CCD Technology

Michael Fitzer
January 2007

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When it comes to video cameras, or even the video industry as a whole, there are tons of buzzwords that people use to convey ideas or explain technology. One of the most popular, when it comes to selecting the right video camera, is the acronym CCD, which stands for charge-coupled device.

What originally started out as a new type of computer memory circuit in the late 1960's, the charge-coupled device quickly found a place in the world of imaging, as the silicon-based circuitry is so sensitive to light. Since that time, CCD technology has revolutionized the way we communicate and conduct business through the use of office equipment like photocopiers and fax machines. However, where CCDs have really come into mainstream popularity has been in the home and professional video communities.

Put simply, these tiny circuits act as the camera's eye, capturing light and then converting that light into a digital signal, or image on tape. While that is a short, sweet and convenient explanation for how CCDs operate, to really grasp how these circuits work and how to choose a camera with the right CCD technology for you, it's best to have a broader understanding of their form and function.

How does the CCD receive information? In a film camera, light is focused through the camera lens in varying levels of intensity. That light then hits a chemically-treated piece of film which reacts to the different intensities of light. The same basic principle is true for video cameras; however, instead of light hitting a strip of chemically-treated film, the light hits the charge-coupled device that measures light photons on a panel of light-sensitive diodes and then converts that light information into an image. However, this simple operation is capable of capturing and transmitting only a black and white image.

To process and redistribute color information, the CCD in your camera has to measure light at three separate wavelengths of red, green, and blue. In other words, it has to be able to recognize color. It does so through use of a CCD Array, which is a device that mounts charge-coupled devices together to capture more pixel information.

From basic video surveillance cameras to high-end consumer and pro-model cameras, color imaging is processed using either one or three CCD arrays.

Single CCD array technology uses exactly what the name implies, just one CCD array to process all color information. This low-cost technology employs use of a grid of color filters on the face of the array so that only red, green, or blue light ever reaches any given pixel. This simple separation allows for color images; however it does have its drawbacks, one of which is known as aliasing.

Aliasing is the term used to describe when a region of sharp color contrast bleeds. For instance, say you shot a white blanket with a wide brown stripe down the center. If you were to magnify the image, you would see where color information at the edge of the wide brown stripe failed to make a sharp transition. Instead, individual pixels would appear to have a rainbow effect at the edges. While it doesn't completely degrade the overall image, aliasing is an after effect of single CCD technology that limits the usefulness of the image. Therefore, single CCD cameras are typically used in applications like security surveillance, where pixel-perfect resolution is not a must.

As the need for high-quality video imaging grew, three chip color cameras made their way into the market. For this technology to work, a complex optical prism assembly is used to separate the image being captured into three components: red, green, and blue. Because of the prism assembly, each of the three colors gets its own charge-coupled device. This means almost all of the light information associated with a particular color channel is captured by its own array and the individual CCD is able to devote all of its pixels to that particular color channel, unlike single CCD technology where just one array has to process and split all of the color information.

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