Color Theory: How to convert Munsell HVC to RGB/HS

Question

I'm looking at at document that describes the standard colors used in dentistry to describe the color of a tooth. They quote hue, value, chroma values, and indicate they are from the 1905 Munsell description of color:

The system of colour notation developed by A. H. Munsell in 1905 identifies colour in terms of three attributes: HUE, VALUE (Brightness) and CHROMA (saturation) [15]

HUE (H): Munsell defined hue as the quality by which we distinguish one colour from another. He selected five principle colours: red, yellow, green, blue, and purple; and five intermediate colours: yellow-red, green-yellow, blue-green, purple-blue, and red-purple. These were placed around a colour circle at equal points and the colours in between these points are a mixture of the two, in favour of the nearer point/colour (see Fig 1.).

VALUE (V): This notation indicates the lightness or darkness of a colour in relation to a neutral grey scale, which extends from absolute black (value symbol 0) to absolute white (value symbol 10). This is essentially how ‘bright’ the colour is.

CHROMA (C): This indicates the degree of divergence of a given hue from a neutral grey of the same value. The scale of chroma extends from 0 for a neutral grey to 10, 12, 14 or farther, depending upon the strength (saturation) of the sample to be evaluated.

There are various systems for categorising colour, the Vita system is most commonly used in Dentistry. This uses the letters A, B, C and D to notate the hue (colour) of the tooth. The chroma and value are both indicated by a value from 1 to 4. A1 being lighter than A4, but A4 being more saturated than A1. If placed in order of value, i.e. brightness, the order from brightest to darkest would be:

A1, B1, B2, A2, A3, D2, C1, B3, D3, D4, A3.5, B4, C2, A4, C3, C4

The exact values of Hue, Value and Chroma for each of the shades is shown below (16)

So my question is, can anyone convert Munsell HVC into RGB, HSB or HSL?

Hue    Value (Brightness) Chroma(Saturation)
===    ================== ==================
4.5    7.80               1.7
2.4    7.45               2.6
1.3    7.40               2.9
1.6    7.05               3.2
1.6    6.70               3.1
5.1    7.75               1.6
4.3    7.50               2.2
2.3    7.25               3.2
2.4    7.00               3.2
4.3    7.30               1.6
2.8    6.90               2.3
2.6    6.70               2.3
1.6    6.30               2.9
3.0    7.35               1.8
1.8    7.10               2.3
3.7    7.05               2.4

They say that Value(Brightness) varies from 0..10, which is fine. So i take 7.05 to mean 70.5%.

But what is Hue measured in? i'm used to hue being measured in degrees (0..360). But the values i see would all be red - when they should be more yellow, or brown.

Finally, it says that Choma/Saturation can range from 0..10 ...or even higher - which makes it sound like an arbitrary scale.

So can anyone convert Munsell HVC to HSB or HSL, or better yet, RGB?

Answer 1

The hue specification you've given here is incomplete (4.5 should be 4.5Y etc). Since the link is dead, if anyone is interested, the specs are still alive here: http://web.archive.org/web/20071103065312/http://lib.umich.edu/dentlib/Dental_tables/Colorshadguid.html

The only free utility for Munsell conversion I could find was this:

http://web.archive.org/web/20020809130910/standards.gretagmacbeth.com/cmc/munsell.exe

Very old as you can see, but seems to work well. Current programs that can do this are not free:

• http://livingstonmanor.net/Munsell2/index.htm
• http://www.babelcolor.com/main_level/download.htm (this one has a free 14 day trial)

The current holders of the Munsell products are X-Rite, they probably have some conversion solutions as well.

Further, note that the link you supplied includes definitions for the same colors in other color coordinates - namely Yxy and CIE lab*. Both can be freely converted online at http://www.colorpro.com/info/tools/convert.htm or offline with this free color converter