Improvement on reflective color measurement using a tri-color LED by multi-point calibration

We present a reflective color measurement using a tri-color LED. The color of the tested sample was determined by measuring three reflected intensities in different colors. Modulation/demodulation technique was used to distinguish three reflected intensities. The three reflected signals can be processed by a computer to give the (x, y) coordinate in CIE chromaticity diagram. Since three-points measurements give poor estimate on the whole spectral reflectance, the predicted results deviate much from those measured from some well-calibrated instrument. We have also successfully developed a calibrating procedure to correct it.