Browsing by Author "Zhang, Yun"

Now showing 1 - 9 of 9
  • No Thumbnail Available
    ItemEmbargo
    Colored Point Cloud Quality Assessment Using Complementary Features in 3D and 2D Spaces
    (IEEE, 2024-08-14) Cui, Mao; Zhang, Yun; Fan, Chunling; Hamzaoui, Raouf; Li, Qinglan
    Point Cloud Quality Assessment (PCQA) plays an essential role in optimizing point cloud acquisition, encoding, transmission, and rendering for human-centric visual media applications. In this paper, we propose an objective PCQA model using Complementary Features from 3D and 2D spaces, called CF-PCQA, to measure the visual quality of colored point clouds. First, we develop four effective features in 3D space to represent the perceptual properties of colored point clouds, which include curvature, kurtosis, luminance distance and hue features of points in 3D space. Second, we project the 3D point cloud onto 2D planes using patch projection and extract a structural similarity feature of the projected 2D images in the spatial domain, as well as a sub-band similarity feature in the wavelet domain. Finally, we propose a feature selection and a learning model to fuse high dimensional features and predict the visual quality of the colored point clouds. Extensive experimental results show that the Pearson Linear Correlation Coefficients (PLCCs) of the proposed CF-PCQA were 0.9117, 0.9005, 0.9340 and 0.9826 on the SIAT-PCQD, SJTU-PCQA, WPC2.0 and ICIP2020 datasets, respectively. Moreover, statistical significance tests demonstrate that the CF-PCQA significantly outperforms the state-of-the-art PCQA benchmark schemes on the four datasets.
  • Thumbnail Image
    ItemOpen Access
    Highly Efficient Multiview Depth Coding Based on Histogram Projection and Allowable Depth Distortion
    (IEEE, 2020-11-16) Zhang, Yun; Zhu, Linwei; Hamzaoui, Raouf; Kwong, Sam; Ho, Yo-Sung
    Mismatches between the precisions of representing the disparity, depth value and rendering position in 3D video systems cause redundancies in depth map representations. In this paper, we propose a highly efficient multiview depth coding scheme based on Depth Histogram Projection (DHP) and Allowable Depth Distortion (ADD) in view synthesis. Firstly, DHP exploits the sparse representation of depth maps generated from stereo matching to reduce the residual error from INTER and INTRA predictions in depth coding. We provide a mathematical foundation for DHP-based lossless depth coding by theoretically analyzing its rate-distortion cost. Then, due to the mismatch between depth value and rendering position, there is a many-to-one mapping relationship between them in view synthesis, which induces the ADD model. Based on this ADD model and DHP, depth coding with lossless view synthesis quality is proposed to further improve the compression performance of depth coding while maintaining the same synthesized video quality. Experimental results reveal that the proposed DHP based depth coding can achieve an average bit rate saving of 20.66% to 19.52% for lossless coding on Multiview High Efficiency Video Coding (MV-HEVC) with different groups of pictures. In addition, our depth coding based on DHP and ADD achieves an average depth bit rate reduction of 46.69%, 34.12% and 28.68% for lossless view synthesis quality when the rendering precision varies from integer, half to quarter pixels, respectively. We obtain similar gains for lossless depth coding on the 3D-HEVC, HEVC Intra coding and JPEG2000 platforms.
  • Thumbnail Image
    ItemEmbargo
    Interactive subjective study on picture-level just noticeable difference of compressed stereoscopic images
    (IEEE, 2019-05) Fan, Chunling; Zhang, Yun; Hamzaoui, Raouf; Jiang, Qingshan
    The Just Noticeable Difference (JND) reveals the minimum distortion that the Human Visual System (HVS) can perceive. Traditional studies on JND mainly focus on background luminance adaptation and contrast masking. However, the HVS does not perceive visual content based on individual pixels or blocks, but on the entire image. In this work, we conduct an interactive subjective visual quality study on the Picturelevel JND (PJND) of compressed stereo images. The study, which involves 48 subjects and 10 stereoscopic images compressed with H.265 intra coding and JPEG2000, includes two parts. In the first part, we determine the minimum distortion that the HVS can perceive against a pristine stereo image. In the second part, we explore the minimum distortion that each subject perceives against a distorted stereo image. Modeling the distribution of the PJND samples as Gaussian, we obtain their complementary cumulative distribution functions, which are known as Satisfied User Ratio (SUR) functions. Statistical analysis results demonstrate that the SUR is highly dependent on the image contents. The HVS is more sensitive to distortion in images with more texture details. The compressed stereoscopic images and the PJND samples are collected in a data set called SIAT-JSSI, which we release to the public.
  • Thumbnail Image
    ItemOpen Access
    Learning-based Satisfied User Ratio Prediction for Symmetrically and Asymmetrically Compressed Stereoscopic Images
    (IEEE, 2021) Fan, Chunling; Zhang, Yun; Hamzaoui, Raouf; Ziou, Djemel; Jiang, Qingshan
    The Satisfied User Ratio (SUR) for a given distortion level is the fraction of subjects that cannot perceive a quality difference between the original image and its compressed version. By predicting the SUR, one can determine the highest distortion level which allows to save bit rate while guaranteeing a good visual quality. We propose the first method to predict the SUR for symmetrically and asymmetrically compressed stereoscopic images. Unlike SUR prediction techniques for 2D images and videos, our method exploits the properties of binocular vision. We first extract features that characterize image quality and image content. Then, we use gradient boosting decision trees to reduce the number of features and train a regression model that learns a mapping function from the features to the SUR values. Experimental results on the SIAT-JSSI and SIAT-JASI datasets show high SUR prediction accuracy for H.265 All-Intra and JPEG2000 symmetrically and asymmetrically compressed stereoscopic images.
  • No Thumbnail Available
    ItemMetadata only
    Optimized Quantization Parameter Selection for Video-based Point Cloud Compression
    (Frontiers, 2024-07-02) Yuan, Hui; Hamzaoui, Raouf; Neri, Ferrante; Yang, Shengxiang; Lu, Xin; Zhu, Linwei; Zhang, Yun
    Point clouds are sets of points used to visualize three-dimensional (3D) objects. Point clouds can be static or dynamic. Each point is characterized by its 3D geometry coordinates and attributes such as color. High-quality visualizations often require millions of points, resulting in large storage and transmission costs, especially for dynamic point clouds. To address this problem, the moving picture experts group has recently developed a compression standard for dynamic point clouds called video-based point cloud compression (V-PCC). The standard generates two-dimensional videos from the geometry and color information of the point cloud sequence. Each video is then compressed with a video coder, which converts each frame into frequency coefficients and quantizes them using a quantization parameter (QP). Traditionally, the QPs are severely constrained. For example, in the low-delay configuration of the V-PCC reference software, the quantization parameter values of all the frames in a group of pictures are set to be equal. We show that the rate-distortion performance can be improved by relaxing this constraint and treating the QP selection problem as a multi-variable constrained combinatorial optimization problem, where the variables are the QPs. To solve the optimization problem, we propose a variant of the differential evolution (DE) algorithm. Differential evolution is an evolutionary algorithm that has been successfully applied to various optimization problems. In DE, an initial population of randomly generated candidate solutions is iteratively improved. At each iteration, mutants are generated from the population. Crossover between a mutant and a parent produces offspring. If the performance of the offspring is better than that of the parent, the offspring replaces the parent. While DE was initially introduced for continuous unconstrained optimization problems, we adapt it for our constrained combinatorial optimization problem. Also, unlike standard DE, we apply individual mutation to each variable. Furthermore, we use a variable crossover rate to balance exploration and exploitation. Experimental results for the low-delay configuration of the V-PCC reference software show that our method can reduce the average bitrate by up to 43% compared to a method that uses the same QP values for all frames and selects them according to an interior point method.
  • No Thumbnail Available
    ItemMetadata only
    Picture-level just noticeable difference for symmetrically and asymmetrically compressed stereoscopic images: Subjective quality assessment study and datasets
    (Elsevier, 2019-05-10) Fan, Chunling; Zhang, Yun; Zhang, Huan; Hamzaoui, Raouf; Jiang, Qingshan
    The Picture-level Just Noticeable Difference (PJND) for a given image and compression scheme reflects the smallest distortion level that can be perceived by an observer with respect to a reference image. Previous work has focused on the PJND of images and videos. In this paper, we study the PJND of symmetrically and asymmetrically compressed stereoscopic images for JPEG2000 and H.265 intra coding. We conduct interactive subjective quality assessment tests to determine the PJND point using both a pristine image and a distorted image as a reference. We find that the PJND points are highly dependent on the image content. In asymmetric compression, there exists a perceptual threshold in the quality difference between the left and right views due to the binocular masking effect. We generate two PJND-based stereo image datasets (one for symmetric compression and one for asymmetric compression) and make them accessible to the public.
  • Thumbnail Image
    ItemOpen Access
    Satisfied user ratio prediction with support vector regression for compressed stereo images
    (IEEE, 2020-07) Fan, Chunling; Zhang, Yun; Hamzaoui, Raouf; Ziou, Djemel; Jiang, Qingshan
    We propose the first method to predict the Satisfied User Ratio (SUR) for compressed stereo images. The method consists of two main steps. First, considering binocular vision properties, we extract three types of features from stereo images: image quality features, monocular visual features, and binocular visual features. Then, we train a Support Vector Regression (SVR) model to learn a mapping function from the feature space to the SUR values. Experimental results on the SIAT-JSSI dataset show excellent prediction accuracy, with a mean absolute SUR error of only 0.08 for H.265 intra coding and only 0.13 for JPEG2000 compression.
  • Thumbnail Image
    ItemOpen Access
    SUR-FeatNet: Predicting the Satisfied User Ratio Curve for Image Compression with Deep Feature Learning
    (Springer, 2020-05-04) Lin, Hanhe; Hosu, Vlad; Fan, Chunling; Zhang, Yun; Mu, Yuchen; Hamzaoui, Raouf; Saupe, Dietmar
    The satisfied user ratio (SUR) curve for a lossy image compression scheme, e.g., JPEG, characterizes the complementary cumulative distribution function of the just noticeable difference (JND), the smallest distortion level that can be perceived by a subject when a reference image is compared to a distorted one. A sequence of JNDs can be defined with a suitable successive choice of reference images. We propose the first deep learning approach to predict SUR curves. We show how to apply maximum likelihood estimation and the Anderson-Darling test to select a suitable parametric model for the distribution function. We then use deep feature learning to predict samples of the SUR curve and apply the method of least squares to fit the parametric model to the predicted samples. Our deep learning approach relies on a siamese convolutional neural network, transfer learning, and deep feature learning, using pairs consisting of a reference image and a compressed image for training. Experiments on the MCL-JCI dataset showed state-of-the-art performance. For example, the mean Bhattacharyya distances between the predicted and ground truth first, second, and third JND distributions were 0.0810, 0.0702, and 0.0522, respectively, and the corresponding average absolute differences of the peak signal-to-noise ratio at a median of the first JND distribution were 0.58, 0.69, and 0.58 dB. Further experiments on the JND-Pano dataset showed that the method transfers well to high resolution panoramic images viewed on head-mounted displays.
  • Thumbnail Image
    ItemOpen Access
    SUR-Net: Predicting the Satisfied User Ratio Curve for Image Compression with Deep Learning
    (IEEE, 2019-06) Fan, Chunling; Lin, Hanhe; Hosu, Vlad; Zhang, Yun; Jiang, Qingshan; Hamzaoui, Raouf; Saupe, Dietmar
    The Satisfied User Ratio (SUR) curve for a lossy image compression scheme, e.g., JPEG, characterizes the probability distribution of the Just Noticeable Difference (JND) level, the smallest distortion level that can be perceived by a subject. We propose the first deep learning approach to predict such SUR curves. Instead of the direct approach of regressing the SUR curve itself for a given reference image, our model is trained on pairs of images, original and compressed. Relying on a Siamese Convolutional Neural Network (CNN), feature pooling, a fully connected regression-head, and transfer learning, we achieved a good prediction performance. Experiments on the MCL-JCI dataset showed a mean Bhattacharyya distance between the predicted and the original JND distributions of only 0.072.