How to scale images (not resources) to iPhone Retina display correctly in a view?

I have a UIImage, from either device's camera or downloaded from a URL. Say resolution is 800x600.

I want to display a scaled image in a UIImageView which is 200x150, and I have a proper image scaling code.

So, I just scale the UIImage to the UIImageView's frame.size (again, 200x150). On a non-retina display it looks OK, but on a retina display it looks bad, like a smaller picture was scaled up, because the actual frame in pixels is 400x300.

The quest开发者_高级运维ion is - should I, manually multiply the frame.size.width/height by 2 when it's a retina display when I resize, so it'll be resized to 400x300, or is there a built in feature for that?

Since the UIImage is not a resource on the device, I don't have the @2x option.

Keep the frame size of the image view at 200x150 in all cases. In case of non-retina display scale the image to 200x150. On retina display devices scale it to 400x300. Set the contentMode of the UIImageView to UIViewContentModeScaleAspectFit.

When you get the image in say 800x600, can't you make a UIImage that is scaled to 400x300 and save it temporarily with the @2x extension, maybe to the Documents folder or tmp folder, and then save another UIImage scaled to 200x150 and save it without the @2x in the same directory.