This repo contains code that accompanies my blog post of the same title: https://www.da.vidbuchanan.co.uk/blog/hello-png.html
hello_png_0.py is the first example given in the article, resulting in ./samples/out_0.png, which has the skeleton of a PNG file but contains no valid data.
hello_png_1.py is the final example given in the article, resulting in ./samples/out_1.png, which should be a completely valid PNG file, visually identical to ./samples/hello_png_original.png. It's larger than the original, for reasons outlined in the article.