The icon composer 2.2 in Xcode 4.3.3 supports the icns of 1024x1024. However, for icon composer 2.4, it doesn\'t support that any more. This is ironic, since Apple pushes for th
Icon Composer 2.4 doesn't support 1024x1024 size icons anymore because the workflow for creating application icons for Mac or iOS apps has changed.
See the Provide High-Resolution Versions of All App Graphics Resources section of the High Resolution Guidelines for OS X.
The new workflow is as follows:
Place .png files with each files size:
icon_16x16.png
icon_16x16@2x.png
icon_32x32.png
icon_32x32@2x.png
icon_128x128.png
icon_128x128@2x.png
icon_256x256.png
icon_256x256@2x.png
icon_512x512.png
icon_512x512@2x.png
iconutil -c icns -o myicon.icns myicon.iconset
in the Terminal (no need to install XCode).After doing this, everytime you build Xcode will compile your .iconset folder into a .icns file and use that in your application bundle. This has the distinct advantage of treating your application icon as a set of 'source images' from which the .icns file is derived.
The latest version of Xcode obsoletes the need for this (I'm using Xcode 5.1). Just click on your Project in the top left of the file listing, then choose the General tab. There is a section for the Icon Assets, click the "Use Asset Catalog" and your project will be updated to automatically build the icons file for you.
Then just click the arrow next to the Asset Catalog and it'll open a screen which shows you each of the required icon sizes with spots for @1x and @2x densities.