how to recognize compression format for graphic file?

[tomekthemessenger]

I extracted from .big files some tga, png files. However You cannot open those files with the aid of photoshop or paint as despite format is .tga/.png file is still compressed! It is unknown what compression algorithm is used, for sure it is not 10FBmode! Does anybody has some experience with recognizing from file hex editor what compression format is used? Thanks to that the proper decompression tool can be used and file really decompressed to png/tga format.
Here is link to file:

aaaa.png

Visit this link to download: aaaa.png

files.fm