[opendtv] Re: Public M/H information
- From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 20 Dec 2008 18:22:53 -0500
Craig Birkmaier wrote:
>> Since each visible cycle is represented by a dark
>> and a light line, or two pixels at least, you're
>> saying that human visual acuity goes up to about
>> one arcminute, or 60 individual lines per degree.
> It take 3 pixels (minimum) to create a line pair.
> In a television system it takes at least five because
> of the need for Nyquist filtering - black to white
> transitions are illegal.
Sorry, Craig, but to discern a line pair, you are not doing a black to white
transition. You are doing a slightly lighter gray to slightly darker gray
transition, at the limit.
In any event, if what you say were true, if anything, it would make your
240-pixel images even less good than they are. Because, by your estimation
anyway, the 240 pixels would deliver even less than 120 line pairs.
> The nominal viewing distance for my iPhone is about five
> picture heights - I cannot see the raster on the
> 480 x 360 screen at this distance, even with reading
> glasses. Properly encoded video is VERY sharp - easily
> as good as my 50" HDTV at 5 picture heights.
Five picture heights is probably about right for a vehicle TV setup too. And
that's certainly closer than ideal for 240 lines. Unless you're trying to
convince me that watching a VHS tape on an HDTV at 5 picture heights distance
is just about HDTV quality.
Bert
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