Saturday, January 19, 2008

Mirror

Update on the (quotable) bathroom-mirror situation: my landlord finally installed a new one.

18 comments:

stefan said...

Photographing the image in the mirror - that's irritating, since I tend to mix up left and right even without that extra complication ;-)

Cheers, Stefan

Uncle Al said...

Mirror the image in Photoshop and keep a straight face thereafter.

a quantum diaries survivor said...

Nice pijama with skulls Bee :)

Cheers,
T.

Bee said...

Pyjama! What Pyjama! That's my presently favourite shirt, I don't wear it to sleep, but to sit through admin meetings.

Uncle, my face has never been straight, and I doubt it ever will be.

Best,

B.

Neil' said...

Folks, did you know that mirrors don't really reverse right and left? Seriously - write something on a transparent sheet and just hold it up, facing you normally, in front of the mirror. The text as seen in the mirror is normal (well, what is near your left hand must still be near it, etc.) But when you have writing on opaque paper, you turn it around so it will face the mirror, only because the letters are hidden to the view from the other side. Similarly for rear-view mirrors etc: You turned around so your left and right switched places, to look at that stuff behind you.

Don't be embarrassed if you had been confused before, this is one of those "how ob(li)vious" things, and you can find more in some popular and cognitive training works. What do mirrors really do? They reverse front to back, the coordinate perpendicular to the mirror: Then z becomes -z, and that does reverse the handness of the mirror-world coordinate system since x and y remain the same as noted.

Phil Warnell said...

Hi Bee,

You now know what the anti-Bee looks like, so if you ever happen to see her you can avoid meeting at all cost:-)

Best,

Phil

Ryder said...

Your white balance is off.

Cheers,
Craig
(may be the only advice I can ever give a site full of physicists so I had to make my play.) lol

CarlBrannen said...

Yeah, the mirror in my bathroom doesn't seemt to reverse left and right. As far as I can tell, it reverses up and down.

Phil Warnell said...

Hi Carl,

“Yeah, the mirror in my bathroom doesn't seemt to reverse left and right. As far as I can tell, it reverses up and down.”

You have to avoid those made by the Stern–Gerlach company.

Regards,

Phil

Phil Warnell said...

Hi Neil,

“Then z becomes -z, and that does reverse the handness of the mirror-world coordinate system since x and y remain the same as noted.”

What you have described is an aspect of symmetry referred to commonly as mirror symmetry. Interestingly enough this is tied in with CP invariance and subsequently one way to define a violation of this. One aspect of nature that violates this invariance is K meson decay. Many physicists consider this small violation is the reason we have a mostly matter, as opposed to anti-matter universe and also why the matter contained in the total universe is so small. I however don’t know how all this recent revelation of matter/dark energy may have altered this view. Perhaps the authors of this blog could shed a little light on this.

Regards,

Phil

Arun said...

Yep, Canon doesn't seem to get white balance right under incandescent lighting. Bee, just sent you an attempted correction.

Best,
-Arun

Bee said...

Dear Arun:

Thanks for sending the file, I've copied it here. I liked the result as it was, so I resisted tuning some scales in photoshop, but yes, now the colors are better balanced, even to my unprofessional eye. Best,

B.

Bee said...

Hi Neil':

Thanks for the clarification. It had occurred to me before that a mirror reflects the axis perpendicular to it. However, if you reflect a 2nd axis (left-right, up-down, whatever), you can turn the result back into the original. Best,

B.

stefan said...

Hi Neil', Carl, dear Bee -


... I was just about to write that on the question: Why does a mirror reverse left and right, but not up and down?, my favourite answer is: Well, actually it reverses neither left/right nor up/down, but front and back.

Then, your neurons map what you see on the usual image of a human (performing a rotation around the vertical axis, which is special because of the symmetry breaking gravitational field), and that's how the left/right problem comes into play ;-)

Best, Stefan

Arun said...

Dear Bee,
Click your way through this tutorial;
it will change what you think of photographic reality forever :)
Best,
-Arun

Bee said...

Dear Arun:

Oh, wow. I think the shadow over the left eye is overdone, but otherwise that's pretty impressive. Though it is similarly depressing. In lack of models, I used to take photos out of magazines for my paintings, but I've given up on that. Most of the photos one finds these days in advertisements are so photo-shopped to smoothness there is nothing to see in them. At some point they can stop taking photos alltogether and just generate the images on the computer. Best,

B.

Arun said...

Dear Bee,
This thread http://www.fredmiranda.com/forum/topic/596107
deals with finding photography models, but maybe some may pose for paintings? I dunno, just a suggestion.

Best,
-Arun

Arun said...

Dear Bee,
In order to view the "People" photography forum on fredmiranda.com, you have to register (you can view all other forums without signing up). Fortunately, you will not be bothered with email or spam if you register. Sometimes there are interesting compositions posted there.

e.g., http://www.fredmiranda.com/forum/topic/601475
which is flawed but interesting.

Best,
-Arun