Measuring Spectral Reflectance and 3D Shape Using Multi-primary Image Projector

This paper presents a method to measure spectral reflectance and 3D shape of an object. For realizing these measurements, we applied a multi-primary image projector as a computational illumination system. This multi-primary image projector employs a light source which is programmable and can reproduce any spectral power distributions. In other words, the projector can reproduce 2D pattern projections with arbitrary spectra. In our actual measurements, we developed an imaging system by synchronizing the multi-primary image projector and a highspeed monochrome camera. First, the surface spectral reflectance of an object in a darkroom was obtained based on a finite-dimensional linear model of spectral reflectances. In the spectral reflectance measurements, nine basis images were projected and captured by the synchronized imaging system. Then spectral reflectance at each camera image coordinate was estimated from the captured nine images. Next, structured lights were projected for reconstructing 3D shape. We applied eight binary image projections and a conventional 3D shape reconstruction algorithm to our study. In summary, seventeen images were projected and captured for measuring spectral reflectance and 3D shape. The projection and capturing speed of the seventeen images is 0.085 s on the system specification. In the validation experiments, we could obtain spectral reflectance of X-rite ColorChecker with the average color difference \(\varDelta E_{ab}^{*}\) of approximately 4. We also confirmed that precise 3D shapes could be reconstructed by our method.