Certainly, if your aim is the simplest code with no regard to compression, you could achieve a PNG writer with a small amount of code.

In such a case, you could also skip the PNG filtering as well (whilst for my case, you wouldn't want to).

I think it'd make more sense to go with BMP for a 'simple as possible' image format, that has wide support, than with PNG. PNG is definitely more geared towards a compressed image (as well as all sorts of other features you may not care about).