Method of and apparatus for printing a color image using dichroic

Abstract

A colored original is scanned in each of the three primary colors red, green and blue to generate a series of electrical imaging signals for each such color. The signals are electronically processed and then sent to a cathode ray tube having a screen which is coated with a phosphor. The cathode ray tube successively converts the signals of the different series into optical images having the respective primary colors red, green and blue. The images are formed on the screen of the cathode ray tube thereby exciting the phosphor which luminesces to generate printing light. The differently colored images are successively printed on photographic color paper using the printing light emitted by the phosphor as well as respective red, green and blue filters. The phosphor is a rare earth phosphor which emits strongly in the red region of the spectrum and only weakly in the green and blue regions of the spectrum. The weak emissions in the green and blue regions of the spectrum are compensated for by using dichroic green and blue filters having high transmissivities. On the other hand, the strong emission of the phosphor in the red region of the spectrum is balanced by employing copy paper having relatively low sensitivity in this region. Such compensation and balancing make it possible to achieve equal or almost equal exposure times in the different primary colors.