Figure 4.2 shows the process of overlapping. Shown here are 3 poles each at a different depth from the other. Longer
one is at the front most, followed by medium and short. The distance between the two poles is not the same. Consider
viewing the poles one by one from the front most to back.
Case 1: When we see the long pole the left eye sees the other two poles towards its left, while the right eye to its
right. The long pole is right on the fovea. In this case the overlap takes place as shown in fig 4.2 (1,3).
Case 2: When we see the medium pole the left eye sees the long pole to its right while the short pole to its left,
while for the right eye it takes place accordingly. The medium pole is right on the fovea. In this case the overlap takes
place as shown in fig 4.2 (2,3). Here the long pole to the right is that of the left eye and the short pole at the right
is that of the right eye.
Case 3: When we see the short pole the left eye sees the other poles to its right, while the right eye
to its left. The short pole is now right on the fovea. In this case the overlap takes place as shown in fig 4.2 (3,3). Here
the long and the medium pole to the right is that of the left eye and that to the left is of the right eye.
In
general, the conclusion is that, the image of the objects closer than the point of interest appear inwards, and outwards are
the objects that are farther away. This is not a universal rule, but is shown when you consider a linear array of objects
one behind the other. All this is fine, but there is always a possibility that the images of two different objects may fall
right one behind the other. So if this kind of an overlapping is to be incorporated in a robot, what should it do in such
a situation? To solve this problem let’s look back into what our brain probably does.
Our brain gives some kind of a priority to one of the eye and so the image of that eye is perceived. But how does our
brain do this? The visual pathway between our eye and the brain can be considered to be having a multiplier to each of the
values that reach the brain from both the eyes. But finally it is only one value from a particular point in the overlapped
region that the brain will be able to perceive. The multiplier can have a value ranging between 0 and 1. This means that even
though it cannot enhance a particular point, it can definitely suppress it. The next question that arises in our mind is,
on what basis does our brain select a value for the multiplier. The role of contrast again comes into play. One more observation
that has to be made from the above explanation of image overlapping is that, for two different images to fall one above the
other they have to be at different depths. Depending on the contrast of the two images our brain decides the one to be
masked. See suppression for more details.
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