Optimization of an image analysis system for the determination of the crystal quality in sucrose crystal suspensions

Based on an off-line image analysis system consisting of a microscope, a sc anning stage, a monochrome camera, a frame-grabber (analog-digital converte r, a PC and the image analysis software ImageC(R) an analytical method was developed at the Berlin Sugar Institute to meet the requirements for the ch aracterization of the crystal quality in sucrose crystal suspensions. The q uantitative analysis is realized by the contour detection of objects (edge tracking with fixed gray threshold values) and the measurement and calculat ion of object characteristics. By carrying out several automation and adapt ation steps, quality criteria such as crystal size, crystal size distributi ons (frequency as well as mass distribution), conglomerates and false grain content can be calculated automatically by a single course of analysis. Th e possibility of manual interaction guarantees the flexibility of the syste m. The accuracy of detection of objects was improved by mathematical filter operations which, for example, result in an increase of the contrast of ob ject boundaries against the background or in cutting the overlapping crysta ls. On the basis of the projected object area and the minimum Feret diameter, s hape factors of sucrose crystals for the mass calculation were determined, which are to a great extent independent of the crystal shape and the amount of conglomerates. Therefore the calculation of mass distributions and the absolute numbers of crystals in the magma is possible. Significant object c haracteristics were compiled, which permit the classification into single c rystals, conglomerates, false grain and foreign particles lair bubbles).