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Posted by Richard Crowley on 10/11/06 00:28
"Radium" wrote ...
> Stephen wrote:
>> The SECAM colour subcarrier frequency is
>> 4.40625 MHz on "Red" lines
>> 4.25000 MHz on "Blue" lines
>
> What about the subcarrier frequency on "Green" lines?
"Compatible" color is called that because it is built on the base
of the original black&white video image. If you know that
"white" is made of 11% blue and 30% red, you can calculate
the green as the remainder. Note that this is the proportion
for NTSC, dunno that PAL/SECAM are exactly the same?
And if you want to get further in, the "red" and "blue" are not
strictly those colors, but named that way because they represent
the closest colors to the "I" (in-phase) and "Q" (quadriture,
90deg out of phase) signals of the phase/amplitude encoded
color subcarrer. Note the vectorscope picture on this page...
http://en.wikipedia.org/wiki/SMPTE_color_bars
The blue vector is slightly "below" the horizontal line, and
the red vector is slightly to the left of the vertical line, but
the I and Q signals are freuquently nick-named "red" and
"blue".
But perhaps that is more than you wanted to know.
It is sheer coincidence that the French flag is also composed
of red and blue and white stripes. :-)
If you want to know why the red and blue subcarriers are slightly
different, it was explained somewhat in Stephen's excellent
description of SECAM.
> AFAIK red, green, and white are necessary for all TV formats.
Well, red, green, and blue, anyway. By tricky math, you can
get away with only two of those colors, as long as you have
the black&white picture to calculate the missing color from.
> If you look closely on any monitor, you'll find extremely
> small red, green, and blue spots.
Yes, wherever pixels are made, it is virtually always done
with a mix of red, green, and blue. Perhaps you have heard
the term "RGB"?
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