A new adaptive compressive sensing-based method is proposed for recovering spectral reflectance from a single RGB image by using dynamic principal components that are calculated from the dynamic eigenvector subspace. The dynamic eigenvector subspace is formed by its similarity to the RGB trichromatic values of the original and not just the neighbors to the target. Unlike recovering spectral reflectance using fixed principal components, the novelty of the proposed method is the use of the dynamic principal component by applying an adaptive compressive sensing method under the dynamic eigenvector subspace. The effectiveness of the proposed and the existing methods are compared by reviewing the spectral recovery accuracy under different illuminants and cameras. As the spectral recovery results show, the proposed method is an effective spectral reflectance recovery method.

An efficient procedure for recovering spectral reflectance using an object’s tristimulus values under multi-illuminants is proposed by adapting with the characteristics of the testing sample to obtain the transformation matrix of pseudoinverse. Specifically, we propose the reference illuminants selection strategy and local sample weighted strategy to obtain the optimal transformation matrix under multi-illuminants condition. Selecting the reference illuminants are based on the result of the spectral angle mapper (SAM) statistics. The number of the selected local training samples and the weighted local samples can be determined by using the multicolor space Euclidean distance. To compare the experimental results, the proposed method significantly increases the spectral and colorimetric accuracy for the spectral reflectance recovery process.

A non-homogeneous composite guided-mode resonant (GMR) filter structure is proposed that avoids the multi-mode resonance effect and increases resonant wavelength tuning range. The composite filter structure is engineered using a combination of a varied-line-spacing (VLS) grating layer with a wedge-shaped waveguide layer. The grating is fabricated by holographic interference lithography (IL), while the wedge-shaped layer is fabricated using masked ion beam etching (MIBE) technology. The resonant wavelength has been observed to vary as a function of the spatial position on the structure. In the fabricated structure, over a length of 30 mm, the grating period increment is measured to be 149.2 nm, whereas the increment of the waveguide film thickness is approximately 100 nm. Experimental results show that a primary reflectance peak is achieved spanning a wavelength range of 805.8-1119.0 nm. The device is designed using the rigorous coupled-wave analysis (RCWA) method, and the proposed device is toward the practical application of GMR filters.

An optimized method based on dynamic partitional clustering was proposed for the recovery of spectral reflectance from camera response values. The proposed method produced dynamic clustering subspaces using a combination of dynamic and static clustering, which determined each testing sample as a priori clustering center to obtain the clustering subspace by competition. The Euclidean distance weighted and polynomial expansion models in the clustering subspace were adaptively applied to improve the accuracy of spectral recovery. The experimental results demonstrated that the proposed method outperformed existing methods in spectral and colorimetric accuracy and presented the effectiveness and robustness of spectral recovery accuracy under different color spaces.