4K resolution
So while 4K UHD sounds like it has a pixel structures with 1/4 the area of 1080p, that does not happen with pixel shifting. Only a true 4K projector offers that level of resolution. That's why "true" 4K projectors cost so much more than 4K UHD projectors with otherwise similar feature sets. They produce smaller pixels, finer resolution, no compromising of detail or color from overlapping pixels. By comparison, the slight difference in aspect ratio between DCI and 3840×2160 pixel displays without overlap is insignificant relative to the amount of detail.
4K resolution
The main advantage of recording video at the 4K standard is that fine spatial detail is resolved well. If the final video quality is reduced to 2K from a 4K recording, more detail is apparent than would have been achieved from a native 2K recording. Increased fineness and contrast is then possible with output to DVD and Blu-ray. Some cinematographers record at 4K with the Super 35 film format to offset any resolution loss that may occur during video processing.