Reduce Image Size with ImageOptim
The size of an ePub file is important. Some retailers— like Kindle’s Direct Publishing program—have very small maximum file sizes or charge you download fees. Each image you add can be—quite literally—costly. But it’s not just that: the size of an ePub file can also contribute to sluggish rendering times and slow downloading times to get it onto your device.
If you create image-heavy eBooks (both reflowable and FXL), you’ve probably seen how quickly your final ePub’s file size can increase. Fortunately there’s a great little program that can help reduce the size of images. Let’s take a look at ImageOptim
What is ImageOptim?
ImageOptim is actually a series of scripts and algorithms that remove unnecessary data from images to make them smaller in size and load faster. Even if you use Save For Web in Photoshop there’s still a lot of additional cruft in that file that can be removed to further reduce the file size. When you run ImageOptim on an image, it tests each algorithm and then applies the one that creates the smallest file size.
It’s important to know what ImageOptim does NOT do as well. Unlike Photoshop’s Save for Web, it does not compress images at all. You shouldn’t see any visual difference in your images when using ImageOptim, only a file size difference.
I recently made an FXL book for a client that had a large number of full page images in it. Before running ImageOptim the folder of images was 51.8 megabytes (these images had already been saved using Photoshop’s Save For Web). After running ImageOptim it squeezed out 3.8MB in total from all the images. That might not seem huge, but that means I reduced the entire folder size by about 4 full images. And depending on how you save your images that could be even more. On some web projects I’ve seen the size reduction be as much as 50%!
How to use ImageOptim
One of the best parts of ImageOptim is just how easy it is to use. Download the app, drag in your image folder and let it do it’s thing.
1. Download ImageOptim
You can download ImageOptim from this link: Download
Once downloaded, open up the zipped file, and drag the application to your Applications folder
2. Drag in your image folder
Once you have installed the app, go ahead and open it up. Then crack open your ePub, and drag the images folder into the ImageOptim window. ImageOptim will begin to run through the images, optimizing each one of them (this can take a awhile, and don’t be surprised if your computers fans get loud—this is a pretty processor heavy procedure).
When it’s finished it will give you a total amount saved in the bottom corner. Even if its .1MB its still something!
There are quite a few options you can set in ImageOptim’s preferences. I encourage you to take a look at the ImageOptim website for more information.