Hi all, Could anyone in the forum please tell me how to exclude the background cell (value R:0, G:0, B:0) in unmxing the spectral input images? I used the linear spectral unmixing tool in ENVI 4.2.; I then displayed the fractional images, using the cursor location/value and found that the background cell has value. They are also included in statistics calculation. I want to exclude them. How should I do it? Thank you very much. Kind regards, Thu