I was working on an image processing project a while ago and was specifically working with raster images in the Hue-Saturation-Value(HSV) image format. Each is determined by mathematical values of these (HSV) parameters. I also worked with other bases such as the Red Blue Green (RGB) format. Now these HSV, RGB and many other image specifying formats are just linear transforms of each other (right?). My question is this: to specify a color of a particular region on a screen, just two values should suffice: Wavelength( or frequency) and intensity. Where does the 3rd independent parameter come in?