Image Acquisition - Introduction to Video and Image Processing - page 16

Fig. 2.13 The sensor consists of an array of interconnected cells. Each cell consists of a housing
which holds a filter, a sensor and an output. The filter controls which type of energy is allowed to
enter the sensor. The sensor measures the amount of energy as a voltage, which is converted into a
digital number through an analog-to-digital converter (ADC)
Fig. 2.14 The input image
was taken with the correct
amount of exposure. The
over- and underexposed
images are too bright and too
dark, respectively, which
makes it hard to see details in
them. If the object or camera
is moved during the exposure
time, it produces motion blur
as demonstrated in the last
image
Another aspect related to the exposure time is when the object of interest is in
motion. Here the exposure time in general needs to be low in order to avoid motion
blur , where light from a certain point on the object will be spread out over more
cells, see Fig. 2.14 .
The accumulated charges are converted into digital form using an analog-to-
digital converter . This process takes the continuous world outside the camera and
converts it into a digital representation, which is required when stored in the com-
puter. Or in other words, this is where the image becomes digital. To fully compre-
hend the difference, have a look at Fig. 2.15 .
To the left we see where the incident light hits the different cells and how many
times (the more times the brighter the value). This results in the shape of the object
and its intensity. Let us first consider the shape of the object. A cell is sensitive to