How are comics shrunk by Comic Zeal?

As you read a comic, Comic Zeal loads the next page in the background.

Each device has a maximum size of image that can be displayed. If the image loaded is larger in a given dimension than that size (1500 pixels on earlier devices, 2000 in later) then the image is resized to fit and then saved so it won't have to be resized again.

When you are ready to turn the page the image is already loaded and the right size for you.