3-D Optical Illusions

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Alan H · #1 Post by **Alan H** » March 16th, 2009, 1:03 am

Fascinating. These two photos are identical:

More on this optical illusion in Scientific American.

Maria Mac · #2 Post by **Maria Mac** » March 16th, 2009, 1:14 am

Is something supposed to happen when you look at them or are they just 'fascinating' because they look different?

OK, I'll click on the link.

Paolo · #3 Post by **Paolo** » March 16th, 2009, 7:55 am

Interesting article and I get it for the leaning tower, but I didn't get it at all for the train tracks. Perhaps my brain doesn't work properly, or maybe I looked at the pictures as 2-D images rather than as representations of 3-D scenes, hmm... I'll have to think about this some more...

Alan H · #4 Post by **Alan H** » March 16th, 2009, 9:26 am

I see the effect far stronger in the rail tracks than in the tower of Pisa photos!

Ken H · #5 Post by **Ken H** » March 16th, 2009, 12:22 pm

They both work for me, but the tracks work a little better.

Paolo · #6 Post by **Paolo** » March 16th, 2009, 1:28 pm

Weird.

When I saw the train tracks I was wondering why Alan felt the need to say that they were identical photos - I couldn't (and still can't) see anything different between them.

Maybe my depth perception is poor (I've never noticed that to be the case before - normally it seems pretty good in fact) or perhaps I automatically treat 2-D images as being 2 dimensional rather than representations of 3 dimensions. This would make some sense, since I have spent quite some time considering methods of avoiding or correcting for error in 2-D projections of 3-D objects. In fact I suggested a simple method of quantifying such error in my thesis and I suggest a simple correction for it in a paper I am about to submit.

I think this might be something worth thinking about some more. Does anyone else not see any difference?

Alan H · #7 Post by **Alan H** » March 16th, 2009, 1:47 pm

I see the left set of tracks going off way to the left in the distance, but the right set of tracks going off virtually straight ahead, even though I know they are identical. The directions do change a bit depending on where I focus my attention, and is most pronounced when I focus on the bottom of the join of the two photos.

jaywhat · #8 Post by **jaywhat** » March 16th, 2009, 2:12 pm

Those train track pictures are so different that I could not believe they were the same picture until I studied them separately and checked distances form corners etc. Same if you close one eye - which I did to test because I have one very bad eye anyway. (As my avatar will tell you)

Fia · #9 Post by **Fia** » March 17th, 2009, 10:45 pm

Paolo wrote: I think this might be something worth thinking about some more. Does anyone else not see any difference?

I can't see any difference in the train tracks either. Tried the old woman / young woman illusion trick by looking away and back. Nope. Wondered if it might be different if I peered close to the screen without my glasses, which correct astigmatism (and myopia). Nope. So that theory out of the window then

But the Pisa pics (when I'd stopped laughing at a comment calling it the tower of 'pizza'

) I could see a difference, bespectacled and otherwise. There appears to be disagreement re perspective, perhaps some clever person could find some old pre-perspective art and try that?

Alan H · #10 Post by **Alan H** » March 17th, 2009, 11:11 pm

The leaning towers of Pisa is the same effect, but I found the railtrack much more vivid. I guess our brains are all a bit different...

Paolo · #11 Post by **Paolo** » March 18th, 2009, 6:48 am

Fia wrote: I can't see any difference in the train tracks either.

Glad it's not just me then!

Alan H · #12 Post by **Alan H** » May 19th, 2009, 5:19 pm

OK...what do you see here?

Please add your comments to Richard Wiseman's website.

getreal · #13 Post by **getreal** » May 19th, 2009, 5:52 pm

Nor can I see any difference in the train tracks. Nice to know I'm not alone in that (and that, in itself, is interesting). I do however, notice the other differences.

Comments were also interesting to read.

Alan H · #14 Post by **Alan H** » May 19th, 2009, 7:24 pm

There is no difference between the photos of the train tracks! That's the point, but they look different side by side, with the two sets of tracks going off in (apparent) different directions.

Fia · #15 Post by **Fia** » May 19th, 2009, 10:21 pm

Alan H wrote: Please add your comments to Richard Wiseman's website.

I thoroughly enjoyed the use of the word décolletage after all those books / boobs

getreal · #16 Post by **getreal** » May 19th, 2009, 11:01 pm

Alan H wrote:There is no difference between the photos of the train tracks! That's the point, but they look different side by side, with the two sets of tracks going off in (apparent) different directions.

Sorry, I didn't put that very well, what I should have said is that I don't see the illusion.

Alan H · #17 Post by **Alan H** » May 19th, 2009, 11:16 pm

Ah!

As someone who can very clearly see the tracks going off in different directions, I find it difficult to understand how anyone can't see it! I assume this is an extrapolation of everyday experience: I'm sure we all see the same thing 99.9999% of the time!

Alan H · #18 Post by **Alan H** » July 1st, 2009, 5:55 pm

Not 3-D, but interesting:

The 'green' and the 'blue' are, in fact, the same colour!

For further details, see Richard Wiseman's blog.

Not that I didn't believe him, but I've checked it as well!

Hundovir · #19 Post by **Hundovir** » July 1st, 2009, 8:06 pm

Oops! Can't remember if i got this link from this forum or "Atheist Forums". Apologies if repost, but a lovely site:
http://www.michaelbach.de/ot/

Emma Woolgatherer · #20 Post by **Emma Woolgatherer** » July 2nd, 2009, 12:32 am

Alan H wrote:The 'green' and the 'blue' are, in fact, the same colour!

For further details, see Richard Wiseman's blog.

Not that I didn't believe him, but I've checked it as well!

See the response from "Carl":

That’s pretty impressive, although there is a bit of a digital-image artefact which could be affecting the result. If you zoom in a lot so you can see the individual pixels, you’ll notice that the jaggy borders between colour regions have significant ‘anti-aliasing’, resulting in several pixels of an in-between colour along the borders. This is a standard digital image technique, making jaggy, pixelated lines look smoother. However, in this case, it could be accused of contributing to the perceived illusion effect.

You’ll note that at the centre of the image, the spirals get so close together that the anti-aliased blends become larger than the spirals themselves, and so most of the pixels of the ‘green’ are very much NOT the same colour as the pixels of the ‘blue’.

However, I will concede that the bands at the outside are wide enough so that there is significant amounts of same-coloured pixels. So, yeah, after all that, it seems the illusion still ‘works’, and it’s damned good.

Still, for complete rigour, I wonder if anyone can be bothered rendering a high-resolution version with no anti-aliasing.

This version has no anti-aliasing, and although it still works as an optical illusion, it's easier to see that the 'blue' and the 'green' are actually the same colour:

Emma

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