GRAIN SORTING MACHINE

PROBLEM TO BE SOLVED: To obtain a grain sorting machine by which grains can be sorted precisely so as to correspond to a change in a detection level caused by a changing light source or the like by a method wherein a reference density value (a threshold value) is initialized on the basis of a density pattern for every pixel and it is reset at every prescribed time. SOLUTION: A front camera and a rear camera are line sensor cameras provided with 512 pixels, and they photograph a region to be photographed. A video signal 116 for a photographed image is sent out to a CPU 102. The CPU 102 sequentially receives the video signal 116 for the image photographed at the respective 512 pixels. The CPU 102 computes data on a threshold value for every pixel so as to be stored in an S-RAM 124. In addition, in order to deal with a time-dependent change in a light source, the CPU 102 periodically updates the threshold value. That is to say, since the quantity of light of the light source is unstable for about 30 minutes from the start of its operation, the threshold value is updated every five minuted, and it is updated every 30 minutes after the quantity of light has been stabilized. Since the corrected threshold value is set for every pixel, a grain sorting treatment can be performed with high accuracy.