A particularly stupid move on my part over the weekend left the tip of my right index finger sliced open. Not enough to need a trip to the hospital, but enough that I'm reminded of its existence every time my finger drifts across a rough surface. And the cut is just enough to get in the way of unlocking my Nexus 6P the way I typically unlock it, which means I have to shift my finger just a bit to confirm the unlock and move on with the rest of my interaction. No big deal, there's plenty of finger there for the sensor to grab and I've got other fingers stored if it becomes a problem.
Only it shouldn't have been a problem at all, remember? My phone is supposed to be learning as I use it, and I don't think that has been happening.
When Google introduced the Nexus 6P and Nexus 5X, one of the big features was "Nexus Imprint." Not only did these two phones include some of the fastest fingerprint sensors on the market at the time, but the act of registering a new fingerprint was by far the fastest in the industry. This fingerprint process is fast because it only captures six images to make up your whole fingerprint, which wouldn't normally be enough to cover a whole fingerprint effectively. Google's explanation for using so few steps in the capture process was a special learning process baked into Nexus Imprint. Dave Burke told us so on stage during the Nexus 6P launch event.
What's really cool? It's that Nexus Imprint gets better over time. With each use it learns more about your unique fingerprint.
While that sounded really special, we never actually got an explanation of what specifically was happening during this process. We did learn that unless you're very careful with the six "pictures" the Nexus 6P and 5X take to save your fingerprint to memory, there's a very real chance of creating fingerprint records that are incomplete. Nexus Imprint is supposed to fill in these gaps over time, seamlessly, so you barely even notice they're happening. It's a terribly clever idea, a spectacularly Google thing to do. It's also not happening on my Nexus 6P.
For a phone that has been sucking up my fingerprint just about every day for the last month and a half, my Nexus 6P still fails to unlock my phone in all the same places it did when I first set it up. The only difference is, now that I've sliced the tip of my finger open I'm using those parts of my finger deliberately instead of accidentally. While this could absolutely be resolved by remapping my finger after the cut heals or just using another finger, it's strange to see absolutely no evidence of Nexus Imprint learning more about my fingerprint or getting better over time. It still feels the same, and while that still means this is a great fingerprint sensor, it'd be nice to see some evidence of Google's claim.