Texture Compression doesnt compress same extension?

Texture Compression doesnt compress same extension?
0

I have very large PNG textures in my project (12 mb). I set up Texture Compression for png with quality 80 and after build it doesnt compress. I dont want compress this texture because then compress in other formats being less effective.
Cocos Version: v2.1.3`

If it work as excpected can you please update docs?