zopfli VS optipng-bin

This project uses HTMLMinifier, optipng, and zopfli to create a custom production Elm build pipeline. You can see how I make use of these tools in this build script. Here are the results in case you're interested. I used the same ideas from this project to build and deploy dwayne/elm-conduit, which you can learn more about in my article Yet Another Tour of an Open-Source Elm SPA.

I'm making a 2D game with lots of PNG assets. I recently found that ZopfliPNG regularly reduces the sizes of my assets by ~3x compared to Asesprite's output. I've tried a few other PNG compression tools, but ZopfliPNG consistently outperforms the others.

I mean something better than Google's best engineers trying to optimize LZ77's compression as much as humanly possible, while remaining compatible with the DEFLATE/zlib bitstream.

zopflipng typically beats pngcrus and optipng (on Linux at least) but by default it drops auxillary PNG chunks [0] which can result in browsers (and other applications) using a different color space, causing the resulting images to look more washed out than the original. To prevent this you need to explicitly pass --keepchunks=cHRM,gAMA,pHYs,iCCP,sRGB,oFFs,sTER to zopflipng.

Unfortunately it (and most other tools) don't have APNG support, keeping only the first frame.

[0] https://github.com/google/zopfli/issues/113

I tried going with a lot of different compression algorithms, in the end a lot of iterations of Zopfli delivers the best result. With that, I got the image down to 591 kB.

I tried zopflipng [1] with the very expensive option suggested from the usage and got 2,493 bytes (original 2,740 bytes, nowhere practical as it took 3 minutes) so you don't have to sacrifice the palette, though I'm not sure if 16 or even 4 color palette will significantly alter the visual.

[1] https://github.com/google/zopfli

This project uses HTMLMinifier, optipng, and zopfli to create a custom production Elm build pipeline. You can see how I make use of these tools in this build script. Here are the results in case you're interested. I used the same ideas from this project to build and deploy dwayne/elm-conduit, which you can learn more about in my article Yet Another Tour of an Open-Source Elm SPA.

Did you compare to PNG crush and optipng? Those are what I used to use because they're easily installable Linux/brew packages.

It seems that the package was updated around 2019 May to not do that -- https://github.com/imagemin/optipng-bin/commit/6bb7f1c2edab67297c7d72fa0bd604ecc214b9f1 -- published as version 6, so maybe you're using an older one.

The script optimised the SVG using Scour. This removes some metadata and also shortens IDs as well as strip out comments. For the PNG files we used OptiPNG on the maximum optimisation setting. This can be slow on larger files, but for favicons should not take long. Here’s the before and after comparison of files sizes for a particular favicon, using the script: