METHOD AND AN APPARATUS FOR DETECTING THE BASE CONCENTRATION OF A PHOTOGRAPHIC FILM

A method of detecting the base concentration of a film comprises the steps of generating a concentration histogram from the film image in each of the RGB color components, shifting and stretching the histograms in the other colors towards the histogram in the reference color in the concentration axial direction, calculating an superimposed area between the two histograms in the two color components after the stretching process, and finding the shift rate and the stretch ratio when a total of the respective superimposed areas calculated is the greatest value. As the minimum of the lowest concentration in the histograms at the shift rate and the stretch ratio determined is specified to represent the location of the base concentration in the original histogram, the base concentration in each color component of the film can be calculated from the location of the base concentration in the histogram.