[opendtv] Re: Math of oversampling

>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

 
 
----------------------------------------------------------------------
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.

Other related posts: