I would like to extract urban end-members from a Minimum Noise Fraction(MNF) Image of my study area. But i am not sure how pixel purity index(PPI) image is converted to the four fundamental end-members (Vegetation, High Albedo, Low Albedo and Soil). I have a 3 band MNF image, and derived the PPI but have no idea how to extract four classes of pure pixels.
