Question

How to combine ALPHA channel extracted from the PNG file into the RGB-pixel of the same source file?

context

In ETC1 algorithm texture compression , the alpha channel unhandled will be saved in another single PNG file with the same size (width, height, and block size) , then after ETC1 compression there are two PNG files, one with rgb pixel, and another aaa pxiel.

However the question is now, how to recover the source PNG file ?

Reference

the commited file mainly reference to the source file https://gist.github.com/niw/5963798#file-libpng_test-c-L68

Requirement

Png.h library needed