We're using retina images in our iPhone app (i.e., double the size).
The images render great on an iPhone 4 -- sharp and crisp. However, for the same app, the images look grainy on an iPad when run in "1x" mode (i.e., iPhone app size).
The code is exactly the same for both apps. There is no iPad version. People just download the iPhone version on iPads.
Are we supposed to use different images for the iPad?
Here is the app: http://itunes.apple.com/app/dumpling/id514239919
If you download it on an iPhone and then again on an iPad, you'll see the difference.
If the app is not universal then they are rendering the iPhone version on the iPad. I'm assuming you aren't in "2X" mode so if you are on an iPad 1 or 2 your app would not be using the retina graphics so it'll look grainy. Have you tested this on an iPad 3? This should render correctly for you with the @2x images.