Rendition of SD ECR-1-1978 color barsColors are only approximate due to different transfers and color spaces used on web pages (sRGB) and video (BT.601 or BT.709)
SMPTE color bars are a televisiontest 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.[1] Its components are a known standard, and created by test pattern generators.[2][3][4] 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.
A precursor to the SMPTE test pattern was conceived by Norbert D. Larky (1927–2018)[5][6] and David D. Holmes (1926–2006)[7][8] of RCA Laboratories and first published in RCA Licensee Bulletin LB-819 on February 7, 1951. U.S. patent 2,742,525 Color Test Pattern Generator (now expired) was awarded on April 17, 1956, to Larky and Holmes.[9] Later, the EIA published a standard, RS-189A, which in 1976 became EIA-189A, which described a Standard Color Bar Signal, intended for use as a test signal for adjustment of color monitors, adjustment of encoders, and rapid checks of color television transmission systems.[10] In 1977, A. A. Goldberg, of the CBS Technology Center, described an improved color bar test signal developed at the center by Hank Mahler (1936–2021)[11][12] that was then submitted to the SMPTE TV Video Technology Committee for consideration as a SMPTE recommended practice.[13] This improved test signal was published as the standard SMPTE ECR 1-1978. Its development by CBS was awarded a Technology & Engineering Emmy Award in 2002.[14] CBS did not file a patent application on the test signal, thereby putting it into the public domain for general use by the industry.
Early concept of color bar test patternRecreation of EIA-189A color bars without castellations
An extended version of the SMPTE color bars, SMPTE RP 219:2002[15] was introduced to test HDTV signals (see subsection).[16]
Although color bars were originally designed to calibrate analog NTSC equipment, they remain widely used in transmission and within modern digital television facilities. In the current context color bars are used to maintain accurate chroma and luminance levels in CRT, LCD, LED, plasma, and other video displays, as well as duplication, satellite, fiber-optic and microwave transmission, and television and webcast equipment.
In a survey of the top standards of the organizations' first 100 years, SMPTE EG-1 was voted as the 5th-most important SMPTE standard.[17]
SMPTE ECR 1-1978 (SDTV)
NTSC vectorscope display, showing 75% color bar targets and a properly adjusted signalRendition of ECR-1-1978 color bars with 1kHz sine wave tone
In a SMPTE color bar image, the top two-thirds of the television picture contain seven vertical bars of 75% intensity. In order from left to right, the colors are white or gray, yellow, cyan, green, magenta, red, and blue.[18] The choice of white or gray depends on whether that bar's luminance is 100% or not. This sequence runs through all seven possible combinations that use at least one of the three basic color components of green, red, and blue, with blue cycling on and off between every bar, red cycling on and off every two bars, and green on for the leftmost four bars and off for the rightmost three. Because green contributes the largest share of luminance, followed by red, then blue, this sequence of bars thus appears on a waveform monitor in luminance mode as a downward staircase from left to right. The graticule of a vectorscope is etched with boxes showing the permissible regions where the traces from these seven bars are supposed to fall if the signal is properly adjusted.
Below the main set of seven bars is a strip of blue, magenta, cyan, and white or gray castellations. When a television receiver is set to filter out all colors except for blue, these castellations, combined with the main set of color bars, are used to adjust the color controls; they appear as four solid blue bars, with no visible distinction between the bars and the castellations if the color controls are properly adjusted.
The bottom section contains a square of 100% intensity white and a rectangle of 7.5% intensity black, for use in setting the luminance range. More modern versions of the pattern feature a PLUGE pulse. The white square lines up so that it is below the yellow and cyan bars, and on a waveform monitor this will show up with the white bar overlapping the peak of the yellow and cyan chroma at 100 IRE units. The pluge (short for picture line-up generation equipment) pulse is positioned within the black rectangle, below the red bar (it is present in the illustration but may be hard to see). It comprises three small vertical bars, a rightmost one with intensity 4% above black level (11.5 IRE), a middle one with intensity exactly equal to black (7.5 IRE), and a leftmost one with intensity 4% below black (super-black or blacker than black, 3.5 IRE). The pluge pulse aids in adjusting the bottom of the luminance range to avoid either washing out the black tones into grays or collapsing picture information into the signal clipping that occurs a small distance below the black level (known as crushing the blacks). When a monitor is properly adjusted, the rightmost pluge bar should be just barely visible, while the left two should appear indistinguishable from each other and completely black. Also in the bottom section are two sections that contain -In-phase and +Quadrature signals (see YIQ), centered on black level and having the same gain as the color burst signal; these show up on the pattern as a square of very dark blue, and a square of very dark purple. On a vectorscope, they appear as two short lines ninety degrees apart. These are used to ensure that the television receiver is properly demodulating the 3.58 MHzcolor subcarrier portion of the signal. The vectors for the -I and +Q blocks should fall exactly on the I and Q axes on the vectorscope if the chrominance signal is demodulated properly.
These bars give rise to the former portion of the casual term bars and tone. Typically, a television network, TV station, or other originator of video programming transmits SMPTE color bars together with a continuous 1,000 Hzsine wave before sending program material, in order to assert ownership of the transmission line or medium, and so that receiving stations and intermediary telecommunications providers may adjust their equipment. Likewise, producers of television programs typically record bars and tone at the beginning of a videotape or other recording medium so that the playback equipment can be calibrated. Often, the name or callsign of the TV station, other information such as a real-time clock, or another signal source is graphically superimposed over the bars.
Analog NTSC
Values of 75% (75/7.5/75/7.5) SMPTE ECR 1-1978 color bars as analog NTSC signals:[19][20][21][22]
Note:IRE units apply to both NTSC composite video and broadcast signals while mV values only apply to NTSC composite video. Values sourced from the Tektronix TSG95 test pattern generator manual[22]
Digital video
For digital video sources, the 10-bit YCbCr values for SD color bars[23] are based on the SMPTE formula for Y from the NTSC system (Y = 0.299R + 0.587G + 0.114B).[24] The following table show the expected digital values, for example when measured using a signal analyzer.[25]
10-bit YCbCr values for SD 75% color bars
Color
Y
Cb
Cr
White
940
512
512
Yellow
646
176
567
Cyan
525
625
176
Green
450
289
231
Magenta
335
735
793
Red
260
399
848
Blue
139
848
457
Black
64
512
512
Note: Values sourced from "Leader Teleproduction Test Volume 3 Number 4 - Digital Video Levels"[24]
The colors below are presented using sRGB transfer of CSS. Since sRGB is the standard colorspace for webpages and computer screens, this gives only an idea of the intended colors. They are not completely representative of how they look on TV displays, since these follow the ITU-R BT.1886 standard, specifying a different gamma correction value, and thus colors below will look darker on such a display, and those darker colors will be the reference ones. The off-by-one errors (for example 254 instead of 255 and 1 instead of 0) happen because the 8 bit Y'PbPr values were used when decoding to R'G'B', if you use 10-bit Y'PbPr that does not happen.
The source data for 10-bit and 12-bit Y'PbPr is 8-bit Studio R'G'B', so 10-bit data is not just a bitshift operation (that means multiply by 4) from 8-bit Y'PbPr, as usually the case. For example, for 75% Blue 28-212-120 would be just 112-848-480, but it is actually 111-848-481.[27]
Per ITU-R BT.2111-2 TABLE 2
SMPTE RP 219:2002 (HDTV version)
Rendition of HD SMPTE RP 219:2002 color barsColors are only approximate due to different transfer used on web pages (sRGB) and video (BT.709 is using BT.1886)
An extended version of SMPTE Color Bars signal, developed by the Japanese Association of Radio Industries and Businesses as ARIB STD-B28 and standardized as SMPTE RP 219:2002[15] (High-Definition, Standard-Definition Compatible Color Bar Signal) was introduced to test HDTV signal with an aspect ratio of 16:9 that can be down converted to a SDTV color bar signal with an aspect ratio of either 4:3 or 16:9. The Color Bar signal is generated with unconventionally slow rise and fall time value to facilitate video level control and monitor color adjustments of HDTV and SDTV equipment.
Digital test images generated following the RP 219:2002 specifications and adapted to perfectly fit 114 standard and non-standard resolutions for both 16bpp and 8bpp, are freely available in the COLOR dataset of the TESTIMAGES archive.[16]
Later RP 219:2002 became RP 219-1:2014, with RP 219-2:2016[28] and ARIB STD-B66[29] adding details for UHD. ITU-R Rec. BT.2111[30] and ARIB STD-B72[31] further added PQ and HLGHDR transfer functions.
Values
The values of 100% (100/0/100/0) SMPTE RP 219:2002 color bars (1.00 * 219 + 16 = 235) using BT.709 matrix coefficients (only white and black are the same using BT.601 matrix), taken from the standard:
NTSC is the first American standard for analog television, published in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
Gamma correction or gamma is a nonlinear operation used to encode and decode luminance or tristimulus values in video or still image systems. Gamma correction is, in the simplest cases, defined by the following power-law expression:
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.
Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.
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.
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.
YPbPr or Y'PbPr, also written as YPBPR, is a color space used in video electronics, in particular in reference to component video cables. Like YCbCr, it is based on gamma corrected RGB primaries; the two are numerically equivalent but YPBPR is designed for use in analog systems while YCBCR is intended for digital video. The EOTF may be different from common sRGB EOTF and BT.1886 EOTF. Sync is carried on the Y channel and is a bi-level sync signal, but in HD formats a tri-level sync is used and is typically carried on all channels.
For televisions the picture line-up generation equipment is a greyscale test pattern used in order to adjust the black level and contrast of the picture monitor. Various PLUGE patterns can be generated, the most common consisting of three vertical bars of super-black, normal black, and near-black and two rectangles of mid-gray and white. These three PLUGE pulses are included in the SMPTE color bars used for NTSC, PAL, and SÉCAM.
A video signal generator is a type of signal generator which outputs predetermined video and/or television oscillation waveforms, and other signals used in the synchronization of television devices and to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses or sync words. Generators of composite video signals will also include a colorburst signal as part of the output.
In video, luma represents the brightness in an image. Luma is typically paired with chrominance. Luma represents the achromatic image, while the chroma components represent the color information. Converting R′G′B′ sources into luma and chroma allows for chroma subsampling: because human vision has finer spatial sensitivity to luminance differences than chromatic differences, video systems can store and transmit chromatic information at lower resolution, optimizing perceived detail at a particular bandwidth.
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.
Blue Only mode is a special display mode on display units such as projectors and television sets whereby only the blue pixels or the blue cathode ray tube is used to generate the image.
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.
ITU-R Recommendation BT.2100, more commonly known by the abbreviations Rec. 2100 or BT.2100, introduced high-dynamic-range television (HDR-TV) by recommending the use of the perceptual quantizer or hybrid log–gamma (HLG) transfer functions instead of the traditional "gamma" previously used for SDR-TV.
High-dynamic-range television (HDR-TV) is a technology that uses high dynamic range (HDR) to improve the quality of display signals. It is contrasted with the retroactively-named standard dynamic range (SDR). HDR changes the way the luminance and colors of videos and images are represented in the signal, and allows brighter and more detailed highlight representation, darker and more detailed shadows, and more intense colors.
Images and videos use specific transfer functions to describe the relationship between electrical signal, scene light and displayed light.
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, though some broadcasters – such as TVP in Poland, and Gabon Télévision in Gabon – were known to have aired a horizontal version of the EBU bars.
Clear-Vision is a Japanese EDTV television system introduced in the 1990s, that improves audio and video quality while remaining compatible with the existing broadcast standard. Developed to improve analog NTSC, it adds features like progressive scan, ghost cancellation and widescreen image format. A similar system named PALPlus was develop in Europe with the goal of improving analog PAL broadcasts.
Snell & Wilcox SW2 and SW4 "Zone Plate" Test Chart were TV test cards introduced in the 1990s and used with NTSC, PAL and SDTV systems.
↑ USpatent 2742525,Norbert D. Larky, Somerville&David I. Holmes, New Brunswick, N.J.,"Color Test Pattern Generator",issued April 27, 1956, assigned to Radio Corporation of America
↑ Goldberg, A. A. (June 30, 1977). "A Monitor Alignment Color Bar Test Signal"(PDF). Proceedings, 31st Annual Broadcast Engineering Conference, National Association of Broadcasters. 31: 84–85.
↑ Jack, Keith (2005). "Chapter 8: NTSC, PAL, and SECAM Overview". Video Demystified: A Handbook for the Digital Engineer (4thed.). Amsterdam: Elsevier. pp.321–331. ISBN0-7506-7822-4.
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