The Floyd-Steinberg dithering test cart. It takes a source image (which has 255 possible colors, see input_image.png) and tries to represent it with just 4 colors that wasm-4 provides. The results are not that great due to lack of resolution, the normal 4-color image looks better (see botan). It works better for gradual change (see lines), maybe it might even work if you choose red-green-blue palette. Probably there is an easier way to do that though.
from the target/wasm32-unknown-unknown/release folder:
cargo build --release; stat cart.wasm | rg Size ; w4 run ./cart.wasm --no-open --no-qr
src/image_preproc.rs is a file with witch I converted a png into a string that I copied into the source code, and also generated a 4 colour version just to check how the end result might look like.
You can find Botan ch. here.