This menu groups operations on colorimetric images and patches of colour. A colour patch is three float numbers plus a tag saying how those number should be interpreted as colour (for example, as a colour in CIE LAB colourspace). You can drag and drop between colour patches, and into and from the inkwell in an image paint window. Double-left-click on a colour patch to open a colour select dialog.
nip2 has 9 main types of colorimetric image, see Table 5.1. All these types are D65 (that is, daylight) absolute colorimetric. When it displays an image, nip2 uses the Type field in the image header as a hint on how to transform the numbers in the image into RGB for the display. The current Type is displayed at the end of the caption line below an image thumbnail.
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D65 to D50 and D50 to D65 transform using either a 3x3 matrix which is numerically minimal in XYZ space with respect to the colours on a Macbeth Color Checker, or via Bradford cone space. The Bradford transform omits the power term.
The final two items go from XYZ to LAB and back, but with D50 normalisation rather than the default D65.
You need to be careful about colour temperature issues: all printers work with D50, and nip2 is all D65. Use the D65 to D50 interchange items in the Colour Temperature menu to swap back and forth.
All printers also work with relative colorimetry, and nip2 is generally absolute. Use Absolute to Relative to scale an absolute colorimetric image by a media white point.
Use Make Synthetic Colour Chart to make a colour chart image from a matrix of measurements.