[opendtv] Re: Math of oversampling - a REALITY CHECK

  • From: Tom Barry <trbarry@xxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 02 May 2005 19:09:16 -0400

Jeroen Stessen wrote:
 > Read Watkinson: http://www.microsoft.com/whdc/archive/convrg1.mspx
 > It's more than mere wiggling, it actually makes a lot of sense.

I'm very familiar with that link since I've probably posted it at 
least a half dozen times to this list already.  But I confess I've 
never really understood his math of why display resolution should 
likely be greater.  It just seems to work out that way.

- Tom


> Hi, 
> 
> Tom to Craig: 
> 
>>You sort of touched on it but let's also not forget the optimal 
>>difference between the delivery and display resolutions.
>>Most effectively you can hide the pixel/raster structure by having 
>>a higher resolution display even though both the horizontal and 
>>vertical display rez are maybe each 50% higher than the actual 
>>images being broadcast. 
> 
> 
> As proposed by John Watkinson. Very sensible indeed, because of 
> the slow roll-off of the anti-aliasing filter of the camera and 
> the anti-imaging filter of the display. You can get a better fill 
> factor of the transmission channel if you apply steeper electronic 
> filters that will dominate over the weak optical filters. 
> 
> 
>>The results end up being similar to the various upscaled images of 
>>Jeroen's.  Extra softness becomes noticeable in extreme conditions 
> 
> 
> I bet that most display manufacturers can't resist the challenge 
> of applying sharpness enhancement algorithms to the up-sampled 
> images. While that typically won't increase the detail, it will 
> at least repair some of the sharpness impression. We do it now 
> for SD input signals, so why not do it for down-sampled HD ? 
> (That is not to say that real HD can be replaced with up-converted 
> SD, the difference will still be visible...) 
> 
> 
>>but not, say, when viewing a 720p image on a 1080p display at a 
>>viewing distance designed for the display instead of the image. 
> 
> 
> But such a small lack of sharpness is easily repaired with a bit 
> of transient improvement. Or a lot, depending on your taste. 
> This trend is unstoppable anyway, that "we" will try to improve 
> everything. I was almost tempted to apply a bit of LTI to the 
> up-sampled images, but have decided not to do it. Not yet. 
> 
> By the way, did anybody notice how much ringing was added by my 
> down-sampling filter ? Especially on the dark side of grey-white 
> edges you can see it very well. What did you think of it ? 
> 
> 
>>All this just adds a bit more wiggle room.
> 
> 
> Read Watkinson: http://www.microsoft.com/whdc/archive/convrg1.mspx
> It's more than mere wiggling, it actually makes a lot of sense. 
> 
> Greetings, 
> -- Jeroen 
> 
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