[opendtv] Re: Popular screen aspect ratios

  • From: Albert Manfredi <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Sat, 15 Jan 2011 17:13:35 -0500

Craig Birkmaier wrote:
 
>> When you set the STB to 4:3 or to 16:9, you are giving it either
>> of two very specific display attributes.
>
> Correct!
>
> If you set the STB to 4:3 it assumes it is delivering the decoded
> source to a legacy 4:3 display and that any aspect ratio accommodation
> will be performed by the STB.
>
> If you set the STB to 16:9 it assumes that you are connecting the box
> to a DTV display.
 
You seem to be laboring under the misconception that "16:9" means "anything at 
all," but it's simply false. Funny how I could communicate with Jeroen in one 
quick exchange, to figure out how his 21:9 display works, and weeks later, 
you're still confused.
 
> The computer industry, which has a far greater variety of displays
> to serve, chose to develop a solution based on the metadata that
> accompanies ANY source ... the metadata is used to automate the
> accommodation of the source to the display.
>
> THAT IS:
>
> 1. It knows the resolution and aspect ratio of the display;
 
Wrong! The CPU must be TOLD about the display resolution and aspect ratio. 
That's the part you continue to be befuddled by. I thought we had made an 
enormous breakthrough when you FINALLY, during the holidays, admitted that the 
CPU and the display negotiate this info over the DVI or HDMI interface. Well, 
without those digital interfaces, you manually select the setting in the 
"display" section of the configuration settings. If you have a display with 
non-square pixels, at least if you use the RGB interface, you can still make it 
work right.
 
The res setting is important in computers also because that is what determines 
how much text and graphics can be crammed into the display. But THE CPU HAS TO 
BE TOLD. It doesn't just "know," as you said above. This info DOES NOT arrive 
from the MPEG-2 metdata, Craig. You're looking at the wrong side of the decoder!
 
> Yes, as I said above, the CE and TV industries chose the path of limited
> options.
 
They didn't want to have to depend on more elaborate STBs that can accommodate 
any and all display shapes. You don't ever have to run a CD ROM to set up your 
cable box, right? Nor are you dependent on a digital interface. Nor does HDMI 
support ratios for displays other than 4:3 or 16:9 anyway, it looks like.
 
> The fact is that is is trivially easy to create 2.7:1 source at ANY
> resolution, encode it using h.264, and expect a computer to display
> it properly,
 
ONLY if the decoder knows that the image is going to a 2.7:1 display. If the 
decoder thinks the image is going to a 16:9 display, the 2.7:1 will distort. If 
the 2.7:1 display is smart enough to say, "I know that the decoder thinks I'm a 
16:9 display," ONLY THEN can the 2.7:1 display post process that image 
correctly. And give up some resolution in the process (zooming in, as Jeroen 
described).
 
> You may even be able to do this on your computer that is connected
> to your new LG display, at least for a single frame (otherwise known
> as a still image or photo).
 
What you described works just fine, clearly, until I disconnect the LG and 
connect a different shape of display (without informing the computer).
 
> The ATSC standard REQUIRES what you are objecting to. In order
> to watch the SD formats they must be scaled to fill your HDTV
> screen.
 
You mean, you've never seen SD or HD images that don't fill the entire screen? 
I have, many times. I will agree that images sent to the upsteam side of ATSC 
decoders are more limited than MPEG-2 requires, but the 16:9 aspect ratio 
standard is needed for the downstream side of the decoder ANYWAY.
 
> You are making a mountain out of a mole hill.
 
No, I am demonstrating why 16:9 does not simply mean "anything other than 4:3." 
The simple fact, that you cannot deny, is that anamorphic stretching in DTVs is 
limited to only a ratio 1.77/1.33. It's absolutely not wide open, as your "no 
standards necessary" position would require.
 
I'm fully aware of how this could be made to work differently, Craig. And I can 
also appreciate why ATSC, and DVB by the way, chose to do things this way.
 
Bert
                                           
 
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