At integer scaling ratios, full-screen upscaling should be done just by duplicating pixels, with no blur at all. For example, Full HD (1920×1080) image could be displayed on a 4K display (3840×2160) with no blur, just by displaying one image pixel as a group of exactly 4 (2×2) absolutely identical physical pixels with no interpixel diffusion whatsoever.
On the contrary, full-screen upscaling via graphics driver is currently blurry even if scaling ratio is integer (e.g. 2x, 3x, 4x). For FHD (1920×1080) and HD (1280×720) images on 4K (3840×2160) monitors of 24-27-inch size where individual image pixels are almost indistinguishable, such blur unreasonably decreases perceptible sharpness without adding anything useful.
There should be a driver option to disable blur or at least to switch between bilinear/bicubic and nearest-neighbour interpolation.
For better understanding of what nonblurry integer-ratio scaling is, please see the demo. Thanks.
See also the “Nonblurry integer-ratio scaling” article which is an attempt to explain the blur issue and collect and summarize all the important relevant information about the issue and nonblurry integer-ratio scaling by pixel duplication as a solution.
See also a corresponding petition on Change.org.
Update (2017-07-06): The feature is now supported by nVidia GeForce driver 384.47 (Beta) for Linux via the “Nearest” transform filter.