[opendtv] Re: Microsoft Exec: 1080p HDTV Is Meaningless

Craig -

I'm still not sure why you single out non-nyquist filtered images as being a special problem for non-square pixels.

To me, the main problem with non-nyquist images is the values at the designated sample points are correct but there is an ambiguity about what the values are between those points. Especially with moving images any interpolation or scaling to calculate the missing values will likely disagree from frame to frame.

But this means a problem with all scaling or shifting, not just on non-square pixels. Do you just mean that non-square pixels implies a higher likelihood of scaling?

- Tom

Craig Birkmaier wrote: 
At 4:28 PM +0100 8/21/06, peter wilson wrote:

Non Square pixels were never a real problem, TV 2D and 3D DVE's worked fine
in the 1980's. Now even the computer guy's who didn't understand the math
can use square or rectangular pixels at will. The great majority of Flat
displays are using odd numbers of rectangular pixels and yes you do get a
significant number of incompetent processors but most of the main brands are
now ok. 


My 2 cents...

Pixel geometry has never been an issue when working with images that are acquired using proper sampling techniques - i.e. proper filtering according to Shannon, Nyquist, etc. These images can easily be resampled and displayed using any pixel geometry. The only significant issue here is that there are always some quality losses when resampling to higher sample counts, or for very small changes in sample counts.

Pixel geometry has ALWAYS been an issue when generating and displaying non-Nyquist limited samples, as is the case with most computer applications and displays. When these samples are resampled most of the benefits of using non-Nyquist samples are lost; in most cases the results are far worse than resampling Nyquist limited samples.

Square pixels quickly became the "lingua franca" of the computer world, as they allow maximum contrast for applications that do not need the filtering required for "natural" imagery. Virtually all "lithographed" displays manufactured today use orthogonal sample grids so that they can take full advantage of non-Nyquist limited sources (including their own internally generated graphics).

Many of these displays use sample grids with aspect ratios and sample densities that have nothing to do with the "video formats" that some people think are important. Hence we see 16:10 aspect ratios and sample grids with 768 lines. These displays have no problem presenting natural images (video and still images) since the samples are properly filtered, and resampling to the display raster can be accomplished with minimal degradation of image quality.

So Square pixels do matter, at least in the display, if you intend to use the display to present video, still images and non-Nyquist limited images.

Regards
Craig



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--
Tom Barry                           trbarry@xxxxxxxxxxx 
Now seeking new full time position as video software developer
Find my resume and video filters at www.trbarry.com


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