This has been the briefest possible introduction to Core Image, yet we still managed to make something useful, using
UISlider for the first time and even writing images to the photo album.
Unless you really do intend to make Yet Another Core Image Filters Program (best of luck!) your use of Core Image will mostly be about manipulating a picture in a very specific way, using a filter you have hand-crafted to look great.
If you want to try other filters, search on Google for "Core Image Filter Reference" and have a read – it will list the input keys for each of them so that you can get really fine-grained control over the filters.
If you want to spend more time working on this app, you could start by making the Change Filter button change title to show the name of the current filter.
If you fancy something bigger, then you should definitely investigate having separate sliders to control each of the input keys you care about. For example, one for radius and one for intensity.
If you want to tackle something small, see if you can make tapping "Save" do nothing if there is no image loaded.
One of the most effective motivators of success is sharing your progress with other people – when you tell folks what you're doing and what you've learned, it encourages you to come back for more, which in turn will help you reach your app development goals faster.
So, now that you've done all the hard work it's time to share your success: tell folks that you've completed this project, either by clicking the button below to start composing a tweet, or by writing your own message from scratch. This will definitely encourage you to keep learning, but it will also help other folks discover my work – thank you!
Paul Hudson is the creator of Hacking with Swift, the most comprehensive series of Swift books in the world. He's also the editor of Swift Developer News, the maintainer of the Swift Knowledge Base, and Mario Kart world champion. OK, so that last part isn't true. If you're curious you can learn more here.