We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
514 History of Three-Color Photography
measurements as to the diffusion of the light, and the consequent degradation of the sharpness, etc. He pointed out that the reason why Chaboseau found no reduction of exposure was due to the latter having used a matt surface, but that a glazed one gave different results.
The first test was two transparent plates laid side by side, one red and the other green ; and these were photographed on one plate, one half being backed by a white and the other by a black card. All appreciable diffusion would thus be rendered visible in consequence of those rays reaching the backing from the test object being diffused to that part of the plate representing the greens of the test object. There would thus be produced by this, an analagous diffusion of green to red, a central band of greater or less width and more or less completely free from color. But the results when examined under a lens, showed a perfectly denned and clear line where the black and white cards joined. Nor was there any appreciable alteration of the colors. It was found on microscopic examination that the sharpness on both plates was the same up to the limit of the resolving power of the emulsion. Comparative side by side exposures proved that with the glazed card there was a reduction of exposure of about one-third. It was only necessary to slip the glazed card between the usual black one and the plate, but as the glaze was due to gelatin care should be taken that it was not damp.
It should be pointed out that R. Colson19 stated that the use of a white card behind an ordinary plate reduced the exposure, and that the same emulsion coated on glass and paper was faster on the latter, due to the reflection of light from the white surface. The author tested this statement with very careful experiments by the Hurter and Driffield system, and could find no increase in speed, though there was a slight increase in fog.
H. Quentin20 stated that there was no advantage in this method, and assuming that one had an orange-yellow color, which was formed of 25 green, 100 red and 0 violet, then if it was assumed that an additional 5 was* added to these colors, the result would be green 30, red 100, as this was the maximum attainable, and violet 5, with the result that the color would be paler. G. Henry21 and Comte de Dalmas raised the question of the diffusion of the light. Benoist22 pointed out that the increase in exposure thus obtained would also increase the overexposure, and to this he ascribed the assumption that it was a case of diffusion fog.
The Compensating Filter. — The purpose of this is to so adjust the action of light on the sensitive emulsion that the colors shall be rendered with correct visual luminosity. Therefore, it must be accurately adjusted to the sensitiveness of the emulsion under the screen elements. The methods of making suitable filters have already been given when dealing with filters generally.
G. Eastman23 patented the incorporation of the compensating filter in