I have discovered that the Bookari app (=Mantano reader) is rather inefficient in storing covers. (Android). It seems that it extracts the (usually) well compressed JPG cover embedded in an epub eBook and store the image as a PNG picture in original size on internal storage, in a hidden folder structure. This may mean that the stored cover can be a few MB in size when the book itself is significantly smaller than 1MB, perhaps only 150-250KB or so. This is typically the case when the cover is in the form of a large busy photo with text and the book is a novel without any other illustrations. PNG is bad at compressing busy photos, while JPG is much better. It seems ridiculous to store the covers as files several times bigger than the books from which the cover is extracted, converted from JPG, but that is sometimes the case now.
And it doesn't seem to be possible to move the stored covers to external storage, even if Bookari itself can be moved to external sd-card.
So if you have a 128 GB external sd-card and perhaps only 8 GB interna storage and a lot of books and magazines to store, perhaps periodicals with big photo covers, you may encounter serious problems since the covers takes up a lot of space on the internal storage. The covers take a lot more room on the internal storage than the books on the external sd-card. And if you have limited internal memory you may want to use it for other apps as well...
I suggest that you use JPG format instead of PNG to store the covers and/or reduce the size. Or make it possible to store the covers on an external storage. Perhaps automatically if the app is moved to external storage? I tested resizing the PNGs and was able to reduce the space needed to store covers to a similar size as the storage needed to store the actual books.
Otherwise, I am very pleased with the app!
