[opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Tue, 19 Oct 2004 11:11:57 -0400

At 4:11 PM -0400 10/18/04, Manfredi, Albert E wrote:
>Craig Birkmaier wrote:
>
>>  But to imply that an OPEN specification will lead to
>>  a few de facto standards where no standard is needed
>>  is absurd.
>
>Then explain why Alan Roberts mentions 1920 X 1080 and
>1280 X 720, 50/60i or p, as HD formats, and not
>others.

Because that is the way the debate is being framed by those who seek 
to control the evolution of DTV. This is to be expected, since the 
standards processes are controlled by the special interests who seek 
to impose these format restrictions.

An obvious artifact of this reality is that we are even discussing 
the need for both 50P and 60P. In the future displays will easily 
support both, so why even have two frame rate families for Europe and 
the US?

For instruction, look at the motion picture industry, which somehow 
seems to manage their business with literally hundreds of format 
options.

>
>By the way, I would think that the way these Grand
>Alliance de-facto hold-over standards would handle
>1440 X 1080 would simply be to draw two black columns
>on the left and right screen edges. At least, that
>would be the correct way.

How could this be correct, when the camera is capturing a 16:9 image 
at 1920 x 1080 samples.  1440 samples is what some cameras use for 
compression, since there is no useful information in the upper 
spectra of the 1920 samples. Likewise, 1440 is used for emission, 
again to deal with the reality that you get more information out of 
the encoder by reducing the number of samples while improving the 
accuracy of the remaining samples.

We fought very hard for square pixels. They are REALLY important on 
the display if you are going to base the non-Nyquist rasterizing 
capabilities on a single pixel geometry as is the defacto standard 
for computers. But we also learned that for Nyquist filtered imagery 
the sample geometry is not all that critical. You can stretch or 
squeeze, and distort these samples  as much as you want, if you use 
proper filtering techniques.


>My PC monitor has a 1.25:1 aspect ratio. How does it
>manage this oddball ratio? Very simple: distortion.
>It won't display a circle unless I draw an ellipse
>(when it's set to anything other than 1280 X 1024).
>
>For a PC, who cares. For a TV or a movie theater?

I care. The reality is that your display is optimized for 1280 x 
1024, providing square pixels that fill the available screen real 
estate. Yes, you can change scanning rates and introduce distortions; 
you can also adjust the vertical size to eliminate these distortions 
by allowing small black bands at the top and bottom of the screen.

I don't want distortion in any display, unless I choose to distort 
the images for  some aesthetic reason. Clearly the accommodation of 
different aspect ratio sources on a fixed aspect ratio display 
involves the possibility of such aesthetic compromises. I do not mind 
letter or pillar boxing. I'd love to use these throw away areas for 
other kinds of information as I do on my computer desktop. But some 
people want to stretch 4:3 sources to fill their new 16:9 screens, or 
to crop widescreen sources on their 4;3 screens. It is easy to 
support both approaches.

By the way, Movie theaters have a low tech solution for the problem. 
They can change the masking of the screen to support different aspect 
ratios by simply moving the curtains that define the top, bottom and 
sides of the screen.

Regards
Craig

>
>Bert
>
>
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