I recently completed reading Core Image for Swift by Simon Gladman. The book is available for free on iBooks. I had little previous exposure to Core Image, nor writing GLSL (the language Core Image filters are defined in) and I found this book a thorough and well written introduction.
To my knowledge, this is one of only two full-length book about Core Image. I have not read the other, but since its publication date (2012) predates Core Image for Swift (2016) by four years, I imagine it is somewhat out of date. Gladman is comprehensive in his coverage of the technology. He covers the built-in filters, creating various kinds of filters from scratch, image display options like GLView and MetalView, and peripheral technologies like vImage. In short, everything you would need to get started using Core Image for almost any purpose is covered in this book.
Gladman’s approach is one of using copious source code examples. Some people learn better from English explanations and some people learn better from code. This book will mostly appeal to the latter kind of reader. With that said, Gladman does take the time to explain basic information that the uninitiated in the digital image manipluation world will likely find helpful. Such as, how does a convolution filter work? The difference between various techniques and why you would use each is made clear throughout.
I read the book from cover-to-cover, which is probably not how most people would approach this book. The chapters are self-contained enough that you could probably just read the first few and then pick and choose chapters on topics that interest you. In my opinion each chapter is a more cogent explanation of the topic at hand than Apple’s documentation provides.
The biggest downside of Core Image for Swift is that it was written in the Swift 2 era, meaning its source code is now outdated and requires translation. Most of the source code in the book is provided in online repositories. However the repositories themselves have not been updated in over a year. Since Mr. Gladman began working at Apple last year, I think there is little hope the book itself will be updated either. We cannot blame book authors for writing books that get outdated. I just finished writing Classic Computer Science Problems in Swift, and with a fast moving target like Swift, it is likely that my book too will have some syntax incompatibilities with the latest version of Swift in a couple years. Xcode 9 is able to translate most of the code from Core Image for Swift into Swift 4 with little manual intervention beyond a lot of clicking “fix.”
Overall, Core Image for Swift is an excellent introduction to Core Image and I highly recommend it to anyone interested in this technology. Since it is free, it is a no brainer to at least download it and checkout the first chapter. Mr. Gladman’s blog is also work checking out. Many of the older posts are about Core Image.