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<HTML><HEAD><TITLE>Xlib Programming Manual: Supplied White Point Adjustment Procedures</TITLE></HEAD><BODY><H1 ALIGN=center>6.10.4 Supplied White Point Adjustment Procedures</H1>White point adjustment procedures provided by Xlib are as follows:<UL><P><LI>XcmsCIELabWhiteShiftColors<P>This uses the CIE L*a*b* color space for adjusting the chromatic characterof colors to compensate for the chromatic differences between the sourceand destination white points.This procedure simply converts the color specifications to <B>XcmsCIELab</B>using the source white point and then converts to the target specificationformat using the destinations white point.No client data is necessary.<P><LI><B>XcmsCIELuvWhiteShiftColors</B><P>This uses the CIE L*u*v* color space for adjusting the chromatic characterof colors to compensate for the chromatic differences between the sourceand destination white points.This procedure simply converts the color specifications to <B>XcmsCIELuv</B>using the source white point and then converts to the target specificationformat using the destinations white point.No client data is necessary.<P><LI><B>XcmsTekHVCWhiteShiftColors</B><P>This uses the TekHVC color space for adjusting the chromatic characterof colors to compensate for the chromatic differences between the sourceand destination white points.This procedure simply converts the color specifications to<B>XcmsTekHVC</B>using the source white point and then converts to the target specificationformat using the destinations white point.An advantage of this procedure over those previously describedis an attempt to minimize hue shift.No client data is necessary.</UL>From an implementation point of view,these white point adjustment procedures convert the color specificationsto a device-independent but white-point-dependent color space (for example, CIE L*u*v*, CIE L*a*b*, TekHVC) using one white pointand then converting those specifications to the target color space using another white point.In other words,the specification goes in the color space with one white point but comes out with another white point, resulting in a chromatic shift based on the chromatic displacementbetween the initial white point and target white point.The CIE color spaces that are assumed to be white-point-independentare CIE u'v'Y, CIE XYZ, and CIE xyY.When developing a custom white point adjustment procedure that uses adevice-independent color space not initially accessible for use in thecolor management system, use<B><A HREF="../management-extensions/XcmsAddColorSpace.html">XcmsAddColorSpace()</A></B>to insure that it is added.<P>As an example, if the CCC specifies a white point adjustment procedureand if the Client White Point and Screen White Point differ, the<B><A HREF="../XcmsAllocColor.html">XcmsAllocColor()</A></B>function will use the white point adjustmentprocedure twice: <UL><P><LI>Once to convert to<B>XcmsRGB</B><P><LI>A second time to convert from<B>XcmsRGB</B></UL><P>For example, assume the specification is in<B>XcmsCIEuvY</B>and the adjustment procedure is<B>XcmsCIELuvWhiteShiftColors</B>.During conversion to<B>XcmsRGB</B>,the call to <B><A HREF="../XcmsAllocColor.html">XcmsAllocColor()</A></B>results in the following series of color specification conversions:<UL><P><LI>From <B>XcmsCIEuvY</B>to<B>XcmsCIELuv</B>using the Client White Point<P><LI>From <B>XcmsCIELuv</B>to<B>XcmsCIEuvY</B>using the Screen White Point<P><LI>From<B>XcmsCIEuvY</B>to<B>XcmsCIEXYZ</B>(CIE u'v'Y and XYZ are white-point-independent color spaces)<P><LI>From <B>XcmsCIEXYZ</B>to <B>XcmsRGBi</B><P><LI>From <B>XcmsRGBi</B>to<B>XcmsRGB</B></UL>The resulting RGB specification is passed to<B><A HREF="../XAllocColor.html">XAllocColor()</A></B>,and the RGBspecification returned by<B><A HREF="../XAllocColor.html">XAllocColor()</A></B>is converted back to <B>XcmsCIEuvY</B>by reversing the color conversion sequence.<H5 ALIGN=right><I>Next: <A HREF="../gamut-querying/">Gamut Querying Functions</A></I></H5><HR><ADDRESS><A HREF="http://tronche.com/">Christophe Tronche</A>, <A HREF="mailto:ch.tronche@computer.org">ch.tronche@computer.org</A></ADDRESS></BODY></HTML>⌨️ 快捷键说明
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