How do you convert to and from Munsell colour space ?

Converting to or from Munsell is a complex matter as this colour space has been created visually before the digital age and it contains only a limited list of colours. In short, it is not a real colour space but closer to a colour chart (like pantone…). So translating to a colour space is prone to interpretation. It is also complex to compute the gaps between 2 Munsell colours as this had never been designed for that.

However, we can try to approximate it thanks to the work of students at RIT which have compiled and made measurement of the Munsell Book of Color. So this data are considered as the base data for converting. However there is another issue there : the table are given in Spectrum, Cie Values and RGB colour spaces. As there are also different methods for converting one colour space to another, there might be differences depending on which source has been used.

In iModelKit, we use Cie values (we plan to use spectrum directly later on). So for standard Munsell values (the ones from the book), there should be no differences between converters, provided they use the same set of values.

The other issue comes when using the method to compute colours that are between 2 colours of the book : You have to interpolate the values to find a correct conversion. There are several ways to interpolate the results, the 2 main being Centore and Newhall which uses different linear interpolation approach. Unfortunately, we found that these methods gave poor results when trying to convert values back. So we use our own 3D interpolation method which is far better (98% of conversions are under a Delta E of 0.5). However, this is still approximation as Munsell space has simply not been designed for this.