Fingerprint scanners: How it works and what happens during a scan

Let us see in detail what fingerprint scanner is all about.


    Fingerprint security system is not the latest one. We have seen such systems long ago where the fingerprint of a person is registered on paper using inkpad.

    Fingerprint scanners: How it works and what happens during a scan

    But due to the advancement in the technology, the same concept have been evolved to form a fingerprint scanner which we use on daily basis nowadays. Biometric being difficult to forge, it is used everywhere to secure the data further. Right from accessing any machine, smartphone till registering your attendance in office, this technology have been used everywhere.

    In simple term, we can describe it as a system which scans the surface of your finger to turn them into a code which can then be used to verify against the database. If you observe carefully, you will get to know that different types of fingerprint scanners are used in a security system. Let us see what are they.

    Optical scanner

    An optical scanner shines a bright light over your fingerprint to capture a digital photograph which is then fed into your computer for further verification.

    A light-sensitive microchip such as a CCD, charge-coupled device, or a CMOS image sensor is used to produce a digital image by the scanner.

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    The image is automatically analyzed by selecting the only fingerprint which is then converted into code using some sophisticated pattern-matching software.

    Capacitive scanner

    A capacitive scanner works by measuring your finger electrically. Since there are varying distances between each part of your finger and the surface below, a capacitive scanner creates a picture of your fingerprint by calculating these distances.

    This type of scanners is somewhat similar to the touchscreens on iPhones and iPads.

    But what happens when someone tries to scan their fingerprint?

    Let us see how this process guarantees the authentication required to safeguard any data. Here is the process which takes place in an optical scanner when you place your finger to scan.

    - Firstly, a row of LEDs in the device scans bright light onto the surface where your finger is placed.

    - This reflected light bounces back onto a CCD or CMOS image sensor from your finger through the glass.

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    - The image formed on the image sensor will be brighter if the image capture process takes a long time.

    - An algorithm is used here to test whether the captured image is too light or dark. This is when you hear that beep sound which alerts the operator to go back to the first step.

    - The device also alerts you when there are no alternative light and dark areas in the captured image. For this to happen, another algorithm is used to test the level of detail. This works by counting the number of ridges and making sure that there are alternate light and dark areas. If it does not find it, then signals to go back to step 1.

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    - After these two tests, the scanner tells that the image is OK by beeping or using different LED indicator. This accepted image is then stored in flash memory which can then be transmitted to a computer for the next step of processing.

    - Now it's the work of the computer to either store it on a database or automatically compare it against other fingerprints in the database.

    The images captured here will be of 512×512 pixels usually, whereas the standard image is 2.5cm (1 inch) square, 500 dots per inch, and 256 shades of gray.

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