DECREASING COLOUR MEASURING SYSTEMATIC ERROR IN IMAGE TAKING TRISTIMULUS COLORIMETERS

In image taking colorimetry the tristimulus technique is still the practical viable method if the measuring time should be kept in limits. Due to the fact that the number of coloured glasses that are available to adjust the detector responsivity to the CIE colour matching functions (CMF) is limited and the thickness of the filters can not be increased without limits to decrease the adjustment error, as this would decrease the sensitivity of the colorimeter, the systematic errors of such instruments is considerable. A possibility to decrease the systematic errors is to increase the number of channels in the measurement, i.e. to use beside the Xlong, Xshort, Y, Z channels a fifth, sixth, etc. channel, and to adjust to the CIE colour matching functions by the help of matrixing. We have investigated what the reasonable number of channels should be, designed a five channel image taking colorimeter, determined the optimum matrix for this arrangement and tested what the systematic errors in measuring a number of coloured and white LEDs is. As in case of matrixing the noise propagation can increase the measurement uncertainty, also the influence of noise was investigated.