For a damaged image, the loss of pixel information can be roughly divided into two categories, random missing and non-random missing. The missing of an entire row or column of the image is a specific structural missing pattern that is extremely difficult to deal with. Although most of the existing methods have partially fixed this information missed problem, the diffusion-based methods tend to produce blur, the exemplar-based methods are prone to error filling, and the neural network-based methods are highly dependent on data, which cannot handle this special structural missing very well. Using the nonlocal self-similarity prior and the low-rank prior, we present multidirectional search and nonlocal low-rank tensor completion (MS-NLLRTC) algorithm based on the tensor ring (TR) decomposition and multidirectional search (MS). The MS method is a newly proposed method that can search similar patches much more diversified. Using MS method, we directly stack the similar patches into a three-dimensional similar tensor instead of pulling them into column vectors, then the similar tensor can be completed by TR decomposition. The optimization results can be obtained by leveraging the alternating direction method under the augmented Lagrangian multiplier framework. Moreover, we add a weighted nuclear norm to the tensor completion model (WNLLRTC), achieving a better inpainting performance. We also combine a noise removal method with WNLLRTC algorithm, which can handle image random missing and image noise removal simultaneously. Experimental results indicate that our proposed algorithms are competitive with some state-of-the-art inpainting algorithms in terms of both numerical evaluation and visual quality.
We present an improved Criminisi image inpainting algorithm through kriging pretreatment and facet model. We propose three improvement strategies. First, we propose an improved priority. A priority used in Criminisi algorithm consists of confidence term and data term. As iteration progresses, the confidence term is updated and plays a key role in the confidence term of the next edge block. At the same time, the confidence term gradually tends to 0, leading to a weakening of the role of priority, and ultimately affecting the repair effect. We propose an improved priority, which is represented by a piecewise function. Importantly, this improved priority reduces the risk of being weakened during iteration. Second, Criminisi algorithm uses fixed-size sample blocks to repair damaged images, regardless of whether the image content is a textured area or a structure area. We introduce an adaptive method to select sample block size based on the facet model. The size of the sample block is adaptively adjusted for different image contents, thereby improving the quality of the repaired image. Third, we show a weighted sum of squares differences matching principle based on the facet model. The matching formula is determined by the pixel gray value of a sample block and the structure value of four directions, which improves matching accuracy between target block and optimal matching block. Finally, experimental results show that the proposed algorithm is competitive with some state-of-the-art inpainting techniques in terms of both objective metrics and subjective visual inspection.
We present a method for image denoising based on singular value shrinkage that fuses soft and hard thresholds. The technique simply groups similar patches from a noisy image as low-rank matrices and shrinks the singular values by the combination of soft and hard thresholds. On one hand, a hard threshold approximation method based on nonlocal self-similarity and low-rank approximation is used for fast selection of hard threshold; on the other hand, a soft threshold selection method based on random matrix and asymptotic matrix reconstruction theory is designed. In addition, we also propose an adaptive backward projection algorithm based on image phase congruency and gradient calculation so that the input images participating in the iteration are adaptive. This method improves the traditional fixed coefficient backward projection method and makes the robustness of the algorithm better. The experimental results of denoising and enhancement for a number of natural images show that the proposed algorithms have significant improvement in both subjective visual effect and objective quantization index by comparing with some related state-of-the-art denoising algorithms.
As a high-resolution imaging mode of biological tissues and materials, optical coherence tomography (OCT) is widely used in medical diagnosis and analysis. However, OCT images are often degraded by annoying speckle noise inherent in its imaging process. Employing the bilateral sparse representation an adaptive singular value shrinking method is proposed for its highly sparse approximation of image data. Adopting the generalized likelihood ratio as similarity criterion for block matching and an adaptive feature-oriented backward projection strategy, the proposed algorithm can restore better underlying layered structures and details of the OCT image with effective speckle attenuation. The experimental results demonstrate that the proposed algorithm achieves a state-of-the-art despeckling performance in terms of both quantitative measurement and visual interpretation.
Image denoising while preserving image features is a key problem in image processing and computer vision. This letter proposes an adaptive mixed method for image restoration. First, this method decomposes a given image as the sum of two components: geometric structure and oscillating pattern according to Meyer's theory. Second, a coupled bidirectional diffusion equation is used to restore the structure part, and a nonlocal means filter is used to remove noise in the oscillating part. Experimental results show advantages of this method in feature-preserving denoising.
In the past decade there has been a growing amount of research concerning partial differential equations in image sharpening. Most of these models indicate edges by a binary zero-crossing decision, however, which will produce a false result with piecewise constant regions, whose textures and fine part are lost. In this paper, we propose a feature preserving coupled bidirectional flow process, where an inverse diffusion is performed to sharpen edges along the normal directions to the isophote lines (edges), while a normal diffusion is done to remove noise and artifacts ("jaggies") along the tangent directions on the contrary. To preserve image features, the nonlinear diffusion coefficients are locally adjusted according to the directional derivatives of the image. Experimental results demonstrate that our algorithm substantially improves the subjective quality of the enhanced images.
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