[opendtv] Re: Image perception
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 12 Jan 2007 17:41:40 -0500
Mark Schubin wrote:
> Actually, ATSC can theoretically do better than that, but
> people don't perceive MHz. They perceive "sharpness."
>
> Filtering means that sharpness (proportional to the square
> of the area under an MTF curve) can be greatly increased
> by increasing resolution in the camera and in the display.
> What happens in between is more questionable.
In the very first demoes of S-VHS, the demo tapes always had very high
contrast scenes, even cartoons. Sure, the images looked "sharp," but
they did not really include a whole lot of small detail.
Had they provided a demo of a low contrast scene with lots of fine
detail, maybe a scenic on a cloudy day, that same S-VHS system would not
have appeared so impressive. HDTV would beat it hands down.
Similarly, in audio, one can impress an audience with sudden loud bursts
of music even from a band-limited amp, but then when the music gets more
complicated and less contrasty, the limitations of the band-limited amp
will become easily perceptible.
It seems to me that the 3 dB bandwidth limitation of video is as good a
single number to use to indicate image quality potential as is the 3 dB
bandwidth spec in an audio amp, for audio quality, no?
> If Americans still sit at the Lechner distance (9 feet)
> when watching TV, then, up to a screen size of 25 inches,
> they cannot perceive a resolution greater than 480-line if
> they have 20/20 vision or worse.
I've seen these numbers before. Assuming they correctly reflect how
human vision works, that 480 line you mention would describe EDTV, or
480p, not NTSC and not 480i (where each line has to be softened
somewhat).
If that's the case, that means you must get beyond NTSC or SDTV to fully
satisfy human vision and a 25" screen at 9' viewing distance. It would
also mean that I should be able to perceive the difference between DVDs
and HDTV, on my 26" set, from my normal sitting position. And that would
be correct. I can.
The difference is just starting to be noticeable, from where I sit. And
given that 26" sets are toward the low end of where consumers seem to be
headed, I'd conclude that SDTV will also satisfy primarily the low end.
In a broadcast scheme, that's not a really good place to be.
Craig will bring up cell phone screens etc. I'm not talking about that.
I'm talking about broadcast TV to home TV sets.
Bert
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