Re: [v4l-dvb-maintainer] bttv driver errors

[Trent Piepho <xyzzy@xxxxxxxxxxxxx>]

On Fri, 22 Aug 2008, Andy Walls wrote:
> On Thu, 2008-08-21 at 15:50 -0700, Trent Piepho wrote:
> > And this is a pretty common way to do it.  The formula the bt878 uses is:
> > 1.0 * x(0)
>
> This is straight decimation, which is what I would think is the "real"
> way to do things - for non-video signals at least.  It limits the
> highest spatial frequency that can be accurately recovered for the
> chroma.

You have to do a low-pass filter before decimation, otherwise the high
frequencies will alias.

I think the mathematically correct filter would be a sinc function with an
infinite base, though in practice such sinc filters can produce undesirable
ringing effects.

> > That's also a perfectly valid and real formula to use, though not a
> > particularly good one.
>
> What are the measures you are using to make a good/bad declaration?  If
> only the complexity of a capture implementation is the measure, then
> straight decimation is the best, I would think.

Quality.  For example, see
http://www.glennchan.info/articles/technical/chroma/chroma1.htm

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