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 cinematography
The DCI standard for cinema usually relies on a 1.89:1 aspect ratio, thus defining the maximum container size for 4K as 4096×2160 pixels and for 2K as 2048×1080 pixels. When distributed in the form of a Digital Cinema Package (DCP), content is letterboxed or pillarboxed as appropriate to fit within one of these container formats.
In the early years of digital cinematography, 2K was the most common format for digitally acquired major motion pictures however, as new camera systems gain acceptance, 4K is becoming more prominent. The Arri Alexa captured a 2.8k image. During 2009 at least two major Hollywood films, "Knowing" and "District 9", were shot in 4K on the RED ONE camera, followed by "The Social Network" in 2010. , 4k cameras are now commonplace, with most high-end films being shot at 4k resolution.