Then turn it back into HTML with an experiment of mine: https://github.com/andershaig/img-con - It takes an image, writes a span with a background-color for each pixel. Turns a 100x100 image into a 7 MB HTML file.
You're right and I should have paid more attention. I had thought you were generating just the image from a web page. Having actually worked on something similar, I can say I'm very very impressed with the load time.
Probably mostly the Gzip - the code is very repetitive. The RLE helps too.