I'm new here, and had a question about how to adjust images that clearly have a brightness gradient from one side to the other side - due to sun angle or sensor angle etc.. These are old 1985 CIR images, and I have several that show the same effect. What's the best way to make corrections on these? I am imagining something involving averaging values across each column of pixels, on all the images with this effect, and subtracting that value? If so, how is that done on ENVI? thank you!