Optics 101

CCD Sensors - A Basic Look at How The Fundamental Key to Modern Digital Imaging Works

Without CCD detectors our modern lives would not have the current influx of ubiquitous video cameras, digital cameras, and camera telephones. CCD detectors or sensors are the light sensitive detectors that capture the image in the majority of these cameras. Other sensors, like CMOS sensors, are available but in this article we will concentrate on CCD detectors.

How CCD Sensors Work

CCD sensors are semiconductor based imaging chips. The name CCD is derived from Charge Coupled Device. A Charge Coupled Device is a special kind of semiconductor chip covered in an array of individual light sensitive components. Each of these components corresponds to a image pixel. When light strikes a CCD chip photoelectrons are generated. For each pixel these photoelectrons are built up and stored in a special ‘well’. This well acts like a capacitor to hold the charge while the image is exposed. Once the exposure is complete, the built up charge is electronically ‘read’.

The greater the number of photoelectrons that has built up, the greater the brightness of light that had hit that pixel. CCD sensors can only read light intensity and therefore only take a black and white image. By using a system of filters on the sensors, colour intensities can be measured and a colour image produced.

Figure 1. Charge coupled devices, or CCDs (Image source NASA)

Advantages

The latest versions of these sensors are able to be mass produced while being more sensitive to a wide range of light than film. In low light, the CCD can build up image information over a long exposure duration in the same manner as film. CCD Sensors also have low image ‘noise’ or grain.

Source: AZoOptics

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