Image size

2 posts / 0 new
Log in or register to post to the forum.
Last post
Submitted by maru_vdv on December 27, 2016 - 6:10am
#1

Hi everyone!
I´m new here and I need some help with image formatting for ebooks in epub.
I been working on text files, mostly, but now I have an ebook with over 300 images (pictures and illustrations).
I generally use JPG or PNG files RGB 1400x2006 px, 150 dpi for full page images. With so many images, the result is a really heavy file, but in lower resolutions the quality of the final image is really bad.
Is there any way I can reduce the final file size without loosing image quality?
Thanks in advance.

Submitted by rkwright on December 28, 2016 - 7:07am

Well, this is a complex subject since there are so many variables.  However, there are several points that can be made:

  • 300 images is  a lot.  If you assume that an image of that size is typically going to be at least 150 kB as a JPEG (this is based on picture books I have created with images that size), then  300 x 150 = 45000 kB or 45 MB.  So your EPUB can't be much smaller than that unless...
  • You can reduce the quality of the JPEG, which will help.  Experiment and see how far down you can reduce the JPEG quality before it is perceptible.
  • You mention illustrations.  If by illustrations you mean line art - either stroked or filled with color, PNG is usually  a better choice as it will encode the image in such a way (run-length encoding) that better compression is achieved.  For photographs and similar images (where most pixels are a different color then their neighbor, JPEG is usually better.

Net net, 300 images is a lot and all you can do is experiment.  Hope this helps.

Secondary menu