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Procedures for preparing a series of photographs of 
contiguous areas must include provisions for retaining 
the ground reflectance relationship between scenes. 
In practice this implies that all scenes reproduced 
would receive identical treatment. Compared with 
conventional color reproduction of terrestrial color 
photographs, when conditions are tailored to one specific 
scene, departure from true ground reflection levels is 
significant. It became evident that a project concept 
for density control was necessary. 
To correct conditions due to sun angle effect (see 
Figure 3) where a contrast shift of the imagery is 
evident, the preparation of silver masks was undertaken 
using the original film and a contact printer. 
Zero shadow 
perspective angle sun angle 
lens perspective 
Figure 3»—Sun angle diagram 
The use of an automatic dodging printer such as the 
LogEtronic Mark IV (MRK IV) was not used for this 
procedure due to the nature of the black-and-white 
reproducing cathode ray tube (CRT). The blue-white 
phosphor in the CRT would not permit the accurate 
recording of the colors in the original film. Instead 
a tungsten, single white light source, nondodging 
printer was used to prepare the silver masks. 
One mask was fabricated for each quad-centered exposure, 
using Dupont EN-7 film, in conjunction with the aerial 
film to prepare the RED, GREEN and BLUE separates. 
The implementation of the silver mask rendered a den 
sity-contrast balanced exposure. However, since the 
project contains close to 200 quadrangles, the tailoring 
of individual exposures proved too costly and time con 
suming. For these reasons other approaches to solve the 
problems were considered.