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How do I scale down retina display UI elements to normal, using photoshop?

• We are building an iOS app, and am trying to crop images from a photoshop mockup which was optimized for retina display. I understand that retina display is having double the resolution that the normal assets to be used in previous versions of the iPhone. Any pointers to practices that help me to crop images from this hi res mockup, and convert it to the normal resolution supported by older iPhone versions, will be gr8!

• Answer:

  The question doesn't make much sense. Cropping is going to select the boundaries of the image and, as such, is resolution independent. From there, you may want to scale the image, but that's dependent on the source size and resolution and target size and resolution, which is independent of the screen resolution. Assuming a square image that's NxN pixels that you want displayed as a 1"x1" image with a 1:1 pixel ratio on an iPhone that has a resolution of 326 ppi, then you need to scale the source image by 326/N. If you wanted an image that's 0.5"x0.5", you need to scale the image by 326/2N ... and so on.