What causes SingleFile saved pages to be larger than other types of archives?

[MaximoRoboto]

For example, a page that is made up of many images might be 5 MB, but when saved as a Safari Web Archive might only be 1.1 MB. Is this because of how SingleFile saves images, as data streams?

For my own purposes SingleFile is great for archiving, but I'm wondering if there's any ways to reduce the sizes when re-hosting pages. Do I need to convert the images back into their original form? Or are some other asset the cause for the large page sizes?

Would converting my SingleFile archives into SingleFileZ zipped archives help? Is that even possible to do? Can SingleFileZ archives be accessed as webpages online?

[gildas-lormeau]

There are probably multiple factors, I guess first SingleFile saves more resources in your example. This is also due to the fact that images are encoded in base64 with SingleFile.
If you want to optimize the size of the resulting page, the most efficient solution is to select the "self-extracting ZIP (universal)" format in the options page. Thus, images will be stored as-is and the HTML/CSS content will be compressed.