Try https://vectorizer.ai/ it's main purpose is to convert images (rasters) into vectors (SVG). But it has great line detection and color acquisition, give it a go. Bare in mind that this will only work for images, so you will first need to convert the png into an image.
I know that it seems an odd suggestion, but I had to try different vectorization methods for a project of mine and this one was performing very well with low resolution images. Hope it helps.
What are the issues you're having with Calibre? I've found it to preserve the formatting I'm looking for. What formatting are you talking about that it's not preserving?
Try https://vectorizer.ai/ it's main purpose is to convert images (rasters) into vectors (SVG). But it has great line detection and color acquisition, give it a go. Bare in mind that this will only work for images, so you will first need to convert the png into an image.
I know that it seems an odd suggestion, but I had to try different vectorization methods for a project of mine and this one was performing very well with low resolution images. Hope it helps.