4K resolution
As noted above, DCI 4K is 40962160, while 4K UHD is 38402160, producing a slight difference in aspect ratio rather than a significant difference in resolution. Traditional displays, such as LCD or OLED, are 3840 pixels across the screen, with each pixel being 1/3840th of the screen width. They do not overlap—if they did, they would suffer reduced detail. The diameter of each pixel is basically 1/3840th of the screen width or 1/2160th of the screen height - either gives the same size pixel. That 38402160 works out to 8.3 megapixels, the official resolution of 4K UHD (and therefore Blu-ray UHD discs).
Camcorder
In early 2014 Sony released the FDR-AX100 which represents the next generation of camcorders. It is capable of shooting in 4K resolution. It currently has a price tag of £1,699 and 4K camcorders are not expected to come into the mainstream market for at least another eight to ten years as most current Blu-ray players are not capable of playing 4K video. Virtually all mainstream TVs are not 4K ready either with the only 4K TVs available being very expensive at £2,500 or over. The only means of archiving 4K video is the 100 GB Blu-ray Disc XL but the discs are very expensive.