Icns Maker is available from the Mac App Store.
Make an icns in 2 steps:
1: Drag an image into the window.
2: Click “Create icns”.
This creates a .icns file that can be imported directly into your Xcode project for use in your app.
Why is this necessary?
In versions of Xcode before 4.4, Apple provided an app called “Icon Composer”. It allowed you to drag images into a window and export a .icns file for use in your apps. With Xcode 4.4, Apple has changed the way icons are handled for Mac apps and “Icon Composer” is no longer supplied.
Search the Xcode documentation for “Icon Design Guidelines” and scroll down to “Provide the Correct Resources” and “Packaging Your Icon Resources” for more info.
But basically, you now create a special .iconset folder and load it up with various sized images. Then you run a shell command to stitch these specifically named files into a single .icns file that can be used in your Xcode project. None of this is rocket science, but it is tedious and repetitive – just the right sort of task for a computer.
Note that apps submitted to the Mac App Store now require a 1024×1024 version of the icon.
If you want more control:
Click the “Smaller sizes” switch to show all the other image sizes.
When you drag an image into the 1024 x 1024 area, it is resized to supply all the required images. If you have a smaller version of your icon image that you want to use for some of the smaller sizes, just drag the image into the largest image area that you want it to be used for.
As an example, if you want to show a lower resolution image for 64×64, 32×32 and 16×16, create the lower resolution image at 64×64 pixels and drag it into the 64×64 area. It will be used for the 64×64 image and resized to make the 32×32 and 16×16 images. The larger images will still use the original 1024×1024 image scaled down.
If you want, you can specify a different image for every required size.
512×512 images will be resized to 1024×1024 if required to assist when converting older icons, but no other images will be enlarged.
Q. What image types can I use?
A. Any image type compatible with QuickTime, including JPEG, PNG, TIFF, GIF, PDF, PSD, BMP.
Q. What if my starting image is the wrong size?
A. If your image is not square, it will be cropped when you drag it in. If it is the wrong size for the image area you are dragging it into, it will be resized to fit.
Q. Do I have to drag images in?
A. No, you can copy & paste an image file, or an image.
Q. How I start again with a blank slate?
A. Choose “New” from the File menu, or press Command-N.
Q. What if I want to update an existing .icns file?
A. Drag it in or choose “Open icns…” from the File menu. You may find that you need to make a new image for the 1024×1024 size.
Q. Does Mac Icns Maker create icons suitable for Retina displays?
A. Yes. That is why it uses a 1024×1024 version of your image.
Q. Does Icns Maker create icons for use in iPad and iPhone apps?
A. No. icns files are used in Mac apps only. For iOS apps, check out the companion product: Icon Builder.
Q. I’m a programmer, not a graphic designer. How do I make icon images?
A. One easy way to create basic shapes with gradients, text, added images etc. is to use Keynote. I presume PowerPoint has the same sort of abilities.