The fingerprint scanner system has two basic tasks: one is to obtain an image of the finger, and the other is to determine whether the lines and troughs in the image match the lines and troughs in the previously scanned image.

There are several ways to get a person's fingerprint image. The most common methods nowadays are optical scanning and capacitive scanning. These two scanning methods work in a completely different way, but all get the same image. The following mainly talk about the working principle of the optical fingerprint scanner.

The core component of the optical scanner is the charge coupled device (CCD), which is identical to the closed sensor system used in digital cameras and cameras. A CCD is nothing more than a group of photodiodes (called photosensors) that generate electrical signals under the action of photons. Each photosensor records one pixel, a tiny dot representing the beam hitting that point. The light and dark pixels together form an image of a scanned scene (eg, a finger). Typically, there is an analog to digital converter in the scanner system that processes the analog electronic signals to produce a digital representation of the image.

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The scanner is equipped with a light source, usually a set of light-emitting diodes, to illuminate the lines of the fingers. When you put your finger on the glass, the scanning process begins and the CCD camera takes a photo of the fingerprint. In fact, the CCD system produces an inverted image of the finger, the darker area represents more reflected light (the pattern of the finger), and the brighter area represents the smaller reflected light (the valley of the finger).

Before comparing fingerprints with stored data, the scanner processor ensures that the CCD captures a sharp image. It checks the average of the darkness of the pixel or the overall value of a small sample if the image is too dark or too bright overall. The scan will be abandoned. The scanner then adjusts the exposure time to allow more or less light to enter, once in the scan.

If the darkness is appropriate, the scanner system will continue to check the sharpness of the image (sharpness of the fingerprint scan). The processor will look at several lines that move vertically and horizontally across the image. If the line perpendicular to the texture consists of very dark pixels and very bright pixels, it means that the fingerprint image has good clarity.

When the processor finds that the image is clear and the exposure is correct, it continues to compare the captured fingerprint to the fingerprint on the file. We will soon understand this process, but first let's take a look at another major scanning technology, the capacitive fingerprint scanner.

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