[opendtv] Re: Popular screen aspect ratios

From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Date: Sat, 8 Jan 2011 14:47:07 -0500
Craig Birkmaier wrote:
 
> No Bert, the decoder does not need to know ANYTHING about the
> display.
 
Apparently, it does. From Ron's examples, to the HDMI spec, to Cliff's 
real-world experience, to my own real world experience. In every case, the 
decoder needs to obtain the display aspect ratio info, or the display 
resolution in case of RGB, before it can output the image correctly. And then 
still, it can be fooled, in analog cases (since these don't provide a two-way 
interface), if you connect the display to an STB that was not configured 
correctly for that display. The evidence is there, Craig. I offered a potential 
solution for a limited two-way interface scheme for analog, based on the input 
impedance of the display interface, but evidently no such interface standards 
exist.
 
My conclusion is that VBI aspect ratio info is to help the display's own 
zoom/crop/what have you features, which are applied after the fact. It is not 
intended as an independent instruction to any random display, and it seems to 
require first that the MPEG-2 decoder be configured correctly. And that's why 
its intentions can easily be fooled, as Cliff clearly demonstrated. And, as all 
my 16:9 digital TVs have also demonstrated, when I misconfigured the STB.
 
In order to support the sort of "no standards necessary" utopia you and the FCC 
thought you had, you would need to transmit all of the MPEG-2 metadata to the 
display, over the baseband interface. Or at least, the same information 
contained therein. Which is not what is being done. In short, correct operation 
of the display's own image accommodation tools DEPENDS ON receiving the correct 
signal from the MPEG-2 decoder, for that particular display.
 
And even worse, the only two ratios accommodated in the STB-to-display 
interface standards seem to be 4:3 and 16:9 image frame rendering, including in 
the case of HDMI. RGB does provide many more options of display aspect ratio, 
but it depends on installing the correct configuration for your dislay, 
provided by the display manufacturer via CD ROM.
 
> The ability of the computer - connected to the display - to decode any
> random raster of video is completely unrelated to this standard. Once
> the computer is properly connected to the display it can do anything to
> fill that screen the way it wants to.
 
Yes, but this has never been an issue. It's obvious that once the display and 
STB have been correctly interfaced, the source can do anything it wants. Heck, 
even in the 1950s, a TV transmission could incorporate tiles of any aspect 
ratio on 4:3 TV screens, or letterboxing or pillarboxing, to create an infinite 
variety of image aspect ratios on those 4:3 screens. Big whoop. I never 
understood why you put so much importance in that. This has nothing to do with 
the argument that a reasonable set of display aspect ratio settings are needed 
for TV-type STBs (which typically do not support CD ROM inputs for specific TV 
monitors), especially back in the 1990s.
 
Bert
                                           
 
----------------------------------------------------------------------
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.
Follow-Ups:
- [opendtv] Re: Popular screen aspect ratios
  - From: Craig Birkmaier
[opendtv] Re: Popular screen aspect ratios

Other related posts:
