rawx_hdr{
   u8 magic[4];
   u32 width;
   u32 height;
   u32 bpp; (or type ?)
   u32 reserved; (checksum...)
}

--------
hdr [20bytes]
--------
palette [256bytes] (optional / 8bits mode only)
--------
data [width*height*4bytes] (32bits (argb) & 24bits (rgb) modes)
data [width*height*2bytes] (16bits (565) mode)
data [width*height*1bytes] (8bits (palette) mode)
--------

endianess considerations
magic = "RAWL" for little endian file
magic = "RAWB" for big endian file

data 24bits (rgb) => alpha channel ingnored / set to 0xff (agrb compatibility alpha=100%).

--types--

ARGB32            32bits/pixel
RGB32             32bits/pixel (alpha channel ignored (set to 0xff))
RGB16 (RGB 565)   16bits/pixel
AP8               16bits/pixel (palette + alpha channel)
P8                8bits/pixel  (palette)
A8                8bits/pixel  (alpha channel/mask only)
BW                ?            (black & white)