This procedure makes use of the principle employed in the transmission of images through the distance (phototelegraphy, television) by analyzing the original, dot by dot, and by reproducing it in the same manner. The original’s reading circuits or those of the subsequent amplification of the electric impulses provide the means for selection in the original of a certain band of optical densities; this band will be enhanced at a maximum in the reproduction, from the white (density 0) to the black (density 3 or more). There is included a sample of a reproduction at great contrast obtained with the rudimentary apparatus built on this principle.
The high degree of amplification of contrast which can be obtained with this procedure of quick and easy application makes it possible to show objects, details, and shapes in the reproduction unseen in the original; furthermore, it makes it possible to obtain reproductions at normal contrast of photographs and x-rays taken with a considerable reduction in the time of expoure.
PABLO DAUMAS LADOUCE, "Procedure for the Reproduction of Images with Amplification of Contrast," J. Opt. Soc. Am. 44, 464-464 (1954)