Optical Illusion - Black Squares and Gray Dots

In this optical illusion you will see gray dots at the intersections in the grid below. This is known as the Hermann-grid illusion. Those gray dots aren't really there. You can make them disappear by looking directly at the intersection.

In this Instructable we will go over a quick method for recreating such a grid and see some variations as well.

Step 1 Starting the grid

Get your favorite graphics program and we'll get started.

Start by making your basic building block: a black square with two identical smaller blue squares attached to the right side and bottom. The blue squares will determine the distance between the black squares.

Comments

[Dumchicken]

reel cool

[samirsky]

This is easy to create in only a few lines of script with Context Free Art

[Plasmana]

That is really weird and cool...

[ac1D]

never seen the red one, my eye act weird when i look at it! nice idea to have modified a simple illusion :) I have a question, what if you make each square a different color?

[didibemi]

Me tooo that was tooo weird!!!!! nice

[DoubleVision]

Good question. I'll see if I can make some color combinations that do something... interesting.

[braingram]

I'm a big fan of this illusion. My personal favorite involves using a gray background, black squares, and whit e circles at the 'intersections':
http://en.wikipedia.org/wiki/File:Grid_illusion.svg

It would be nice to add a brief description of classical (but wrong) explanation of why we see the gray ghost images. There are quite a few good explanations online (here's just one):
http://www.michaelbach.de/ot/lum_herGrid/index.html

Although incorrect (source: http://www.michaelbach.de/ot/lum_herGridCurved/index.html ) it does illustrate an important type of processing (lateral inhibition) that's found throughout the nervous system.

[DoubleVision]

That's another great illusion. I was thinking of recreating and doing some variations with that next week.

[bFusion]

My brain really doesn't like the image in that first link. It's like my eyes slide off the picture. That's wild :D

[hominid]

Please everyone look up Amsler Grid
http://en.wikipedia.org/wiki/Amsler_grid
as it is interesting and important and easy to do.
This tructible reminded me of this.
One of the commonest causes of blindness.

[Boss_Sauce]

You can see similar effects by reading a white-text-on-black web page, then switching to a black-on-white page-- your brain will try to "fill in" with black, and things look... strange!

[braingram]

What you described is a good example of an 'afterimage' (another involves the a flag of odd colors: http://www.moillusions.com/2006/04/american-flag-optical-illusion.html ) This is caused by bleaching (and un-bleaching) of your visual pigment. The hermann grid doesn't involve any such process.

[duck-lemon]

I did this ages ago when i jsut joined instructables and was a complete noob and 'it didnt get featured.

[Dorkfish92]

cool! The red one hurts my eyes though. hehe.

[hg341]

nice i love^{fing hate}this one

good 'ible