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 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.
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.
Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality. 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.