Raindrop Removal With Light Field Image Using Image Inpainting

Learning from EPI-Volume-Stack for Light Field image angular super-resolution

As light field images continue to increase in use and application, it becomes necessary to adapt existing image processing methods to this unique form of photography. In this paper we explore methods for applying neural style transfer to light field images. Feed-forward style transfer networks provide fast, high-quality results for monocular images, but no such networks exist for full light field images. Because of the size of these images, current light field data sets are small and are insufficient for training purely feed-forward style-transfer networks from scratch. Thus, it is necessary to adapt existing monocular style transfer networks in a way that allows for the stylization of each view of the light field while maintaining visual consistencies between views. To do this, we first generate disparity maps for each view given a single depth image for the light field. Then in a fashion similar to neural stylization of stereo images, we use disparity maps to enforce a consistency loss between views and to warp feature maps during the feed forward stylization. Unlike previous work, however, light fields have too many views to train a purely feed-forward network that can stylize the entire light field with angular consistency. Instead, the proposed method uses an iterative optimization for each view of a single light field image that backpropagates the consistency loss through the network. Thus, the network architecture allows for the incorporation of pre-trained fast monocular stylization network while avoiding the need for a large light field training set.

The light field image, also known as the plenoptic image, contains the information about not only the intensity of light in a scene but also the direction of the light rays in space. Since the light field image contains very rich photometric and geometric information, it will have very widespread application in the future. For example, immersive content capture for virtual and mixed reality presentation or depth from light field for auto driving applications. To be more specific, a light field image can be enhanced with physical models for an autonomous decision making process, which is also an important task of the Dynamic Data Driven Applications Systems (DDDAS) [11]. Besides, the rich geometry and photometric information contained in the light field can be updated with real-time measurements, which is a focus of DDDAS such as smart city related image and video processing tasks. However, to make the light field images easier to be utilized, one of the most important tasks is to compress the light field images efficiently so they can be easily distributed over the current communication infrastructure.

Light field images can record multiple information about the light rays in a scene and provide multiple views from a single image, offering a new data source for 3D reconstruction. However, ensuring the quality of light field images themselves is challenging, and distorted image inputs may lead to poor reconstruction results. Accurate light field image quality assessment can pre-judge the quality of light field images used as input for 3D reconstruction, providing a reference for the reconstruction results before the reconstruction work, significantly improving the efficiency of 3D reconstruction based on light field images. In this paper, we propose an Adaptive Vision Transformer-based light-field image-quality assessment model (AViT-LFIQA). The model adopts a multi-view sub-aperture image sequence input method, greatly reducing the number of input images while retaining as much information as possible from the original light field image, alleviating the training pressure on the neural network. Furthermore, we design an adaptive learnable attention layer based on ViT, which addresses the lack of inductive bias in ViT by using adaptive diagonal masking and a learnable temperature coefficient strategy, making the model more suitable for training on small datasets of light field images. Experimental results demonstrate that the proposed model is effective for various types of distortions and shows superior performance in light-field image-quality assessment.

Light Field, a computational photography technique has various exciting features like refocusing and novel view synthesis. Previous works in light field photography have focused their work on creating light field images having a limited field of view. This limitation of light field images motivates the research for a acquisition system which can capture light field images with larger field of view. Recent works have been done to acquire light fields using a cylindrical arrangement of cameras which resolve the conventional complexity issue of acquisition of light field and subsequently merging them by essentially combining the capture and merging processes into a single exercise. We use this cylindrical system to generate a novel True Zoomed Light field panorama from the captured light field, which gives a wide 360? field of view similar to traditional panoramas along with the zoom applied to the whole panorama. The captured panorama can also be manipulated in various ways as is possible with other light field recordings. Also various zooming options which can be easily found in traditional camera, either tends to change the relative shape of the objects in image or introduces pix-elation effect. We use true zoom so as to improvise the zooming effect. We generate novel “True Zoomed Light Field Panorama” using our system. This type of panorama gives user a feeling of being closer to or farther from the whole environment at the same time.

Perceptual encryption has received widespread attention as a technology for protecting multimedia visual information. In multimedia applications, perceptual encryption only protects a portion of the content without previewing all the information. At present, perceptual encryption is mostly oriented to conventional plain images while few methods aim at visual security measures for perceptually encrypted images. Existing solutions usually adopt well-known quality assessment metrics to measure the visual quality of encrypted images. However, they often exhibit undesired behavior on perceptually encrypted images with low quality. As a typical representation of three-dimensional scenes, light field images record the intensity and direction of light during propagation which is distinct from 2-D images. In this paper, we construct a perceptually encrypted light field image database (PE-LFID) for quality assessment based on 14 reference light field plaintext images. For each scene, we employ four encryption methods, each of which has six levels. Additionally, a novel visual security evaluation method based on PE-LFID is proposed by taking into account the local and global features of the light field images. First, we use a multi-threshold edge detection method to obtain the edge similarity in the spatial domain of the light field image. Afterwards, the epipolar plane image (EPI) generated from the angular domain of the light field image is used to calculate the gradient magnitude similarity, which is expressed as a global feature. Furthermore, the final quality prediction score is calculated by adaptively weighting between local and global features. We conduct extensive experiments on the proposed PE-LFID to assess the performance of classical and state-of-the-art IQA models. The experimental results demonstrate the effectiveness of the proposed method for visual security evaluation of perceptually encrypted light field images, as well as the scalability of PE-LFID.

Learning an epipolar shift compensation for light field image super-resolution

No-reference light field image quality assessment based on depth, structural and angular information

How to improve the rendering efficiency and realism of light field images remains a major challenge. This paper proposes a rendering approach to efficiently generate photorealistic light field images. Firstly, the next-generation model optimization technique is used to transform the complex high-polygon model (HPM) into the low-polygon model (LPM). Then, the rendering speed is accelerated by using the LPM and geometric perspective coherence. Next, the normals of the HPM are baked onto the LPM using model baking techniques, and the high-precision light field images are rendered using LPM and the normals of HPM. This process can reduce 95% of the model data, thereby increasing the rendering speed by more than 10 times, while maintaining the rendering quality comparable to the HPM. Secondly, nearly half of the triangles are further decreased by using a two-step backface culling technique, thereby doubling the rendering speed again. The rendering speed is greatly improved using the GPU-CPU hybrid architecture. Thirdly, to enhance realism, anisotropic illumination effects are realized by using the perspective coherence of lighting, and vivid shadows are rendered utilizing an image-space shadow mapping technology. The results indicate that the proposed method can increase the rendering speed by more than 20 times and maintain the image's SSIMs exceeding 0.9 and PSNRs above 30 dB. Finally, a light field display system based on integral imaging was built, and high-resolution and attractive 3D images with a wide viewing angle were synthesized using the light field images and display system.

3D localization of point source is widely used in many fields, such as bioimaging and autonomous driving fields. However, the localization is hard to perform under scattering conditions because of the diffuse effect of the scattering. We propose a novel method for 3D localization of point source under scattering conditions based on light field imaging and deep learning by only one shot. First, we introduce the description of the point source in a light field wise and how to localize a point source by its light field. On the basis, we elaborate on the effect of scattering on a light field and how to retrieve the location of a point source from a light field with scattering. Then, the effect of aberration on a light field will be introduced. We also build an artificial scene and a deep learning framework to perform a 3D localization practically, and the feasibility and accuracy of our method have been evaluated.

Recent advances in light field technologies is fostering the research and development of novel imaging applications. Such applications perform processing of the light field information to create new visual effects such as, for example, refocusing, perspective change, colour adjustment. Light field imaging is very data intensive compared with usual digital photographic imaging, and novel compression algorithms are needed for addressing the problem of light field storage and transmission. Raw digital light field images exhibit low spatial correlation if compared to regular images and hence the performance in terms of rate-distortion of current state-of-the-art image encoders can be superseded by devising novel image compression architectures. In this paper, an architecture for lossy compression of unfocused light field images is proposed. Raw light fields are preprocessed by demosaicing, devignetting and slicing of the raw lenslet array image. The slices are then compressed with the JPEG 2000 image coding standard. The performance of the proposed method is compared against direct application of JPEG 2000 compression on the 4D light field. The experimental analysis has been conducted under a set of different compression ratios and the obtained results show that the proposed method outperforms direct application of the reference architecture.

Ear recognition is an emerging research area in image-based biometrics. The commercial availability of lenslet light field cameras able to capture full spatio-angular information has brought momentum to biometric and forensic research exploiting this new type of imaging sensors. This study is the first to consider the usage of light field cameras for ear recognition, proposing both an appropriate content database and an ear recognition solution. The novel Lenslet Light Field Ear DataBase (LLFEDB) includes 536 light field images corresponding to four different poses, from 67 subjects, captured with a Lytro ILLUM lenslet light field camera. The LLFEDB includes critical cases such as ear images partly occluded by ear piercing, earing, hair and combination of occlusions. The novel light field-based ear recognition solution proposed exploits the richer spatio-angular information available in the light field images. A comparative performance evaluation study using the LLFEDB, and focusing on the most recent light field and non-light field based descriptors for ear recognition, shows a very promising performance of the proposed descriptor, outperforming all the assessed descriptors.

There is a need for affordable and easily deployable rendering and display solutions to take full advantage of light field imaging. In particular, the research community needs ways to better assess the impact of various light field imaging technologies based on different criteria. In this paper, we propose a solution to render light field images on head mounted virtual reality displays using off-the-shelf components. The proposed framework is based on WebGL and supports rendering of narrow baseline light field images with interactions that result in changes of perspective. The system can be used in subjective quality assessments of light field via crowd-sourcing. It also allows for tracking and recording of viewing interactions.

Light field cameras are considered to have many potential applications since angular and spatial information is captured simultaneously. However, the limited spatial resolution has brought lots of difficulties in developing related applications and becomes the main bottleneck of light field cameras. In this paper, a learning-based method using residual convolutional networks is proposed to reconstruct light fields with higher spatial resolution. The view images in one light field are first grouped into different image stacks with consistent sub-pixel offsets and fed into different network branches to implicitly learn inherent corresponding relations. The residual information in different spatial directions is then calculated from each branch and further integrated to supplement high-frequency details for the view image. Finally, a flexible solution is proposed to super-resolve entire light field images with various angular resolutions. Experimental results on synthetic and real-world datasets demonstrate that the proposed method outperforms other state-of-the-art methods by a large margin in both visual and numerical evaluations. Furthermore, the proposed method shows good performances in preserving the inherent epipolar property in light field images.

View synthesis-based light field image compression using a generative adversarial network