Finger Printing

We use our fingerprints so many times a day to unlock our iPhones (or Droids, if you're into that sort of thing). But how does this really work? How can you just put your finger on the home button for a few seconds and then gain access to everything in your phone? We have the world at our fingertips!

Well, the oldest method of fingerprint scanning is optical scanning. This method essentially takes a digital photograph of your fingertip and then uses algorithms to find patterns. The programs look for light and dark areas of the image to identify ridges and lines. The scanner uses LED lights to brighten the image and analyze the data.

The second method is capacitive scanning which is most commonly used today. The capacitors in this method go through a change of charge when a ridge of the fingerprint is pressed against it. Air gaps, or valleys, do not change the charge. The changes in charge are tracked and recorded.

So how can the computer compare and check your fingerprint? Well, each print is analyzed for features called minutiae, where lines in our fingerprint end or split in two. The computer does something similar to connect the dots and measures the distances and angles between the minutiae, creating something like this:

The computer takes this data and uses an algorithm to transform it into a numeric code. It then compares the codes to see if the current fingerprint matches the stored one. To decrease the necessary processing power, the program does not compare the whole finger but rather several minutiae. This allows the process to work more quickly and allows it to work despite smudging or off-centered fingerprints. If the codes match, you gain access! How rad!


References:
http://www.androidauthority.com/how-fingerprint-scanners-work-670934/
http://computer.howstuffworks.com/fingerprint-scanner4.htm
http://www.explainthatstuff.com/fingerprintscanners.html