The EBU colour bars are a television test card used to check if a video signal has been altered by recording or transmission, and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce chrominance and luminance information correctly. The EBU bars are most commonly shown arranged side-by-side in a vertical manner (as in the images in this article), though some broadcasters – such as TVP [1] in Poland, and Gabon Télévision [2] in Gabon – were known to have aired a horizontal version of the EBU bars.
It is similar to the SMPTE color bars, although that pattern is typically associated with the NTSC analogue colour TV system. Many test cards, such as Philips PM5544 or Telefunken FuBK, feature elements equivalent to the EBU colour bars.
The 75% Colour Bars or EBU/IBA 100/0/75/0 Colour Bars pattern [3] [4] [5] is very similar to the SMPTE colour bars pattern, although it only features seven colour bars, and the white bar is at 100% intensity.
There is a variant where the white bar is also at 75% intensity (EBU 75/0/75/0). This pattern is generated by certain types of test equipment – including the Philips PM5519. [6]
The signal values of these bars for the PAL analogue system are: [7]
Luminance | Chroma amplitude | Chroma Φ | |
---|---|---|---|
White 100/0/75/0 | 1.00 | – | – |
White 75/0/75/0 | 0.75 | – | – |
Yellow | 0.67 | 0.33 | 167º |
Cyan | 0.53 | 0.47 | 283º |
Green | 0.44 | 0.44 | 241º |
Magenta | 0.31 | 0.44 | 61º |
Red | 0.23 | 0.47 | 103º |
Blue | 0.08 | 0.33 | 347º |
Black | 0 | – | – |
Displayed colours are converted from the original PAL BT.601 colour space to sRGB – the colour space used on web pages. They are only approximate, giving a notion of how the bars would look on a calibrated PAL display.
An alternate form of colour bars is the 100% Colour Bars or EBU 100/0/100/0 Colour Bars pattern (specified in ITU-R Rec. BT.1729 [8] ), also known as the RGB pattern or full field bars, which consists of eight vertical bars of 100% intensity, and does not include the castellation or luminance patterns. Like the SMPTE colour bars pattern, the colour order is white, yellow, cyan, green, magenta, red, and blue – but with an additional column of saturated black. This pattern is used to check peak colour levels, and colour saturation, as well as colour alignment. The 100% pattern is not as common as the SMPTE bars, or the above-mentioned EBU 75% pattern, but many pieces of test equipment can be selected to generate either one. Many professional cameras can be set to generate a 100% pattern for calibration of broadcast or recording equipment, especially in a multi-camera installation where all camera signals must match.
EBU colour bar values for standard-definition television systems following BT.601, as specified in ITU-R Rec. BT.1729: [9]
Y | Cb | Cr | |
---|---|---|---|
White | 940 | 512 | 512 |
Yellow | 840 | 64 | 585 |
Cyan | 678 | 663 | 64 |
Green | 578 | 215 | 137 |
Magenta | 426 | 809 | 887 |
Red | 326 | 361 | 960 |
Blue | 164 | 960 | 439 |
Black | 64 | 512 | 512 |
Displayed colours are converted from the original PAL BT.601 colour space to sRGB – the colour space used on web pages. They are only approximate, but represent what is seen on a properly calibrated display using the original colour space.
Calculation of (luminance) and (colour difference) signals from , and components according to BT.601 is as follows: [10]
EBU colour bar values for high definition TV systems following BT.709, as specified in ITU-R Rec. BT.1729: [9]
Y | Cb | Cr | |
---|---|---|---|
White | 940 | 512 | 512 |
Yellow | 877 | 64 | 553 |
Cyan | 754 | 615 | 64 |
Green | 691 | 167 | 105 |
Magenta | 313 | 857 | 919 |
Red | 250 | 409 | 960 |
Blue | 127 | 960 | 471 |
Black | 64 | 512 | 512 |
Calculation of (luminance) and (colour difference) signals from , and components according to BT.709 is as follows: [10]
In 2020 the EBU published a newer colour bar pattern named Colour Bars for Use in the Production of Hybrid Log Gamma (HDR) UHDTV, designed for HDR broadcasts, taking into account the extended colour gamut of these systems. [11] It includes 100% and 75% ITU-R BT.2100 HLG colour bars, and colour bars which can be converted to ITU-R BT.709 75% bars when scene-light and display-light mathematical transforms defined in ITU-R BT.2408 are used. [11]
This pattern allows testing of UHDTV to HDTV conversion, measuring luminance response, saturation and hue shifts, and checking near‑black performance. It can also be used to check for correct hardware settings, transmission chain errors, and proper colour space transforms from ITU‑R BT.2100 HLG to ITU‑R BT.709. [11] Versions of the pattern are freely available as a still image [12] or video file. [13]
The pattern is similar to the ITU-R recommendation BT.2111 that also covers the PQ transfer function. [14] Another similar pattern named Colour Bar Test Pattern for Hybrid Log-Gamma (HLG) High Dynamic Range Television (HDR-TV) System was developed by ARIB in 2018 (ARIB STD-B72), based on the SMPTE color bars commonly used in Japan and United States. [15]
Y′UV, also written YUV, is the color model found in the PAL analogue color TV standard. A color is described as a Y′ component (luma) and two chroma components U and V. The prime symbol (') denotes that the luma is calculated from gamma-corrected RGB input and that it is different from true luminance. Today, the term YUV is commonly used in the computer industry to describe colorspaces that are encoded using YCbCr.
A test card, also known as a test pattern or start-up/closedown test, is a television test signal, typically broadcast at times when the transmitter is active but no program is being broadcast.
ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601, is a standard originally issued in 1982 by the CCIR for encoding interlaced analog video signals in digital video form. It includes methods of encoding 525-line 60 Hz and 625-line 50 Hz signals, both with an active region covering 720 luminance samples and 360 chrominance samples per line. The color encoding system is known as YCbCr 4:2:2.
SMPTE color bars are a television test pattern used where the NTSC video standard is utilized, including countries in North America. The Society of Motion Picture and Television Engineers (SMPTE) refers to the pattern as Engineering Guideline (EG) 1-1990. Its components are a known standard, and created by test pattern generators. Comparing it as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. It is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly.
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 component and CB and CR are the blue-difference and red-difference chroma components. Y′ is distinguished from Y, which is luminance, meaning that light intensity is nonlinearly encoded based on gamma corrected RGB primaries.
The Adobe RGB (1998) color space or opRGB is a color space developed by Adobe Inc. in 1998. It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary colors on a device such as a computer display. The Adobe RGB (1998) color space encompasses roughly 30% of the visible colors specified by the CIELAB color space – improving upon the gamut of the sRGB color space, primarily in cyan-green hues. It was subsequently standardized by the IEC as IEC 61966-2-5:1999 with a name opRGB and is used in HDMI.
Multiplexed Analogue Components (MAC) was an analog television standard where luminance and chrominance components were transmitted separately. This was an evolution from older color TV systems where there was interference between chrominance and luminance.
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Rec. 709, also known as Rec.709, BT.709, and ITU 709, is a standard developed by ITU-R for image encoding and signal characteristics of high-definition television.
4K resolution refers to a horizontal display resolution of approximately 4,000 pixels. Digital television and digital cinematography commonly use several different 4K resolutions. In television and consumer media, 3840 × 2160 with a 16:9 aspect ratio is the dominant 4K standard, whereas the movie projection industry uses 4096 × 2160.
ITU-R Recommendation BT.2020, more commonly known by the abbreviations Rec. 2020 or BT.2020, defines various aspects of ultra-high-definition television (UHDTV) with standard dynamic range (SDR) and wide color gamut (WCG), including picture resolutions, frame rates with progressive scan, bit depths, color primaries, RGB and luma-chroma color representations, chroma subsamplings, and an opto-electronic transfer function. The first version of Rec. 2020 was posted on the International Telecommunication Union (ITU) website on August 23, 2012, and two further editions have been published since then.
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ICTCP, ICtCp, or ITP is a color representation format specified in the Rec. ITU-R BT.2100 standard that is used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide color gamut (WCG) imagery. It was developed by Dolby Laboratories from the IPT color space by Ebner and Fairchild. The format is derived from an associated RGB color space by a coordinate transformation that includes two matrix transformations and an intermediate nonlinear transfer function that is informally known as gamma pre-correction. The transformation produces three signals called I, CT, and CP. The ICTCP transformation can be used with RGB signals derived from either the perceptual quantizer (PQ) or hybrid log–gamma (HLG) nonlinearity functions, but is most commonly associated with the PQ function.
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Images and videos use specific transfer functions to describe the relationship between electrical signal, scene light and displayed light.