Chromaticity of the image's white point. 0x013E ∙ 318
IG_ISIS_TAG_WHITEPOINT specifies the chromaticity of the white point of the image. This is the chromaticity when each of the primaries has its ReferenceWhite value.
IG_ISIS_TAG_TYPE_RATIONAL
Drivers for scanners that support setting white point chromaticity. Currently, the only driver that supports this is the Dunord ISIS driver DUNISIS.PXW.
A rational value specifying the white point.
Refer to the TIFF specification.