Hi there, Just wondering if it's possible to create a mask based on pixel values. I'm working on a quickbird image and i've calibrated the pixels to top of atmosphere reflectance. I want to create a mask to mask pixels with NIR (Band 4) reflectance over 0.3. can this be done in ENVI? I've tried building a mask using Build Mask function but it doesn't seem to allow specific band value inputs. can i do it with band math? something like If NIR > 0.3 assign a value of 0 to the pixel? is that possible? if so, whats the correct expression to use? Any help is appreciated! Thanks in Advance =) update 1 i managed to create a mask using this expression on the raw image. can't get it to work on the reflectance image due to decimal values. B4 is my NIR band : (B4 ge 100)*0 + (B4 le 100)*B4 got this from the ENVI user guide. it works for one single ban. Does anyone know the expression to apply this to other bands? if a pixel in band 4 = 0 assign a 0 to the same pixel in all other bands?