This list shows that many of the processes usually implemented in digital 
software can be realised with optical means, with the added advantage of 
interaction with the interpreter who can make use of all the spatial, 
textural and colour clues presented to him on the screen (or print). 
SPECTRAL SIGNATURE DETECTION USING THE FLICKER EFFECT 
As far as the authors know, the flicker effect has been used only for 
change detection. This observation and the interest of ITC in 
intermediate technology for developing countries has led to the construction 
of the so called "caroussel". The"caroussel" has been constructed as an 
8—image (colour) additive viewer with 8 independently operating shutters 
for flicker presentation. 
THE PRINCIPLE OF USING THE FLICKER EFFECT 
For a time-varying intensity the eye acts as if it were a low pass 
filter with a certain threshold for detecting variation in the presented 
itensity signal. 
Fig. 1 illustrates this model: 
fig. 1a Presentation of a low frequency (\^) variation in intensity If» 
to the eye. The variation will be detected because the variation 
at the output to is greater than the threshold THR. 
Io > THR -—flicker detected. 
fig. 1b The frequency ^ i- s n £ w 4x^1 "the corresponding H-2 much lower than 
H^so is Io. Because Io < THR no flicker is detected in this case.