Two-dimensional images can be constructed from
these sensors by producing relative motion between
the object of interest and the camera (Fig. 3).
Throughout this movement, the picture information
is passed from the line-scan device to a storage
medium after each line/column of information has
been obtained. The collection and transferral of
this line/column information is completed at a
sufficient speed to allow continuous movement
between camera and object. As long as there is
strict correlation between the nth pixel in each
line/column stored, ie: they appear alongside each
other in the store, viewing the resulting data
produces a two-dimensional image of the object.
PICTURE ELEMENTS
A
LINE-SCRN
Figure 2 Photosensitive Area of Line-Scan
Sensor
The extent of the field of view in the movement
axis contained in these returned images is
dependent on two parameters:—
a. the frequency at which the camera is
driven, ie: the amount of time that each
pixel has to collect incident photons;
b. the relative speed of movement between
the camera and the object of interest.
By using the correct combination of these two
parameters the field of view in the movement axis,
and therefore the resolution in the object space in
this axis, can be adjusted to suit a particular
application.
OBJECT OF MOVEMENT
INTEREST ue
ge )
= E di
Cr : CONVEYOR
f: CRMERR BELT
FIELD OF VIEW
LINE-SCAN
CAMERA
Figure 3
The axis of the line-scan image along the line of
the sensor can be modelled on the principle of the
pin-hole camera?
, le: as in a two-dimensional
CCD device. Thus, the field of view along the line
of the sensor is dependent on the focal length of
the lens used and the length of the line-scan
device itself.
Figure 4 shows the perspective volume for the
television type sensor. Figure 5 shows a similar
volume obtained from the line-scan device after
the object has passed in front of the camera (or
the camera in front of the object).
PHOTOSENSISTIVE
AREA
Figure 4 Volume of Space Viewed by Area Array
Sensors
