Graphics Programs Reference
In-Depth Information
about 20 in. Using the values 3 and 20, we get tan
θ/
2=1
.
5
/
20, yielding
θ/
2=4
.
29
◦
or
θ
=8
.
58
◦
. This is the average stereo angle between the eyes. To get a stereo pair
that will look natural and will be free of distortions, we should select values for
e
and
k
that should maintain this angle. A natural value for
k
is4in,sincethisisthefocal
length of the lenses used by most commercial stereoscopes. If we reduce
k
from 20 to
4(afactorof5),weshouldreduce
e
from3to3
/
5=0
.
6 to maintain the same stereo
angle.
A stereo pair is therefore calculated by substituting
e
=0
.
6,
k
= 4 in Equa-
tion (3.19) and computing
P
L
=
T
L
·
P
and
P
R
=
T
R
·
P
for every point
P
of the
object.
Exercise 3.30:
What would be good values for
e
and
k
assuming a distance of 2.5 in
between the eyes?
3.12 Creating a Stereoscopic Image
The discussion in Section 3.11 suggests that the simplest way to obtain a left-eye,
right-eye pair of stereoscopic images is to select a camera, choose a good subject, take
a picture and then shift the camera along the baseline (normally about 65 mm) to
the right and take another picture. This pair of two-dimensional images can then be
watched as a single three-dimensional (stereoscopic) image with the methods discussed
in Section 3.13. (Actually, what will be seen in three dimensions are those parts that
are common to both pictures. Any objects that appear only in one picture because they
are near an edge will disappear or will confuse the brain, depending on how the pictures
are watched.) Here we show several simple ways to photograph such a pair, and we
start with the basic rules for obtaining good stereoscopic images.
The first rule is to take sharp pictures. All the objects in the photograph should be
in focus. The professional term for this is a large depth of field. Photographers some-
times take pictures where certain elements, normally in the background, are blurred,
while the main subject is sharp. Such a picture may have artistic value, but it does not
translate well to three dimensions.
The second rule is to select an appropriate subject. The aim is to produce a stereo-
scopic, three-dimensional image, preferably also interesting and in color.
Thus, the
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