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different colour filters on a colour sensitive material. A series of different 
products were obtained using different band-filter combinations to find the most 
suitable one. Because of registration problems in producing the enlargements, 
a colour inter-negative was used before making the final product. 
2.4 Use of I 2 S Additive Colour Viewer, Model 6040 
2 
The I S added viewer can hold up to four different 70x70 mm images and project 
them together on a screen with a 2. 6 X magnification through different colour 
filters and illumination intensities. It is possible to move every image in X and Y 
and to rotate them around the centre. 
Registration of images other than the original 70 mm diapositives, which possess 
four fiducial marks, was achieved using a clear physiographic feature in the centre 
of the image of one band as a reference and adjusting the other images accordingly. 
2 
The solution for the best filter, band, and illumination combination on the I S 
addcol viewer was quite a problem. Theoretically the number of possibilities is 
very large with two or three band projections using four filter combinations 
(none, red, green, blue) and an illumination intensity scale ranging from 0 to 10 . 
It was found that each band filter combination should include at least one represen 
tative of the group 4 and 5 (preferably band 5) and one of the group 6 and 7. In 
dealing with the two-band combinations, initially contrasting colours such as red 
and blue were used for a better differentiation. The results, however, were not 
very good, because viewing the picture was tiring, probably due to differences in 
focussing of the human eye for these contrasting colours. A green/blue combination 
for two bands and red/green/blue for three bands proved to be easy. The illumi 
nation adjustment did not give any problems. 
After the selection of the best two-band and three-band combinations (by trial and 
error), the resulting colour composite images were photographed using a 35 mm 
reflex camera (Minolta SRT 101) with both colour negative and colour positive 
films. This was done a) to start a file of colour pictures for future references and 
educational purposes, b) to obtain colour paper prints for the study, and c) to pro 
vide a series of slides for the study of the area at different scales. 
2 
A draw-back of the I S addcol viewer was the fixed magnification of 2. 6 X. Also 
the nearly vertical projection screen is not very suitable for drawing purposes. 
An improved version (model - 6040 PT) of the above addcol viewer has a magnifi 
cation of 6 . 7 X and a nearly horizontal projection screen, which makes this model 
more suitable for visual interpretation purposes at a more suitable scale. Stereos 
copic vision and a zoom facility combined with an ability to move the screen in X 
and Y direction would greatly improve the addcol viewer for visual interpretation 
purposes.