Generating Images from Regular Expressions


There is an update to this post, which includes colors: https://ssodelta.wordpress.com/2014/03/25/creating-colored-images-from-regular-expressions/

Source code complete with Javadoc can be found at: http://pastebin.com/ccRK75aq

This post will detail a method for using regular expressions to generate images.

A regular expression is an array of characters, which represents a series of instructions, which for any input either matches or doesn’t match. For a simple example, the regular expression

ssodelta

Only matches the string ssodelta. This makes sense, but we can do pretty nice things with regular expressions. If we for example write

ssodelta|delta

Then the regular expression either matches ssodelta or the string delta. This is because the vertical bar | represents the symbol or. We also have so called quantifiers, the most important of which is the kleene star *.

sso(delta)*

The parentheses group strings together, like regular parentheses in mathematical expressions (2+4)*3, for example. The kleene star * means zero or more, meaning that there can be zero or more delta and it will still match the regular expression. A few matches include ssodelta, ssodeltadelta, ssodeltadeltadelta and so on…

I won’t completely detail regular expression, but if want to read up on it, I suggest close-reading the wikipedia article on the matter, but the bottom line is that regular expressions are really cool. But how can they be used to generate images?

Consider a completely square image, which is divided into 4 quadrants:

img1

We can refer to each of these four quadrants by their numbers 0,1,2,3, and we can further divide these quadrants into four numbers, and label them accordingly.

img2

But what does this have to do with regular expresssions? Well, we can have a regular expression, which only uses the characters 0,1,2,3 and every string adresses an area in this area. For example, the string 022 represents the area marked with red:

img3

We can decide on a resolution n, and generate all strings of length n, parse them through a regular expression, and if it matches, paint it black. For example, the regular expression (0|2)(0+1+2+3)* generates the following image (for any resolution >= 2):

test

This is because the regular expression only matches if the cell begins with a 0 or a 2, which is why the 0th and the 2nd quadrants are painted black, and the rest aren’t.

We aren’t limited to boring checkers though, if we feed the generator the regular expression (1+2+3)*0(1+3)*0(0+1+2+3)*:

really_large_triangle_fractal

Notice the self-similarity in the image, that’s because this image is actually a fractal.

Here is a gallery of other images generated using this technique:

also-cool-fractal bars  dots pik

Notice how often triangles appear in these images.

Although the .java file has an included Javadoc, here’s how you use it to generate images:

Generator g = new Generator(RESOLUTION, IMAGE_SIZE);
g.generateAndExport("REGULAR_EXPRESSION", "EXPORTED_FILE_PATH.png"); //Must be a .png file

If you prefer Python code, check out Jack Morris’ post on the same subject, where he implements it in Python: http://jackm.co.uk/posts/2014/03/25/Using-Regular-Expressions-To-Generate-Images/

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