Image Processing Reference
In-Depth Information
Fig. 2.9
Depth-of-field. The
solid lines
illustrate two light rays from an object (a point) on the
optical axis and their paths through the lens and to the sensor where they intersect within the same
pixel (illustrated as a
black rectangle
). The
dashed
and
dotted lines
illustrate light rays from two
other objects (points) on the optical axis. These objects are characterized by being the most extreme
locations where the light rays still enter the same pixel
Fig. 2.10
The field-of-view
of two cameras with different
focal lengths. The
field-of-view is an angle, V,
which represents the part of
the world observable to the
camera. As the focal length
increases so does the distance
from the lens to the sensor.
This in turn results in a
smaller field-of-view. Note
that both a horizontal
field-of-view and a vertical
field-of-view exist. If the
sensor has equal height and
width these two
fields-of-view are the same,
otherwise they are different
where the focal length,
f
, and width and height are measured in mm. So, if we have
a physical sensor with width
=
14 mm, height
=
10 mm and a focal length
=
5 mm,
then the fields-of-view will be
tan
−
1
7
5
108
.
9
◦
,
tan
−
1
(
1
)
90
◦
FOV
x
=
2
·
=
FOV
y
=
2
·
=
(2.5)
Another parameter influencing the depth-of-field is the
aperture
. The aperture
corresponds to the human iris, which controls the amount of light entering the hu-
man eye. Similarly, the aperture is a flat circular object with a hole in the center
with adjustable radius. The aperture is located in front of the lens and used to con-
trol the amount of incoming light. In the extreme case, the aperture only allows
rays through the optical center, resulting in an infinite depth-of-field. The downside
is that the more light blocked by the aperture, the lower
shutter
speed (explained
below) is required in order to ensure enough light to create an image. From this it
follows that objects in motion can result in blurry images.
