Due to the scattering and attenuation of light into the water, the underwater image usually appears with color distortion, blurred details, and low contrast. To address these problems, a novel two-stage underwater image convolutional neural network (CNN) based on structure decomposition (UWCNN-SD) for underwater image enhancement is proposed by considering the characteristics of underwater imaging. Specifically, the raw underwater image is decomposed into high-frequency and low-frequency based on theoretical analysis of the underwater imaging. Then, a two-stage underwater enhancement network including a preliminary enhancement network and a refinement network is proposed. In the first stage, the preliminary enhancement network, which contains the high-frequency and the low-frequency enhancement networks, is proposed. The high-frequency part is enhanced directly by a deep learning network, and the low-frequency enhancement network is based on the underwater imaging, which is integrated transmission map and background light into joint component map. In the second stage, the refinement network is designed to further optimize the color of the underwater image by considering complexity of underwater imaging. The experimental results of synthetic and real-world underwater images/videos demonstrate that the proposed UWCNN-SD method can perform color correction and enhancement on different types of underwater images. The ablation study verifies the effectiveness of each component, and application tests further illustrate that the proposed UWCNN-SD method can obtain underwater images with higher visual quality. The trained model is available at: https://github.com/wushengcong/UWCNN-SD .

The commercial light field camera is able to capture four-dimensional Light Field Image (LFI), which can be visualized to LFI contents on 2D displays by means of the Pseudo Video (PV) or the Refocused Images (RIs) generated with the refocusing function of LFI. However, the quality degradation of LFI will affect user’s visual experience of LFI contents. Hence, it is crucial to develop an effective LFI quality assessment method to monitor the LFI quality. Most existing subjective databases of LFI use PV and RIs visualization techniques to assess the quality of LFI. Therefore, as the way of presenting LFI on 2D display, PV and RIs are closely related to the subjective perception of LFI by human eyes. Based on these two visualization techniques, this paper proposes a novel PV and RIs based blind LFI quality assessment method, in which the feature extraction is divided into two parts. In the first part, the PV’s structure, motion and disparity information are extracted with multi-scale and multi-directional Shearlet transform. In the other part, the spatial structure, depth and semantic information of the RIs are obtained. Finally, support vector regression is used to nonlinear map the perceptual features to quality score of LFI. The experimental results on four LFI databases show that the proposed method has better correlation with human visual perception, compared with the classical 2D image quality assessment methods as well as the state-of-the-art LFI quality assessment methods.

As a popular multimedia representation, 3D Point Clouds (PC) inevitably encounter distortion during their acquisition, processing, coding, and transmission, resulting in visual quality degradation. Therefore, it is critical to propose a Point Cloud Quality Assessment (PCQA) method to perceive the visual quality of PC. In this paper, we propose a no-reference PCQA method through structure sampling and clustering based on graph, which consists of two-stage pre-processing, quality feature extraction, attention-based feature fusion, and feature regression. For pre-processing, considering the Human Visual System (HVS) tendency to perceive distortions in both the global structure and local details of PCs, a two-stage sampling strategy is introduced. Specifically, to adapt to the irregular structure of PCs, it introduces structural key point sampling and local cluster to capture both global and local information, respectively, thereby facilitating more effective learning of distortion features. Then, in quality feature extraction, two modules are designed based on the two-stage pre-processing results (i.e., Global Feature Extraction (GFE) and Local Feature Extraction (LFE)) to respectively extract global and local quality features. Additionally, for attention-based feature fusion, a Unified Feature Integrator (UFI) module is proposed. This module enhances quality perception capability by integrating global features and individual local quality features and introduces the Transformer to interact with the integrated quality features. Finally, feature regression is conducted to map the final features into the quality score. The performance of the proposed method is tested on four publicly available databases, and the experimental results show that the proposed method is superior compared with existing state-of-the-art no-reference PCQA methods in most cases.

The existing deep-learning based robust watermarking model generally applies a discriminator to form generative adversarial network (GAN) for increasing the quality of encoded images, and adopts a single encoder to embed watermark. However, GAN training is unstable, and the single encoder cannot fully adjust the watermarking distribution, thus affecting the watermarking performance. To address those limitations, this paper presents the multi-encoder based on conditional diffusion model (CDM) for robust image watermarking, namely, DiffW. To enhance the stability, the multi-encoder structure based on CDM replaces GAN for optimizing the watermarking distribution iteratively. Specifically, the operation of each timestep in the forward and reverse diffusion processes of the CDM is regarded as an encoder to overcome the shortcomings of the single encoder structure. At the training stage, under the guidance of the conditional noisy image, the forward process trains each encoder to fuse the image and watermark to generate high-quality encoded images. During the testing stage, only a small number of trained encoders of the forward process are used, so as to reduce the time complexity. Furthermore, to improve watermarking robustness, the channel attention module (CAM) is designed to extract main watermark features by mining channel correlations for multi-layer fusion, so that watermark can be embedded into imperceptible and texture areas. The experimental results reveal that compared with the existing watermarking model, the proposed DiffW can achieve better results in terms of watermarking invisibility and robustness.

It is quite challenging to stitch images with continuous depth changes and complex textures. To solve this problem, we propose an optimized seam-driven image stitching method considering depth, color, and texture information of the scene. Specifically, we design a new energy function to reduce the structural distortion near the seam and improve the invisibility of the seam. By additionally introducing depth information into the smoothing term of energy function, the seam is guided to pass through the continuous regions of the image with high similarity. The experimental results show that benefiting from the new defined energy function, the proposed method can find the seam that adapts to the depth of the scene, and effectively avoid the seam from passing through the salient objects, so that high-quality stitching results can be achieved. The comparison with the representative image stitching methods proves the effectiveness and generalization of the proposed method.