Efficient single image super-resolution via graph-constrained least squares regression

In this paper, single- image super-resolution framework is presented by means of sparse representation. Patch-based super resolution is a technique where spatial features from a low-resolution (LR) patches are used as references for the reconstruction of high-resolution (HR) image patches. Sparse representation for each patch is extracted and these coefficients are used to recover super-resolution patch. Two dictionaries are jointly trained for the LR and HR image patches. By this, similarity between sparse representation between the LR and HR patch pair is established. Hence, the sparse representation of a LR image patch can be applied with the HR image patch dictionary to obtain a HR image patch. The dictionary thus learnt is a compact one. The experimental results demonstrate the effectiveness of the proposed algorithm.

This paper presents a new approach to single-image super-resolution, based on sparse signal representation. Research on image statistics suggests that image patches can be well-represented as a sparse linear combination of elements from an appropriately chosen over-complete dictionary. Inspired by this observation, we seek a sparse representation for each patch of the low-resolution input, and then use the coefficients of this representation to generate the high-resolution output. Theoretical results from compressed sensing suggest that under mild conditions, the sparse representation can be correctly recovered from the downsampled signals. By jointly training two dictionaries for the low- and high-resolution image patches, we can enforce the similarity of sparse representations between the low resolution and high resolution image patch pair with respect to their own dictionaries. Therefore, the sparse representation of a low resolution image patch can be applied with the high resolution image patch dictionary to generate a high resolution image patch. The learned dictionary pair is a more compact representation of the patch pairs, compared to previous approaches, which simply sample a large amount of image patch pairs, reducing the computational cost substantially. The effectiveness of such a sparsity prior is demonstrated for both general image super-resolution and the special case of face hallucination. In both cases, our algorithm generates high-resolution images that are competitive or even superior in quality to images produced by other similar SR methods. In addition, the local sparse modeling of our approach is naturally robust to noise, and therefore the proposed algorithm can handle super-resolution with noisy inputs in a more unified framework.

This chapter concentrates the problem of recovery a high-resolution (HR) image from a single low-resolution input image. Recent research proposed to deal with the image super-resolution problem with sparse coding, which is based on the well reconstruction of any local image patch by a sparse linear combination of an appropriately chosen over-complete dictionary. Therein the chosen LR (Low-resolution) and HR (High-resolution) dictionaries have to be exactly corresponding for well reconstructing the local image patterns. However, the conventional sparse coding based image super-resolution usually achieves a global dictionary D=[D l ; D h ] by jointly training the concatenated LR and HR local image patches, and then reconstruct the LR and HR image as a linear combination of the separated D l and D h . This strategy only can achieve the global minimum reconstructing error of LR and HR local patches, and usually cannot obtain the exactly corresponding LR and HR dictionaries. In addition, the accurate coefficients for reconstructing the HR image patch using HR dictionary D h are also unable to be estimated using only the LR input and the LR dictionary D l . Therefore, this paper proposes to firstly learn the HR dictionary D h from the features of the training HR local patches, and then propagates the HR dictionary to the LR one, called as HR2LR dictionary propagation, by mathematical proving and statistical analysis. The effectiveness of the proposed HR2LR dictionary propagation in sparse coding for super-resolution is demonstrated by comparison with the conventional super-resolution approaches such as sparse coding and interpolation.

In this paper we propose a technique for obtaining a high resolution (HR) image from a single low resolution (LR) image -using joint learning dictionary - on the basis of image statistic research. It suggests that with an appropriate choice of an over-complete dictionary, image patches can be well represented as a sparse linear combination. Medical imaging for clinical analysis and medical intervention is being used for creating visual representations of the interior of a body, as well as visual representation of the function of some organs or tissues (physiology). A number of medical imaging techniques are in use like MRI, CT scan, X-rays and Optical Coherence Tomography (OCT). OCT is one of the new technologies in medical imaging and one of its uses is in ophthalmology where it is being used for analysis of the choroidal thickness in the eyes in healthy and disease states such as age-related macular degeneration, central serous chorioretinopathy, diabetic retinopathy and inherited retinal dystrophies. We have proposed a technique for enhancing the OCT images which can be used for clearly identifying and analyzing the particular diseases. Our method uses dictionary learning technique for generating a high resolution image from a single input LR image. We train two joint dictionaries, one with OCT images and the second with multiple different natural images, and compare the results with previous SR technique. Proposed method for both dictionaries produces HR images which are comparatively superior in quality with the other proposed method of SR. Proposed technique is very effective for noisy OCT images and produces up-sampled and enhanced OCT images.

Super‐resolution (SR) is the problem of generating a high‐resolution (HR) image from one or more low‐resolution (LR) images. This study presents a new approach to single‐image super‐resolution based on group sparse representation. Two dictionaries are constructed corresponding to the LR and HR image patches, respectively. The sparse coefficients of an input LR image patch in terms of the LR dictionary are used to recover the HR patch from the HR dictionary. When constructing the dictionaries, the three colour channels in a training image patch are considered a group composed of three atoms. The whole group is selected simultaneously when representing an image patch so that the correlations between the colour channels can be retained. A dictionary training method is also designed in which the two dictionaries are trained jointly to ensure that the corresponding LR and HR patches have the same sparse coefficients. Experimental results demonstrate the effectiveness of the proposed method and its robustness to noise.

The single image super resolution recovers missing high resolution details so as to reconstruct a high resolution image from a single low resolution image. This paper proposes a novel directionally adaptive, learning-based, single image super resolution method using multiple direction wavelet transform, called directionlets. Here, critically sampled directionlets are used to capture directional features effectively and to extract edge information along different directions from a set of available high resolution images. This information is used as the training set for super resolving a low resolution input image. The directionlet coefficients at finer scales of its high resolution image are learned locally from this training set and the inverse directionlet transform recovers the super resolved high resolution image. The simulation results showed that the proposed directionlet approach outperforms standard interpolation techniques like cubic spline interpolation as well as standard wavelet-based learning, both visually and in terms of the mean squared error (MSE) values. The SNR scores for cubic spline interpolation, wavelet and directionlet method are 13.6998 dB, 23.8324 dB and 30.8654 dB respectively for Barbara.

Example-based super-resolution (SR) methods learn the correspondences between low resolution (LR) and high-resolution (HR) image patches, where the patches are extracted from a training database. To reconstruct a single LR image into a HR one, each LR image patch is processed by the previously trained model to recover its corresponding HR patch. For this reason, they are computationally inefficient. We propose the use of a selective patch processing technique to carry out the super-resolution step more efficiently, while maintaining the output quality. In this technique, only patches of high variance are processed by the costly reconstruction steps, while the rest of the patches are processed by fast bicubic interpolation. We have applied the proposed improvement on representative example-based SR methods to super-resolve text images. The results show a significant speed up for text SR without a drop in theocrat accuracy. In order to carry out an extensive and solid performance evaluation, we also present a public database of text images for training and testing example-based SR methods.

We propose a new high-quality up-scaling technique that extends the existing example based super-resolution (SR) framework. Our approach is based on the fundamental idea that a low-resolution (LR) image could be generated from any of the multiple possible high-resolution (HR) images. Therefore it would be more natural to use multiple predictors of HR patch from LR patch instead of single one. In this work we build a generic framework to estimate an HR image from LR one using an adaptive prior (select the predictor locally) based on the local statistics of LR images. We use natural image patch prior as the HR image statistics. We partition the natural images into documents and group them to discover the inherent topics using probabilistic Latent Semantic Analysis (pLSA) and also learn the dual dictionaries of HR and LR image patch pairs for each of the topics using sparse dictionary learning technique. Then for test image we infer locally which topic it corresponds to and then we use the corresponding learned dual dictionary to generate HR image. Experimental results show the effectiveness of our method over existing state-of-art methods.KeywordsSparse RepresentationSparse CodeSuper ResolutionProbabilistic Latent Semantic AnalysisBicubic InterpolationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

In this study, a novel single image super-resolution (SR) method, which uses a generated dictionary from pairs of high-resolution (HR) images and their corresponding low-resolution (LR) representations, is proposed. First, HR and LR dictionaries are created by dividing HR and LR images into patches Afterwards, when performing SR, the distance between every patch of the input LR image and those of available LR patches in the LR dictionary are calculated. The minimum distance between the input LR patch and those in the LR dictionary is taken, and its counterpart from the HR dictionary will be passed through an illumination enhancement process resulting in consistency of illumination between neighbour patches. This process is applied to all patches of the LR image. Finally, in order to remove the blocking effect caused by merging the patches, an average of the obtained HR image and the interpolated image is calculated. Furthermore, it is shown that the stabe of dictionaries is reducible to a great degree. The speed of the system is improved by 62.5%. The quantitative and qualitative analyses of the experimental results show the superiority of the proposed technique over the conventional and state-of-the-art methods.

In this work, a simple and compact-structured convolutional neural network (CNN) entitled as Denoising and Super-Resolution (DnSR) network for single image denoising and super resolution (SISR) is presented. Using sparsity property (a smaller number of large intensity values and a larger number of small intensity values), the training of DnSR is made to converge early. We obtain the sparsity by learning residuals of image pixels instead of learning raw image pixels particularly for SR. We use a smaller receptive field of the image patch for faster training. We use gradient clipping to train DnSR net with an extremely large learning rate to overcome gradient inconsistency during training. An end-to-end mapping is done by learning the complex mapping between low-resolution (LR) image patches and the corresponding residual of high resolution (∆HR) image patches using DnSR net. The proposed DnSR net uses a smaller number of parameters (approximately 3 times lesser) than the existing state-of-the-art (SOTA) SRCNN method. The proposed DnSR provides superior reconstruction accuracy with less artifacts when compared to other SOTA methods. The performance of the DnSR is assessed qualitatively and quantitatively using different image quality metrics.

Single image super-resolution based on compressive sensing and improved TV minimization sparse recovery

Single image super resolution using neighbor embedding and statistical prediction model

Deep learning methods have achieved state-of-the-art accuracy in single image super-resolution (SISR). Yet, how to achieve good balance between efficiency and accuracy in SISR is still an open issue. While most existing methods learn residual features only in low resolution (LR) space in order for higher efficiency, recent studies show that jointly learning residual features in LR and high resolution (HR) space is more preferred for accurate SISR. In this paper, we propose an efficient SISR method via learning hybrid residual features, based on which the residual HR image can be reconstructed. To fulfill hybrid residual feature learning, we propose a compact back-projection network that can simultaneously generate features in both LR and HR space by cascading up-and down-sampling layers with small-sized filters. Extensive experiments on four benchmark databases demonstrate that our proposed method can achieve high efficiency (i.e., small number of parameters and operations) while preserving state-of-the-art SR accuracy.

This paper develops a Coupled Convolution Model (CCM) for Error Concealment (EC), Image Super Resolution (ISR) and Multifocus Image Fusion (MIF) used in unmanned aerial vehicles. The key points of this paper are: i) for EC, to efficiently exploit the inherent correlation relationship between the lost region and its known adjacent region, this paper introduces a special CCM in order that their convolution model results via different convolution filters are close to the counterpart on the convolution space; ii) for ISR, we develop CCM to train two convolution filters and map the original low-resolution(LR) and high-resolution(HR) image patches onto a unified convolution subspace. iii) as for MIF, since image fusion depends on the local information of source images resulting from the same scene, this paper constructs a special Coupled Two-Dimensional Convolution Model (2D-CCM) for the image patches from different source images. Experimental results show that the proposed CCM is very effective for EC, ISR and MIF.

Guided image super-resolution (GISR) aims to obtain a high-resolution (HR) target image by enhancing the spatial resolution of a low-resolution (LR) target image under the guidance of a HR image. However, previous model-based methods mainly take the entire image as a whole, and assume the prior distribution between the HR target image and the HR guidance image, simply ignoring many non-local common characteristics between them. To alleviate this issue, we firstly propose a maximum a posteriori (MAP) estimation model for GISR with two types of priors on the HR target image, i.e., local implicit prior and global implicit prior. The local implicit prior aims to model the complex relationship between the HR target image and the HR guidance image from a local perspective, and the global implicit prior considers the non-local auto-regression property between the two images from a global perspective. Secondly, we design a novel alternating optimization algorithm to solve this model for GISR. The algorithm is in a concise framework that facilitates to be replicated into commonly used deep network structures. Thirdly, to reduce the information loss across iterative stages, the persistent memory mechanism is introduced to augment the information representation by exploiting the Long short-term memory unit (LSTM) in the image and feature spaces. In this way, a deep network with certain interpretation and high representation ability is built. Extensive experimental results validate the superiority of our method on a variety of GISR tasks, including Pan-sharpening, depth image super-resolution, and MR image super-resolution. Code will be released at https://github.com/manman1995/pansharpening.