Petrographic Microscope Digital Image Processing Technique for Texture and Microstructure Interpretation of Earth Materials

The technique of description and characterization of rocks with the aid of a polarized light microscope is a well-established practice in the fields of mineralogy and petrology. However, because geological materials are inherently highly variable on a small scale, capturing good-quality images, particularly of the fine details present in the mineral grains that compose the rock, is the main difficulty encountered when a thin section is examined under a petrographic microscope. Combining petrographic concepts and digital image processing methods, the principal aim of this paper is to provide a practical approach to digital image treatment with specific software, and its immediate application in the micromorphological characterization of minerals. In addition to the basic calibration of color, brightness, and contrast, three different methods of digital image processing in the spatial domain, following the principles of embossed surface, negative image, and edge detection techniques, were applied to the images. The use of these primary filters was found to be efficient for detailed characterization of the mineralogical phases involved in the different types of microstructures. However, special care must be taken regarding the sensitivity and accuracy parameters to avoid the exclusion of information or the addition of noise to the image. Although research has focused on the distinction of several types of textural features in rock-forming minerals, these techniques can be employed in other areas of investigation, in both academic and industrial settings, to diagnose textures of microtectonic deformation, soil micromorphological features, the proportions of the original ingredients in concretes, and the mineralogical modal determination of ceramics of archeological origin and to characterize mineral raw materials for the manufacture of technological products.