The icns (Apple icon format) - as wiki states "supports icons of 16×16, 32×32, 48×48, 128×128, 256×256 and 512×512 pixels, with both 1- and 8-bit alpha channels and multiple image states (example: open and closed folders). The fixed-size icons can be scaled by the operating system and displayed at any intermediate size"
So, I go ahead and install "icnsutils" which gives me the nifty tool icns2png. Then I run the tool:
icns2png -x -s 128 -d 32 netbeans.icns
...and get a nice 128x128 32-bit png file. This I use as the icon for the launcher or use it at the dock.