The present invention relates to method for processing an image, said image representing a rock sample. The method comprises receiving said image; for each current threshold value in a plurality of threshold values determining a threshold image, the threshold image having pixels associated with a first color value or a second color value, the determination of the threshold image being based on the received image and the current threshold; and for each current connected set of pixels associated with the first color value in the threshold image, determining a connected volume or a connected surface area of said current connected set of pixels. In addition, the method comprises determining numbers of connected sets of pixels associated with the first color value for a plurality of connected volumes or connected surface areas and for a plurality of thresholds.