The Export ECW command allows the user to export any loaded raster, vector, and elevation grid data sets to an ECW file. ECW files are highly compressed and great for storing things like satellite imagery. There is no size restriction on exported ECW files, so you can store many terabytes worth of imagery within a single highly compressed ECW file.
When selected, the command displays the ECW Export Options dialog which allows the user to setup the export. The dialog consists of a General options panel which allows the user to set up the pixel spacing and target compression ration, a Gridding panel, and an Export Bounds panel which allows the user to set up the portion of the loaded data they wish to export. If you would like to generate an uncompressed format file, simply slide the Target Compression Ratio slider all the way to the left (1:1 target compression ration).