Abstract: The shape changes of the minerals on the surface reflect the deformation/failure process of the rock material. In the current study, after analyzing the textual features of various mineral regions on a granite specimen surface, the video images photographed during the laboratory uniaxial compression test and the grayscale threshold segmentation were used to investigate the distributions of the minerals in each frame. The shape parameters were extracted from the frame to depict the configuration features of various compositions at any time during the deformations of the rock. The relations between the changes in shape parameters of various compositions and the propagation process of cracks were further explored. It is shown that during the deformation of the granite under the external load, the magnitude sequence of the circularity is feldspar, biotite, and quartz; that of the inscribed circle radius is biotite, feldspar, and quartz; and that of the variance index is feldspar, biotite, and quartz; the feldspar region beard the most part of the axial load; and the shape changes of the feldspar regions are much depended on the actual locations; during the failure of the specimen; the magnitude sequences of the areas are feldspar, quartz, and biotite where new cracks generated; and the most of the cracks propagated on the feldspar and quartz regions if the cracks developed quickly.

Key words: granite, test video, image processing, shape feature