# Accuracy of mirror images

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How accurate are mirror images of the face? I ask this because if one looks in the mirror, one's images reverses. Does the reversal have an effect on the accuracy in showing our face? They have manufactured mirrors that show non reversed images of yourself -- I wonder how an image from one of those mirrors would differ from the image seen from the normal mirrors we encounter everyday -- would there be a significant difference or none at all?

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- Feynmann on mirrors

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If you imagine a vertical line dividing your face into two halves then the two halves will, in almost every case, be unbalanced to some extent. You can get some idea of this by holding a sheet of card that covers half your face and looking in a mirror then repeating with the other side of your face. This why you always feel that there is something "strange" about photos of your face.

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If you place the edges of 2 flat mirrors together so the mirrors faces are at 90 degrees and look into the "corner" you will see a reflection of the reflection of your face so it will be the right way round. You can then compare it with an ordinary mirror image.

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If you imagine a vertical line dividing your face into two halves then the two halves will, in almost every case, be unbalanced to some extent. You can get some idea of this by holding a sheet of card that covers half your face and looking in a mirror then repeating with the other side of your face. This why you always feel that there is something "strange" about photos of your face.

That is simply illusion. Mirrors form perfect images unless they are imperfectly constructed.

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That is simply illusion. Mirrors form perfect images unless they are imperfectly constructed.

I suppose what Tony ment is that our face is not perfectly symmetrical. Perfect symmetry produces a face that looks very weird, like a puppet or a robot.

Another thing:

when you stand in front of a mirror, you think you see yourself as you are. Now take a measuring tape, and measure you face. then put the tape upon the mirror and measure what you see. You will realize that your image is smaller than you. In this sense, accuracy is reduced.

A full-size mirror, that is a mirror where you can see yourself completely in upright position, has no need to be as large as you are. Your image fits in about 3/4 of your size. Usually a 30cm wide and 1,50m high mirror is enough.

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Also, most if not all mirrors have the reflective surface on the back side of a glass. That means the image you get from yoursel has passed through glass 2 times, one going, one coming back. Which reduces accuracy too.

Edited by michel123456

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You are measuring in the wrong plane if you hold the tape measure against the mirror. The reflection object is the same distance into the mirror as you are away, distance makes things.appear smaller.

I think we need to define "accuracy" more precisely.

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You are measuring in the wrong plane if you hold the tape measure against the mirror. The reflection object is the same distance into the mirror as you are away, distance makes things.appear smaller.

I think we need to define "accuracy" more precisely.

By accuracy I meant the face as it is. Does the mirror show that despite the reversal? Personally I don't see how the reversal produces any distortion.

I've gotten conflicting views on the subject when I posed this question on other science forums. Some say there is no distortion -- after all the image is identical. Others say the reversal decreases accuracy and produces distortion.

Another thing I am interested in is does the image of the face in the mirror show what others see of you?

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Another thing I am interested in is does the image of the face in the mirror show what others see of you?

Does your mirror image look the same as video or still-photo images of you? Yes.

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The distortion will depend on the mirror surface. If you take some optically flat piece of aluminium it will appear very close to perfect, slightly off as the metal absorbs slightly more at lower wavelengths. Something like gold will obviously give you less "accuracy" as there is far far more absorption at visible frequencies. And if you roughen the surface you will also induce distortion.

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Does your mirror image look the same as video or still-photo images of you? Yes.

I don't think so.

The image in the mirror is 3D, the video or still-photo is 2D.

And all cameras have distortions.

To have an idea of the reversal effect, you can do that with a webcam. There is almost always an option of "mirrored" or "non-mirrored" image. Switch between the 2 options and see the difference.

Edited by michel123456

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I don't think so.

The image in the mirror is 3D, the video or still-photo is 2D.

And all cameras have distortions.

To have an idea of the reversal effect, you can do that with a webcam. There is almost always an option of "mirrored" or "non-mirrored" image. Switch between the 2 options and see the difference.

Don't videos show 3D? Anyways, good suggestion. Videos and photos produce non reversed images and sequences. The thing is, there actually are differences between videos of myself and the image of my face in a mirror. Whether that is due to my perception or the reversal of the mirror image producing distortion or deviation is unclear to me.

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I don't think so.

The image in the mirror is 3D, the video or still-photo is 2D.

And all cameras have distortions.

To have an idea of the reversal effect, you can do that with a webcam. There is almost always an option of "mirrored" or "non-mirrored" image. Switch between the 2 options and see the difference.

The question as about the fidelity of the image. Any question of distortion is a matter of degree. Eyes have distortions, too. Light going through air has distortions.

Mirror images are 2D if there is no motion. You can make 3D stereoscopic pictures. So that's really not a distinction that matters.

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The image in a mirror is reversed relative to a photo. Whether this reversal itself, as perceived, is the reality, or the way you view the world and your photos, is impossible to say.

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My interpretation of the OP and followup is whether the image is a 1:1 linear mapping of the object, or if there are nonlinearities (distortions). Imperfections will introduce small defects, but the basic answer is yes. Image reversal is simply a minus sign.

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Don't videos show 3D? (...)

Regular video shows 2D + motion, unless you get new technology 3D screen and look with special glasses.

A regular picture of yourself shows you also 2D, projected from 3D reality unto a 2D sheet of paper or display screen.

That difference makes some people look "photogenic" when the projection of their face looks great, while you may not recognize the person in real life when occasionaly you meet him (her).

In a mirror, the image is 3D because you see it with both eyes: each eye sees something different and the superposition of the 2 images in the brain makes the whole thing a 3D picture.

In a photo or regular video, your 2 eyes look at the same picture, the superposition in your brain makes nothing more, the result is a 2D picture.

Edited by michel123456

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The point I made is that the face is not perfectly symmetrical and the image in a mirror is reversed left to right when compared to actuality. To take an extreme example, if by some unfortunate chance you had lost your left ear the image in the mirror would lose its right ear although a photo would show you had lost your left ear. So, as I understand it, the answer to the OP's question is "Yes there would be a significant difference".

Edited by TonyMcC

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