PURPOSE: To easily set up the upper limit values and lower limit values of some colors out of three color elements R, G, B by the small quantity of data even when there are many objects to be identified or respective colors are similar.

CONSTITUTION: Processing capable of resisting a change in a lighting condition can be attained by converting data to be processed from R, G and B into I=R+G+B, r=R/I and g=G/I and using the rate of colors expressed by (r) and (g) normalized by brightness information mainly for the processing. While observing the (r) and (g), a two-dimensional histogram relating to the (r) and (g) of an object to be processed is formed, a feature color is extracted based upon the distributed state of the histogram, an upper limit value and a lower limit value corresponding to the color are automatically set up and relation between the number of picture elements counted based upon the upper limit value and lower limit value corresponding to the color and the object to be identified is automatically constructed.