Pal

video format

1. PAL - Phase Alternating Line
PAL, is a colour encoding system used in broadcast television systems in large parts of the
world. Other common analogue television systems are SECAM and NTSC. This page
discusses the colour encoding system only. See Broadcast television systems and analogue
television for discussion of frame rates, image resolution and audio modulation. For
discussion of the 625-line 25 frame/s television standard, see 576i.
History of the PAL standard
In the 1950s, when the Western European countries were planning to establish colour
television, they were faced with the problem that the already existing American NTSC
standard would not fit the 50 Hz AC frequency of the European power grids. In addition
to that NTSC demonstrated several weaknesses, including colour tone shifting under poor
transmission conditions. For these reasons the development of the SECAM and PAL
standards began. The goal was to provide a colour TV standard with a picture frequency of
50 fields per second (50 hertz), and sporting a better colour picture than NTSC.
PAL was developed by Walter Bruch at Telefunken in Germany. The format was first
unveiled in 1963, with the first broadcasts beginning in the United Kingdom and Germany
in 1967.
[1]
Telefunken was later bought by the French electronics manufacturer Thomson. Thomson
also bought the Compagnie Générale de Télévision where Henri de France developed SECAM,
historically the first European colour television standard. Thomson nowadays also co-
owns the RCA brand for consumer electronics products, which created the NTSC colour
TV standard before Thomson became involved.
The term PAL is often used informally to refer to a 625-line/50 Hz (576i, principally
European) television system, and to differentiate from a 525-line/60 Hz (480i, principally
North American/Central American/Japanese) NTSC system. Accordingly, DVDs are
labelled as either PAL or NTSC (referring informally to the line count and frame rate) even
though technically the European discs do not have PAL composite colour. This usage may
lead readers to believe that PAL defines image resolution, even though it does not. The
PAL colour system can be used in conjunction with any resolution and frame rate, and
various such combinations exist. NTSC, by contrast does define the video line and frame
format.
Technical details
The basics of PAL and the NTSC system are very similar; a quadrature amplitude
modulated subcarrier carrying the chrominance information is added to the luminance
video signal to form a composite video baseband signal. The frequency of this subcarrier is
approximately 4.43 MHz for PAL, compared to approximately 3.58 MHz for NTSC. The
SECAM system, on the other hand, uses a frequency modulation scheme on its colour
subcarrier.
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
PAL - Phase Alternating Line
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2. phase errors in the transmission of the signal by cancelling them out. 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 imperfections of the human eye to do that
cancelling; however this resulted in a comblike effect on larger phase errors. Thus, most
receivers now use a chrominance 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 picture tube. The effect is that phase errors result
in 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
luminance signal.
For a 1:1 pixel aspect (square pixels) on a 50 Hz interlaced PAL signal the pixel rate should
be 14.75 MHz.
spectrum of a system G (bands IV and V) television channel with PAL OR SECAM
colour).
The 4.43361875 MHz frequency of the colour carrier is a result of 283.75 colour clock
cycles per line plus a 25 Hz offset to avoid interferences. Since the line frequency is 15625
Hz, the colour carrier frequency calculates as follows: 4.43361875 MHz = 283.75 * 15625
Hz + 25 Hz.
CVBS is an initialism, but it does not stand for "composite video baseband signal",
CVBS actually stands for (C)hroma, (V)ideo, (B)urst, and (S)ync; which are the
four basic components of a composite video signal. That's why it's called
"composite".
PAL vs. NTSC
NTSC receivers have a tint control to perform colour correction manually. If this is not
adjusted correctly, the colours may be faulty. The PAL standard automatically removes hue
errors by utilizing phase alternation of the colour signal (see technical details), so a tint
control is unnecessary. Chrominance phase errors in the PAL system are cancelled out
PAL - Phase Alternating Line
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3. using a 1H delay line resulting lower saturation, which is much less noticeable to the eye
than NTSC hue errors.
However, the alternation of colour information — Hanover bars — can lead to picture
grain on pictures with extreme phase errors even in PAL systems, if decoder circuits are
misaligned or use the simplified decoders of early designs (to overcome royalty
restrictions). Usually such extreme phase shifts do not occur; this effect will usually be
observed when the transmission path is poor, typically in built up areas or where the
terrain is unfavourable. The effect is more noticeable on UHF signals than VHF as VHF
signals tend to be more robust.
A PAL decoder can be seen as a pair of NTSC decoders:
PAL can be decoded with two NTSC decoders.
By switching between the two NTSC decoders every other line it is possible to
decode PAL without a phase delay line or two phase-locked loop (PLL) circuits.
This works because one decoder receives a colour sub carrier with negated phase
in relation to the other decoder. It then negates the phase of that sub carrier when
decoding. This leads to smaller phase errors being cancelled out. However a delay
line PAL decoder gives superior performance. Some Japanese TVs originally used
the dual NTSC method to avoid paying royalty to Telefunken.
PAL and NTSC have slightly divergent colour spaces, but the colour decoder
differences here are ignored.
PAL supports SMPTE 498.3 while NTSC is compliant with EBU
Recommendation 14.
The issue of frame rates and colour sub carriers is ignored in this technical
explanation. These technical details play no direct role (except as subsystems and
physical parameters) to the decoding of the signal.
PAL vs. SECAM
SECAM is an earlier attempt at compatible colour television which also tries to resolve the
NTSC hue problem. It does so by applying a different method to colour transmission,
namely alternate transmission of the U and V vectors and frequency modulation, while
PAL attempts to improve on the NTSC method.
SECAM transmissions are more robust over longer distances than NTSC or PAL.
However, owing to their FM nature, the colour signal remains present, although at reduced
amplitude, even in monochrome portions of the image, thus being subject to stronger
cross colour. Like PAL, a SECAM receiver needs a delay line.
Broadcast systems PAL has been used with
PAL B/G/D/K/I
The majority of countries using PAL have television standards with 625 lines and 25
frames, differences concern the audio carrier frequency and channel bandwidths. Standards
B/G are used in most of Western Europe, standard I in the UK, Ireland, Hong Kong and
Macau, standards D/K in most of Eastern Europe and Standard D in mainland China. 7-
PAL - Phase Alternating Line
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4. MHz channels are used in VHF (B, D) and 8-MHz channels in UHF (G, K, I), although
Australia used 7-MHz channels in UHF and Ireland uses 8-MHz channels in VHF .
PAL-M standard (Brazil)
In Brazil, PAL is used in conjunction with the 525 line, 29.97 frame/s system M, using
(very nearly) the NTSC colour subcarrier frequency. Exact colour subcarrier frequency of
PAL-M is 3.575611 MHz
Almost all other countries using system M use NTSC.
The PAL colour system (either baseband or with any RF system, with the normal 4.43
MHz subcarrier unlike PAL-M) can also be applied to an NTSC-like 525-line (480i) picture
to form what is often known as "PAL-60" (sometimes "PAL-60/525" or "Pseudo PAL").
PAL-M (a broadcast standard) however should not be confused with "PAL-60" (a video
playback system — see below).
PAL-Nc
In Argentina, the PAL-Nc (combination N) variant is used. It employs the 625 line/50
field per second waveform of PAL-B/G,D/K,H,I but with a chrominance subcarrier
frequency of 3.582 MHz. VHS tapes recorded from a PAL-Nc or a PAL-B/G,D/K,H,I
broadcast are indistinguishable because the downconverted subcarrier on the tape is the
same.
PAL-N
In Paraguay and Uruguay, PAL is used with the standard 625 line/50 fields per second
system, but again with (very nearly) the NTSC subcarrier frequency.
PAL-N should not be viewed as wildly incompatible versions of the PAL system,
only the choice of colour subcarrier is different.
A VHS recorded off TV (or released) in Europe will play in colour on any PAL-N
VCR and PAL-N TV in Argentina, Paraguay, and Uruguay. Likewise, any tape
recorded in Argentina or Uruguay off a PAL-N TV broadcast, can be sent to
anyone in European countries that use PAL (and Australia/New Zealand, etc) and
it will display in colour. This has been very convenient for video collectors in the
past.
People in Uruguay, Argentina and Paraguay usually own TV sets that also display NTSC-
M, in addition to PAL-N of course. Direct TV broadcasts in NTSC-M for North, Central
and South America so this is very convenient too. Most DVD players sold in Argentina,
Uruguay and Paraguay also play PAL discs. However this is usually output in the European
variant (colour subcarrier frequency 4.433618 MHz), so people who own a TV set that
only works in PAL-N (plus NTSC-M in most cases) will have to watch those PAL DVD
imports in black and white, as the colour subcarrier frequency in the TV set is the PAL-N
variation, 3.582056 MHz. Some DVD players (usually lesser known brands) include an
internal transcoder and the signal can be output in NTSC-M, with some video quality loss
because of the systems conversion from a 625/50 PAL DVD disc to the output in NTSC-
PAL - Phase Alternating Line
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5. M 525/60. A few DVD players sold in Argentina and Uruguay allow to output the signal
in NTSC-M, PAL, or PAL-N. In that case, a PAL disc (imported from Europe) can be
played back on a PAL-N TV. Because there is no fields/lines conversion, quality is
excellent.
Extended features of the PAL specification such as teletext are implemented quite
differently in PAL-N. PAL-N supports a modified 608 closed captioning format that is
designed to ease compatibility with NTSC originated content carried on line 18, and a
modified teletext format that can occur several lines.
PAL L
The PAL L (Phase Alternating Line with L-sound system) standard uses the System "PAL"
video standard, which is the same as PAL B/G/H (625 lines, 50 Hz field rate, 15.625 kHz
line rate) except that it uses 6 MHz video bandwidth rather than 5.5 MHz, lifting the audio
subcarrier to 6.5 MHz. When System L is used with SECAM, the audio carrier is amplitude
modulated, but when used with PAL, the more usual FM sound system is usually used.
The sound offset in B and G is +5.5 whereas in L its +6.5. In layman's language, PAL-L is
PAL-BG with positive and AM sound modulation. An 8 MHz channel spacing is used
with PAL L.
PAL L is used on some hotel internal distribution systems, as well as other public display
and plant television systems. It is not used by any national TV networks. One example of a
TV with PAL-L support is Thomson 24WK25. This signal has been defined by Sandipan
Bhattacharjee, India.
System A
The BBC tested their pre-war 405 line monochrome system with all three colour standards
including PAL, before the decision was made to abandon 405 and transmit colour on
625/System I only.
All PAL systems interoperable except PAL-M (525/60)
The PAL colour system is usually used with a video format that has 625 lines per frame
(576 visible lines, the rest being used for other information such as sync data and
captioning) and a refresh rate of 50 interlaced fields per second (i.e. 25 full frames per
second), such as systems B, G, H, I, and N (see broadcast television systems for the
technical details of each format).
Some countries in Eastern Europe which formerly used SECAM with systems D
and K have switched to PAL while leaving other aspects of their video system the
same.
However, some European countries have changed completely from SECAM-D/K
to PAL-B/G.
[2]

On RF (i.e. through a Modulator or TV Aerial) the difference between I, D/H and B/G is
audio. These use different audio subcarriers, so with mismatch on Modulator Settings or
an imported TV there will be perfectly normal Colour Video, but possibly no audio. Some
PAL - Phase Alternating Line
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6. TVs and VHS tuners have multiple filters in parallel or switched for the 6 MHz, 5.5 MHz,
6.5 MHz or 4.5 MHz sound carriers. Nicam is an additional 6.5 MHz offset carrier carrying
stereo digitally, on 6.0 MHz PAL I systems. Germany particularly uses two separate FM
sound carriers on PAL B/G. (Stereo FM Radio uses a mono signal with a DSBSC L-R
audio centred on 38 kHz with a 19 kHz pilot to aid decoding. Hence the German Zweiton
and Nicam both give better performance than FM Radio).
Multisystem PAL support and "PAL 60"
Recently manufactured PAL television receivers can typically decode all of these systems
except, in some cases, PAL-M and PAL-N. Many of them can also receive Eastern
European and Middle Eastern SECAM, though rarely French broadcast SECAM (because
France uses the unique positive video modulation), unless they are made for the French
market. They will correctly display plain CVBS or S-video SECAM signals. Many can also
accept baseband NTSC-M, such as from a VCR or game console, though not usually
broadcast NTSC. Many sets also support NTSC with a 4.43 MHz subcarrier.
Many newer Video Cassette recorders and DVD players sold in Europe can play back
NTSC tapes/discs. When operating in this mode most of them do not output a true
(625/25) PAL signal but rather a hybrid of PAL and NTSC known as "PAL 60" (or
"pseudo PAL") with "60" standing for 60 Hz, instead of 50 Hz. Some video game consoles
also output a signal in this mode. Most newer television sets can display such a signal
correctly but some will only do so (if at all) in black and white and/or with
flickering/foldover at the bottom of the picture, or picture rolling (it can be noted,
however, that many analogue-era TV sets can receive the picture by means of adjusting the
V-Hold and V-Height knobs — assuming they have them). Very few TV tuner cards or
video capture cards will support this mode (a small number can, although software/driver
modification is usually required and the manufacturers specs are usually unclear). A "PAL
60" signal is similar to an NTSC (525/30) signal but with a PAL chrominance subcarrier at
4.43 MHz (instead of 3.58) and with the PAL-specific phase alternation of the red colour
difference signal between the lines.
PAL - Phase Alternating Line
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7. PAL - Phase Alternating Line
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