Icons and tab bars

Apple provide a description of the how they would like icon and tab bars to look. They show example of standard buttons.

Examples of buttons

In keeping with key element of iso 7 a tab bar is translucent and always appears at the bottom of the screen. Must display no more than 5 tabs on the iphone. The tab bar should maintain the same heigh in either orientation.

Tab bar image

Target size of the button. Apple recommend that a size of 44 points, important elements should have a hierarchic. The most important being at the top right hand corner and the least important being at the bottom left hand corner. Using visual weighting is another highlighted aspect. Larger items appear more important than smaller items they catch the eye more quickly and help the use lock on to the element you want them to use first.

The apps icon.

The key element to the the apps icon is the imagery should be easily recognizable in keeping with the iso 7 feel keep it simple and create an abstract interpretation of the app. Make it look good on a verity of back grounds. Icon should be opaque and do not use iso interface elements in the art work and don't use ios app icons in the inter face as this can lead to confusion.

Before and after rounded corners

Size of the icons should be 152 x 152 Retina screens and 76 x 76 for the standard screen resolution.
The icon should have a 90º corners. Apple suggest that you also create an icon for in store display in two sizes 1024 x 1024 pixels and 512 x 512 pixels for their standard resolution.

Ref: MobileHIG pdf from Apple