A Contact Image Sensor (CIS) works by integrating an illumination system, an optical system, and a light-sensing system into a compact module to capture images directly, without the need for lenses like those found in traditional scanners.
Here's a breakdown of the process:
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Illumination:
- The CIS module contains an array of LEDs (Light Emitting Diodes), typically red, green, and blue, that illuminate the document or object being scanned. These LEDs provide a consistent and even light source.
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Light Collection and Reflection:
- The light emitted by the LEDs reflects off the surface of the document.
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Sensing Array:
- The reflected light is then captured by a row of sensors, typically photodiodes, arranged in a linear array. This array acts like the "eye" of the scanner. Each photodiode is a pixel, and the more photodiodes in the array, the higher the resolution of the scan. Like CCDs, CIS sensors also have square cells that light falls upon.
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Signal Conversion:
- The photodiodes convert the light intensity into an electrical signal. The brighter the light, the stronger the signal.
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Data Processing:
- The electrical signals from the photodiodes are processed by an integrated circuit within the CIS module. This processing includes amplification and analog-to-digital conversion, transforming the signals into digital data that can be understood by a computer.
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Image Reconstruction:
- As the CIS module moves across the document (or the document moves past the module), the sensor array captures a line of data at a time. These lines are then combined to create a complete digital image.
Key Features and Advantages of CIS Technology:
- Compact Size: CIS modules are much smaller than traditional scanner setups because they eliminate the need for lenses and mirrors.
- Lower Power Consumption: CIS scanners generally consume less power than CCD (Charge-Coupled Device) scanners.
- Lower Cost: CIS technology is typically more cost-effective to manufacture than CCD technology.
- Shallower Depth of Field: CIS scanners have a shallower depth of field, meaning they are best suited for scanning flat documents. Items with significant surface texture may not be captured as well.
- Integrated Module: A CIS is an integrated module that comprises an illumination system, an optical system and a light-sensing system – all within a single compact component.
In summary, a contact image sensor works by using LEDs to illuminate a document, capturing the reflected light with an array of photodiodes, converting the light into electrical signals, and processing those signals to create a digital image. Its compact design, lower power consumption, and cost-effectiveness make it a popular choice for modern scanners and copiers.
