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Axis network cameras
Image sensors: CCD vs. CMOS
The image sensor of
the camera is responsible for transforming light
into electrical signals. When building a camera,
there are two possible technologies for the camera's
image sensor:
- CCD (Charged Coupled Device)
- CMOS (Complementary Metal Oxide
Semiconductor)
CCD and CMOS are the
critical components that act as a camera's "digital
film." CCD sensors are produced using a technology
developed specifically for the camera industry,
while CMOS sensors are based on standard technology
already extensively used in memory chips--inside
PCs, for example. Today's high quality cameras use
mostly CCD sensors. Although recent advances in CMOS
sensors are closing the gap, they are still not
suitable for cameras where the highest possible
image quality is required. However, CMOS sensors may
be ideal for entry-level network cameras where size
and price are important factors.
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| A
1/3-inch CCD |
A
1/4-inch CMOS sensor |
See placement of an
image sensor in a network camera
CCD technology
CCD sensors have been used in cameras for more than
20 years and present many advantageous qualities;
among them, better light sensitivity than CMOS
sensors. This higher light sensitivity translates
into better images in low light conditions. CCD
sensors are, however, more expensive as they are
made in a non-standard process and more complex to
incorporate into a camera. In addition, when there
is a very bright object in the scene (such as a lamp
or direct sunlight), the CCD may bleed, causing
vertical stripes below and above the object. This
phenomenon is called a smear.
CMOS technology
Recent advances in CMOS sensors bring them closer to
their CCD counterparts in terms of image quality,
but CMOS sensors remain unsuitable for cameras where
the highest possible image quality is required. CMOS
sensors provide a lower total cost for the cameras
since they contain all the logics needed to build
cameras around them. They make it possible to
produce smaller-sized cameras. Large-sized sensors
are available, providing megapixel resolution to a
variety of network cameras. A current limitation
with CMOS sensors is their lower light sensitivity.
While this drawback is not an issue in bright
environments, in low light conditions it becomes
apparent. The result is either a very dark or a very
noisy image.
For more related
information, see:
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