uiimage可以在线程里处理

t is true that apple recommends using elements from the UIKIt on the main thread:

Note: For the most part, UIKit classes should be used only from an application’s main thread. This is particularly true for classes derived from UIResponder or that involve manipulating your application’s user interface in any way.

Since UIImage isn‘t derived from UIResponder, and you do not actually display it on the interface/screen. Then doing operations with UIImages on another thread should be safe.

This is however based on my experience, I haven‘t seen any official documentation about it.