Let me share my personal experience with HDR 4K OLED from LG I bought a few
days ago.
I have not tested it with HDR source, only with regular broadcast and streaming
content - yet I see two remarkable differences to any other TV monitor I ever
had before: of course OLED blacks are total and there is NO WHITE CLIPPING at
most of the useful contrast and brightness levels. This monitor easily competes
with bright daylight in the room. The absence of white clipping makes picture
remarkably three dimensional and real. Also totally white areas of artificial
images such as white OSD graphics produced by internal APP's are very bright
and a bit unusual. I assume the white clipping level was moved up because of
HDR.
Best Regards,
Mike Tsinberg
http://keydigital.com
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Manfredi, Albert E
Sent: Sunday, May 29, 2016 8:20 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] TV Technology: A New Day Dawning... HDR Delivery
Considering that HDR may just be more of a significant improvement than 4K,
this article is particularly interesting.
Being averse to enforced, brute force simulcasting, I think the
Technicolor/Philips "Prime Single" system sounds intriguing. The FM stereo
approach - compatible with the installed base, but carries the info needed for
the new displays. Seems like the right way to go, unless we believe that in the
future, essentially all displays will be HDR capable.
Bert
-----------------------------------------
http://www.tvtechnology.com/expertise/0003/a-new-day-dawning-hdr-delivery/278733
A New Day Dawning... HDR Delivery
A look at the proposed distribution methods for HDR May 27, 2016 By Jim
DeFilippis
LOS ANGELES-My last post introduced high dynamic range concepts and some
background to the technology. We discussed the concept of 'whiter whites' and
'darker shadows' with the ability of modern display technology that can not
only output more light but also increase the dynamic range of the displayed
image by reducing the minimum black level.
SMPTE standardized a HDR EOTF (electronic to optical transfer function) called
PQ (perceptual quantization) as ST-2084. The PQ transfer function has been
optimized to cover a wide range of light values (from .0001 to 10,000 cd/m2)
while minimizing the visual effect of 10-bit or 12-bit quantization
(contouring).
We touched on an alternate approach called hybrid log gamma (HLG) transfer
curve. HLG is not associated with a specific light value(s) but rather is a
relative light value based on an assumed dynamic range and peak white. HLG can
be used as an image capture curve as well as the final display transfer curve.
While HLG has no metadata associated with the HDR signal, one has to have an
agreed upon peak white reference value (typically 1000 cd/m2) for a display to
be able to process the HLG HDR signal and render the image appropriately for
the given display capabilities.
I promised to talk about the distribution of HDR video over a variety of
channels such as Blu-ray, OTT, OTA, satellite and cable in the this next
article. Each mode of distribution has it's own unique challenges and options
to delivery of video content.
A common element for the delivery of HDR is HEVC (high-efficiency video
coding). The latest video codec from MPEG not only has the ability to encode 4K
video but enables full 10-bit resolution to the consumer display. HEVC also
supports wide color gamut, defined in BT.2020. However, HEVC still relies on
the non-constant luminance equations (YCrCb) that are defined in BT.1886. HEVC
has the ability to signal HDR metadata in a variety of methods (SEI and VUI
metadata) to assist the HDR display to properly process the HDR imagery. While
MPEG-4 AVC does have a mode to support 10-bit encoding, it has not been
deployed in the consumer product space, thus limiting HDR consumer delivery to
8-bits.
I'll go over the different methods of distribution for HDR in the order that
they have been adopted and/or proposed:
BLU-RAY
The Blu0-ray spec was amended for 4K (UHDTV) including HDR and wide color (BT
2020). This spec, known as HDR10 is summarized as:
- HEVC Main level encoding
- 10-bit
- (PQ) EOTF (HDR)
- BT.2020 color space (wide color)
- 4:2:0 subsampling (YCrCb)
This format for 4K/HDR has also been adopted by some over-the-top (OTT)
delivery platforms including Netflix and Amazon. HDR10 is one of the simpler
methods of HDR distribution but does require static metadata (MaxFLL and
MaxCALL) to inform the display device of the average brightness as well as peak
brightness values. HDR 10 is not backward compatible for non-HDR displays,
although some Blu Ray players may provide conversion to SDR if the detected
display is not HDR compatible. For the OTT services, based on the type of
display, the appropriate format is streamed to the display.
LIVE LINEAR BROADCAST OF HDR
While HDR10 works for optical media and internet delivery of content, for
broadcast channels HDR10 has some drawbacks with respect to live broadcasting:
- Requires static HDR meta data
- Requires 'two layer' approach (simulcast of HDR and SDR).
A joint proposal from Samsung, Sharp and Qualcomm support use of HDR10 for ATSC
3.0. Here are the other proposals being considered by S34-1 of the ATSC 3.0
Technical Standards Group:
HYBRID LOG GAMMA (HLG), PROPOSED BY BBC AND NHK
As mentioned above, HLG uses a dual curve approach, gamma in the dark region
and a log function for the bright region. By optimizing the coefficients of the
HLG equation, the tone mapping for HDR and SDR can be accommodated without
metadata or additional processing.
However in practice it has been shown that the optimization leads to
limitations in terms of the overall dynamic range of the HLG HDR signal to
protect the SDR signal. In addition, while there is no defined meta data, there
needs to be an assumed reference peak white level so that the displayed image
tonal range can match the image as 'graded' by the video operator. Finally,
there is the challenge of color space conversion between BT.2020 and BT.709
(HDTV color gamut).
HLG is documented in ARIB standard B67 and will be included in an update to ITU
BT.1886.
DOLBY VISION
Dolby's proposal is based upon the use of the PQ EOTF curve and optionally a
new color space with a new set of color difference equations called ITP
(Intensity, Tritanope, Protanope). ITP, compared to the established YCrCb color
space, has three components, I (lightness, similar to Y'), CP(red-green
dimension, similar to C'r) and CT( yellow-blue dimension, similar to C'b). The
underlying color space is based on LMS, which is based on long-medium-short
cone color response of human vision. Dolby summarizes this format as ITP-PQ.
The key benefit of ITP is the property of isoluminance that minimizes the
chroma/luma cross-talk that can happen with the classic Y'Cr'Cb' non-constant
luminance approach as well as 'linearize' hue versus saturation.
In the encoding process, the ST 2084 PQ-based HDR video (along with static ST
2086 metadata) is converted to ITP-PQ space and subsampled to 4:2:0. Adaptive
reshaping is applied prior to the HEVC encoder to improve compression
efficiency. Specific Dolby metadata is combined with the converted HDR signal
and transmitted as part of the HEVC encoding (SEI messages).
On decoding, the signal is processed through tonal mapping and then converted
to full 4:4:4 color. This reconstructed 10-bit/4:4:4 HDR/BT.2020 signal is
converted from 10-bit to 12-bit and then reverse ITP matrix is applied to
output HDR RGB.
Additional metadata (ST 2094) can be created to provide tonal mapping of full
range HDR signals to displays with constrained HDR performance or to SDR
displays, either for professional or consumer conversions.
PRIME SINGLE, PROPOSED BY TECHNICOLOR/PHILIPS
Prime Single is a single layer approach that converts the HDR signal to a SDR
signal with dynamic metadata to provide both tone re-mapping as well as color
gamut correction. Prime Signal supports PQ, HLG, Log or SDR input video
signals. At the decoding side, Prime Signal takes the SDR as decoded and with
the tone mapping and CRI color correction metadata can provide HDR outputs
signals (PQ or HLG) as well as a native SDR (without any further processing or
meta data).
This approach provides a backward compatible SDR output, which is determined by
the pre-processing encoding process. The tone mapping and CRI metadata is used
to re-create the HDR signal from the SDR. The Prime Signal metadata is carried
within the HEVC data stream as SEI messages, with an ability to update on a
frame by frame basis.
ERICSSON PROPOSAL
Ericsson has proposed a pre-processing approach to a HDR10 HDR signal to
mitigate errors caused by 4:2:0 subsampling in the HEVC process. Basically the
pre-process calculates the error due to conversion of RGB to YCrCb,
quantization to 10-bit and downsample to 4:2:0 and then compensates the luma
samples to minimize errors on the decode/reconstruction end.
In addition there is an optimization of the HEVC QP Chroma offset values to
mitigate chroma errors.
No support for conversion to SDR or BT.709 color space.
QUALCOMM PROPOSAL
Pre-processing analysis of the input HDR signal (HDR 10) to create a set of
dynamic range adjustment parameters to minimize errors in the HEVC (4:2:0
YCrCb) encoding. These parameters are carried in private SEI messages inside of
the HEVC bit stream. Similar to Ericsson's proposal, no support for conversion
to SDR/BT.709 color space.
SUMMARY
While there are common features between the HDR proposals, there are different
approaches to fitting the full HDR signal into the limitations of HEVC as well
as providing a solution for multiple display and production formats. Key to
evaluating these proposals will be the head to head evaluation of each proposal
scheduled for this June at the ATSC 3.0 S34-1 committee meeting.
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