Instructables
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.
 
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Step 1: Starting the grid

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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!