IEC 62977-3-7:2022

IEC 62977-3-7 ®
Edition 1.0 2022-01
INTERNATIONAL
STANDARD
colour
inside
Electronic displays –
Part 3-7: Evaluation of optical performance – Tone characteristics
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IEC 62977-3-7 ®
Edition 1.0 2022-01
INTERNATIONAL
STANDARD
colour
inside
Electronic displays –
Part 3-7: Evaluation of optical performance – Tone characteristics

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120 ISBN 978-2-8322-1070-7

– 2 – IEC 62977-3-7:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 9
4 Standard measuring equipment . 9
4.1 Video signal generator . 9
4.2 Measuring equipment and conditions . 10
4.3 Test equipment setup. 10
5 Standard measuring conditions . 11
5.1 Standard measuring environmental conditions . 11
5.2 Standard measuring darkroom conditions . 11
5.3 Adjustment of display . 12
5.4 Starting conditions of measurement . 12
5.5 Standard test pattern . 12
5.5.1 General . 12
5.5.2 Test pattern for grey and colour tone measurement . 13
5.5.3 Test pattern for colour saturation tone measurement . 16
6 Measurements and evaluation of tone characteristics . 16
6.1 EOTF and display gamma . 16
6.1.1 Measured data . 16
6.1.2 Measuring method . 17
6.1.3 Average gamma calculation . 18
6.1.4 Log-log gamma calculation . 20
6.1.5 Grey scale tracking accuracy . 22
6.1.6 Directional EOTF . 22
6.2 Colour saturation tone accuracy . 23
6.2.1 Measured data . 23
6.2.2 Measuring method . 23
6.2.3 Evaluation of colour saturation tone accuracy . 24
6.3 Tone additivity function . 26
6.4 Functional tone quantization . 27
6.4.1 Measuring method . 27
6.4.2 Evaluation of functional tone quantization . 28
7 Reporting. 30
7.1 Required reporting . 30
7.2 Measurement results . 31
Annex A (informative) Interlevel gamma . 32
A.1 General . 32
A.2 Interlevel gamma calculation . 33
Bibliography . 36

Figure 1 – Hue saturation lightness (HSL) colour model . 6
Figure 2 – Measuring layout for non-close-up measurement . 10

Figure 3 – Measuring layout for close-up type LMD . 10
Figure 4 – Setup for viewing directional measurements. 11
Figure 5 – RGB input ranges for 7 tones and 6 colour saturations . 13
Figure 6 – Multi-colour pattern for grey tone measurement . 14
Figure 7 – Multi-colour pattern for colour tone measurement (example for red tone) . 15
Figure 8 – Equivalent pattern for APL calculation of multi-colour pattern (example for
grey tone) . 15
Figure 9 – Multi-colour pattern for colour saturation tone measurement (example for
red saturation) . 16
Figure 10 – Example of a measured EOTF compared with ideal power law curves . 20
Figure 11 – Example of linear regression formula and plot for log-log gamma . 21
Figure 12 – Example of colour saturation tone evaluation . 25
Figure 13 – Examples of tone additivity functions for non-additive displays with (solid
line) and without (dashed line) tone clipping . 27
Figure 14 – Minimum luminance difference between neighbouring inputs . 28
Figure 15 – Graphic result for the bit depth evaluation in Table 9 . 30
Figure A.1 – Example of EOTF variation by enhancement processing . 33
Figure A.2 – Example of interlevel gamma graph . 35

Table 1 – RGB input level for 11 steps and 17 steps . 14
Table 2 – RGB input composition for grey tone and colour tone . 15
Table 3 – RGB input composition for colour saturation tone . 16
Table 4 – Selected measured data for display gamma from the 602-point measurement . 17
Table 5 – Example of average gamma calculation . 19
Table 6 – Example of log-log gamma calculation. 21
Table 7 – Selected measured data for colour saturation tone function from the 602-
point measurement . 23
Table 8 – Example of colour saturation tone evaluation (cyan saturation) . 25
Table 9 – Example of bit depth evaluation . 29
Table A.1 – Example of Interlevel gamma calculation . 34

– 4 – IEC 62977-3-7:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRONIC DISPLAYS –
Part 3-7: Evaluation of optical performance –
Tone characteristics
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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consensus of opinion on the relevant subjects since each technical committee has representation from all
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62977-3-7 has been prepared by IEC technical committee 110: Electronic displays. It is an
International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
110/1371/FDIS 110/1397/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 62977 series, published under the general title Electronic displays,
can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

– 6 – IEC 62977-3-7:2022 © IEC 2022
INTRODUCTION
Images as formed by electronic displays have lateral variations of for example hue, saturation
and intensity of visual stimuli. For displays of gradual smooth transitions no unwanted contours
and no quantization artefacts should be visible. Therefore, the displays should render the
required gradation of an image through tone reproduction. Tone is the variation in luminance,
ideally with constant hue and saturation, at (r, g, b) input (n, 0, 0), (0, n, 0), (0, 0, n), and (n, n,
n), respectively, where n:{0, 1,…N}, and N + 1 is the number of quantization levels. Similarly,
colour saturation tone is defined as the luminance variation, ideally with constant hue, but with
varying saturation of the input (= 1 – min (r, g, b) / max (r, g, b)), for input (N, n, n), (n, N, n),
and (n, n, N). Tone can also be defined for complementary colour (r, g, b) input (0, n, n), (n, 0,
n), (n, n, 0) and (n, N, N), (N, n, N), and (N, N, n), respectively. This is conceptually shown in
Figure 1 which is the hue saturation lightness/intensity (HSL or HSI) model with RGB inputs for
single colour tone, grey tone and colour saturation tone signal, where the lightness is defined
as 0,5 × ((max (r, g, b) + min (r, g, b)). Note that this colour space is different from the device
RGB colour space. Grey and RGB tone reproduction, and their additive relation, are
fundamental optical properties of displays since they affect the fidelity with which colour is
rendered from the input code values.

Figure 1 – Hue saturation lightness (HSL) colour model
In contemporary displays, nonlinear transformations into perceptually equidistant spaces are
required to reduce visual artefacts while maintaining data economy. Also, the transformations
linearize the opto-electrical transfer function, the nonlinearity of which is beneficial for reduction
of artefacts such as quantization noise, banding, contouring, as well as for quantization
efficiency.
The variation of electro-optical transfer functions (EOTFs) with viewing direction introduces
further complications. The resulting impact omnidirectional image quality is more multifaceted
compared to the viewing direction dependence of contrast, peak luminance, and colour of a
limited number of patches.
This document describes methods for the measurement of EOTF and evaluation, and points
out necessary precautions and diagnostics. The document is a reference for forthcoming
standards to make the work of the involved experts more efficient and to avoid duplication of
efforts.
ELECTRONIC DISPLAYS –
Part 3-7: Evaluation of optical performance –
Tone characteristics
1 Scope
This part of IEC 62977 specifies the standard measurement and evaluation of optical
performance for grey and colour tone reproduction of electronic displays under darkroom
conditions. This document describes the measuring methods and evaluation of tone rendering
of neutral grey, primary and secondary input colours. This document applies to displays with
unbounded input signals.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 62977-2-1:2021, Electronic displays – Part 2-1: Measurements of optical characteristics –
Fundamental measurements
IEC TS 62977-3-1:2019, Electronic displays – Part 3-1: Evaluation of optical performances –
Colour difference based viewing direction dependence
IEC 62341-6-3, Organic light emitting diode (OLED) displays – Part 6-3: Measuring methods of
image quality
IEC 61966-2-1, Multimedia systems and equipment – Colour measurement and management –
Part 2-1: Colour management – Default RGB colour space – sRGB
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

– 8 – IEC 62977-3-7:2022 © IEC 2022
3.1.1
electro-optical transfer function
EOTF
nonlinear decoding
variation of the optical output of electronic visual displays in terms of for example luminance
and chromaticity, as a function of the input signals
Note 1 to entry: The input signals could be R, G, B, C, M, Y, and grey for (r, g, b) input (n, 0, 0), (0, n, 0), (0, 0, n),
(0, n, n), (n, 0, n), (n, n, 0), and (n, n, n), respectively, where n:{0,1,…N}, and N + 1 is the number of quantization
levels per primary colour.
Note 2 to entry: The EOTFs for the C, M and Y inputs are optional.
Note 3 to entry: Generally, nonlinear decoding is the reciprocal of nonlinear encoding, but custom decoding is also
available in many display products (“gamma” pre-sets).
3.1.2
nonlinear encoding [4], [7]
signal transform mostly expressed by a combination of a linear function for low input values and
a power function with a single exponent above a certain level of input values as an opto-
electrical transfer function (OETF) [4]
Note 1 to entry: It is used in image acquisition devices such as digital cameras for mapping scene luminance to
digital code values prior to encoding, transmission, and/or compression.
Note 2 to entry: In conventional non-constant luminance systems, the nonlinear decoding is done in the RGB domain,
whereas it is done in the YC C domain for constant luminance systems.
b r
Note 3 to entry: The reason for the linear transformation for low input values is that the steepness of the power
function is too close to zero (infinite), leading to artefacts (e.g. excessive noise).
3.1.3
display gamma
exponent of the power function specifying the target EOTF of a display
Note 1 to entry: Deviations from the ideal power function are possible and should be specified.
Note 2 to entry: Generally, the display gamma value is calculated from an EOTF with the luminance of the black
level subtracted (de-biasing). Gamma is only defined if the de-biased EOTF obeys a power law, the exponent of
which is the gamma. The gamma value of an ideal display is the same for R, G, B, C, M, Y and grey tone.
3.1.4
colour saturation tone function
variation of the optical output of electronic visual displays in terms of for example luminance
and chromaticity, as a function of input signals with at least one RGB input kept at its maximum
value and the remaining R, G or B inputs being varied and of equal value
Note 1 to entry: An ideal display renders constant colorimetric hue for the inputs.
Note 2 to entry: When the luminance at maximum saturation is subtracted from the colour saturation tone function
(bias correction), and the resulting function obeys a power law, its exponent is called colour saturation gamma.
Note 3 to entry: The input signals could be R, G, B, C, M, and Y for (r, g, b) input (N, n, n), (n, N, n), (n, n, N), (n, N, N),
(N, n, N), and (N, N, n), respectively, where n:{0,1,…N}, and N + 1 is the number of quantization levels per primary
colour.
_____________
Numbers in square brackets refer to the Bibliography.

3.1.5
display bit depth
number of quantization levels, assuming binary-encoded levels
Note 1 to entry: It is the number of display bits or log [number of addressable shades] in the tone rendering.
Note 2 to entry: The actual number of renderable shades is often reduced when white balancing is done by gain
control [4], [7].
Note 3 to entry: Display colour depth is the sum of the bit depths of the rendered primary colours (RGB). Primary
colours can have different bit depths, for example 5-, 6- and 5-bit RGB depth for 16-bit colour depth.
3.1.6
tone additivity function
sum of the R, G, and B tones divided by the grey tone
Note 1 to entry: An ideal display has unity additivity for all inputs.
3.1.7
unbounded input signal
input signal for which there is neither any host-side colour management nor any handshaking
taking place between the host and the DUT
3.2 Abbreviated terms
ABC automatic brightness control
ALL average light level
ALS ambient light sensor
APL average picture level
CIELAB CIE 1976 L*a*b* colour space
CMY cyan, magenta, and yellow
DUT device under test
EOTF electro-optical transfer function
GOGO gain-offset-gamma-offset
HSI hue saturation intensity (device dependent colour space, also called HSL (hue
saturation lightness))
JND just noticeable difference
LMD light measuring device
OETF opto-electrical transfer function
OOTF opto-optical transfer function
RGB red, green, and blue
RGBCMY red, green, blue, cyan, magenta, and yellow
SLET stray light elimination tube
sRGB a standard RGB colour space as defined in IEC 61966-2-1 (sRGB has the same
colour gamut as the gamut of Recommendation ITU-R BT.709 [11])
4 Standard measuring equipment
4.1 Video signal generator
A digital video signal generator or a computer with digital RGB outputs, each with at least 8-bit
depth, shall be used. The signal bit depth supported by the DUT shall be reported according to
Clause 7.
– 10 – IEC 62977-3-7:2022 © IEC 2022
4.2 Measuring equipment and conditions
Refer to IEC 62977-2-1:2021, 5.3.4.
4.3 Test equipment setup
The setup of a non-close-up light measuring device (LMD) is shown in Figure 2 in the case of
a perpendicular direction measurement. The optical axis of the LMD shall be centred on the
screen and perpendicular to the plane of the display screen. The general conditions of the
measuring equipment, such as angular aperture, shall follow IEC 62977-2-1. A close-up type
LMD as shown in Figure 3 can be used only for measurements perpendicular to the DUT. A
close-up LMD shall have input optics with a well-defined measurement field angle similar to that
of non-close-up LMDs. The accuracy of the close-up type LMD shall be verified by a non-close-
up spectroradiometer.
The measuring layout for viewing directional measurement shall be applied by moving the LMD
or by rotation of the display in the horizontal viewing direction as shown in Figure 4a) and b),
where a vertical arrangement for a vertical viewing direction is also possible. Alternatively, the
spherical coordinate system as shown in Figure 4c) shall be applied (refer to
IEC TS 62977-3-1:2019, 6.1, and IEC 62977-2-1:2021, 5.6 and 6.10). The directional
measurement shall be done with a non-close-up measurement.

Figure 2 – Measuring layout for non-close-up measurement

Figure 3 – Measuring layout for close-up type LMD

a) Measurement by moving the LMD (top view) b) Measurement by rotating the DUT (top view)

c) Measurement in spherical coordinate system

Figure 4 – Setup for viewing directional measurements
5 Standard measuring conditions
5.1 Standard measuring environmental conditions
Refer to IEC 62977-2-1:2021, 5.1, where the standard environmental conditions are defined as
follows:
– temperature: 25 °C ± 3 °C,
– relative humidity: 25 % to 85 %,
– atmospheric pressure: 86 kPa to 106 kPa.
When different environmental conditions are used, they shall be noted in the report.
5.2 Standard measuring darkroom conditions
Refer to IEC 62977-2-1:2021, 5.2.

– 12 – IEC 62977-3-7:2022 © IEC 2022
5.3 Adjustment of display
The display shall be warmed up prior to taking measurements. Measurements shall be started
after the displays and measuring instruments achieve stability. The DUT shall be turned on first
and operated for at least 30 min prior to the measurement. Some display technologies may
need a loop of colour patterns rendered on the screen during the warm-up period. Sufficient
warm-up time has been achieved when the luminance of the test feature to be measured varies
by less than ±3 % over the entire measurement period for a given display image.
The standard operating conditions of the display shall be set by the following sequence.
a) Initialized status
The DUT shall be set to the factory settings. Other modes (including white coordinates such
as D65) may be selected after power-on and the selected mode shall then be noted in the
test report and used throughout all measurements.
b) Adjustment of ambient light control (if applicable)
Turn off the ABC by disabling the ALS. If it cannot be disabled, place a shielded light source
in front of the ALS that provides an illuminance of at least 300 lx at the surface of the ALS.
Make sure that the darkroom conditions are maintained while the shielded light source is
on. The details of the ABC-disabling light source shall be noted in the report.
c) Adjustment of protective and energy saving settings
Turn off all customer functions for power management and DUT protection and keep them
off throughout the measurement. If such functions are turned on automatically when
continuously displaying test images, reset or change the test pattern until such functions
are turned off again. Some displays adapt to content to save power and/or render the image
in special ways but these functions shall remain at their default settings.
d) Adjustment of aspect ratio
The test pattern shall be displayed in the aspect ratio identical to that of the display screen
without over scan.
5.4 Starting conditions of measurement
The display system shall be warmed up prior to taking measurements according to
IEC 62977-2-1:2021, 5.3.3.
5.5 Standard test pattern
5.5.1 General
Figure 5 schematically shows the tonal range of the measurements in the device-dependent
colour space RGB. In terms of the input signal, the tone measurements can be divided into:
1) single colour (or two colours with identical value) input tone,
2) constant single colour (or two colours) at maximum input adding the tones of the two other
colours with identical value (or the other colour tone), respectively, and
3) grey tone where RGB values are identical.
Numbers 1) and 3) are called RGBCMY and grey tonal curves, respectively, whereas number
2) is called colour saturation tonal curves, whose range is from fully saturated RGBCMY colour
to white.
If there is no specific comment, all measured and calculated data are recommended to have at
least 4-digit significant figures.

Figure 5 – RGB input ranges for 7 tones and 6 colour saturations
5.5.2 Test pattern for grey and colour tone measurement
Tone is directly related to the DUT luminance, and the power consumption generally increases
with luminance. Some displays have a limited power supply and/or dimming/boosting functions
[19], which means that luminance can depend on the APL [20]. In that case, the power
consumption might be proportional to the ALL of average luminance on the screen.
In the grey and colour tone measurements, the input APL is kept constant at 24,7 % using a
test pattern with complementary colour blocks (see Figure 6 to Figure 8). The RGB values of
'
V
these blocks, , are complementary to the RGB values of the centre test patch,
Q
N
VV' 21−−
(1)
QQ( )
where
Q is {R, G, B};
N is the bit depth;
V is the signal value of colour Q of the centre test patch.
Q
For the calculation of APL, the colour box pattern is converted as shown in Figure 8. The APL
of Figure 8 corresponds to 5 white boxes that are white, R + C, G + M, B + Y, and centre +
complementary colour block. The APL of the test pattern is therefore 24,7 % (= 5 × (2 / 9) ).
While the pattern in Figure 6 and Figure 7 provides constant APL, it is also a potential source
of stray light, particularly for larger APLs and when using a non-close-up LMDs. If stray light is
a problem, a frustum or SLET shall be used.
The test pattern shall consist of 11 or 17 steps (n = 11 or 17) of equally spaced inputs (see
IEC 62977-2-1:2021, Annex A). Some displays under some viewing conditions exhibit saturated
and/or non-monotonic EOTFs. In such cases, more steps can be necessary to properly sample
=
– 14 – IEC 62977-3-7:2022 © IEC 2022
the EOTFs. Table 1 shows an example of input code values (V) of RGB for grey tone
i
measurement.
Table 2 shows the input code values (V ) of RGB for colour tone measurement for 8- and 10-bit
i
cases and 11 and 17 levels. Some measurements can require a larger number of inputs.

Figure 6 – Multi-colour pattern for grey tone measurement
Table 1 – RGB input level for 11 steps and 17 steps
11-step inputs (V ) 17-step inputs (V )
Input
i i
no. (i)
10 bits 8 bits 10 bits 8 bits
1 0 0 0 0
2 102 25 63 15
3 205 51 127 31
4 307 76 191 47
5 409 102 255 63
6 511 127 319 79
7 613 153 383 95
8 716 178 447 111
9 818 204 511 127
10 920 229 575 143
11 1 023 255 639 159
12 703 175
13 767 191
14 831 207
15 895 223
16 959 239
17 1 023 255
Table 2 – RGB input composition for grey tone and colour tone
Input code
Tone colour
R' G' B'
V V V
Grey
i i i
V
Red 0 0
i
V
Green
0 0
i
V
Blue 0 0
i
V V
Cyan 0
i i
V V
Magenta 0
i i
V
V
Yellow 0
i i
Figure 7 – Multi-colour pattern for colour tone measurement (example for red tone)

Figure 8 – Equivalent pattern for APL calculation of multi-colour pattern
(example for grey tone)
– 16 – IEC 62977-3-7:2022 © IEC 2022
5.5.3 Test pattern for colour saturation tone measurement
The constant APL pattern shall be used also for the colour saturation tone measurement. The
centre box of the pattern shall be changed in 11, 17, or more steps depending on the required
accuracy and considering the colour saturation tone function shape. The standard test pattern
for the measurement shall be as shown in Figure 9. When measurement by a non-close-up LMD
is affected by stray light from the background tiles, a frustum or SLET shall be used.
Table 1 and Table 3 show the input code values (V ) and input colour composition for the colour
i
saturation tone measurement.
Table 3 – RGB input composition for colour saturation tone
Input code
Saturation colour
R' G' B'
V V
Red 255
i i
V V
Green 255
i i
V V
Blue 255
i i
V
Cyan 255 255
i
V
Magenta 255 255
i
V
Yellow 255 255
i
Figure 9 – Multi-colour pattern for colour saturation tone measurement
(example for red saturation)
6 Measurements and evaluation of tone characteristics
6.1 EOTF and display gamma for grey and colour tone
6.1.1 Measured data
If 11 steps are sufficient and colour gamut volume already is measured according to
IEC 62977-2-1, no further measurement of RGBCMY is necessary. However, an additional
11-point measurement of the grey tone shall be performed using the input levels in Table 4. If
the EOTF obeys a power law, the display gamma can be calculated according to the methods
in 6.1.3 to 6.1.5. If the EOTF does not obey a power law, steps e) and f) in 6.1.2 do not apply,
and it is then recommended that the number of steps be increased from 11 or 17.

Table 4 – Selected measured data for display gamma from the 602-point measurement
Input level Colour number in 602 inputs (see IEC 62977-2-1)
Input
Code value
no. (i)
% R G B C M Y
(V )
i
1 0 0 1 1 1 1 1 1
2 10 25 122 12 2 13 123 232
3 20 51 133 23 3 25 135 243
4 30 76 144 34 4 37 147 254
5 40 102 155 45 5 49 159 265
6 50 127 166 56 6 61 171 276
7 60 153 177 67 7 73 183 287
8 70 178 188 78 8 85 195 298
9 80 204 199 89 9 97 207 309
10 90 229 210 100 10 109 219 320
11 100 255 221 111 11 121 231 331

6.1.2 Measuring method
In many cases, the display luminance follows a power function of the input signal, where the
exponent is called gamma. The tone reproduction of such a display would be explained and
evaluated as follows:
γ
LV()= a V−+V L (2)
( )
ii KK
where
a is a constant,
V is the input level for black (normally, V = 0), and
K K
L is the black luminance.
K
For the EOTF measurement, the contrast and brightness controls, if any, shall be set to their
default values or disabled. The measurement shall be performed as follows:
a) Input the pattern of Figure 6 and Figure 7 with the required number of patches. If the boxes
cause image sticking, a full black frame can be inserted between each input levels. The
duration of the full black frame may have to be adjusted in order to eliminate image sticking.
b) Measure the luminance (or tristimulus values for colour tracking) at the screen centre
perpendicularly to the display screen.
c) Measure in order from low to high luminance of the centre box.
d) Repeat the luminance measurements of colour patterns from black to maximum input of
each RGB colour signal and optionally for CMY.
e) If R of the linear regression formula is over 90 % in the log-log plot (see 6.1.4), the tone
function can be considered to be a power function. In that case, calculate the gamma value
by linear regression.
f) Report the average gamma for each pattern. If necessary, report the other gamma value
such as log-log gamma.
g) Report the measured EOTFs by plotting the result and tabulating the values.

– 18 – IEC 62977-3-7:2022 © IEC 2022
6.1.3 Average gamma calculation
Gamma value is a useful, single-value parameter that can be used to estimate the non-linearity
of an EOTF that obeys a power law. It can also be used to calculate the gamma accuracy with
respect to a target gamma.
When calculating the gamma from a power law EOTF, the offset by the black-state luminance
shall first be subtracted (de-biasing). The display gamma value (power law exponent) can be
calculated by taking the logarithm of the de-biased luminance function. The average gamma is
then calculated by averaging the gamma values of each input (refer to IEC 61988-2-6 [20] and
IEC 62341-6-4 [10]) [2], [4], [5]. Among the gamma calculation methods, this method gives the
best linearity, that is, there is a strong correlation between a smaller gamma and average image
luminance.
nn−−11log LV − L
( ( ) )
iK,Q
norm
γγ (3)
A,Q ∑∑i,Q
nn−−22
log VV−
( )
ii22 i,Q K
norm
where
γ is the average gamma,
A,Q
Q is W, R, G, B, C, M or Y,
st th
n is the number of inputs (from 1 to n ), and L(V ) = L
1,Q K,
(L(V ) – L ) is the normalized value of the luminance measured for input i, (L(V ) – L )
i,Q K norm i,Q K
/ (L(V ) – L ), and
n,Q K
(V – V ) is the normalized value of the code value for input i.
i,Q K norm
Due to the smaller luminance range (smaller slope of the EOTF), the gamma values calculated
from the lower input values have a smaller deviation from the mean gamma value compared to
gamma values calculated from the higher input values. Even when the EOTF is not exactly
following a power law, it shall at least be monotonic in order to use this calculation method.
Data points which make the EOTF non-monotonic have to be discarded and the accuracy of the
calculated average gamma is then reduced. When evaluating the luminance saturation with
signal processing between two neighbouring levels, the interlevel gamma can be available (see
Annex A).
Provided that the EOTF is a power function (see 6.1.4), the standard deviation of the gamma
values for each input can be used to check how well the DUT gamma matches the power
function. The standard deviation of the averaged gammas is calculated according to Formula
(4).
n−1
()γγ−
∑ i,Q S
(4)
i=2
SD =
Q
n − 3
where
Q is W, R, G, B, C, M or Y.
Gamma accuracy can be calculated by comparing the measured gamma with the target gamma:
==
==
γγ−
S A,Q
σ ×100(%)
(5)
γ
γ
S
where
𝜎𝜎 is the gamma accuracy,
𝛾𝛾
Q is W, R, G, B, C, M or Y, and
γ is the target gamma value (for example, 2,2 for sRGB or 2,4 for Recommendation ITU-R
S
BT.1886 [13]).
Recommendation ITU-R BT.1886 assumes that the black luminance is 0 whereas the standard
EOTF includes the non-zero black level of the display system [13].
Table 5 shows an example of an average gamma calculation. In Figure 10, it is shown that an
average gamma value larger than 2,2 results in lower luminance. From Table 5 and Figure 10
it can be seen that the power law EOTF with an average gamma value of 2,755 best matches
the EOTF with a gamma of 2,8 at input levels where the two gammas are close (input nos 10
to 12).
Table 5 – Example of average gamma calculation
Input
Input level (V )
Gamma value
L (cd/m )
i
no. (i)
1 0 0,29 -
2 15 0,85 2,247
3 31 2,81 2,309
4 47 6,67 2,326
5 63 12,70 2,338
6 79 20,00 2,394
7 95 28,97 2,462
8 111 39,49 2,547
9 127 51,89 2,644
10 143 68,31 2,709
11 159 86,55 2,815
12 175 108,80 2,922
13 191 135,23 3,052
14 207 166,27 3,237
15 223 205,77 3,442
16 239 253,73 3,885
17 255 326,29 -
Average gamma 2,755
Gamma standard deviation 0,477 3
Gamma accuracy (versus gamma 2,2) 74,76 %

=
– 20 – IEC 62977-3-7:2022 © IEC 2022

Figure 10 – Example of a measured EOTF compared with ideal power law curves
6.1.4 Log-log gamma calculation
As explained in 6.1.3, provided that the EOTF is a power function, the log function can yield the
gamma value. The gamma value can be also estimated by the slope of a linear regression of
each measured point (refer to IEC 62341-6-3) [1], [9]. For the linear regression, the following
log-log formula from Formula (2) is rewritten as a linear formula, y = mx + b. In this formula, the
slope m corresponds to the value of the log-log gamma (γ) [16]. When performing the linear
regression, black input data for the y-axis intersection is excluded as follows:
logLV -L  γlogVV−+ loga
( ) ( ) ( ) (6)
iiKK
 
Table 6 shows an example of log-log gamma calculation with the same data as in Table 5.
Figure 11 shows the result of a linear regression of the data in Table 6. The y value in Figure 11
is slightly different from the logarithm of the luminance in Table 6 because the regression in
Figure 11 is an approximated line to estimate the luminance. If R of the log-log linear
regression is larger than 0,90, the EOTF can be considered to be a power function. If R < 0,90,
gamma shall not be used and the EOTF shall instead be tabulated.
=
Table 6 – Example of log-log gamma calculation
y value
Input level (V )
Input no. (i) L (cd/m )
i
(y = mx + b)
1 0 0,29 -2,792
2 15 0,85 -0,252
3 31 2,81 0,400
4 47 6,67 0,805
5 63 12,70 1,094
6 79 20,00 1,295
7 95 28,97 1,458
8 111 39,49 1,593
9 127 51,89 1,713
10 143 68,31 1,833
11 159 86,55 1,936
12 175 108,80 2,035
13 191 135,23 2,130
14 207 166,27 2,220
15 223 205,77 2,313
16 239 253,73 2,404
17 255 32
...