Sudoku multispectral filter arrays for spectral snapshot cameras
Date
2023
Authors
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Volume Title
Publisher
University of Delaware
Abstract
Multispectral filter arrays (MSFAs) are optical components that incorporate pixelated colored filters to selectively filter light at different wavelengths. MSFAs are used in a range of multispectral imaging (MSI) systems such as mosaic color image sensing and compressive spectral imaging (CSI). The former being cameras with generalized Bayer color filter masks that are used in RGB cameras, and the latter where the color filter array is used in concert with a dispersive element to compressively capture spectral images with a 2D focal plane array. Several approaches to optimize the color patterns in MSFAs have been proposed; notably, the placement of the optical elements in most of the proposed approaches are guided by generalizing the constraints defined by Bayer half a century ago. While Bayer dither matrices place constraints spatially on 2D dimensions, MSFA's generalize these constraints to the 3D spatial and spectral dimensions. The principles, however, remain the same and MSFA design reduces to improving the array matrices to adhere to the 3D spatio spectral constraints. This thesis proposes a new, simple, yet surprisingly effective optimization strategy guided by the principles of the worldwide popular combinatorial puzzle "Sudoku," which provides the mechanisms to constrain the spatial distribution of colors in the MSFA that result in homogeneous patterns with high frequency components across the spatial and spectral dimensions --- traits that are desirable in MSFA for improved image reconstruction. The Sudoku guidelines naturally provide colored patterns that follow blue-noise distributions characterized by the absence of low frequency components. Notably, if the Sudoku "single digit" constraints along cells, rows, and columns are further generalized to gradually have inter-cell constraints, further separating same digits across cells, the resulting colored patterns become increasingly periodic. The proposed framework thus provides the mechanisms to generate a broad spectrum of colored patterns, from aperiodic random blue-noise patterns, to periodic Bayer-like patterns. All characterized by the absence of low frequency components. Simulations show that mosaic and CASSI measurements using Sudoku color codes lead to multispectral data cube reconstructions that are comparable if not better than those produced using state-of-the-art MSFA design strategies.
Description
Keywords
Aperture codes, CASSI measurements, Compressive spectral imaging, Multispectral imaging, Multispectral filter arrays