# Optical Illusion - Black Squares and Gray Dots

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## Introduction: 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.

## Step 2: First Copy

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

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...

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

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

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

Have fun!

## Recommendations

• ### 3D CAM and CNC Class

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• ### Space Challenge

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## Questions

reel cool

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

That is really weird and cool...

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?

2 replies

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

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

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.

2 replies

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

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.

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!