Icon Glue is probably the easiest way to quickly create an Apple Icon Image (.icns) for your mac app from a single 1024x1024 pixels sized PNG or TIFF image.
You can also create all iOS app icons you need for submitting apps to the App Store in just one go.
Just open your image, select what you want to create (Icon Glue will remember these settings) and save it. You can also open an OS X application bundle to easily extract its icon without having to browse through the bundle's internal folder structure.
Icon Glue can ...
• create .icns files or .iconset image sets from a single PNG file
• create the iTunesArtwork.png images required for app submissions on the Mac App Store
• create all app icons for your iOS apps (version 1.2 supports the new iOS 7 app icon sizes)
• extract all image representations from an existing .icns file
• extract an application bundle's icon and export it as .iconset and/or PNG file
• show previews of all iOS and OS X Icons to be created and allows you to save them one at a time (added in version 1.2)
Rectangular (non-square) or too small images will be adjusted accordingly to ensure that the result is always a valid, retina-compatible .icns image file.
If you find a bug in this app, please report it to the bug tracker so I can fix it as soon as possible. You can reach the bug tracker directly via the "Icon Glue Support" link.
A free tryout version is available on the website.
• now also creates 40/80px Settings & Spotlight Icon for iOS 7
• fixes a layout bug on the icon preview screen
A complete changelog of all previously released versions is available on the website.
More detailed informations on the various changes are available in the bug tracker (reachable via the "Icon Glue Support" link)