PS4 Pro 4k checkerboard interpolation explained

The PlayStation 4 Pro is an upgraded version of the original PlayStation 4, with a more efficient CPU and graphics chip. New to the console is native support for 4k displays, in other words 3840x2160 pixels (which is exactly double that of the standard 1920x1080 "full-HD" resolution in both directions, or, in other words, exactly four times as many pixels.)

The 4k resolution is, however, quite demanding in terms of graphics hardware, and even the PS4 Pro is not capable of rendering many existing PS4 games at that resolution (as it requires four times as much fill rate from the graphics hardware.)

In order to take advantage of the 4k display, however, the PS4 Pro uses by default (unless a game specifically wants to use native 4k) an interpolation mode in which only twice as much fill rate is needed, rather than quadruple. In other words, it renders the game at 1080p twice, covering half of the entire 4k screen, and then interpolating the other half.

It does this by first rendering the game normally at 1080p, and then again, but with the viewport shifted by half a pixel diagonally. When these two images are then interweaved onto the screen, it will cover the entire 4k display with a kind of checkerboard pattern. The remaining pixels are then just interpolated from the surrounding pixels, which is a lightweight operation for the graphics hardware to do.

The following image (which has enlarged pixels) demonstrates this process (click on any of the images below for a full-sized version). The first image is a small section of one of the two 1080p images, the second image demonstrates the checkerboard pattern formed by the two 1080p images, and the third image has the remaining pixels interpolated from those.

As you can see, the final result will have more details to it than the original 1080p version.

Below is the same example in four modes for comparison, how they would look like in a 1080p and a 4k display: The original 1080p version, that version simply upscaled to 4k, the checkerboard interpolated version, and a version rendered in native 4k.

While the checkerboard-interpolated version doesn't exactly match the quality of the native 4k resolution, it's nevertheless closer to it than the 1080p version.

That section, as well as the following ones, are taken from this screenshot. The locations of the details being demonstrated are marked in the image. Click on the images to see a full sized version.

As the last image demonstrates, this technique is not always without its flaws, as it sometimes introduces a very distinctive dithering-like pattern. The quality of the technique is highly dependent on what kind of content the image contains.