# Coupled Cellular Automata

Origins

Back in 2007 I was trying to figure out the algorithms behind Jonathan McCabe’s cellular automata pictures. I was never able to determine the algorithm to get the same results and coloring as Jonathan, but this is an explanation of my own Coupled Cellular Automata that arose from trying.

Algorithms

The principal of this method is to have 3 CAs with different settings running mostly independently of each other, but have their values interact with each other to create a new interesting result.

To start with you need 3 arrays to keep track of the 3 separate CAs. I used a 3D array to store them, ie c[0,x,y] c[1,x,y] and c[2,x,y].

Each cell is updated using a kernel which is very similar to an image processing kernel. For example, this kernel

is like a weighted blur image processing kernel.

Initialise a value to 0. The current cell value is multiplied by 4 and added to the total. The north, south, east and west neighbour cell values are mutlipled by 2 and added to the total. The corner cell values are mutliplied by 1 and added to the total.

Depending on which of the 3 CA layers is being processed, the value is updated by

```case level of 0:value:=value div k1total-(c[2,x,y] mod k1mod+1); 1:value:=value div k2total-(c[0,x,y] mod k2mod+1); 2:value:=value div k3total-(c[1,x,y] mod k3mod+1); end;```

k1total, k2total and k3total are the total of all the kernel values. For the above kernel the total value is 16 (4+2+2+2+2+1+1+1+1).

k1mod, k2mod and k3mod are the 3 “Mod value” settings that can be customised.

The value is also modified by using the cell value in another layer. This gets the CAs feeding through each other and causes the multiple layered look of the CA.

Once you have the new value for the cell, it is then kept within the range of 0 to 255 by the Wrap Method. The 3 wrap methods (Mod, Inverse and Clamp) make the following changes to the value

```case wrapmethod of 0:value:=value mod 255; 1:if value > 255 then value:=-255 else if value < -255 then value:=255; 2:if value > 255 then value:=255 else if value < -255 then value:=-255; end;```

At this stage you now have a new value for the cell. Put this cell into a temp array and then swap the temp array into the cell array once all cells are processed (like any other CA you want to update all the cells simultaneously).

Repeat the above steps as long as you need to.

Display Methods

You now have the 3 CA layers updated with their new values. I use 3 different methods to display the CA.

1. Color Palette. Index a 256 color palette with abs(c[0,x,y]+c[1,x,y]+c[2,x,y] div 3) mod 255;

2. RGB. Convert the layer values to a color by using RGB(abs(c[0,x,y]),abs(c[1,x,y]),abs(c[2,x,y]));

3. YUV. Pass the layer values as YUV into a YUV to RGB converter routine YUVtoRGB(abs(c[0,x,y]),abs(c[1,x,y])-128,abs(c[2,x,y]-128),r1,g1,b1);

Results

Here are some more example kernels and the resulting images. The settings dialog screen captures also show off the new skinning theme support that Visions Of Chaos now includes.

Of course like any CA these need to be seen dynamically changing and updating. To see the above samples and others in motion download Visions Of Chaos.

If you are a coder who experiments with the above algorithms and has any other ideas or enhancements let me know.

Jason.