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<HTML><HEAD><TITLE>Xlib Programming Manual: Supplied Gamut Compression Procedures</TITLE></HEAD><BODY><H1 ALIGN=center>6.10.2 Supplied Gamut Compression Procedures</H1>The following equations are useful in describing gamut compressionfunctions:<P><I>CIELab Psychometric Chroma = sqrt(a_star<SUP>2</SUP> + b_star<SUP>2</SUP>)<P><TABLE CELLPADDING=0 CELLSPACING=0><TR><TD ROWSPAN=3><I>CIELab Psychometric Hue = tan<SUP>-1</SUP> <TD ALIGN=center><I>b_star<TR><TD><HR><TR><TD ALIGN=center><I>a_star</TABLE><P>CIELuv Psychometric Chroma = sqrt(u_star sup 2 + v_star sup 2 )</I><P><TABLE><TR><TD ROWSPAN=3><I>CIELuv Psychometric Hue = tan<SUP>-1</SUP> <TD ALIGN=center><I> v_star<TR><TD><HR><TR><TD><I>u_star</TABLE><P>The gamut compression callback procedures provided by Xlib are as follows:<UL><P><LI><B>XcmsCIELabClipL</B><P>This brings the encountered out-of-gamut color specification into the screen's color gamut by reducing or increasing CIE metric lightness (L*) in the CIE L*a*b* color space until the color is within the gamut.If the Psychometric Chroma of the color specification is beyond maximum for the Psychometric Hue Angle,then while maintaining the same Psychometric Hue Angle,the color will be clipped to the CIE L*a*b* coordinates of maximumPsychometric Chroma.See<B><A HREF="../gamut-querying/XcmsCIELabQueryMaxC.html">XcmsCIELabQueryMaxC()</A></B>.No client data is necessary.<P><LI><B>XcmsCIELabClipab</B><P>This brings the encountered out-of-gamut color specification into the screen's color gamut by reducing Psychometric Chroma,while maintaining Psychometric Hue Angle,until the color is within the gamut.No client data is necessary.<P><LI><B>XcmsCIELabClipLab</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by replacing it with CIE L*a*b* coordinatesthat fall within the color gamut while maintaining the originalPsychometric HueAngle and whose vector to the original coordinates is the shortest attainable.No client data is necessary.<P><LI><B>XcmsCIELuvClipL</B><P>This brings the encountered out-of-gamut color specification into the screen's color gamut by reducing or increasing CIE metric lightness (L*)in the CIE L*u*v* color space until the color is within the gamut.If the Psychometric Chroma of the color specificationis beyond maximum for the Psychometric Hue Angle,then, while maintaining the same Psychometric Hue Angle,the color will be clipped to the CIE L*u*v* coordinates of maximumPsychometric Chroma.See<B><A HREF="../gamut-querying/XcmsCIELuvQueryMaxC.html">XcmsCIELuvQueryMaxC()</A></B>.No client data is necessary.<P><LI><B>XcmsCIELuvClipuv</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by reducingPsychometric Chroma, while maintaining Psychometric Hue Angle,until the color is within the gamut.No client data is necessary.<P><LI><B>XcmsCIELuvClipLuv</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by replacing it with CIE L*u*v* coordinatesthat fall within the color gamut while maintaining the originalPsychometric HueAngle and whose vector to the original coordinates is the shortest attainable.No client data is necessary.<P><LI><B>XcmsTekHVCClipV</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by reducing or increasing the Value dimensionin the TekHVC color space until the color is within the gamut.If Chroma of the color specification is beyond maximum for the particular Hue,then, while maintaining the same Hue,the color will be clipped to the Value and Chroma coordinatesthat represent maximum Chroma for that particular Hue.No client data is necessary.<P><LI><B>XcmsTekHVCClipC</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by reducing the Chroma dimensionin the TekHVC color space until the color is within the gamut.No client data is necessary.<P><LI><B>XcmsTekHVCClipVC</B><P>This brings the encountered out-of-gamut color specification into thescreen's color gamut by replacing it with TekHVC coordinatesthat fall within the color gamut while maintaining the original Hueand whose vector to the original coordinates is the shortest attainable.No client data is necessary.</UL><H5 ALIGN=right><I>Next: <A HREF="prototype-white-point-adjustment.html">Prototype White Point Adjustment Procedure</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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