlaced and progressive analog component video, and interlaced and progressive digital component video, all at 576 active scan lines per frame[8](https://www.sciencedirect.com/topics/engineering/video-signal).
## Origin in the 625-line standard
The 625-line, 50 Hz scanning standard from which 576i descends was developed in the Soviet Union in the early 1940s; Professor Mark Krivocheev of the USSR was one of its originators. The system, requiring an 8 MHz channel width, was approved as an official USSR standard in 1945, and the first transmissions went on air in Moscow in September 1948. The 625-line concept was later adopted in the Western European standard, which used a 7 MHz channel, and it was carried forward into color television standards and digital modulation schemes[9](https://www.itu.int/itunews/manager/display.asp?ext=html&ipage=visionary&issue=04&lang=en&year=2004).
Interlaced scanning was central to these standards. Using 2:1 interlace for the line-scan to field-scan relationship economized on channel bandwidth and, in one step, eliminated large-area flicker and doubled temporal resolution compared with the 24 frames per second of cinema film[10](https://journal.smpte.org/conferences/138th%20SMPTE%20Technical%20Conference%20Technical%20Papers%20Program/26/). Of the original 405, 525, 625, and 819 line standards, the 405 and 819 line systems fell away while 525 and 625 remained in service[10](https://journal.smpte.org/conferences/138th%20SMPTE%20Technical%20Conference%20Technical%20Papers%20Program/26/).
## Digital sampling and pixel geometry
ITU-R BT.601, the studio encoding standard for 4:3 and widescreen 16:9 digital television, specifies a 13.5 MHz luminance sampling rate for both aspect ratios, with an alternative 18 MHz rate for 16:9 systems needing proportionately higher horizontal resolution. It was written to give the greatest possible commonality of parameter values between 525-line and 625-line systems, so that equipment could be shared and programs exchanged internationally[4](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-5-199510-S%21%21PDF-E.pdf).
Because 720×576 pixels are displayed across a 4:3 or 16:9 screen, the pixels are not square. Editing software assigns PAL footage at D1 or DV resolution of 720×576 a pixel aspect ratio of 1.094, meaning pixels are wider than they are tall[5](https://helpx.adobe.com/premiere/desktop/edit-projects/intro-to-editing/aspect-ratio-preservation.html). Some consumer documentation instead quotes SDTV 576i as 704×576 pixels, reflecting a narrower active-picture definition than the full 720-sample production aperture[11](https://www.documents.philips.com/assets/20230223/9850ae30a15e49588062afb200a4b4a1.pdf).
## Use in broadcasting and DVD
576i has served as the standard-definition format in national digital television rules. Thailand's technical standard for DVB-T2 transmission specifies Standard Definition as 720×576 interlaced at 25 frames per second with 16:9 and 4:3 aspect ratios, alongside HD formats of 1080i at 25 frames/sec and 720p at 50 frames/sec[6](https://broadcast.nbtc.go.th/data/tv_standard/Technical-Standard-for-Transmission-revised-Final-Postweb.pdf). In Australia, the parliamentary inquiry into digital television described the SDTV picture as 576 lines × 720 pixels at 50 Hz interlaced, carried in about one quarter of the spectrum capacity of an analog signal[7](https://www.aph.gov.au/%20Parliamentary_Business/Committees/House_of_Representatives_Committees?url=cita%2Fdigitaltv%2Freport%2Fchapter2.pdf). DVD-Video in PAL regions stores 720×576 at 25 frames per second[6](https://broadcast.nbtc.go.th/data/tv_standard/Technical-Standard-for-Transmission-revised-Final-Postweb.pdf).
## Interlacing and deinterlacing
Interlacing splits each frame into an odd field and an even field scanned at different moments. When the two fields do not align, comb-teeth aliasing appears in moving areas, which is why 576i material displayed on modern progressive screens requires deinterlacing, the reconstruction of missing lines to produce full frames[12](https://arxiv.org/abs/2011.13675). Simple spatial or temporal deinterlacing leaves many artifacts on detailed moving content; motion-compensated methods that propagate information along the motion trajectory handle it better, though the problem is fundamentally ill-posed because half the lines were never captured in a given field[13](https://di.ku.dk/forskning/Publikationer/tekniske_rapporter/tekniske-rapporter-2007/07-03.pdf).
## References
1. [EBU Technical Report 005, Information Paper on HDTV Formats, Appendix 1](https://tech.ebu.ch/docs/techreports/tr005.pdf)
2. [What means 576i? AfterDawn Glossary](https://www.afterdawn.com/glossary/term.cfm/576i)
3. [Recommendation ITU-R BT.1683, Objective perceptual video quality measurement techniques](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1683-0-200406-I%21%21PDF-E.pdf)
4. [Recommendation ITU-R BT.601-5, Studio encoding parameters of digital television](https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.601-5-199510-S%21%21PDF-E.pdf)
5. [Preserve aspect ratios in Premiere, Adobe Help](https://helpx.adobe.com/premiere/desktop/edit-projects/intro-to-editing/aspect-ratio-preservation.html)
6. [Technical Standard for Transmission, NBTC BS 4001-2555 (Thailand)](https://broadcast.nbtc.go.th/data/tv_standard/Technical-Standard-for-Transmission-revised-Final-Postweb.pdf)
7. [Chapter 2: Digital television in Australia, House of Representatives Committee report](https://www.aph.gov.au/%20Parliamentary_Business/Committees/House_of_Representatives_Committees?url=cita%2Fdigitaltv%2Freport%2Fchapter2.pdf)
8. [Video Signal, ScienceDirect Topics](https://www.sciencedirect.com/topics/engineering/video-signal)
9. [In the Vanguard of Television Broadcasting, ITU News 2004](https://www.itu.int/itunews/manager/display.asp?ext=html&ipage=visionary&issue=04&lang=en&year=2004)
10. [CCIR 601, Future File Image or the Last Universal Video Standard? SMPTE Technical Conference](https://journal.smpte.org/conferences/138th%20SMPTE%20Technical%20Conference%20Technical%20Papers%20Program/26/)
11. [Glossary of Digital TV Resolutions, Philips documentation](https://www.documents.philips.com/assets/20230223/9850ae30a15e49588062afb200a4b4a1.pdf)
12. [Rethinking deinterlacing for early interlaced videos, arXiv:2011.13675](https://arxiv.org/abs/2011.13675)
13. [Deinterlacing, DIKU Technical Report 07-03](https://di.ku.dk/forskning/Publikationer/tekniske_rapporter/tekniske-rapporter-2007/07-03.pdf)
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*Topic: Encyclopedia › Technology and the built world › Communications and everyday technology › Phonographic and magnetic recording media › Videotape formats and video recording equipment*
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