Wen Yu-Che, Wen Senfar, Hsu Long, Chi Sien
Department of Electrophysics, National Yang Ming Chiao Tung University, No. 1001 University Road, Hsinchu 30010, Taiwan.
Department of Electrical Engineering, Yuan Ze University, No. 135 Yuan-Tung Road, Taoyuan 32003, Taiwan.
Sensors (Basel). 2022 Nov 4;22(21):8498. doi: 10.3390/s22218498.
The spectrum of light captured by a camera can be reconstructed using the interpolation method. The reconstructed spectrum is a linear combination of the reference spectra, where the weighting coefficients are calculated from the signals of the pixel and the reference samples by interpolation. This method is known as the look-up table (LUT) method. It is irradiance-dependent due to the dependence of the reconstructed spectrum shape on the sample irradiance. Since the irradiance can vary in field applications, an irradiance-independent LUT (II-LUT) method is required to recover spectral reflectance. This paper proposes an II-LUT method to interpolate the spectrum in the normalized signal space. Munsell color chips irradiated with D65 were used as samples. Example cameras are a tricolor camera and a quadcolor camera. Results show that the proposed method can achieve the irradiance independent spectrum reconstruction and computation time saving at the expense of the recovered spectral reflectance error. Considering that the irradiance variation will introduce additional errors, the actual mean error using the II-LUT method might be smaller than that of the ID-LUT method. It is also shown that the proposed method outperformed the weighted principal component analysis method in both accuracy and computation speed.
相机捕获的光谱可以使用插值方法进行重建。重建光谱是参考光谱的线性组合，其中加权系数通过对像素信号和参考样本进行插值计算得出。这种方法被称为查找表（LUT）方法。由于重建光谱形状依赖于样本辐照度，所以它与辐照度有关。由于现场应用中辐照度可能会变化，因此需要一种与辐照度无关的查找表（II-LUT）方法来恢复光谱反射率。本文提出了一种在归一化信号空间中对光谱进行插值的II-LUT方法。以D65照射的孟塞尔色卡作为样本。示例相机为三色相机和四色相机。结果表明，所提出的方法能够实现与辐照度无关的光谱重建并节省计算时间，但代价是恢复的光谱反射率存在误差。考虑到辐照度变化会引入额外误差，使用II-LUT方法的实际平均误差可能小于ID-LUT方法。研究还表明，所提出的方法在精度和计算速度方面均优于加权主成分分析方法。
