View source for ProPhoto RGB color space

{{short description|Photographic color space developed by Kodak}}
{{Infobox technology standard
| title             = ProPhoto RGB
| long_name         = Reference Output Medium Metric RGB
| native_name       = {{Plainlist|
* Reference Output Medium Metric RGB
* ISO 22028-2:2013<ref name="standard-iso">{{Cite web|url=https://www.iso.org/standard/56591.html|title=ISO - ISO 22028-2:2013 - Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 2: Reference output medium metric RGB colour image encoding (ROMM RGB)|website=ISO|author=ISO|author-link=International Electrotechnical Commission|version=2013|date=April 2013|access-date=2021-04-19}}</ref>
* ANSI/I3A IT10.7666-2002<ref name="standard-ansi">{{Cite web|url=https://webstore.ansi.org/Standards/I3A/ANSII3AIT1076662002|website=ANSI Webstore|title=ANSI/I3A IT10.7666-2002 - Photography - Electronic Still Picture Imaging - Reference Output Medium Metric RGB Color Encoding (ROMM-RGB)|date=2002|access-date=2021-04-19|author=International Imaging Industry Association|author-link=International Imaging Industry Association}}</ref>
}}
| native_name_lang  = en
| image             = CIExy1931 ProPhoto.svg
| caption           = CIE 1931 xy chromaticity diagram showing the chromaticities enclosed by the ProPhoto RGB color space and location of the primaries. The D50 [[white point]] is shown in the center.  The areas of the triangle that are outside the colored area are [[imaginary colors]].
| status            = Published
| year_started      = <!-- {{Start date|YYYY|MM|DD|df=y}} -->
| first_published   = <!-- {{Start date|YYYY|MM|DD|df=y}} -->
| version           = 2013
| version_date      = {{Start date and age|2013|04}}<ref name="standard-iso" />
| preview           = 
| preview_date      = 
| organization      = {{Plainlist|
* [[Kodak]]
* {{abbr|[[International Electrotechnical Commission|IEC]]|International Electrotechnical Commission}}
* {{abbr|[[American National Standards Institute|ANSI]]|American National Standards Institute}}
}}
| committee         = ISO/TC 42 ({{abbr|TC|Technical Committee}})<ref name="standard-iso" />
| editors           = 
| authors           = [[Kodak]]
| base_standards    = [[RGB]]
| related_standards = 
| abbreviation      = ROMM RGB
| domain            = [[Color space]], [[color model]]
| license           = 
| website           = {{Plainlist|
* '''ISO''': {{URL|https://www.iso.org/standard/56591.html}}
* '''ANSI''': {{URL|https://webstore.ansi.org/Standards/I3A/ANSII3AIT1076662002}}
}}
}}
{{CIE1931xy_gamut_comparison.svg|325px}}

The '''ProPhoto RGB color space''', also known as '''ROMM RGB''' (Reference Output Medium Metric), is an output referred [[RGB color space]] developed by [[Kodak]]. It offers an especially large [[gamut]] designed for use with [[photographic]] output in mind. The ProPhoto RGB color space encompasses over 90% of possible surface colors in the [[International Commission on Illumination|CIE]] [[Lab color space|L*a*b* color space]], and 100% of likely occurring real-world [[Munsell color system|surface colors]] documented by Michael Pointer in 1980,<ref>{{Cite journal|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/col.5080050308|author=Pointer, M. R.|title=The Gamut of Real Surface Colours. Color Res. Appl., 5|journal=Color Research & Application|pages=145–155|doi=10.1002/col.5080050308|date=1980|volume=5|issue=3|publication-date=2007-03-15|access-date=2021-04-19}}</ref><ref>{{Cite web|url=https://www.tftcentral.co.uk/articles/pointers_gamut.htm|title=The Pointer's Gamut - The coverage of real surface colors by RGB color spaces and wide gamut|website=TFT Central|author-first=Kid|author-last=Jansen|date=2014-02-19|access-date=2017-10-29}}</ref> making ProPhoto even larger than the [[Wide-gamut RGB color space]]. The ProPhoto RGB primaries were also chosen in order to minimize hue rotations associated with non-linear tone scale operations. One of the downsides to this color space is that approximately 13% of the representable colors are [[imaginary color]]s that do not exist and are not visible colors.

When working in [[color space]]s with such a large gamut, it is recommended to work in 16-bit color depth to avoid [[posterization]] effects. This will occur more frequently in 8-bit modes as the gradient steps are much larger.

There are two corresponding scene space color encodings known as [[RIMM RGB]] (Reference Input&nbsp;Medium Metric) intended to encode standard dynamic range scene space images, and [[ERIMM RGB]] intended to encode extended dynamic-range scene space images.<ref name="standard-iso-rimm">{{Cite web|url=https://www.iso.org/standard/58005.html|title=ISO - ISO/TS 22028-3:2012 - Photography and graphic technology — Extended colour encodings for digital image storage, manipulation and interchange — Part 3: Reference input medium metric RGB colour image encoding (RIMM RGB)|website=ISO|author=ISO|author-link=International Electrotechnical Commission|version=2012|date=August 2012|access-date=2021-04-19}}</ref><ref name="standard-ansi-rimm">{{Cite web|url=https://webstore.ansi.org/Standards/I3A/ANSII3AIT1074662002|title=ANSI/I3A IT10.7466-2002 - Photography - Electronic still picture imaging - Reference Input Medium Metric RGB Color encoding (RIMM-RGB)|date=2002|access-date=2021-04-19|author=International Imaging Industry Association|author-link=International Imaging Industry Association|website=ANSI Webstore}}</ref>

==Development==

The development of the ProPhoto RGB and other color spaces is documented in an article<ref>{{Cite web|url=http://www.realtimerendering.com/blog/2011-color-and-imaging-conference-part-vi-special-session/|title=Real-Time Rendering · 2011 Color and Imaging Conference, Part VI: Special Session|website=www.realtimerendering.com|language=en-US|date=2011-12-21|access-date=2017-10-29|author=Naty}}</ref> summarizing a presentation by one of its developers [[Geoff Wolfe]] at [[Kodak]], currently senior research manager at Canon Information Systems Research Australia, at the IS&T/SPIE Color Imaging Conference in 2011.

==Encoding primaries==
{| class="wikitable"
! Color
! CIE x
! CIE y
!CIE X
!CIE Y
!CIE Z
|-
| Red
| 0.734699
| 0.265301
|0.79767
|0.28804
|0.00000
|-
| Green
| 0.159597
| 0.840403
|0.13519
|0.71188
|0.00000
|-
| Blue
| 0.036598
| 0.000105
|0.03134
|0.00009
|0.82491
|-
| White
| 0.345704
| 0.358540
|0.96420
|1.00000
|0.82489
|}

==Viewing environment==

* [[Luminance|Luminance level]] is in the range of 160–640&nbsp;cd/m<sup>2</sup>.
* [[Viewing surround]] is average.
* There is 0.5–1.0% [[viewing flare]].
* The adaptive [[white point]] is specified by the [[chromaticity]] values for CIE [[Standard illuminant]] D50 (<math>x = 0.345704</math>, <math>y = 0.358540</math>).
* The image color values are assumed to be encoded using flareless (or flare corrected) colorimetric measurements based on the CIE 1931 [[Standard colorimetric observer|Standard Colorimetric Observer]].

==Encoding function==

:<math>
X'_\mathrm{ROMM} = I_\mathrm{MAX} \cdot \begin{cases} 0; & X_\mathrm{ROMM} < 0.0 \\ 16\cdot X_\mathrm{ROMM}; & 0.0 \le X_\mathrm{ROMM} < E_t \\ X_\mathrm{ROMM}^{1/1.8}; & E_t \le X_\mathrm{ROMM}<1.0 \\ 1; & X_\mathrm{ROMM} \ge 1.0
\end{cases}
</math>

where

:<math>X = R,\, G,\, or\, B</math>

and

:<math>I_\mathrm{MAX}</math> is the maximum integer value used in the encoding function (e.g. 255 for 8-bit configuration)

and

:<math>E_t = 16^{1.8/(1-1.8)} = 2^{-9} = 1/512 = 0.001953125</math>

==References==
{{reflist}}

==External links==
*[https://www.color.org/ROMMRGB.pdf Specification of ROMM RGB]
*[https://www.color.org/chardata/rgb/rommrgb.xalter Information page about ROMM RGB] including a downloadable ICC format profile.
*[https://luminous-landscape.com/understanding-prophoto-rgb/ Understanding ProPhoto RGB]
*[http://www.naturephotographers.net/articles1203/mh1203-1.html Color Spaces: Beyond Adobe RGB]
*[http://www.outbackphoto.com/color_management/cm_06/essay.html Why Use the ProPhoto RGB Color Space?]

{{Color space}}

{{DEFAULTSORT:Prophoto Rgb Color Space}}
[[Category:Color space]]