We propose a unified view of non-local methods for single-image denoising, for which BM3D is the most popular representative, that operate by gathering noisy patches together according to their similarities in order to process them collaboratively. Our general estimation framework is based on the minimization of the quadratic risk, which is approximated in two steps, and adapts to photon and electronic noises. Relying on unbiased risk estimation (URE) for the first step and on ``internal adaptation'', a concept borrowed from deep learning theory, for the second, we show that our approach enables to reinterpret and reconcile previous state-of-the-art non-local methods. Within this framework, we propose a novel denoiser called NL-Ridge that exploits linear combinations of patches. While conceptually simpler, we show that NL-Ridge can outperform well-established state-of-the-art single-image denoisers.

我们提出了一种统一的非局部方法的观点，用于单图像去噪，其中BM3D是最流行的代表，根据它们的相似性将噪声补丁收集在一起以进行协同处理。我们的一般估计框架基于二次风险的最小化，在两个步骤中近似，并适应光子和电子噪声。在第一步中依靠无偏风险估计（URE），在第二步中依靠从深度学习理论中借鉴的“内部适应”概念，我们展示了我们的方法能够重新解释和融合先前的最先进的非局部方法。在这个框架内，我们提出了一种名为NL-Ridge的新型去噪算法，它利用了补丁的线性组合。虽然在概念上更简单，但我们展示了NL-Ridge可以胜过成熟的最先进的单图像去噪算法。

图像去噪的非局部参数方法统一框架