Changing Image quality for the iPhone 4 users in an iPhone app

I want to display an image to my users which is larger than the screen area and will overscroll to let the users drag it around and zoom in.

Do I need different images with different dpi for iPhone 4 users because of the higher resolution?

Or can I just set the zoom leve开发者_运维问答l differently depending on device?

Yes, you need to use different images. iOS 4 will automatically detect a higher-res image if you name it with a @2x suffix. e.g. image.png => image@2x.png

https://developer.apple.com/iphone/prerelease/library/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/SupportingResolutionIndependence/SupportingResolutionIndependence.html

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