ISO 13322-2:2006
(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
ISO 13322-2:2006 describes methods for controlling the position of moving particles in a liquid or gas and on a conveyor, as well as the image capture and image analysis of the particles. These methods are used to measure the particle sizes and their distributions, the particles being appropriately dispersed in the liquid or gas medium or on the conveyor. The practical limitations of the derived particle size are addressed when using ISO 13322-2:2006.
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
First edition
2006-11-01
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 13322-2:2006(E)
©
ISO 2006
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ISO 13322-2:2006(E)
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ISO 13322-2:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Terms, definitions and symbols. 1
3.1 Terms and definitions. 1
3.2 Symbols. 2
4 Principle. 3
4.1 General. 3
4.2 Particle motion. 4
4.3 Particle positioning. 4
5 Operational procedures. 5
5.1 General. 5
5.2 Still image resolution. 5
5.3 Calibration and traceability. 6
5.4 Size classes and magnification. 6
5.5 Particle edges. 6
5.6 Measurements. 7
6 Sample preparation. 7
7 Sample and measurement variability . 7
Annex A (informative) Particle velocity and exposure time recommended. 8
Annex B (informative) Maximum particle size recommended . 11
Annex C (informative) Typical examples of sample feed and image capture systems . 16
Bibliography . 24
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ISO 13322-2:2006(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 13322-2 was prepared by Technical Committee ISO/TC 24, Sieves, sieving and other sizing methods,
Subcommittee SC 4, Sizing by methods other than sieving.
ISO 13322 consists of the following parts, under the general title Particle size analysis — Image analysis
methods:
⎯ Part 1: Static image analysis methods
⎯ Part 2: Dynamic image analysis methods
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ISO 13322-2:2006(E)
Introduction
The purpose of this part of ISO 13322 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 part of ISO 13322.
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INTERNATIONAL STANDARD ISO 13322-2:2006(E)
Particle size analysis — Image analysis methods —
Part 2:
Dynamic image analysis methods
1 Scope
This part of ISO 13322 describes methods for controlling the position of moving particles in a liquid or gas and
on a conveyor, as well as the image capture and image analysis of the particles. These methods are used to
measure the particle sizes and their distributions, the particles being appropriately dispersed in the liquid or
gas medium or on the conveyor. The practical limitations of the derived particle size are addressed when
using this part of ISO 13322.
2 Normative references
The following referenced documents are indispensable for the application 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 13322-1:2004, Particle size analysis — Image analysis methods — Part 1: Static image analysis methods
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
flow-cell
measurement cell inside which the fluid-particle mixture flows
3.1.2
orifice tube
tube with an aperture through which a stream of fluid with dispersed particles flows
3.1.3
sheath flow
clean fluid flow surrounding particle-laden fluid for directing particles into a specific measurement zone
3.1.4
particle illumination
continuous illumination for image capture device with an electronic exposure time controller, or illumination of
short duration for synchronized image capture device
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ISO 13322-2:2006(E)
3.1.5
measurement volume
volume in which particles are measured by an image analyser
3.1.6
depth of field
region where the sharpness of the edges of the images reaches the pre-set optimum
3.1.7
image capture device
matrix camera or line camera
3.2 Symbols
a moving distance of a particle during time t
A projected area of particle i
i
b measured diameter of binary image
t exposure time
v particle velocity
x diameter of particle
x projected area equivalent diameter of particle i
Ai
x maximum Feret diameter of particle i
imax
x minimum Feret diameter of particle i
imin
ε ratio of the measured particle diameter to the static particle diameter
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ISO 13322-2:2006(E)
4 Principle
4.1 General
A general diagram for dynamic image analysis is shown in Figure 1.
Key
1 dispersed particles
2 device for control of particle motion
3 measurement volume
4 light source
5 optical system
6 depth of field
7 image capture device
8 image analyser
9 display
Figure 1 — Flow diagram for typical dynamic image analysis method
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ISO 13322-2:2006(E)
4.2 Particle motion
Moving particles can be introduced into the measurement volume 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).
4.3 Particle positioning
Particles are introduced into the measurement volume and an image is taken when particles reach the object
plane. The depth of the measurement volume is determined by the depth of field of the optical system used.
Figure 2 shows an example of measurement volume.
Key
1 light source
2 camera
3 measurement volume
Figure 2 — Example of measurement volume
The direction of observation (e.g. parallel or perpendicular) of the particles affects the interpretation of particle
size and shape, as shown in Figure 3. However, this part of ISO 13322 is not concerned with the influence of
particle shape on the overall measurement.
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ISO 13322-2:2006(E)
Key
1 measurement volume parallel to particle motion
2 measurement volume perpendicular to particle motion
Figure 3 — Particle movement and direction of observation
The focus of the image capture equipment shall be adjusted so as to acquire the exact image of the particles
moving in the fluid. There are two recommended ways to achieve this:
a) by controlling the position of the moving particles so that they pass only within the measurement volume
of the image capture equipment;
b) by illuminating the particles for a short time period (e.g. by flash light) or capturing the image of the
moving particles when they pass through the measurement volume of the image capture equipment.
5 Operational procedures
5.1 General
Modern image analysers usually have algorithms to enhance the quality of the image prior to analysis. It is
acceptable to use enhancement algorithms provided that the measured results are traceable back to the
original image.
5.2 Still image resolution
The resolution of an image captured by a dynamic image analysis system depends not only on the optical
system (lens magnification and camera resolution) but also on the lighting system and the velocity of the
particles.
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ISO 13322-2:2006(E)
When a spherical particle of diameter x moves at a velocity v, the centre of the projected area of the particle
moves a distance a during a time t, where t is either the strobe light emission time or camera shutter opening
time (see Figure A.1), i.e.
av=×t (1)
2
Without appropriate grey level handling, a shall not exceed either 0,5 pixel or x × (ε − 1) pixel, where ε is the
ratio of the measured particle diameter to the static particle diameter.
Grey level handling between pixel level and background level should ensure that the measured diameter of
binary image b equals the diameter, x, of the static particle.
The total system resolution should be determined based on the particle size distribution and the desired
confidence limits (see ISO 13322-1).
5.3 Calibration and traceability
The equipment shall be calibrated to convert pixels into SI length units (e.g. nanometres, micrometres,
millimetres) for the final results. The calibration procedure shall include verification of the uniformity of the field
of view. An essential requirement of the calibration procedure is that all measurements shall be traceable back
to the standard metre. This can be achieved by calibration of the image analysis equipment with a certified
standard stage micrometre.
Movement of particles during the capture of particle images, especially for smaller particles, may introduce
serious error in determining particle sizes. It is therefore recommended that the whole system be verified with
a standard reference material under motion.
The calibration particles shall be selected to include the dynamic range of the entire system. It is
recommended to calibrate with three sizes of certified particles, i.e. with values near the maximum, mid-point
and minimum particle sizes to be measured with the system.
5.4 Size classes and magnification
The theoretical limit for resolution of objects by size using image analysis is 1 pixel, and counts should be
stored particle by particle, with the maximum resolution of 1 pixel. However, it is necessary to define size
classes for the final reporting of the result, which is a function of the total number of particles, the dynamic
range and the number of pixels included in the smallest considered objects. It is recommended that pixel size
be converted to actual size prior to any reporting of size for quantitative analysis.
For a system in which not all the particles are measured, large particles may often be positioned on an edge
of the image frame. Therefore, the magnification should be selected so that the maximum diameter of the
largest particle does not exceed one-third of a shorter side of a rectangular image frame of the measuring
area (see Annex B).
It is strongly recommended to address within the report any errors resulting from the loss of information of
larger particles positioned at the edge of an image frame.
Optical resolution, where applicable, is normally better than electronic resolution.
5.5 Particle edges
In an image, the particle edge shall be defined by a suitable threshold level. The technique for doing this
depends on the sophistication of the image analysis equipment.
It is strongly recommended that the threshold level be adjusted by comparing the processed binary images
with the original grey images, in order to ensure that they are a reliable representation of the original grey
images.
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ISO 13322-2:2006(E)
5.6 Measurements
The measurement of the perimeter of a particle is heavily dependent on the image analysis system used. It is
recommended that the primary measurements are:
a) the projected area of each particle in pixels (A ),
i
b) the longest dimension of each particle in pixels (maximum Feret diameter, x ), and
imax
c) the shortest dimension of each particle in pixels (minimum Feret diameter, x ),
imin
thus allowing the definition of a shape factor with the greatest discrimination.
The projected area of each particle can be converted to the area equivalent circular diameter, x .
Ai
4A
i
x = (2)
Ai
π
6 Sample preparation
The number of particles in the dispersion medium shall be controlled so that overlapping images of particles
are not generated.
7 Sample and measurement variability
The measurement of the total number of particles or the total particle number count is possible under certain
conditions. Such methods should ensure that no particles are lost or counted more than once.
The minimum number of particles to be counted shall be based upon the particle size distribution and the
desired confidence limits (see ISO 13322-1).
To incr
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