4K resolution is a display device or content having horizontal resolution on the order of 4,000 pixels. Several 4K resolutions exist in the fields of digital television and digital cinematography. In the movie projection industry, Digital Cinema Initiatives (DCI) is the dominant 4K standard.
4K has become the common consumer-friendly name for ultra high definition television (UHDTV), although its resolution is only 3840 x 2160 (at a 16:9, or 1.78:1 aspect ratio), which is lower than the 4K industry standard of 4096 x 2160 (at a 19:10 or 1.9:1 aspect ratio).
The use of width to characterize the overall resolution marks a switch from the previous generation, high definition television, which categorized media according to the vertical dimension instead, such as 720p or 1080p. Under the previous convention, a 4K UHDTV would be equivalent to 2160p.
The television industry has adopted UHDTV as its 4K standard. As of 2013, some UHDTV models were available to general consumers for under US$1000. However, due to lack of available content, 4K television has yet to achieve mass market appeal.
The first commercially available 4K camera for cinematographic purposes was the Dalsa Origin, released in 2003. YouTube began supporting 4K for video uploads in 2010. Users could view 4K video by selecting "Original" from the quality settings until December 2013, when the 2160p option appeared in the quality menu. In November 2013, YouTube started to use the VP9 video compression standard, saying that it was more suitable for 4K than High Efficiency Video Coding (HEVC); VP9 is being developed by Google, who owns YouTube.
Sony is one of the leading studios promoting UHDTV content, as of 2013 offering a little over 70 movie and television titles via digital download to a specialized player that stores and decodes the video. The large files (~40GB), distributed through consumer broadband connections, raise concerns about data caps.
In 2014, Netflix began streaming House of Cards, Breaking Bad  and "some nature documentaries" at 4K to compatible televisions with an HEVC decoder. Most 4K televisions sold in 2013 did not natively support HEVC, with most major manufacturers announcing support in 2014. Amazon Studios began shooting their full-length original series and new pilots with 4K resolution in 2014.
|Format||Resolution||Display aspect ratio||Pixels|
|Ultra high definition television||3840 × 2160||1.78:1 (16:9)||8,294,400|
|Ultra wide television||5120 × 2160||2.37:1 (21:9)||11,059,200|
|WHXGA||5120 × 3200||1.60:1 (16:10, 8:5)||16,384,000|
|DCI 4K (native resolution)||4096 × 2160||1.90:1 (19:10)||8,847,360|
|DCI 4K (CinemaScope cropped)||4096 × 1716||2.39:1||7,028,736|
|DCI 4K (flat cropped)||3996 × 2160||1.85:1||8,631,360|
UHD is a resolution of 3840 pixels × 2160 lines (8.3 megapixels, aspect ratio 16:9) and is one of the two resolutions of ultra high definition television targeted towards consumer television, the other being FUHD which is 7680 pixels × 4320 lines (33.2 megapixels). UHD has twice the horizontal and vertical resolution of the 1080p HDTV format, with four times as many pixels overall.
The Digital Cinema Initiatives consortium established a standard resolution of 4096 pixels × 2160 lines (8.8 megapixels, aspect ratio ~17:9) for 4K film projection. This is the native resolution for DCI-compliant 4K digital projectors and monitors; pixels are cropped from the top or sides depending on the aspect ratio of the content being projected. The DCI 4K standard has twice the horizontal and vertical resolution of DCI 2K, with four times as many pixels overall. DCI 4K does not conform to the standard 1080p Full HD aspect ratio (16:9), so it is not a multiple of the 1080p display.
4K digital films may be produced, scanned, or stored in a number of other resolutions depending on what storage aspect ratio is used. In the digital film production chain, a resolution of 4096x3112 is often used for acquiring "open gate" or anamorphic input material, a resolution based on the historical resolution of scanned super 35mm film.
YouTube and Vimeo allow a maximum upload resolution of 4096 × 3072 pixels (12.6 megapixels, aspect ratio 4:3). High Efficiency Video Coding should allow the streaming of content with a 4K resolution with a bandwidth of between 20 to 30 Mbps.
The main advantage of recording video at the 4K standard is that fine detail is resolved well. This contrasts with 2K resolutions in which fine detail in hair is displayed poorly. If the final video quality is reduced to 2K from a 4K recording more detail is apparent than would have been achieved from a 2K recording. Increased fineness and contrast is then possible with output to DVD and Blu-ray. Some cinematographers choose to record at 4K when using the Super 35 film format to offset any resolution loss which may occur during video processing.
List of 4K monitors, TVs and projectors
- 8K resolution
- Digital cinema
- Ultra wide television
- Rec. 2020: ITU definitions for various aspects of UHDTV
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