Image analysis of particles is effectively determining particle physical parameters from pictures.
Particle size and shape can be determined with photos of the particles. Since a typical particle sample consists of a range of size and shapes, modern analysis is done with a computer that automatically analyzes particle images to rapidly determine size and shape. Data from a large number of particles can then be summarized into distributions that describe the sample.
The major steps for image analysis of particles. First, high quality images are acquired, then the particles (or second phase for an emulsion) are identified. Finally, size and shape parameters are extracted for analysis of the population.
There are three major steps in image analysis: image acquisition and enhancement, object detection, and measurement. The first step, image acquisition is easily phrased as taking a photograph. However, modern analyzers all include features to ensure high quality images with, for example, bright, uniform lighting. The major differences between the image analysis techniques presented here are primarily in the approach to image capture.
Object/phase detection can be simple for well dispersed particles and can be extended to include special lighting and software algorithms to separate touching particles. The final step is computation of the desired parameters for particle size and shape of each particle. This data is build up to generate a distribution from which population statistics can be extracted.
These steps are independent of the imaging method. The sizes that can be measured depend on the wavelength of the radiation used. For the smallest particles, electron microscopes can provide data, at the cost of challenging sample preparation and expensive equipment. For particles that are over about ½ micron in size, visible light (optical microscopy) is preferred.
When using visible light, the particle image analysis can be further broken down into dynamic image analysis, static image analysis, and in-line image analysis. And generally these different techniques primarily represent differences in image acquisition.
Dynamic image analysis refers to a laboratory technique where the particles are passed in front of the camera optics. Static image analysis refers to a laboratory technique where the particles are on a stationary slide. In contrast, in-line image analysis is used directly on a process where the particles are passing by a window on a pipe or piece of process equipment, such as the bottom of a fluidized bed coater.
Each technique has advantages and disadvantages and the best technique depends on the application. Contact us for guidance on your instrument selection.
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