Let's say you have image assets in two sizes - 1x and 2x. If you want to show an image at 1.5x, you don't upscale from 1x, you downscale from 2x so that you hav

Let's say you have image assets in two sizes - 1x and 2x. If you want to show an image at 1.5x, you don't upscale from 1x, you downscale from 2x so that you have a crisper image. If you're looking for a practical application of this, watch a YouTube video fullscreen that has 720p and 1080p options on a display that's 1680x1050 or anything in between the two video sizes. The 1080p version is better looking because it's scaled down, not up. This is the concept behind running a 3820x2400 framebuffer and downscaling it to 2880x1800 for display - you're getting a crisper image because of the use of 2x drawing by the system for text and standard UI elements. Of course, third-party bitmaps aren't going to benefit from this until they're updated, but Apple developers have been through this before with retina displays on iOS devices.