title: use photoshop to change image resolution for iphone4 vs iphone3
body: <p>I have a psd which is for iphone4 640x960.  Inside photoshop, the image size says the resolution is 72pixels/inch.  How do I decrease the resolution by half for the iphone3's 320x480?  I tried changing 72 to 36, but that didn't do anything.</p>