To generate an image in greyscale, enter a function f(x,y). For example:

sin(x)*cos(y)

To generate an image in color, enter a function f(x,y,r,g,b). For example:

r*sin(x)+g*cos(y)+b*(x+y)

The image has an x and y range of -10, 10 and a z (brightness) range of -1, 1. This means if your function evaluates to -1 at a pixel, it will be as dark as possible. If it evaluates to 0, it will be at half brightness. If it evaluates to 1, it will be full brightness. Because 0 is half brightness, you must subtract colors to get rid of them from an image. Here is an example of an entirely red image:

r*sin(x)-g-b

The math functions available are on display to the left. Here is documentation for them. Some python constructs are also available (if, in, etc.) if you can figure out how to use them. Some restrictions apply. Have fun!