You’ll want to design your icons and launch screen at a size of 1920×1080 and then trim down as needed. Leave at least 90 pixels to each side and 60 at the top and bottom to account for potential overscanning issues. Details are found at the Apple tvOS HIG.
I built my icons in Photoshop (here’s hoping El Cap won’t kill my Photoshop!) and imported them into the App Icon & Top Shelf image template. Not all image sizes are listed in the Identity and Type inspector so I had to hunt around a bit. To save you time, here are my sizes:
Front, Middle, and Back (Large): 1280×768
Front, Middle, and Back (Small): 400×240
Launch Image: 1920×1080 (see advice above)
Top Shelf image: 1920×720
For the Top Shelf (this is the MOOSE image in my video), make sure you design side-to-side with enough space and visual punch. This image has a big role in setting mood.
The front/middle/back sliced images are used to create some of the visual parallax effects. I designed mine all together in Photoshop layers and then saved each one to a different file. I think I may update Art Helper to make this easier.
Your launch image is stored in a separate slot in your xcassets folder so don’t forget it (I did initially) when setting up your art.