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The ratio here considered in steps of different value gives 
a description taking into account the correction of the dif 
ferent angular position of the targets towards the incident 
light. In fact the cosine characterizing the position of a 
target is the same for the different bands. 
Visible and photographic I.R.: multispectral electronic techniques 
a) Slicing. 
The slicing of an image is achieved by scanning the pho 
tography with a TV camera followed by an electronic slicer. 
This device consists primarily of a series of triggers. 
Each couple of triggers forms a " simple window discrimina 
tor" . With an electronic system we change the position and 
the width of the level by changing the offset of the video 
signal and the triggers threshold(analogue to the exposure and 
yellow filter density in the AGFA contour chemical system). 
b) Electronic images chopper. 
The device which is presently in an experimental stage 
( Fig. 2) is designed for the treatment and emphasization of 
the colour images. It consists of a Tv camera pointing one 
colour and/or I.R. false colour image through a wheel holding 
filters blue, green and red. The signals corresponding to 
blue green and red content of the image are switched to three 
video amplifiers able to modify amplitude offset and sign of 
the original information. In this way the original colours 
are converted in other hues in such a manner that they increa 
se the interpreter capability of distinguishing very little 
chromatic contrast. The same system is able to carry out the 
" cross density slicing" seen before in the photographic pro 
cesses. The signals corresponding to the blue, green and red 
filters are sliced each at a chosen level (with the same width). 
What is needed now is a reference point, completely known 
( ground truth ) which has to be contained by each of the three 
isolevels. ’ We solve in this case the same system of before: 
band A = K-j ; band B = band C = 
with K,j , K 2 , characteristics of the ground truth. 
c) Digital approach. 
A slow TV camera scans the colour and/or the I.R. false 
colour image storing the information, converted by an A/D unit, 
in the computer memory. Then the quantified modulations of 
the three bands are compared making the ratios: 
A 
B 
K< 
K 
n 
H 
n