(click to zoom) overlapping the luma signal ) are present across transition areas (click to zoom). Most PAL systems encode the colour information using a variant of the
Y′UV colour space. Y'comprises the monochrome
luma signal, with the three RGB colour channels mixed down onto two, U and V. Like NTSC, PAL uses a
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
MHz for PAL 4.43, compared to 3.579545 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 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
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
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 luma signal. of an actual PAL-I transmission with
NICAM showing a 20ms long interlaced PAL frame with high FFT resolution 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 (number of lines per second) is 15625 Hz (625 lines × 50 Hz ÷ 2), the colour
carrier frequency calculates as follows: 4.43361875 MHz = 283.75 × 15625 Hz + 25 Hz. The frequency 50 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 is required by the colour decoder to recreate the
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 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
back porch. This colour burst is not actually in phase with the original colour subcarrier, but leads it by 45 degrees on the odd lines and lags it by 45 degrees on the even lines. This
swinging burst enables the colour decoder circuitry to distinguish the phase of the R-Y'vector which reverses every line.
PAL signal details For PAL-B/G the signal has these characteristics. (Total horizontal sync time 12.05 μs) After 0.9 μs a
colourburst of cycles is sent. Most rise/fall times are in range. Amplitude is 100% for white level, 30% for black, and 0% for sync. ) signal used in systems M and N before combination with a sound carrier and
modulation onto an
RF carrier The vertical timings are: (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 x,y coordinates: The assumed
display gamma is defined as 2.8. The
PAL-M system uses color primary and gamma values similar to NTSC. Color is encoded using the
YUV color space.
Luma (E'{\scriptstyle\text{Y}}) is derived from red, green, and blue (E'{\scriptstyle\text{R}}, E'{\scriptstyle\text{G}}, E'{\scriptstyle\text{B}}) gamma pre-corrected (E') primary signals: • E'{\scriptstyle\text{Y}}= 0.299E'{\scriptstyle\text{R}} + 0.587E'{\scriptstyle\text{G}} + 0.114E'{\scriptstyle\text{B}} E'{\scriptstyle\text{U}} and E'{\scriptstyle\text{V}} are used to transmit
chrominance. Each has a typical bandwidth of 1.3 MHz. • E'{\scriptstyle\text{U}} = 0.492(E'{\scriptstyle\text{B}}-E'{\scriptstyle\text{Y}}) • E'{\scriptstyle\text{V}} = 0.877(E'{\scriptstyle\text{R}}-E'{\scriptstyle\text{Y}}) Composite PAL signal = E'{\scriptstyle\text{Y}} + E'{\scriptstyle\text{U}} \sin (\omega t) + E'{\scriptstyle\text{V}} \cos (\omega t) +timing where \omega = 2\pi F_{SC}. Subcarrier frequency F_{SC} is 4.43361875 MHz (±5 Hz) for PAL-B/D/G/H/I/N. == PAL broadcast systems ==