Viscarra Rossel,R.A., Minasny,B., Roudier,P. and McBrantney,A.B.(2006): Colour space models for soil science. Geoderma, 133, 320-337.


 Soil colour is an important soil property. It is frequently used by soil scientists for the identification and classification of soil. It is also used as an indicator of field soil physical, chemical and biological properties as well as of the occurrence of soil processes. Measurements of soil colour are commonly made using the Munsell soil colour charts. A number of other colour space models, that overcome some of the limitations of the Munsell HVC system exist and may be used to more aptly describe soil colour. we looked at nine colour space models and a redness index: Munsel HVC, RGB, decorrelated RGB (DRGB), CIE XYZ, CIE Yxy, CIELAB, CIELUV, CIELHC, and Helmholtz chromaticity coordinates. The aim of this paper are to (i) describe the algorithms used for transformations between these colour space models, (ii) compare their representational qualities and their relationships to the Munsell soil colour system, and (iii) in a case study, determine the model best suited to describe the relationship between soil colour and soil organic carbon. The type of colour model to use will depend on the purpose. For example, if soil colour is being used for merely descriptive purposes, then the Munsell HVC system will remain appropriate; if it is being used for numerical statistical or predictive analysis, as in our case study, then colour models that use Cartesian-type coordinate systems will be more useful. Of these, the CIELUV and CIELCH models appear to be more suitable for predictions of soil organic carbon.

Keywords: Soil colour; Munsell soil colour; CIE; RGB; Helmholtz chromaticity coordinates; Soil organic carbon』

1. Introduction
 1.1. Colour space models
  1.1.1. Munsell HVC soil colour system
  1.1.2. RGB
  1.1.3. CIE XYZ CIE Yxy
  1.1.4. Helmholtz chromaticity
  1.1.5. CIELUV and CIELAB
2. Methods
 2.1. Munsell HVC to CIE XYZ
  2.1.1. CIE XYZ to Munsell HVC
 2.2. CIE XYZ to Yxy
 2.3. CIE xy chromaticity to Helmholtz chromaticity coordinates
  2.4.1. CIELCH
  2.4.2. Redness index
 2.5. CIE XYZ to RGB
  2.5.1. RGB to CIE XYZ
 2.6. Decorrelation of RGB data
 2.7. Case study: soil colour and its relationship to soil organic carbon
  2.7.1. Soil sampling and laboratory analyses
  2.7.2. Soil sample preparation for colour measurements
  2.7.3. Munsell measurements of soil colour
  2.7.4. Spectrometric measurements of soil colour
  2.7.5. Relationship between soil colour and soil organic carbon (OC)
3. Results
 3.1. Relationships between Munsell HVC and other colour space models for soil
 3.2. Case study: soil colour an its relationship to soil organic carbon
 3.3. Relationship between colour model parameters and soil organic carbon (OC)
4. Conclusions