Editing PAL (section)

== Colour encoding ==
{{More citations needed section|date=May 2021}}
[[File:Mousepad_in.jpg|thumb|Un-decoded PAL image, showing chroma information as fine patterns [[chroma dots]] (click to zoom) overlapping the luma signal]]
[[File:Mousepad_out.jpg|thumb|Decoded PAL image, with chroma fully recovered. Some minor artifacts (see [[dot crawl]]) are present across transition areas (click to zoom).]]

Most PAL systems encode the colour information using a variant of the [[Y′UV|Y'UV]] colour space. <math>Y'</math>comprises the monochrome ''luma'' signal, with the three RGB colour channels mixed down onto two, <math>U</math> and <math>V</math>.

Like NTSC, PAL uses a [[quadrature amplitude modulation|quadrature amplitude modulated]] [[subcarrier]] carrying the ''chrominance'' information added to the luma video signal to form a [[composite video]] baseband signal. The frequency of this subcarrier is 4.43361875&nbsp;[[Hertz|MHz]] for PAL 4.43, compared to 3.579545&nbsp;MHz for NTSC 3.58. The SECAM system, on the other hand, uses a frequency modulation scheme on its two line alternate colour subcarriers 4.25000 and 4.40625&nbsp;MHz.

The name "Phase Alternating Line" describes the way that the phase of part of the colour information on the video signal is reversed with each line, which automatically corrects phase errors in the transmission of the signal by cancelling them out, at the expense of vertical frame colour resolution. Lines where the colour phase is reversed compared to NTSC are often called PAL or phase-alternation lines, which justifies one of the expansions of the acronym, while the other lines are called NTSC lines. Early PAL receivers relied on the human eye to do that cancelling; however, this resulted in a comb-like effect known as [[Hanover bars]] on larger phase errors. Thus, most receivers now use a chrominance [[Analog delay line|analogue delay line]], which stores the received colour information on each line of display; an average of the colour information from the previous line and the current line is then used to drive the [[cathode-ray tube|picture tube]]. The effect is that phase errors result in [[Colorfulness|saturation]] changes, which are less objectionable than the equivalent hue changes of NTSC. A minor drawback is that the vertical colour resolution is poorer than the NTSC system's, but since the human eye also has a colour resolution that is much lower than its brightness resolution, this effect is not visible. In any case, NTSC, PAL, and SECAM all have chrominance bandwidth (horizontal colour detail) reduced greatly compared to the luma signal.

[[File:Pal channel.svg|thumb|400px|Spectrum of a System I television channel with PAL]]
[[File:PAL-I.png|thumb|400px|RF spectrogram and [[Waterfall plot|waterfall]] of an actual PAL-I transmission with [[NICAM]]]]
[[File:PAL picture.png|thumb|400px|Oscillogram of composite PAL signal—one frame]]
[[File:PAL multi lines.png|thumb|400px|Oscillogram of composite PAL signal—several lines]]
[[File:PAL 2 lines.png|thumb|400px|Oscillogram of composite PAL signal—two lines]]
[[File:An interlaced PAL frame with 20ms duration.jpg|thumb|400px|A [[waterfall display]] showing a 20ms long interlaced PAL frame with high FFT resolution]]
[[File:PAL signal frame (20ms) and line (64µs) decoding.jpg|thumb|400px|Analyzing a PAL signal and decoding the 20ms frame and 64&nbsp;μs lines]]

The 4.43361875&nbsp;MHz frequency of the colour carrier is a result of 283.75 colour clock cycles per line plus a 25&nbsp;Hz offset to avoid interferences. Since the line frequency (number of lines per second) is 15625&nbsp;Hz (625&nbsp;lines ×&nbsp;50&nbsp;Hz ÷&nbsp;2), the colour [[Carrier wave|carrier frequency]] calculates as follows: 4.43361875&nbsp;MHz = 283.75 × 15625&nbsp;Hz + 25&nbsp;Hz.

The frequency 50&nbsp;Hz is the optional refresh frequency of the monitor to be able to create an illusion of motion, while 625 lines means the vertical lines or resolution that the PAL system supports.

The original colour [[Carrier wave|carrier]] is required by the colour decoder to recreate the [[Color difference|colour difference]] signals. Since the carrier is not transmitted with the video information it has to be generated locally in the receiver. In order that the [[Phase (waves)|phase]] of this locally generated signal can match the transmitted information, a 10 cycle burst of colour [[subcarrier]] is added to the video signal shortly after the line sync pulse, but before the picture information, during the so-called [[Analog television|back porch]]. This colour burst is not actually in phase with the original colour subcarrier, but leads it by 45&nbsp;degrees on the odd lines and lags it by 45&nbsp;degrees on the even lines. This [[Burst phase|swinging burst]] enables the colour decoder circuitry to distinguish the phase of the <math>R-Y'</math>vector which reverses every line.

=== PAL signal details ===
For PAL-B/G the signal has these characteristics.

{| class="wikitable"
! Parameter
! Value
|-
| Bandwidth
| {{val|5|u=MHz}}<ref name="dvd-replica_com-palnations">{{cite web |title=PGC categories – Countries using PAL standard |url=http://www.dvd-replica.com/DVD/palnations.php |url-status=dead |archive-url=https://web.archive.org/web/20090422030617/http://www.dvd-replica.com/DVD/palnations.php |archive-date=22 April 2009 |website=dvd-replica.com}}</ref>
|-
| Horizontal sync polarity
| Negative
|-
| Total time for each line
| {{val|64|ul=μs}}<ref name="pembers_freeserve_co_uk-HBI">{{cite web |title=Horizontal Blanking Interval of 405-, 525-, 625- and 819-Line Standards |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/HBI.pdf |url-status=dead |archive-url=https://web.archive.org/web/20090529195823/http://www.pembers.freeserve.co.uk/World-TV-Standards/HBI.pdf |archive-date=29 May 2009}} 090426 pembers.freeserve.co.uk</ref><ref name="deetc_isel_ipl_pt-ch08">{{cite web |title=NTSC, PAL, and SECAM Overview |url=http://www.deetc.isel.ipl.pt/Analisedesinai/sm/downloads/doc/ch08.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120707033657/http://www.deetc.isel.ipl.pt/Analisedesinai/sm/downloads/doc/ch08.pdf |archive-date=2012-07-07 |access-date=26 April 2009 |page=52}}</ref>
|-
| [[Analog television|Front porch]] (A)
| {{val|1.65|+0.4|-0.1|u=μs}}
|-
| Sync pulse length (B)
| {{val|4.7|0.20|u=μs}}
|-
| [[Analog television|Back porch]] (C)
| {{val|5.7|0.20|u=μs}}
|-
| Active video (D)
| {{val|51.95|+0.4|-0.1|u=μs}}
|}

(Total horizontal sync time 12.05 μs)

After 0.9 μs a {{val|2.25|0.23|u=μs}} [[Colorburst|colourburst]] of {{val|10|1}} cycles is sent. Most rise/fall times are in {{val|250|50|ul=ns}} range. Amplitude is 100% for white level, 30% for black, and 0% for sync.<ref name="pembers_freeserve_co_uk-HBI" />

The [[Composite video|CVBS]] electrical amplitude is Vpp {{val|1.0|ul=V}} and impedance of 75 [[ohm|Ω]].<ref name="thomsongrassvalley_com-3922-496-46791_s03_v01">{{cite book |url=https://wwwapps.grassvalley.com/docs/Manuals/cameras/ldk5400/3922-496-46791.s03.v01.pdf |title=LDK 5400 Triax Adapter Technical Manual |publisher=Thomson Multimedia Broadcast Solutions |year=2002 |pages= |access-date=27 February 2023 |archive-date=31 March 2023 |archive-url=https://web.archive.org/web/20230331025205/https://wwwapps.grassvalley.com/docs/Manuals/cameras/ldk5400/3922-496-46791.s03.v01.pdf |url-status=live}}</ref><!-- 2,0V Vpp at http://www.rfcandy.biz/shop/images/fq916.pdf ..? -->

[[File:Composite Video.svg|thumb|350px|right|The composite video ([[composite video|CVBS]]) signal used in systems M and N before combination with a sound carrier and [[modulation]] onto an [[Radio frequency|RF]] [[carrier signal|carrier]]]]

The vertical timings are:
{| class="wikitable"
! Parameter
! Value
|-
| Vertical lines
| 312.5 (625 total)
|-
| Vertical lines visible
| 288 (576 total)
|-
| Vertical sync polarity
| Negative (burst)
|-
| Vertical frequency
| {{val|50|u=Hz}}
|-
| Sync pulse length (F)
| {{val|0.576|ul=ms}} (burst)<ref name="pembers_freeserve_co_uk-VBI-625-PAL">{{cite web |title=Vertical Blanking Interval of 625-Line Standard (PAL Colour) |url=http://www.pembers.freeserve.co.uk/World-TV-Standards/VBI-625-PAL.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160428234231/http://www.pembers.freeserve.co.uk/World-TV-Standards/VBI-625-PAL.pdf |archive-date=28 April 2016 |access-date=2015-09-03}}</ref>
|-
| Active video (H)
| 18.4<!--287.5 lines (576 PAL-B/G)--> ms
|}

(Total vertical sync time 1.6 ms)

As PAL is interlaced, every two fields are summed to make a complete picture frame.

==== Colorimetry ====
PAL colorimetry, as defined by the ITU on REC-BT.470, and based on [[CIE 1931 color space|CIE 1931]] x,y coordinates:<ref name="auto">{{cite web |title=Recommendation ITU-R BT.470-6 - Conventional Television Systems |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |access-date=19 January 2022 |archive-date=21 January 2022 |archive-url=https://web.archive.org/web/20220121001941/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf |url-status=live}}</ref>

{| class="wikitable"
|+ PAL colorimetry
! rowspan="3" |
! rowspan="3" | Standard
! rowspan="3" | Year
! rowspan="3" | [[Standard illuminant#White points of standard illuminants|White point]]
! colspan="6" | [[Primary color|Primaries]]
! rowspan="3" | Display [[Gamma correction|gamma]] [[Transfer functions in imaging|EOTF]]
|-
! colspan="2" | Red
! colspan="2" | Green
! colspan="2" | Blue
|-
! xʀ
! yʀ
! xɢ
! yɢ
! xʙ
! yʙ
|-
! PAL
| [[European Broadcasting Union|EBU]] 3213-E, [[Rec. 601|ITU-R BT.470/601 (B/G)]]
| 1970
| [[Standard illuminant#Illuminant series D|D65]]
| 0.64
| 0.33
| 0.29
| 0.6
| 0.15
| 0.06
| 2.8
|-
! PAL-M
| BT.470-6<ref name="auto2">{{cite web |title=Recommendation ITU-R BT.470-6 - Conventional Television Systems, p.16 |url=https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf#page=16 |access-date=14 March 2022 |archive-date=21 January 2022 |archive-url=https://web.archive.org/web/20220121001941/https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.470-6-199811-S!!PDF-E.pdf#page=16 |url-status=live}}</ref>
| 1972
| [[Standard illuminant#Illuminants B and C|C]]
| 0.67
| 0.33
| 0.21
| 0.71
| 0.14
| 0.08
| 2.2
|}

The assumed [[Gamma correction|display gamma]] is defined as 2.8.<ref name="auto"/> The [[PAL-M]] system uses color primary and gamma values similar to NTSC.<ref name="auto2" /> Color is encoded using the [[Y′UV|YUV]] color space.

[[Luma (video)|Luma]] (<math>E'{\scriptstyle\text{Y}}</math>) is derived from red, green, and blue (<math>E'{\scriptstyle\text{R}}, E'{\scriptstyle\text{G}}, E'{\scriptstyle\text{B}}</math>) gamma pre-corrected (<math>E'</math>) primary signals:<!-- p20 --><ref name="deetc_isel_ipl_pt-ch08" />
* <math>E'{\scriptstyle\text{Y}}= 0.299E'{\scriptstyle\text{R}} + 0.587E'{\scriptstyle\text{G}} + 0.114E'{\scriptstyle\text{B}}</math>

<math>E'{\scriptstyle\text{U}}</math> and <math>E'{\scriptstyle\text{V}}</math> are used to transmit [[chrominance]]. Each has a typical bandwidth of 1.3&nbsp;MHz.
* <math>E'{\scriptstyle\text{U}} = 0.492(E'{\scriptstyle\text{B}}-E'{\scriptstyle\text{Y}})</math>
* <math>E'{\scriptstyle\text{V}} = 0.877(E'{\scriptstyle\text{R}}-E'{\scriptstyle\text{Y}})</math>

Composite PAL signal <math>= E'{\scriptstyle\text{Y}} + E'{\scriptstyle\text{U}} \sin (\omega t) + E'{\scriptstyle\text{V}} \cos (\omega t) +</math>timing<!-- p21 --><ref name="deetc_isel_ipl_pt-ch08" /> where <math>\omega = 2\pi F_{SC}</math>.

Subcarrier frequency <math>F_{SC}</math> is 4.43361875&nbsp;MHz (±5&nbsp;Hz) for PAL-B/D/G/H/I/N.