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After updating my UK HTC Sensation to Android 4.0 I was keen to try out Face Unlock. I'm happy to say that it works reasonably well, however the setup process has led to me having a query.

When setting up face lock, after your face has been captured for the first time and setting up your backup access, you are given the following prompt:

You've Finished!

To unlock your phone, just look at it.

Tip: Improve face matching by having your face captured in different conditions

The tip sounds good, however it doesn't actually tell you how to have your face captured in different conditions! After clicking OK to the prompt you are returned to the security menu and any attempt to re-set-up face unlock just seems to over-write your previous settings (or at least I assume it does as it asks you to set up a new backup system).

How can I recapture my face multiple times to improve face recognition?

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    Through frustration I have now created the app to train the face recognition. I need to test it further but I'm already seeing the difference xD Assuming that it works fine over the next few days I'll publish it
    – Rory
    Commented Apr 28, 2012 at 15:56

4 Answers 4

Reset to default
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Go to Settings -> Security -> Lock screen -> Improve face matching. You will need to confirm your PIN, and then follow the on-screen directions to capture your face again.

After each successful capture you will be placed back to the Lock screen settings menu, so just keep going into the Improve face matching section to repeat the process as many times as you wish.

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  • Unfortunately I don't have that pathway. Instead of Lock Screen I have Screen lock which then doesn't have an improve face matching option. This then just resets the face lock as described above :(
    – Rory
    Commented Apr 10, 2012 at 13:29
  • I am going by the menu structure on my Galaxy Nexus which is running "vanilla" Android 4.0.4 version. HTC must've shuffled things around with Sense 4 again. I wish manufacturers would stop trying to distinguish themselves by messing up basic OS functions.
    – Chahk
    Commented Apr 10, 2012 at 13:33
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As discovered here, HTC have removed the link to the training option in the settings menu. However, the actual feature remains intact so I have created a quick app to access it.

Please note that we don't know why HTC took it out, they may have had a very good reason and I could be meddling, however I have used the training feature successfully on my sensation without any negative effects and the recognition is much improved.

enter image description here

I've put the application on Google Code, the download link being here (including CR code for devices). Please note that all use is under the MIT License - hope this helps others with the same problem!

Also, the option seems to have been returned to it's normal position in the menu in the following android/HTC versions:

Android 4.0.3
HTC Sense 3.6
Software number 3.33.401.53

Viewable in Settings --> About Phone --> Software Information

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  • The possibility exists that the more you train it, the easier it is to fool it. The first time you train it, perhaps it's literally doing a fairly tight comparison but now there are all sorts of possible yes that's a match situations on your eyes, nose, hair etc?
    – user5506
    Commented Sep 22, 2012 at 13:12
  • That would be a poor algorithm, and I'd expect better from Google. The more you train it, the better it knows your face (assuming you always do use your own face), so the chances of both a false negative and a false positive should decrease if implemented well.
    – Prateek
    Commented Jan 22, 2014 at 9:41
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One hypothesis is this:

Face unlock learns automatically. Each time you unlock successfully, the function learns a new variation of your face image. Therefore the "Improve face matching" function is not needed. Just keep unlocking, and your phone will get better and better at it. But be patient, because of security concerns the learning has to be slow and reluctant.

This is only a hypothesis. I have asked in a Google forum whether it is true or not, but got no answer.

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  • even if it does learn, it may have difficulty detecting your face in a radically different lighting condition. For example, if you unlock in your own bedroom which with overhead warmlight lamp vs unlocking in your workplace with overhead daylight lamp vs outdoors in a shade with lots of ambient lighting but no overhead light. Manually triggering learning mode can help the phone learns how your face look on all these different conditions.
    – Lie Ryan
    Commented Sep 22, 2012 at 12:15
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To train face unlock for the fastest unlock:

  • hold your phone perpendicular, like taking a selfie
  • allow for the offset between where front lens is and your nose
  • blink before training, and when opening

Blinking is important, and results in a virtually instantaneous unlocking.

AFAIK, only fingerprints can be registered multiple times; that is done by reusing the same finger and registering it as a different finger. While most people only have one face to register reusing your finger gives misrecognition a chance to carry over to the next finger, increasing the opportunity to recognize a dirty finger.

If the option is available on your phone there is an "Add alternative look", for glasses, hairstyle, or a second chance:

enter image description here

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