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(v13) RelativeWhitePoint

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

RelativeWhitePoint is an array of three numbers containing XYZ values for the media white. The RelativeWhitePoint key is a Harlequin extension that is optionally applied to the standard PostScript language and PDF color spaces of CIEBasedA, CIEBasedABC, CIEBasedDEF, CIEBasedDEFG, Lab, CalRGB, and CalGray, and to CRDs. CRDs may be used directly from the graphics state, or in Legacy CRDs (see (v13) Legacy CRDs for more information). The intention is that the RelativeWhitePoint represents the media white of the device modeled by the color space or rendering. All these resources are required to contain a WhitePoint key for the XYZ of the illuminant. If the RelativeWhitePoint key is not present it defaults to the WhitePoint.

Standard PostScript language and PDF device independent color resources contain one conversion that encodes for one rendering intent. The setrenderingintent extension (see (v13) Rendering intent), would not normally have any effect when these resources are used. The RelativeWhitePoint extension provides a way of switching between a relative and absolute intent when using these resources.

A chromatic adaptation step is always performed between the color space and the CRD using their respective WhitePoint values, as described in (v13) Chromatic Adaptation Transform (CAT).

If a relative intent is used, the RIP performs an additional color mapping. The RIP treats the RelativeWhitePoint within the PostScript language resources identically to the media white point within the mediaWhitePointTag of ICC profiles. The white point mapping is the same as that done for mediaWhitePointTag values for source and destination ICC profiles. This step normally ensures that the media white of the color space results in rendering white on the output medium.

An example of the use of RelativeWhitePoint is this XYZ color space, where the media white is somewhat darker than the illuminant:

[ /CIEBasedABC
		/WhitePoint [0.9642 1 0.8249]
		/RangeABC [0 0.9642 0 1 0 0.8249]
		/RangeLMN [0 0.9642 0 1 0 0.8249]
		/RelativeWhitePoint [0.9065 0.9349 0.8119]

RelativeWhitePoint would normally only be set in resources for devices such as printers where the media white is distinct from the illuminant. It would not normally be set in resources for devices such as displays where there is no such distinction.

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