While exact implementations tend to vary between developers, the technique generally involves rendering only 50% of any given scene, often rendering it in a grid of 2×2 pixels. A
reconstruction filter is then employed to extrapolate the appearance of the unrendered parts of the scene, with the final image then being presented to the viewer as (theoretically) the same as if it had been rendered natively at the target resolution. In some implementations the checkerboard grid will be alternated between frames, with the previous frame's image data being held in memory, and then used to aid with reconstructing the scene. A similar technique was used in the 1993 video game
Doom, which had a "low detail" mode that only rendered every other column of pixels to improve performance. ==Implementation==