Rip Android games sprites!

[Sanicderpy]

But how do I open .ipk files? Or I can convert to another file type?

You mean .ipa files? (The application files used in Iphones, etc.)  If it is .apk files. It's already been answered for you:

I prefer to download the .apk off the internet and then open it using 7-Zip. Just keep in mind that some files may be using proprietary file formats and can't be opened using any of the currently available sound/video/image/3D modeling programs that are available to the average consumer.