The quality of digital manga varies a lot, mainly depending on the manga itself (how old is it, how big are the letters by default, etc etc), a bit less so depending on where you buy from. In Amazon’s case, it even matters if you are reading through their online viewer, or through a kindle/the amazon app.
For reference, this manga to me seems very good quality. This is a screenshot I took on my phone using the Amazon app:
But using the amazon web reader would get me this sort of resolution:
It’s just the fact, that storing images is inherently costly compared to text. As for the ば-ぱ distinction, they are usually easier to tell apart if you have a ton of experience dealing with the issue. But gotta remember, they are small dots on top of a piece of text that’s already smaller than the main text.
You have two main ways of solving this issue, but both of these require to you have the manga as a set of images, which is harder to do for bookwalker, but not impossible.
- You can run mokuro on the images, this is an ocr tool, and it will try to extract the (main) text from the images. After this, you can use a browser extension, like yomichan to look up the words you can’t read the furigana of.
- It’s less reliable, but some ai image upscalers can to some extent fix up text. I experimented with this a bit a few months back, and the results, while not great, where pretty decent.