Domain coloring

In complex analysis, domain coloring or a color wheel graph is a technique for visualizing complex functions by assigning a color to each point of the complex plane. By assigning points on the complex plane to different colors and brightness, domain coloring allows for a function from the complex plane to itself — whose graph would normally require four space dimensions — to be easily represented and understood. This provides insight to the fluidity of complex functions and shows natural geometric extensions of real functions. A graph of a real function can be drawn in two dimensions because there are two represented variables, and . However, complex numbers are represented by two variables and therefore two dimensions; this means that representing a complex function (more precisely, a complex-valued function of one complex variable ) requires the visualization of four dimensions. One way to achieve that is with a Riemann surface, but another method is by domain coloring. Representing a four dimensional complex mapping with only two variables is undesirable, as methods like projections can result in a loss of information. However, it is possible to add variables that keep the four-dimensional process without requiring a visualization of four dimensions. In this case, the two added variables are visual inputs such as color and brightness because they are naturally two variables easily processed and distinguished by the human eye. This assignment is called a "color function". There are many different color functions used. A common practice is to represent the complex argument, , (also known as "phase" or "angle") with a hue following the color wheel, and the magnitude by other means, such as brightness or saturation. The following example colors the origin in black, 1 in green, −1 in magenta, and a point at infinity in white: There are a number of choices for the function . should be strictly monotonic and continuous. Another desirable property is such that the inverse of a function is exactly as light as the original function is dark (and the other way around).