1. The ability to set the Session State was added in ENVI 5.1 which is now available for download from our website. 2. There is a new mosaic tool in ENVI 5.1 that performs a color balancing. The ENVI Classic mosaic also includes a color balancing. It is true that images that have very different dynamic ranges because the images were taken at different times of the year or day can be difficult to get a good color matching along the borders. It may help if the data are all calibrated to reflectance and perhaps atmospherically corrected. I would give the new Seamless Mosaic tool in ENVI 5.1 a try. 3. A transparent background can be achieved by setting the Data Ignore value in the header. You will need to use the Edit ENVI Header tool and it helps if the files are in ENVI format.

I accidentally hit Report the Post...so I am awakard. Thanks MariM for the information however, I am under US Government and we don't get upgrade until they okay it. Please delete my Report Post