Represents the "WhitePoint" entry of the lab colour space dictionary object.

It is a required entry defined as part of the PDF 1.0 specification.

It contains an array which contains doubles, representing PDF numeric objects.

Items in this array should have a positive value.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 65, page 148.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 64, page 186.

The white point gives the CIE XYZ of the reference illuminant for the L*a*b* encoding. Its Y value must be 1.0. L* is computed from the Y component of the input XYZ relative to this white point's Y value.