[opendtv] Re: Sparkle
- From: Craig Birkmaier <brewmastercraig@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 27 Nov 2016 09:59:55 -0500
On Nov 26, 2016, at 3:12 PM, Manfredi, Albert E
<albert.e.manfredi@xxxxxxxxxx> wrote:
Obviously, but it's incidental technologically. You don't need smaller pixels
to achieve HDR or WCG, Craig. You can quite credibly also achieve HDR and WCG
on SD and HD sets, although I'm now fairly certain that this will *not*
happen.
It is difficult to say what will happen, given the huge amount of money
invested in LCD fabs. The biggest problem is that it is very difficult to
deliver the dynamic range needed for HDR with LCD displays. In particular,
providing true blacks and detail in dark areas of an image is very difficult
due to the need to control the backlighting. The approach that is being taken
is to significantly increase display brightness, and to control the backlight
levels in dark areas.
The net result is not good. LCD displays that claim to be HDR don't look much
better than SDR LCD panels.
Why might it never happen? Simple. Getting those 4k pixels on the screen is
NOT a big cost issue! This is obvious when you visit any TV retailer these
days. So, might as well start with 4K, and build up from there. This is where
the industry seems to be heading. The new normal is 4K.
You are only considering one aspect of the problem: the display. There is
significant cost in creating and delivering 4K content, and it is not even
necessary to get most of the benefits afforded by a 4K display with HDR and
WCG. Once again, the important principle has a name: OVERSAMPLING.
If you cannot resolve all those pixels at normal TV viewing distances, what are
they good for?
The answer is contrast and detail - the same reason we are moving to higher
pixel densities for computer displays that typically address each pixel without
dumbing down (filtering) for motion. Another way to say this is that the
resolution of TV content is reduced by about half due to filtering.
An oversampling display takes advantage of the extra pixels to create new
correlated samples from lower resolution source. This works very well if the
source is accurate, not so good when the source is full of noise and
compression artifacts.
Ron just informed us about what can happen when compression is abused, as
appears to be the case with Comcast. So the correct way to think about
delivered TV resolution in a 4K world, is how to deliver a very high quality
stream to the display for upsampling. This is likely to be no more than 2K for
maximum quality, and significantly lower for constrained communications
channels.
Do we use the available emission bits to deliver the maximum number of
over-compressed samples (4K) or use those bits to deliver higher quality
samples (2K)?
Or do we drop to 720P or 360P when the emission channel is constrained?
Obviously the answer is: LESS is MORE.
Most of what we watch on mobile devices is 360P, maybe 480P. But this stuff
looks good on the high pixel density displays used today on all computing
devices, thanks to local upsampling.
The goal of digital video compression should be to deliver accurate samples,
not to squeeze so hard that the detail is replaced with correlated noise that
will look bad on EVERY display.
Remember, digital compression is a noisy low pass filter.
Bottom line, we don't need to deliver 4K video streams to 4K displays.
What is more important is improving the quality of TV imagess to
delivered to all of the HDTV sets in people's homes.
Sorry, Craig, but no way will you get HDR and WCG on existing TV sets. You
might get small improvements at best, from higher quality source material.
Similar to sending HD images to SD sets.
Obviously these legacy sets cannot render the HDR details - the color gamut
issue is less clear, as many existing displays may support a wider color gamut.
But you can improve TV for everyone by creating HDR/WCG 4K masters, then
encoding at appropriate resolutions for emission. Even the SD and HD streams
will benefit from the higher quality masters, with more detail mapped into the
8 bit samples. And compression efficiency improves after down sampling as we
are eliminating entropy.
If the 10 bit HDR metadata is also available, it will provide an incentive for
people to upgrade their TVs.
This site explains that 4K will be available in regular sets, which offer
smaller pixels only, and premium sets, where the premium will offer HDR and
WCG.
http://www.digitaltrends.com/home-theater/4k-ultra-hd-buying-guide/
This sounds credible to me.
Of course it's credible. This is what the current debate about HDR and WCG
standards is all about.
But it verifies what I've been saying: There is little if any benefit in buying
a 4K set without HDR/WCG, unless you are going to use it as a computer display.
Regards
Craig
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