Epub file size

PS I found that RIOT (Radical Image Optimization Tool) works best for these images. It allows the user full manual control over chroma subsampling.

Be sure to use the portable version, and not the installer (which includes advertisements)! Here is the direct link (unzip, and run riot.exe):

http://luci.criosweb.ro/riot/thank-you-for-downloading-riot/?sid=portable-app

This only works on Windows. If you are on a Mac, you will have to optimize the images on a Windows machine first. Or use a command line tool like ImageMagick and use the same settings.

To learn more about (fixed layout) epub publishing, Bob Levine has two good courses on Lynda:

Adobe Digital Publishing Suite Essential Training

InDesign: Multistate Objects

There are others on there as well.

Now, I checked your sample! First, really interesting topic and book: seems like your project will become almost a library of carpet types. I learned new things while I browsed your pages.

As for the images: those really do represent the worst case scenario for optimization. The problem with the main carpet overview photos is that those include transparency, and that should be removed for best optimization. That means including the background colour in the transparent parts of each carpet image.

I tested this, and the Ardabil 01 photo is reduced from 2.27MB down to 928kb using a 95% quality with no chrome subsampling (4:4:4). A reduction of almost 250%. I zoomed in to a pixel level to ensure quality was more or less unaffected.

The close-up shots of the weaving can be optimized with jpg, though. With a chroma subsampling of 4:4:4 (no chroma subsampling) and a quality of 90% one of the weave close-ups was optimized from 1.83mb down to 378kb: a reduction by a factor 4-5.

Quick calculation based on having 500 overview images, and 500 weave close ups:

500 x 1mb = 500mb

500 x 400kb = 200mb

Total: 700mb

Remember that this is a worst-case scenario, and I noticed that the Ardabil 02 image compressed down to 463kb (half the size of the first one). So 700mb would be a maximum, and you'd probably end up with a (much) smaller epub file. And if you reduce the quality settings a bit more (which will not be visible to the eye), this could be further reduced.

One more issue I noticed is that InDesign doesn't properly crop the images, and includes a lot of white space. This increases the file sizes a bit as well, but more importantly, takes up WAY more video memory on a mobile device, affecting the processing speed. So you really want to crop those images somehow.

The trick and solution is to prepare your images OUTSIDE InDesign as optimized JPG files, and import them. Photoshop probably will not give you enough control here, since we need separate control over quality and chroma subsampling, something Photoshop does automatically.

The way I would work in this case is as follows:

1. Save all your images as full colour 24bit PNG files from Photoshop. Make sure no transparency is used, and the background colour is the same as the background colour in your book.
2. Divide the images into two groups: the large carpet overviews, and the weave pattern closeups.
3. Use a jpg compressor tool to compress each group of files using the above settings (use a batch conversion option to have it done automatically for you).
4. Import each image in your project. For each image make sure the export options are set to "Use Existing Image for Graphic Objects". It is best to create an object style which includes this, and assign that to each image object.
5. Export the epub. InDesign will now use your versions, rather than create new ones.

More work, but it will result in a FAR smaller epub, while retaining the quality of the images.

This link explains about step (4) (scroll down to How to Set the Quality for Individual Images:

How to Control Image Quality — Becoming a Digital Publishing Master with in5

Cheers!

What kind of "high definition" images are we talking about? What is your export platform in InDesign (iPad retina)? Do the images have to be zoomed in, or not? Are the images shown full screen? All full colour, or not?

What resolution are you exporting the epub at?

Would you be able to share one of the images with us?

I ask, because 1.6GB for a 1000 images seems overkill.

Fixed layout epubs are not responsive and 1,000 images at 1.6 MB each would give y 1.6GB.

There is no optimal size and without seeing your files, it's difficult to say whether this is appropriate or how to help.