We knew Apple had improved Touch ID recognition in iOS 7.1.1, but now – thanks to Redditor iOSecure – we know how and why.
Apparently, the reason that accuracy would decay over time was down to users screwing up their first scans, when the auto-correction feature needed a perfect start to work properly going forward.
Here’s the relevant chunk of iOSecure’s post. The first part tells how Touch ID works. The second paragraph details the changes.
Touch ID takes a 88×88 500ppi scan of your finger and temporarily sends that data to a secure cache located near the RAM, after the data is vectorized and forwarded to the secure enclave located on the top left of the A7 near the M7 processor it is immediately discarded after processing. The fingerprint scanner uses subdermal [sic] ridge flows (inner layer of skin) to prevent loss of accuracy if you were to have micro cuts or debris on your finger.
With iOS 7.1.1 Apple now takes multiple scans of each position you place finger at setup instead of a single one and uses algorithms to predict potential errors that could arise in the future. Touch ID was supposed to gradually improve accuracy with every scan but the problem was if you didn’t scan well on setup it would ruin your experience until you re-setup your finger. iOS 7.1.1 not only removes that problem and increases accuracy but also greatly reduces the calculations your iPhone 5S had to make while unlocking the device which means you should get a much faster unlock time.
I love that fixing the accuracy also speeds things up. It’s like a double win, almost as if your the heat energy from your apple pie could keep the ice-cream cold, and vice versa. You can read about Touch ID and iOS security in this Apple white paper.