1. An automated, computerized method for determining an illumination field in an image, comprising the steps of: a computer executing the following steps: providing an image file depicting the image, in a computer memory; automatically identifying linear tokens in the image of the image file by testing each pixel of the image to determine a linear token relationship between the pixel and neighboring pixels in the image, each one of the linear tokens defining a connected region of the image having colors extending as a cylinder in a color space, from a dark end to a light end, along a positive slope and corresponding to a single material depicted in the image, according to a bi-illuminant dichromatic reflection model; and utilizing the linear tokens to identify an illumination field.