I'll back @theducks recommendation for using external viewers for some formats. Calibre has to convert all formats to a common format before viewing. That is basically ePub. For PDF, it is unlikely to be a good conversion for even simple books. For comic books, the viewer does work, but, I think if you try one of the comic book readers, you would find it better. I have Cdisplayex installed which is simple and works for the occasions I need it.
But, in the viewer, if you right-click on the image, there is a "View image" option. That supports zooming and other functions.
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