Leader Electronics Corporation Technical Information Series Vol. 02

HDR Measurement
01

What Is HDR?

02

What Is Gamma?

03

SDR System

04

HDR System

05

HDR Measurement

06

Glossary

The content of this document is as of December 2018.
The company and product names in this document are trademarks orregistered trademarks of their respective holders.

HDR Measurement

01 What Is HDR?
Overview of HDR

What Is HDR?
HDR, which stands for high dynamic range, is a technology that extends the dynamic range,
which is the range of brightness expressible by video. The wider the dynamic range, the wider
the range of expression from the darker parts to the lighter parts and the more it is possible tosuppress overblown highlights and crushed shadows.
For example, suppose we have a scene that has a mixture of bright and dark areas on one screen.

Figure | Scene example

When this scene, which appears to the human eye as shown above, is shot with the conventional
SDR (standard dynamic range) system, adjusting the exposure to the bright parts outside thewindows causes the dark parts to be underexposed, and conversely, adjusting the exposure to
the dark parts of the room causes the bright parts outside the windows to be overexposed. Dueto the narrow dynamic range, either the tones of the bright parts or those of the dark parts mustbe sacrificed.

Figure | Crushed shadows

Figure | Overblown highlights

Shot this scene with HDR technology makes it possible to achieve a more realistic rendition freeof overexposure and underexposure because of the wider dynamic range.

01

HDR Measurement

Luminance
The quality of video is considered to be determined by five factors, namely resolution, bit depth,
frame rate, color gamut, and luminance. In 1990, the standard for full HD, which is the current
format, was codified by ITU-R Recommendation BT.709. Later, in 2012, the standards for 4K and
8K were codified by ITU-R Recommendation BT.2020. As a result, of the five factors determining
video quality, four, namely resolution, bit depth, frame rate, and color gamut evolved, but thefactor of luminance remained unchanged from conventional SDR. Then, in 2016, the standard
for HDR was codified by ITU-R Recommendation BT.2100. Luminance evolved from SDR to HDR.
Luminance, which has to do with the above-mentioned dynamic range, refers to the range ofbrightness that can be expressed by video. To what extent is the range of expressible brightness
increased by switching from the SDR system to the HDR system?
First, an explanation of the unit of brightness, cd/m2 (candela per square meter), is in order. The
term candela comes from the Latin word for candle. 1 cd/m2 is approximately equivalent to thelight intensity produced by one candle to light an area of 1 m2. Although the unit of brightness issometimes called the "nit", which is synonymous with "cd/m2", in this document, "cd/m2", whichis the term used by the International System of Units, is used.
The natural world under sunlight is said to have brightness ranging from 10-6 to 109 cd/m2. The
human eye is said to be able to recognize brightness on the order of 1014, which is close to thebrightness level found in the natural world, but this is the range that is visible by opening andclosing the pupil, and the range that can be seen at once is around 105.
In the conventional SDR system, the maximum value is 100 cd/m2 and the dynamic range is on
the order of 103. As such, this system can be said to express only a narrow range compared withthe humanly visible range.

Figure | SDR System

02

HDR Measurement

On the other hand, with the HDR system, the maximum value is 10,000 cd/m2 and the dynamic
range is extended to 105, which allows for more realistic expression. However, the maximum
luminance of the HDR displays currently being sold is about 1,000 cd/m2, and displays that can
produce luminance of 10,000 cd/m2 are not commercially available.

Figure | HDR System

03

HDR Measurement

02 What Is Gamma?
Camera gamma and display gamma

Basics of Gamma
Gamma refers to the power function “y=xn”, which can be defined as follows in terms of input
and output:
Output = Input Gamma

Let's check the characteristics of this function by varying the gamma value between 0.5, 1, and 2
and looking at what this looks like on a graph. Here, let's assume that the input and output arenormalized in the range of 0 to 1.
In this figure, we can see that even for different gamma values, if the input value is 0 or 1, theoutput value is also 0 or 1, respectively; if the gamma value is smaller than 1, the input value islarger, and if the gamma value is larger than 1, the input value is smaller.

Figure | Gamma curve04

HDR Measurement

From Shooting to Display
In this section, we will consider a case of a scene shot by a camera and shown on a display, fromthe viewpoints of the display, the camera, and the viewers.

Figure | From shooting to display

DisplayIn the past, CRT monitors (CRTs) were used as displays. CRT monitors have the physical gamma
characteristic (Gamma = 2.2) of their electron gun, which tends to display things darker
compared with the input signal.
Note that on the display side, the characteristic when converting an electric signal to brightness
is called display gamma, and its transfer function is called the electro-optical transfer function(EOTF).

CameraOn the display side, things are displayed darker, which can be offset by creating bright data on
the camera side. Since the gamma value of a CRT monitor is 2.2, the camera side uses the gamma
value with the opposite characteristics (gamma = 1/2.2 = 0.45).
On the camera side, the characteristic when converting an electric signal to brightness is called
camera gamma, and its transfer function is called the opto-electronic transfer function (OETF).

Viewers
By combining camera characteristics and display characteristics, one can watch with the correct
brightness. For example, if the brightness of the scene is 0.5, an electrical signal of 0.50.45 = 0.73 is
input to the display via the camera. That electrical signal of 0.73 on the display side is converted
to 0.732.2 = 0.5, so that the viewers see an image with 0.5 times the original brightness.
Note that the characteristic when considering camera gamma and display gamma in total iscalled system gamma, and its transfer function is called opto-optical transfer function (OOTF).

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HDR Measurement

Effective Brightness Recording
There is another reason for gamma correction on the camera side besides canceling out the
gamma characteristic of the CRT monitor. That is to record the brightness effectively.
Human vision is sensitive in dark places and insensitive in bright places. For example, if there are
100 lights in a room, one can recognize the difference in brightness between 0 lights and 1 light,
and the difference in brightness between 1 light and 2 lights, but the difference in brightness
between 99 lights and 100 lights is difficult to recognize.
Based on this characteristic, the brightness of a scene can be efficiently converted to an electric
signal by allocating a larger amount of data (higher resolution) for darker light and a smaller
amount of data (lower resolution) for brighter light.

Figure | Effective brightness recording

LCD monitors have different input and output characteristics than CRT monitors, and since
gamma correction on the camera side is performed in the same way as when a CRT monitor isused, the input and output characteristics of the LCD monitor are created by simulating the
gamma curve of CRT monitors.

06

HDR Measurement

03 SDR System
Gamma curve of the conventional SDR system

Camera Gamma (OETF)
The camera gamma for SDR is defined as follows in ITU-R Recommendation BT.709.
V = 1.099 L0.45 - 0.099

1 ≧ L ≧ 0.018

V = 4.500 L

0.018 ＞ L ≧ 0

L: Scene brightness (0 to 1)
V: Electrical signal (0 to 1)(excerpted from ITU-R Recommendation BT.709-6)

Putting this in graph form, one can see that the gamma curve approximates that of the gamma
value of 0.5.

Figure | Camera gamma (OETF) for SDR

07

HDR Measurement

Display Gamma (EOTF)
The camera gamma for SDR is defined as follows in ITU-R Recommendation BT.1886.
The following graph shows the electric signal and display brightness normalized in the range of
0 to 1.

Figure | Display gamma (EOTF) for SDR

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HDR Measurement

System Gamma (OOTF)
The system gamma for SDR when the camera gamma is 0.5 and the display gamma is 2.4 is 1.2.
Display brightness= (electrical signal)2.4= {(brightness of scene)0.5}2.4= (brightness of scene)1.2

The following graph shows the scene brightness and display brightness normalized in the rangeof 0 to 1, combined with the gamma curve for the gamma value of 1.

Figure | System gamma (OOTF) for SDR

Is it okay for system gamma to be a value other than 1?
As many people perceive a system gamma value between 1.1 to 1.2 as natural, the system
gamma value does not necessarily have to be 1. Further, the appropriate gamma value varies
according to the surrounding environment. A value of 1.1 is considered appropriate for a brightoffice, a value of 1.2 suitable for a dimly lit living room, and a value of 1.5 fitting for a dark movie
theater.

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HDR Measurement

04 HDR System
Gamma curve of the HDR system

Standards
There are two systems for HDR, namely HLG and PQ, both of which are codified as standards.
The HLG system being compatible with conventional displays, it is suitable for broadcasting, and
the PQ system is considered suitable for movies, a field where the emphasis is on reproducibility.
HLG (Hybrid Log Gamma)

PQ (Perceptual Quantization)

Like SDR, luminance is expressed as a

Luminance is expressed as an absolute

relative value (%).

value (cd/m2).

Use a gamma curves compatible with

Uses a gamma curve that is based on

SDR.

human visual characteristics.

Proposed by:NHK, BBC

Dolby

Standards

ITU-R BT.2100, ARIB STD-B67

ITU-R BT.2100, SMPTE ST 2084

Peak luminance

Varies depending on the display

10,000 cd/m2

Transfer function

OETF

EOTF

Compatible with SDR

Yes

No

Features10

HDR Measurement

HLG System
Overview
If the range of brightness that can be recorded by SDR is considered to be in the range of 0 to 1,
the brightness that can be recorded with the HLG (Hybrid Log Gamma) system is in the range of
0 to 12.
The combination of transfer functions of HLG is defined as follows in ITU-R Recommendation
BT.2100. Display gamma EOTF uses the combination of the inverse function OETF-1 of camera
gamma and system gamma OOTF.

Figure | HLG system overview

11

HDR Measurement

Camera Gamma (OETF)
The camera gamma for HLG is defined as follows in ITU-R Recommendation BT.2100.
Per its name of “Hybrid Log Gamma", this is a hybrid (combination) of the gamma curve (SDRpart) and log curve (HDR part).
E' = √3E

E' = a･ln(12E - b) + c

0 ≦ E ≦ 1/12

(SDR part)

1/12 ＜ E ≦ 1(HDR part)a = 0.17883277
b = 1 - 4a = 0.28466892
c = 0.5 - a･ln(4a) = 0.55991073
E: Scene brightness (0 to 1)
E': Electrical signal (0 to 1)(excerpted from ITU-R Recommendation BT.2100-1)

Figure | HLG camera gamma (OETF)

12

HDR Measurement

In the following, we compare HLG camera gamma with SDR camera gamma.
Since the SDR curve approximates the gamma 0.5 curve, it can be expressed as
E' = (12E)0.5 = √12E = 2×√3E

On the other hand, the HLG curve being
E' = √3E

doubling the HLG curve results in a curve that almost matches the SDR curve. The HLG system iscompatible with the conventional SDR system.
Moreover, compared with SDR, HLG’s electrical signal level has twice the dynamic range,
allowing recording of brightness 12 times greater.

Figure | HLG and HDR camera gamma (OETF)

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HDR Measurement

Display gamma (EOTF)
Display gamma of HLG uses the combination of the inverse function OETF-1 of camera gamma
and system gamma OOTF.
First, the inverse function of camera gamma is defined as follows in ITU-R Recommendation
BT.2100.
E = E'2/3

0 ≦ E' ≦ 1/2

E = {exp((E' - c)/a) + b}/12

1/2 ＜ E' ≦ 1

a = 0.17883277
b = 1 - 4a = 0.28466892
c = 0.5 - a･ln(4a) = 0.55991073
E: Display brightness (0 to 1)
E: Electrical signal (0 to 1)(excerpted from ITU-R Recommendation BT.2100-1)

Figure | HLG OETF-1

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HDR Measurement

Next, system gamma varies depending on the peak brightness of the display, and it is defined asfollows in ITU-R Recommendation BT.2100.
γ = 1.2 + 0.42Log10(LW/1000)
γ: Gamma value
LW: Peak luminance of display (cd/m2)(excerpted from ITU-R Recommendation BT.2100-1)

Based on the fact that peak luminance of the display is
γ = 1.2 in the case of 1,000 cd/m2
γ = 0.98 in the case of 300 cd/m2
γ = 1.62 in the case of 10,000 cd/m2
the larger the peak luminance value, the larger the gamma value.
Here, the vertical axis represents display brightness [cd/m2], peak brightness of the display is
1,000 cd/m2 and 300 cd/m2, and the EOTF obtained by combining the inverse function ofcamera gamma and system gamma is plotted.

Figure | Display gamma of HLG (EOTF = OETF-1 + OOTF)

The HLG system is said to be a relative value display system, which means that the gamma curvechanges according to the peak luminance of the display. Therefore, even if one watches HDR
video on a conventional SDR TV, the video can be displayed with some compatibility.

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HDR Measurement

PQ system
Overview
If the maximum brightness that can be recorded with SDR is 100 cd/m2, the maximum brightnessthat can be recorded in the PQ (Perceptual Quantization) system is 100 times greater, meaning
up to 10,000 cd/m2.
The combination of transfer functions of PQ is defined as follows in ITU-R Recommendation
BT.2100. Camera gamma OETF uses a combination of system gamma OOTF and inverse function
EOTF-1 of display gamma.

Figure | PQ system overview

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HDR Measurement

Camera gamma (OETF)
Camera gamma of PQ uses a combination of system gamma OOTF and inverse function EOTF-1 ofdisplay gamma.
First, system gamma is defined as gamma value 1.2 in ITU-R Recommendation BT.2100.
(OOTF[E] = G1886[G709[E]], G1886 = 2.4, G709 ≒ 0.5)
Next, the inverse function of display gamma is defined as follows in ITU-R Recommendation
BT.2100.

c1+c2Ym1

E' = �

m2

�
1+c3Ym1

Y = FD / 10000

m1 = 2610/16384 = 0.1593017578125
m2 = 2523/4096 × 128 = 78.84375
c1 = 3424/4096 = 0.8359375 = c3 - c2 + 1
c2 = 2413/4096 × 32 = 18.8515625
c3 = 2392/4096 × 32 = 18.6875
E: Electrical signal (0 to 1)
Y: Scene brightness (0 to 1)
FD: Scene brightness (cd/m2)(excerpted from ITU-R Recommendation BT.2100-1)

Figure | EOTF-1 of PQ

17

HDR Measurement

Display Gamma (EOTF)
The display gamma for PQ is defined as follows in ITU-R Recommendation BT.2100.
FD = 10000Y

Y= �

1max��E′ m2 −c1�,0�
1c2−c3E′ m2

�

1
m1

m1 = 2610/16384 = 0.1593017578125
m2 = 2523/4096 × 128 = 78.84375
c1 = 3424/4096 = 0.8359375 = c3 - c2 + 1
c2 = 2413/4096 × 32 = 18.8515625
c3 = 2392/4096 × 32 = 18.6875
FD: Display brightness (cd/m2)
Y: Display brightness (0 to 1)
E: Electrical signal (0 to 1)(excerpted from ITU-R Recommendation BT.2100-1)

18

HDR Measurement

The PQ system is said to be an absolute value display system, which means that the gamma curveis constant and is not affected by the peak luminance of the display. For example, if the peakbrightness of the display is 1,000 cd/m2, the part exceeding 1,000 cd/m2 will be overexposed.

19

HDR Measurement

05 HDR Measurement
HDR measurement using a Leader waveform monitor

Here, as an example, the procedure for measuring the HDR signal using Leader's LV5600
waveform monitor is explained.
Measurement of HDR signals requires the LV5600-SER23 waveform monitor.

Preparations
HLG System
To measure HLG system signals, set the HDR Mode on the HDR tab to "HLG".
SYS ➡ F1 (SIGNAL IN OUT) ➡

Figure | HDR tab

Also make the following additional settings.
Item

Description

Ref.Level

On the WFM display and PIC CINEZONE display, select the reference level.
On the WFM display, a dash-dot line is displayed as the reference level.
On the PIC CINEZONE display, this is the boundary line between SDR display and HDR
display.
[50% (default value) / 75%]

VARIABLE

When set to ON, the reference level can be varied with Ref.Level as the initial value.
[OFF (default value) / ON]

System Gamma

When set to ON, the peak luminance of the display is 1,000 cd/m2, and system
gamma 1.2 is applied. Regardless of HLG Scale selection, the scale is displayed from 0
to 1,000 cd/m2.
[OFF (default value) / ON]

Range

Narrow: Set the range as 64 to 940 (10 bits) or 256 to 3760 (12 bits).
Full: Set the range as 0 to 1023 (10 bits) or 0 to 4095 (12 bits).
[Narrow (default value) / Full]

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HDR Measurement

Item

Description

HLG Scale

When System Gamma is OFF, the scale is displayed from 0 to 1200% or 0 to 100%.
(When System Gamma is ON, the scale is displayed from 0 to 1,000 cd/m2 regardlessof the value here.)[1200% (default value) / 100%]

PQ System
To measure PQ system signals, set the HDR Mode on the HDR tab to "PQ".
SYS ➡ F1 (SIGNAL IN OUT) ➡

Figure | HDR tab

Also make the following additional settings.
Item

Description

Ref.Level

On the WFM display and PIC CINEZONE display, select the reference level.
On the WFM display, a dash-dot line is displayed as the reference level.
On the PIC cine zone display, this is the boundary line between SDR display and HDR
display.
[51% (default value) / 58%]

VARIABLE

When set to ON, the reference level can be varied with Ref.Level as the initial value.
[OFF (default value) / ON]

Range

Narrow: Set the range as 64 to 940 (10 bits) or 256 to 3760 (12 bits).
Full: Set the range as 0 to 1023 (10 bits) or 0 to 4095 (12 bits).
[Narrow (default value) / Full]

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HDR Measurement

Measurement
By setting the HDR Mode on the HDR tab to "HLG" or "PQ", measurements supporting HDR
signals can be made with WFM display, VECT display, and PIC display.

WFM Display
Scale Display
The normal scale is displayed on the left, and the scale for HDR signals is displayed on the right.
Depending on the setting of the HDR tab, the HDR scale is displayed as 0 to 1200%, 0 to 100%,or 0 to 1000 cd/m2.
The horizontal graduation line can be switched between the one corresponding to the normal
scale and the one corresponding to the HDR scale by the following procedure.
WFM ➡ F1 (WFM INTEN/CONFIG) ➡ F5 (WFM SCALE) ➡ F3 (SCALE SETTING) ➡
F3 (SCALE DISPLAY): OFF / MAIN / HDR / BOTH

Figure | Scale display

22

HDR Measurement

Reference Level Display
A dash-dot chain line is displayed at the level selected for Ref.Level on the HDR tab. Also, thereference level is displayed in the lower right of the screen.
When VARIABLE is ON on the HDR tab, the reference level can be varied by the following
procedure.
WFM ➡ F1 (WFM INTEN/CONFIG) ➡ F5 (WFM SCALE) ➡ F3 (SCALE SETTING) ➡
F4 (REF.LEVEL [%]): 0.0 - 100.0

Figure | Reference level display

23

HDR Measurement

Cursor Display
When HDR is selected by the following procedure, the measured values corresponding to the
HDR scale are displayed.
WFM ➡ F4 (CURSOR) ➡ F3 (Y UNIT): mV / % / R% / DEC / HEX / HDR

Figure | Cursor display

24

HDR Measurement

VECT Display
A scale for HDR signals can be displayed on the histogram display. Depending on the setting of
the HDR tab, the HDR scale is displayed as 0 to 1200%, 0 to 100%, or 0 to 1000 cd/m2.
To display the HDR scale, select HDR by the following procedure.
VECT ➡ F2 (HISTGRAM SCALE): % / HDR

Figure | Histogram display

25

HDR Measurement

PIC Display%DISPLAY Display
On CINELITE's %DISPLAY display, the measurement values for HDR signals can be displayed by
selecting HDR by the following procedure. Depending on the setting of the HDR tab, themeasurement values are displayed as 0 to 1200%, 0 to 100%, or 0 to 1000 cd/m2.
PIC ➡ F2 (CINELITE/HDR) ➡ F2 (% DISP SETUP) ➡ F4 (UNIT SELECT): Y% / RGB% / RGB255 / CV
/ CV(DEC) / HDR

Figure | %DISPLAY display

26

HDR Measurement

CINEZONE Display
On the CINEZONE display, to display the SDR area in monochrome and the HDR area in color,
follow the procedure below to select ON.
PIC ➡ F2 (CINELITE/HDR) ➡ F5 (HDR ZONE): OFF / ON

Figure | CINEZONE display

27

HDR Measurement

When VARIABLE is ON on the HDR tab, the reference level can be varied by the following
operation. The reference level is the boundary line between the SDR display and the HDR display.
In the upper left of the screen, the HDR equivalent value of the value set with F2 (UPPER [%]), F3(LOWER [%]), and F4 (REF [%]) is displayed.
PIC ➡ F2 (CINELITE/HDR) ➡ F2 (CINEZONE SETUP) ➡ F4 (REF [%]): 0.0 - 100.0

Figure | CINEZONE display

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HDR Measurement

MAX FALL/CLL display
For CINELITE display, MAX FALL (Maximum Frame Average Light Level) and MAX CLL (MaximumContent Light Level) can be displayed. MAX FALL is the average maximum luminance per frame,and MAX CLL is the maximum value of the content's brightness, respectively.
To display MAX FALL/CLL, select ON by the following procedure.
PIC ➡ F2 (CINELITE/HDR) ➡ F3 (MAX FALL/CLL) ➡ F1 (MAX FALL/CLL DISPLAY): OFF / ON

Next, set the measurement period by the following procedure. Select START to startmeasurement and STOP to end measurement.
PIC ➡ F2 (CINELITE/HDR) ➡ F3 (MAX FALL/CLL) ➡ F2 (MEASURE): START / STOP

The measurement can be cleared by the following procedure. The measured value returns to 0%
and F2 (MEASURE) changes to STOP.
PIC ➡ F2 (CINELITE/HDR) ➡ F3 (MAX FALL/CLL) ➡ F3 (CLEAR)

Figure | MAX FALL/CLL display

29

HDR Measurement

06 Glossary
HDR-related terms

Term

Definition

EOTF

Acronym of Electro-Optical Transfer Function.
Transfer function when converting an electric signal to brightness on the display side.

HDR

Acronym of High Dynamic Range.
Dynamic range expanded compared with SDR, extends up to 10,000 cd/m2.

HLG

Acronym of Hybrid Log Gamma.
One of the two HDR systems. Proposed by NHK and BBC.
Compatible with SDR, suitable for broadcasting.

ITU-R BT.2100

International standard for HDR.

OETFAcronym of Opto-Electronic Transfer Function.
Transfer function for converting brightness to electric signal on the camera side.

OOTF

Acronym of Opto-Optical Transfer Function.
Transfer function when considering camera gamma and display gamma in total.

PQ

Acronym of Perceptual Quantization.
One of the two HDR systems. Proposed by Dolby.
Suitable for movies, packages, etc.

SDR

Acronym of Standard Dynamic Range.
Conventional dynamic range, defined as extending up to 100 cd/m2.

Camera gamma

Characteristic when converting brightness to electric signal on the camera side.

System gamma

Characteristic when considering camera gamma and display gamma in total.

Display gamma

Characteristic when converting an electric signal to brightness on the display side.

Address

2-6-33 Tsunashima-Higashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture 223-8505, JapanPhone+81-45-541-2123

Emailsales@leader.co.jp

URL

www.leader.co.jp/en

Published

December 5, 2018

1st Edition30