HDR in der Live-Produktion Von der Kamera bis zu einem HDR / SDR kompatiblen Workflow

Klaus Weber Principal Camera Solutions & Technology

Agenda

• UHD Options & Challenges

– More Pixel

– Better Pixel

– Better Colors

• HDR in Live Production

– HDR Standards

– HDR Workflows

• Summary

UHD Options & Challenges

• UHD = a large palette of options to choose from:

– More Pixels

• 4K resolution

• 8x more bandwidth than HD

– Better Pixels

• High Dynamic Range

• Larger contrast in a given signal range

– Better Colors

• Extended Color Gamut

• New (incompatible) mapping of colors

UHD Options & Challenges – More Pixels

• 4K resolution

– 8x more bandwidth than HD

• 4K requires much more resources than HD

– 4x 3G channels in routers, switchers, servers, etc.

• Sensitivity

– 4-times smaller UHD pixel collect 4-times less photons as HD pixels

• If same technology applied at least two f-stop lower sensitivity

1080i 1080p

2160p 3G

12G

1.5G

UHD Options & Challenges – 4K and lens diffraction

• Light rays passing through a small aperture will begin to diverge and

interfere with one another

– This becomes more significant as the size of the aperture decreases, but

occurs to some extent for any aperture or concentrated light source

• Why does it matter more in 4K acquisition?

– In 4K acquisition the resolution loss hurts two F-stops earlier than in HD!

Large Aperture

Small Aperture

UHD Options & Challenges – 4K and lens diffraction

F8.0 F4.0 F2.0

5µm pixel Native HD

2.5µm pixel Native 4K

Acceptable performance Optimal performance Optimal performance

Poor performance Acceptable performance Optimal performance

UHD Options & Challenges – 4K and lens diffraction

Focus aberration limit (HD) Focus aberration limit (4K)

Desired resolution Diffraction limit (HD)

Diffraction limit (4K)

Aperture in f-stops

Optical Resolution LP/mm

250

200

150

100

50

500

400

300

200

100

2 4 6 8 10 12 14 16

4K HD

HD

4K

‘sweet range,’

4K

‘sweet range,’

HD

Point of maximum lens resolution

UHD Benefits – More Pixels

• 4K resolution

– Future proof solution

– Support the trend towards

larger screen sizes

UHD Options & Challenges – Better Colors

• Extended Color Gamut

– New mapping of a larger color volume

• BT.709 HDTV standard does NOT support

capabilities of latest display technology

– Current standard is still based on CRT

displays

• With the new BT.2020 nearly all natural

colors can be reproduced

– With BT.709 only about 69% can be reproduced

• But BT.709 and BT.2020 are NOT compatible with each other

– Conversion between the different color volumes is a must, but not trivial

CIE 1931 = Visible colors

Pointer’s Gamut = Natural colors

BT.709 = HDTV standard gamut

DCI P3 = Cinema standard gamut

BT.2020 = UHD standard gamut

UHD Benefits – Better Colors

• Extended Color Gamut

– Support of the larger color

volume supported by the latest

television screens

• Higher saturated colors can

be reproduced without

clipping

• More natural color

reproduction possible

BT.709 versus BT.2020

HDR in Live Production

Why HDR - For Artistic Reasons

• High scene contrasts are often requested by the production

Why HDR - For Live

• High contrast scenes are most challenging in live broadcast applications

– Lighting conditions are

typically not under our

control

– Pictures must be perfect

at all times and can’t be

‘fixed in post’

Camera-to-Display Transfer Functions

• OETF => Opto-Electronic transfer function => Camera transfer function

• EOTF => Electro-optical transfer function => Display transfer function

• OOTF => Opto-Optical transfer function => Artistic or rendering intent

EOTF OETF

Distribution

OOTF

Camera-to-Display Transfer Functions - SDR

EOTF OETF

Distribution

OOTF

HDR Standards - Status

• Two HDR curves are standardized worldwide for:

– Production

– Distribution

– Presentation

• SMPTE 2084 / PQ

• Hybrid Log Gamma / HLG

To a SDR monitor the HLG signal look like a regular

signal where the knee point is set to a very low level

HDR Solutions – BBC/NHK Hybrid Log-Gamma

Source: BBC

The lower half of the

HLG signal is close to

a regular gamma curve

In the upper half the

signal is mapped in a

logarithmic curve

HDR Solutions – SMPTE 2084 (Dolby PQ)

• PQ use available bid depth following human eye sensitivity

– The Barten ramp describe the eye sensitivity seeing level differences

• Whatever the bid depth is PQ use it in the most optimum way

delivering the selected dynamic range

– Up to 10.000 nits

peak white are

supported

– 10 bit end-to-end

are required

as minimum

HDR Standards – Requirements / PQ & HLG

• HLG offer more headroom in the darker parts of the image

– But in some of the brighter parts it is even more on the “wrong side”

– Does offer less dynamic range than PQ means its less future proof

• Conversion from one curve into the other add the weak points

of both to each other

– Any HDR

workflow must

avoid any

unnecessary

conversion

Why a native OETF should be used

• How applying artistic controls in HDR

Why a native OETF should be used

Processing

RGB in 34 bit

17.179.869.184

Imaging

RGB linear in 14-16 bit

16.384-65.536

Transmission

YCrCb in 10 bit

1.024

Camera System

HDR Workflows – Parallel SDR & HDR workflow

• Native SDR and HDR signals delivered simultaneously by the camera

and processed independently from each other

– Highest flexibility

• Allow optimizing SDR & HDR images independent from each other

– Double workflow require

more resources and add

complexity to the

production

• Might not be acceptable

on longer term

HDR Workflows – Adopted film workflow

• What is a film workflow? “Capture and record everything what might be needed in post”

– In live the time between light reaching the imagers and the

signal gets “On Air” is typically less than 100 msec

– Live workflows currently

support 10 bit signal only

• Conversion from one 10 bit

signal into another 10 bit

signal reduces the

performance of the signal

HDR Workflows – HDR workflow with SDR conversion

• Native 10 bit HDR signals from camera through the production

– For uncompromised HDR image quality

– SDR images are derived by down-mapping the HDR contend

• Require a dependable high quality conversion which can be done with

dynamic or with static

down-mapping

• Both have their strength

and their limitations

– Providing an efficient and

future proof live workflow

HDR Workflows – HDR workflow with SDR conversion

• Type of down-mapping define how shading need to be done

What are the challenges producing HDR?

• In most cases

quite a large

number of up- and

down-mappers are

required

– Requirements

must be

carefully

calculated

upfront to avoid

any shortage

What are the challenges producing HDR?

• Lessons learned from test productions completed since 2014 *

– European Athletics Championships Zurich - August 2014

• First live HDR recordings in PQ/1080p

– Moto GP Final Valencia - November 2014

• First multi camera test in PQ/1080p

– Woman World Cup Soccer Vancouver - June 2015

• Comparing 4K SDR and 1080p in HDR

– Formula 1 several tests during 2016/2017

• 1080p, 4K, SDR, HDR, etc.

– LA Dodgers Baseball Los Angeles - August 2017

• Live production in HLG/1080p with dynamic down-mapping

– Cinderella Ballet at Sadler Wells London - December 2017

• 4K PQ/HLG under extremely challenging lighting conditions

– Red Bull Crashed Ice Saint Paul - January 2018

• Live production in HLG/1080p with SDR static down-mapping * Selected events only

Summary - Understanding HDR, WCG & Workflows

• UHD has a large palette of options to choose from

• HDR (including WCG) is a major topic and for good reasons

– Much improved viewer experience independent from the screen size

• Different HDR workflow are available and all their strength and weaknesses

– Full parallel HDR / SDR workflows

– HDR/SDR workflow using conversion

• Adopted Film Workflow

• Native HDR conversion to SDR