title: Where does UIImage operations run on watchOS extension
body: <p>I am still new to watchOS and trying to understand how the architecture works. I have a watchOS 3 app that I have been working on that uses UIImage in my WatchKit extension. I do some operations with UIImage from assets in the extension. What I can't tell is where these UIImage manipulations happen, is it on the watchOS or on iOS? In some tutorials I read, it sounds like assets for extensions are stored in iOS and UIImage being form UIKit makes me believe its on iOS. Apple's WatchOS programmers guide has these 2 images:</p>
  
  <p><a href="https://i.stack.imgur.com/r6GEW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/r6GEW.png" alt="Relationship between the Watch app interface, the WatchKit extension, and the iOS app"></a>
  Apple says this image shows the relationship between the Watch app interface, the WatchKit extension, and the iOS app. </p>
  
  <p><a href="https://i.stack.imgur.com/Uhrfa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Uhrfa.png" alt="Target structure in watchOS"></a>
  Apple says this image show the structure of a watchOS app. This seems to imply images are stored on watch.</p>
  
  <p>I couldn't find any answers in the tutorials or programmers guide and the images used to describe how the watchOS works confused the situation even more. </p>