Differences in Color Encoding in PAL and NTSC
The PAL standard manages color automatically, using phase alternation of the color signal that removes hue errors. Also, chrominance phase errors are eliminated in PAL systems. NTSC receivers have a manual tint control for color correction, so if colors are off-hue, the higher saturation of NTSC systems makes them more noticeable and an adjustment has to be made.
Another technical aspect is that the alternating color information — Hanover bars — can lead to grainy pictures if there are extreme phase errors. This can even happen in PAL systems, especially if decoder circuits are not properly aligned, or with early-generation decoders. However, extreme phase shifts of this nature are seen more often in ultra high frequency (UHF) signals (less robust than VHF), or in areas where terrain or infrastructure limit transmission paths and affect signal strengths.
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 color 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 color decoder differences here are ignored.
PAL supports SMPTE 498.3 while NTSC is compliant with EBU Recommendation 14.
The issue of frame rates and color 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.
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23.98 Frame per second (FPS)
Most people will consider frame rate as 24 fps but it actually means 23.98fps. The actual NTSC video frame rate is 29.97 fps while the film frame rate is modified to 23.98 fps in order to create the 3:2 pattern.
Thanks, Sylvester. I would be wary of calling these "colour encoding systems" - this could cause some confusion. Television systems is more strictly accurate. Also, automated colour management (rather than colour correction) would be a more appropriate way to describe it.
ReplyDeletePlease remember to cite your sources if you are copy and pasting from a another website. Ideally, I would like to see you paraphrase this in your own words in order to demonstrate evidence of processing these concepts.