[opendtv] Image quality
- From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 10 Nov 2005 09:42:35 -0500 (GMT-05:00)
> "high quality out of focus picture" does seem humorously
> oxymoronic to me.
Indeed! But it might be worthwhile for HDTV shooters to consider lens
diffraction and other optical foibles that can degrade images.
Here is the formula for monochromatic diffraction-limited modulation transfer
function:
MTF = 1-(1.22*f*lamda*lp/mm)
where f is the numerical aperture,
lamda is the wavelength of light, and
lp/mm is the number of line pairs per millimeter (nominally the number of
lighter and darker points per scanning line divided by two divided the width of
the imager)
Because it is a "one-minus" equation, the only way to get 100% MTF is to have
either zero input frequency (the whole screen is one shade) or a zero numerical
aperture (the lens is infinitely large).
We do a lot of dancing around about 1920 x 1080 when it's becoming less and
less likely (with smaller and smaller imagers) that there will be any
significant energy at the high end of that.
TTFN,
Mark
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