4K resolution

4K resolution refers to a horizontal display resolution of approximately 4,000 pixels. Digital television and digital cinematography commonly use several 4K resolutions. The movie projection industry uses 4096 × 2160 (DCI 4K). In television, 3840 × 2160 (4K UHD) with a 16:9 aspect ratio is the dominant standard. Many 4K Blu-ray releases of ultrawide films use a letterboxed form of this, keeping the horizontal resolution of 3840 pixels while the effective vertical resolution is about 1600–1620 pixels.^{[citation needed]}

The 4K television market share increased as prices fell dramatically throughout 2013 and 2014.

The term "4K" is generic and refers to any resolution with a horizontal pixel count of approximately 4,000. Several different 4K resolutions have been standardized by various organizations.

The terms "4K" and "Ultra HD" are used more widely in marketing than "2160p" (cf. "1080p"). While typically referring to motion pictures, some digital camera vendors have used the term "4K photo" for still photographs, making it appear like an especially high resolution even though 3840×2160 pixels equal approximately 8.3 megapixels, which is not considered to be especially high for still photographs.

In 2005, Digital Cinema Initiatives (DCI), a prominent standards organization in the cinema industry, published the Digital Cinema System Specification. This specification establishes standardized 2K and 4K container formats for digital cinema production, with resolutions of 2048 × 1080 and 4096 × 2160 respectively. The resolution of the video content inside follows the SMPTE 428-1 standard, which establishes the following resolutions for a 4K distribution:

2K distributions can have a frame rate of either 24 or 48 FPS, while 4K distributions must have a frame rate of 24 FPS. Some articles claim that the terms "2K" and "4K" were coined by DCI and refer exclusively to the 2K and 4K formats defined in the DCI standard. However, usage of these terms in the cinema industry predates the publication of the DCI standard, and they are generally understood as casual terms for any resolution approximately 2000 or 4000 pixels in width, rather than names for specific resolutions.

In 2007, the Society of Motion Picture and Television Engineers published SMPTE ST 2036-1, which defines parameters for two UHDTV systems called UHDTV1 and UHDTV2. The standard defines the following characteristics for these systems:

In 2012, the International Telecommunication Union, Radiocommunication Sector published Recommendation ITU-R BT.2020, also known as the Ultra High Definition Television (UHDTV) standard. It adopts the same image parameters defined in SMPTE ST 2036–1.