4K resolution

4K resolution, also called 4K, refers to a horizontal display resolution of approximately 4,000 pixels.[1] There are several different 4K resolutions commonly used in the fields of digital television and digital cinematography. In television and consumer media, 3840 × 2160 (4K UHD) is the dominant 4K standard. In the movie projection industry, 4096 × 2160 (DCI 4K) is the dominant 4K standard.

The 4K television market share increased as prices fell dramatically during 2014[2] and 2015. By 2020, more than half of U.S. households are expected to have 4K-capable TVs,[3] which would be a much faster adoption rate than that of Full HD (1080p).[4]

Comparison of common broadcast resolutions

4K standards and terminology

The term "4K" is generic and refers to any resolution with a horizontal pixel count of approximately 4,000.[5](p2) Several different 4K resolutions have been standardized by various organizations.

DCI Digital Cinema System Specification

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.[6](§4.3.1) The resolution of the video content inside follows the SMPTE 428-1 standard,[6](§3.2.1) which establishes the following resolutions for a 4K distribution:[7](p6)

  • 4096 × 2160 (full frame, 256∶135 or ≈1.90∶1 aspect ratio)
  • 3996 × 2160 (flat crop, 1.85∶1 aspect ratio)
  • 4096 × 1716 (CinemaScope crop, ≈2.39∶1 aspect ratio)

2K distributions can have a frame rate of either 24 or 48 FPS, while 4K distributions must have a frame rate of 24 FPS.[6](§3.1.4.2) 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.[8] However, usage of these terms in the cinema industry predates the publication of the DCI standard,[9][10][11][12] and they are generally understood to be casual terms referring to any resolution approximately 2000 or 4000 pixels in width rather than names for specifically defined resolutions.[5](p2)[13](p109)

SMPTE UHDTV Standard

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.[14][15] The standard defines the following characteristics for these systems:

  • A resolution of 3840 × 2160 (UHDTV1) or 7680 × 4320 (UHDTV2)[15](§5.2)
  • Square (1∶1) pixels, for an overall image aspect ratio of 16∶9[15](§5.1)
  • A framerate of 23.976, 24, 25, 29.97, 30, 50, 59.94, 60, 100, 119.88, or 120 Hz with progressive scan[15](§1.2)
  • RGB, Y′CBCR 4:4:4, 4:2:2, or 4:2:0 pixel encoding[15](§7.7)
  • 10 bpc (30 bit/px) or 12 bpc (36 bit/px) color depth[15](§1.2)
  • Colorimetry characteristics as defined in the standard, including color primaries, quantization parameters, and the electro-optical transfer function. These are the same characteristics later standardized in ITU-R BT.2020. UHDTV1 systems are permitted to use BT.709 color primaries up to 60 Hz.[15](§6.2)

ITU-R UHDTV Standard

In 2012, the International Telecommunication Union, Radiocommunication Sector published Recommendation ITU-R BT.2020, also known as the Ultra High Definition Television (UHDTV) standard.[16] This standard adopts the same image parameters defined in SMPTE ST 2036-1.[17]

Although the UHDTV standard does not define any official names for the formats it defines, ITU typically uses the terms "4K", "4K UHD", or "4K UHDTV" to refer to the 3840 × 2160 system in public announcements and press releases ("8K" for the 7680 × 4320 system).[18] In some of ITU's other standards documents, the terms "UHDTV1" and "UHDTV2" are used as shorthand.[19]

CEA Ultra HD

In October 2012, the Consumer Electronics Association (CEA) announced their definition of the term Ultra High-Definition (or Ultra HD) for use with marketing consumer display devices.[20] CEA defines an Ultra HD product as a TV, monitor, or projector with the following characteristics:[21]

  • A resolution of 3840 × 2160 or larger
  • An aspect ratio of 1.77∶1 (16∶9) or wider
  • Support for color depth of 8 bpc (24 bit/px) or higher
  • At least one HDMI input capable of supporting 3840 × 2160 at 24, 30, and 60 Hz progressive scan (though not necessarily with RGB / Y′CBCR 4:4:4 color), and HDCP 2.2
  • Capable of processing images according to the color space defined in ITU-R BT.709
  • Capable of upscaling HD content (i.e. 720p / 1080p)

The CEA definition does allow other terms, such as "4K", to be marketed alongside the Ultra HD logo.[5](p9)

Since the resolution in CEA's definition is only a minimum requirement, displays with higher resolutions such as 4096 × 2160 or 5120 × 2880 also qualify as "Ultra HD" displays, provided they meet the other requirements as well.

2160p resolution

Some 4K resolutions like 3840 × 2160 are often casually referred to as "2160p".[22][23] This name follows from the previous naming convention used by HDTV and SDTV formats, which refer to a format by the number of pixels/lines along the vertical axis (such as "1080p" for 1920 × 1080 progressive scan, or "480i" for the 480-line interlaced SDTV formats) rather than the horizontal pixel count (≈4000 or "4K" for 3840 × 2160).

The term "2160p" could be applied to any format with a height of 2160 pixels, but it is most commonly used in reference to the 4K UHDTV resolution of 3840 × 2160 due to its association with the well-known 720p and 1080p HDTV formats. Although 3840 × 2160 is both a 4K resolution and a 2160p resolution, these terms cannot always be used interchangeably since not all 4K resolutions are 2160 pixels tall, and not all 2160p resolutions are ≈4000 pixels wide. However, some companies have begun using the term "4K" to describe devices with support for a 2160p resolution, even if it is not close to 4000 pixels wide. For example, many "4K" dash cams only support a resolution of 2880 × 2160 (4∶3);[24][25] although this is a 2160p resolution, it is not a 4K resolution. Samsung also released a 5120 × 2160 (64∶27) TV, but marketed it as a "4K" TV despite its 5K-class resolution.[26][27]

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