Colorimetric device and colour determination process

A method of determining an unknown colour of a substance comprising the steps of:

• (i) irradiating the substance using light in at least two different spectral segments each encompassing a different band of wavelengths,
• (ii) detecting light diffusely reflected from the substance and producing a corresponding electrical signal, and
• (iii) using a set of stored/predetermined transform coefficients, calculating from the electrical signal a set of colorimetric coordinates including luminous reflectivity (Y) and chromaticity values (u,v) representing the colour of the surface-under-test (SUT);
• (iv) determining whether or not the calculated colorimetric coordinates are within any one of a plurality of previously-defined contiguous volumes in three-dimensional colour space, the unknown colour being determined as the colour represented by the volume encompassing the calculated coordinates.

A colorimetric device for determining the colour of a surface-under-test (SUT) which, when illuminated, will produce at least diffusely reflected light, comprising:

• a sensor unit having light source means for irradiating the SUT,
• photodetector means for detecting light diffusely reflected from the SUT and producing a corresponding electrical signal, and
• processor means for using a set of stored/predetermined transform coefficients to derive from the electrical signal a set of colorimetric coordinates including luminous reflectivity coordinate (Y) and chromaticity coordinates (u′,v′) together representing the colour of the SUT;
• wherein the processor means determines the colour of the SUT by determining whether or not the derived colorimetric coordinates are within any one of a plurality of previously-defined contiguous volumes in three-dimensional colour space, the unknown colour being determined as the velour represented by the volume encompassing the derived coordinates.