optical illusion question...

I’m not sure how to ask this question, so forgive me if it’s hard to understand what I’m saying here…

Is there any type of optical illusion or special optical device where if you’re looking at… say a computer screen… and you can’t read what’s on the computer screen it’s just lines… and you put on glasses or something special and it reveals to you what’s really on the computer screen? Or something like a comic book where the image looks jumbled… put on special glasses and the image is revealed to you?

The phrase ‘optical illusion’ usually (but not always) refers to a static image that is designed so as to highlight particular quirks of our visual and perceptual mechanisms. For example, an optical illusion might show us that our judgement as to whether or not two lines are the same length can be influenced - and thrown off - by surrounding perceptual cues (or intentional mis-cues). There are of course hundreds if not thousands of different optical illusions, and you can find them easily enough all over the web.

What you seem to be asking about, remisser, is something that works in a slightly different but related way, and is essentially about disguised or scrambled information. When you look at the item one way it reveals very little information, but looking at it another way with some sort of additional viewing device or mechanism reveals much more information.

I am not aware of anything that I would describe as an ‘optical illusion’ that works in this precise way, although there are many wherein what you see as a ‘first impression’ gives way to the awareness that the image actually contains far more detailed ‘covert’ content or is actually ambiguous.

However, I can list a few things that may approximate what you’re after.

(1) Magic Eye images. These appear to contain no information or ‘image’ at all except a bizarre pattern of repeated elements. When you learn to view them correctly, the brain can process the image to ‘perceive’ a three dimensional shape ‘concealed’ or ‘encoded’ within the pattern. ‘Magic Eye’ is a trademark, I think, but the term is widely used. Google is your friend. It’s harder to find the information you need to make your own, although you just have to dig a little deeper.

(2) Random dot stereogram. This consists of two squares, side by side, each of which appears to be the same random pattern of black and white dots. However, when you fuse them together with your eyes, you perceive some of the dots as floating higher than the base plane, and some of them as lower. In this way, some useful information can be ‘coded’ into the RDS. It’s easy to make these. Google away!

(3) Mirror writing. If you just write a message backwards, it is fairly obvious (to anyone who reads and writes the same language) that it is mirror writing, and that to read the message properly it is only necessary to hold the text up to a mirror (or just work it out in your head). However, if you take a simple line of text, write it in a slightly distorted or ‘jazzed up’ way, mirror-reflect it and then embed the text in a larger pattern or design intended to disguise the fact that there is any writing there at all, you can achieve an image that doesn’t look like itcontains a message at all. However, when you hold it up to a mirror, the text tends to ‘jump out’.

(4) Colour filters using dilute inks. Create any random or distracting design you like, the more fine details the better, using predominantly red ink. Take some green ink, and make a dilute solution of it (e.g. try one part ink to five parts water at first , and experiment from there). Take a paintbrush, and paint your secret message or image on the red pattern with the dilute green ink solution. Let it dry. When you look at the result usuing normal vision, you won’t see much if anything of whatever you wrote or drew using the dilute green ink. Look at it through a red-tinted lens, however, and the green ink message should appear fairly conspicuous. It takes a lot of experimentation to get this to work satisfactorily.

(5) Polarising filters. It is possible to create artwork and use polarising filters such that when the nearest filter is in one position you see one thing, and when it is rotated 90 degrees you see something different. There are places where you can buy inexpensive polarising filters printed on plastic, and experiment with them yourself.

(6) Mosaics. You can create both mosaic and pixellated images that don’t seem to contain any information close-up, but when you look from a sufficient distance away you can see that they are a portrait or a recognisable scene. It’s easy to explore this in Photoshop, and there are many examples online. To see this kind of artistry taken to its limits, Google the name ‘Frank Knowlton’.

(7) Ambigrams. Pieces of artwork or text designed so that they can be read in two or more distinct ways. Google on ‘ambigram’ or ‘Scott Kim’.

That’s all I can suggest for now. Good hunting.

There are a number of ways you can do that. The simplest is probably with colour filters.

Here’s one very simple way you could do it using a standard pair of red/blue 3D glasses, if you have photoshop or a similar application.

Make a Photoshop image with a random dot pattern, like this.

Make another Photoshop image the same size. Set the foreground colour to white and the background colour to black, and FILTER–>“Render clouds” to give a random background.

Put the content you want to encode in black on another layer. I chose super-secret hidden text, like this. We’re going to use this image to manipulate the first one. Set the image mode to greyscale, flatten it, and save it as a .psd.

Now go back to the first (“static”) image, click on the “channels” tab, and select the “red” channel.

Select FILTER–>DISTORT–>DISPLACEMENT

Set the parameters to 10% for “horizontal” and 0% for vertical, and click okay. Now you’ll get a file browser. Select the .psd you saved of the image you want encoded. What this does is manipulate the image you’ll see through the blue filter of your 3D glasses like so: For every pixel in the image, the darker the corresponding pixel is on your “encoding” file, the further to the right it gets moved. Switch back to the RGB channel, and you’ll see the effect – like this.

Without the glasses, it looks like a random distribution of red, blue, and grey dots. But if you put the glasses on, two slightly different images go to each eye, and your brain interprets the difference as depth. So you’ll see a mountainous background with legible cut-out text floating on top of it.

Easy peasy.

preview

ianzin, “Magic Eye” images and random dot stereograms are basically the same thing – single-image stereograms. More complicated single-image sterograms like those in “Magic Eye” books just use more interesting tesselated patterns instead of a random distribution of dots. These are also fairly easy to make without any special software - I’ve made a few in Photoshop using basically the same technique outlined above (as far as making a displacement map is concerned.) It’s just that you organize the image differently instead of working with colour channels.

My only nitpick is that they aren’t two squares side-by-side – you’d have to go way cross-eyed to make that work. The two images are broken up into several alternating vertical stripes – that way you only have to adjust your eyes very slightly to get the corresponding parts of the image to line up.

Here’s a picture that has puzzled me for years. At first sight it seems like a field of flowers, but when you hit Ctrl + a, it changes to a picture of a nude girl. It seems that the “blueing” that Internet Explorer applies to the image when it’s selected brings out the hidden picture. It doesn’t seem to work in FireFox. I guess Firefox doesn’t highlight selected images in the same way as Internet Explorer.

Here is the picture ( Safe for work only if you dont highlight it. )

Can anyone figure out how it was done, and how to duplicate the effect ?

Rockystone; this is quite a well-known trick. Imagine your standard, run-of-the-mill checkerboard. You fill all the black faces with parts of one picture (say, sunflowers), while you fill the white fields with some kind of pornographic image. You tamper that last image a bit, so it has very little contrast. (say, the image is not white on black, but dark grey on black). If viewed from a distance, the checkerboard shows the sunflowers, since the eye can’t distinguish the tones on the low-contrast porn pic, so those get ignored.

The analogy with the checkerboard is that an image on a computer screen is built with tiny squares, pixels. the checkerboard field stands for the different pixels in an image. If, in IE, you select an image, IE fills half of the pixels in a checkerboard pattern with blue, thus obscuring all the pixels of the sunflower image. This way, you can see th low-contrast porn image.
What internet explorer does when you select an image

Thank you mahj. Of course its so obvious once it’s been pointed out. Now I’m off to make my own “Jekyll & Hyde” pictures

There used to be a related trick involving images resized in the browser. Suppose you take an image that’s actually 400 pixels by 200 pixels, say, and tell the browser that to display it as 200 by 200. The browser has to shrink the image horizontally somehow, and the easiest way to do that is to just display every other column of pixels. But IE used the even columns, and Netscape used the odd columns (or the other way around, I don’t recall). So if you made your original 400 by 200 image by interleaving two different 200 by 200 images, users of IE and Netscape would see two completely different images, with no hint of the other image. Modern browsers, alas, seem to use some sort of averaging and interpolation, so nowadays if you try it with either, you’ll just gut both images ghostly overlaid.

I was fiddling about today and made a single image stereogram.

Don’t go crazy looking for the sailboat though, it’s a lazy one – the 3D is based on a fractal image, so it’s totally abstract.