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Picture of 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

Picture of 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.
 
Dumchicken4 years ago
reel cool
samirsky6 years ago
This is easy to create in only a few lines of script with Context Free Art
Plasmana6 years ago
That is really weird and cool...
ac1D6 years ago
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 ac1D6 years ago
Me tooo that was tooo weird!!!!! nice
DoubleVision (author)  ac1D6 years ago
Good question. I'll see if I can make some color combinations that do something... interesting.
braingram6 years ago
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)  braingram6 years ago
That's another great illusion. I was thinking of recreating and doing some variations with that next week.
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
hominid6 years ago
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_Sauce6 years ago
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!
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-lemon6 years ago
I did this ages ago when i jsut joined instructables and was a complete noob and 'it didnt get featured.
Dorkfish926 years ago
cool! The red one hurts my eyes though. hehe.
hg3416 years ago
nice i lovefing hatethis one

good 'ible