Hello Arshad, In what way does it not work. Do you get an error message? One important thing to remember when building a filter function file in ENVI, all spectral response bands must cover the same spectral range. So, if your bands range from 300nm to 2400nm, each band response must span the entire spectral range. Of course, the spectral response for a band in the SWIR does not have a value at 300nm but you must enter a 0 for each wavelength which is not covered by this band so that there is a value for each wavelength for the entire spectral range of the sensor. Have a look at one of the filter functions in ENVI via the Spectral Library Viewer. Load each band and you will see how they each span the entire range of all the bands in the file and have 0's where there is no response for that particular band. The easiest way to do this is to make one file where the first column contains all of the wavelengths of the entire spectral range of the sensor, the second column contains the response of band 1 in each wavelength (0s where there is no response), band 2 in column 3 and so on.