Image export before Altair 5 was a bit complicated because it required either selenium plus a system web browser, or a node.js installation. In Altair 5, we switched to using vl-convert for image export, which is just a regular Python wheel with no external dependencies. So now, `chart.save("file.png")` should be just as easy to use as matplotlib's savefig!

(Disclaimer: I'm a Vega-Altair maintainer and the author of vl-convert)