BLK files are basically S16 files with a slightly different header, and with slightly incorrect offsets due to the different header. They contain 128x128 sprites which are the 'blocks' which make up the background. The header is as follows (all values are little-endian): Then, for each sprite: The rest of the file consists of image data at the file offsets defined in the header. Sprites are stored as an array of horizontal scanlines of the sprite. Each pixel is represented as a 16-bit little-endian integer in the format specified in the header.