I was complaining the other day about how Mojave still doesn't support writing 16bpc HEIC images (aka, deep color). I know most people still don't quite get why it's important, and it occurred to me that maybe there was another way to talk about it, rather than saying "more bits per pixel!" or "It's deep".
How about, "It's like @2x for color"?
So deep pixels are like @2x images. When we (developers) got our Retina displays, we didn't just size up our existing images with nearest neighbor scaling. That would have created blocky images! Instead, we added more pixels which made our curves more crisp and accurate. The same thing happens when you work with higher bits per color.
You get accuracy. You get less banding. Sure, you could dither your images to hide banding, but that's a temporary hack- sort of like subpixel antialiasing for text is (or was; Apple removed support for subpixel antialiasing in Mojave and iOS never had it).
At any rate, I filed it this past summer as radar://41731847: Mojave does not support writing 16bpc/deep color HEIC images.
The format supports it, and we've got DP3 color profiles on iOS and MacOS now. We just need the encoders to catch up.
Ironically, the introduction of a wider color gamut such as Display P3 will increase the amount of banding in our images, unless you move from 8 to 16bpc.