[opendtv] Image perception
- From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 12 Jan 2007 16:45:35 -0500
Manfredi, Albert E wrote:
The bottom line is that the very best analog TV standard is limited to 6
MHz of video bandwidth, whereas ATSC is limited to 31 MHz.
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.
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.
According to CEA, the average screen size sold to U.S. dealers as
recently as 2005 was 27.3 inches (actually DOWN a hair from 2004).
That's a little more than the 480-line limit but well within 576-line
perception.
To "need" the resolution of an HDTV channel, viewers need to sit closer,
to watch bigger screens, or to do both. But, again, they can see the
increased sharpness of HDTV production even on an analog TV fed from a
VHS tape, and an HDTV display will provide benefits as well.
The EBU demonstrated one aspect of this at IBC in September, using
identical cameras, identical displays, and varying only the compression
constraints in between.
TTFN,
Mark
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