IEC 62679-3-1:2014

IEC 62679-3-1 ®
Edition 1.0 2014-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electronic paper displays –
Part 3-1: Optical measuring methods

Afficheurs de papier électroniques –
Partie 3-1: Méthodes de mesures optiques

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IEC 62679-3-1 ®
Edition 1.0 2014-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Electronic paper displays –
Part 3-1: Optical measuring methods

Afficheurs de papier électroniques –

Partie 3-1: Méthodes de mesures optiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 31.120; 31.260 ISBN 978-2-8322-1515-9

– 2 – IEC 62679-3-1:2014 © IEC 2014
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 7
3.1 Terms and definitions . 7
3.2 Abbreviations . 8
4 Standard measuring conditions . 8
4.1 Standard measuring environmental conditions . 8
4.2 Viewing direction coordinate system . 8
4.3 Standard lighting conditions . 9
4.3.1 General comments and remarks on the measurement of
electronic paper displays . 9
4.3.2 Dark-room conditions . 9
4.3.3 Standard ambient illumination spectra . 10
4.3.4 Standard illumination geometries . 11
4.4 Standard conditions of measuring equipment . 16
4.4.1 General . 16
4.4.2 Adjustment of EPD . 16
4.4.3 Conditions of measuring equipment . 16
4.4.4 Contact measurements with integrated illumination/detection
instruments . 17
4.5 Working standards and references . 18
4.5.1 Diffuse reflectance standard . 18
4.5.2 Specular reflectance standard . 18
4.6 Standard locations of measurement field. 19
4.6.1 Matrix displays. 19
4.6.2 Segment displays . 19
5 Optical measuring methods . 20
5.1 Reflection measurements . 20
5.1.1 Purpose . 20
5.1.2 Measuring conditions . 20
5.1.3 Measuring the hemispherical diffuse spectral reflectance
factor . 20
5.1.4 Measuring the reflectance factor for a directed light source . 22
5.2 Display photometric in-plane uniformity . 23
5.2.1 Purpose . 23
5.2.2 Measuring equipment . 23
5.2.3 Measurement method . 23
5.2.4 Definitions and evaluations . 24
5.3 Contrast ratio . 24
5.3.1 Purpose . 24
5.3.2 Measuring equipment . 24
5.3.3 Measurement method . 24
5.3.4 Definitions and evaluations . 25
5.4 Ambient contrast ratio . 25
5.4.1 Purpose . 25
5.4.2 Measuring conditions . 25

5.4.3 Measuring method . 25
5.5 Cross-talk . 26
5.5.1 Purpose . 26
5.5.2 Measuring equipment . 26
5.5.3 Greyscale matrix displays . 26
5.5.4 Black and white (two-level) matrix displays . 28
5.6 Display colour, colour gamut, and colour gamut area . 28
5.6.1 Purpose . 28
5.6.2 Measuring equipment . 28
5.6.3 Measurement method . 29
5.6.4 Definitions and evaluations . 29
5.6.5 Display colour gamut . 30
5.6.6 Display colour gamut area . 30
5.7 Display colorimetric in-plane uniformity . 32
5.7.1 Purpose . 32
5.7.2 Measuring equipment . 32
5.7.3 Measurement method . 32
5.7.4 Definitions and evaluations . 33
5.8 Daylight display colour . 34
5.8.1 Purpose . 34
5.8.2 Measuring conditions . 34
5.8.3 Measuring method . 34
5.9 Daylight colour gamut volume . 35
5.9.1 Purpose . 35
5.9.2 Measuring conditions . 35
5.9.3 Measuring method . 35
5.9.4 Reporting . 37
5.10 Viewing direction dependence . 37
5.10.1 Purpose . 37
5.10.2 Measuring conditions . 37
5.10.3 Measuring method . 38
5.10.4 Definitions and evaluations . 39
5.11 Ghosting . 41
5.11.1 Purpose . 41
5.11.2 Measuring equipment . 41
5.11.3 Measuring method . 41
5.11.4 Definitions and evaluations . 42
Annex A (informative) Calculation method of daylight colour gamut volume . 43
A.1 Purpose . 43
A.2 Procedure for calculating the colour gamut volume . 43
A.3 Surface subdivision method for CIELAB gamut volume calculation . 45
A.3.1 Purpose . 45
A.3.2 Assumptions . 45
A.3.3 Algorithm . 45
A.3.4 Software example . 45
Bibliography . 50

– 4 – IEC 62679-3-1:2014 © IEC 2014
Figure 1 – Representation of the viewing direction, or direction of measurement,
defined by the angle of inclination, and the angle of rotation (azimuth angle) in a polar
coordinate system . 9
Figure 2 – Illustrated examples for directional illumination . 12
Figure 3 – Example of the measuring setup using directional illumination where
θ = 40° and θ = 30° . 12
S R
Figure 4 – Example of the ring light illumination measuring setup where θ ± ∆ = 35°±
S
5° and θ = 20° . 13
R
Figure 5 – Detailed schematic of ring light characteristics . 14
Figure 6 – Example of measurement geometries for hemispherical illumination using
an integrating sphere (left) and sampling sphere (right) . 15
Figure 7 – Layout diagram of measurement setup . 17
Figure 8 – Standard measurement positions . 19
Figure 9 – Window pattern for cross-talk measurement . 27
Figure 10 – Example of display colour gamut . 30
Figure 11 – Example of evaluation results for the colour gamut area on the a*b* plane
of the CIELAB colour space . 32
Figure 12 – An example of range in colours produced by a given display as
represented by the CIELAB colour space . 36
Figure 13 – Illumination/detection geometry for measuring the viewing direction
properties of the display . 38
Figure 14 − Example of contrast ratio dependence on viewing direction . 40
Figure 15 – Display pattern used to characterize ghosting. . 42
Figure A.1 – Analysis flow chart for calculating the colour gamut volume . 43
Figure A.2 – Graphical representation of the colour gamut volume for sRGB in the
CIELAB colour space . 44

Table 1 – Eigenvalues M and M for CIE daylight Illuminants D50 and D75 . 21
1 2
Table 2 – Input signals for CIELAB and CIE UCS u’v’ colour gamut area
measurements . 31
Table 3 – Example data of in-plane colour non-uniformity . 33
Table 4 – Example of minimum colours required for gamut volume calculation of a 3-
primary 8-bit display . 35
Table 5 – Measured tristimulus values for the minimum set of colours (see Table 4)
required for gamut volume calculation under the specified daylight illumination
conditions . 37
Table 6 – Colour gamut volume in the CIELAB colour space . 37
Table 7 – Example format used for reporting viewing direction performance . 41
Table A.1 – Tristimulus values of the sRGB primary colours . 44
Table A.2 – Example of sRGB colour set represented in the CIELAB colour space . 44
Table A.3 – Example of sRGB colour gamut volume in the CIELAB colour space . 45

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRONIC PAPER DISPLAYS –
Part 3-1: Optical measuring methods

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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.
International Standard 62679-3-1 has been prepared by IEC technical committee 110:
Electronic display devices.
The text of this standard is based on the following documents:
FDIS Report on voting
110/548/FDIS 110/561/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62679 series, published under the general title Electronic paper
displays, can be found on the IEC website.

– 6 – IEC 62679-3-1:2014 © IEC 2014
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication 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.
ELECTRONIC PAPER DISPLAYS –
Part 3-1: Optical measuring methods

1 Scope
This part of IEC 62679 specifies the standard measurement conditions and measurement
methods for determining the optical performance of Electronic Paper Display (EPDs). The
scope of this document is restricted to EPDs using either segment, passive, or active matrix
with either monochromatic or colour type displays. The measuring methods are intended for
EPDs operated in a reflective mode. The EPDs may include an integrated lighting unit (ILU),
but the ILU will be turned off for these measuring methods. Colour systems beyond three
primaries are not covered in this document.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
www.electropedia.org)
IEC 62679-1-1 , Electronic paper displays – Part 1-1: Terminology
IEC 61966-2-1, Multimedia systems and equipment – Colour measurement and management
– Part 2-1: Colour management – Default RGB colour space – sRGB
CIE 15, Colorimetry
CIE 38, Radiometric and Photometric Characteristics of Materials and their Measurement
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62679-1-1,
IEC 60050, as well as the following apply.
3.1.1
ambient contrast ratio
contrast ratio of a display with both hemispherical diffuse and directional illumination incident
onto its surface used to simulate real lighting environments
3.1.2
daylight display colour
colour of a display with both hemispherical diffuse and directional illumination incident onto its
surface at a defined geometry, spectra, and illumination levels that simulate a realistic
daylight lighting environment
—————————
To be published.
– 8 – IEC 62679-3-1:2014 © IEC 2014
3.1.3
colour gamut volume
single number corresponding to the largest possible range of display colours (including all
possible mixtures of the primaries, white W and black K), described as a volume in a three-
dimensional colour space such as CIELAB
3.1.4
daylight colour gamut volume
colour gamut volume of a display with both hemispherical diffuse and directional illumination
incident onto its surface at a defined geometry, spectra, and illumination levels that simulate a
realistic daylight lighting environment
3.2 Abbreviations
CCT correlated colour temperature
CIE International Commission on Illumination
CIELAB CIE 1976 (L*a*b*) colour space
DUT device under test
EPD electronic paper display
ILU integrated lighting unit (e.g. an edge-lit front guide plate)
ISO International Organization for Standardization
LED light emitting diode
LMD light measuring device
RGB red, green, blue
SDCM standard deviation of colour matching
sRGB a standard RGB colour space as defined in IEC 61966-2-1
4 Standard measuring conditions
4.1 Standard measuring environmental conditions
Optical and electro-optical measurements shall be carried out under the standard
environmental conditions, at a temperature of 25 °C ± 3 °C, a relative humidity of 25 % to
85 %, and a pressure of 86 kPa to 106 kPa. When different environmental conditions are used,
they shall be noted in the report.
4.2 Viewing direction coordinate system
The viewing direction is the direction under which the observer looks at the point of interest
on the device under test (DUT). During the measurement, the light-measuring device (LMD)
simulates the observer, by aiming the LMD at the point of interest on the DUT from the
viewing direction. The viewing direction is defined by two angles: the angle of inclination θ
(relative to the surface normal of the DUT) and the angle of rotation φ (also called azimuth
angle) as illustrated in Figure 1. Although the azimuth angle is measured in the counter-
clockwise direction, it is related to the directions on a clock face as follows: φ = 0° is the 3-
o'clock direction ("right"), φ = 90° the 12-o'clock direction ("top"), φ = 180° the 9-o'clock
direction ("left") and φ = 270° the 6-o'clock direction ("bottom").

IEC  1023/14
Figure 1 – Representation of the viewing direction, or direction of measurement,
defined by the angle of inclination, and the angle of rotation (azimuth angle)
in a polar coordinate system
4.3 Standard lighting conditions
4.3.1 General comments and remarks on the measurement of electronic paper
displays
This document treats electronic paper displays (EPDs) as reflective displays. A reflective
information display is a display that modulates the reflected light so that the information is
carried by the reflected light. Reflective displays do not emit any light so that ambient light is
required to view that information. Therefore it is critical that measurement specifications on
reflective displays include the illumination conditions during measurement. The measurement
illumination consists of one or more light sources, each of whose spectral distribution and
illumination geometry have to be specified. Thus, display performance measurements shall be
carried out under specific and well defined conditions of illumination and detection in order to
be reproducible.
ILUs are integrated into an EPD to provide supplemental illumination to compensate for the
lack of adequate ambient illumination. The measuring methods in this document are
performed with the ILU turned off.
Subclause 4.3 describes a selection of standard lighting conditions for measuring the
performance metrics of the EPD. The EPD may also be measured under other illumination
and detection geometries in addition to the standard geometries.
A warm-up time may be necessary. The light source signal shall remain stable to within ±5 %
over the course of the complete measurement.
4.3.2 Dark-room conditions
The EPD is intended to be measured under controlled lighting conditions. Unwanted
background illumination shall be minimized, typically by illuminating the display in a darkroom.
The darkroom spectral radiance contribution from the background illumination, that is the
th
measured spectral radiance reflected off the DUT, shall be not more than 1/100 of the
spectral radiance from the device black state with the illumination source on. If this condition
is not satisfied, then background subtraction is required and it shall be noted in the report. In
addition, if the sensitivity of the LMD is inadequate to measure at these low levels, then the
lower limit of the LMD shall be noted in the report.
Unless stated otherwise, the standard background lighting conditions shall be the dark-room
conditions.
– 10 – IEC 62679-3-1:2014 © IEC 2014
4.3.3 Standard ambient illumination spectra
The following illumination conditions are specified for optical and electro-optical
measurements of reflective displays under ambient illumination. The ambient illumination shall
simulate indoor or outdoor illumination conditions. A combination of two illumination
geometries is generally used to simulate either ambient indoor illumination, or outdoor
daylight illumination under a clear sky.[1,2] Uniform hemispherical diffuse illumination will be
used to simulate the background lighting in a room with the directed light source such as a
luminaire in a room occluded, or the hemispherical skylight incident on the display, with the sun
occluded. A directed light source in a dark room will simulate the effect of directional
illumination on a display by a luminaire in a room, or from direct sunlight.
The following illumination conditions shall be used to simulate indoor and outdoor display
viewing environments:
• Indoor room illumination conditions:
Uniform hemispherical diffuse illumination – Use a light source closely approximating CIE
Standard Illuminant A, CIE Standard Illuminant D65, or CIE Standard Illuminant D50 as
defined in CIE 15. For spectral measurements, a spectrally smooth broadband light source
(such as an approximation to CIE Standard Illuminant A) shall be used. A measurement of
the spectral reflectance factor using a broad light source (such as Illuminant A) enables
the indoor photopic and colour metrics to be calculated later for the desired reference
spectra (for example CIE D65 Illuminant). The performance metrics shall be calculated
using 300 lx for an indoor reading environment.[3] The actual hemispherical diffuse
reflectance factor measurement may require higher illumination levels for better
measurement accuracy. The results are then scaled down to the required illumination
levels.
Directional illumination – The same source spectra shall be used as with hemispherical
diffuse illumination. The indoor room photopic and colour metrics shall be calculated using
directional illumination of 200 lx incident on the display surface for an indoor reading
environment with the display in the vertical orientation. The actual reflectance factor
measurement may require higher illumination levels for better measurement accuracy. The
results are then scaled down to the required illumination levels. The directed source shall be
θ = 45°) and have an angular subtense of no more than 5°.
45° above the surface normal (
s
The angular subtense is defined as the full angle span of the light source from the centre
of the display’s measurement area.
Other illumination levels may be used in addition to those defined above for calculating the
ambient contrast ratio under indoor illumination conditions. However, approximately 60 %
of the total illuminance should be hemispherical diffuse, and 40 % directional illumination.
• Daylight illumination conditions:
Uniform hemispherical diffuse illumination – Use a light source closely approximating
skylight with the spectral distribution of CIE Illuminant D75.[4] Additional CIE daylight
illuminants (such as D65) may also be used, depending on the intended application. For
spectral measurements, the spectral reflectance factor measurements can be made using
a spectrally smooth broadband source (such as an approximation to CIE Standard
Illuminant A). Skylight photopic and colour metrics can be calculated later for the CIE D75
Illuminant spectra. The skylight photopic and colour metrics shall be calculated using
15 000 lx of hemispherical diffuse illumination (with specular included) incident on a
display surface in a vertical orientation.[4,5] The actual hemispherical diffuse reflectance
factor measurement may be taken at lower illumination levels. The results are then scaled
up to the required illumination levels.
Directional illumination – The directional light source shall approximate CIE daylight
Illuminant D50.[4] Additional CIE daylight illuminants (such as D65) may also be used,
depending on the intended application. A spectrally smooth broadband source (such as an
approximation to CIE Standard Illuminant A) may be used for the reflectance factor
measurement. The sunlight photopic and colour metrics can be calculated later with the
—————————
Numbers in square brackets refer to the Bibliography.

D50 Illuminant spectra. The daylight contrast ratio or colour shall be calculated using
65 000 lx for a directed source at an inclination angle of θ = 45° to the display surface,
s
and the LMD shall be aligned normal to the display surface (θ = 0°).[4,5] The actual
d
reflectance factor measurement may be taken at lower illumination levels. The results are
then scaled up to the required illumination levels. The contrast ratio and colour are
calculated for the scaled-up illuminance levels. The directed source shall have an angular
subtense of approximately 0,5°.
For daylight photopic and colour metric calculations from spectral reflectance factor
measurements, the relative spectral distributions of CIE Illuminants A, D50, D65 and D75
tabulated in CIE 15 shall be used. Additional CIE daylight illuminants shall be determined
using the appropriate eigenfunctions, as defined in CIE 15.
The UV region (< 380 nm) of the light source shall be cut off by a UV blocking filter. When
high light source illumination levels are used, an infrared-blocking filter is recommended to
minimize device heating.
4.3.4 Standard illumination geometries
4.3.4.1 General
Three types of illumination geometries shall be used for determining the performance of the
EPD. Standard configurations for implementing these illumination geometries are defined in
4.3.4. Additional illumination geometries may also be used. The details of the illumination
geometry used for a given measurement shall be reported. Further guidance on the proper
implementation of these illumination geometries is given in the SID display measurement
standard. [1]
4.3.4.2 Directional illumination
Directional illumination is obtained when a light source produces approximately parallel rays
incident on the DUT. The maximum deviation of the rays from the optical axis depends on the
diameter of both the source and measuring spot. The maximum angle of deviation from the
optical axis is given by
arctan ([r + r ] / |d|) < 5° (1)
ms s
where r is the source radius, d is the distance to the measuring spot, and r is the
s ms
measuring spot radius. The illumination across the cross-section of the beam shall be uniform
to within 5 %. A source of light sufficiently distant from the DUT can provide directional
illumination (e.g. sun and moon). When simulating outdoor directional ambient illumination
like the sun and moon, the subtense of the source (as observed by the DUT) should be ≤ 0,5°.
Directional illumination can be realized with three different types of sources when the source
dimensions are small enough compared to the distance between source and the measuring
spot on the sample. These geometries are depicted in Figure 2:
• flat Lambertian source, e.g. the exit port of an integrating sphere (top),
• spherical isotropic source (e.g. incandescent bulb inside a diffusing glass-sphere) (middle),
• projection system with lenses or mirrors (bottom).

– 12 – IEC 62679-3-1:2014 © IEC 2014

r
s
5° max.
d
r
ms
rr
r
sss
5° max. d
r
ms
r
s
5° max.
d
r
ms
IEC  1024/14
Figure 2 – Illustrated examples for directional illumination
Directional illumination is implemented by using a light source with a small diameter
(compared to the distance to the measurement spot) aligned to form an inclination angle θ
S
with respect to the surface normal of the DUT. This directed light source produces an
illumination spot on the DUT. The LMD is placed at an inclination angle θ in the plane of the
R
incident light, and its measurement field centred within the illumination spot. The light source
and LMD can be adjusted over a range of inclination angles, but the LMD shall remain in the
plane of incidence (i.e. φ = φ + 180°). This configuration is shown in Figure 3 (left) with its
S R
representation in a polar coordinate system (right). The measurement field on the DUT is
defined by the DUT area element that is imaged on the detector in the LMD.
IEC  1025/14
Figure 3 – Example of the measuring setup using
directional illumination where θ = 40° and θ = 30°
S R
The standard conditions are θ = 45° and θ = 0°. Alignment accuracy to within ± 0,4° is
S R
recommended to keep measurement error within ± 5 %.

4.3.4.3 Ring light illumination
Ring light illumination can be considered a special case of directional illumination. It provides
directional illumination with rotational symmetry about the display’s surface normal and
centred on the measurement spot. Ring light illumination can be realized in the following
ways:
• fiber-optic ring light,
• integrating sphere with a ring-shaped aperture (annulus),
• optical systems with lenses and mirrors, for example a concave ring mirror.
A ring-shaped light source centred about the surface normal of the DUT illuminates the DUT
from an angle of inclination θ ± ∆ for all azimuthal angles φ = 0° to 360°. The LMD is
S S
aligned to form an angle θ < θ – ∆ with respect to the surface normal of the DUT. Figure 4
R S
shows a side view of the measuring setup (left) and its representation in a polar coordinate
system (right). A more detailed illustration of the ring light characteristics is given in Figure 5.
The subtense of the ring light (2∆ in this case) shall be specified. The source and detector
shall be aligned to the defined geometry to within ± 3°. The illumination of the measuring spot
on the DUT shall be uniform within 5 %. This setup is used with the light source fixed, and the
LMD can be adjusted within the limits of the ring light opening. The standard conditions are
θ = 0° and a source inclination angle of θ ± ∆ = 45° ± 3°.
R S
IEC  1026/14
Figure 4 – Example of the ring light illumination
measuring setup where θ ± ∆ = 35°± 5° and θ = 20°
S R
The ring light and LMD are recommended to have an alignment accuracy of ± 0,7° in order to
keep the measurement error within ± 5 %. When simulating outdoor directional ambient
illumination using the ring light, the subtense 2∆ of the source (as observed by the DUT)
should be ≤ 0,5°. A fiber-optic ring light is recommended in this case.

– 14 – IEC 62679-3-1:2014 © IEC 2014

D
s
m
a
r
s
Ring light subtense
( 2 ∆ ,K )
s s
Ring light inclination
( θ ,θ )
s r
Ring light distance ( c )
s
Light radius ( r )
s
Ring light width ( D )
s
2 ∆
s
θ Measurement field ( m )
s K a
MFs
c
s
Illumination field (aperture ) ( D )
a
Meas. field illumination subtense ( )
KM Fs
Illumination aperture
(optional)
DUT
D
a
IEC  1027/14
Figure 5 – Detailed schematic of ring light characteristics
The maximum angle of deviation from the optical axis is given by:
 
 
 c  c
s s
 
 
arctan − arctan < 5°
(2)
 
 m 
r
a
 s 
r −
 
s
 2 
Thus, the ring light diameter (D ) should be at least six times larger than the measurement
s
field diameter (m ).
a
The illuminated area diameter (D ) should be at least 1,5 times larger than the measurement
a
field diameter (m ).
a
If the display consists of thick layers above the reflective surface, care should be taken to
) from the farthest
...