eBook loads slowly

Generally slow loading and choppy performance is caused by heavy images. Many users make the mistake to choose 300ppi when preparing images and exporting an epub when they picked the iPad or other tablet templates in InDesign.

This is en entirely wrong workflow, since InDesign expects an effective 72ppi. In simple terms, ensure you are working at the native resolution of the main deployment targets' screen resolution, or close to it.

So for a typical iPad a 2560x1536 target resolution is what should be kept in mind. A full screen image should adhere to that resolution. Then when exporting the epub, select 72 ppi. NOT 300 or 150, or whichever, because you run the risk of exporting graphic elements which are then converted to bitmap elements at more than 4 times bigger than the required base resolution. Which will not only blow up (more than quadruple) the size of your epub in worst case scenarios, but also  tax the devices resource FAR more, trying to shift quadruple the pixels (because all graphics are stored in the video ram as uncompressed images!).

First thing to check is the resolution of your assets in the exported epub.

And be aware that InDesign is notoriously bad at optimizing bitmap assets. Best practice is to do a last manual optimization run after the final epub version is exported from InDesign. It can mean a 50% reduction in book size, which means more content can be delivered as well.

Hello Simon,

are you using something like Readium to view your epub on the web browswer?

https://chrome.google.com/webstore/detail/readium/fepbnnnkkadjhjahcafoaglimekefifl?hl=en-US

have you validated your file?

this is the gold standard for doing so (if you are afraid of code, this is not for you):

https://github.com/w3c/epubcheck

if all of this information is new to you. i recommend you wantch this video course:

https://www.linkedin.com/learning/indesign-creating-fixed-layout-epubs/validating-the-epub?u=76821178

these is also this:

https://www.pagina.gmbh/produkte/epub-checker/

this is an app you install, and you run your file via this to see what needs to be fixed.

Lets just be clear that publish online and epub are two totally different things. You publishing online the same does not help you fix your epub not working on readers. They are two totally different animals.

Last, what version of epub are you publishing to?

are there any features that you used that are not supported by that version?

Which reader are you using? That can be the problem with FXL epubs. For fun export the publication as a Publish Online document to see the difference.

Which version of InDesign and OS?

FXL ePub or Reflowable ePub?