Facebook's "people recognition" algorithm

A place to discuss the science of computers and programs, from algorithms to computability.

Formal proofs preferred.

Moderators: phlip, Moderators General, Prelates

zenten
Posts: 3799
Joined: Fri Jun 22, 2007 7:42 am UTC
Location: Ottawa, Canada

Facebook's "people recognition" algorithm

Postby zenten » Fri Nov 23, 2007 7:01 pm UTC

I'm in the process of tagging 600+ wedding photos there, and I noticed that it's really good at telling where one person stops and the other person begins. How might it be doing this? It seems to be more than just identifying regions of colour.

User avatar
OfficiallyHaphazard
Age=postcount/60
Posts: 209
Joined: Tue Aug 28, 2007 2:56 pm UTC

Re: Facebook's "people recognition" algorithm

Postby OfficiallyHaphazard » Fri Nov 23, 2007 8:13 pm UTC

There is software already out there that does this:
http://www.dpreview.com/news/0502/05021 ... faceaf.asp
"Who are you, how did you get in my house?" - Donald Knuth

Felford
Posts: 9
Joined: Mon Nov 26, 2007 10:04 pm UTC

Re: Facebook's "people recognition" algorithm

Postby Felford » Mon Nov 26, 2007 10:35 pm UTC

There was a guy up at Imperial doing this for his third year project I think, and I think it went along the lines of :-

:- Colour change recognition; identifies regions on the picture which *could* be faces
:- Scan those regions - if they're dark it looks for a pair of light patches (eyes), or if the picture's light it looks for a pair of dark patches (pupils)
:- If it then finds a pair of what could be eyes, it uses that as the centre of the face, then uses the distance apart of the eyes to judge how far away the mouth should be
:- It then scans for a third feature (the mouth) at that distance away from the centre...

If it finds all those things, it recognises that as a face and tags it...

I think he was also talking about adding a "nose detector" to avoid some false positives - I think the idea was to draw a line between the centre of the eyes and the mouth, and scan for a ridge there (significantly darker or lighter)...

Seemed to work pretty well actually, and I'd guess they use a similar system on facebook. I could be wrong, but I think he was talking about using his algorithm for real-time face tracking on video footage, which I thought was pretty sweet.

Well... that was quite an FYI... Hope someone found it interesting :P

User avatar
Pathway
Leon Sumbitches...?
Posts: 647
Joined: Sun Oct 15, 2006 5:59 pm UTC

Re: Facebook's "people recognition" algorithm

Postby Pathway » Tue Nov 27, 2007 12:29 am UTC

Doesn't that fail pretty badly when you have pictures from weird angles?
SargeZT wrote:Oh dear no, I love penguins. They're my favorite animal ever besides cows.

The reason I would kill penguins would be, no one ever, ever fucking kills penguins.

User avatar
quintopia
Posts: 2906
Joined: Fri Nov 17, 2006 2:53 am UTC
Location: atlanta, ga

Re: Facebook's "people recognition" algorithm

Postby quintopia » Tue Nov 27, 2007 1:13 am UTC

All known face detectors fail in strange places. . .but if you look at those places, somehow those areas look like faces too.

Felford
Posts: 9
Joined: Mon Nov 26, 2007 10:04 pm UTC

Re: Facebook's "people recognition" algorithm

Postby Felford » Tue Nov 27, 2007 5:45 pm UTC

Pathway wrote:Doesn't that fail pretty badly when you have pictures from weird angles?


Well I think he was talking about something to do with if the distance between eyes doesn't match up with the distance to the mouth (ie. it's out of proportion) then it could still be a face, but at an angle... There was a trade off between tolerance for deviation from the norm, and getting false positives...

User avatar
Pathway
Leon Sumbitches...?
Posts: 647
Joined: Sun Oct 15, 2006 5:59 pm UTC

Re: Facebook's "people recognition" algorithm

Postby Pathway » Wed Nov 28, 2007 9:56 pm UTC

Yeah. Take a picture of yourself, with the camera placed near your chin and facing upwards, to get an idea of what I mean.
SargeZT wrote:Oh dear no, I love penguins. They're my favorite animal ever besides cows.

The reason I would kill penguins would be, no one ever, ever fucking kills penguins.

Robin S
Posts: 3579
Joined: Wed Jun 27, 2007 7:02 pm UTC
Location: London, UK
Contact:

Re: Facebook's "people recognition" algorithm

Postby Robin S » Wed Nov 28, 2007 10:03 pm UTC

Does it really do all that? I thought you tagged a rectangle of the photo (defined by the centre pixel that you click on) and then, when other people viewed the photo, it just worked out which tagged pixel was closest to the cursor, or displayed no name at all if the cursor was sufficiently distant from all tagged pixels.

Unless they've changed it since I last used it...
This is a placeholder until I think of something more creative to put here.

zenten
Posts: 3799
Joined: Fri Jun 22, 2007 7:42 am UTC
Location: Ottawa, Canada

Re: Facebook's "people recognition" algorithm

Postby zenten » Thu Nov 29, 2007 3:37 pm UTC

Robin S wrote:Does it really do all that? I thought you tagged a rectangle of the photo (defined by the centre pixel that you click on) and then, when other people viewed the photo, it just worked out which tagged pixel was closest to the cursor, or displayed no name at all if the cursor was sufficiently distant from all tagged pixels.

Unless they've changed it since I last used it...


Well, I didn't say it was face recognition. But it's not based on just simple distance, it seems to at least be able to identify shapes of bodies.


Return to “Computer Science”

Who is online

Users browsing this forum: No registered users and 4 guests