Advice on image format when there is a lot of stretching

[Showakun]

If a game features images that need to be stretched to look different size a lot of times, what image format would you recommend? I know that overly stretching it is not recommended at all but sometimes it's unavoidable (like when something zooms out quickly). Some said that using *webp helps but I don't know how much/whether it's true. (I'd appreciate it if someone posted a visual comparison) Beyond which size (in Renpy proportion terms, I mean, like 2.0) you wouldn't recommend it? How do you preserve sharpness at all?
Makes me kind of sad Renpy doesn't support vector graphics.

In any case, post your advice on preserving sharpness, any kind.

[fierylion]

If you only use Renpy then your options are limited to raster graphics (webP, png, jpg, bmp, and static GIF). If you want your images to be reusable in other places, then png is the highest quality format. But if you only use it in renpy then you should look into render with webP because it is a newer format that is superior to png in every way. Although many places don't support it yet, such as some browsers (but Renpy supports it). Don't even think about using the other formats unless you want stretching artifacts and overall just bad image quality!

For further explaining webP, it actually is not better than png at stretching (both are lossless to begin with, which means neither of them lose image quality). But since you need to stretch the image by a lot, you should use images that are very large in size to begin with. This is where WebP comes in, it is significantly smaller in size compared to PNG due to it being much newer. The thing about lossless image formats like png or webp is that their image size will always be significantly larger than when using other formats (especially jpg which will be like 1/10th the size), hence its always good to use the latest tech (WebP) to make sure your images are in the best possible quality, and with the smallest size possible.

Lastly, you may need to change how renpy scales the image, perhaps it might look better with no interpolation (or more interpolation). Though a few years ago this is still hardcoded so I'm not sure if it's possible now. Maybe ask the folks on discord?