nstead of Band Math, I think you would want to use the Spectral Math tool. The expression would be something like: (float(s1)-float(s2))/(float(s3)-float(2)) . . . where you set s1 equal to the whole spectral image, s2 equal to the dark spectrum, and s3 equal to the white spectrum. So, you would first open your spectral image. Then you'd bring up a plot showing your white and dark spectra (for example, if they are from pixel spectra, you could use the Spectral Profile tool). Then you would start the Spectral Math tool and enter the above expression. Then you would pair the variables in the equation with the different spectra and images that you already have open. I hope that helps! Peg Exelis VIS