Panasonic proposed
Studio system
SDR / HDR Hybrid
Operation Ver. 1.3c

August, 20171

Overview
Improving image quality and impact is an underlying goal of all video
production teams and equipment manufacturers. Over time we atPanasonic have taken approaches such as increasing resolution andadvancing compression technology.
In recent years, the advancement of image display technology, hasenabled presentation of images exceeding the capability of standard
television including expansion of both expressible dynamic range andcolor gamut.
Changing the published standards for terrestrial broadcasting as
public infrastructure is more than simply a technical issue, but forcable, satellite and over the top (OTT) internet video delivery, a UHD/ HDR / BT.2020 based standard is planned, with the goal of
expanding resolution, dynamic range, and color gamut.
For live broadcast images utilizing these new standards (UHD,
HDR, BT.2020 color gamut) distribution must include a simultaneous“normal” HDTV signal for the current broadcasting pipe, and do so
without a significant cost increase.
In this paper, we will explain technological developments for image
production equipment so far as Panasonic seeks to realize an UHDTV
future.

Live broadcast on HDR
The process for creating HDR video, for pre-recorded and postproduced content is very different from that of a live broadcasted
event.
In the first case, post produced HDR image finishing (grading), utilizes
specific tools, and an elaborate process to painstakingly fine tune theimage on the evaluation monitor(s) and deliver the final results to theviewer so there are few chance of failures (i.e., poorly represented
images).
In the case of live broadcast, the video quality is determined in thecamera, with minimal downstream correction added by the switcher.
Since the video quality is confirmed in near real time and it is shown
to the viewer as it is; the camera must have a means of determining
the video quality and avoiding a failure .
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As mentioned above, with live broadcasting, we will produce newimages in new standards (UHD, HDR, BT 2020 color gamut) for new
video distribution systems, and simultaneously deliver existing video
standards (HD, SDR, BT.709 color gamut) therefore the camera
system must create images in both standards without difficulty.
NB:
In this paper we will describe UHD, HDR, BT.2020 color
gamut in the aggregate as a new standard image, but we
can handle resolution, dynamic range and color gamut
separately as it seems that the HDR image in HD
resolution with or without BT.2020 color gamut is viable fordelivery in many applications.

HDR in live broadcast BT. 2084 or HLG?
The primary display characteristics under consideration for HDR are
BT.2084 (PQ) standard based on the requirements of the reference
display system, and HLG (Hybrid Log Gamma) focused on therequirements of the live production system - cameras, switching etc.
HLG follows the example of the current BT.709 gamma in that it is arelative system that expresses black near zero and peak luminanceat 100% of the signal. BT.2084 specifies the brightness on the screenof the display in absolute value, hence the name PQ which stands forperceptually quantized. PQ is an easy-to-understand system for thecinema or to show packaged media or streaming movies in the homeas intended by the producer. PQ is an appropriate standard whencreating images with grading and post-production where post viewing
conditions are well standardized.
In a UHD Blu-ray Disc package intended for HDR distribution(primarily of movies) HDR10 is standardized as a characteristic.
HDR10 is a subset of the full PQ curve, thus it appropriately matches
the directors intent.
On the other hand, for live broadcasting, considering simultaneous
output with the current standards (HD resolution, SDR, BT.709 color
gamut), and TVs with various luminance performance capabilities,
HLG material can to make use of the camera or display’s maximum
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dynamic range and only contrast levels will vary. In addition, the HLG
characteristic considers compatibility with the current HD SDR signal
to be simulcast.
The HLG signal characteristic is specified as part of the ITU-R
BT.2100. Standard alongside PQ.

Table - 1

Live camera output: HLG? or Log?
Even if HDR broadcasts are delivered under the HLG standard, there
are cases where the same content may later be converted by another
PQ based distribution path such as a Blu-ray package; the signal for
Blu-ray HDR will be encoded with the PQ-based standard HDR 10.
For this reason, it has been proposed that an interim Log
characteristic should be used in live production. Although this would
add additional conversion requirements at all viewing outputs theargument for this approach is that the log signal carries the full camera
dynamic range and can be converted equivalently to HLG for the live
output and to PQ for packaged media – e.g., HDR10 material
converted from a Log signal would be superior to HDR10 material
cross converted from HLG.
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Practical differences converting HLG to PQ vs Log to PQ:
We start with an assumption that live broadcast content should be
limited to a 1,000 nit display. Why such a limitation?
Currently, the luminance of the latest consumer TV set is set to 1000
nits as a certain upper limit, ITU etc., the industry assumes that thebrightness of the TV set to be 1000 nits at the time of conversion of
PQ and HLG so any dynamic range above 1000 nits will not be viewed
on consumer TV at this time. It has also been suggested that highbrightness is too dazzling for both the film producer and the viewer
and eyes simply get tired. So brightness levels beyond 1000 nits will
surely need to be carefully managed and even if viable for postproduced content may never come into use in live production.
If the content is limited to 1000 nits or less, there is no loss
between grading from HLG cross conversion and the ST.2084
content completed by grading from Log.

Figure – 1
Another possible source for fidelity loss is if the gradation resolution
from an HLG cross conversion is less than Log source when both are
only 10 bits. We don’t believe this will incur an observable loss
because the downstream signal exchange and distribution are
performed on the basis of 422 10 bits maximum, and any errors will
be beyond the limited gradation expression capability of the final
viewers display.
Furthermore, when the switcher system is configured on a Log basis,
it is necessary to convert any HLG signal feed sent from other facilities
5to Log, and convert back again to HLG, so the necessity of equipment
and conversion errors may grow.
While ongoing technological development may eliminate concerns in
the future, at the present time a live production system based on HLG
has the following advantages:(1) Camera output can be used for delivery or monitoring as it is,
so no need for conversion equipment from Log to HLG for QC
display or playback display in the case of a recorded image(2) Camera output can be sent directly to any HLG compatible
monitor(3) Commercially available TV without log conversion functions canbe used for video confirmation(4) There may be differences among Log capable displays due todifferences in the maximum brightness level but the entire
signal is guaranteed by the HLG monitor.
Potential for errors introduced by misconfigured conversion
equipment is eliminated by unifying a system to HLG.

Live Output HLG signal Adjustment
SDR studio cameras are equipped with various image manipulation
functions such as black gamma, knee adjustment, color matrix
adjustment, and so on to manage difficult scene content and provide
more tools to deliver a desired look.
In HDR shooting, the same image manipulation functions are
expected.
Our HDR compatible studio cameras have introduced black gamma,
knee adjustment, color matrix and similar image quality adjustment
functions popular in SDR to the HDR image, and therefore can create
an appropriate picture according to the scene content and thesensibilities of the producer. With these adjustment capabilities
confirmation of this picture quality is critical, so we think that it isimportant to output directly viewable HDR from the camera with HLG
so it can be viewed as it adjusted.

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Figure – 2

Figure – 3

Studio camera SDR / HDR Hybrid(Simultaneous output) operation
In the case of broadcasting and distribution of live events, terrestrial
broadcasting in HD-SDR, with premium distribution in HDR (HD or
UHD) performed simultaneously is expected to be the case early on.
For SDR / HDR simultaneous broadcasting, it is unrealistic (not tomention prohibitively costly) to install separate SDR and HDRcameras and signal processing systems so SDR and HDR signals
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from one camera output at the same time is a requirement.
Although there is only one iris adjustment for the camera, the operator(cameraman, or VE: video engineer) must adjusts the iris so that boththe SDR and HDR have a pleasing image (based on the experienceand judgment of the VE).The VE must confirm the images for both
HDR and SDR, such that the HDR high brightness characteristics
being touted for their viewer impact are appearing in frame (above
100% or the SDR range) while being able to express that image
properly in SDR with all content 100% or less. It is necessary toconfirm this has been achieved.
A camera capable of performing the SDR / HDR hybrid operationmust provide functionality capable of achieving the above describediris adjustment without hesitation by the operator. For this purpose,
it is necessary to develop functionality to define and manipulate therelationship between the HDR signal and the SDR signal output fromthe camera. Since the characteristic curves of SDR and HDR (HLG)
are strictly defined, one might assume that it is only necessary to
issue signals along the proscribed curves curve, but with a great dealof scene compositions if you do this the HDR compatible monitor willappear darker than the SDR compatible monitor. In addition,although the signal standard in SDR-TV assumes 100% maximum
brightness 100 nits, in practice modern current displays tend to be
adjusted to the full brightness capability, so the SDR monitor will beeven brighter than the HDR compatible monitor, causing a kind of
Inversion phenomenon. Hereinafter, to be described in detail using
Figure 4.

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Figure – 4
Figure 4 shows the standard gamma characteristics of SDR (BT.709)
in blue, and HDR (HLG / STD - B 67) in solid red.
Although 100% of SDR peak scene brightness is 50% of HDR-HLG,
it is necessary to be aware that this graph shows the camera side
conversion curve - optical electrical transfer function (OETF). The
relationship between the HLG signal and the final brightness ofbrightness of the monitor display is the electro-optical transfer
function (EOTF) and the combined relationship between the scene
light (the brightness of the subject to be shot) and the brightness
shown on the display is the optical-optical (OOTF) and this is shownin figure - 5 below.

9Figure - 5
When a white object is exposed with a level of 100% of the scene
light, a properly adjusted SDR-TV follows the standard whendisplaying this as 100 nits, and HDR-TV can also show an object
outside of the SDR TV range up to 1200% (12x) of the maximum
100% brightness as 1000 nits; but when exposing in this way theoriginal SDR 100% white object will only display as 50 nits (Figure –5)
Level of white object SDR-TV
Level of white object HDR - TV

100 nits on screen
50 nits on screen(half brightness of SDR - TV)

Thus at the normal brightness levels (presumably most of the content),
the SDR-TV will be brighter (blue line).
Furthermore, in the current consumer SDR-TV, since the highest
brightness of the screen tends to be set above 100nits, the SDR-TV
looks even brighter, which means that for many scenes HDR will10

simply not match.
In order to match the HDR and SDR images for content within the
SDR range, a gain difference can be applied to the HDR and SDR
signals such that they converge in the lower exposures. Once thisHDR/SDR difference or offset has been set to specific scene
conditions it then becomes possible to set iris levels for both HDR
and SDR by simply setting the iris to the proper SDR level relying on
years of experience, and best practices.
With this technique it is also possible to match the image of theconventional SDR image for darker areas while still using the highdynamic range of HDR effectively in the HLG image.
Although it is necessary to set the optimum value for the gain
difference between the HDR video and the SDR video by observation,
it is assumed that it will be a fixed value for a given condition.
A study of the mapping method of SDR signal to HDR signal for SDR/ HDR simultaneous output operation has revealed an effective offset
level corresponding to 100% SDR signal to 75% HLG signal(equivalent to 200 cd / m 2 at peak 1000 cd/m2 : Pink line) and anothermode (green line) corresponding to a 100% SDR signal
corresponding to a 63% HLG signal (corresponding to 100 cd/m2 at
a peak of 1,000 cd/m2) has been studied.

Difference between OOTF in HLG and
OOTF in SDR
In the video system, a real scene (linear signal) is converted into anelectric signal by a camera, and the electric signal is then converted
into light (linear signal) of a display by a monitor. The conversion on
the camera side is called the Opto-Electronic Transfer Function(OETF), and the conversion on the monitor side is called ElectroOptical Transfer Function (EOTF). Normally, the characteristic on thecamera side is an inverse-geometric or inverse logarithmic, in otherwords that the dark areas are lifted and the bright areas compressed;on the monitor side the characteristic is geometric or logarithmic
hence the reverse happens where highlight are lifted and dark areas
compressed.
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In the conventional SDR system (BT.709), the OETF on the camera
side is a power function and the (less than unity) coefficient (gamma
value) is typically around 0.45 (1 / 2.2), the EOTF on the monitor side
is a power function with a 2.4 coefficient. This mimics the physicalcharacteristic of the original cathode ray tube (CRT) displays, and it
is not strictly a reverse characteristic to the camera so a slight ~1.2
power law remains, this is called OOTF (Opto-Optical Transfer
Function) and is the characteristic of the whole system. Thus, OOTF
is a conversion function between real scene and display light, and is
not necessarily a linear relationship. The OOTF represents end to end
image conversion between a real scene and a monitor display, andincludes an adjustment that is an aesthetic choice of the producer.
Within the conventional SDR context, OOTF adjustment can beapplied individually to red green and blue signals as R, G, B gamma,
but in the HLG specifications in BT.2020, “gamma” is applied only toluminance. This is to avoid color distortion when applying a gamma
adjustment. The gamma values of the OOTF are also changed
according to the peak luminance of the display. This is to reproduce
the same perceptual appearance regardless of the specific display’s
peak luminance.
The differences in OOTF between HLG and SDR, include managing
the increased dynamic range of HLG as has been discussed but also
some small appearance differences (HLG appears to be thinner incolor etc.) Managing the contrast differences has been addressed
above but as color saturation and other differences have been
introduced considering the design of the consumer TV set withreceiving an HLG signal, we believe that it is preferable to stay withincompliance with these regulations without attempting corrections.

Specific Control of gain (offset) and Knee toestablish SDR / HDR image adjustment
In this paper we have explained the advisability of providing a gain
difference or offset between HDR & SDR according to the scene for12the simulcast of SDR and HDR.
For a case where the screen is bright and there are many highluminance areas/objects (bright objects with a wide dynamic range),
adjusting the gain difference by about -10 dB between SDR andHDR thereby setting the 75% point of HDR to the 100% level in
SDR , matching SDR and HDR images become manageable.
With a narrow dynamic range image, setting a reduced gain difference
offset becomes appropriate.
Thus setting the proper gain difference between SDR and HDR
according to the scene brings out both characteristics and it becomesa practical solution to make HDR video by setting proper SDR video
exposure.
It is not however recommended to dynamically change this offset gain
during shooting. It is sensible to follow set the offset according to thelarger contrast conditions which will likely not change for a given
camera position. A consensus is building among HDR production
teams accumulating experience of simultaneous shooting of HDR &SDR.

Figure - 6

HDR Knee control
In SDR image capture it has been possible to compress more
dynamic range into the legal SDR signal contrast by utilizing the knee
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circuit. The knee takes much of the out-of-range bright areas thecamera imager captures and compresses them into the top ~80%100% of the SDR characteristic; engineers will adjust the knee point
and slope to control these highlight areas. When the offset between
HDR and SDR is reduced to match pictures there is now someunused dynamic range in the highlights of the HLG image that can beutilized for an HDR knee adjustment.

Figure - 7

Color gamut conversion BT.2020 and BT.709
color gamut
The UHD (3840 x 2160) signal standardized by BT.2020 has adynamic range of HDR and also has recommended color gamut (alsocalled BT.2020 color gamut) that is wider than the conventional
BT.709.
In recent years, the expansion of the color gamut in display devices
such as TVset has progressed along with brightness and contrast,
and it seems that the future BT. 2020 color gamut will be used in a
wider range of products. Even in the studio system, with the14performance of the camera output, vision mixer and switcher, it is an
expectation that BT. 2020 color gamut will be covered. Therefore it isnecessary to be able to select the color gamut of BT.709 or BT.2020.
When the color gamut of the monitor is BT.2020, vivid colors
exceeding the conventional BT.709 color gamut can be correctlytransmitted and displayed. Care must be taken as accurate color
reproduction cannot be obtained unless the color gamut of thecamera matches the monitor or display.

VE operation During Simultaneous SDR /HDR Broadcasting - Summary
1. When assuming simultaneous operation of HDR and SDR, it isnecessary to consider image output and exposure level suitablefor both formats
2. To achieve matching exposure levels a predetermined gain
difference/offset can be pre-set between the HDR and SDR
signals (based on scene contrast levels) and then the video
engineer or shader can adjust the iris level based only on the
SDR video. In this way images are created that effectively
utilize the high dynamic range of HDR while attaining correct
SDR video as before and operation is transparent to the shaderutilizing existing qc monitors and wave form monitors
3. The gain difference between the HDR video and the SDR video
is realized in the downconverter section of the studio camera’s
CCU. In addition, conversion of characteristic curve, color
gamut and knee processing are also performed here.
4. The same offset value is set for the newly developed HDR-SDR“downconverter” installed at the switcher output as the offset
setting for the “downconverter” in the CCU. This makes it
possible to have the HD output from the camera match the mainline HD output from the final down converter, so accurate
adjustments can be made at the camera side..

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Figure 8

Switching in SDR / HDR Hybrid operation
So far, we have described SDR and HDR signals from studiocameras, and the necessary functions for the camera system to havesufficient manipulation of the images. Although using such methods
one may established each parallel SDR and HDR signal and even set
each to match the look of all other sources for the full set of HDR andof SDR sources, when considering simultaneous broadcasting, there
is a switcher to consider. The switcher not only switches the matchedvideo signals from the cameras but also performs video effects andgraphics insertion. Effects and graphics must also be rendered forboth the HDR and SDR product. Assuming cameras are matched
then, how should producers and directors perform hybrid operation of
SDR/HDR broadcasts including switching, graphics, and effects.
Here are two possible system configurations possible at this time:

Parallel operation of UHD-HDR and HD-SDR
Here a ganged switcher processes a UHD and HD signals completely
in parallel, including effects, graphics and transitions. With current
processing power it is conceivable to manage two signals (even when
one is UHD) with optimal signal processing. Although this16

configuration has advantages such as the sense of a schematicallyredundant system and the ability to construct a system with theshortest possible latency, such a dual signal system with either two
synchronized switching/processing platforms or massive bandwidthand processing power will certainly come with a high price tag, andthe hardware investment would not be returned on traditional
broadcast projects which might still represent a majority of rentals.

Core Operation in UHD-HDR
In this method, all processing is performed in the UHD-HDR BT.2020
space, and finally, since all HD, SDR BT.709 image data is a subset
UHD-HDR, conversion to HD-SDR is performed at the output. In thiscase, only one signal processing engine for the switcher is sufficient,but the parameters at the time of SDR conversion will need to matchthe original intent of the production team utilizing the SDR camera
outputs and SDR adjustments. From the viewpoint of quality image
creation, it ought to be sufficient to apply the knowledge of HDR/SDR
gain-offset setting (applied at the camera based on the contrast
conditions) and the SDR knee settings. These settings are notadjusted dynamically so incorporating them into the SDR conversion
can be managed. How closely the final SDR output image can bematched to the SDR QC image will be a addressed through ongoingexperience and tools still in development
In both the parallel HDR/SDR and HDR to SDR output conversion
methods, it will be necessary to prepare all the input images for HDR
as required for UHD-HDR processing. For example reuse of stock
content and images from the other video feeds/sources are most
likely to be SDR, as will some graphics packages, these will need tobe converted to HDR. The internal processing of an HDR switcher,will need all of its sources to be HDR in order to perform special
effects and other processing, then output the HDR main line signal. It
is practical for a switcher to operate in an all HDR mode to avoid an
undue processing load on a switcher that may be reset for SDR on its
next job. Thus there is a system requirement to convert SDR sources
to HDR and apply also apply SDR broadcast characteristic to the17Output. It will also be necessary in many cases to convert BT.709
color space inputs to BT.2020 and of course upscale some HD to UHD,
and do the reverse on the output. In order to simplify systemarchitecture, simplify system upgrades and enable more flexibility inswitcher choice we plan to provide a rack mount type signal
conversion device that provides various conversion functions for
multiple channels as a peripheral device to the switcher. Such a
device can communicate with cameras (to enable better matching ofcamera SDR and final broadcast SDR look) and as a separate device
will be ready for operational upgrades or to be excluded from thedesign in the event of a pure UHD system.

Conclusion
In this paper, we have discussed problems and solutions as theystand in the summer of 2017 to enable simultaneous distribution of
SDR and HDR. This simultaneous distribution is a global concern forbroadcasters and rights holders aiming for advanced operation, andresearch experimentation and discussions are ongoing. To realize asystem that achieves both a high performance and practical operation,
consideration will be made to further the discussed approach, but as
new data is collected develop a different approach from this paper
may be attempted as well.
As Panasonic, it is not our position to dictate best practices this earlyin the life of HDR. We would prefer to respond flexibly to building
better systems by repeated discussions with the users, and further
testing.

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