[opendtv] Re: Learning From the Veterans - local news in HD

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Wed, 28 Apr 2010 09:28:12 -0400

At 8:22 AM -0400 4/28/10, John Shutt wrote:

----- Original Message ----- From: "Craig Birkmaier" <craig@xxxxxxxxx>
The best answer is to send ANY content in any resolution and any aspect ratio following one simple rule. Encode the content using orthogonal samples (square pixels) and report the raster size and aspect ratio in the headers. Make every set accommodate the content the best way possible for the local display. 

Craig,
Why are orthogonal samples required for this? Raster size and aspect ratio should be sufficient information. 

John
Technically they are not required, however, there is no good reason to use anything other than square pixels when the target displays are all (or nearly all) square pixel. This allows you to view the source without any further scaling/filtering if you want to see the exact samples that are transmitted.
Also note that this is only taking place on the emission side where the most severe compression is taking place. In the production chain you can do anything you want, so if the source is acquired using anamorphic lenses (very common with 35mm film acquisition) you can scan the film and maintain the non-square samples throughout the production if you so desire.
For heavily compressed source you may see more distortion in one axis than the other when anamorphic source is compressed.
Another reason to keep everything square is to support very low complexity devices that may not need scaling, although scaling is built into just about everything these days.
The real question to ask is in a world where virtually all information is created assuming square pixels - i.e. computer and web applications - why would you NOT want to do the same with still images and image streams (i.e. video) that become part of more complex digital content? 

Regards
Craig


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