I want to do a simple ratio of image(*, cols, rows) over spectral (*) using ENVI. I have a IDL code as below, but it does not work through band math function. Any help will be appreciated it. function atmc, b1, s1 ; do the ratio of image to atmos correction spectra imgdim=size(b1,/dimensions) cols=imgdim[1] rows=imgdim[2] for i = 0, rows -1 do begin for m = 0, cols - 1 do begin result = b1(*, m, i) / s1(*) endfor endfor return, result end