I tried the tutorial from raywenderlich.com but the behavior was incorrect. The canvas or UIImageView seems to move after lifting my finger.

It tried to run the official project from raywenderlich.com but it has the same strange behavior.

Luckily I found a solution, you need to change this line inside touchesEnded function

// from
UIGraphicsBeginImageContext(mainImageView.frame.size)
// change to 
UIGraphicsBeginImageContext(view.frame.size)

And that’s it.