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.
The Mono, GREY16 and RGB16 types are not really calibrated themselves: they are usually whatever you get by loading an image from a file. You’ll usually need an extra step, such as applying an embedded ICC profile, before you get accurate colour.
|Mono||One band 8 bit||Not calibrated|
|sRGB||Three band 8 bit||Screen device space for the sRGB standard|
|GREY16||One band 16 bit||Not calibrated|
|RGB16||Three band 16 bit||Not calibrated|
|Lab||Three band float||The 1976 version of the CIE perceptual colourspace|
|LabQ||Four band 8 bit||Like Lab, but represented as 10:11:11 bits|
|LabS||Three band 16 bit||Like Lab, but represented as 15:16:16 bits|
|LCh||Three band float||Lab, but with polar coordinates|
|XYZ||Three band float||The base CIE colourspace|
|Yxy||Three band float||Sometimes useful for colour meters|
|UCS||Three band float||Highly uniform space from the CMC(l:c) standard|
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.
Images in this format used a packed floating point layout for their pixels. Items in this menu pack and unpack pixels for you.
Use Make Synthetic Colour Chart to make a colour chart image from a matrix of measurements.