# Rec. 601

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Standard from the International Telecommunication Union

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Rec. 601 Rec. 601 chromaticity diagram, with 625-line (PAL and SECAM) and 525-line (NTSC SMPTE C primaries) areas shown in black and white Status Approved First published 1982; 44 years ago (1982) Latest version BT.601-7 March 8, 2011; 15 years ago (2011-03-08) Authors ITU-R (CCIR) Base standards Rec.601, BT.601, CCIR 601 Related standards ISO/IEC MPEG, ITU-T H.26x Domain Digital image processing Website www.itu.int/rec/R-REC-BT.601/

**[ITU-R](/source/ITU-R) 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](/source/Comit%C3%A9_consultatif_international_pour_la_radio) (an organization, which has since been renamed as the [International Telecommunication Union – Radiocommunication sector](/source/ITU-R)) for encoding [interlaced](/source/Interlaced_video) [analog video](/source/Analog_video) signals in [digital video](/source/Digital_video) form.[1] It includes methods of encoding 525-line 60 [Hz](/source/Hertz) and 625-line 50 Hz signals, both with an active region covering 720 [luminance](/source/Luma_(video)) samples and 360 [chrominance](/source/Chrominance) samples per line. The [color](/source/Color) encoding system is known as [YCbCr 4:2:2](/source/Chroma_subsampling#4:2:2). The Rec. 601 is also used for [SDTV](/source/SDTV) and [DVD](/source/DVD).[2]

The Rec. 601 video raster format has been re-used in a number of later standards, including the ISO/IEC [MPEG](/source/Moving_Picture_Experts_Group) and ITU-T [H.26x](/source/Video_Coding_Experts_Group) compressed formats, although compressed formats for consumer applications usually use [chroma subsampling](/source/Chroma_subsampling) reduced from the 4:2:2 sampling specified in Rec. 601 to [4:2:0](/source/Chroma_subsampling#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.

## Background and history

In the early 1980s, digital television equipment was beginning to emerge, but each manufacturer was developing their own proprietary digital versions of existing analog standards like [PAL](/source/PAL), [SECAM](/source/SECAM), and [NTSC](/source/NTSC).[3]

At an ITU meeting in 1981, CCIR Study Group 11 approved document 11/1027 describing the parameter values for a unified digital video format. This was adopted as Draft Rec. AA/11 "Encoding Parameters for Digital Television for Studios" by the CCIR Plenary Assembly in February 1982, later becoming ITU-R Rec. 601.[3]

The key feature allowing a globally accepted digital standard were the use of component coding and choosing a luminance sampling frequency that was a common multiple of the line frequencies used in analog standards. This "orthogonal" sampling approach originated from Stanley Baron of NBC.[3]

Preparation preceded the CCIR approval, including laboratory testing around the world to validate the proposed parameter values. International negotiations and efforts to build consensus were led by figures like [Mark Krivosheev](/source/Mark_Krivosheev), [Richard Green](/source/Richard_Green_(telecommunication)), and representatives from Japan and Europe.[3]

## Signal format

The Rec. 601 signal can be regarded as if it is a digitally encoded analog [component video](/source/Component_video) 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](/source/Quantization_(signal_processing)) using 8- or 10-bit [PCM](/source/Pulse-code_modulation) codes in the [YCbCr](/source/YCbCr) 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](/source/Ringing_artifacts). 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](/source/Offset_binary) and use the value 128 to encode the neutral color difference value, as used when encoding a white, grey or black area.

## Primary chromaticities

BT.601 525-line color cube (image encoded with an ICC profile)

BT.601 625-line color cube (image encoded with an ICC profile)

Slightly different primaries are specified for the 625-line ([PAL](/source/PAL) and [SECAM](/source/SECAM)) and 525-line ([NTSC SMPTE C](/source/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.

RGB color space parameters for Rec. 601 Color space White point (D65) Primary color xW yW xR yR xG yG xB yB 625 lines 0.3127 0.3290 0.64 0.33 0.29 0.60 0.15 0.06 525 lines 0.63 0.34 0.31 0.595 0.155 0.07

## Transfer characteristics

Rec. 601 defines a [nonlinear](/source/Nonlinear_system) [transfer function](/source/Transfer_functions_in_imaging) which is [linear](/source/Linear_system) near 0 and then transfers to a [gamma curve](/source/Gamma_correction) for the rest of the [luminance](/source/Luminance) range:

- E = { 4.500 L L < 0.018 , 1.099 L 0.45 − 0.099 L ≥ 0.018. {\displaystyle E={\begin{cases}4.500L&L<0.018,\\1.099L^{0.45}-0.099&L\geq 0.018.\end{cases}}}

## Awards

The CCIR received a 1982–83 [Technology and Engineering Emmy Award](/source/Technology_and_Engineering_Emmy_Award) for its development of the Rec. 601 standard.[4]

## See also

- [Digital component video](/source/Digital_component_video)

- [YCbCr](/source/YCbCr)

- [Rec. 709](/source/Rec._709), the corresponding standard for [high-definition television](/source/High-definition_television) (HDTV)

- [Rec. 2020](/source/Rec._2020), ITU-R Recommendation for [ultra-high-definition television](/source/Ultra-high-definition_television) (UHDTV)

- [ITU-R BT.656](/source/ITU-R_BT.656), ITU-R Recommendation for parallel and serial transmission formats for BT.601 video

- [Pixel aspect ratio](/source/Pixel_aspect_ratio)

## References

1. **[^](#cite_ref-1)** ["BT.601: Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios"](https://www.itu.int/rec/R-REC-BT.601/). ITU. [Archived](https://web.archive.org/web/20260422133452/https://www.itu.int/rec/R-REC-BT.601/) from the original on 2026-04-22.

1. **[^](#cite_ref-2)** ["Create graphics for DVD and Blu-ray menus in Final Cut Pro, Motion, and Compressor"](https://support.apple.com/en-us/101877). *Apple Support*. Retrieved 2026-05-28.

1. ^ [***a***](#cite_ref-wood_3-0) [***b***](#cite_ref-wood_3-1) [***c***](#cite_ref-wood_3-2) [***d***](#cite_ref-wood_3-3) Wood, David. ["Rec. ITU-R BT.601 25th Anniversary and still ´in force´ - the bridge that joined the analogue and digital worlds (1982-2007)"](https://www.itu.int/net/ITU-R/index.asp?category=information&rlink=rec-601&lang=en). *www.itu.int*. Retrieved 10 March 2024.

1. **[^](#cite_ref-4)** [Rec. ITU-R BT.601 25th Anniversary and still "in force" – the bridge that joined the analogue and digital worlds (1982–2007)](https://www.itu.int/ITU-R/index.asp?category=information&rlink=rec-601&lang=en), ITU-R, 2007.

v t e Color space List of color spaces Color models CAM CIECAM02 iCAM CAM16 CIECAM16 CIE XYZ (1931) RGB (1931) YUV (1960) UVW (1964) CIELAB (1976) CIELUV (1976) CIECAM02 CIECAM16 RGB RGB color spaces sRGB rg chromaticity Adobe Wide-gamut ProPhoto scRGB DCI-P3 Rec. 601 SMPTE 240M/"C" Rec. 709 Rec. 2020 Rec. 2100 Y′UV YUV PAL YDbDr SECAM YIQ NTSC YCbCr Rec. 601 Rec. 709 Rec. 2020 Rec. 2100 ICtCp Rec. 2100 YPbPr MAC xvYCC YCoCg Other CcMmYK CMYK ColorADD Coloroid LMS Hexachrome HSL, HSV HCL Imaginary color Oklab OSA-UCS PCCS RG RYB HWB YJK TSL Color systems and standards ACES ANPA Colour Index International CI list of dyes DIC Federal Standard 595 HKS ICC profile ISCC–NBS Munsell NCS Ostwald Pantone RAL list JIS Z8102 [ja] For the vision capacities of organisms or machines, see Color vision.

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Adapted from the Wikipedia article [Rec. 601](https://en.wikipedia.org/wiki/Rec._601) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Rec._601?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.