Abstract: A method is disclosed herein for measuring similarity between a first vector and a second vector wherein (i) each element of the first vector represents a first reflectance associated with a respective one of a plurality of spectral bands, and (ii) each element of the second vector represents a second reflectance associated with a respective one of such plurality of spectral bands. The method contemplates determining a magnitude difference and a shape difference between the first vector and the second vector. A similarity between the first vector and the second vector is computed on the basis of the magnitude difference and the shape difference. Further, an image processing method is disclosed herein in which a first input pixel is extracted from a received spectral image or other data source. The first input pixel is converted into a first vector, wherein each element in the first vector represents a reflectance of a respective one of a plurality of spectral bands.