Hello, I am tryying to identify changes using three date composite image using image diffrence technique. I got two date difference images as Diff1 = Date2-Date1 and Diff2 = Date3-Date2. My problem is , I want to detect three-date composite change as YYN, NNY, YYY, NNN etc. where YYN stands for presence of a class in Date1 and Date2 and not present in Date 3 and so on. 1. I know there is s method called RGB-NDVI which depicts the changes based on RGB combination of each date image displayed. 2. There is other method using each date classifiaction grid and combining them in GIS. 3. But I want to use difference image for such Change... Any help in this will be highly appreciated Thanks Pk