[opendtv] Re: Mediaflo Technology
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 11 Nov 2006 19:22:56 -0500
Mark Schubin wrote:
>
> How do we get more contrast? If there's filtering, it's by increasing
> the number of pixels. With sin x/x filtering, 1920 pixels across offer
> zero contrast at 960 cycles per picture width. With the same filtering
> and a 3840-pixel display (like the CMO), the contrast at 960 cycles per
> picture width would be about 64% of maximum -- quite a difference! As
> Craig pointed out, more pixels in the display is usually better.
I guess another way of looking at it is the delivery resolution should
be approaching (with diminishing returns) what we CAN see. But the
display resolution should be safely into the zone of what we CAN'T see,
letting our visual limitations furnish that free filtering for the tiny
square pixels on fixed pixel displays. This again goes back to my
liking for a 720p delivery but 1080p displays, at least when bandwidth
is expensive.
- Tom
Tom Barry wrote:
And I also point out our eyes will likely provide some of that
filtering if we are sitting more than maybe 3 screen heights from the
display.
It's an interesting issue. I've been doing some research into it
recently for one of my clients.
IF we buy the Snellen criterion for visual acuity (no detail finer than
one arc minute), then visual filtering kicks in for 480-line pictures at
7.2 times the picture height, 576-line at 6x, 720-line at 4.8x,
1080-line at 3.2x, and 2160-line (the CMO and Sharp LCDs or 4K digital
cinema) at about 1.5x.
Clearly, we can see detail finer than one arc minute if there's enough
contrast. Just about anyone can see Sirius, the brightest star in the
sky (after the sun) though it fills a visual angle of only about one
ten-thousandth of one arc minute. Conversely, our limited contrast
sensitivity can easily limit our visual acuity to a mere half a degree
when there's not a lot of contrast.
How do we get more contrast? If there's filtering, it's by increasing
the number of pixels. With sin x/x filtering, 1920 pixels across offer
zero contrast at 960 cycles per picture width. With the same filtering
and a 3840-pixel display (like the CMO), the contrast at 960 cycles per
picture width would be about 64% of maximum -- quite a difference! As
Craig pointed out, more pixels in the display is usually better.
One final comment on the Snellen criterion: If 20/20 (one arc-minute
visual acuity) is the limit of human vision, why are there two more
lines on a Snellen chart?
TTFN,
Mark
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--
Tom Barry trbarry@xxxxxxxxxxx
Find my resume and video filters at www.trbarry.com
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