The downsampling isn't for fun (Destiny)

by uberfoop , Seattle-ish, Monday, July 31, 2017, 21:52 (2717 days ago) @ Cody Miller

Interestingly, I recall a trick I learned a long time ago in photoshop which is now incorporated as one of the scaling modes. Blurring your image slightly before downscaling resulted in a sharper image. As such, a straight up downscale is not always the best result.

On a theoretical level that's not really a "trick", but intertwined with the concept of scaling, or really resampling in general.

The same thing is done in antialiasing. If you're carrying out some form of supersampling, perhaps you have four samples per pixel in the final image; but nothing says that each final pixel need only be constructed from the four samples closest to the pixel center, nor what the weighs should be on each sample. Wider kernels, incorporating colors from neighboring pixels, are quite common. A well-known example would be a quincunx resolve, although that's crude and was unfortunaterly tarnished by very poor marketing/explanation.

Wide kernels can be leveraged to minimize reconstruction aliasing, i.e. assigning color in a geometrically-inaccurate way (such as pretending that pixels are "square regions" of a solid color). This can also be relevant at the final output; that CRTs naturally reconstruct pixels as fuzzy blobs is part of why they produce such a smooth image, albeit sometimes a little soft.
(And similarly, I disagree about 1080p images "scaling perfectly" to 4K via nearest neighbor. You can certainly do worse, but there's nothing theoretically "correct" about taking the color at a sample point - i.e. a pixel - and solidly filling a rectangular region with it.)