[opendtv] Re: VHF vs UHF coverage
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 27 May 2009 16:16:36 -0700
Bert wrote:
> Without doing the math, if Y = 0, then the U and V cannot be zero,
> right?
*If* I understand this correctly - it seems to me that if Y = 0 the image is
then black and there is no RGB or color difference signal.
> Similarly, pure green takes up only one component of RGB, but it
> requires all three components of Y Pb Pr.
True, Luma is part of that equation.
For no real purpose, my review of the Composite NTSC color signals
components follows:
1. luminance (monochrome video): When derived from a modern RGB camera* or
other sources, consists of:
G = 59%
R = 30%
B - 11%
2. Color difference signal:
RGB are matrixes into two color difference signals which are then quadrature
modulated onto a 3.579 MHz color carrier. These color difference signals are
known as: I (in phase) and Q (quadrature.
http://books.google.com/books?id=t2cOddQJQPYC&pg=RA1-PA589&lpg=RA1-PA589&dq
=YIQ+matrix&source=bl&ots=bWTXs3rRkW&sig=f0YGB3g37ziUVVthU512KT9QTx4&hl=en&e
i=dsYdSrG5G570tQOdndyFCg&sa=X&oi=book_result&ct=result&resnum=3
3. Sync and blanking
The color carrier is mixed (interleaved) into luminance and sync is added to
complete the composite video signal; which is then restored to RGB in a TV
display.
Negative modulation is used for NTSC transmission (the video signal is
inverted). That results in the sync tip and black picture being at high
power levels while the whites are at the lowest power level. This
significantly reduced the noise in the blacks where it has the most negative
impact on viewing. Whites tend to mask noise.
*Early color cameras had four pickup devices: one was higher resolution and
acquired Luma(Y) while three lower resolution devices were used to acquire
RGB.
Dale
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Manfredi, Albert E
Sent: Tuesday, May 26, 2009 3:10 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: VHF vs UHF coverage
Dale Kelly wrote:
> A darker video requires more transmitter power than does a
> brighter video. (which you know but a few others on this list
> may not)
Must be one of those initially unexpected differences between RGB and Y
Pb Pr, or YUV, color. If it's one way in RGB, it's the opposite in
YPbPr.
Without doing the math, if Y = 0, then the U and V cannot be zero,
right?
Similarly, pure green takes up only one component of RGB, but it
requires all three components of Y Pb Pr.
Bert
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