Actually, you can get some stereograms where you have to cross your eyes.
You can see the 3D effect by crossing your eyes and letting them uncross until the image appears. I cannot do it by the “unfocusing” technique, but I can easily do that. One trouble with the “eye-crossing” method is that it reverses the image - the bits which are supposed to be sticking out are recessed instead. This sometimes makes it difficult to see exactly what the image is supposed to be, although the 3D effect is obvious.
I suppose the ones where “you have to cross your eyes” are designed to produce the intended image when you cross them, and you will see a reverse image via the “unfocus” technique.
If I do it for very long it also gives me a headache.
I was able to make two different images out of this one – First the single teapot (which is the intended one) and then at a ‘different’ level of out-of-focus I got a much smaller but same shaped teapot floating in front of two larger ones. The two larger ones were the same shape but much larger, and one was offset about half way to each side of the front one.
Never had that happen before.
Really? I’ve never seen any, links welcome.
The sample image of the OP is of the uncrossed-eyes type, you can get a stereogram effect with crossed eyes but the image is “inside-out” for want of a better expression.
In the Book “Super Stereograms”, they had a whole variety of different sorts of stereograms including ones which can only be viewed properly by crossing your eyes.
[nitpick]There are many types of sterograms, including various kinds that require special glasses or viewing apparatus. This particular type is called a single-image random dot sterogram.[/nitpick]
I claim my £5
It has nothing to do with un-focusing. You really have to focus very well to see it. But you have to focus while being cross-eyed. If you just crossed your eyes things get blurry right? Now the trick is focus while your eyes are crossed. I can certainly agree with the kitchen floor with similar tiles being the same color and size. It will look like twice the amount of tiles, but they are all crystal clear, because your eyes are focused while crossed. Make sense? For me, it was practicing on a set of LED panels here at work in a grid pattern. Crossing my eyes just a little would make the panel look like it had a 1/3 of the amount of lights but at the same time, making the whole panel looking smaller. The more I crossed and focused, the more lights and the small it got. Hope this helps.
You are not “crossing your eyes” any more than you are when you are looking at an object placed about a foot away. If you look at the retouched graphic I have marked with arrows two points, on in the foreground, one in the background. The separation between their pairs (marked by arrows) increases by about 10% so that one appears farther than the other. If you look in a mirror both your focus and convergence are adapted to the same virtual distance but here you have to adjust your focust to the actual distance to the screen while you have to adjust your convergence to the distance to the virtual image located behind the screen at a distance of 30 -40 cm (depending on the size of the image on your monitor.
You can see how the effect of the tilted plane is achieved by gradually increasing separation.
Also, I find it very easy to "find"the image if I look for the straing line which divides the backgrounds on the lower left. Once that straight line appears then I can move around the rest of the picture.
You may realize this, but what happened is that you crossed (or uncrossed) your eyes twice as much as you needed to to give you that second image.
I just focus on the reflection on the surface (monitor, glass, etc) and I see the Stereograms within 15 seconds.
Hey… look! A sailboat!
I have always been very good at stereograms. I think it harkens back to one day when I was at my grandparents’ and I was given an entire book of the things. I sat there, and for two hours that is all I did. Ever since then, I see them in seconds.
What I do is I stare at it with one eye and cross the other. (I think.)
Crossing your eyes is easier for some people. If you do this on the image in the OP, you get a teapot-shaped hole in a foreground that looks like an overhead view of a roof.
There are freeware and shareware programs that will create images like this. The trick is producing the original 3-d representation of the object.
I once saw a short SIRDS animation (.avi, IIRC) using tiny black and white dots so each frame looked completely random unless you uncrossed your eyes. It was just one block-printed word moving above and beneath the background, but it was pretty cool.
Here’s a very simple relative of these images that may help you to see and understand the effect. Cross your eyes, and the words “front” will appear closer than the words “back”. Uncross them and you will see the reverse.
f f f f
b b b b b b
r r r r
a a a a a a
o o o o
c c c c c c
n n n n
k k k k k k
t t t t
I see uncrossed images so quickly and automatically that to check I had constructed this correctly I had to cross my eyes extremely (to make sure that’s what I was doing) then slowly reduce the crossing.
Um … folks … how does one intentionally cross one’s eyes?
I too am one of those people who can see this nearly instantly. The first one I saw took about 5 minutes, then a minute or so. But, I used to have one on my wall at home in high school, so I got to the point where I can unfocus my eyes the exact amount instantly. The teapot here was the first one I’ve seen in a few years and it took me about 1 second to see.
Jman
Look at the tip of your nose. Your eyes are now crossed.
For looking at SIRDS (Single Image Random Dot Stereograms), you don’t cross your eyes. You let your eyes “focus” on a point farther than the piece of paper (or screen). By “focus” I don’t mean the optical focus, I mean the alignment of the two eyes.
I don’t know if this helps at all, but the way I used to practice was simply to draw two dots or circles, like so:
o o
Now put your face close to the screen (say 5 inches), relax your eyes and pretend you are looking through the screen at something much farther away. Your eyes will lose their “lock” on the screen and you’ll see four ghostly circles instead of two. Now pretend that the inner two of the four ghostly images are one object, and try to focus on it. If you do it right, you’ll see three circles. The middle one should be solid, and the two on the sides should be sort of fuzzy. But don’t look at those, keep staring at the one in the center. What’s happening is that your right eye is looking at the right circle, your left eye is looking at the left circle, and your brain is fooled into thinking it’s looking at the same object. When you learn to do that, try the SIRDS which sailor retouched. Do the same thing with the two arrows.
You can even draw your own stereogram (not SIRDS) if you are interested. Here’s one:
____ ____
| | | |
| o | | o |
|____| |____|
The circle should be floating in front of the box. When you focus through the screen, your right eye sees the right image and left eye sees the left image. So just draw two images from the appropriate perspectives. SIRDS is a bit more complex, but the principle is the same. The two images are merged into a single image.
By the way, don’t do the two dot excercise by looking at my post. It should be easier if you draw two dots on a completely blank sheet of paper.
Whoa! The OP’s is the first I’ve ever been able to make out. Probably because I’ve had 11 hours sleep in the last 50-something hours. That’s pretty cool (the image, not the lack of sleep).
Something similar- When I had a picture tiled on my desktop, after a while, my eyes would get lazy, and I’d start seeing double (as you do when you cross your eyes). At the right moment, two of the adjacent desktop tiles would appear to overlap. At that point, any open window (anything that’s not a part of the pattern) would appear to have a 3D look to them. Try it, use a picture roughly two by two inches that doesn’t repeat within itself.