Optical Illusion - Black Squares and Gray Dots
6 Steps
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.
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## 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.
Dumchicken says: Sep 29, 2010. 5:45 PM
reel cool
samirsky says: Apr 17, 2009. 9:37 PM
This is easy to create in only a few lines of script with Context Free Art
Plasmana says: Mar 16, 2009. 12:11 PM
That is really weird and cool...
ac1D says: Feb 19, 2009. 6:41 PM
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 says: Feb 21, 2009. 3:55 PM
Me tooo that was tooo weird!!!!! nice
DoubleVision (author) says: Feb 21, 2009. 10:48 AM
Good question. I'll see if I can make some color combinations that do something... interesting.
braingram says: Feb 20, 2009. 4:56 AM
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 (author) says: Feb 21, 2009. 10:46 AM
That's another great illusion. I was thinking of recreating and doing some variations with that next week.
bFusion says: Feb 20, 2009. 7:17 AM
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 says: Feb 20, 2009. 5:15 AM
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 says: Feb 19, 2009. 3:46 PM
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 says: Feb 20, 2009. 5:01 AM
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 says: Feb 19, 2009. 9:20 PM
I did this ages ago when i jsut joined instructables and was a complete noob and 'it didnt get featured.
Dorkfish92 says: Feb 19, 2009. 1:52 PM
cool! The red one hurts my eyes though. hehe.
hg341 says: Feb 19, 2009. 1:02 PM
nice i lovefing hatethis one

good 'ible