I have spent the last week trying everything I could to reduce the file size of my latest book. The book has over 100 images, all created with care at 300dpi. I used my Retina Macbook Pro to ensure the original files had the highest resolution (144dpi) in lossless PNG format. The results were very encouraging in the beginning….
Amazon charge a delivery fee for every kindle book sold. The cost is based upon the file size of the mobi7 folder. The greatest contributor to the file size is the image folder. I uploaded a draft copy of the book to the KDP and the delivery fee was shocking!
I tried various image optimisers. I hoped they would help optimise the images to reduce the file size whilst retaining quality. These worked extremely well. I had great results with Tinypng and ImageOptim.
Vellum is my formatting application of choice. I enjoy the experience, the simple and intuitive interface, and the results are always great.
I created larger dimension images at 300dpi, but smaller in file size than Vellum generates. I unpacked the Vellum generated mobi file and replaced every image with my own JPG version. I then recompiled using the Kindle Previewer. The results, in local testing, were very promising. The total mobi file size was reduced by over 35%.
Finally, I uploaded the file to Amazon KDP and the delivery cost was greater!
I now understand what happens in the background and, I must say, I am disappointed. Despite my optimised image files being smaller in file size than the original Vellum images, the mobi7 images are simply a reduced quality jpg. I had assumed the mobi7 images would be reduced in dimension, not quality.
I had increased the image size to a width of 1500px for all of my images and optimising them meant they were a smaller file size than the Vellum images. The Amazon conversion process for the mobi7 images is to simply reduce the jpg quality (to 69%). Because the image dimensions were greater (Vellum uses a 97% quality 1280px wide file) the mobi7 images were also larger in file size.
I even tested replacing a jpg with a gif. Unfortunately, the gif was over 200kb and Kindle Previewer converted it to a jpeg resulting in the same mobi7 size.
The conclusion to this sorry tale, at least for the moment, is the only way to reduce your Kindle book file size is to either reduce the image dimensions or the number of images contained within the book. The other option, one I am reluctant to entertain, is to increase the price of the book. My original target price was $5.99 or £3.99. The Amazon download fee means the price of the book may have to rise to $6.99 or £4.99, something I really don’t want to do.
