Content deleted Content added
m Fix misspelling found by Wikipedia:Typo Team/moss – you can help! |
Sunnytober23 (talk | contribs) grammar |
||
(8 intermediate revisions by 5 users not shown) | |||
Line 1: | Line 1: | ||
{{AFI}} |
|||
{{Short description|To measure and/or adjust the color response of a device to a known state}} |
{{Short description|To measure and/or adjust the color response of a device to a known state}} |
||
{{Use American English|date=March 2021}} |
{{Use American English|date=March 2021}} |
||
{{Use mdy dates|date= |
{{Use mdy dates|date=October 2023}} |
||
{{More citations needed|date= |
{{More citations needed|date=October 2023}} |
||
The aim of '''color calibration''' is to measure and/or adjust the color response of a device (input or output) to a known state. In [[International Color Consortium]] (ICC) terms, this is the basis for an additional color characterization of the device and later profiling.<ref>{{cite web | title = Calibration vs. Characterization | author = Graeme Gill | |
The aim of '''color calibration''' is to measure and/or adjust the color response of a device (input or output) to a known state.<ref>{{Cite book |last=Wransky |first=Michael |url=https://books.google.com/books?id=F2n0jgEACAAJ |title=Color Calibration Techniques for True Color Measurement: Computer Interpretation of Color |date=November 3, 2015 |publisher=Lap Lambert Academic Publishing GmbH KG |isbn=978-3-659-78939-7 |language=en}}</ref> In [[International Color Consortium]] (ICC) terms, this is the basis for an additional color characterization of the device and later profiling.<ref>{{cite web | title = Calibration vs. Characterization | author = Graeme Gill |url=http://www.argyllcms.com/doc/calvschar.html | publisher = Graeme Gill | access-date = November 4, 2011 | archive-date = October 30, 2011 | archive-url=https://web.archive.org/web/20111030224901/http://www.argyllcms.com/doc/calvschar.html | url-status = live }}</ref> In non-ICC workflows, calibration sometimes refers to establishing a known relationship to a standard [[color space]]<ref>{{cite book | title = Introduction to color imaging science | author = Hsien-Che Lee | publisher = Cambridge University Press | year = 2005 | isbn = 0-521-84388-X |url=https://books.google.com/books?id=CzAbJrLin_AC&dq=%22color+calibration%22+camera+monitor&pg=PA388 }}</ref> in one go. The device that is to be calibrated is sometimes known as a ''calibration source''; the color space that serves as a standard is sometimes known as a ''calibration target''.{{Citation needed|date=April 2008}} Color calibration is a requirement for all devices taking an active part in a [[color management|color-managed]] workflow and is used by many industries, such as television production, gaming, photography, engineering, chemistry, medicine, and more. |
||
== Information flow and output distortion == |
== Information flow and output distortion == |
||
Input data can come from device sources like [[digital cameras]], [[image scanner]]s or any other measuring devices. Those inputs can be either monochrome (in which case only the [[Tone reproduction|response curve]] needs to be calibrated, though in a few select cases one must also specify the color or spectral power distribution |
Input data can come from device sources like [[digital cameras]], [[image scanner]]s, or any other measuring devices. Those inputs can be either monochrome (in which case only the [[Tone reproduction|response curve]] needs to be calibrated, though in a few select cases, one must also specify the color or spectral power distribution that that single channel corresponds to) or specified in [[Additive color|multidimensional]] color, most commonly in the three-channel [[RGB color model|red-green-blue]] model. Input data is, in most cases, calibrated against a [[Color management#Color translation|profile connection space (PCS)]].<ref>{{cite web | title = Color Imaging Workflow Primitives | author = Ann L. McCarthy |url=https://www.color.org/primitives.pdf | publisher = International Color Consortium | access-date = September 14, 2021 | archive-date = July 31, 2021 | archive-url=https://web.archive.org/web/20210731100754/https://www.color.org/primitives.pdf | url-status = live }}</ref> |
||
One of the most important factors to consider when dealing with color calibration is having a valid source. If the color measuring source does not match the |
One of the most important factors to consider when dealing with color calibration is having a valid source. If the color measuring source does not match the display's capabilities, the calibration will be ineffective and give false readings. |
||
The main distorting factors on the input stage stem from the amplitude nonlinearity of the channel responses, and in the case of a multidimensional datastream the non-ideal wavelength responses of the individual color separation filters, most commonly a [[color filter array]], in combination with the [[Light temperature#Spectral power distribution|spectral power distribution]] of the scene illumination. |
The main distorting factors on the input stage stem from the amplitude nonlinearity of the channel responses, and in the case of a multidimensional datastream, the non-ideal wavelength responses of the individual color separation filters, most commonly a [[color filter array]], in combination with the [[Light temperature#Spectral power distribution|spectral power distribution]] of the scene illumination. |
||
After this the data is often circulated in the system translated into a [[Color management#Working spaces|working space RGB]] for viewing and editing. |
After this, the data is often circulated in the system and translated into a [[Color management#Working spaces|working space RGB]] for viewing and editing. |
||
In the output stage when exporting to a viewing device such as a [[cathode ray tube]] |
In the output stage, when exporting to a viewing device such as a [[cathode ray tube]], [[liquid crystal display]] screen, or digital projector, the computer sends a signal to the computer's graphic card in the form of RGB [Red, Green, Blue]. The dataset [255,0,0] signals only a device instruction, not a specific color. This instruction [R,G,B]=[255,0,0] then causes the connected display to show Red at the maximum achievable brightness [255], while the Green and Blue components of the display remain dark [0]. The resultant color being displayed, however, depends on two main factors: |
||
*the [[phosphor]]s or another system actually producing a light that falls inside the red spectrum; |
*the [[phosphor]]s or another system actually producing a light that falls inside the red spectrum; |
||
*the overall brightness of the color resulting in the desired [[Color vision|color perception]]: an extremely bright light source will always be seen as white, irrespective of spectral composition. |
*the overall brightness of the color, resulting in the desired [[Color vision|color perception]]: an extremely bright light source will always be seen as white, irrespective of spectral composition. |
||
Hence every output device will have its unique color signature, displaying a certain color according to manufacturing tolerances and material deterioration through use and age. |
Hence, every output device will have its own unique color signature, displaying a certain color according to manufacturing tolerances and material deterioration through use and age. If the output device is a printer, additional distorting factors are the qualities of a particular batch of paper and ink. |
||
If the output device is a printer, additional distorting factors are the qualities of a particular batch of paper and ink. |
|||
The conductive qualities and standards-compliance of connecting cables, circuitry and equipment can also alter the electrical signal at any stage in the signal flow. (A partially inserted [[VGA connector]] can result in a monochrome display, for example, as some pins are not connected.) |
The conductive qualities and standards-compliance of connecting cables, circuitry, and equipment can also alter the electrical signal at any stage in the signal flow. (A partially inserted [[VGA connector]] can result in a monochrome display, for example, as some pins are not connected.) |
||
== Color perception == |
== Color perception == |
||
Line 31: | Line 31: | ||
==Calibration techniques and procedures== |
==Calibration techniques and procedures== |
||
[[File:PIA16132-MarsCuriosityRover-CalibrationTarget-20120909.jpg|thumb|left|200px|''[[Color chart|Calibration Target]]'' of the "[[Curiosity rover#Mars Hand Lens Imager .28MAHLI.29|Mars Hand Lens Imager (MAHLI)]]" on the [[Mars]] [[Curiosity rover]] (September 9, 2012) ([http://mars.jpl.nasa.gov/images/MAHLIcaltarget-br2.jpg 3-D image]).]] |
[[File:PIA16132-MarsCuriosityRover-CalibrationTarget-20120909.jpg|thumb|left|200px|''[[Color chart|Calibration Target]]'' of the "[[Curiosity rover#Mars Hand Lens Imager .28MAHLI.29|Mars Hand Lens Imager (MAHLI)]]" on the [[Mars]] [[Curiosity rover]] (September 9, 2012) ([http://mars.jpl.nasa.gov/images/MAHLIcaltarget-br2.jpg 3-D image]).]] |
||
The most common form of calibration aims at adjusting cameras, scanners, monitors and printers for photographic reproduction. The aim is that a printed copy of a photograph |
The most common form of calibration aims at adjusting cameras, scanners, monitors, and printers for photographic reproduction. The aim is that a printed copy of a photograph appears identical in saturation and dynamic range to the original or a source file on a computer display. This means that three independent calibrations need to be performed: |
||
* The camera or scanner needs a device-specific calibration to represent the original's estimated colors in an unambiguous way. |
* The camera or scanner needs a device-specific calibration to represent the original's estimated colors in an unambiguous way. |
||
Line 45: | Line 45: | ||
=== Scanner === |
=== Scanner === |
||
[[File:IT8target.jpg|right|thumb|350px|An [[IT8]].7 Target by [[LaserSoft Imaging]]]] |
[[File:IT8target.jpg|right|thumb|350px|An [[IT8]].7 Target by [[LaserSoft Imaging]]]] |
||
For creating a scanner profile it needs a target source, such as an [[IT8]]-target, an original with many small color fields, which was measured by the developer with a [[photometer]]. The scanner reads this original and compares the scanned color values with the target's reference values. Taking the differences of these values into account an [[ICC profile]] is created, which relates the device |
For creating a scanner profile it needs a target source, such as an [[IT8]]-target, an original with many small color fields, which was measured by the developer with a [[photometer]]. The scanner reads this original and compares the scanned color values with the target's reference values. Taking the differences of these values into account an [[ICC profile]] is created, which relates the device-specific color space ([[RGB color space]]) to a device-independent color space ([[Lab color space|L*a*b* color space]]). Thus, the scanner is able to output with color fidelity to what it reads. |
||
=== Display === |
=== Display === |
||
[[File:ColorHug2 - 03.jpg|thumb|Color calibration of a monitor using ColorHug2, an open source colorimeter, placed on the screen.]] |
[[File:ColorHug2 - 03.jpg|thumb|Color calibration of a monitor using ColorHug2, an open source colorimeter, placed on the screen.]] |
||
For calibrating the monitor a [[Tristimulus colorimeter|colorimeter]] is attached flat to the display's surface, shielded from all ambient light. The calibration software sends a series of color signals to the display and compares the values that were actually sent against the readings from the calibration device. This establishes the current offsets in color display. Depending on the calibration software and type of monitor used, the software either creates a correction matrix (i.e. an [[ICC profile]]) for color values before being sent to the display |
For calibrating the monitor a [[Tristimulus colorimeter|colorimeter]] is attached flat to the display's surface, shielded from all ambient light. The calibration software sends a series of color signals to the display and compares the values that were actually sent against the readings from the calibration device. This establishes the current offsets in color display. Depending on the calibration software and type of monitor used, the software either creates a correction matrix (i.e. an [[ICC profile]]) for color values before being sent to the display or gives instructions for altering the display's brightness/contrast and RGB values through the [[on-screen display|OSD]]. |
||
This tunes the display to reproduce fairly accurately the in-[[gamut]] part of a desired color space. The calibration target for this kind of calibration is that of print stock paper illuminated by [[CIE Standard Illuminant D65|D65]] light at 120 cd/m<sup>2</sup>. |
This tunes the display to reproduce fairly accurately the in-[[gamut]] part of a desired color space. The calibration target for this kind of calibration is that of print stock paper illuminated by [[CIE Standard Illuminant D65|D65]] light at 120 cd/m<sup>2</sup>. |
||
=== Printer === |
=== Printer === |
||
The ICC profile for a printer is created by comparing a test print result using a photometer with the original reference file. The test chart contains known [[CMYK]] colors, whose offsets to their actual L*a*b* colors scanned by the photometer |
The ICC profile for a printer is created by comparing a test print result using a photometer with the original reference file. The test chart contains known [[CMYK]] colors, whose offsets to their actual L*a*b* colors scanned by the photometer result in an ICC profile. Another possibility to ICC profile a printer is to use a calibrated scanner as the measuring device for the printed CMYK test chart instead of a photometer. A calibration profile is necessary for each printer/paper/ink combination. |
||
== See also == |
== See also == |
||
Line 68: | Line 68: | ||
== External links == |
== External links == |
||
* [http://www.dohm.com.au/coca/index.html CoCa |
* [http://www.dohm.com.au/coca/index.html CoCa – www.dohm.com.au/coca/index.html] {{Webarchive|url=https://web.archive.org/web/20120114003424/http://www.dohm.com.au/coca/index.html |date=January 14, 2012 }} Color Camera Calibrator – an open source scanner and digital camera color calibration (ICC profiling) software by Andrew Stawowczyk Long. |
||
{{Color topics}} |
{{Color topics}} |