Do you see the phantom colours or not, though? This animated gif will mask out everything except the grey that should appear yellow on the right and blue on the left, unmasked.
I saw those last week. My brain still hurts.
#3 is just nuts. I work with color and photographs all the time, so I know how our eyes can automatically “color correct” for different colored lighting, but this one still weirds me out. No matter how hard I try, the central cross on the right looks yellow. My brain cannot comprehend that it’s actually gray. The central cross on the left looks bluish-grey. I had to Print-Screen it, too, to believe it.
Larry Mudd - The effect you tried to reproduce doesn’t work for me. They both look pretty neutral gray to me.
Larry Mudd - On the left I see yellow letters on a gray background, and an orange strip at the bottom with yellow letters. On the right I see yellow letters on a blue background, and a red strip at the bottom with yellow letters.
Me either, the one that was supposed to look yellow just looked gray to me, though the rest of the structures were different colors. The first one was the only one that worked for me, but I think I’ve seen the middle one somewhere before, so maybe that’s why.
My mother always warned me that if I kept on doing that, I’d go blind.
I guess I never knew she meant color blind.
I see basically the same thing as yoyodyne, but I’m fairly sure you didn’t set up your illusion correctly. I made a paper mask to look at just the banners without the surrounding stuff. When the yellow and blue filters are on, the banners definitely have actual colors to them. On the other hand, illusion #3 actually has medium gray crosspieces that only appear different colors. I suspect your graphics program is applying a filter calculation to the banners, to simulate looking through a physical yellow or blue filter. What you want to do instead is only apply the filter to the background, and put your black and gray banner on top afterwards.
I hope y’all are happy. I just burst a blood vessel in my eye!
Just kidding. 
If you’re seeing the same stuff as yoyodyne, then it’s working correctly.
Heh. Actually, that’s exactly how the image is made. The grey parts of the image are on top, and 100% opaque, 50% grey. The banners underneath are altered from the original colours to primary additive colours. The simulated filters do subtrace, and make grey – but done that way the closest I could get each to being “perfect” grey was 127,127,128 and 128,128,127. The top layer is just to make them exactly the same grey, although that tiny difference would hardly be noticible to the naked eye.
Here’s a screen-shot of the Photoshop layers panel. (The animated .gif showing the grey areas isolated cycles between all layers being visible, and only the top (grey) and bottom (black) layers showing.) If you have a graphics editor, you can confirm for yourself that it’s really grey.
…subtract. Argh.
Me too. When I drag the mask over them they appear to me to be quite different; the one on the right has a substantial amount of yellow in it.
Heh, sorry I was looking at the wrong things. I was comparing the letters on the left with the background on the right.
Wow. Cool. The green dot popped up almost immediately for me, and I saw it going round and round.
As for the original optical illusions in this thread, I had seen #1 before (it is amazing though), and #2 wasn’t that amazing to me, but #3 is just… unreal.
There’s an interesting article on How You Think You See in the University of Chicago Magazine from June of 2004. Just the cover of the magazine (shown on the linked-to page) was a pretty cool color illusion; there are a couple more in the article AND it explains how some of this freaky stuff works.
A lot of this comes from the powerful post processing our brain does to what we see, constantly adjusting for color and brightness. Normal white light is anything but that. If your digital camera has settings for white balance set it to daylight and take a photo outside then compare it to one inside under tungsten or florescent lights and see how dramatic the color is. You can do the opposite, set it for tungsten then take shots in daylight or with flash.
Hey, this isn’t exactly the same thing, but her’s a guy who does pavement art which, when seen from the correct angle, looks 3-dimensional. Very cool
I seem to be another person for whom the two crosses doesn’t work. The centerpiece on the left looks like a slightly darker version of the one on the right. And while the left centerpiece looks slightly purplish, I can’t detect any “yellow” in the right centerpiece.
The other illusions worked very well however. The checkerboard and the green spot were especially effective.
Looking at it some more, I found it greatly enhances the effect if you start out at the ends of one of the arms of the cross and then work your way to the center, stopping to look at each color in succession.
I blew them both up. Gosh, maybe it’s our computers or something, but they do have different mixes of color. There’s just no question about it when they’re blown up. They are not identical and have a different mix of pixel colors.
Obviously the illusion exaggerates the difference, but they are not really the same.
Cool! It reminds me of the advertising beside the goals that I see on soccer games on the Spanish channel. They’re designed so that the camera shows them as 3D like that, then you see a player run across the top of them…and they’re flat. Freaky.