Specifications
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3.3 Image sensors
As light passes through a lens, it is focused on the camera’s image sensor. An image sensor is
made up of many photosites and each photosite corresponds to a picture element, more com-
monly known as “pixel”, on an image sensor. Each pixel on an image sensor registers the amount
of light it is exposed to and converts it into a corresponding number of electrons. The brighter
the light, the more electrons are generated.
When building a camera, there are two main technologies that can be used for the camera’s
image sensor:
> CCD (charge-coupled device)
> CMOS (complementary metal-oxide semiconductor)
Figure 3.3a Images sensors: CCD (at left); CMOS (at right).
While CCD and CMOS sensors are often seen as rivals, each has unique strengths and weak-
nesses that make it appropriate for dierent applications. CCD sensors are produced using a
technology that has been developed specically for the camera industry. Early CMOS sensors
were based on standard technology already extensively used in memory chips inside PCs, for
example. Modern CMOS sensors use a more specialized technology and the quality of the sen-
sors is rapidly increasing.
3.3.1 CCD technology
CCD sensors have been used in cameras for more than 30 years and present many advantageous
qualities. Generally, they still oer slightly better light sensitivity and produce somewhat less noise
than CMOS sensors. Higher light sensitivity translates into better images in low light conditions.
CCD sensors, however, are more expensive and more complex to incorporate into a camera. A CCD
can also consume as much as 100 times more power than an equivalent CMOS sensor.
3.3.2 CMOS technology
Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image
quality. CMOS sensors lower the total cost for cameras since they contain all the logics needed
to build cameras around them. In comparison with CCDs, CMOS sensors enable more integration
CHAPTER 3 - CAMERA ELEMENTS