[opendtv] Re: Math of oversampling
- From: Bob Miller <bob@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 22 Apr 2005 16:02:34 -0400
Mark Schubin wrote:
>>If a broadcaster uses a 1080p camera and broadcast as 480P and on the
>>reception end it is upconverted to 720P or stays 480P I understand that
>>because of oversampling both the 720P or 480P image would be better than
>>otherwise would be expected. What I would like to do is quantify this
>>value. How would you compare a straight thru 720P broadcast to one such
>>as that above. Would the 1080P>480P>720P route be 75% of the quality of
>>the 720P>720P>720P route? Would 1080P>480P>480P be 110% of 480P>480P>480P?
>>
>>
>>
>>
>
>The calculable quality is not betterness but potential sharpness. The
>psychovisual sensation of sharpness is proportional to the square of the
>area under a modulation-transfer-function (MTF) curve, a curve plotting
>contrast ratio against detail fineness. There are many factors
>contributing to the function (lens, aperture, etc.), but, for the
>purposes of your question, two "all-else-being-equal" (meaning an HD
>lens on an SD camera) factors will affect the sharpness: the number of
>samples in the imaging chip and the optical low-pass filtering. Even
>dealing with just the former involves significant math:
>http://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/scribed_notes/09_sampling.pdf
>
>I understand that I can't include attachments on this list server, but,
>if anyone wants a diagram of the various contributions to MTF, contact
>me directly, and I'll send it. It's only about 70 KB.
>
>TTFN,
>Mark
>
Yes please I would like the diagram and anything else you have that is
on the subject.
Thanks
Bob Miller
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