Hello, There is not a module for IDL which explicitly performs entropy calculations for images, but there is a function called IMAGE_THRESHOLD which has a keyword MAXENTROPY which is (from the documentation): This is an entropy-based thresholding method developed by J. N. Kapur, et. al. It considers the thresholding image as two classes of events, with each class characterized by Probability Density Function (PDF). The method then maximizes the sum of the entropy of the two PDFs to converge on a single threshold value. This function was introduced in IDL 8.2.2, which means that you need the following minimum system requirements i fyou want to upgrade: Kernel 2.6.9, glibc 2.3.4, GTK+ 2.4.13