Online Tensor Sparsifying Transform based on Temporal Superpixels from Compressive Spectral Video Measurements

Spectral videos contain highly redundant information across spatial, spectral and temporal axes which can be exploited through a temporal-data-learned sparsifying basis. However, in compressive spectral video acquisition, tackling dictionary learning is time-consuming since it increases the computational complexity and presents drawbacks for realtime processing, where offline learning is required. This paper introduces a tensor-decomposition learning (TenDL) framework for simultaneous online sparsifying and recovering the spatialspectral- temporal information of a spectral video performed on several temporal superpixels (TSP-TenDL) for time processing reduction. The framework is composed of two main stages: preprocessing and joint estimation. The preprocessing stage includes a strategy for a grayscale approximation of the video to provide a suitable initialization of the sparsifying basis to be learned. To fully exploit the high signal correlation, a set of temporal superpixels is estimated from the grayscale approximation, reducing the reconstruction time of the large-scale data. Then, the outcome of the first stage is used to estimate the basis and the signal coefficients, where an optimization problem is solved to learn and reconstruct the basis and the signal, respectively, following a block-descent coordinate strategy. The proposed approach is compared from simulations with an offline-learned based method, traditional matrix-based recovery algorithms and the tensor-based recovery, the two latter using a fixed basis, where TSP-TenDL exhibits higher image quality results and lower computation time. Specifically, our methodology gains up to 7dB in terms of PSNR and a speedup of up to 6.6× compared with state-of-the-art counterparts.