View source for Engineering:Color depth

{{short description|Number of bits used to represent a color}}
'''Color depth''' or '''colour depth''' (see [[Social:American and British English spelling differences#-our, -or|spelling differences]]), also known as '''bit depth''', is either the number of [[Bit|bit]]s used to [[User interface|indicate]] the color of a single [[Pixel|pixel]], or the number of bits used for each color component of a single pixel. When referring to a pixel, the concept can be defined as '''bits per pixel''' (bpp). When referring to a color component, the concept can be defined as '''bits per component''', '''bits per channel''', '''bits per color''' (all three abbreviated bpc), and also '''bits per pixel component''', '''bits per color channel''' or '''bits per sample''' (bps).<ref name=OverviewHEVCIEEE2012/><ref name=CodingEfficiencyHEVCIEEE2012/><ref name=AdobeEffectsColorBasic>{{cite news |title=After Effects / Color basics |publisher=[[Software:Adobe Systems|Adobe Systems]] |url=http://help.adobe.com/en_US/aftereffects/cs/using/WSB48B246A-E34D-4d3f-A0A4-B932FD3F12E6a.html |access-date=2013-07-14}}</ref> Modern standards tend to use bits per component,<ref name="OverviewHEVCIEEE2012">{{cite news|author=G.J. Sullivan|author2=J.-R. Ohm|author3=W.-J. Han|author4=T. Wiegand|author4-link=Thomas Wiegand|date=2012-05-25|title=Overview of the High Efficiency Video Coding (HEVC) Standard|publisher=IEEE Transactions on Circuits and Systems for Video Technology|url=http://iphome.hhi.de/wiegand/assets/pdfs/2012_12_IEEE-HEVC-Overview.pdf|access-date=2013-05-18}}</ref><ref name="CodingEfficiencyHEVCIEEE2012">{{cite news|author=G.J. Sullivan|author2=Heiko Schwarz|author3=Thiow Keng Tan|author4=Thomas Wiegand|author4-link=Thomas Wiegand|date=2012-08-22|title=Comparison of the Coding Efficiency of Video Coding Standards – Including High Efficiency Video Coding (HEVC)|publisher=IEEE Trans. on Circuits and Systems for Video Technology|url=http://iphome.hhi.de/wiegand/assets/pdfs/2012_12_IEEE-HEVC-Performance.pdf|access-date=2013-05-18}}</ref><ref name="HEVCdraft10">{{cite news|date=2013-01-17|title=High Efficiency Video Coding (HEVC) text specification draft 10 (for FDIS & Consent)|publisher=JCT-VC|url=http://phenix.it-sudparis.eu/jct/doc_end_user/current_document.php?id=7243|access-date=2013-05-18}}</ref><ref name="HEVCOctober2012K0109">{{cite news|author=Alberto Dueñas|author2=Adam Malamy|date=2012-10-18|title=On a 10-bit consumer-oriented profile in High Efficiency Video Coding (HEVC)|publisher=JCT-VC|url=http://phenix.it-sudparis.eu/jct/doc_end_user/current_document.php?id=6479|access-date=2013-05-18}}</ref> but historical lower-depth systems used bits per pixel more often.

Color depth is only one aspect of color representation, expressing the precision with which the amount of each primary can be expressed; the other aspect is how broad a range of colors can be expressed (the [[Gamut|gamut]]). The definition of both color precision and gamut is accomplished with a color encoding specification which assigns a digital code value to a location in a [[Color space|color space]].

The number of  bits of resolved intensity in a color channel is also known as '''radiometric resolution''', especially in the context of satellite images.<ref name="Thenkabail 2018 p. 20">{{cite book | last=Thenkabail | first=P. | title=Remote Sensing Handbook - Three Volume Set | publisher=CRC Press | series=Remote Sensing Handbook | year=2018 | isbn=978-1-4822-8267-2 | url=https://books.google.com/books?id=c2O1DwAAQBAJ&pg=PA20 | access-date=2020-08-27 | page=20}}</ref>

==Comparison==
<gallery class="center" showfilename="yes" widths="300" heights="225" caption="Same image on five different color depths, showing resulting (compressed) file sizes. 8 and smaller use an [[Palette (computing)#Adaptive palette|adaptive palette]] so quality may be better than some systems can provide.">
File:24 bit.png|16,777,216 colors<br/>98 [[Kilobyte|KB]]
File:8 bit.png|256 colors<br/>37 KB (−62%)
File:4 bit.png|16 colors<br/>13 KB (−87%)
File:2 bit.png|4 colors<br/>6 KB (−94%)
File:1 bit.png|2 colors<br/>4 KB (−96%)
</gallery>

==Indexed color==
{{Main|Indexed color}}
With the relatively low color depth, the stored value is typically a number representing the index into a color map or [[Palette (computing)|palette]] (a form of [[Vector quantization|vector quantization]]). The colors available in the palette itself may be fixed by the hardware or modifiable by software. Modifiable palettes are sometimes referred to as '''[[False color|pseudocolor]]''' palettes.

Old graphics chips, particularly those used in [[Engineering:Home computer|home computer]]s and [[Engineering:Video game console|video game console]]s, often have the ability to use a different palette per [[Sprite (computer graphics)|sprite]]s and tiles in order to increase the maximum number of simultaneously displayed colors, while minimizing use of then-expensive memory (and bandwidth). For example, in the [[Engineering:ZX Spectrum|ZX Spectrum]] the picture is stored in a two-color format, but these two colors can be separately defined for each rectangular block of 8×8 pixels.

The palette itself has a color depth (number of bits per entry). While the best [[Video Graphics Array|VGA]] systems only offered an 18-bit (262,144 color) palette<ref name=":1">{{Cite patent|number=US5574478A|title=VGA color system for personal computers|gdate=1996-11-12|invent1=Bril|invent2=Pett|inventor1-first=Vlad|inventor2-first=Boyd G.|url=https://patents.google.com/patent/US5574478/en}}</ref><ref name=":2">{{Cite web |date=2017-12-26 |title=Reading and writing 18-bit RGB VGA Palette (pal) files with C# |url=https://www.cyotek.com/blog/reading-and-writing-18-bit-rgb-vga-palette-pal-files-with-csharp |access-date=2023-03-27 |website=The Cyotek Blog |language=en}}</ref><ref name=":3">{{Cite web |title=VGA/SVGA Video Programming--Color Regsters |url=http://www.osdever.net/FreeVGA/vga/colorreg.htm |access-date=2023-03-27 |website=www.osdever.net}}</ref><ref name=":4">{{Cite web |title=VGA Palette Conversion \ VOGONS |url=https://www.vogons.org/viewtopic.php?t=38713 |access-date=2023-03-27 |website=www.vogons.org}}</ref> from which colors could be chosen, all color Macintosh video hardware offered a 24-bit (16 million color) palette. 24-bit palettes are nearly universal on any recent hardware or file format using them.

If instead the color can be directly figured out from the pixel values, it is "direct color". Palettes were rarely used for depths greater than 12 bits per pixel, as the memory consumed by the palette would exceed the necessary memory for direct color on every pixel.

==List of common depths==
{{Hatnote|Headings of subsections refer to bits-per-pixel.}}
===1-bit color===
{{Main|Binary image}}
2 colors, often black and white (or whatever color the [[Engineering:Cathode-ray tube|CRT]] phosphor was) direct color. Sometimes 1 meant black and 0 meant white, the inverse of modern standards. Most of the first graphics displays were of this type, the X window system was developed for such displays, and this was assumed for a [[Engineering:3M computer|3M computer]]. In the late 80's there were professional displays with resolutions up to 300dpi (the same as a contemporary laser printer) but color proved more popular.

===2-bit color===
4 colors, usually from a selection of fixed palettes. Gray-scale early [[Engineering:NeXTstation|NeXTstation]], color Macintoshes, Atari ST medium resolution.

===3-bit color===
8 colors, almost always all combinations of full-intensity red, green, and blue. Many early home computers with TV displays, including the [[Engineering:ZX Spectrum|ZX Spectrum]] and [[Engineering:BBC Micro|BBC Micro]].

===4-bit color===
16 colors, usually from a selection of fixed palettes. Used by IBM [[Color Graphics Adapter|CGA]] (at the lowest resolution), [[Enhanced Graphics Adapter|EGA]], and by the least common denominator [[Video Graphics Array|VGA]] standard at higher resolution. Color Macintoshes, Atari ST low resolution, [[Engineering:Commodore 64|Commodore 64]], and Amstrad CPCs also supported 4-bit color.

===5-bit color===
32 colors from a programmable palette, used by the Original Amiga chipset.

===6-bit color===
64 colors.  Used by the [[Engineering:Master System|Master System]], Enhanced Graphics Adapter, GIME for TRS-80 Color Computer 3, Pebble Time smartwatch (64 color e-paper display), and [[Engineering:Parallax Propeller|Parallax Propeller]] using the reference VGA circuit.

===8-bit color===
256 colors, usually from a fully-programmable palette: Most early color Unix workstations, [[Super VGA]], color [[Engineering:Macintosh|Macintosh]], Atari TT, Amiga AGA chipset, Falcon030, [[Engineering:Acorn Archimedes|Acorn Archimedes]]. Both X and Windows provided elaborate systems to try to allow each program to select its own palette, often resulting in incorrect colors in any window other than the one with focus.

Some systems placed a color cube in the palette for a direct-color system (and so all programs would use the same palette). Usually fewer levels of blue were provided than others, since the normal human eye is less sensitive to the blue component than to either red or green (two thirds of the eye's receptors process the longer wavelengths<ref>{{cite web |title=How we see color |website=Pantone (pantone.co.uk) |url=http://www.pantone.co.uk/pages/pantone/Pantone.aspx?pg=19357&ca=29 |archive-url=https://web.archive.org/web/20111229022826/http://pantone.co.uk/pages/pantone/Pantone.aspx?pg=19357&ca=29 |archive-date=29 December 2011 }}</ref>).
Popular sizes were:
* 6×6×6 (web-safe colors), leaving 40&nbsp;colors for a gray ramp, or for programmable palette entries.
* 8×8×4. 3&nbsp;bits of R and G, 2&nbsp;bits of B, the correct value can be computed from a color without using multiplication. Used, among others, in the [[Software:MSX2|MSX2]] system series of computers in the early to mid 1990s.
* a 6×7×6 color cube, leaving 4&nbsp;colors for a programmable palette or grays.
* a 6×8×5 cube, leaving 16&nbsp;colors for a programmable palette or grays.

===12-bit color===
4096 colors, usually from a fully-programmable palette (though it was often set to a 16×16×16 color cube). Some [[Company:Silicon Graphics|Silicon Graphics]] systems, Color NeXTstation systems, and [[Engineering:Amiga|Amiga]] systems in [[Hold-And-Modify|HAM]] mode have this color depth.

RGBA4444, a related 16bpp representation providing the color cube and 16 levels of transparency, is a common [[Texture mapping|texture format]] in mobile graphics.

===High color (15/16-bit)===
In high-color systems, two bytes (16 bits) are stored for each pixel. Most often, each component (R, G, and B) is assigned 5 bits, plus one unused bit (or used for a mask channel or to switch to indexed color); this allows 32,768 colors to be represented. However, an alternate assignment which reassigns the unused bit to the G channel allows 65,536 colors to be represented, but without transparency.<ref>{{cite book
|title= iTV handbook: technologies and standards
|author= Edward M. Schwalb
|publisher= Prentice Hall PTR
|year= 2003
|isbn= 978-0-13-100312-5
|page= 138
|url= https://books.google.com/books?id=DM_EV4yJKYUC&pg=PA138}}</ref> These color depths are sometimes used in small devices with a color display, such as mobile phones, and are sometimes considered sufficient to display photographic images.<ref>{{cite book
|title= Windows 98 annoyances
|author= David A. Karp
|publisher= O'Reilly Media
|year= 1998
|isbn= 978-1-56592-417-8
|page= [https://archive.org/details/windows98annoyan00karp/page/156 156]
|url= https://archive.org/details/windows98annoyan00karp|url-access= registration
}}</ref> Occasionally 4 bits per color are used plus 4 bits for alpha, giving 4096 colors. Among the first hardware to use the standard were the Sharp X68000 and IBM's [[Graphics display resolution#Extended Graphics Array|Extended Graphics Array]] (XGA).

The term "high color" has recently been used to mean color depths greater than 24 bits.

===18-bit===

Almost all of the least expensive LCDs (such as typical [[Engineering:TFT LCD#Twisted nematic (TN)|twisted nematic]] types) provide 18-bit color (64×64×64 = 262,144 combinations) to achieve faster color transition times, and use either [[Dither|dither]]ing or [[Engineering:Frame rate control|frame rate control]] to approximate 24-bit-per-pixel true color,<ref>{{cite web|title=TR's Summer 2012 system guide|url=http://techreport.com/review/23204/tr-summer-2012-system-guide/14|page=14|date=July 2, 2012|first1=Cyril|last1=Kowaliski|first2=Geoff|last2=Gasior|first3=Scott|last3=Wasson|publisher=[[The Tech Report]]|access-date=January 19, 2013}}</ref> or throw away 6 bits of color information entirely. More expensive LCDs (typically [[Engineering:IPS panel|IPS]]) can display 24-bit color depth or greater.

{{anchor|true color}}
===True color (24-bit)===
<!-- This section is linked from [[Engineering:Amiga|Amiga]] -->

[[File:16777216colors.png|thumb|200px|All 16,777,216 colors (downscaled, click image for full resolution)]]
24 bits almost always use 8 bits each of R, G, and B (8&nbsp;bpc). As of 2018, 24-bit color depth is used by virtually every computer and phone display {{Citation needed|date=June 2020}} and the vast majority of [[Image file formats|image storage formats]]. Almost all cases of 32 bits per pixel assigns 24 bits to the color, and the remaining 8 are the [[Alpha compositing|alpha channel]] or unused.

2<sup>24</sup> gives 16,777,216 color variations. The human eye can discriminate up to ten million colors,<ref>
{{cite book
|author= D. B. Judd and G. Wyszecki
|title=Color in Business, Science and Industry
|publisher=Wiley-Interscience
|series=Wiley Series in Pure and Applied Optics
|edition=third
|location=New York
|year= 1975
|pages=388
|isbn=0-471-45212-2
}}
</ref> and since the [[Gamut|gamut]] of a display is smaller than the range of human vision, this means this should cover that range with more detail than can be perceived. However, displays do not evenly distribute the colors in human perception space, so humans can see the changes between some adjacent colors as [[Colour banding|color banding]]. [[Grayscale|Monochromatic images]] set all three channels to the same value, resulting in only 256 different colors; some software attempts to dither the gray level into the color channels to increase this, although in modern software this is more often used for [[Subpixel rendering|subpixel rendering]] to increase the space resolution on LCD screens where the colors have slightly different positions.

The [[Engineering:DVD-Video|DVD-Video]] and Blu-ray Disc standards support a bit depth of 8 bits per color in [[YCbCr]] with 4:2:0 [[Chroma subsampling|chroma subsampling]].<ref name="AudioholicsHDMIApril2008">{{cite news|url=https://www.audioholics.com/home-theater-calibration/hdmi-black-levels-xvycc-rgb|title=HDMI Enhanced Black Levels, xvYCC and RGB|author=Clint DeBoer|date=2008-04-16|access-date=2013-06-02|publisher=Audioholics}}</ref><ref name=TelairityDigitalColorCodingPDF>{{cite news |title=Digital Color Coding |publisher=Telairity |url=http://www.telairity.com/assets/downloads/Digital%20Color%20Coding.pdf |access-date=2013-06-02 |archive-url=https://web.archive.org/web/20140107171831/http://www.telairity.com/assets/downloads/Digital%20Color%20Coding.pdf |archive-date=2014-01-07 |url-status=dead }}</ref> YCbCr can be losslessly converted to RGB.

MacOS refers to 24-bit colour as "millions of colours". The term ''true colour'' is sometimes used to mean what this article is calling ''direct colour''.<ref>
{{cite book
|title= Digital Video and HDTV
|author= Charles A. Poynton
|publisher= Morgan Kaufmann
|year= 2003
|isbn= 1-55860-792-7
|page= 36
|url= https://books.google.com/books?id=ra1lcAwgvq4C&q=truecolor&pg=RA1-PA36
}}</ref> It is also often used to refer to all color depths greater or equal to 24.

{{anchor|deep color}}

===Deep color (30-bit)===
''Deep color'' consists of a billion or more colors.<ref>
{{cite book
 |first=Keith  |last=Jack
 |year=2007
 |title=Video demystified: a handbook for the digital engineer
 |edition=5th  |page= 168
 |publisher=Newnes
 |isbn=978-0-7506-8395-1
 |url=https://books.google.com/books?id=6dgWB3-rChYC&pg=PA168
}}
</ref> 2<sup>30</sup> is 1,073,741,824. Usually this is 10&nbsp;bits each of red, green, and blue (10&nbsp;bpc). If an [[Alpha compositing|alpha channel]] of the same size is added then each pixel takes 40&nbsp;bits.

Some earlier systems placed three 10-bit channels in a 32-bit [[Word (computer architecture)|word]], with 2&nbsp;bits unused (or used as a 4-level [[Alpha compositing|alpha channel]]); the [[Cineon#Cineon file format|Cineon file format]], for example, used this. Some [[Company:Silicon Graphics|SGI]] systems had 10- (or more) bit [[Digital-to-analog converter|digital-to-analog converter]]s for the video signal and could be set up to interpret data stored this way for display. BMP files define this as one of its formats, and it is called "HiColor" by [[Company:Microsoft|Microsoft]].

[[Engineering:Graphics card|Video cards]] with 10&nbsp;bits per component started coming to market in the late 1990s. An early example was the [[Company:Radius Inc.|Radius]] ThunderPower card for the Macintosh, which included extensions for [[Software:QuickDraw|QuickDraw]] and [[Software:Adobe Photoshop|Adobe Photoshop]] plugins to support editing 30-bit images.<ref>
{{cite news
 |title= Radius Ships ThunderPower&nbsp;30/1920 Graphics Card Capable of Super Resolution 1920&nbsp;×&nbsp;1080 and Billions of Colors
 |date=1996-08-05
 |work=Business Wire
 |url= http://findarticles.com/p/articles/mi_m0EIN/is_1996_August_5/ai_18554540
}}
</ref> Some vendors call their 24-bit color depth with [[Engineering:Frame rate control|FRC]] panels 30-bit panels; however, true deep color displays have 10-bit or more color depth without FRC.

The [[Engineering:HDMI|HDMI]]&nbsp;1.3 specification defines a bit depth of 30&nbsp;bits (as well as 36 and 48&nbsp;bit depths).<ref name="HDMI2006Specs6.7.2">
{{cite news
 |title=HDMI Specification 1.3a Section 6.7.2
 |date=2006-11-10
 |publisher=HDMI Licensing, LLC.
 |url=http://www.hdmi.org/learningcenter/kb.aspx?c=3
 |url-status=dead  |access-date=2009-04-09
 |archive-url=https://web.archive.org/web/20090710105139/http://www.hdmi.org/learningcenter/kb.aspx?c=3 
 |archive-date=2009-07-10
}}
</ref>
In that regard, the [[Engineering:Nvidia Quadro|Nvidia Quadro]] graphics cards manufactured after 2006 support 30-bit deep color<ref>
{{cite web
 |title=Chapter&nbsp;32. Configuring Depth&nbsp;30 Displays (driver release notes)
 |publisher=NVIDIA
 |url=http://uk.download.nvidia.com/XFree86/Linux-x86/295.59/README/depth30.html
}}
</ref> and Pascal or later GeForce and Titan cards when paired with the Studio Driver<ref>
{{cite web
 |title=NVIDIA Studio Driver&nbsp;431.70 (Release Highlights)
 |publisher=NVIDIA
 |url=https://www.nvidia.com/Download/driverResults.aspx/149125/en-us
}}
</ref> as do some models of the [[Engineering:Radeon|Radeon]] HD&nbsp;5900 series such as the HD&nbsp;5970.<ref>
{{cite web
 |title=ATI Radeon HD&nbsp;5970 Graphics Feature Summary
 |publisher=AMD
 |url=https://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-5000/hd-5970/Pages/ati-radeon-hd-5970-specifications.aspx
 |access-date=2010-03-31
}}
</ref><ref>
{{cite web
 |publisher=AMD
 |title=AMD's 10-bit Video Output Technology
 |url=http://ati.amd.com/products/pdf/10-Bit.pdf
 |access-date=2010-03-31  |url-status=dead
 |archive-url=https://web.archive.org/web/20100216125406/http://ati.amd.com/products/pdf/10-Bit.pdf
 |archive-date=2010-02-16
}}
</ref> The ATI FireGL V7350 [[Engineering:Graphics card|graphics card]] supports 40- and 64-bit pixels (30 and 48 bit color depth with an alpha channel).<ref>
{{cite web
 |first=Tony |last=Smith
 |date=20 March 2006
 |title=ATI unwraps first 1GB graphics card
 |url=http://reghardware.co.uk/2006/03/20/ati_firegl_v7350/
 |access-date=2006-10-03  |url-status=dead
 |archive-url=https://web.archive.org/web/20061008103416/http://www.reghardware.co.uk/2006/03/20/ati_firegl_v7350/
 |archive-date=8 October 2006
}}
</ref>

The [[DisplayPort]] specification also supports color depths greater than 24&nbsp;bpp in version&nbsp;1.3 through "[[Display Stream Compression|VESA Display Stream Compression]], which uses a visually [[Lossless compression|lossless]] low-latency algorithm based on predictive DPCM and YCoCg-R color space and allows increased resolutions and color depths and reduced power consumption."<ref>{{cite web
 |title=Looking for a HDMI&nbsp;2.0 displayport to displayport for my monitor
 |series=[Solved] - Displays
 |website=Tom's Hardware
 |language=en
 |url=https://www.tomshardware.co.uk/forum/id-2792898/hdmi-displayport-displayport-monitor.html
 |access-date=2018-03-20
 |archive-date=March 21, 2018
 |archive-url=https://web.archive.org/web/20180321192555/http://www.tomshardware.co.uk/forum/id-2792898/hdmi-displayport-displayport-monitor.html
 |url-status=dead
 }}</ref>

At WinHEC 2008, Microsoft announced that color depths of 30&nbsp;bits and 48&nbsp;bits would be supported in [[Software:Windows 7|Windows 7]], along with the wide color gamut [[ScRGB|scRGB]].<ref name="winhec">
{{cite web
 |title=WinHEC 2008 GRA-583: Display Technologies
 |date=2008-11-06
 |publisher=Microsoft
 |url=http://download.microsoft.com/download/5/E/6/5E66B27B-988B-4F50-AF3A-C2FF1E62180F/GRA-T583_WH08.pptx
 |access-date=2008-12-04  |url-status=dead
 |archive-url=https://web.archive.org/web/20081227074524/http://download.microsoft.com/download/5/E/6/5E66B27B-988B-4F50-AF3A-C2FF1E62180F/GRA-T583_WH08.pptx
 |archive-date=2008-12-27
}}
</ref><ref>
{{cite web
 |title=Windows&nbsp;7 High Color Support
 |date=2008-11-26
 |publisher=Softpedia
 |url=http://news.softpedia.com/news/Windows-7-High-Color-Support-98741.shtml
 |access-date=2008-12-05
}}
</ref>

[[High Efficiency Video Coding]] (HEVC or H.265) defines the Main&nbsp;10 profile, which allows for 8 or 10&nbsp;bits per sample with 4:2:0 [[Chroma subsampling|chroma subsampling]].<ref name=CodingEfficiencyHEVCIEEE2012/><ref name=HEVCdraft10/><ref name=HEVCOctober2012K0109/><ref name=EricssonHEVCBackgroundJune2013>
{{cite news
 |first=Carl  |last=Furgusson
 |date=2013-06-11
 |title=HEVC: The background behind the game-changing standard- Ericsson
 |series=Focus on ...
 |publisher=Ericsson
 |url=http://www.ericsson.com/televisionary/blog/focus-hevc-background-behind-game-changing-standard-ericsson/
 |access-date=2013-06-21  |url-status=dead
 |archive-url=https://web.archive.org/web/20130620000218/http://www.ericsson.com/televisionary/blog/focus-hevc-background-behind-game-changing-standard-ericsson/
 |archive-date=2013-06-20
}}
</ref><ref name=ImaginationEmergenceHEVC10bitJune2013>
{{cite news
 |first=Simon  |last=Forrest
 |date=2013-06-20
 |title=The emergence of HEVC and 10-bit colour formats
 |publisher=Imagination Technologies
 |url=http://withimagination.imgtec.com/index.php/powervr-video/the-emergence-of-hevc-and-10-bit-colour-formats
 |access-date=2013-06-21  |url-status=dead
 |archive-url=https://web.archive.org/web/20130915075921/http://withimagination.imgtec.com/index.php/powervr-video/the-emergence-of-hevc-and-10-bit-colour-formats
 |archive-date=2013-09-15
}}
</ref> The Main&nbsp;10 profile was added at the October&nbsp;2012 HEVC meeting based on proposal JCTVC-K0109 which proposed that a 10-bit profile be added to HEVC for consumer applications.<ref name=HEVCOctober2012K0109/> The proposal stated that this was to allow for improved video quality and to support the [[Rec. 2020]] color space that will be used by [[Engineering:Ultra-high-definition television|UHDTV]].<ref name=HEVCOctober2012K0109/> The second version of HEVC has five profiles that allow for a bit depth of 8&nbsp;bits to 16&nbsp;bits per sample.<ref name=HEVCJuly2014R1013>
{{cite news
 |first2=Jianle     |last2=Chen
 |first3=Ying       |last3=Chen
 |first4=David      |last4=Flynn
 |first5=Miska M.   |last5=Hannuksela
 |first6=Matteo     |last6=Naccari
 |first7=Chris      |last7=Rosewarne
 |first8=Karl       |last8=Sharman
 |first9=Joel       |last9=Sole
 |first10=Gary J.   |last10=Sullivan
 |first11=Teruhiko  |last11=Suzuki
 |first12=Gerhard   |last12=Tech
 |first13=Ye-Kui    |last13=Wang
 |first14=Krzysztof |last14=Wegner
 |first15=Yan       |last15=Ye
 |display-authors=6
 |date=2014-07-11
 |title=Draft high efficiency video coding (HEVC) version&nbsp;2, combined format range extensions (RExt), scalability (SHVC), and multi-view (MV-HEVC) extensions
 |publisher=JCT-VC
 |url=http://phenix.it-sudparis.eu/jct/doc_end_user/current_document.php?id=9466
 |access-date=2014-07-11
}}
</ref>

As of 2020, some smartphones have started using 30-bit color depth, such as the [[Engineering:OnePlus 8|OnePlus&nbsp;8 Pro]], [[Engineering:Oppo Find X2|Oppo Find X2]] & Find&nbsp;X2 Pro, [[Engineering:Sony Xperia 1 II|Sony Xperia 1 II]], [[Engineering:Xiaomi Mi 10 Ultra|Xiaomi Mi 10 Ultra]], [[Engineering:Motorola Edge Plus|Motorola Edge+]], [[Engineering:ROG Phone 3|ROG Phone 3]] and [[Company:Sharp Corporation|Sharp]] Aquos Zero&nbsp;2.

=== 36-bit ===
Using 12 bits per color channel produces 36 bits, 68,719,476,736 colors. If an alpha channel of the same size is added then there are 48 bits per pixel.

=== 48-bit ===
Using 16 bits per color channel produces 48 bits, 281,474,976,710,656 colors. If an alpha channel of the same size is added then there are 64 bits per pixel.

[[Software:Graphics software|Image editing software]] such as [[Software:Adobe Photoshop|Adobe Photoshop]] started using 16 bits per channel fairly early in order to reduce the quantization on intermediate results (i.e. if an operation is divided by 4 and then multiplied by 4, it would lose the bottom 2 bits of 8-bit data, but if 16 bits were used it would lose none of the 8-bit data). In addition, [[Engineering:Digital camera|digital camera]]s are able to produce 10 or 12 bits per channel in their raw data; as 16 bits is the smallest addressable unit larger than that, using it would make it easier to manipulate the raw data.

== Expansions ==

===High dynamic range and wide gamut{{anchor|hdr and wcg}}===
Some systems started using those bits for numbers outside the 0–1 range rather than for increasing the resolution. Numbers greater than 1 were for colors brighter than the display could show, as in [[High-dynamic-range imaging|high-dynamic-range imaging]] (HDRI). Negative numbers can increase the gamut to cover all possible colors, and for storing the results of filtering operations with negative filter coefficients. The [[Engineering:Pixar Image Computer|Pixar Image Computer]] used 12 bits to store numbers in the range [-1.5,2.5), with 2 bits for the integer portion and 10 for the fraction. The [[Cineon]] imaging system used 10-bit professional video displays with the video hardware adjusted so that a value of 95 was black and 685 was white.<ref>{{cite news |url= http://www.qvolabs.com/acrobat/8bitvs10bit.pdf |title= 8-bit vs. 10-bit Color Space |date= January 2010 |access-date= May 15, 2014 |archive-date= March 12, 2014 |archive-url= https://web.archive.org/web/20140312104048/http://www.qvolabs.com/acrobat/8bitvs10bit.pdf |url-status= dead }}</ref> The amplified signal tended to reduce the lifetime of the CRT.

===Linear color space and floating point===
More bits also encouraged the storage of light as linear values, where the number directly corresponds to the amount of light emitted. Linear levels makes calculation of computer graphics much easier. However, linear color results in disproportionately more samples near white and fewer near black, so the quality of 16-bit linear is about equal to 12-bit [[SRGB|sRGB]].

Floating point numbers can represent linear light levels spacing the samples semi-logarithmically. Floating point representations also allow for drastically larger dynamic ranges as well as negative values. Most systems first supported 32-bit per channel [[Single-precision floating-point format|single-precision]], which far exceeded the accuracy required for most applications. In 1999, Industrial Light & Magic released the [[Engineering:Open standard|open standard]] image file format [[OpenEXR]] which supported 16-bit-per-channel [[Half-precision floating-point format|half-precision]] floating-point numbers. At values near 1.0, half precision floating point values have only the precision of an 11-bit integer value, leading some graphics professionals to reject half-precision in situations where the extended dynamic range is not needed.

===More than three primaries===
Virtually all television displays and computer displays form images by varying the strength of just three [[Primary color|primary color]]s: red, green, and blue. For example, bright yellow is formed by roughly equal red and green contributions, with no blue contribution.

For storing and manipulating images, alternative ways of expanding the traditional triangle exist: One can convert image coding to use fictitious primaries, that are not physically possible but that have the effect of extending the triangle to enclose a much larger color gamut. An equivalent, simpler change is to allow negative numbers in color channels, so that the represented colors can extend out of the color triangle formed by the primaries. However these only extend the colors that can be represented in the image encoding; neither trick extends the [[Gamut|gamut]] of colors that can actually be rendered on a display device.
<!-- replaced by new paragraph below --- {{Incomprehensible inline span |text=As humans are primarily [[Biology:Trichromacy|trichromats]], (though tetrachromats exist){{citation needed|date= July 2023}} the benefit conferred by an additional primary is not in computer representation, but in the computational ease of showing inputs on a four-primary display. |reason=I cannot identify how the parts of this sentence are related or what most of this is even talking about. |date=September 2021}} -->
[[Image:CIExy1931 srgb gamut.png|240px|right|thumb|A typical CRT monitor{{efn|The cathode-ray tube monitor (CRT) is obsolete technology, but its more limited color-rendering clearly illustrates the problem that LCD monitors also have, despite their somewhat broader color [[Gamut|gamut]].}} [[Gamut|gamut]]: Inside the colored triangle represents colors that the monitor can display. The horseshoe-shaped surrounding grey area represents colors humans can see, but that the monitor cannot show.]]
Supplementary colors can widen the [[Gamut|color gamut]] of a display, since it is no longer limited to the interior of a triangle formed by three [[Primary color|primaries]] at its corners, e.g. the [[CIE 1931 color space]]. Recent technologies such as [[Company:Texas Instruments|Texas Instruments]]'s ''BrilliantColor'' augment the typical red, green, and blue channels with up to three other primaries: cyan, magenta, and yellow.<ref name="digitv info 1">
{{cite news
 |first=David |last=Hutchison
 |date=5 April 2006
 |magazine=Digital TV DesignLine
 |title=Wider color gamuts on DLP display systems through ''BrilliantColor'' technology
 |url=http://www.digitaltvdesignline.com/showArticle.jhtml?printableArticle=true&articleId=184425677 |access-date=2007-08-16 |url-status=dead
 |archive-url=https://web.archive.org/web/20070928122247/http://www.digitaltvdesignline.com/showArticle.jhtml?printableArticle=true&articleId=184425677
 |archive-date=28 September 2007
}}
</ref> Cyan would be indicated by negative values in the red channel, magenta by negative values in the green channel, and yellow by negative values in the blue channel, validating the use of otherwise fictitious negative numbers in the color channels. 

[[Company:Mitsubishi|Mitsubishi]] and [[Company:Samsung|Samsung]] (among others) use ''BrilliantColor'' in some of their TV sets to extend the range of displayable colors.{{citation needed|date=April 2014}}
The Sharp Aquos line of televisions has introduced [[Quattron]] technology, which augments the usual RGB pixel components with a yellow subpixel. However, formats and media that allow or make use of the extended color [[Gamut|gamut]] are at present extremely rare.{{citation needed|date=October 2021}}

Because humans are overwhelmingly [[Biology:Trichromacy|trichromats]] or [[Medicine:Dichromacy|dichromats]]{{efn|Some women have tested as functional tetrachromats but they are exceedingly rare.{{citation needed|date= July 2023}} Less rare are [[Medicine:Color blindness|"color blind"]] dichromats, who theoretically would only need two [[Primary color|primary color]]s.}} one might suppose that adding a fourth "primary" color could provide no practical benefit. However humans can see a broader [[Gamut|range of colors]] than a mixture of three colored lights can display. The deficit of colors is particularly noticeable in saturated shades of bluish green (shown as the left upper grey part of the horseshoe in the diagram) of RGB displays: Most humans can see more vivid blue-greens than any color video screen can display.

==See also==
{{div col |colwidth=15em |content=
* [[Audio bit depth]] – corresponding concept for digital audio
* Bit plane
* [[Image resolution]]
* [[List of color palettes]]
* [[List of colors (alphabetical)]]
* [[Physics:Mach bands|Mach banding]]
* [[RGB color model]]
}} <!-- end "content=" -->

==Footnotes==
{{notelist|30em}}

==References==
{{reflist}}

{{Color topics}}

[[Category:Television technology]]

{{Sourceattribution|Color depth}}