Editing CMYK color model (section)

== Conversion ==
[[File:NIEdot367.jpg|thumb|Early representation of the three-color process (1902)]]
[[File:NIEdot367-modern.jpg|thumb|Approximation of the image using CMY colors.]]
Since RGB and CMYK spaces are both device-dependent spaces, there is no simple or general conversion formula that converts between them. Conversions are generally done through [[color management]] systems, using [[color profile]]s that describe the spaces being converted. An ICC profile defines the bidirectional conversion between a neutral "profile connection" color space (CIE XYZ or Lab) and a selected [[colorspace]], in this case both RGB and CMYK. The precision of the conversion depends on the profile itself, the exact methodology, and because the gamuts do not generally match, the [[rendering intent]] and constraints such as ink limit.

ICC profiles, internally built out of lookup tables and other transformation functions, are capable of handling many effects of ink blending. One example is the [[dot gain]], which show up as non-linear components in the color-to-density mapping. More complex interactions such as Neugebauer blending can be modelled in higher-dimension lookup tables.

The problem of computing a colorimetric estimate of the color that results from printing various combinations of ink has been addressed by many scientists.<ref name = Sharma>{{cite book | title = Digital Color Imaging Handbook | author = Gaurav Sharma | year = 2003 | publisher = CRC Press | isbn = 0-8493-0900-X | url = https://books.google.com/books?id=AkByHKRGTsQC&pg=PA68|page=68}}</ref> A general method that has emerged for the case of halftone printing is to treat each tiny overlap of color dots as one of 8 (combinations of CMY) or of 16 (combinations of CMYK) colors, which in this context are known as [[Neugebauer primary|Neugebauer primaries]]. The resultant color would be an area-weighted colorimetric combination of these primary colors, except that the [[Dot gain#Yule–Nielsen effect and "optical dot gain"|Yule–Nielsen effect]] of scattered light between and within the areas complicates the physics and the analysis; empirical formulas for such analysis have been developed, in terms of detailed dye combination absorption spectra and empirical parameters.<ref name = Sharma/>

Standardization of printing practices allow for some profiles to be predefined. One of them is the US [[Specifications for Web Offset Publications]], which has its ICC color profile built into some software including [[Microsoft Office]] (as [[Agfa-Gevaert|Agfa]] RSWOP.icm).<ref>{{cite web |title=KB933845 How to obtain and install the Microsoft Standard CMYK Profile (RSWOP.icm) in Windows Vista |url=https://www.betaarchive.com/wiki/index.php/Microsoft_KB_Archive/933845 |website=Beta Archive > Microsoft KB Archive |access-date=1 September 2023 |quote=The RSWOP.icm cyan-magenta-yellow-black (CMYK) color profile targets the "Specifications for Web Offset Publications" (SWOP) printing standard. This color profile is installed when you install Microsoft Office. However, by default, this color profile is not installed in Windows Vista. Therefore, you may experience unexpected results when you use certain programs that manage color.|date=March 15, 2007}}</ref>

The device-dependency of RGB and CMYK also means that a set of RGB or CMYK values cannot uniquely represent a color, so long as no device or paper–ink–process combination is specified. With RGB the [[sRGB]] standard is widespread enough to be the implied default, but there is not a single form of CMYK which is widespread enough to be the default.