Abstract
Shading effects induced by illumination and local object surface orientation could strongly deteriorate the accuracy of colour imaging. Therefore, a shading correction is needed for high colour fidelity. In this work a 3D model based inverse rendering approach is proposed for a narrowband multispectral 3D colour imaging system with a calibrated extern broadband light source. The colourimetric evaluation with an X-Rite colour checker shows that the proposed method could ensure a mean colour difference value CIEDE2000 ΔE < 3 for the viewing angle range -30° to 30°, while the maximal improvement factor concerning mean ΔE comes to 2.86.
Highlights
Introduction and related workMultispectral colour imaging technique could transcend the accuracy limitation of conventional RGB cameras and recognize minor colour differences
It consists of a halogen lamp emitting at 30° as permanent illumination for the multispectral colour measurement and a sensor head composed of one digital pattern projector and two 8-bit multispectral filter wheel cameras [11] for the synchronous colour and 3D shape acquisition
The rendered spectral values are mapped to the CIE XYZ colour space under standard illuminant D65 using the linear matrix transform method in [14], whereas the matrix coefficients were estimated by a colour calibration with the X-Rite colour checker Passport
Summary
Multispectral colour imaging technique could transcend the accuracy limitation of conventional RGB cameras and recognize minor colour differences. At non-planar objects the local surface orientation is overall varying, so it is impossible to realize the CIE geometries for all object surface points, leading to shading effects that downgrade the colour accuracy. For this problem, an inverse image rendering as shading correction could be performed to retrieve the pure material characteristics from raw image data.
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