An Imaging System for Fourier Coefficients of Spectral Reflectance

This paper proposes a system for acquiring the images of complex Fourier coefficients of the spectral reflectance of an object up to the second order at an ordinary frame rate. This feature is realized by a correlation camera and a special illumination called sinusoidally-modulated phase-shift spectral illumination (SMPSSI). The correlation camera produces the temporal correlation between the intensity signal of incident light and external global reference signals pixel by pixel in every frame. The SMPSSI consists of a sum of spectral illuminations sinusoidally modulated at different frequencies with wavelength-linear phase shifts. The proposed system realizes high spectral resolution by performing spectral correlation with sinusoidal reference spectra in the wavelength domain, while maintaining the same temporal and spatial resolution as that of an ordinary video camera. An experimental system is developed with a digital correlation camera and a programmable spectral light source. Experimental results on color guide chips confirm that the proposed system extracted the Fourier coefficients up to the second order accurately.