ColorFunction Image Generator is a program that generates images
that you can use for desktop or web backgrounds or for any other
use, it generates the image calculating a math expression for every pixel
and every component of the color (red,green or blue),the math expression
uses this variables:

$X:horizontal position from -100 to 100.

$Y:vertical position from -100 to 100

$R:Radius of the position from the center of the image:is sqrt($X^2+$Y^2)

$A:Angle of the position from the center of the image in radians

The math expression is an expression that can use any math function: sin(Angle),
cos, tan, asin, acos, atan(in radians), pow(base,exponent), log(value),log10,
abs(value), sinh(value), cosh, tanh, floor, round,rand() (returning a value
from 0 to 1), fmod, ceil,...
see the TCL expr help for more info.