The most important reason EPUB and Mobi came up as the widely accepted formats for e-books is their support for reflowing of text. This makes it easy and comfortable to read the content on devices of different screen sizes. Since text reflows to fit the screen size, the reader does not have to zoom or pan around to read the entire page, as would be the case with a PDF. Most e-book reading apps also allow readers to change the typeface, font-size etc. to suit themselves. So, people with weak vision can increase the font-size. One can also use assistive technologies like screen reader to consume the content.
These formats work well for most books which have text-heavy content. But there are categories of books that have relied on the fixed layout of print medium for correct presentation of content to the users. For example, image-heavy coffee-table books, comics and graphic novels, children’s picture books, photo-books etc. Typically these are the books which are image-heavy and exact layout and design is a major part of the appeal apart from the content.
To handle such books, we need to give up on the reflowability of the e-books and have fixed layout e-books. PDF is one way to do it. Initially EPUB did not have support for fixed layout (FXL). But now EPUB3 specifications include support for fixed-layout EPUBs. Almost all major e-book selling and reading platforms also support it, including Amazon’s Kindle and Apple’s iTunes. The obvious disadvantage of fixed layout e-books is that if viewed on a screen smaller than the one it is designed for, it will not be easy to consume.
Creating fixed layout EPUBs from scratch essentially means including some metadata that identifies it as such, and using HTML and CSS to set the exact width and height of the pages. Each page needs to be a separate HTML file in the EPUB. There are ways to specify how the reader should handle spreads.
InDesign and some other tools support creation of fixed layout EPUBs. InstaScribe currently doesn’t support it, but we would keep an eye on user feedback and accordingly decide the priority for this.
One word of caution: Some designers and publishers use fixed-layout EPUBs as a short-cut to designing an e-book properly. They just put the pages of printed book in fixed layout. This is not good idea. It hinders the distributability of e-books. Reflowability is an important property that makes e-books tick. Fixed layout should not be used unless there is an absolute, unavoidable need for it.