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.
8K resolution
8K resolution refers to any screen or display with around 8000 pixels width. 8K UHD, also known as Full UHD, FUHD, or Full Ultra HD is the current highest ultra high definition television (UHDTV) resolution in digital television and digital cinematography. 8K in 8K UHD refers to the horizontal resolution of 7,680 pixels, forming the total image dimensions of (7680×4320), also known as 4320p, which refers to the vertical resolution.