There are two different things to consider. One is resolution. 20/20 vision is defined as the ability to just make out a high-contrast feature (like the bar of the "E" in an eye chart) that subtends an angle of one arc minute. Some have better than 20/20 vision; many have worse. For 20/20 vision, 480-line detail would just be visible on a 25-inch 4:3 screen at 9 feet.
The other thing is sharpness. It is proportional to the square of the area under a curve plotting contrast ratio against resolution. The more samples in the source, the higher the curve at any given resolution. That's visible to anyone who can perceive a picture on any size set. The difference between an HD camera and an SD camera is perceptible even on a 6-hour-mode VHS recording.
TTFN, Mark Cliff Benham wrote:
I remember Craig saying if you are watching a 40 inch screen480p is adequate. ;^)-----Original Message----- From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Manfredi, Albert E Sent: Wednesday, May 16, 2007 5:56 PM To: opendtv@xxxxxxxxxxxxx Subject: [opendtv] Re: 1080p @ 60 is Next? John Shutt wrote:Based on what? An arbitrary screen size viewed at an arbitrary distance?I keep seeing claims that 720p is as good as anyone should need, but these perceptual things are not to be taken too religiously, IMO. Real world tests sometimes give unexpected results. Just doing the numbers, with a simplistic model, 720p does seem adequate, for 3 picture height seating. You see claims that human vision resolves down 2 arcmin or 1.6 arcmin, depending on the source. That's 0.0267 degrees, at most, for "normal" eyes. http://en.wikipedia.org/wiki/Human_eye just over half way down the page. Okay, so take a 50" screen, dimensions 24.6" H X 43.5" W. Everyone seems to say 3 picture heights distance for HDTV. So that 50" screen sits 73.8" or 6.15' distant. That sounds close enough to me, for a 50" screen. Assume you can perceive 0.0267 degrees, so 0.0343" separation between pixels is the closest one can perceive on this 50" screen. If the horizontal vertical dimension is 24.6", the distance between pixels is: 0.0228" if 1080 pixels, and 0.0342" if 720 pixels. Since 0.0343" was the limit we figured could be perceived, that says that the 720p is just right for human visual acuity, and 1080p is more than you need, for 3 picture height distance. So if you really believe that visual acuity can be determined this way, and there's nothing more to it, then 720p is it. But if real-world tests show something different, then there are other mechanisms at work that this simple model doesn't consider. Perhaps the fact that the image can be scanned multiple times, for example, rather than just fixed upon, makes the difference. If a part of the image is sampled multiple times, it is not hard to believe that the eye-brain may be able to detect edges that are less than 0.0343" ambiguity. So, IMO, it's pointless to get hung up one one answer and ignore tests that might dispute that result. Bert----------------------------------------------------------------------You can UNSUBSCRIBE from the OpenDTV list in two ways:- Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org- By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.
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