Editing Adobe RGB color space

{{Short description|Color space developed by Adobe}}
{{Use American English|date=March 2021}}
{{Use dmy dates|date=March 2021}}
{{Infobox technology standard
| title             = Adobe RGB
| long_name         = Adobe RGB (1998) color space
| native_name       = {{Plainlist|
* Adobe RGB (1998) color space
* IEC 61966-2-5:2007
* ISO 12640-4:2011
}}
| native_name_lang  = en
| image             = CIE1931xy AdobeRGB.svg
| caption           = The [[CIE 1931 color space#chromaticity diagram|CIE 1931 ''xy'' chromaticity diagram]] showing the primaries of the Adobe RGB (1998) color space. The [[Illuminant D65]] [[white point]] is shown in the center.
| status            = Published
| year_started      = 1997
| first_published   = 1998
| version           = 2007
| version_date      = {{Start date and age|2007|11|07}}<ref name="iec-standard">{{Cite web|title=IEC 61966-2-5:2007 {{!}} IEC Webstore|url=https://webstore.iec.ch/publication/6175|access-date=2021-02-08|website=webstore.iec.ch}}</ref>
| preview           = 
| preview_date      = 
| organization      = {{Plainlist|
* [[Adobe Systems|Adobe Systems, Inc.]]
* {{abbr|[[International Electrotechnical Commission|IEC]]|International Electrotechnical Commission}}<ref name="iec-standard" />
* {{abbr|[[International Organization for Standardization|ISO]]|International Organization for Standardization}}<ref name="iso-standard">{{Cite web|url=https://www.iso.org/standard/45115.html|title=ISO - ISO 12640-4:2011 - Graphic technology — Prepress digital data exchange — Part 4: Wide gamut display-referred standard colour image data [Adobe RGB (1998)/SCID]|website=ISO|author=ISO|author2=Adobe Systems, Inc.|author-link2=Adobe Systems|date=May 2011|access-date=2021-04-18}}</ref>
}}
| committee         = {{Plainlist|
* '''IEC''': TC 100/TA 2 ('''{{abbr|TC|Technical Committee}}'''/'''{{abbr|SC|Sub-committee}}''')<ref name="iec-standard" />
* '''ISO''': ISO/TC 130<ref name="iso-standard" />
}}
| editors           = 
| authors           = [[Adobe Systems|Adobe Systems, Inc.]]
| base_standards    = [[sRGB]]
| related_standards = 
| abbreviation      = opRGB
| domain            = [[Color space]], [[color model]]
| license           = 
| website           = {{Plainlist|
* {{URL|https://webstore.iec.ch/publication/6175}}
* {{URL|https://www.iso.org/standard/45115.html}}
}}
}}

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 [[color printing|printers]], but by using [[RGB color model|RGB]] [[primary color]]s on a device such as a [[computer display]]. The Adobe RGB (1998) [[color space]] encompasses roughly 30% of the [[visible spectrum|visible colors]] specified by the [[CIELAB color space]] – improving upon the [[gamut]] of the [[sRGB]] color space, primarily in cyan-green [[hue]]s. It was subsequently standardized by the [[International Electrotechnical Commission|IEC]] as IEC 61966-2-5:1999 with a name opRGB (optional RGB color space) and is used in [[HDMI]].<ref name="iec-standard" />

==Historical background==
Beginning in 1997, Adobe Systems was looking into creating [[ICC profile]]s that its consumers could use in conjunction with [[Adobe Photoshop|Photoshop's]] new [[color management]] features. Since not many applications at the time had any ICC color management, most [[operating system]]s 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 the [[Society of Motion Picture and Television Engineers|SMPTE]] 240M standard, the precursor to [[Rec. 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 BT.470 NTSC (System B, G). 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|date=February 2021}} 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 had made an error when copying the red primary chromaticity coordinates, resulting in an even more inaccurate representation of the SMPTE standard.{{Dubious|date=February 2021}} On the other hand red and blue primary are the same as in PAL and green is the same as in [[NTSC#Colorimetry|NTSC 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 the [[Standard illuminant#Illuminant series D|CIE 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 to ''Adobe RGB (1998)'' in order to avoid a trademark search or [[trademark infringement|infringement]].<ref name = HistoryOfAdobeRGB>{{cite web |url = http://www.realtimerendering.com/blog/2011-color-and-imaging-conference-part-vi-special-session/ |title = 2011 Color and Imaging Conference, Part VI: Special Session |date = 21 December 2011 |website = Real-Time Rendering}}</ref>

==Specifications==

===Reference viewing conditions===
{| class="wikitable"
|-
! Parameter
! Value
|-
| White Point Luminance Level
| 160.00&nbsp;cd/m<sup>2</sup>
|-
| Black Point Luminance Level
| 0.5557&nbsp;cd/m<sup>2</sup> (0.34731% of white point luminance)
|-
| Contrast Ratio
| 287.9
|-
| Ambient Illuminance Level
| 32 lx
|-
| Reference Display Surround Level
| 32.00&nbsp;cd/m<sup>2</sup> (20% of white point luminance)
|-
| Viewing Surround
| 2&nbsp;cd/m<sup>2</sup>
|-
|}

In Adobe RGB (1998), colors are specified as [''R'',''G'',''B''] triplets, where each of the ''R'', ''G'', and ''B'' components have values ranging between 0 and 1. When displayed on a monitor, the exact [[chromaticity|chromaticities]] of the reference [[white 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, the [[luminance]] of the monitor must be 160.00 [[candela|cd]]/m<sup>2</sup> at the white point, and 0.5557&nbsp;cd/m<sup>2</sup> at the black point, which implies a [[contrast 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.<ref name = AdobeRGBColorImagingEncoding>{{cite tech report |url = http://www.adobe.com/digitalimag/pdfs/AdobeRGB1998.pdf |title = Adobe RGB (1998) Color Image Encoding |publisher = Adobe Systems Incorporated |date = 13 May 2005}}</ref> The ambient [[illuminance|illumination]] level at the monitor faceplate when the monitor is turned off must be 32 [[lux|lx]].

As with sRGB, the ''RGB'' component values in Adobe RGB (1998) are not proportional to the luminances. Rather, a [[gamma correction|gamma]] 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 the [[CIE 1931 color space]] the Adobe RGB (1998) color space covers 52.1%.<ref name=InformationDisplayDecember2012SuperHi-Vision>{{cite journal |last1 = Yamashita |first1 = Takayuki |last2 = Masuda |first2 = Hiroyasu |last3 = Masaoka |first3 = Kenichiro |last4 = Ohmura |first4 = Kohei |last5 = Emotot |first5 = Masaki |last6 = Nishida |first6 = Yukihiro |last7 = Sugawara |first7 = Masayuki |date = November–December 2012 |title = "Super Hi-Vision" as Next-Generation Television and Its Video Parameters |url = http://informationdisplay.org/Portals/InformationDisplay/IssuePDF/12_2012.pdf |journal = Information Display |publisher = Society for Information Display |volume = 28 |issue = 11 & 12 |pages = 12–17 |doi = 10.1002/j.2637-496X.2012.tb00565.x |s2cid = 86626642 |access-date = 1 December 2013 |archive-url = https://web.archive.org/web/20150420223449/http://informationdisplay.org/Portals/InformationDisplay/IssuePDF/12_2012.pdf |archive-date = 20 April 2015 |url-status = dead }}</ref>

The chromaticities of the primary colors and the white point, both of which correspond to the CIE Standard Illuminant D65, are as follows:<ref name=AdobeRGBColorImagingEncoding />
{| class="wikitable"
|-
!
! ''x''
! ''y''
|-
! Red
| 0.6400
| 0.3300
|-
! Green
| 0.2100
| 0.7100
|-
! Blue
| 0.1500
| 0.0600
|-
! White
| 0.3127
| 0.3290
|}

The corresponding absolute ''XYZ'' [[CIE 1931 color space#Tristimulus values|tristimulus values]] for the reference display white and black points are as follows:<ref name = AdobeRGBColorImagingEncoding/>
{| class="wikitable"
|-
!
! ''X''
! ''Y''
! ''Z''
|-
! White
| 152.07
| 160.00
| 174.25
|-
! Black
| 0.5282
| 0.5557
| 0.6052
|}

Normalized ''XYZ'' tristimulus values can be obtained from absolute luminance ''X<sub>a</sub>Y<sub>a</sub>Z<sub>a</sub>'' tristimulus values as follows:<ref name = AdobeRGBColorImagingEncoding/>
:<math>X=\frac{X_a-X_K}{X_W-X_K} \frac{X_W}{Y_W}</math>
:<math>Y=\frac{Y_a-Y_K}{Y_W-Y_K}</math>
:<math>Z=\frac{Z_a-Z_K}{Z_W-Z_K} \frac{Z_W}{Y_W}</math>
where ''X<sub>K</sub>Y<sub>K</sub>Z<sub>K</sub>'' and ''X<sub>W</sub>Y<sub>W</sub>Z<sub>W</sub>'' 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:<ref name = AdobeRGBColorImagingEncoding/>

:<math>
\begin{bmatrix}R\\G\\B\end{bmatrix}=
\begin{bmatrix}
2.04159&-0.56501&-0.34473\\
-0.96924&1.87597&0.04156\\
0.01344&-0.11836&1.01517
\end{bmatrix}
\begin{bmatrix}X\\Y\\Z\end{bmatrix}
</math>

:<math>
\begin{bmatrix}X\\Y\\Z\end{bmatrix}=
\begin{bmatrix}
0.57667&0.18556&0.18823\\
0.29734&0.62736&0.07529\\
0.02703&0.07069&0.99134
\end{bmatrix}
\begin{bmatrix}R\\G\\B\end{bmatrix}
</math>
As was later defined in the IEC standard opYCC uses [[YCbCr#ITU-R BT.601 conversion|BT.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.

===ICC PCS color image encoding===
An image in the [[International Color Consortium|ICC Profile Connection Space (PCS)]] is encoded in [[Color depth#True color .2824-bit.29|24-bit]] Adobe RGB (1998) [[NTSC#Color encoding|color image encoding]]. Through the application of the 3x3 [[matrix (mathematics)|matrix]] below (derived from the inversion of the color space chromaticity coordinates and a [[chromatic adaptation]] to CIE Standard Illuminant D50 using the Bradford transformation matrix), the input image's normalized ''XYZ'' tristimulus values are transformed into ''RGB'' tristimulus values. The component values would be [[clipping (photography)|clipped]] to the range [0, 1].<ref name = AdobeRGBColorImagingEncoding/>

:<math>
\begin{bmatrix}R\\G\\B\end{bmatrix}=
\begin{bmatrix}
1.96253&-0.61068&-0.34137\\
-0.97876&1.91615&0.03342\\
0.02869&-0.14067&1.34926
\end{bmatrix}
\begin{bmatrix}X\\Y\\Z\end{bmatrix}
</math>

The ''RGB'' tristimulus values are then converted to Adobe RGB ''R'G'B''' component values through the use of the following component transfer functions:

:<math>R'=R^\frac{256}{563},</math> <math>G'=G^\frac{256}{563},</math> <math>B'=B^\frac{256}{563}</math>

The resulting component values would be then represented in [[floating point]] or [[integer]] encodings. If it is necessary to encode values from the PCS back to the [[input device]] space, the following matrix can be implemented:

:<math>
\begin{bmatrix}X\\Y\\Z\end{bmatrix}=
\begin{bmatrix}
0.60974&0.20528&0.14919\\
0.31111&0.62567&0.06322\\
0.01947&0.06087&0.74457
\end{bmatrix}
\begin{bmatrix}R\\G\\B\end{bmatrix}
</math>

==Comparison to sRGB==

===Gamut===

[[File:CIExy1931 AdobeRGB vs sRGB.png|250px|right|thumb|A comparison of the Adobe RGB (1998) color space and sRGB color gamuts space within the CIE 1931 ''xy'' chromaticity diagram. The sRGB gamut is lacking in cyan-green hues.]]

[[sRGB]] is an RGB color space proposed by [[Hewlett-Packard|HP]] and [[Microsoft]] 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 richer [[cyan]]s 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 in [[exposure (photography)#Blacks|shadows]] (~25% luminance) and [[exposure (photography)#Highlights|highlights]] (~75% luminance) as well. In fact, Adobe RGB (1998) expands its advantages to areas of intense orange, yellow, and [[magenta]] regions.<ref name="sRGBVsAdobeRGB">{{cite web|url=https://www.cambridgeincolour.com/tutorials/sRGB-AdobeRGB1998.htm|title=sRGB vs. Adobe RGB 1998|website=Cambridge in Colour}}</ref>

Although there is a significant difference between gamut ranges in the CIE ''xy'' chromaticity diagram, if the coordinates were to be transformed to fit on the [[CIELUV|CIE ''u′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) can ''theoretically'' 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.

===Bit depth distribution===
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's [[color depth|bit depth]]. Color spaces with larger gamuts "stretch" the bits over a broader region of colors, whereas smaller gamuts concentrate these [[bit]]s 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.<ref name = sRGBVsAdobeRGB/> On the contrary, one may have plenty of "spare" bits if using a [[16-bit color|16-bit]] image, thus negating any reduction due to the choice of working space.

==See also==
*[[International Electrotechnical Commission|International Electrotechnical Commission (IEC)]]
*[[Society for Imaging Science and Technology|Society for Imaging Science and Technology (IS&T)]]
*[[Society for Information Display|Society for Information Display (SID)]]

==References==
{{Reflist}}

==External links==
*[https://web.archive.org/web/20050505000309/http://www.adobe.com/products/adobemag/archive/pdfs/98auhtbf.pdf ''Adobe Magazine'' discussion of Photoshop 5.0's new RGB working spaces]
*[https://www.adobe.com/digitalimag/adobergb.html Adobe RGB (1998) Color Image Encoding]
*[https://www.eizoglobal.com/library/management/management/03.html Color Management in Practice – Advantages of the Adobe RGB Color Space]
*[https://www.color.org/chardata/rgb/adobergb.xalter ICC Adobe RGB (1998) Encoding Characteristics]
*IEC 61966-2-5:2007: [https://webstore.iec.ch/publication/6175 optional RGB color space - opRGB]
*Adobe Color - https://color.adobe.com

{{Color space}}
{{Authority control}}

[[Category:Color space]]