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).
Red Digital Cinema
The early team members engaged in undisclosed research on how to make a digital camera feasible for Hollywood productions. Part of this involved using 4K resolution instead of 2K which was most common at the time. Another technical hurdle was to achieve the focusing quality of DSLR cameras without sacrificing frame rate. Part of Red's solution to this problem was developing a sensor with a physical size comparable to that of analog film. At the 2006 NAB Show, Jannard announced that Red would build a 4K digital cinema camera, called the Red One, and began taking pre-orders.