Apple’s eBook requirements around images can be confusing at first. Requirements can seem reminiscent of Goldilocks, some images can’t be too big, some images can’t be too small, and images must be prepared with display on computer screens in mind, not printing.
When supplying an eBook to Apple two assets are used:
--The eBook file, whether it’s an ePub or ibooks author file.
--A separate cover image.
Even if the eBook file contains a cover image a separate image needs to be provided for Apple, and the same applies for all the other retailers.
In order for the eBooks on the iBook Store to fit with iPad Retina display requirements, Apple specifies the cover image to be a certain size, specifically its smallest dimension must be no less than 600 pixels, but ideally if the image’s smallest side is 1000 pixels or larger it will look better. Bigger is better. Images need to be prepared to display on tablet screens, so colours need to be RGB, any CMYK images will be rejected by Apple.
Where Apple requires the cover image to be over a certain size, Apple requires the images inside the book file to be under a certain size. This is so that the book file the user has to download isn’t too big as that fills up devices and leaves the user waiting for large books to download. Images inside books must have fewer than 3.2 million pixels, think of it as a 1700 square, or a rectangle about 2,250,000 pixels by 1,400,000 pixels.
Any image larger than this will cause your book to be rejected from the iBooks store. Again images embedded in the book need to be prepared for screen display so they need to be RGB not CMYK.
If anyone has any questions on this, or on anything else, please get in touch!
Mark Watkins is Head of IT at Vearsa. His favourite read of the year so far was Herman Koch's The Dinner, and in this blog he hopes to be a reliable narrator. (See what he did there? If not you'll have to read it too).
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