[opendtv] Re: Popular screen aspect ratios

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 14 Jan 2011 16:58:04 -0600

Craig Birkmaier wrote:

>> You are once again, now, presuming the 16:9 standard that you previously
>> claimed we didn't need.

> No Bert. This has NOTHING to do with aspect ratios. It has EVERYTHING to
> do with the requirement that a DTV support multiple formats and provide
> the means to accommodate different formats to the display.

When you set the STB to 4:3 or to 16:9, you are giving it either of two very 
specific display attributes. If you set the STB to the wrong display aspect 
ratio, which I have done and apparently you haven't, you WILL encounter cases 
of distorted images that *cannot* be undistorted. This is true whether you're 
trying to go to a 4:3 or a brand new 16:9 display, if you set the wrong 
configuration in the STB. I'll bet it's also true for the Philips 21:9 display. 
I'll bet the STB can only be set to 16:9 for it to work, not to 4:3 and not to 
anything else either (such as 2.21:1, if any STB even has that option).

> EVERYTHING needed to handle ANY format, as a PC does today,

Again, PCs can ONLY do this because their monitors come with a CD or DVD. That 
disc enters the required settings into the video card. It's not like I haven't 
dealt with this time and time again. You get a new display, it might be some 
odd shape (like 1.25:1 or 16:10 or other oddity), the existing video card 
entries **don't** support that display shape, and you see **distortion**. So 
the solution is, play the doggoned disc, then go back to the display settings, 
and like magic, there is/are the correct setting(s) suddenly in front of you. 
Now, you can either continue to see distorted images, or you can use one of the 
new settings available to you. That's how PCs do it, Craig. But TV STBs do NOT 
typically come with an optical disc reader or other such device.

> And it is NOT a safe assumption to say that "After-the-fact image
> accommodation assumes the distortion problem has been addressed already."

True, but only in the case of anamorphically compressed SD images. And that 
means, only to expand a 16:9 image which was squeezed into a 4:3 frame. No 
other anamorphic decompression (to create undistorted images) is supported.

The other post-processing accommodations are typically zoom options, but these 
do depend on the image having been undistorted initially, and then they zoom in 
by STANDARD amounts, to accommodate 16:9 images (that standard again). Also, 
various ugly partial stretching techniques, but EVEN THESE assume undistorted 
4:3 images coming in and going to a 16:9 display, so they can distort them in 
unnatural ways to fill a 16:9 screen. Always these two standards are involved 
(that you claimed we didn't need).

> My cable STB outputs a variety of formats via the analog component
> connectors; SD in both 4:3 and 16:9, 1280 x 720, and 1920 x 1080. The
> display processor in the TV deals with all of these, scaling SD up to
> 1280 x 720 and 1920 x 1080 HD down to 1280 x 720. Since the STB assumes
> that the analog component connections are going to a DTV, it does
> expand 16:9 SD to 854 x 480 ands present 4:3 (640 x 480) in pillarbox,
> in a 854 x 480 raster.

Craig, try connecting the cable box via component, composite, or Y/C, and set 
the display aspect ratio in the cable box setup to 4:3. Now tell me whether you 
can undistort the images. Also, this limited set of options is what your "we 
don't need standards anymore" ignored.

It is obvious that different displays will paint their screens using whatever 
technique they need. A DLP screen will have to do different things internally 
than a CRT. Ditto for a non-square pixel LCD or plasma, compared with square 
pixel displays. Ditto for my 1366 X 768 display. That's obvious, but the fact 
is, the STB does not need to support all of the native screen pixel counts or 
painting techniques out there. That's the WHOLE POINT.

Just one example. What if I wanted to create an image with 2.7:1 aspect ratio? 
Can I do that without standards? Heck no. Can I just blindly transmit that 
image, say over an analog interface, *even if* I assumed one of the standard 
options for number of horizontal lines? No. In order to make it work, I have to 
send that image either in a 4:3 or in a 16:9 container. And at best, I can 
squeeze it down horizontally by a factor of 1.77/1.33. That's it. I can't 
vaguely mention "MPEG-2 metadata" to the unwashed masses, and expect such a 
no-standards system to work.

Bert
 
 
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