4K resolution, also called 4K, refers to 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.
A 4K resolution, as defined by Digital Cinema Initiatives, is 4096 x 2160 pixels (256:135, approximately a 1.9:1 aspect ratio). This standard is widely respected by the film industry along with all other DCI standards.
DCI 4K should not be confused with ultra-high-definition television (UHDTV) AKA "UHD-1", which has a resolution of 3840 x 2160 (16:9, or approximately a 1.78:1 aspect ratio). Many manufacturers may advertise their products as UHD 4K, or simply 4K, when the term 4K is traditionally reserved for the cinematic, DCI resolution. This often causes great confusion among consumers.
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.
YouTube and the television industry have adopted Ultra HD 1 [UHD-1] as its 4K standard and "UHD-2" for NHK/BBC R&D's 7680x4320 pixels UHDTV 2 with their basic parameter set is defined by the ITU BT.2020 standard.  As of 2014[update], 4K content from major television networks remains limited. On April 11, 2013, Bulb TV created by Canadian serial entrepreneur Evan Kosiner became the first broadcaster to provide a 4K linear channel and VOD content to cable and satellite companies in North America. The channel is licensed by the Canadian Radio-Television and Telecommunications Commission to provide educational content. However, 4K content is becoming more widely available online including on YouTube, Netflix and Amazon. As of 2015[update], some UHDTV models were available to general consumers in the range of US$400.
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, which owns YouTube.
In February 2014, HIGH TV (High 4K) launched the first Ultra HD, 24/7 General Entertainment TV Channel available worldwide. The channel was the first of its kind and featured a unique mix of Entertainment, Lifestyle, Extreme Sport, Movies and everything in Ultra HD Quality, with 200 hours of New Content each year. The High 4K Team already distributes the channel to Pay TV Operators, IPTV, Mobile, Web TV, etc, as well as distributing 4K content worldwide.
Sony is one of the leading studios promoting UHDTV content, as of 2013[update] 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||2.33:1 (21:9)||11,059,200|
|WHXGA||5120 × 3200||1.60:1 (16:10)||16,384,000|
|DCI 4K (native resolution)||4096 × 2160||1.90:1 (256:135)||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 256:135) 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 4096 × 3112 is often used for acquiring "open gate" or anamorphic input material, a resolution based on the historical resolution of scanned Super 35mm film.
YouTube, since 2010, and Vimeo allow a maximum upload resolution of 4096 × 3072 pixels (12.6 megapixels, aspect ratio 4:3). Vimeo's 4k content is currently limited to mostly nature documentaries and tech coverage.  Recently YouTube opened 4k to all users. 
This is expected to grow as 4k adoption increases. High Efficiency Video Coding should allow the streaming of content with a 4K resolution with a bandwidth of between 20 to 30 Mbps. VP9 is also being developed for 4k streaming. In 2015 YouTube started to offer 8K resolution Video. The Full Ultra HD (FUHD) or Ultra-high-definition television (also known as Super Hi-Vision, Ultra HD television, UltraHD, UHDTV, or UHD) includes 4K UHD (2160p) and 8K UHD (4320p), which are two digital video formats proposed by NHK Science & Technology Research Laboratories and defined and approved by the International Telecommunication Union (ITU).
The main advantage of recording video at the 4K standard is that fine spatial 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.
- 8K resolution
- Digital cinema
- Ultra-wide television
- Rec. 2020: ITU definitions for various aspects of UHDTV
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