ISO 13322-2:2021
(Main)Particle size analysis — Image analysis methods — Part 2: Dynamic image analysis methods
Particle size analysis — Image analysis methods — Part 2: Dynamic image analysis methods
This document describes a method to transfer the images from particles having relative motion to binary images within practical systems, in which the particles in the images are individually separated. Images of moving particles are created by an optical image capture device. Effects of particle movement on the images are either minimized by the instrumentation or corrected by software procedures. This method is applicable to the particle images that are clearly distinguishable from static background. Further processing of the binary image, which is then considered as static, is described in ISO 13322-1. A dynamic image analysis system is capable of measuring a higher number of particles compared to static image analysis systems. This document provides guidance on instrument qualification for particle size distribution measurements by using particulate reference materials. This document addresses the relative movement of the particles with respect to each other, the effect of particle movement on the image (motion blur), the movement and position along the optical axis (depth of field), and the orientation of the particles with respect to the camera.
Analyse granulométrique — Méthodes par analyse d'images — Partie 2: Méthodes par analyse d'images dynamiques
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 13322-2
Second edition
2021-12
Particle size analysis — Image analysis
methods —
Part 2:
Dynamic image analysis methods
Analyse granulométrique — Méthodes par analyse d'images —
Partie 2: Méthodes par analyse d'images dynamiques
Reference number
© ISO 2021
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ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 5
4 Principle . 6
4.1 Key components of a dynamic image analyser . 6
4.2 Illumination . 8
4.2.1 Time performance. 8
4.2.2 Direction of illumination . 8
4.2.3 Spectrum of illumination . 9
4.2.4 Stability of the light source . 9
4.2.5 Special types of illumination . 9
4.3 Particle motion . 9
4.4 Particle positioning . 10
4.5 Optical system . 11
4.5.1 General . 11
4.5.2 Lens design . 11
4.5.3 Optical magnification . 11
4.5.4 Optical resolution .12
4.5.5 Lens errors. 12
4.6 Image capture device .12
4.6.1 Matrix camera . 12
4.6.2 Line scan camera .12
4.6.3 Exposure time .12
4.6.4 Frame rate/line rate . .12
4.6.5 Sensor resolution .12
4.7 Image analysis methods .13
4.7.1 Image analysis process .13
4.7.2 Robustness of the image analysis method . 13
4.7.3 Image correction . 13
4.7.4 Segmentation methods . 14
4.7.5 Particle classification . 14
4.8 Conversion to meaningful particle descriptors . 14
4.9 Statistical representation of descriptors . 14
4.10 Particle dispersion technique .15
4.11 Systematic corrections dealing with set-up characteristics . 15
5 Operational procedures .15
5.1 General . 15
5.2 Instrument set-up and calibration . 15
5.2.1 Preliminaries . 15
5.2.2 Site of installation. 15
5.2.3 Magnification and sensor resolution . 15
5.2.4 Illumination . 16
5.2.5 Segmentation . 17
5.2.6 Contamination . 17
5.3 Dispersing systems . 18
5.3.1 Preliminary considerations . 18
5.3.2 Particle velocity . . 18
5.3.3 Frame coverage . 19
iii
5.3.4 Medium . 19
5.3.5 Homogeneous dispersion and segregation . 19
5.4 Operational qualification . 20
5.5 Image enhancement algorithms . 20
5.6 Measurements . 20
5.6.1 Particle size and shape . .20
5.6.2 Pixel to length conversion . 20
5.6.3 Size class limits . 21
6 Sample preparation .21
6.1 Sample splitting and reduction . 21
6.2 Touching particles . 21
6.3 Number of particles to be counted . 21
7 Accuracy and instrument qualification .22
7.1 General .22
7.2 Trueness . 22
7.2.1 General .22
7.2.2 Qualification test .23
7.2.3 Qualification acceptance . 23
7.3 Repeatability . 23
7.3.1 General .23
7.3.2 Repeatability test . 23
7.4 Intermediate precision . 24
7.4.1 General . 24
7.4.2 Qualification acceptance . 24
8 Test report .25
8.1 General . 25
8.2 Sample . 25
8.3 Dispersion . 25
8.4 Image analysis instrument . 25
8.5 Analyst identification . 26
Annex A (informative) Theoretical background.27
Annex B (informative) Comparison between particle size distributions by number and by
volume .30
Annex C (informative) Recommended particle velocity and exposure time .31
Annex D (informative) Particle diameter dependence on threshold selection .34
Annex E (normative) Requirements for reference material .38
Annex F (informative) Robustness and ruggedness of the image analysis method .41
Annex G (informative) Optional methods . 44
Annex H (informative) Typical examples of sample feed and image capture systems .45
Bibliography .53
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 13322-2:2006), which has been
technically revised.
The main changes compared to the previous edition are as follows:
— the text has been aligned with changes introduced in ISO 13322-1:2014;
— clauses on instrumentation (principle) and operational procedures have been significantly
expanded;
— a new clause on accuracy and instrument qualification using particulate reference materials has
been added.
A list of all parts in the ISO 13322 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
The ISO 13322 series is applicable to the analysis of images for the purpose of determining particle
size distributions. The purpose of this document is to provide guidance for measuring and describing
particle size distribution, using image analysis methods where particles are in motion. This entails
using techniques for dispersing particles in liquid or gas, taking in-focus, still images of them while
the particles are moving and subsequently analysing the images. This methodology is called dynamic
image analysis.
There are several image capture methods. Some typical methods are described in this document.
ISO 13322-1 on static image analysis methods assumes that an adequate image has already been
captured and concentrates upon the analysis of these images.
vi
INTERNATIONAL STANDARD ISO 13322-2:2021(E)
Particle size analysis — Image analysis methods —
Part 2:
Dynamic image analysis methods
1 Scope
This document describes a method to transfer the images from particles having relative motion to
binary images within practical systems, in which the particles in the images are individually separated.
Images of moving particles are created by an optical image capture device. Effects of particle movement
on the images are either minimized by the instrumentation or corrected by software procedures. This
method is applicable to the particle images that are clearly distinguishable from static background.
Further processing of the binary image, which is then considered as static, is described in ISO 13322-1. A
dynamic image analysis system is capable of measuring a higher number of particles compared to static
image analysis systems. This document provides guidance on instrument qualification for particle
size distribution measurements by using particulate reference materials. This document addresses
the relative movement of the particles with respect to each other, the effect of particle movement on
the image (motion blur), the movement and position along the optical axis (depth of field), and the
orientation of the particles with respect to the camera.
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.
ISO 9276-1, Representation of results of particle size analysis — Part 1: Graphical representation
ISO 9276-2, Representation of results of particle size analysis — Part 2: Calculation of average particle
sizes/diameters and moments from particle size distributions
ISO 9276-6, Representation of results of particle size analysis — Part 6: Descriptive and quantitative
representation of particle shape and morphology
ISO 13322-1, Particle size analysis — Image analysis methods — Part 1: Static image analysis methods
ISO 14488, Particulate materials — Sampling and sample splitting for the determination of particulate
properties
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13322-1 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
acceptable depth of field
depth with respect to the focal depth where the sharpness of the edges of
the particle images is accepted for segmentation
Note 1 to entry: The acceptable depth of field is decided by the software based on the sharpness of the images
and is also dependent on the particle size.
3.1.2
accuracy
closeness of agreement between a test result or measurement result and the true value (3.1.20)
Note 1 to entry: In practice, the accepted reference value is substituted for the true value.
Note 2 to entry: The term “accuracy”, when applied to a set of test or measurement results, involves a combination
of random components and a common systematic error or bias component.
Note 3 to entry: Accuracy refers to a combination of trueness (3.1.19) and precision (3.1.12).
[SOURCE: ISO 3534-2:2006, 3.3.1]
3.1.3
certified reference material
CRM
reference material (3.1.13) characterised by a metrologically valid procedure for one or more specified
properties, accompanied by an RM certificate that provides the value of the specified property, its
associated uncertainty, and a statement of metrological traceability
Note 1 to entry: The concept of value includes a nominal property or a qualitative attribute such as identity or
sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence.
Note 2 to entry: Metrologically valid procedures for the production and certification of RMs are given in, among
others, ISO 17034 and ISO Guide 35.
Note 3 to entry: ISO Guide 31 gives guidance on the contents of RM certificates.
Note 4 to entry: ISO/IEC Guide 99:2007 has an analogous definition.
[SOURCE: ISO Guide 35:2017, 3.2]
3.1.4
flow cell
measurement cell inside which the gas- or liquid-particle mixture flows
3.1.5
frame coverage
fraction of the image area that is obscured by the projection area of all
segmented particles counted in the image
Note 1 to entry: Frame coverage can be expressed as a part or percentage of the image area.
3.1.6
intermediate precision
accuracy (3.1.2) and precision under intermediate precision conditions (3.1.7)
[SOURCE: ISO 3534-2:2006, 3.3.15, modified — "and precision" and the field of application "dynamic
image analysis" have been added.]
3.1.7
intermediate precision conditions
conditions where test results or measurement results are obtained on
different dynamic image analysis instruments and with different operators using the same prescribed
method
Note 1 to entry: There are four elements to the operating condition: time, calibration, operator and equipment.
3.1.8
image capture device
matrix camera or line scan camera for converting an optical image to digital image data
3.1.9
measurement zone
volume in which particles are measured by an image analyser, formed by the measurement frame
including a third dimension from the acceptable depth of field (3.1.1)
Note 1 to entry: The measurement zone is defined by the software (see 3.1.1).
3.1.10
orifice tube
tube with an aperture through which a stream of fluid with dispersed particles flows
3.1.11
illumination
continuous illumination for an image capture device (3.1.8) with an electronic exposure time controller,
or illumination of short duration for a synchronized image capture device
3.1.12
precision
closeness of agreement between independent test/measurement results obtained under stipulated
conditions
Note 1 to entry: Precision depends only on the distribution of random errors and does not relate to the true value
(3.1.20) or the specified value.
Note 2 to entry: The measure of precision is usually expressed in terms of imprecision and computed as a
standard deviation of the test results or measurement results. Less precision is reflected by a larger standard
deviation.
Note 3 to entry: Quantitative measures of precision depend critically on the stipulated conditions. Repeatability
conditions (3.1.15) and reproducibility conditions are particular sets of extreme stipulated conditions.
[SOURCE: ISO 3534-2:2006, 3.3.4]
3.1.13
reference material
RM
material, sufficiently homogeneous and stable with respect to one or more specified properties, which
has been established to be fit for its intended use in a measurement process
Note 1 to entry: RM is a generic term.
Note 2 to entry: Properties can be quantitative or qualitative, e.g. identity of substances or species.
Note 3 to entry: Uses may include the calibration of a measurement system, assessment of a measurement
procedure, assigning values to other materials, and quality control.
Note 4 to entry: ISO/IEC Guide 99:2007 has an analogous definition, but restricts the term “measurement” to
apply to quantitative values. However, ISO/IEC Guide 99:2007, 5.13, Note 3 (VIM), specifically includes qualitative
properties, called “nominal properties”.
[SOURCE: ISO Guide 35:2017, 3.1]
3.1.14
repeatability
precision (3.1.12) under repeatability conditions (3.1.15)
Note 1 to entry: Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the
results.
[SOURCE: ISO 3534-2:2006, 3.3.5]
3.1.15
repeatability conditions
observation conditions where independent test/measurement results are obtained with the same
method on identical test/measurement items in the same test or measuring facility by the same
operator using the same equipment within short intervals of time
Note 1 to entry: Repeatability conditions include:
— the same measurement procedure or test procedure;
— the same operator;
— the same measuring or test equipment used under the same conditions;
— the same location;
— repetition over a short period of time.
[SOURCE: ISO 3534-2:2006, 3.3.6]
3.1.16
sampling volume
volume in which the particles are within the field of view of the image analyser including a third
dimension from the sampling volume depth (3.1.17)
3.1.17
sampling volume depth
length which describes the extent of the particle field in front of the camera
3.1.18
sheath flow
particle-free fluid flow surrounding particle-laden fluid for directing particles into a specific
measurement zone (3.1.9)
3.1.19
trueness
closeness of agreement between the expectation of a test result or a measurement result and a true
value (3.1.20)
Note 1 to entry: The measure of trueness is usually expressed in terms of bias.
Note 2 to entry: Trueness is sometimes referred to as “accuracy of the mean”. This usage is not recommended.
Note 3 to entry: In practice, the accepted reference value is substituted for the true value.
[SOURCE: ISO 3534-2:2006, 3.3.3]
3.1.20
true value
value which characterizes a quantity or quantitative characteristic perfectly defined in the conditions
which exist when that quantity or quantitative characteristic is considered
Note 1 to entry: The true value of a quantity or quantitative characteristic is a theoretical concept and, in general,
cannot be known exactly.
Note 2 to entry: For an explanation of the term “quantity”, refer to ISO 3534-2:2006, Note 1 of 3.2.1.
[SOURCE: ISO 3534-2:2006, 3.2.5]
3.2 Symbols
In this document the symbol x is used to denote the particle sizes. However, it is recognized that the
symbols d and D are also widely used to designate these values (see ISO 9276-2).
a moving distance of a particle during time t
A projected area of particle i after segmentation
i
A projected area of the static spherical particle whose shape has been approximated by an
real
ellipsoid
A projected area of the measured particle whose shape has been approximated by an ellipsoid
meas
b measured size of binary particle image, including effects from motion blur
k coverage factor
q* distribution density
q * distribution density by number
q * distribution density by volume
Q cumulative undersize distribution of quantity r
r
cumulative distribution at selected particle sizes x
Qx()
r
quantity type; number ( r =0), area ( r =2) or volume ( r =3)
r
σ standard deviation of the test samples
s
σ standard deviation
t effective exposure time
T threshold level
u measurement uncertainty
m
u uncertainty of an assigned value of a certified reference material
CRM
u uncertainty of a characterized value of a reference material
RM
U total value of the uncertainty used as the final acceptance/rejection limits for qualification tests
lim
v particle velocity
x particle size
x
particle size corresponding to 10 % of the cumulative undersize distribution
10,r
x particle size corresponding to 50 % of the cumulative undersize distribution
50,r
x particle size corresponding to 90 % of the cumulative undersize distribution
90,r
x area equivalent diameter
A
x area equivalent diameter of a static particle
A,real
x area equivalent diameter of the measured particle
A,meas
x Feret diameter of projected area perpendicular to the direction of motion
F
x projected area equivalent diameter of particle i
A,i
x maximum Feret diameter of particle i
Fmax,i
x minimum Feret diameter of particle i
Fmin,i
ε ratio of the measured particle size b (under motion) to the static particle size x
4 Principle
4.1 Key components of a dynamic image analyser
Each system designated as a dynamic image analyser consists of the following essential key components.
Additionally, some optional components can be used to either enhance the quality of the measurements
or to deal with particular set-up characteristics:
a) essential:
— illumination,
— particle feed,
— optical system,
— image capture device,
— image analysis,
— conversion to meaningful particle size parameters, and
— statistical representation of descriptors;
b) optional:
— particle dispersers, and
— particle positioning.
A general diagram for dynamic image analysis is shown in Figure 1 and Figure 2. The illumination can
be set-up in a transmitted light arrangement (see Figure 1), in a reflection arrangement (see Figure 2)
or in a combination of both. In a reflection arrangement, a reflecting device, the vessel wall or even the
particles can reflect the light back through the measurement zone as transflected light. The type of
lighting has a great influence on the appearance of the particle images.
Key
1 dispersed particles 6 particle flow
2 device for control of particle feed (optional) 7 image capture device
3 measurement zone 8 image analyser
4 illumination 9 representation of results
5 optical system
Figure 1 — Flow diagram for typical dynamic image analysis method (transmission set-up)
Key
1 dispersed particles 8 image analyser
2 device for control of particle feed (optional) 9 representation of results
3 measurement zone 10 angle of illumination (can be set-up to zero)
4 illumination 11 reflected light from particles
5 optical system 12 reflecting objects (mirror, wall or particles, optional)
6 particle flow 13 transflected light
7 image capture device
Figure 2 — Flow diagram for typical dynamic image analysis method (reflection set-up)
4.2 Illumination
4.2.1 Time performance
4.2.1.1 General
An optimum exposure time is a crucial component of proper imaging. In principle, there are two
different methods to achieve a time performance balanced between minimised motion blur and
sufficient contrast. In both cases, the instrument manufacturer shall care for providing as much
intensity as required for sufficient contrast between background and particles.
4.2.1.2 Pulsed illumination
At first, limiting the exposure time via short light pulses has been a method for several decades. Various
electrical illumination sources in combination with condenser and collector lenses such as electric
discharge flashlight bulbs, light emitting diodes (LED) and laser diodes have different properties like
slew rate when switching on and off, light intensity, stability and durability.
4.2.1.3 Continuous illumination
The second method uses a permanent light source while the capturing device itself electronically
handles the exposure time (shuttered detection). Typically, cold cathode fluorescent lamp (CCFL) tubes,
permanent LED grids or lamps in combination with condenser and collector lenses are used. Another
solution is the usage of an adapted wide light screen.
4.2.2 Direction of illumination
4.2.2.1 General
At least two different set-ups are widely common: illumination from the back of the particles
(transmission set-up, see Figure 1) or direct illumination from the front with an angle between the
direction of illumination and that of observation (reflection set-up, see Figure 2). Both methods
shall care to have sufficient contrast between background and foreground (particles) and hence for
detectable particle edges.
4.2.2.2 Back illumination
Back illumination requires a set-up with a light source and image capture device at opposite sides of
the particles. Back illumination provides a projection area like a shadow of the particle perpendicular
to the direction of observation (shadow or bright field method). Parallel light minimises reflected light
on the sides of the particles which can otherwise reduce the contrast of the image edges. The method
should cope with the challenge of (partially) transparent particles creating even more complex shadow
structures. It delivers the projection area of the particle and information about its shadow’s shape
whereas colour and 3D information of the particles on the single instance are lost.
4.2.2.3 Illumination from the front and other directions
Front illumination is widely used in classic photography, for example, flashlights or ring illumination
mounted near to the camera lens. As in photography the capturing device as well as the subsequent
image processing should deal with the classical drawbacks of this set-up like reflections, deflections
and refractions. As for back illumination, the image quality of the edges becomes important for the
quality of the results. For the reflected light used to obtain the information about the particles, some
information of the visible particle surface and the edges is obtained.
4.2.3 Spectrum of illumination
4.2.3.1 Polychromatic
Polychromatic illumination allows for colour information of the particles whereas additional errors like
chromatic aberration should be taken into account. In addition, the position of the particle edges and
possible blurs can depend on the used spectrum. Typical light sources providing polychromatic light
are the classic flashlight, daylight, incandescent lamps and some multiply coloured LEDs.
4.2.3.2 Monochromatic
As a consequence of using single-colour LEDs or lasers for illumination monochromatic light is also
used. Obviously, no colour information is obtained. Using laser light for illumination of the capturing
device, the image evaluation respectively should deal with speckles and interference effects from the
coherent light source.
Together with the numerical aperture of the imaging lens, the wavelength of the illumination limits the
theoretical maximum optical resolution of a lens (see Reference [4]).
4.2.4 Stability of the light source
All systems should illuminate the particles' images captured at different times with at least comparable
intensity to avoid later contrast or segmentation fluctuations or even imaging artefacts. Illumination
stability should be given in the long run as well as from image to image (pulse-to-pulse). Instability
should be handled by using adapted segmentation algorithms.
4.2.5 Special types of illumination
4.2.5.1 Dark and bright field illumination
Some special types of illumination can enhance the contrast of fine structures, for example, dark field
illumination where the unscattered beam from the illumination is excluded from the image. The main
limitations of dark field microscopy are the low light levels in the final image and the interpretation of
the image structures.
Bright field microscopy can use critical or Köhler illumination to increase the optical resolution, but
then bright field microscopy typically has low contrast with transparent particles.
4.2.5.2 Polarized light
Polarized light and filters can be used to enhance the contrast by using optical phase contrast
microscopy techniques.
4.3 Particle motion
Moving particles can be introduced into the measurement zone by three means:
a) particle motion in a moving fluid (e.g. particles in suspension, in an aerosol, in a duct, in an air jet, in
a sheath flow, in turbulent flow or in a push-pull flow regime);
b) particle motion in a still fluid, i.e. in an injection or free-falling system, where particles are
intentionally moved by an external force (e.g. gravity, electrostatic charge);
c) particle motion with a moving substrate, where particles are on the moving substrate (e.g. conveyor
belt), provided that the frame coverage of the particles is low and the particles are separated.
4.4 Particle positioning
Images are taken when particles reach the measurement zone. The depth of the measurement zone in
front of the image capture device is determined either by the sampling volume depth of the particles (i.e.
the width of a flow cell) or by the acceptable depth of field. The acceptable depth of field is a combination
of the depth of field of the optical system together with a software decision to accept or reject blurred
particle images. The acceptable depth of field and thus the measurement zone effectively depends on
the particle size (see D.3). There are two possible arrangements for a dynamic particle image analyser.
a) The particle movement can be controlled in order for all particles to be within the acceptable depth
of field of the smallest particles measured. By using this arrangement, all particle images in the
measurement frame shall be accepted for segmentation. Figure 3 shows an example of this type of
arrangement.
b) The particles can be allowed to move freely into or out of the acceptable depth of field. Since
all recorded images of particles detected outside the acceptable depth of field shall be rejected,
corrections to the proportions of the particle numbers shall be applied to the result. Figure 4 shows
an example of this type of arrangement.
NOTE The particles can also be allowed to move freely into or out of the acceptable depth of field if the
focus of the image capture equipment can be controlled fast enough to acquire the exact image of the particles
moving in the fluid for example by capturing the image of the moving particles only when they pass through
the measurement zone of the image capture equipment. In this case, a correction of the particle count is not
necessary.
It is also required that the particles move freely relative to each other. It is also necessary that all
particles traverse the measurement zone at the same velocity if the effects of velocity bias are to be
avoided. If the different velocities are known, corrections may be applied as if the particles travel at the
same speed.
The orientation of th
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