US 4,873,546 A · Color printing method and apparatus

Abstract

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.

Claims30

Dependent claims

A method of copying a colored original onto color copy material, comprising the steps of passing light through said original, said light having blue, green and red components;

forming a color spectrum from the light transmitted through said original, said spectrum extending across a first wavelength range corresponding to blue-containing radiation, a second wavelength range corresponding to green-containing radiation and a third wavelength range corresponding to red-containing radiation, and said copy material having respective first, second and third spectral sensitivities in said first, second and third ranges, said first, second and third spectral sensitivities being represented by first, second and third factors, respectively;
measuring the intensity of the transmitted light in said first, second and third ranges to obtain respective first, second and third raw intensities;
modifying said first, second and third raw intensities by said first, second and third factors, respectively, to obtain first, second and third corrected intensities;
and calculating the amounts of blue, green and red copy light which will produce a copy of said original on said copy material in such a manner that said copy has a desired density, the calculating step being performed using said corrected intensities.

1 more element

An apparatus for copying a colored original onto color copy material, comprising means for illuminating the original with light having blue, green and red components;

means for forming a color spectrum from light transmitted through the original such that the spectrum extends across a first wavelength range corresponding to blue-containing radiation, a second wavelength range corresponding to green-containing radiation and a third wavelength range corresponding to red-containing radiation, the copy material having respective first, second and third spectral sensitivities in the first, second and third ranges;
means for measuring the intensity of the transmitted light in the first, second and third ranges to obtain respective first, second and third raw intensities;
and means for processing the raw intensities, said processing means including storage means for first, second and third factors respectively representing the first, second and third spectral sensitivities of the copy material, and said processing means further including calculating means programmed to modify the first, second and third raw intensities by the first, second and third factors, respectively, so as to obtain first, second and third corrected intensities, said calculating means also being programmed to use the corrected intensities in calculating the amounts of blue, green and red copy light which will produce a copy of the original on the copy material in such a manner that the copy has a desired density.

Dependencies are inferred from the claim text.

Color printing method and apparatus

Life of this patent

Color printing method and apparatus

Life of this patent

Abstract

Claims30