Scanning Microscopy


Image analysis is a technique for determining quantities, grain size distributions, grain orientations, intergrowths, associations, liberations and degrees of alteration of minerals or phases in naturally occurring and processed materials. It is performed by analysing images of polished or thin sections of the material under study. To obtain accurate results the images must be faithful reproductions of the material, and each mineral or phase displayed in the images must be distinct enough to be automatically discriminated and identified without operator interaction. An image analysis system that meets these requirements was developed in the Process Mineralogy Section at CANMET by interfacing a microprobe, an energy dispersive X-ray analyser (EDXA), and an image analyser with communication in both directions between the units. The analytical procedure involves transferring a backscattered electron image (BSE) from the microprobe to the image analyser. The minerals or phases are discriminated and identified on the basis of their grey levels in the image. If the grey levels of two or more minerals or phases are too close for discrimination and identification, the minerals or phases are identified by scanning each grain with the electron beam of the microprobe under control of the image analyser, and analysing the grains with the EDXA. To perform the analysis a binary image is produced for each mineral displayed in the BSE image and prepared for analysis by using a variety of image analysis routines. The binary images are analysed and the data are classified, summarized and output in simple tables and graphs.

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