Etc1tool is a command line utility that lets you encode PNG images to the ETC1 compression standard and decode ETC1 compressed images back to PNG. It is part of the Android SDK for working with media files for game apps. The standard for the ETC1 texture format is here: http://www.khronos.org/registry/gles/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt