How to setup your Photoshop document if you want to design for iPhone 3 and iPhone 4.
For those who already read my article «Designing for the iPhone 4» I have some more things I’ve learned when working with Photoshop. Very important are the Photoshop document settings you should work with.
For iPhone 3.
For iPhone 4.
The iPhone 4 features a superior display resolution (640 × 960 pixels at 326 ppi) compared to previous iPhone models, containing quadruple the display (320 × 480 pixels at 163 ppi) of the iPhone 3GS. You will need to create two sets of images for either resolution unless you are only going for the retina screen. If it comes to the ppi forget what you have read or heard. Set it on 72ppi and leave it. Why is that? iOS ignores the ppi settings of your document. The only important things are the set pixels. Also PNGs, your end format, are calculated in ppm (pixels per meter). This can cause rounding errors when converting between pixels per inch (ppi) and pixels per meter (ppm). You don’t want to run into those. As well it makes it more simple for you to move files between the iPhone 3 and the iPhone 4 photoshop files because they have both the same ppi settings.
Also ditch the color management. The color management will do you no good and if you hand out your files to a third party company you will run into trouble. With those settings you are good to go. If you would like to get some more inputs these links might help: Designing for Retina display and OS Photoshop Actions & Workflows.