Hi Steve, I'm not really following your description of the problem, but I have a feeling that if you give a few more details, I may be able to help.  Where I'm confused is your statement about misclassifications due to background and offset at the edge of the tile.  Are these misclassifications what you are trying to resolve?  So, the problem is that ENVI is creating some incorrect ofset along tile boundaries during classification?  Or is it the original Landsat data that has some type of offset inherent in it, and the classification tools in ENVI just respond naturally to these offsets, but then you would like to mask out those effects? Maybe you could go through all of the steps in your workflow, and describe what you see, and exactly what the problem is. Also, this might be a situation where you can get better help via ITT VIS tech support (support@ittvis.com).  For example, you could send them screen shots or example data, etc., to better describe the situation.  That might be more efficient for you. Regards, Peg