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Face ID works via a mirror

jamin00

jamin00

macrumors 6502a
Original poster
Apr 14, 2012
616
168
Essex, UK.
Which I guess is just the lasers bouncing off the mirror and being able to check your facial features. depths etc?

It does not work from a picture so the above must be true?
 
jamin00 said:
Which I guess is just the lasers bouncing off the mirror and being able to check your facial features. depths etc?

It does not work from a picture so the above must be true?
Click to expand...

Have you actually tested this to see if it indeed does work?
 
Is it because mirrors are mirrors? :eek:

Snark aside, I wonder how effective it is at dealing with mirrors. There must be some degree of distortion there.
 
That doesn't make sense to me. The IR dots are supposed to map depth, hence why a 2D photograph won't work. A mirror is a 2D surface as well. It shouldn't detect any depth and therefore shouldn't work.
 
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joeblow7777 said:
That doesn't make sense to me. The IR dots are supposed to map depth, hence why a 2D photograph won't work. A mirror is a 2D surface as well. It shouldn't detect any depth and therefore shouldn't work.
Click to expand...

Light bounces off mirrors. It doesn’t see them. If it used ultrasound then it would see a flat plane, but it uses light.
 
There's a couple of different IR techs for depth sensing cameras, but in general it's like indicated above, the "IR dots" are being reflected from a 3D surface, the mirror isn't introducing any change to the data (or providing data of its own so to speak).
 
w7ay said:
The virtual image is behind the mirror.
Click to expand...

Yeah, I know that, which is why the image looks like it's behind the mirror to our eyes, but the mirror is still a flat surface. the IR array that's projected onto it shouldn't detect any depth.

Diorama said:
Light bounces off mirrors. It doesn’t see them. If it used ultrasound then it would see a flat plane, but it uses light.
Click to expand...

Yes, and all the light will be bouncing off a flat plane, so there shouldn't be any depth.
 
joeblow7777 said:
Yeah, I know that, which is why the image looks like it's behind the mirror to our eyes, but the mirror is still a flat surface. the IR array that's projected onto it shouldn't detect any depth.



Yes, and all the light will be bouncing off a flat plane, so there shouldn't be any depth.
Click to expand...

Perhaps I have explained myself badly.

Mirrors reflect light, the light does not “know” that it has hit a flat plane as it travels “through” the mirror and back in the direction it came.

If you have used a laser rangefinder in a room 5 metres wide, pointed at the mirror from the opposite wall it will give you a measurement of 10 metres.

Infra red is just light which is very slightly past the visible spectrum, but it still acts pretty much the same as visible light.

As I said, if you used some kind of ultrasound range finder/scanner (like a bat) then it would see a mirror as a flat plane.
[doublepost=1510164037][/doublepost]Imagine a blind man poking a stick forward to guess the general shape/size of an object in front of him. He pushes it forward and when it stops he knows he has hit something solid.

If the stick was made of light, it wouldn’t ‘stop’ when it hit a mirror, it would continue at a new angle.
 
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joeblow7777 said:
Yeah, I know that, which is why the image looks like it's behind the mirror to our eyes, but the mirror is still a flat surface. the IR array that's projected onto it shouldn't detect any depth.



Yes, and all the light will be bouncing off a flat plane, so there shouldn't be any depth.
Click to expand...
Face ID works with a mirror.

You need to google how mirrors work...
 
Diorama said:
Perhaps I have explained myself badly.
Click to expand...


Nice follow up clarification and examples. I've been involved in AR/VR/CV, worked with depth sensing tech, etc., but sometimes it's tricky to convey to someone how it works without getting into the [technical] weeds.
 
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Diorama said:
Perhaps I have explained myself badly.

Mirrors reflect light, the light does not “know” that it has hit a flat plane as it travels “through” the mirror and back in the direction it came.

If you have used a laser rangefinder in a room 5 metres wide, pointed at the mirror from the opposite wall it will give you a measurement of 10 metres.

Infra red is just light which is very slightly past the visible spectrum, but it still acts pretty much the same as visible light.

As I said, if you used some kind of ultrasound range finder/scanner (like a bat) then it would see a mirror as a flat plane.
[doublepost=1510164037][/doublepost]Imagine a blind man poking a stick forward to guess the general shape/size of an object in front of him. He pushes it forward and when it stops he knows he has hit something solid.

If the stick was made of light, it wouldn’t ‘stop’ when it hit a mirror, it would continue at a new angle.
Click to expand...

Thanks, that makes a bit more sense. I'm just struggling to wrap my head around how the IR beams detect the virtual image behind the mirror. I think of ray diagrams and I see the incident rays bouncing off the mirror

Recognition said:
Face ID works with a mirror.

You need to google how mirrors work...
Click to expand...

Thanks, but I actually do know how mirrors work. If anything I'm foggy on how the IR detection works.
 
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I just tried and it works in a mirror. Even though it is a longer distance via reflection for the depth sensor, it should only look at the differences of depth otherwise you would have to hold phone at same distance each time you unlock it.
 
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joeblow7777 said:
Yes, and all the light will be bouncing off a flat plane, so there shouldn't be any depth.
Click to expand...
If the mirror wasn't a mirror, then it would look like a flat plane.

But everything you see in a mirror has depth, doesn't it? Your own face looks 3D, right? You reach towards your reflection, and your reflection's hand reaches towards you in 3D, yes?

Just because the surface is flat doesn't make its optics flat.

Your face, shown on a video display, becomes 2D because all the points of light creating the visual appearance of your face are all originating in a 2D plane. But a mirror is not the same as a video display.
[doublepost=1510170692][/doublepost]
Recognition said:
You need to google how mirrors work...
Click to expand...
Googling might make him think that the Earth is flat and Jenny McCarthy's boobs were always real. :p
[doublepost=1510172411][/doublepost]Let's get a little more meta here...

To you, a person, a mirror is "flat" -- because you know it's a mirror. You know the definition of the word "mirror". You know that it's a piece of reflective glass, mounted on a wall, where you can get a better look at the hairs hanging out of your nose.

To an array of scattered light beams and a couple cameras, it's an unusually deep hole in an otherwise solid surface. The camera's "brain" has no context -- it doesn't know that it's looking at a pane of glass with a reflective backing. All it knows is, the distances of the surfaces it can visually resolve, such as the towel rack on the opposite wall of your bathroom, are farther away.

So what?

When the FaceID array sees your face in a mirror, it doesn't know that it's looking at a mirror. It has no knowledge of context. It only knows that your face is a little farther away than usual, but it's still your face, and unlike with a photograph, your nose appears a few inches closer to the camera than your ears do.
 
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I love how Apple likes to avoid the use of the term laser (prob to avoid safety concerns) even though they are technically low powered laser beams.
 
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