The American annual of photography . objects distinctly at a distance, the dotsmerging and forming a combination image of a color re-sultant which is the addition of all the colors of adjacent is this latter method and corresponding optical charac-teristic which forms the bajs of the three color processeswith which this article will deal, viz., the Lumiere or Auto-chrome, the Dufay and the Paget. Before proceeding to consider these processes in detail, itwill be necessary to dwell for a moment on another character-istic of colored light, viz., the difference between its action onthe re
The American annual of photography . objects distinctly at a distance, the dotsmerging and forming a combination image of a color re-sultant which is the addition of all the colors of adjacent is this latter method and corresponding optical charac-teristic which forms the bajs of the three color processeswith which this article will deal, viz., the Lumiere or Auto-chrome, the Dufay and the Paget. Before proceeding to consider these processes in detail, itwill be necessary to dwell for a moment on another character-istic of colored light, viz., the difference between its action onthe retina of the eye, and its chemical effect upon a photo-graphic plate. We require of a photographic image that it shall duplicatein proper light relation the object as seen by the eye; how-ever, the ordinary plate or film emulsion is insensitive to theyellow, red and infra red portions of the spectrum and highlysensitive to the ultra violet portion. An object, therefore,illuminated by the uninterrupted light of a bright portion of ii8. w CMI QOOO sky (which is composed in great part of ultra violet) willshow greater contrasts between lights and shadows thanactually exist to the eye. On the other hand, blue and green will come out as whiteor light shades, whereas yellow and red will appear as blackor dark shades instead of the reverse as viewed by the eye. In order to correct this difficulty it is necessary to findsome way of making the emulsion. I :—Insensitive to ultra violet, 2:—Less sensitive to blue, 3 :—Sensitive to red. Considered additively the color yellow is a combination ofred and green so that a transparent object which appearsyellow by transmitted light is one which absorbs blue andtransmits red and green. It is obvious, therefore, that wemay accomplish i and 2 above, that is, eliminate the ultraviolet and subdue the blue by interposing between the emul-sion and object a yellow transparent filter of just the righthue to transmit the proper amount of blue. The in
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