Hi,
I have written a new plug-in for GIMP3.2 named XYZ Pixel Value Calculator.
This plug-in enables you pixel value calculation (addition, subtraction, multiply, divide, Gamma application) in XYZ color space.
This plug-in has XYZ and RGB tone curve graphs on its dialog as XYZ Sigmoid curve plug-in, so users can easily confirm what they does. And this plug-in premises operating in sRGB color space, so if your image is applied other color space the result may be inappropriate.
Wow @yasuo, you’re very busy! 
I’m curious, what is the use case for this plugin? What inspired you to create it?
Hi,
The first purpose of this plug-in it is to help intuitive understanding of XYZ primaries or color space with its tone curve graph.
XYZ color space conversion is used in many image processing programs. Much of its usages are as intermediate color space in color space conversion, but some programs use it as working color space in image processing. However XYZ primaries are imaginary and it is difficult to understand them intuitively. This plug-in may help such understanding and to make new ideas of image processing.
The second purpose is as below.
I am much interested in restoration of faded film images. The condition of film fading varies greatly, and various restoration methods or tools are needed for the restoration. Therefor I try to make new various restoration tools for it which aren’t known ever even if its usability is unknown.
Are there any safety features to prevent user from producing false or out-of-gamut colours?
@chuckhenrich Y is the only axis that I would be comfortable adjusting.
Hi,
It doesn’t contain any gamut compression or adjustment, as its main purpose is to know simply the conversion results. So the values out of sRGB will be simply clipped.
