Particle Image Analysis

Particle properties are rarely defined by size alone. To characterize particles more fully, it is often necessary to evaluate size, shape, count, agglomeration state, and contaminants. Particle Image Analysis is one approach that combines imaging with software-based analysis to measure these properties. Depending on the method, image-based analysis can be performed on static images of prepared samples, on particles in motion, or in in-line/on-line systems for real-time process monitoring. These methods help you understand particle populations and support both R&D and quality control.

1. Image Acquisition: The process begins by capturing an image of the sample. Modern analyzers use bright, uniform lighting to ensure high-quality image capture. 
    
2. Image Enhancement: The acquired image is processed to improve contrast, sharpness, and background uniformity. This step helps make the subsequent particle or phase detection easier and more accurate. 
    
3. Object/Phase Detection: A single image typically contains multiple objects, whose regions can be separated from the background based on brightness differences. Depending on the optical system, objects may appear bright (white) or dark (black). The object and phase regions in the image are then identified and segmented. While well-dispersed objects are easy to detect, touching or overlapping objects may require more advanced algorithms that consider shape and brightness.
    
4.  Measurement: Based on the detected outlines, the final step is to quantitatively measure particle size, shape, and other properties. The resulting measurements can then be summarized as distributions that describe the sample.

Particle Size Accuracy and Minimum Detectable Diameter

Detected particles are represented as groups of pixels. Therefore, particle-size accuracy is determined by the pixel size, that is, the actual length represented by one pixel. In contrast, the minimum detectable particle diameter depends on both the pixel size and the optical system. For example, if a particle image is captured with an optical system that has a 5 µm resolution and a pixel size of 100 nm, the particle size can be measured with an accuracy of approximately 100 nm, while the minimum detectable particle diameter is approximately 5 µm.

Within optical microscopy, Particle Image Analysis can be divided into Static Image Analysis, Dynamic Image Analysis, and In-Line/On-Line Image Analysis. These methods differ mainly in how the sample is presented during image acquisition, which in turn affects throughput, particle tracking, and the type of analysis that can be performed.

- Static Image Analysis: Particles are measured from a stationary sample, typically on a prepared slide. This approach is useful when detailed analysis of individual particles is needed, and it can also support correlative analysis with other techniques.

- Dynamic Image Analysis: Particles are measured as they pass through the field of view. This approach is often preferred when high-throughput statistics are required.

- In-Line/On-Line Image analysis: ​​​​​​Measurements are performed directly in the process, either through a window or via a bypass line. This approach is well-suited for real-time monitoring and continuous data acquisition. 

Please refer to the respective pages for more details.