4k is one of the highest level of video resolution in digital cinema. 4k is nearly five times the resolution of 1080p and requires expensive cameras and very powerful and high-resolution projectors to reproduce the resolution natively in the digital domain. 4k can be down-converted to 2k and printed on 35-millimeter film for wide distribution to theaters that don't have 4k digital projectors.

The first full 4k film ever produced is April Showers.

Notable 4k projectors include Sony's Cinealta models and Meridian's 810 HD-ILA projector. Both use LCoS technologies.

4k video has a resolution of 4,096x2,160, as compared to the 1,920x1,080 of 1080p HD.

Read a review for the Sony SRX-R220 4k CineAlta projector.

Learn about the 4k Video Digital Cinema Standard.

See a review of YouTube's 4k video streaming.

Read about Sony's expansion of 4k in movie theaters.