I published a section from my book Barcodes with iOS on DZone. My book is not only about barcodes but also gives short introductions to a plethora of other frameworks which you might not normally come into contact with.
The Core Graphics framework is written in pure C, meaning that it’s impossible to use CGImage instances directly with UIKit. Apple created UIImage as an Objective-C wrapper class around CGImage to bridge the gap. We explore Core Image in this article.
My book currently available at a discount via the promo code mentioned on DZone.