ISO/TC 24/SC 4/WG 8 - 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.

ISO 13322-1:2014 is applicable to the analysis of images for the purpose of determining particle size distributions where the velocity of the particles against the axis of the optical system of the imaging device is zero. The particles are appropriately dispersed and fixed in the object plane of the instrument. The field of view may sample the object plane dynamically either by moving the sample support or the camera provided this can be accomplished without any motion effects on the image. Captured images can be analysed subsequently. ISO 13322-1:2014 concentrates upon the analysis of digital images created from either light or electron detection systems. It considers only image evaluation methods using complete pixel counts.

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.

ISO 13322:2004 is applicable to the analysis of images for the purpose of determining particle size distributions. The particles are appropriately dispersed and fixed on an optical or electron microscope sample stage such as glass slides, stubs, filters, etc. Image analysis can recover particle images directly from microscopes or from photomicrographs. Even though automation of the analysis is possible, this technique is basically limited to narrow size distributions of less than an order of magnitude. A standard deviation of 1,6 of a log-normal distribution corresponds to a distribution of less than 10:1 in size. Such a narrow distribution requires that over 6 000 particles be measured in order to obtain a repeatable volume-mean diameter. If reliable values are required for percentiles, e.g. D90 or other percentiles, at least 61 000 particles must be measured.