# Creating Colored Images from Regular Expressions

Note: This post creates some cool colors, but to see something truly stunning, check out dln385’s images, inspired by these posts.

In my last post, I detailed an algorithm for generating images using regular expressions. However, I found them a tad boring and mundane, so in this post I’m going to add colors to the images.

We follow exactly the same algorithm for choosing where to color the pixels, but we need a method to decide what color to paint. To accomplish this, we introduce three colors channels C, M, Y which are basically a long string, composed of the same alphabet as the areas (0, 1, 2, 3).

For each string S (area) do the following:

• If S matches the regular expression, mark it as painted.
• Define a blank color CMY(0, 0, 0).
• For each color channel, xor the string accompanying the channel, and if it matches the regular expression, change the color channel from 0.0 to 1.0.

Let’s do an example. Let R be the regular expression (1+2+3)*0(1+3)*0(0+1+2+3)*.

Let the following be the color channels C,M,Y:

• C – 032102
• M – 033122
• Y – 132212

If we test the string S = 330100, we find it matches, so we must paint it.

Calculate S XOR C = 330100 XOR 032102 = 302002, which matches the regular expression, so the cyan color channel is 1.0.

Calculate S XOR M = 330100 XOR 033122 = 303022, which also matches the regular expression, so the magenta color channel is also 1.0.

Calculate S XOR Y = 330100 XOR 132212 = 202321, which does not match the regular expression, so the yellow color channel is 0.0.

This means we paint the area, marked by the string 330100 with the CMY-color (1, 1, 0).

Here is a visual example to showcase this new method:

You can also do AND instead of XOR, it produces images like the following:

It’s obviously less visually stunning, but still interesting. Here is OR instead:

It’s also less visually diverse, but still cool to look at.

# 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:

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.

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:

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):

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)*:

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:

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/