[opendtv] Re: Mediaflo Technology

  • From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 11 Nov 2006 17:32:57 -0500

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?


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