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Posted by Radium on 10/10/06 05:43
R. Mark Clayton wrote:
> "Radium" <glucegen1@excite.com> wrote in message
> news:1160431017.628911.56120@b28g2000cwb.googlegroups.com...
> > Hi:
> >
> > What is the color sub carrier frequency in SECAM video?
> >
> > http://www.high-techproductions.com/pal,ntsc.htm
> >
> Maybe (a) In SECAM, U and V signals are modulated using separate. color
> subcarriers at 4.25 MHz and 4.41 MHz respectively. (b) They are sent in
> alternate lines
>
> However as with PAL and NTSC these need not be the same in different places.
> Have go with Google to try and find out.
>
> > The above site shows the color sub carrier frequency for NTSC [3.579545
> > MHz] and PAL [4.433618 MHz].
> >
> > Of the video frequencies described [horizontal frequency, vertical
> > frequency, color subcarrier frequency], the color subcarrier is the
> > highest? Why is this?
>
> This is because for all three systems color was added to existing black and
> white (which is / was the same the world over) on a sub carrier well clear
> of the existing picture signal and sound sub carrier. If you use a set in
> the wrong colour standard you get a black and white picture.
>
> > How would the picture quality look like if the
> > color sub carrier frequency was only 1 hz?
>
> Terrible, the subcarrier signal would interfere with the main signal and
> vice versa.
> >
> >
> > Thanks,
> >
> > Radium
> >
In the old days when only B&W TV existed, was anythere any such thing
as a "subcarrier" in the video signal?
B&W TV had only greyscale. So I think that there would be something
similar to color subcarrier, except the "colors" would actually be
different shades of gray along with black and white. After all, images
couldn't convey much with just pure black and pure white, there needs
to be grays of different darkness in order to add some meaning to the
image.
Converting an analogue greyscale image to a 1-bit digital image signal
will result in the greys turning into pure black and/or white. The
lighter greys would turn pure white while the darker greys would turn
pure black.
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