If you are including images in your book, we strongly recommend you try to keep the image file sizes as low as possible, while still ensuring you get the level of quality you're looking for in all of your images.
The short version of this article is: try to keep each of your image files under 1MB, and the total in the book under 100MB.
When you have images that have huge files sizes, this may cause a number of frustrating problems for you as an author. For example, if you're writing the Dropbox writing mode, it may cause syncing problems, as Dropbox can have trouble with large files. Large files can also cause the Leanpub book generation process to take longer, every time you preview or publish.
But most importantly, if your image files are too big, that means the ebook files we produce with all those images in them will themselves have a huge file size. This can cause problems for your readers, who may have download limits, and who might be using devices with limited storage space.
In this article, we are going to provide some guidance for keeping image file sizes manageable.
Recommended File Types
For photos, use the JPG image file format.
For line drawings, use the PNG file format.
Image Pixel Density
We provide specific guidance on pixels sizing for every Leanpub book, depending on each book's Book Theme settings. You can find this guidance if you go here:
...making sure to replace YOUR_BOOK with your books's unique web address.
Checking Image File Size
How you check your image's file size can vary, depending on your device and your operating system. Typically, if you right-click on an image, you will get a list of options, including something like "Get Info":
If you select that option, you will see a box that displays the images size information:
If the image is too big (like this one), you should create a new copy of the image, that has a smaller file size.
Exporting a Smaller Copy of the Image File
How you create a copy of the image with a smaller file size will depend on the app and device you are using. However, the steps are usually the same:
Open the image file in the app
Look for an "Export" or "Share" or "Save as..." option
When you select that option, you will have an option to change the file size of the exported image
Additionally, at this stage you will have an option to change the file type for the new image file you are creating
In this article, we are going to do this in the Preview app on a Mac. We're also using an image from Unsplash, which is a great resource for images you are free to use (though you should always check attribution requirements, of course!).
First, open the image in Preview:
Next, under the "File" option in the menu for Preview at the top left, select "Export..."
This will open a box with an option that looks like this at the bottom:
First, since this is a photo, you will want to make sure the format is JPG (or JPEG). In this case, it is correctly set to JPEG.
Second, we want to reduce the File Size. Note that you can actually see the File Size under the "Quality" slider in the image above.
Slide the "Quality" slider to the left until the file size is under 500KB (after you move the slider and release the mouse button, it will re-calculate the file size):
Click the "Save" button at the bottom right. You can then open the new image, and you will almost certainly see that it still looks great, even after reducing the file size:
Exception: Cover Images
The one exception to these rules regarding image sizes is cover images. It is ok for cover images to be bigger, because the cover image is displayed all the time on your Leanpub landing page.