CIE 1931 RGB Colour Space

This colour model tries to mimic the colours percieved by the human eye using RGB Tristimulus values.

It was defined by two independent experiments in 1920 by W. David Wright with ten observers and John Guild with seven observers.

On the basis of these experiments, three colour matching functions were formed. These results were summarized and standardized as the CIE RGB colour matching functions \(\bar{r}(\lambda)\), \(\bar{g}(\lambda)\) and \(\bar{b}(\lambda)\), obtained using three monochromatic primaries at standardized wavelengths of 700 nm (red), 546.1 nm (green) and 435.8 nm (blue). These colour matching functions define what is known as the 1931 CIE Standard Observer.

The RGB Tristimulus values for any colour could computed using these colour matching functions to form the CIE 1931 RGB colour space as:

\(R=\int_{\lambda}S(\lambda)\bar{r}(\lambda)d\lambda\)
\(G=\int_{\lambda}S(\lambda)\bar{g}(\lambda)d\lambda\)
\(B=\int_{\lambda}S(\lambda)\bar{b}(\lambda)d\lambda\)

where \(\lambda\in [380, 780]\),
\(S(\lambda)\) is the Spectral Power Distribution function of the colour source
and \(\bar{r}(\lambda)\), \(\bar{g}(\lambda)\) and \(\bar{b}(\lambda)\) are the colour matching functions in the standard observer