- dezoomify ( https://dezoomify.ophir.dev ) is a web application. It is super easy to use, but the final size of the image is limited by the browser. No browser can create gigapixel canvases.

- dezoomify-rs ( https://lovasoa.github.io/dezoomify-rs/ ) is a command-line desktop application for Linux, MacOS, and Windows that does the same thing. It has no limitation (other than the one imposed by the file formats themselves) on the final image size.

- dezoomify-extension ( https://lovasoa.github.io/dezoomify-extension/ ) is a browser extension to extract zoomable image URLs from webpages. It is less relevant for google arts and culture, where the zoomable image URL is the URL of the viewer page itself.

If someone is interested by how the zoomable image format used by google arts works, the source code of dezoomify-rs is quite understandable: https://github.com/lovasoa/dezoomify-rs/tree/master/src/goog...

In the case of this image, I'm not sure the highest zoom level saved as a single PNG makes a lot of sense. No image viewer will accept to open a PNG file of this size. For JPEG, the format does not even allow images of that size.