Verfahren und Vorrichtung zur Messung der Dichtewerte einer Kopiervorlage

Light containing blue, green and red radiation is passed through a colored original which is to be printed on color copy material. The transmitted light is spread out into a color spectrum which extends across a first wavelength range generally corresponding to the blue portion of the spectrum, a second wavelength range generally corresponding to the green portion of the spectrum and a third wavelength range generally corresponding to the red portion of the spectrum. The intensity of the transmitted light is measured throughout the spectrum and average of the resulting raw intensities are taken oer each of a series of wavelength intervals which are much shorter than the first, second and third ranges. The copy material has a gamma value for each wavelength interval and such gamma value represents the spectral sensitivity of the copy material in the corresponding interval. The average intensity for each wavelength interval is multiplied by the respective gamma value to yield a corrected intensity. The corrected intensities for each wavelength range are summed to generate first, second and third sums corresponding to the first, second and third ranges and respectively representing the blue, green and red densities of the original. The first, second and third sums are used to calculate the respective amounts of blue, green and red light required to print the original with a neutral gray density.