Hello goliard,
I'm glad the webp works !
As I mentioned above, compressing your images is essential; it's THE technical limitation of encapsulation. Furthermore, what's the point of using 4K or 2K for a visual novel? 720p displays perfectly well on a large computer screen. I even recommend, when compressing to WebP, keeping only 75% of the quality; that's more than enough.
Regarding repeating a background across multiple scenes, it's a good idea, but there's a technical issue: In the architecture (JSON), each scene is independent. If we allow an "empty" background to "keep the previous one," it creates a major problem for loading save files.
For example: The player saves at Scene B. If they load that save, the engine won't know what the background was in Scene A, and the player will get a black screen.
However, the "Duplicate Scene" feature partially solves this problem! By duplicating Scene A to create Scene B, the background image link is copied. This is transparent for the player, efficient for the creator, and safe for the code.
It's a good idea, I'll add it, thank you very much :)
EDIT: i've just added it in v1.1.4, enjoy :)