[opendtv] Re: 625 video quality is good enough....
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 20 Oct 2004 15:59:26 +0100
Who says the cameras aren't oversampling? The sensors all have "precision
offset" G from R/B, so they're effectively oversampling, read the specs.
It's only when you get down to the level of the FX1 that oversampling goes
away. And have you seen any pictures from a Viper with a decent lens? I
have, and they're sharp to well oiver 30MHz.
----- Original Message -----
From: "Craig Birkmaier" <craig@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, October 20, 2004 3:37 PM
Subject: [opendtv] Re: 625 video quality is good enough....
> At 4:45 PM +0100 10/19/04, Alan Roberts wrote:
> >You'll find that the current crop of cameras will happily produce content
at
> >30MHz, I've measured it many times. The limit isn't the camera, it's the
> >lens, put a Zeiss prime on an HD camera and you'll easily get 30MHz. If
> >you're not seeing anything above 22-24MHz it's either because of filters
of
> >poor lenses, don't blame the cameras.
>
> First, we must take into consideration MTF. Because these cameras are
> NOT oversampling, the MTF at higher frequencies is WAY down. Any real
> detail will be at very low contrast levels. When you view this
> through the noise produced by the camera at these higher frequencies,
> you might be able to perceive some detail on a good display.
> Unfortunately, the consumer will never see this for two reasons.
>
> First, most cameras do use roll-off filters that typically start
> around 22-24 MHz, eliminating any info at frequencies above 25 MHz.
> Sony does this with HD Cam, resampling to 1440 horizontal samples per
> line prior to compression. The major reason they state for this is
> the high levels of noise in the information above 22 MHz.
>
> Second, There's no chance that these frequencies are going to make it
> through an MPEG-2 emission encoder, except perhaps in the case where
> the camera is locked down on a test chart. The noise reduction and
> other pre-processing techniques used in current generation encoders
> will in most cases roll off the high frequency detail prior to
> encoding.
>
> Let's talk about high frequency detail in HD when we get real
> oversampling cameras with enough sensitivity to raise the noise floor
> at these frequencies to acceptable levels.
>
> Regards
> Craig
>
>
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