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 CEA definition does allow manufacturers to use other terms—such as "4K"—alongside the Ultra HD logo. Since the resolution in CEA's definition is only a minimum requirement, displays with higher resolutions such as 40962160 or 51202880 also qualify as "Ultra HD" displays, provided they meet the other requirements.