Image Super-Resolution via Dual-Dictionary Learning And Sparse Representation

Learning-based image super-resolution aims to reconstruct high-frequency (HF) details from the prior model trained by a set of high- and low-resolution image patches. In this paper, HF to be estimated is considered as a combination of two components: main high-frequency (MHF) and residual high-frequency (RHF), and we propose a novel image super-resolution method via dual-dictionary learning and sparse representation, which consists of the main dictionary learning and the residual dictionary learning, to recover MHF and RHF respectively. Extensive experimental results on test images validate that by employing the proposed two-layer progressive scheme, more image details can be recovered and much better results can be achieved than the state-of-the-art algorithms in terms of both PSNR and visual perception.Comment: 4 pages, 4 figures, 1 table, to be published at IEEE Int. Symposium of Circuits and Systems (ISCAS) 201

Single image super resolution using compressive K-SVD and fusion of sparse approximation algorithms

Super Resolution based on Compressed Sensing (CS) considers low resolution (LR) image patch as the compressive measurement of its corresponding high resolution (HR) patch. In this paper we propose a single image super resolution scheme with compressive K-SVD algorithm(CKSVD) for dictionary learning incorporating fusion of sparse approximation algorithms to produce better results. The CKSVD algorithm is able to learn a dictionary on a set of training signals using only compressive sensing measurements of them. In the fusion based scheme used for sparse approximation, several CS reconstruction algorithms participate and they are executed in parallel, independently. The final estimate of the underlying sparse signal is derived by fusing the estimates obtained from the participating algorithms. The experimental results show that the proposed scheme demands fewer CS measurements for creating better quality super resolved images in terms of both PSNR and visual perception

Sparse Recovery and Representation Learning

This dissertation focuses on sparse representation and dictionary learning, with three relative topics. First, in chapter 1, we study the problem of low-rank matrix recovery in the presence of prior information. We first study the recovery of low-rank matrices with a necessary and sufficient condition, called the Null Space Property, for exact recovery from compressively sampled measurements using nuclear norm minimization. Here, we provide an alternative theoretical analysis of the bound on the number of random Gaussian measurements needed for the condition to be satisfied with high probability. We then study low-rank matrix recovery when prior information is available. We analyze an existing algorithm, provide the necessary and sufficient conditions for exact recovery and show that the existing algorithm is limited in certain cases. We provide an alternative recovery algorithm to deal with the drawback and provide sufficient recovery conditions based on that. In chapter 2, we study the problem of learning a sparsifying dictionary of a set of data, focusing on learning dictionaries that admit fast transforms. Inspired by the Fast Fourier Transform, we propose a learning algorithm involving $O(N)$ unknown parameters for a $N\times N$ linear transformation matrix. Empirically, our algorithm can produce dictionaries that provide lower numerical sparsity for the sparse representation of images than the Discrete Fourier Transformation (DFT). Additionally, due to its structure, the learned dictionary can recover the original signal from the sparse representation in $O(N\log N)$ computations. In chapter 3, we study the representation learning problem in a more complex setting. We use the concept of dictionary learning and apply it in a deep generative model. Motivated by an application in the computer gaming industry where designers needs to have an urban layout generation tool that allows fast generation and modification, we present a novel solution to synthesize high quality building placements using conditional generative latent optimization together with adversarial training. The capability of the proposed method is demonstrated in various examples. The inference is nearly in real time, thus it can assist designers to iterate their designs of virtual cities quickly

Mathematically inspired approaches to face recognition in uncontrolled conditions: super resolution and compressive sensing

Face recognition systems under uncontrolled conditions using surveillance cameras is becom-ing essential for establishing the identity of a person at a distance from the camera and providing safety and security against terrorist, attack, robbery and crime. Therefore, the performance of face recognition in low-resolution degraded images with low quality against im-ages with high quality/and of good resolution/size is considered the most challenging tasks and constitutes focus of this thesis. The work in this thesis is designed to further investigate these issues and the following being our main aim: “To investigate face identification from a distance and under uncontrolled conditions by pri-marily addressing the problem of low-resolution images using existing/modified mathemati-cally inspired super resolution schemes that are based on the emerging new paradigm of compressive sensing and non-adaptive dictionaries based super resolution.” We shall firstly investigate and develop the compressive sensing (CS) based sparse represen-tation of a sample image to reconstruct a high-resolution image for face recognition, by tak-ing different approaches to constructing CS-compliant dictionaries such as Gaussian Random Matrix and Toeplitz Circular Random Matrix. In particular, our focus is on constructing CS non-adaptive dictionaries (independent of face image information), which contrasts with ex-isting image-learnt dictionaries, but satisfies some form of the Restricted Isometry Property (RIP) which is sufficient to comply with the CS theorem regarding the recovery of sparsely represented images. We shall demonstrate that the CS dictionary techniques for resolution enhancement tasks are able to develop scalable face recognition schemes under uncontrolled conditions and at a distance. Secondly, we shall clarify the comparisons of the strength of sufficient CS property for the various types of dictionaries and demonstrate that the image-learnt dictionary far from satisfies the RIP for compressive sensing. Thirdly, we propose dic-tionaries based on the high frequency coefficients of the training set and investigate the im-pact of using dictionaries on the space of feature vectors of the low-resolution image for face recognition when applied to the wavelet domain. Finally, we test the performance of the de-veloped schemes on CCTV images with unknown model of degradation, and show that these schemes significantly outperform existing techniques developed for such a challenging task. However, the performance is still not comparable to what could be achieved in controlled en-vironment, and hence we shall identify remaining challenges to be investigated in the future