Pmd2 AT4PX

The AT4PX container is a format used to contain compressed image data exclusively, as opposed to PKDPX which is more of a generic compressed container. Its not unusual to find AT4PX containers wrapped itself by a SIR0 container. Its content is compressed using a custom compression format dubbed PX Compression for the lack of a better name.

File Structure

The structure is very simple. A 18 bytes long header followed with the compressed data.

Overview

Offset	Length	Endianness	Type	Name	Description
0x00	5	big		Magic Number	The magic number, made of the ASCII characters "AT4PX" {0x41, 0x54, 0x34, 0x50, 0x58}
0x05	2	little	uint16	Container Length	The length from the beginning of the header to the end of the compressed data.
0x07	9		byte array	Ctrl Flags Array	A list of flags to be used in decompressing the container's content. More detail about their purpose on the PX Compression page. They're really nybbles stored in the lower half of a single byte each.
0x10	2	little	uint16	Decompressed Data Length	This is the length of the raw input data before it was compressed. Note how the length of this field differ from the PKDPX format's own Decompressed Data Length !
0x12	..The PX compressed data begins immediately here!..

Credits

A big thanks to Zhorken who figured out the header and the compression format!