Here is the basic workflow for how I create all the icon sizes I need for my cross platform Unity games. I start by creating the main icon in PhotoShop, or wherever, at 152×152. Here is the new icon graphic for Flappy Jetroid:
Once I have this in PhotoShop I can use Save For Web to generate each different size:
Since my icons are all pixel art I can just change the size and use Nearest Neighbor scaling. If you are not doing pixel art you can choose a different quality but I highly suggest generating out all the sizes you need by hand so they look clean. I’ve seen unity create blurry icons before if you don’t manually set each one up. If Unity does the resize it will probably look blurry on lower resolutions.
Once I have all my icons I keep them in my Assets/Artwork/Icons folder:
From there you just open up the platform settings and manually drag them over:
Make sure you check Override for [PLATFORM X] so you can manually add the resized images you created.
Going to keep sorting out all the icons I need for each platform. My Flappy Jetroid game is turning out to be the perfect cross platform tester!