Introduction: Optical Illusion - Black Squares and Gray Dots

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.

Step 2: First Copy

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Grab the group of three squares, copy them and shift them to the right. This should give you what you see below. If you've mastered that step, the rest is a cakewalk.

Step 3: Keep Copying

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You can grab all of the squares, copy them, and shift them over. Do this twice and you'll have the first row of your grid.

Step 4: Second Verse...

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Apply the same technique you just used to create the row to create a series of rows.

Grab the whole row, copy it, and shift it down. Keep doing this until you have the grid you see below.

Step 5: Clean It Up

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Now select all the blue squares and delete them to get a nice clean grid of black squares. There are a few other ways of doing this, but for me this is the fastest.

Step 6: Play With Variations

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Try using different colors to see what happens and even inverse it so that there are white squares on a black field.

Have fun!


Dumchicken (author)2010-09-29

reel cool

samirsky (author)2009-04-17

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

Plasmana (author)2009-03-16

That is really weird and cool...

ac1D (author)2009-02-19

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 (author)ac1D2009-02-21

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

DoubleVision (author)ac1D2009-02-21

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

braingram (author)2009-02-20

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':

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):

Although incorrect (source: ) it does illustrate an important type of processing (lateral inhibition) that's found throughout the nervous system.

DoubleVision (author)braingram2009-02-21

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

bFusion (author)braingram2009-02-20

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 (author)2009-02-20

Please everyone look up 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 (author)2009-02-19

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 (author)Boss_Sauce2009-02-20

What you described is a good example of an 'afterimage' (another involves the a flag of odd colors: ) This is caused by bleaching (and un-bleaching) of your visual pigment. The hermann grid doesn't involve any such process.

duck-lemon (author)2009-02-19

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

Dorkfish92 (author)2009-02-19

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

hg341 (author)2009-02-19

nice i lovefing hatethis one

good 'ible

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