The document discusses pseudo color images and techniques for converting grayscale images to color. It defines pseudo color images as grayscale images mapped to color according to a lookup table or function. It describes various color schemes for this mapping, including grayscale schemes that use shades of gray and oscillating schemes that emphasize certain grayscale ranges in color. The document also discusses using piecewise linear functions and smooth non-linear functions to transform grayscale levels to color for purposes such as enhancing contrast or reducing noise in images.