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.
Digital cinema
The theoretical resolution of 35 mm film is greater than that of 2K digital cinema. 2K resolution (2048×1080) is also only slightly greater than that of consumer based 1080p HD (1920x1080). However, since digital post-production techniques became the standard in the early 2000s, the majority of movies, whether photographed digitally or on 35 mm film, have been mastered and edited at the 2K resolution. Moreover, 4K post production is becoming more common (Dec 2013). As projectors are replaced with 4K models the difference in resolution between digital and 35 mm film is somewhat reduced. Digital cinema servers utilize far greater bandwidth over domestic "HD", allowing for a difference in quality (e.g., Blu-ray colour encoding 4:2:0 48Mbit/s MAX datarate, DCI D-Cinema 4:4:4 250Mbit/s 2D/3D, 500Mbit/s HFR3D). Each pixel has greater detail per frame.