Proprietary image format for the engine. Mainly created to get around the lack of 16bit indexed image formats. Stores most data in XML, binary is stored after the document. Most data is little endian, future versions might be able to specify big endian data in the binary, but due to the main targets (x86 and ARM) are mainly little endian, it's unlikely.
Does a Huffman encoding/decoding to convert between 8bit and 16bit.