Hi Dave,

Thanks,but I want to ask a further question because I don't totally
understand how that's true. If I'm looking at an NTSC color composite video
signal, isn't the subcarrier just added in to the signal? If so, why
wouldn't a comparator pick it up (i.e., if the B/W video level is -0.25,
and the subcarrier instantaneous voltage is 0.5 V, then why doesn't the
comparator act like the level is 0.25 V ?)

Thanks,

Sean

At 01:29 AM 11/29/00 -0500, you wrote:
>At 12:33 AM 11/29/00 -0500, Sean H. Breheny wrote:
> >Hi all,
> >
> >Quick video question: I want to try taking a color video signal and use a
> >high speed comparator to compare the brightness of pixels to some set value
> >(trying to detect a dark object against a light background). I want to
> >reject the color information in this process (luma only). How can I do
> >this? I know it must be fairly simple since B/W TV's can accept color
>signals.
>
>You're already there.
>NTSC carries chroma on a subcarrier.
>The baseband signal is only lumiance and sync.
>B/W TVs don't pay any attention to the subcarrier, and neither should you.
>
>
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