GIS and Remote sensing expert here is to do the job. Have done lots of LandSat classifications earlier, and have experience of using geo-spatial software like ArcGIS, ERDAS imagine, IDRIS over 8 years. Using IDRIS, from histogram, we can make the subtraction, and then do classification, based on the signature. I can do these easily, let us discuss to find more. Best Wishes, Labib [DO check my feedback of cartography and remote sensing projects]