Have you ever found yourself in a situation where you need to scan a document, but your phone camera just won’t cut it? That’s where scanners come in handy. But have you ever wondered how these machines work?
Typically, a scanner uses something called a charge-coupled device (CCD) to determine what’s on the page. The CCD can convert light into an electrical charge, which it then sends to your computer as digital data. When you start scanning a document, a bright light from inside the scanner – typically from either a xenon lamp or a cold cathode – hits the sheet of paper and is reflected back to a series of mirrors underneath the glass surface. The light is then focused by a lens onto an array of CCD sensors.
Darker areas of the page containing text and clip art will reflect less light than the blank, usually white areas. The CCD array will see these differences, which show up as an accurate image of your document on your computer screen. CCD arrays also determine a scanner’s true resolution. The more sensors in the array, the more points of light it can capture and the more pixels it can send to your computer.
Color scanning uses additional lenses and built-in color filters to separate the scan into red, blue, and green versions, which are then processed to determine the actual colors of your original document. Although this is usually done with just one pass of the scanner, some older models lack these additional lenses and need multiple passes to complete a color scan.
Consumer-level scanners also use something called a contact image sensor (CIS) instead of CCDs. These are simpler in construction and use an array of LEDs to shine light on the document so an image sensor can essentially take a snapshot of it. Although the scans from the CIS are typically lower quality than CCD scanners, they are a cheaper, more lightweight, and more efficient technology. They are commonly found in small portable scanners that can be powered solely from a USB port.
Of course, there are other types of scanners out there, such as expensive drum scanners with high dynamic range for professional applications, as well as 3D scanners. But hopefully, this post has given you a better understanding of how your scanner at home works. If you’re in the market for a scanner, make sure to check that the resolution on the spec sheet is the hardware resolution that reflects the true capabilities of the CCD array.
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