Hi Monisha, 1. It sounds like your different LIS-III images have different dynamic ranges. There are some different things you can do to try to get them to look more alike. Which one is best depends on your ultimate goals for the mosaicked image. If you don't intend to do further processing, and just want the mosaic to look nice, then you may want to try using ENVI's color balancing option during mosaicking. You can find more information about this from the ENVI Help under Using ENVI > Map Tools > Image Mosaicking > Building Pixel-Based Mosaics > Color Balancing Images. 2. If your images were collected by an aerial frame camera, then you will need to have fiducial marks and the camera calibration report for ENVI (or any software) to understand how to create RPCs. 3. I am afraid that I don't understand this question. Are you trying to convert your DEM in GeoTIFF format into a different format? What format do you want to have it in? I think the .dem filename extension is used by ArcGIS for some digital elevation image files. But I am not familiar with what that format would be. ENVI does not have tools to write image data out to a .dem format file. Is there any other image format that would work for you? - Peg