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About this Article
Written by: Kenneth Newton
Written on: May 3rd, 2003
Tags: electrical engineering, lifestyle
Thumbnail by: John Carney/Wikimedia Commons
About the Author
At the time of writing, Kenneth Newton was a senior graduating with a B.S. in Electrical Engineering from the University of Southern California. He will be continuing his education at the University of Southern California as a Ph.D. student in the Electrophysics Department of Electrical Engineering.
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Volume V Issue III > The Digital Image Sensor
The digital image sensor is a technology used to record electronic images. The most commonly recognized application of the digital image sensor is the digital camera. In digital cameras, the image sensor is used in conjunction with a color separation device and signal processing circuitry to record images. The two main technologies used to fabricate the sensors are CCD (Charge Coupled Device) and CMOS (Complimentary Metal-Oxide Semiconductor), each bearing certain advantages and disadvantages. Applications of the digital image sensor, including the pill camera and vision in robotics, are rapidly expanding, and soon sensors will be an everyday occurrence.

Introduction

The digital image sensor is a technology used to record electronic images. These image sensors are silicon microchips that are engineered to operate in different ways. The engineering involved in these circuits is very complex and the techniques used to manufacture these devices are not standardized in the industry. It is impractical to discuss the entire spectrum of manufacturing processes here, but they are noted because they give rise to the wide variety of applications for the digital image sensor. These engineering practices involve creating features that are added to the bare sensor for use in specific applications ranging from machine vision in robotics, to cameras integrated into cellular phones and PDAs, to ultraviolet sensors on the Hubble Space Telescope.
The most commonly recognized application of the digital image sensor is the digital camera. To get a sense of how image sensors are integrated in this application, their use in digital cameras will be explored. This exploration will also include an explanation of some of the other major features of a digital camera, as one must having a working knowledge of the lens and the mechanism for determining color in order to fully understand the role of the digital image sensor. One important thing to note about digital image sensors is that they are not all manufactured through the same processes. The two main technologies used to fabricate the sensors are CCD(Charge Coupled Device) and CMOS (Complimentary Metal-Oxide Semiconductor), which have certain key differences particularly in terms of performance, cost, and size.
The digital camera is not the only application of the image sensor. Another interesting application that has just recently become possible is the pill camera, which is a camera that can be swallowed and take pictures of the inside of the intestinal tract. As the technology used in the sensors progresses, there should be a multitude of exciting possible uses for the digital image sensor.

Digital Camera Technology

The most common application of the digital image sensor is the digital camera. In order to better understand the integration of the sensor into the camera, some of the external components used in the camera will be explained. The key components of the digital camera are the lens, which focuses light onto the image sensor, and the image sensor, which is used to replace conventional film. Image sensors used in digital cameras have special features, the most important of which is the ability to detect color. Currently three technologies are available to perform this function: a beam splitter, a spinning disk filter, and a color filter array.

The Lens

The lens is probably the chief similarity between the way digital cameras and conventional cameras work. The lens is the portal through which the image of the outside world reaches the image sensor. It focuses the light from the scene onto the sensor. The lenses used in digital cameras obey the exact same physics as lenses used in traditional cameras. Light from the subject passes through the lens and is focused on the film. The lens is chosen appropriately based on this principle so that the entire sensor is illuminated by the light. By moving the lens away from the film, the image of the subject is magnified, and only a portion of this magnified image appears on the film. The part of the image that appears on the film is a zoomed-in portion of the object, meaning this movement of the lens is the mechanism by which optical zoom works.