What exactly is particle size and particle shape?
Describing a 3D particle is often a more complex matter than it first appears.For simplicity it is convenient to describe particle size as one single number. However, unless the particle is a perfect sphere (which is rare in ‘real-world’ samples) there are many ways to describe the size of a particle.
Image analysis systems capture a 2-dimensional image of the 3D particle and calculate various particle size and particle shape parameters from this 2D image. Calculating size and shape parameters like the ones shown in the list below allow even the most subtle differences to be identified and quantified.
Parameter |
Example value |
Definition |
CE diameter (µm) |
904.14 |
The diameter of a circle with the same area as the particle |
Length (µm) |
1306.35 |
All possible lines from one point of the perimeter to another point on the perimeter are projected on the major axis (axis of minimum rotational energy). The maximum length of these projections is the length of the object. All possible lines from one point of the perimeter to another point on the perimeter are projected on the minor axis. The maximum length of these projections is the width of the object. |
Width (µm) |
678.54 |
Largest distance between any two pixels in particle |
Max. Distance (µm) |
1318.07 |
Actual perimeter of particle |
Perimeter (µm) |
3619.42 |
Axis of minimum rotational energy |
Major axisº |
105.52 |
Actual area of particle in sq. microns |
Area (µm2) |
371550.78 |
Number of pixels in particle |
Area (pixels) |
215018 |
Circumference of equivalent area circle divided by the actual perimeter of the particle |
Circularity |
0.785 |
= 2 x square root (π Area)/Perimeter |
HS Circularity |
0.616 |
High sensitivity circularity (circularity squared) =4 πArea/perimeter2 |
Convexity |
0.919 |
Convex hull perimeter divided by actual particle perimeter |
Solidity |
0.905 |
Actual particle area divided by convex hull area |
Aspect ratio |
0.519 |
Width divided by length |
Elongation |
0.481 |
1 - aspect ratio |
Intensity mean |
61.310 |
Average of all the greyscale values of every pixel in the particle |
Intensity standard deviation |
29.841 |
Standard deviation of all the greyscale values of every pixel in the particle |
Centre x position (µm) |
6898271.5 |
x co-ordinate of centre of mass of particle |
Centre y position (µm) |
1797186.3 |
y co-ordinate of centre of mass of particle |
More information:
Image analysis systems from Malvern:
Malvern offers three image analysis systems. These image analysis systems have been developed specifically for routine and repeatable particle size and particle shape analysis. The choice of instruments depends upon the nature of the application and sample form:
Morphologi G3 - High sensitivity particle analyzer The Morphologi G3 is based on automated microscopy and enables characterization of particle size, particle shape and particle count in wet and dry materials in the range 0.5µm to 3000µm.
Sysmex FPIA-3000 - for wet samples (suspensions and emulsions). The Sysmex FPIA-3000 is based upon flow cytometry and enables characterization of particle size and particle shape of wet materials in the range 0.8µm to 300µm.
Sysmex FPIA-3000 - for wet samples (suspensions and emulsions). The Sysmex FPIA-3000 is based upon flow cytometry and enables characterization of particle size and particle shape of wet materials in the range 0.8µm to 300µm.
