Last edited on May 2, 2010 by gs/ gs. - Home page: WWW StatLab Heidelberg or CD home.

Data set:

Short description

The data set contains colour matching functions of 20 individual observers.

The observers are trying to match a reference light of given frequency lambda by mixing red (r) green (g) and blue (b) light with adjustable intensity.

more information

The data set is from the final report of the Commission Internationl de l'Eclairage (CIE) on the National Physical Laboratory's investigation of colour-matching, the historical experiment which laid the foundation for many modern color matching systems. This is the basis which made colour systems like RGB useful. But far beyond that, it is one of the basic experiments for understanding the human visual colour system.

The green intensity for observer MCB(14) at lambda=620nm is reported as 5.881E-1. This gives an extreme outlier. Presumably the correct value was 5.881E-2, given the lower plot in this display:

outlier removal

The following plot shows the individual date for the r,g,b components in the top rows, together with a smoothed fit. The middle row gives the residuals, that is the differences (observed - fitted value). The outlier has been removed in this plot. The colour code in this plot is not calibrated and should be used for rough orientation only.

color matching

The original data refer to coordinates in RGB space. Each response corresponds to one point in this 3 dimensional space. Here is a movie to show the three dimensional data structure for 20 individual observers. A Quicktime viewer must be installed to view this movie.

The original data set is in four dimensions - one for the regressor, three dimensions for the reponse. Encoding the regresor by colour and using rotation gives a full picture, revealing a one dimension curve imbedded (non plnar) in three space.

Qicktime video: Color matching functions in RGB space for 20 individual observers.

Taking residuals from one dimensional marginal regression gives another view in four dimensional space. It shows a disk in the red/green plane, and a very distinct rod in the direction dominated by blue.

We did not make use of the background theory of colour perception. But the residuals give a picture that fits.

Qicktime video:Color matching function residuals in RGB space for 20 individual observers.

Quicktime for Windows or Macintosh can be downloaded from


Günter Wyszecki & W.S. Stiles (1982) Color Science, 2nd ed. NY: Wiley , pp 817-822
after Stiles and Burch 1959


G.Sawitzki, StatLab Heidelberg

The data analysis has been done using DataDesk.