[opendtv] Re: Case for 720p60
- From: Kilroy Hughes <Kilroy.Hughes@xxxxxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 22 Apr 2010 16:09:21 +0000
I picked 3 screen heights as an extreme closeness for normal viewing, and near
the edge of visual acuity for detecting 1920 MTF. I'd guess the number of TV
viewers with big enough screens or small enough TV rooms to watch at 3 screen
heights or less is in the 5 - 10% range.
If I was closer, I probably would have noticed the difference between 1920 and
854 a little more.
I viewed at 1X on a 1920x1080P display. You might be seeing some effects from
your display rescaling.
Regarding the impact of bitrate starvation and subsampling; practical
application has shown that for a given low bitrate and a display size, best
visual quality can usually be achieved by subsampling more as the bitrates go
down.
Some codecs subsample automatically on a frame basis based on lowest error
comparison of different attempts in the encoder, and automatic upsampling in
the decoding process. Other codecs (like MPEG-2, AVC) have to do it outside
the loop, and upscale in the display process.
Internet streaming of "HD" ""quality"" video often involves 6 - 8 alternate
streams using different subsampling and bitrates, each sampled with optimum
sample density for the particular bitrate and content. Sometimes the
subsampling is dynamic, e.g. 1920 for the talking head, but 960x540 or whatever
when the camera pans or scene cuts ... to maintain VBR peaks under some limit
while keeping quality as consistent as possible. Playback also switches
between streams every few seconds depending on network throughput, and the
quality gradations usually go unnoticed.
1920 may go in, but what goes over the wire has a probability density graph
like the covalent bonds that hold your TV set together. The cable guys are
starting to take advantage of this on their two way networks. Maybe one-way
broadcasters will get creative to squeeze mobile services, file downloads, etc.
through their pipes.
Kilroy Hughes
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
Behalf Of Manfredi, Albert E
Sent: Thursday, April 22, 2010 8:24 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Case for 720p60
Tom Barry wrote:
> The first is a fairly detailed 1920x1080p image. See:
>
> <www.trbarry.com/spring_2008_1920x1080.jpg>
>
> The second image is the result of using Irfanview to scale this down
> to 856x480 and then scaling back up again to
> 1920x1080 to match what your 1080p TV might display.
>
> <www.trbarry.com/spring_2008_1920x1080_from_856x480.jpg>
>
> It of course has visibly less detail than the 1080p image.
>
> The third image is the result of scaling the first 1080p image all the
> way down to 704x480 and then scaling back up again to 1920x1080. See:
>
> <www.trbarry.com/spring_2008_1920x1080f_from_704x480.jpg>
> Anyway, apart from that, what does everyone think? Would you pay much
> extra for 856 vs 704 wide?
Nice! I'm toggling between among the three pictures, on a 1680 X 1050 display,
set to 1680 X 1050 in my display setup, and viewed up close. The three images
are exactly superimposed, using three tabs on IE8, so there's no shifting of
eyes between images. And I'm focusing on whatever it's called in the middle of
the central flower, with little tentacles and black dots on the tips.
Since my display is only 1680 X 1050, the goodness of the 1920 X 1080 image
will obviously be muted somewhat. I'd say subjectively, though, that the 1920 X
1080 image is still more of an improvement on the second image than is the
difference between the lesser two images.
But let's get back to reality here. The 704 X 480 SD stream, in a typical ATSC
multicast, would be bit starved, as most SD subchannels are. So you wouldn't
expect to see the ultimate quality anyway. I'm still wondering whether 704 X
480 at 60p can be sent at the same low bitrates that are now being used for 480
at 60i. And you would need to use 60i or 60p for sports, anyway.
Sure would be nice if broadcasters started transmitting their SD multicasts as
16:9 anamorphic, though. I know that some of that material was shot widescreen,
certainly in the US and the ThisTV multicasts.
Bert
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