I am a graduate student working on a classification thesis project using WorldView-2, IKONOS, and Quickbird from different years. I need to atmospherically correct each image before I can begin processing, and my advisor suggested using Dark Subtract. I've tried this method using band minimum on the WV2 image with the full scene, and all 8 bands, but the output pixel values were all the same. The values did, however, change significantly when I used a small subset of the image, but how do I apply this tool to the entire image? I'm aware that there can be no No Data values in my image, so I've also tried subsetting the image to an ROI that includes my study area (all pixels have values) just in case, and still no luck. Thanks, Matt