Comments on: Unbelievable Magic Illusion Thingie

By: MrMarkAZ

MrMarkAZ — Tue, 03 Jun 2008 16:26:18 +0000

I took a screen capture of the picture and pasted it into PaintShop Pro. The color dropper confirms it. Both squares have RGB values of 121,121,121. Wow. I never would have believed it otherwise.

By: sailor

sailor — Tue, 03 Jun 2008 11:38:16 +0000

Visual illusions are a wonderful demonstration of our ability to model the world we live in rather than see it as it is. Anything you care to do to cut away the cues that tell you this is a checkerboard with black and white squares will help destroy the illusion.

By: lylebot

lylebot — Tue, 03 Jun 2008 09:32:25 +0000

I’m finding that if I cover up either the half-shadowed light square that’s below A or the half-shadowed dark square above B, I can easily see that A and B are the same color. Without either of those squares covered, A looks darker. I’m not sure how much that’s influenced by already knowing the truth, though—after each “covering-up” experiment, I have to look away from the picture for a while before I can see A and B as different again.

By: Dave Munger

Dave Munger — Tue, 03 Jun 2008 08:31:26 +0000

There is a really cool interactive version of this at Shapiro Lab. Click on the top-left icon under "lightness illusions" and go crazy!

By: Ian

Ian — Tue, 03 Jun 2008 08:21:55 +0000

You guys have wa-ay too much time on your hands!

By: Greg Laden

Greg Laden — Tue, 03 Jun 2008 07:38:18 +0000

If you use the eyedropper tool from The Gimp (I’m not sure what this photoshop thing is you speak of) you can test the color value numerically. They are essentially the same.

By: Martin Richard

Martin Richard — Mon, 02 Jun 2008 21:01:57 +0000

Note to Photoshop Users:Ever tried to find neutral gray by eye, to set the midpoint in the color picker on the curves screen? This illusion demonstrates quite succinctly why you can’t.Here’s a trick to finding the all important neutral gray in your image.Select the image layer in which you need to find a neutral gray. Create a layer directly above it, filled with neutral gray (50% each red, green, and blue). Set the blending mode for this layer to difference. Now create an threshold adjustment layer immediately above that. Click on the icon to bring up the slider which sets the threshold, and move the slider all the way to the left. The image will go white. Start moving the slider very slowly to the right (you can use the up arrow key for greater precision). The first black dots to appear will mark neutral gray in your image. To mark this precisely, zoom in down to the pixels, use the second eyedropper tool to put a numbered marker on the gray pixel(s).There’s your neutral gray.Hide the fill layer and the adjustment layer, select your image layer, zoom in to your marker, call up the curves dialog, click the middle eyedropper, then click the marked pixels. You’ll know you have succeeded if the foreground color changes to gray. Ta-daaaa.To find the black points and white points is easier by eye, but you can use this same trick. Just delete or hide the gray fill layer, and use the slider in the threshold layer. Slide it all the way left, then slowly back right, and the first black pixels are the darkest pixels in your image. Slide it all the way right, the slowly back left, and the first white pixels mark the lightest parts of your image. You can mark these with that second eyedropper, then use the curves dialog to set your black and white points. (Hint: when selecting the white points, do not choose secular highlights–bright reflections such as glare. Choose the lightest white which is NOT such a highlight.)Not a photoshop user? Sorry to bother you.

By: Stephanie Z

Stephanie Z — Mon, 02 Jun 2008 20:58:56 +0000

minusRusty, I cropped out the B and moved it over next to the A. The B is definitely darker, which adds greatly to the illusion.Becca, if you want some fun (when you don’t have to be at the bench, of course), paint in lines that are the color of those two squares. And my husband figured out why the black doesn’t work. It’s already as dark as it’ll get, so you don’t expect it to get any darker in the shadows.

By: Will TS

Will TS — Mon, 02 Jun 2008 19:28:09 +0000

I didn’t believe it either and I couldn’t figure out how to hold my fingers to see just the A and B squares. So I ripped two little holes in a piece of paper so that only those squares could be seen. As I pulled the paper closer to my eyes, more of the picture was revealed and the apparent contrast changed. Brains are weird.

By: minusRusty

minusRusty — Mon, 02 Jun 2008 18:59:18 +0000

What’s extremely interesting to me is that the “B” seems to contrast more than the “A” relative to their local background!