These are all fully-synthetic images, and the formulas they use come preconfigured with the plugin. It is also possible to operate on existing images, e.g. lightening/darkening, addition/subtraction/averaging and many other operations where the mathematically precise manipulation of pixel values matters.
The formulas used for these images are just simple one-liners. It is also possible to define new functions that can be as complex as anything that can be expressed in Java (e.g. involving lookup of values in a file or a database).