To enable application to a granular specimen wherein particles overlap without gaps, by picking up the image of the specimen, performing the A/D conversion of the image signal, detecting the picture element when the lightness changes across a specified value or one of a plurality of specified values in a specified direction, as a change point, and counting the number of picture elements.
An image signal of a granular specimen 10 which is picked up by a CCD camera 14 is A/D converted 16, and sent to a binary part 18, and a binary image is formed. A horizontal change detecting part 20 and a vertical change detecting part 22 detect a picture element wherein the binary image changes from '0' to '1' or from '1' to '0' in the horizontal and the vertical directions, as a change point from the binary image obtained by the binary part 18. A counting part 30 counts the number of picture elements which are detected as the change point by at least one out of the horizontal change detecting part 20 or the vertical change detecting part 22. A grain diameter calculating part 32 calculates the average grain diameter of particles of the specimen 10 on the basis of the number of the picture elements counted by the counting part 30.
KINOSHITA KATSUTOSHI
DOU MICHIHISA
