IEC 62906-5-4:2018

Laser display devices - Part 5-4: Optical measuring methods of colour speckle

IEC 62906-5-4:2018(E) specifies the fundamental colour speckle distribution in CIE colour systems and the measuring methods of the colour speckle of laser display devices (LDDs).
The contents of the corrigendum of juin 2022 have been included in this copy.

General Information

• Status: Published
• Publication Date: 08-Jan-2018
• ICS: 01.040.29 - Electrical engineering (Vocabularies)
• ICS: 29.240 - Power transmission and distribution networks
• ICS: 31.260 - Optoelectronics. Laser equipment
• Technical Committee: TC 110 - Electronic displays
• Drafting Committee: WG 10 - TC 110/WG 10
• Current Stage: PPUB - Publication issued
• Start Date: 09-Jan-2018
• Completion Date: 02-Feb-2018

Relations

• Corrected By: IEC 62906-5-4:2018/COR1:2022 - Corrigendum 1 - Laser display devices - Part 5-4: Optical measuring methods of colour speckle
• Effective Date: 05-Sep-2023

Overview

IEC 62906-5-4:2018 - “Laser display devices - Part 5-4: Optical measuring methods of colour speckle” defines how to characterize and measure colour speckle produced by laser display devices (LDDs). The standard specifies the fundamental colour speckle distribution in CIE colour systems and provides both calculation-based and direct optical measurement methods. This edition (1.0, 2018-01) includes the corrigendum of June 2022.

Key technical topics and requirements

The document is structured to guide repeatable, traceable measurement and analysis of colour speckle. Major topics include:

• Theory of colour speckle: mechanisms that generate colour speckle and its representation in CIE colour systems.
• Calculation methods: procedures for estimating colour speckle from component (B/G/R) behaviour, including:
  • Spectral behaviour measurement of BGR laser sources.
  • Target chromaticity and BGR power-ratio adjustment.
  • Two calculation approaches: (a) using monochromatic speckle contrasts (Cs‑B, Cs‑G, Cs‑R) and (b) using measured spatial distributions of monochromatic speckles.
  • Evaluation metrics, background‑effect elimination, and error analysis (including data‑size effects).
• Direct measuring methods: instrument design and measurement geometries using laser measuring devices (LMDs) with XYZ or BGR filter sets, plus flow charts and example setups.
• Spatial variation measurements: angular colour speckle variation, photometric speckle-contrast uniformity/non‑uniformity, and variance/covariance assessments.
• Calibration and annexes: procedures for calibrating XYZ mismatches, example distributions, and informative explanations to support interpretation.

The standard includes illustrative figures, flow charts and tables to support implementation (measurement geometries, sample distributions, and metric examples).

Practical applications and users

IEC 62906-5-4 is intended for professionals who design, test or certify laser-based displays and projection systems, including:

• Laser display manufacturers - to quantify speckle performance during R&D and production.
• Optical engineers and systems integrators - to optimize B/G/R balance, optics, and speckle mitigation strategies.
• Test and calibration laboratories - to implement standardized measurement procedures and report comparable metrics.
• Standards bodies and certification agencies - to assess compliance and consistency across devices.
• Academic researchers studying speckle phenomena and visual quality in laser displays.

Using the standard helps assess visual quality (speckle perceptibility), compare devices objectively, support product specifications, and guide speckle-reduction design choices.

Related keywords (for SEO)

IEC 62906-5-4, colour speckle, laser display devices, speckle measurement, speckle contrast, BGR, XYZ filters, LMD, optical measuring methods, speckle uniformity, laser projection testing.

Standards Content (Sample)

IEC 62906-5-4 ®
Edition 1.0 2018-01
INTERNATIONAL
STANDARD
colour
inside
Laser display devices –
Part 5-4: Optical measuring methods of colour speckle

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IEC 62906-5-4 ®
Edition 1.0 2018-01
INTERNATIONAL
STANDARD
colour
inside
Laser display devices –
Part 5-4: Optical measuring methods of colour speckle

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.260 ISBN 978-2-8322-5243-7

– 2 – IEC 62906-5-4:2018  IEC 2018
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, letter symbols and abbreviated terms . 7
3.1 Fundamental terms . 7
3.2 Terms related to colour speckle distribution . 7
3.3 Terms related to spatial variation . 8
3.4 Letter symbols . 8
3.5 Abbreviated terms . 9
4 Theory of colour speckle . 9
4.1 General . 9
4.2 Mechanism for generating colour speckle . 9
5 Calculation methods of colour speckle . 11
5.1 General . 11
5.2 Measuring method of spectral behaviour of BGR light sources . 12
5.3 Target chromaticity . 12
5.4 Adjustment of BGR power ratio . 14
5.5 Calculation method (a) using BGR speckle contrast C , C , C . 15
s-B s-G s-R
5.5.1 General . 15
5.5.2 Examples of measured distributions. 16
5.6 Evaluation metrics . 20
5.7 Calculation method (b) using the measured spatial distribution of BGR
monochromatic speckles . 21
5.7.1 General . 21
5.7.2 Examples of measured distributions. 21
5.7.3 Comparison between methods (a) and (b) . 23
5.7.4 Elimination of the background effects . 25
5.8 Error analysis based on data size . 28
6 Direct measuring methods of colour speckle . 32
6.1 General . 32
6.2 Fundamental design of LMD for colour speckle measurement . 33
6.3 Colour speckle measuring method using LMD with XYZ filters . 34
6.4 Colour speckle measuring method using LMD with BGR filters . 35
7 Measuring methods related to spatial variation . 36
7.1 General . 36
7.2 Angular colour speckle variation . 36
7.3 Photometric speckle contrast uniformity/non-uniformity . 37
7.4 Colour speckle variance/covariance non-uniformity . 38
Annex A (informative) Complementary explanation of colour speckle . 39
Annex B (informative) Examples of colour speckle distributions . 40
B.1 Colour speckle distributions (one of the BGR: 90 %, the others: 1 %) . 40
B.2 Colour speckle distributions (two of the BGR: 90 %, the other: 1 %). 43
Annex C (informative) Calibration of XYZ errors . 48
C.1 General . 48
C.2 Formulation of XYZ mismatches . 48

C.3 Calibration of the mismatched XYZ errors using the true BGR chromaticity
values . 50
Bibliography . 51

Figure 1 – Two speckle measuring methods and their flow charts . 12
Figure 2 – Target chromaticity and colour gamut . 13
Figure 3 – S (λ) with an FWHM of 2 nm. 13
B,G,R
Figure 4 – Adjustment method of BGR power ratio . 15
Figure 5 – Colour speckle distribution for C = 100 %, C = 100 %, C = 100 % . 16
s-B s-G s-R
Figure 6 – Photometric speckle distribution for C = 100 %, C = 100 %,
s-B s-G
C = 100 % . 17
s-R
Figure 7 – Colour speckle distribution for C = 50 %, C = 50 %, C = 50 % . 18
s-B s-G s-R
Figure 8 – Photometric speckle distribution for C = 50 %, C = 50 %, C = 50 % . 18
s-B s-G s-R
Figure 9 – Colour speckle distribution for C = 10 %, C = 10 %, C = 10 % . 19
s-B s-G s-R
Figure 10 – Photometric speckle distribution for C = 10 %, C = 10 %, C = 10 % . 20
s-B s-G s-R
Figure 11 – Colour speckle distribution for C = 9,2 %, C = 9,7 %, C = 9,2 %
s-B s-G s-R
obtained by method (b) . 22
Figure 12 – Colour speckle distribution for C = 9,2 %, C = 19,2 %, C = 23,2 %
s-B s-G s-R
obtained by method (b) . 23
Figure 13 – Colour speckle distribution for C = 9,2 %, C = 9,7 %, C = 9,2 %
s-B s-G s-R
obtained by method (a) . 24
Figure 14 – Colour speckle distribution for C = 9,2 %, C = 19,2 %, C = 23,2 %
s-B s-G s-R
obtained by method (a) . 24
Figure 15 – Raw data of BGR speckle distributions (upper row) and post-processed
data (lower row) for BGR monochromatic speckles (left: B, centre: G, right: R) . 26
Figure 16 – Colour speckle distribution directly using the raw data in Figure 15 . 26
Figure 17 – Colour speckle distribution for C = 16,2 %, C = 17,4 %, C = 17,3 %
s-B s-G s-R
obtained by indirect measuring method (a). 27
Figure 18 – Calculated average chromaticity values of the colour speckle distribution
with respect to data size for C = C = C = 80 % . 28
s-B s-G s-R
Figure 19 – Calculated average values of the normalized speckle illuminance speckle
distribution and the normalized monochromatic speckle intensity distribution with
respect to data size for C = C = C = 80 %. 29
s-B s-G s-R
Figure 20 – Calculated average chromaticity values of the colour speckle distribution
with respect to data size for C = C = C = 60 % . 29
s-B s-G s-R
Figure 21 – Calculated average values of the normalized speckle illuminance speckle
distribution and the normalized monochromatic speckle intensity distribution with
respect to data size for C = C = C = 60 %. 30
s-B s-G s-R
Figure 22 – Calculated average chromaticity values of the colour speckle distribution
with respect to data size for C = C = C = 40 % . 30
s-B s-G s-R
Figure 23 – Calculated average values of the normalized speckle illuminance speckle
distribution and the normalized monochromatic speckle intensity distribution with
respect to data size for C = C = C = 40 %. 31
s-B s-G s-R
Figure 24 – Calculated average chromaticity values of the colour speckle distribution
with respect to data size for C = C = C = 20 % . 31
s-B s-G s-R
Figure 25 – Calculated average values of the normalized speckle illuminance speckle
distribution and the normalized monochromatic speckle intensity distribution with
respect to data size for C = C = C = 20 %. 32
s-B s-G s-R
Figure 26 – Example of LMDs using XYZ filters for colour speckle measurement . 33

– 4 – IEC 62906-5-4:2018  IEC 2018
Figure 27 – Example of LMDs using BGR filters for colour speckle measurement . 34
Figure 28 – Example of measurement geometries for colour speckle using an LMD with
XYZ filters . 35
Figure 29 – Example of measurement geometries for colour speckle using an LMD with
BGR filters . 36
Figure 30 – Representation of the viewing direction, or direction of measurement,
ϕ ) in a
defined by the angle of inclination θ, and the angle of rotation (azimuth angle
polar coordinate system . 37
Figure A.1 – Photograph of colour speckle . 39
Figure B.1 – Colour speckle distribution for C = 90 %, C = 1 %, C = 1 % . 40
s-B s-G s-R
Figure B.2 – Photometric speckle distribution for C = 90 %, C = 1 %, C = 1 % . 41
s-B s-G s-R
Figure B.3 – Colour speckle distribution for C = 1 %, C = 90 %, C = 1 % . 42
s-B s-G s-R
Figure B.4 – Photometric speckle distribution for C = 1 %, C = 90 %, C = 1 % . 42
s-B s-G s-R
Figure B.5 – Colour speckle distribution for C = 1 %, C = 1 %, C = 90 % . 43
s-B s-G s-R
Figure B.6 – Photometric speckle distribution for C = 1 %, C = 1 %, C = 90 % . 43
s-B s-G s-R
Figure B.7 – Colour speckle distribution for C = 90 %, C = 1 %, C = 90 % . 44
s-B s-G s-R
Figure B.8 – Photometric speckle distribution for C = 90 %, C = 1 %, C = 90 % . 45
s-B s-G s-R
Figure B.9 – Colour speckle distribution for C = 1 %, C = 90 %, C = 90 % . 45
s-B s-G s-R
Figure B.10 – Photometric speckle distribution for C = 1 %, C = 90 %,
s-B s-G
C = 90 % . 46
s-R
Figure B.11 – Colour speckle distribution for C = 90 %, C = 90 %, C = 1 % . 46
s-B s-G s-R
Figure B.12 – Photometric speckle distribution for C = 90 %, C = 90 %,
s-B s-G
C = 1 % . 47
s-R
Figure C.1 – Deviated values (marker points) and ideal colour matching functions . 49
Figure C.2 – Correct plot by spectral measurements and plot with XYZ errors . 49

Table 1 – Values of measurement metrics for the calculated examples . 21
Table 2 – Values of measurement metrics for the examples in Figure 11 to Figure 14 . 25
Table 3 – Values of measurement indices for the examples in Figure 16 and Figure 17 . 27
Table C.1 – Mismatch coefficients. 49

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LASER DISPLAY DEVICES –
Part 5-4: Optical measuring methods of colour speckle

FOREWORD
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International Standard IEC 62906-5-4 has been prepared by IEC technical committee TC 110:
Electronic display devices.
The text of this International Standard is based on the following documents:
FDIS Report on voting
110/926/FDIS 110/938/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62906 series, published under the general title Laser display
devices, can be found on the IEC website.

– 6 – IEC 62906-5-4:2018  IEC 2018
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
A bilingual version of this publication may be issued at a later date.

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
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LASER DISPLAY DEVICES –
Part 5-4: Optical measuring methods of colour speckle

1 Scope
This part of IEC 62906 specifies the fundamental colour speckle distribution in CIE colour
systems and the measuring methods of the colour speckle of laser display devices (LDDs).
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 62906-1-2, Laser display devices – Part 1-2: Vocabulary and letter symbols
IEC 62906-5-2:2016, Laser display devices – Part 5-2: Optical measuring methods of speckle
contrast
CIE publication 15:2004, Colorimetry
3 Terms, definitions, letter symbols and abbreviated terms
For the purposes of this document, the following terms and definitions given in IEC 62906-1-2
and the following 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
3.1 Fundamental terms
3.1.1
colour speckle distribution
colour distribution in a specified colour space of the speckle patterns which are generated by
colour mixing of monochromatic screen speckles
3.1.2
photometric speckle distribution
distribution of photometric variables such as illuminance, luminance or luminous flux of a
colour speckle pattern which are generated by colour mixing of monochromatic screen
speckles
3.2 Terms related to colour speckle distribution
3.2.1
colour speckle variance
variance for either of the chromaticity coordinates of colour speckle distribution data, used as
one of the metrics of colour speckle distribution

– 8 – IEC 62906-5-4:2018  IEC 2018
3.2.2
colour speckle covariance
covariance between chromaticity coordinates of colour speckle distribution data, used as one
of the metrics of colour speckle distribution
3.2.3
photometric speckle contrast
photometric speckle contrast ratio
ratio of the standard deviation to the average of the photometric distribution, such as
illuminance, luminance, or luminous flux
3.2.4
colour difference variance
variance of distribution of colour difference of colour speckle between the target chromaticity
in an appropriate colour space
Note 1 to entry: See Annex B.
3.3 Terms related to spatial variation
3.3.1
angular colour speckle variation
variation of colour speckle contrast and variance/covariance with zenith (θ) or azimuth (ϕ)
angles on a point of the projection plane (screen)
3.3.2
photometric speckle contrast uniformity/non-uniformity
uniformity or non-uniformity of photometric speckle contrast on the predefined points of the
projection plane (screen)
3.3.3
colour speckle variance/covariance non-uniformity
non-uniformity of colour speckle variance/covariance on the predefined points of the
projection plane (screen)
3.4 Letter symbols
x(λ)λ,λ,λ, y(λ) , z(λ) Colour matching functions
X, Y, Z Tristimulus values
S (λ) Spectral power distribution for each B, G, R (normalized as unity)
B,G,R
r , r , r , Average power ratio for each B, G, R (r + r + r = 1)
B G R B G R
E Monochromatic speckle (relative illuminance) distributions
E Monochromatic speckle distributions for each B, G, R
B,G,R
M Number of independent coherent light sources
C Monochromatic speckle contrast
s
C Monochromatic speckle contrast for each B, G, R
s−B,G,R
C Photometric speckle contrast
ps
Standard deviation of monochromatic spatial speckle distribution
σ
2 2
Colour speckle variance (CIE 1976)
σ , σ
u' v'
µ Colour speckle covariance (CIE 1976)
u'v'
NU Photometric speckle contrast non-uniformity
ps
NU , NU Colour speckle variance non-uniformity
csu' csv'
NU Colour speckle covariance non-uniformity
csu'v'
3.5 Abbreviated terms
B,G,R (BGR) Blue, green, red
DUT Device under test
FDS Fully developed speckle
FWHM Full width at half maximum
LD Laser diode
LDD Laser display device
LMD Light measuring device
MTF Modulation transfer function
4 Theory of colour speckle
4.1 General
The colour speckle of laser display devices (LDDs) is defined as speckle when the light
source is multi-coloured (see IEC 62906-1-2). It is recognized as fine colour patterns different
from the colour intended to be displayed (see Annex A).
The colour speckle of the LDDs using coherent or partially coherent light sources emitting at
different wavelengths is created by spatially superposing their monochromatic speckle
patterns. Particularly for hybrid LDDs, the colour speckle is also created by superposing such
monochromatic speckle patterns on speckle-less colour patterns generated by incoherent light
sources.
The colour speckle is theoretically obtained as distribution in CIE colour spaces (see CIE
publication 15:2004) using the measured data of monochromatic speckles created by
coherent or partially coherent light sources.
Clause 4 specifies the colour speckle creation mechanism, examples of colour speckle
distribution in CIE 1976 chromaticity diagram and the evaluation indices.
4.2 Mechanism for generating colour speckle
Subclause 4.2 specifies the mechanism for generating colour speckle.
Monochromatic speckle contrast C is expressed as follows:
s
σ
C = (1)
s
< E >
T
where, E is the relative irradiance of spatial distribution for monochromatic speckle, is
T
the total average in the probability density function shown later, and σ is the standard
deviation. Speckle is recognized as an interference pattern projected on human retina.
Therefore, illuminance E on the retina is used here. This is the same definition as in
IEC 62906-5-2.
– 10 – IEC 62906-5-4:2018  IEC 2018
The number of independent coherent light sources is defined as M. Therefore, the probability
density function of speckle is given by the gamma distribution as follows [1], [3] :
M M−1
M E ME
p (E) = exp{− } (2)
M
M
Γ (M ) < E>
< E>
T
T
where, Γ (M) is the gamma function. The number M is usually an integer. However, M can be
used as a decimal number.
Formula (2) is normalized as < E > /M = 1 for the colour speckle estimation. The
T
monochromatic speckle contrast given by Formula (1) is then expressed as follows:
M 1
C = = (3)
s
< E >
M
T
Using Formula (3), the probability density function in Formula (2) is simply rewritten as a
function of C instead of M.
s
−2
C −1
s
E
p(E) = exp(−E) (4)
−2
Γ(C )
s
The illuminance values E at a given C value can be obtained statistically by generating
s
random numbers for the inverse function of Formula (4). However, it should be noted that
E shall be scaled down as E/M because it has already been normalized as < E > /M = 1. This
T
statistical speckle formulation is based on radiometry.
To apply the above radiometric formulation to colour speckle, it is necessary to couple it with
colourimetry. For BGR laser light sources, the normalized spectral power distribution is
expressed as S (λ) (∫S (λ) dλ = 1). To realize the target white point by mixing the BGR
B,G,R B,G,R
, r , r , (r + r + r = 1) shall be determined. The target
colours, the average power ratio, r
B G R B G R
white point is not affected by monochromatic speckles. In actual measurements, it is obtained
by averaging the spatial distribution of each monochromatic speckle. The monochromatic
speckle distributions for each colour are expressed as E . In case of incoherence,
B,G,R
E = 1.
B,G,R
Therefore, the tristimulus values, X, Y, and Z are given by
X = x(λ) ⋅{r E S (λ) + r E S (λ) + r E S (λ)}dλ
B B B G G G R R R
∫
Y = y(λ) ⋅{r E S (λ) + r E S (λ) + r E S (λ)}dλ (5)
B B B G G G R R R
∫
Z = z(λ)⋅{r E S (λ) + r E S (λ) + r E S (λ)}dλ
B B B G G G R R R
∫
where, x(λ) , y(λ) , z(λ) are the colour matching functions.
______________
Numbers in square brackets refer to the Bibliography.

The CIE 1931 chromaticity coordinates, x, y, are given by
X Y
x = , y =
(6)
X + Y + Z X + Y + Z
The CIE 1976 chromaticity coordinates, u’, v’ are thus given by
4x 4X 9y 9Y
′ ′
u = = , v = = (7)
− 2x +12y + 3 X +15Y + 3Z − 2x +12y + 3 X +15Y + 3Z
The above formulation can be applied in this document not only to the case of a narrow
spectral linewidth of BGR LDs but also to the much wider spectra of an incoherent light
source such as phosphor emission.
In the theoretical analysis of the colour speckle distribution, S (λ) shall be given first.
B,G,R
Then the target chromaticity point is determined. Next, the power ratio r , r , r shall be
B G R
calculated to realize the target chromaticity. After that, the monochromatic speckles,
r E S (λ), r E S (λ), r E S (λ) are calculated by generating a random number using
B B B G G G R R R
Formula (4) at the given C values for each B, G, R colour, which are denoted as C , C ,
s s-B s-G
C .
s-R
Repeating the above procedure, the colour speckle distribution x, y can be obtained in the
CIE 1931 chromaticity diagram using Formula (6), or u’, v’ in the CIE 1976 chromaticity
diagram using Formula (7).
If Y only is used, the distribution of the relative illuminance, luminance or luminous flux, as
photometric speckle distribution, can be obtained.
5 Calculation methods of colour speckle
5.1 General
For the calculation of colour speckle, it is necessary to determine the following physical
parameters on the imaging plane:
a) target chromaticity (determine),
b) spectra of light sources (assumed or measure),
c) spectral power ratio of the BGR outputs (calculated to realize the target chromaticity),
d) speckle contrast of the BGR outputs (assume or measure).
The flow charts of the calculation methods of colour speckle are illustrated in Figure 1.
Two calculation methods of colour speckle are given as follows.
1) Method superposing statistically-calculated spatial distribution of BGR monochromatic
, C , C .
speckles using BGR speckle contrast values, C
s-B s-G s-R
2) Method superposing the measured spatial distribution of BGR monochromatic speckles.
The above two methods theoretically reach the same results within the statistical errors based
on the law of large numbers.
– 12 – IEC 62906-5-4:2018  IEC 2018

Colour speckle calculation
Monochromatic speckle measurement
Target chromaticity
BGR spectra
BGR spectra
BGR power ratio
(b)
(a)
BGR spatial distributions BGR spatial distributions
C , C C C , C , C
sB sG, sR sR sG sB
Statistic re-calculation of
BGR spatial distributions
Superposition of BGR spatial distributions
Colour speckle distribution in colour space

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Figure 1 – Two speckle measuring methods and their flow charts
5.2 Measuring method of spectral behaviour of BGR light sources
The normalized spectral power distribution S (λ) (∫S (λ)dλ = 1) shall be obtained to
B,G,R B,G,R
calculate colour speckle distribution because it is necessary for calculating tristimulus values,
X, Y, and Z, as in 4.2.
The spectral measurements should be carried out at the driving currents of the BGR LDs for
the light output powers of each BGR LD realizing the target chromaticity of the measurement.
This is because S (λ) usually varies with the driving currents or modulation method of the
B,G,R
LDs.
The spectral measurement of coherent light sources such as RGB LDs (laser diodes) of which
linewidth is much narrower than LEDs requires an LMD with higher resolution of wavelength,
such as a spectrometer, or a spectrum analyser (see IEC 62906-5-2:2016, 4.5.3; examples of
LD spectra are shown in IEC 62906-5-2:2016, Annex A). The accuracy of S (λ)
B,G,R
measurement affects the calculation accuracy of colour gamut and/or chromaticity coordinates.
The spectral measurement of incoherent light sources with a broad spectrum can be carried
out by the conventional methods.
If the LDD (DUT) uses BGR colour filters, S (λ) shall be measured or calculated through
B,G,R
the colour filters.
5.3 Target chromaticity
The target chromaticity shall be determined for the colour speckle measurement. The target
chromaticity can be chosen at any point within the colour gamut created by the BGR spectral
power distribution S (λ). It should be chosen at a white point because it is easier to
B,G,R
observe an effect of each of the BGR colours on colour speckle distribution.
It should be noted that the target chromaticity is theoretically equal to the average
chromaticity of the colour speckle distribution.

Figure 2 illustrates an example of the chromaticity diagram plotting the colour gamut triangle
for BT.2020 (Recommendation ITU-R BT.2020-2 [6]). The target chromaticity, u’ = 0,198,
v’ = 0,468 corresponds to the BT.2020 reference white point. The BGR points are plotted
slightly inside the wavelength rim because S (λ) is assumed to have a Lorentzian spectral
B,G,R
profile with an FWHM of 2 nm as in Figure 3. This profile is approximately equal to actual
high-power BGR LDs. It should be noted that the peak wavelengths are 449 nm, 520 nm, and
636 nm, which are not perfectly in accordance with BT.2020 parameter values. They are
chosen for comparison with the measured results shown in 5.7, considering availability of LDs.
0,6
500 620
0,5
Target chromaticity
0,4
0,3
0,2
0,1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
u'
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Figure 2 – Target chromaticity and colour gamut
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
400 450 500 550 600 650 700
Wavelength (nm)
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Figure 3 – S (λ) with an FWHM of 2 nm
B,G,R
v'
Relative intensity
– 14 – IEC 62906-5-4:2018  IEC 2018
5.4 Adjustment of BGR power ratio
The BGR power ratio on the projection screen, r , r , r , for the realization of the target
B G R
chromaticity shall be determined as shown in 4.2. This is the method common to the
conventional projector using incoherent BGR light sources. In actual measurements, the
target chromaticity is adjusted by changing the BGR power ratio. For colour speckle
measurements, it is approximately equal to the average chromaticity of colour speckle when
the speckle data are statistically large enough.
An example of the methods for calculating r , r , r is shown below using Figure 4. This
B G R
method has two steps, and considers the line segments from one primary colour point to the
cross-point with the line connecting the other two primary colour points, including the target
point. In Figure 4, the primary colour is green and denoted as the point G, the cross-point with
the BR-segment is denoted as P, and the target point is W. The line segment from G to P on
the BR segment is called the G-BR line.
– Step 1: Calculation of BR power ratio, r’ , r’ (r’ + r’ = 1)
B R B R
The BR power ratio, r’ , r’ is calculated on the BR line first. The point P is the tentative
B R
target chromaticity for obtaining r’ , r’ . It is obtained by changing either r’ or r’ linearly
B R B R
on the BR line.
– Step 2: Calculation of GP power ratio, r , r (r + r = 1)
G P G P
The GP power ratio, r , r is then calculated on the GP line. This time, the point W is the
G P
target chromaticity for obtaining r , r on the GP line. It is obtained similarly by changing
G P
either r or r linearly on the GP line. Using the result of step 1, the final BR power ratios
G P
r and r are obtained as, r = r r’ and r = r r’ , respectively (r , r , r = r r’ , r ,
B R B P B R P R B G R P B G
r r’ , r + r + r = 1).
P R B G R
The above method is applicable to the other line segment arrangements, such as the R-GB
line, or the B-GR line.
As in Figure 4 the BGR power ratio for realizing the target chromaticity (the BT.2020
reference white) is calculated as r , r , r = 0,200: 0,345: 0,456 (see also Figure 3).
B G R
0,6
G 640
0,5
R
W
0,4
0,3
P
0,2
0,1
B
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
u'
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Figure 4 – Adjustment method of BGR power ratio
5.5 Calculation method (a) using BGR speckle contrast C , C , C
s-B s-G s-R
5.5.1 General
The colour speckle distribution can be calculated using the monochromatic speckle
distributions for each colour E as in Formulae (5) to (7) after determination of the
B,G,R
normalized spectral power distribution S (λ) and the BGR power ratio r .
B,G,R B,G,R
The speckle generation is considered as a statistical process expressed as Formulae
(1) to (4). Therefore, the monochromatic speckle distributions for each colour E can be
B,G,R
statistically calculated using Formula (4) if the BGR speckle contrast C , C , C is known.
s-B s-G s-R
Furthermore, E can be obtained by generating a random number in the inverse function
B,G,R
of Formula (4) at the given C , C , C values. For example, as a popular and easy
s-B s-G s-R
approach, common spreadsheets have a gamma distribution function “gamma.dist” and its
inverse function “gamma.inv”. The random numbers can be generated using the function
“rand()”. The cell for calculating E is specified as: = GAMMA.INV(RAND(),$B$2,1)/$B$2.
B,G,R
−2
The value of C is stored in the cell $B$2.
s−B,G,R
Repeating the above procedure up to an appropriate data size, the colour speckle distribution
in the CIE 1976 chromaticity diagram is obtained.
If the values of the BGR speckle contrast C , C , C are assumed, the calculated results
s-B s-G s-R
would be a kind of theoretical simulation which implies an ideal colour speckle distribution
without any background effects under actual experiment conditions. However, if the measured
values of the BGR speckle contrast C , C , C , are used, they are considered as
s-B s-G s-R
measurement results which reflects the actual measurement conditions.
This method is practically useful when the LMD which is designed only for monochromatic
speckles, or when only the measured data of the BGR speckle contrast C , C , C are
s-B s-G s-R
available.
v'
– 16 – IEC 62906-5-4:2018  IEC 2018
The measuring method of the BGR monochromatic speckle contrasts C , C , C is well-
s-B s-G s-R
established as in IEC 62906-5-2. The measurements of the BGR speckle contrasts C , C ,
s-B s-G
C shall be compliant with IEC 62906-5-2.
s-R
5.5.2 Examples of measured distributions
Examples of colour speckle distributions and photometric speckle distributions with the same
speckle contrast values for all colours are given.
Figure 5 illustrates a colour speckle distribution in the CIE 1976 chromaticity diagram, plotting
the chromaticity of each of 10 000 spatial data for the case where C = 100 %, C = 100 %,
s-B s-G
C = 100 %, which is fully developed speckle (FDS). As Kuroda et.al demonstrated in [1],
s-R
the colour speckle distribution spreads all over the gamut triangle formed by the apex points
of the BGR wavelengths. The photometric speckle distribution, such as illuminance,
luminance or flux, is shown in the histogram of Figure 6. The histogram spreads widely from
less than a tenth of the average to more than three times the average.
0,6
0,5
0,4
0,3
0,2
0,1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
u'
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Figure 5 – Colour speckle distribution for C = 100 %, C = 100 %, C = 100 %
s-B s-G s-R
v'
0 1 2 3
Normalized illuminance, E
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Figure 6 – Photometric speckle distribution for C = 100 %, C = 100 %, C = 100 %
s-B s-G s-R
Figure 7 illustrates a colour speckle distribution in the CIE 1976 chromaticity diagram for the
case where C = 50 %, C = 50 %, C = 50 %. The colour speckle distribution becomes
s-B s-G s-R
much smaller than the gamut triangle. The photometric speckle distribution is shown in the
histogram of Figure 8. The histogram distributes more narrowly.
Frequency
– 18 – IEC 62906-5-4:2018  IEC 2018
0,6
500 620
0,5
0,4
0,3
0,2
0,1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
u'
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Figure 7 – Colour speckle distribution for C = 50 %, C = 50 %, C = 50 %
s-B s-G s-R
1 200
1 000
0 1 2 3
Normalized illuminance, E
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Figure 8 – Photometric speckle distribution for C = 50 %, C = 50 %, C = 50 %
s-B s-G s-R
Figure 9 illustrates a colour speckle distribution in the CIE 1976 chromaticity diagram for the
case where C = 10 %, C = 10 %, C = 10 %. The colour speckle distribution is
s-B s-G s-R
Frequency
v'
converging on the target white chromaticity. The photometric speckle distribution is shown in
the histogram of Figure 10. The photometric speckle distribution also converges on the
average within almost 0,8 to 1,2.
0,6
500 620
0,5
0,4
0,3
0,2
0,1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
u'
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Figure 9 – Colour speckle distribution for C = 10 %, C = 10 %, C = 10 %
s-B s-G s-R
v'
– 20 – IEC 62906-5-4:2018  IEC 2018
4 500
4 000
3 500
3 000
2 500
2 000
1 500
1 000
0 1 2 3
Normalized illuminance, E
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Figure 10 – Photometric speckle distribution for C = 10 %, C = 10 %, C = 10 %
s-B s-G s-R
The other specific examples of colour speckle distributions and photometric speckle
distributions are shown in Annex B. The cases when the speckle contrast of one of the
primary colours is 90 % and the others are 1 % are shown in Clause B.1, and the cases when
the speckle contrast of two of the primary colours is 90 % and the other is 1 % are shown in
Clause B.2.
5.6 Evaluation metrics
The evaluation metrics for colour speckle are specified in 5.6.
The photometric speckle contrast ratio C is defined in 3.2.3 as the standard deviation σ to
ps Y
the average of the photometric distribution , such as illuminance, luminance, or luminous
flux. This is mathematically analogous to the monochromatic spe
...