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What Is a Contact Image Sensor?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 10 September 2016
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A contact image sensor (CIS) scans materials in close proximity, rather than using mirrors to reflect light to an image sensor inside a device. In a flatbed scanner, for example, the image sensor is directly below the glass, as close as possible to the media in the scanner bed. These devices can be more efficient than older scanning techniques, but they also tend to produce images of a lower quality. The tradeoff may be acceptable with some scans and settings.

These devices include an array of light emitting diodes (LEDs) to illuminate the media, along with an optical head and a sensor to detect and record light. The contact image sensor provides scans at a one to one ratio, with no magnification of the image or other distortions. These life-size scans can include documents, three dimensional objects, and materials like textiles that may need to be evaluated with the assistance of a scanner.

This technology includes some advantages for manufacturers and users. It can be very compact, which is useful for mobile scanners and devices that need to fit in compact areas. It's also highly efficient and is usually less expensive to produce than similar products. The LEDs use less energy than other light sources and can be turned off and on between uses. Unlike scanners which use older forms of illumination, a device that uses a contact image sensor is ready for use immediately, and does not need to be warmed up.

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The disadvantage is the lower image quality. Documents produced with a contact image sensor may have a narrower range of colors and a lower resolution. Three dimensional objects can also be more challenging to scan, as the device works best with materials in close proximity. Shadowing and other artifacts can develop in the image when the technician works with materials that do not lie flat against the scanning bed.

Product developers who focus on contact image sensor technology also work on ways to make the technology better. Increases in image quality are a topic of research at some companies that make contact image sensor heads and integrated devices. Like other technology, it can progress rapidly, and newer equipment tends to offer the most advantages to users. Consumers interested in the technology may want to research to determine what kinds of products are currently on the market, and when companies are likely to issue new releases that might be of better quality.

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Mammmood
Post 2

@MrMoody - I bought a portable, handheld scanner once when I was in college. It was a tremendous help when I needed to do research. It was a wand shaped device, powered by two AA batteries.

I was able to scan pages from books, with reasonably good character recognition, enough to at least enable me to understand the text. The portable scanner used a contact image sensor and the quality was ideal for text in that sense.

I don’t know how it would have worked for photos. I never tried it on that.

MrMoody
Post 1

I have two scanners in my office. One is a dedicated scanner that boasts a potential 12 megapixel resolution. The image quality from this device is amazing, for clarity and sharpness.

Another scanner is my Lexmark, which is not a dedicated scanner actually but a combination printer, copier and scanner all in one.

Needless to say, the image quality of the Lexmark scanner leaves something to be desired.

Based on the comparison of the image quality and after reading this article, I assume that the dedicated scanner is using CCD technology while the all in one scanner is using a contact image sensor.

The difference between the two images is night and day, so much so that I don’t even try to reproduce photo images with my all in one unit. I just use it if I need to scan lower resolution images or documents, where I am not that concerned about quality.

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