Adobe RGB
Adobe RGB (1998) color space
TheCIE 1931xy chromaticity diagram showing the primaries of the Adobe RGB (1998) color space. TheIlluminant D65white point is shown in the center.
Abbreviation	opRGB
Native name	Adobe RGB (1998) color space IEC 61966-2-5:2007 ISO 12640-4:2011
Status	Published
Year started	1997
First published	1998
Latest version	2007 November 7, 2007; 17 years ago (2007-11-07)[1]
Organization	Adobe Systems, Inc. IEC[1] ISO[2]
Committee	IEC: TC 100/TA 2 (TC/SC)[1] ISO: ISO/TC 130[2]
Authors	Adobe Systems, Inc.
Base standards	sRGB
Domain	Color space,color model
Website	webstore.iec.ch/publication/6175 www.iso.org/standard/45115.html

TheAdobe RGB (1998) color space oropRGB is acolor space developed byAdobe Inc. in 1998. It was designed to encompass most of the colors achievable onCMYK colorprinters, but by usingRGBprimary colors on a device such as acomputer display. The Adobe RGB (1998)color space encompasses roughly 30% of thevisible colors specified by theCIELAB color space – improving upon thegamut of thesRGB color space, primarily in cyan-greenhues. It was subsequently standardized by theIEC as IEC 61966-2-5:1999 with a name opRGB (optional RGB color space) and is used inHDMI.^[1]

Beginning in 1997, Adobe Systems was looking into creatingICC profiles that its consumers could use in conjunction withPhotoshop's newcolor management features. Since not many applications at the time had any ICC color management, mostoperating systems did not ship with useful profiles.

Lead developer of Photoshop,Thomas Knoll decided to build an ICC profile around specifications he found in the documentation for theSMPTE 240M standard, the precursor toRec. 709 (but not in primaries: 240M also defined EOTF and thus was display referred, sRGB was created by connecting BT.470 PAL and SMPTE C). SMPTE 240M's gamut is wider than that of the BT.709 gamut and the same as SMPTE ST 170 also known as SMPTE C. However, with the release of Photoshop 5.0 nearing, Adobe made the decision to include the profile within the software.

Although users loved the wider range of reproducible colors, those familiar with the SMPTE 240M specifications contacted Adobe, informing the company that it had copied the values that described idealized primaries, not actual standard ones (in a special annex to the standard).^{[failed verification]} The real values were much closer to sRGB's, which avid Photoshop consumers did not enjoy as a working environment. To make matters worse, an engineer (Thomas Knoll) had made an error when copying the red primary chromaticity coordinates, resulting in an even more inaccurate representation of the SMPTE standard.^[3] On the other hand red and blue primaries are the same as in PAL and green is the same as inNTSC 1953 (blue is the same as in BT.709 and sRGB).

Adobe tried numerous tactics to correct the profile, such as correcting the red primary and changing the white point to match that of theCIE Standard Illuminant D50 (though that will also change the primaries and is thus pointless), yet all of the adjustments made CMYK conversion worse than before. In the end, Adobe decided to keep the "incorrect" profile, but changed the name toAdobe RGB (1998) in order to avoid a trademark search orinfringement.^[4]

In Adobe RGB (1998), colors are specified as [R,G,B] triplets, where each of theR,G, andB components have values ranging between 0 and 1. When displayed on a monitor, the exactchromaticities of the referencewhite point [1,1,1], the reference black point [0,0,0], and the primaries ([1,0,0], [0,1,0], and [0,0,1]) are specified. To meet the color appearance requirements of the color space, theluminance of the monitor must be 160.00cd/m² at the white point, and 0.5557 cd/m² at the black point, which implies acontrast ratio of 287.9. Moreover, the black point shall have the same chromaticity as the white point, yet with a luminance equal to 0.34731% of the white point luminance.^[5] The ambientillumination level at the monitor faceplate when the monitor is turned off must be 32lx.

As with sRGB, theRGB component values in Adobe RGB (1998) are not proportional to the luminances. Rather, agamma of approximately 2.2 is assumed, without the linear segment near zero that is present in sRGB. The precise gamma value is 563/256, or 2.19921875. In coverage of theCIE 1931 color space the Adobe RGB (1998) color space covers 52.1%.^[6]

The chromaticities of the primary colors and the white point, both of which correspond to the CIE Standard Illuminant D65, are as follows:^[5]

The corresponding absoluteXYZtristimulus values for the reference display white and black points are as follows:^[5]

NormalizedXYZ tristimulus values can be obtained from absolute luminanceX_aY_aZ_a tristimulus values as follows:^[5]

${\displaystyle X=\frac{X_a-X_K}{X_W-X_K}\frac{X_W}{Y_W}}$

${\displaystyle Y=\frac{Y_a-Y_K}{Y_W-Y_K}}$

${\displaystyle Z=\frac{Z_a-Z_K}{Z_W-Z_K}\frac{Z_W}{Y_W}}$

whereX_KY_KZ_K andX_WY_WZ_W are reference display black and white points in the table above.

The conversion between normalized XYZ to and from Adobe RGB tristimulus values can be done as follows:^[5]

As was later defined in the IEC standard opYCC usesBT.601 matrix for conversion to YCbCr, that can be full range matrix and limited range matrix. Display can signal YCC quantization range support and sink can send either one.

An image in theICC Profile Connection Space (PCS) is encoded in24-bit Adobe RGB (1998)color image encoding. Through the application of the 3x3matrix below (derived from the inversion of the color space chromaticity coordinates and achromatic adaptation to CIE Standard Illuminant D50 using the Bradford transformation matrix), the input image's normalizedXYZ tristimulus values are transformed intoRGB tristimulus values. The component values would beclipped to the range [0, 1].^[5]

TheRGB tristimulus values are then converted to Adobe RGBR'G'B' component values through the use of the following component transfer functions:

${\displaystyle R^{\prime }=R^{\frac{256}{563}},}$${\displaystyle G^{\prime }=G^{\frac{256}{563}},}$${\displaystyle B^{\prime }=B^{\frac{256}{563}}}$

The resulting component values would be then represented infloating point orinteger encodings. If it is necessary to encode values from the PCS back to theinput device space, the following matrix can be implemented:

sRGB is an RGB color space proposed byHP andMicrosoft in 1996 to approximate the color gamut of the (then) most common computer display devices (CRTs). Since sRGB serves as a "best guess" metric for how another person's monitor produces color, it has become the standard color space for displaying images on the Internet. sRGB's color gamut encompasses just 35% of the visible colors specified by CIE, whereas Adobe RGB (1998) encompasses slightly more than 50% of all visible colors. Adobe RGB (1998) extends into richercyans and greens than does sRGB – for all levels of luminance. The two gamuts are often compared in mid-tone values (~50% luminance), but clear differences are evident inshadows (~25% luminance) andhighlights (~75% luminance) as well. In fact, Adobe RGB (1998) expands its advantages to areas of intense orange, yellow, andmagenta regions.^[7]

Although there is a significant difference between gamut ranges in the CIExy chromaticity diagram, if the coordinates were to be transformed to fit on theCIEu′v′ chromaticity diagram, which illustrates the eye's perceived variance in hue more closely, the difference in the green region is far less exaggerated. Also, although Adobe RGB (1998) cantheoretically represent a wider gamut of colors, the color space requires special software and a complex workflow in order to utilize its full range. Otherwise, the produced colors would be squeezed into a smaller range (making them appear duller) in order to match sRGB's more widely used gamut.

Although the Adobe RGB (1998) working space clearly provides more colors to utilize, another factor to consider when choosing between color spaces is how each space influences the distribution of the image'sbit depth. Color spaces with larger gamuts "stretch" the bits over a broader region of colors, whereas smaller gamuts concentrate thesebits within a narrow region.

A similar, yet not as dramatic concentration of bit depth occurs with Adobe RGB (1998) versus sRGB, except in three dimensions rather than one. The Adobe RGB (1998) color space occupies roughly 40% more volume than the sRGB color space, which concludes that one would only be exploiting 70% of the available bit depth if the colors in Adobe RGB (1998) are unnecessary.^[7] On the contrary, one may have plenty of "spare" bits if using a16-bit image, thus negating any reduction due to the choice of working space.

• International Electrotechnical Commission (IEC)
• Society for Imaging Science and Technology (IS&T)
• Society for Information Display (SID)

• Adobe Magazine discussion of Photoshop 5.0's new RGB working spaces
• Adobe RGB (1998) Color Image Encoding
• Color Management in Practice – Advantages of the Adobe RGB Color Space
• ICC Adobe RGB (1998) Encoding Characteristics
• IEC 61966-2-5:2007:optional RGB color space - opRGB
• Adobe Color -https://color.adobe.com

• Color space

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