CCIR 601
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ITU-R The ITU Radiocommunication Sector (ITU-R) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU) and is responsible for radio communications. Its role is to manage the international radio-frequency sp ...
Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 (or its former name CCIR 601) is a standard originally issued in 1982 by the CCIR (an organization, which has since been renamed as the International Telecommunication Union Radiocommunication sector) for encoding interlaced
analog video Video is an electronic medium for the recording, copying Copying is the duplication of information Information is an Abstraction, abstract concept that refers to that which has the power to Communication, inform. At the most fundam ...
signals in
digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises ...
form. It includes methods of encoding 525-line 60  Hz and 625-line 50 Hz signals, both with an active region covering 720
luminance Luminance is a Photometry (optics), photometric measure of the luminous intensity per units of measurement, unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflecte ...
samples and 360
chrominance Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying Luma (video), luma signal (or Y' for short). Chrominance is usua ...
samples per line. The
color Color (American English) or colour (British English) is the visual perception, visual perceptual Physical property, property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physica ...
encoding system is known as YCbCr 4:2:2. The Rec. 601 video raster format has been re-used in a number of later standards, including the ISO/IEC
MPEG The Moving Picture Experts Group (MPEG) is an alliance of working groups established jointly by International Organization for Standardization, ISO and International Electrotechnical Commission, IEC that sets standards for media coding, includ ...
and ITU-T
H.26x The Video Coding Experts Group or Visual Coding Experts Group (VCEG, also known as Question 6) is a working group of the ITU Telecommunication Standardization Sector The ITU Telecommunication Standardization Sector (ITU-T) is one of the three s ...
compressed formats, although compressed formats for consumer applications usually use
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for Chrominance, chroma information than for luma (video), luma information, taking advantage of the human visual system's lower acuity for color differences tha ...
reduced from the 4:2:2 sampling specified in Rec. 601 to 4:2:0. The standard has been revised several times in its history. Its seventh edition, referred to as BT.601-7, was approved in March 2011 and was formally published in October 2011.


Signal format

The Rec. 601 signal can be regarded as if it is a digitally encoded analog
component video Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is Transmission (telecommunications), transmitted or stored ...
signal, and thus the sampling includes data for the horizontal and vertical sync and blanking intervals. Regardless of the frame rate, the luminance sampling frequency is 13.5 MHz. The samples are uniformly quantized using 8- or 10-bit PCM codes in the
YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the Luma (video), luma component and CB and CR are t ...
domain. For each 8-bit luminance sample, the nominal value to represent black is 16, and the value for white is 235. Eight-bit code values from 1 through 15 provide footroom and can be used to accommodate transient signal content such as filter undershoots. Similarly, code values 236 through 254 provide headroom and can be used to accommodate transient signal content such as filter overshoots. The values 0 and 255 are used to encode the sync pulses and are forbidden within the visible picture area. The Cb and Cr samples are
unsigned Unsigned can refer to: * An unsigned artist is a musical artist or group not attached or signed to a record label ** Unsigned Music Awards, ceremony noting achievements of unsigned artists ** Unsigned band web, online community * Similarly, the ...
and use the value 128 to encode the neutral color difference value, as used when encoding a white, grey or black area.


Primary chromaticities

Slightly different primaries are specified for the 625-line (
PAL Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...
and
SECAM SECAM, also written SÉCAM (, ''Séquentiel de couleur à mémoire'', French for ''color sequential with memory''), is an analog television, analog color television system that was used in France, some parts of Europe and Africa, and Russia ...
) and 525-line ( NTSC SMPTE C primaries) systems. Earlier versions of the standard (prior to BT.601-6, approved in January 2007) did not contain an explicit definition of the color primaries.


Transfer characteristics

Rec. 601 defines a
nonlinear In mathematics and science, a nonlinear system is a system in which the change of the output is not proportionality (mathematics), proportional to the change of the input. Nonlinear problems are of interest to engineers, biologists, physicists, m ...
transfer function In engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range ...
which is
linear Linearity is the property of a mathematical relationship ('' function'') that can be graphically represented as a straight line Line most often refers to: * Line (geometry) In geometry, a line is an infinitely long object with no width, ...
near 0 and then transfers to a gamma curve for the rest of the
luminance Luminance is a Photometry (optics), photometric measure of the luminous intensity per units of measurement, unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflecte ...
range: : E = \begin 4.500 L & L < 0.018,\\ 1.099 L^ - 0.099 & L \ge 0.018. \end


Awards

The CCIR received a 1982–83
Technology and Engineering Emmy Award The Technology and Engineering Emmy Awards, or Technology and Engineering Emmys, are one of two sets of Emmy Awards The Emmy Awards, or Emmys, are an extensive range of awards for artistic and technical merit for the American and internat ...
for its development of the Rec. 601 standard.Rec. ITU-R BT.601 25th Anniversary and still "in force" the bridge that joined the analogue and digital worlds (1982–2007)
ITU-R, 2007.


See also

*
YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the Luma (video), luma component and CB and CR are t ...
* Rec. 709, the corresponding standard for
high-definition television High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the ...
(HDTV) * Rec. 2020, ITU-R Recommendation for
ultra-high-definition television Ultra-high-definition television (also known as Ultra HD television, Ultra HD, UHDTV, UHD and Super Hi-Vision) today includes 4K resolution#Resolutions, 4K UHD and 8K resolution#Resolutions, 8K UHD, which are two digital video formats with an ...
(UHDTV) * ITU-R BT.656, ITU-R Recommendation for parallel and serial transmission formats for BT.601 video *
Pixel aspect ratio Pixel aspect ratio (often abbreviated PAR) is a mathematical ratio that describes how the width of a pixel in a digital image compares to the height of that pixel. Most digital imaging systems display an image as a grid of tiny, square pixel ...


References

{{color space Digital television Film and video technology ITU-R recommendations Color space