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Nick
2005-Jan-26, 07:44 PM
Hello all, looooong time since I posted in here :)

I was looking at the latest SMART-1 photo's, and the same old question that has always hit me when seeing these pictures of the moon arose - why do the craters look like mounds?

Here is the image from ESA:

http://www.esa.int/export/images/imageL,141.jpg

A typical example of craters showing as mounds.



Now, I wacked that into Gimp, and just inversed the image.

http://linicks.net/inverse.jpg


Now, this is all to do with the way the light reflects, I know. By why does it show as mounds? You would think 'inversing' it would still show as mounds, but with the light on the opposite side?

Nick[/img]

Ilya
2005-Jan-26, 07:50 PM
Because of the way human brain processes information. We expect (unconsciously) for the light to come from above, and interpret shadows accordingly. When light comes from below -- as in your image, -- our brain visual center is fooled.

Instead of inversing the image, rotate it 180 degrees, and see the difference.

Trebuchet
2005-Jan-26, 07:52 PM
Your brain is accustomed to assuming light comes from the top. In this image it comes from the bottom. Try just rotating the image 180 degrees, it will look like a crater.

Edit: Dang, Ilya beat me to it while I was playing with the image!

W.F. Tomba
2005-Jan-26, 07:57 PM
It might help to get a different crater image and turn that upside down. I find that once I've identified one particular image as concave or convex, it's hard to see that image the other way, even if I turn it around.

Nick
2005-Jan-26, 07:59 PM
Amazing. I really never looked into this before. I am amazed!

Nick

Swift
2005-Jan-26, 07:59 PM
This is a common problem in electron microscopy work - telling if something is a mound or a dimple.

Nicolas
2005-Jan-26, 08:15 PM
Amazing!

Turning both 180 makes the normal one look like a crater, and the inversed one like a hill. All just because of us expecting unconsciously a light source from above.

I saw the picture before, and thought "that would look more like a crater if it was inversed (B/W inversed I mean)" but I never really did it. Turning it around (180) really nicely prooves that lightsource thing in your head!

Jorge
2005-Jan-26, 09:14 PM
try practing reading upside down, afte a while you will start to get used to this and you will not see it a hill but you'll see it as a crater.

i been reading upside down latley(in school) and i didn't have probems with the original picture.

ToSeek
2005-Jan-26, 09:46 PM
I can get the original picture to look the way it should if I concentrate for a moment.

Evan
2005-Jan-26, 09:47 PM
For another interesting illusion try turning your computer monitor 90 degrees. It doesn't work to turn your head either. We are so accustomed to looking at the 4/3 ratio screen that it looks nearly square. When you rotate it 90 it is then 3/4 and looks very strange.

Nick
2005-Jan-26, 09:48 PM
i been reading upside down latley(in school) and i didn't have probems with the original picture.

You in Australia?

Nick :wink:

The Bad Astronomer
2005-Jan-26, 11:12 PM
I talk about this in reference to the "glass worms" on Mars in the Hoagland section of the main site.

Here is the best example ever:

http://www.badastronomy.com/pix/shading1.jpg

You see one dimple and 5 bumps, right? Now look here:

http://www.badastronomy.com/pix/shading2.jpg

Now there are 5 dimples and one bump. However, it's the same image! I just flipped it upside down. Amazing, eh?

R.A.F.
2005-Jan-27, 12:30 AM
Hmmm, I must be weird or something. (hey, no comments from the back of the room!) I see both images as craters...I don't perceive any mounds. Does that make me weird, or what? (...and don't answer that either). :lol:

Arkyan
2005-Jan-27, 12:55 AM
Even stranger, when I looked at just the top image it looked perfectly normal to me. I scrolled down to the second image, and it too looked normal. When I then scrolled back up, the craters suddenly looked punched out in the wrong direction!

Splitter
2005-Jan-27, 01:05 AM
No one has mentioned that if the crater or dimple you're viewing is steep enough in relation to the light source, you will have an effect of shadows, which will screw up any attempt to turn a mound into a dimple by simple color inversion. The albedo of the material probably further upset the experiement as well.

Charlie in Dayton
2005-Jan-27, 08:27 AM
try practing reading upside down, afte a while you will start to get used to this and you will not see it a hill but you'll see it as a crater.

i been reading upside down latley(in school) and i didn't have probems with the original picture.

It also can win you some bar bets...

When I was a kid, there was a 'teach yourself French' comic strip in the funnies. It was The Count Of Monte Cristo (I think), with the captions in French, and the English translations under the panels upside down. I got tired of turning the paper around to read the translations.

It blows people away when I read something upside down, and get it right...lotza fun...

the_shaggy_one
2005-Jan-27, 09:21 AM
Reading upside-down is not that impressive a feat, for those of us who are lexdysic. :P

ToSeek
2005-Jan-27, 03:19 PM
try practing reading upside down, afte a while you will start to get used to this and you will not see it a hill but you'll see it as a crater.

i been reading upside down latley(in school) and i didn't have probems with the original picture.

It also can win you some bar bets...

When I was a kid, there was a 'teach yourself French' comic strip in the funnies. It was The Count Of Monte Cristo (I think), with the captions in French, and the English translations under the panels upside down. I got tired of turning the paper around to read the translations.

It blows people away when I read something upside down, and get it right...lotza fun...

I was at the Smithsonian years ago at the information desk looking for a particular exhibit. The docent was blown away that I was able to spot the information I wanted in her schedule sheet quicker than she could when I was reading it upside-down.

Tom
2005-Jan-27, 03:37 PM
Here's a picture I took in the early morning, at a beach:

http://notforprophet.org/pictures/smallprint.jpg

On the camera LCD, and in all smaller pictures, it DOES look inverted. My son asked me how we made the footprint! However, in a larger copy, the impression is obvious. Here's a link to the original if anybody wants to compare:

Original footprint (http://notforprophet.org/pictures/footprint.jpg)

Hee hee... or is it obvious? Until I read this thread I had no problem seeing the impression, now I am struggling. There's probably a government grant in here somewhere...[/url]

Nick
2005-Jan-27, 05:22 PM
Turn it upside down! Heh.

I am really amazing at this. Forget the Universe, the mind is just as strange!

Nick

John Dlugosz
2005-Jan-27, 07:12 PM
try practing reading upside down, afte a while you will start to get used to this and you will not see it a hill but you'll see it as a crater.

i been reading upside down latley(in school) and i didn't have probems with the original picture.

I read an entire book upside down ("Through the Looking Glass") and found that I read measurably slower that way. No effects noted on shadow processing, though.

A Thousand Pardons
2005-Jan-27, 07:14 PM
back to front? or front to back? top to bottom?