Game Development Reference
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Zone of observation
3.5
3
2.5
f
Prohibited
area
2
f
1.5
f
1
f
0.5
z max
Prohibited area
0
S
Z p o
Figure 13.11 Zone of observation possible without ocular strain as per the focal lengths
between 16 and 32mm and also for a zone of observation more than 1.5m (all values
can be > 1 . 5m for z p 0 in this case). On the other hand, if the zone of observation
is between 1 and 1.5m, it is limited (depending on f ) around the distance z p 0 that
must be the distance from the main object observed. Viewing with wide focal length
f > 48mm is done with depth flattening. Near vision (less than 1m) is very difficult.
It can only be accomplished with low focal length and only if the objects observed are
at an approximate depth.
These theoretical calculations on the acceptable viewing areas were verified exper-
imentally. The results of tests on stereoscopic vision in the same conditions confirm
that areas are unobservable for some values of focal lengths of zoom lenses. In practice,
this prompts us to prohibit the operator from selecting f and z p 0 that do not respect
the constraints. Thus, we prevent the conditions which are unsuitable for stereoscopic
vision through software. The study in case of cameras with convergent axes shows
similar conditions and curves that the reader can find in our paper by Fuchs et al.
(1995).
13.1.4 LIMITATION OFVISUAL STRAIN
IN STEREOSCOPICVISION
13.1.4.1 Problem of visual strain
We mentioned in chapter 3 on “the senses of man'' that easy fusion of two stereoscopic
images depends on their parallaxes at all homologous points and also on their spatial
frequencies in these homologous points. We wish to limit the visual strain due to stereo-
scopic screens not only by controlling the disparity between left and right images but
also by controlling the spatial frequency content of images. This method is thus more
effective than the one described previously because now in addition to disparity we are
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