Perceptual Metrics for Static and Dynamic Triangle Meshes

Almost all mesh processing procedures cause some more or less visible changes in the appearance of objects represented by polygonal meshes. In many cases, such as mesh watermarking, simplification or lossy compression, the objective is to make the change in appearance negligible, or as small as possible, given some other constraints. Measuring the amount of distortion requires taking into account the final purpose of the data. In many applications, the final consumer of the data is a human observer, and therefore the perceptibility of the introduced appearance change by a human observer should be the criterion that is taken into account when designing and configuring the processing algorithms. In this review, we discuss the existing comparison metrics for static and dynamic (animated) triangle meshes. We describe the concepts used in perception‐oriented metrics used for 2D image comparison, and we show how these concepts are employed in existing 3D mesh metrics. We describe the character of subjective data used for evaluation of mesh metrics and provide comparison results identifying the advantages and drawbacks of each method. Finally, we also discuss employing the perception‐correlated metrics in perception‐oriented mesh processing algorithms.     

The effect of depth map up-sampling on the overall quality of stereopairs

The quality of depth maps affects the quality of generated 3D content. Practically, the depth maps often have lower resolution than that of color images, thus, Depth map Up-sampling (DU) is needed in various 3D applications. DU can yield specific artifacts which can degrade the quality of depth maps as well as constructed stereoscopic (color plus depth map) images. This paper investigates the effect of DU on 3D perception. The depth maps were up-sampled using seven approaches and the quality of stereoscopic images obtained from up-sampled depth maps was estimated through subjective and objective tests. The objective quality prediction was performed using a depth map quality assessment framework. The method is able to predict the quality of stereoscopic images through evaluation of their corresponding up-sampled depth maps using 2D Image Quality Metrics (IQMs). In order to improve the quality estimation, the framework selects the 2D IQMs with highest correlation to subjective test. Furthermore, motivated by previous researches on multiple metrics combination, a new metric fusion method is proposed. Experimental results show that the combined metric delivers higher performance than single metrics in 3D quality prediction.     

Subjective tests for image fusion evaluation and objective metric validation

This paper focuses on the methodology for perceptual image fusion assessment through comparative tests and validation of objective fusion evaluation metrics. Initially, the theory of subjective fusion evaluation, adopted practice and methods to gauge relevance and significance of individual trials are examined. Further in this context, the methodology, experiences and results of a series of specific, subjective preference tests aimed at relative evaluation of fusion algorithms are presented. Test conditions and experimental procedure are described in detail and a number of explicit fusion metrics derived from the subjective test data are proposed. Relative fusion quality, fusion performance robustness (to content) and personal preference are all assessed by the metrics as different aspects of general image fusion performance. Finally, the methodology for subjective validation of objective fusion metrics using the reported test procedures is presented. In particular, explicit subjective–objective validation algorithms are defined and applied to a range of established objective measures of fusion performance in order to evaluate their subjective relevance.     

Dihedral Angle Mesh Error: a fast perception correlated distortion measure for fixed connectivity triangle meshes

In computer graphics, triangle meshes are ubiquitous as a representation of surface models. Processing of this kind of data, such as compression or watermarking, often involves an unwanted distortion of the surface geometry. Advanced processing algorithms are continuously being proposed, aiming at improving performance (compression ratio, watermark robustness and capacity), while minimizing the introduced distortion. In most cases, the final resulting mesh is intended to be viewed by a human observer, and it is therefore necessary to minimise the amount of distortion perceived by the human visual system. However, only recently there have been studies published on subjective experiments in this field, showing that previously used objective error measures exhibit rather poor correlation with the results of subjective experiments. In this paper, we present results of our own large subjective testing aimed at human perception of triangle mesh distortion. We provide an independent confirmation of the previous result by Lavoué et al. that most current metrics perform poorly, with the exception of the MSDM/MSDM2 metrics. We propose a novel metric based on measuring the distortion of dihedral angles, which provides even higher correlation with the results of our experiments and experiments performed by other researchers. Our metric is about two orders of magnitude faster than MSDM/MSDM2, which makes it much more suitable for usage in iterative optimisation algorithms.     

基于混沌和运动矢量的视频水印算法*

针对新一代视频压缩标准H.264,提出一种基于混沌置乱以及运动矢量域的视频水印方案.该方案在运动矢量域自适应嵌入水印和提取经过混沌置乱的水印信息,再经过置乱逆变换恢复得到原水印信息.混沌序列的伪随机性和初值敏感性为水印的安全性提供了保证.实验结果表明,主客观视频质量都与原始视频序列相当,码率误差小.     

VRML animated model watermarking scheme using geometry and interpolator nodes

Distinct from image and video watermarking, a watermarking scheme for 3D animation content is required in the 3D industry market for various applications. This paper develops a watermarking scheme for copyright protection and authentication of 3D animation content. A 3D animated model generally has a hierarchical structure with a number of transform nodes of a geometry node and an interpolator node for the timeline in contrast to a 3D polygon mesh model. The proposed scheme embeds not only a robust watermark into the geometry node for copyright protection but also a fragile watermark into the position and orientation interpolators for content authentication. We named the former “robust geometry watermarking” and the latter “fragile interpolator watermarking”. The proposed scheme performs the two watermarking schemes independently to realize simultaneously robust and fragile watermarked 3D animated model. Experimental results confirm that a watermark embedded by geometry watermarking robust to many attacks from commercial 3D editing tools while a watermark embedded by interpolator watermarking fragile to the same attacks.     

基于轮廓波数字水印的JPEG图像质量评价方法

半参考图像质量评价方法是一种利用原始图像的部分信息对失真图像进行质量预测的方法,提出了一种基于轮廓波变换数字水印的JPEG图像压缩半参考质量评价方法。首先参考人类视觉系统（Human Visual System,HVS）的思想,选取轮廓波变换的低频区域作为水印嵌入区域,从而生成半脆弱数字水印。然后根据已嵌入水印图像与原始图像之间的结构相似度（Structural Similarity,SSIM）的值,设计自适应水印嵌入系统,以保证水印的不可见性。最后分别在LIVE图像数据库2和TID2008图像数据库中,根据已嵌入水印图像进行数据库重建,并测试该算法的性能。实验结果对比显示,该算法与其他算法相比较,具有较好的准确性、单调性以及一致性,能够较好地反应JPEG失真图像的质量。     

Structure compliant local warping of images with applications to watermarking attack

Localized geometric warping of images is known to be one of the most effective attacks against image watermarking systems. However, the existing local geometrical attacks, when applied to images with regular structures, cause perceptible distortion because they are not adaptive to the content of the images. In this work, we present a multi-scale directional smoothing framework in which local displacement vectors are smoothed by locally adaptive directional kernels. Both the displacement vectors for large structures and those for fine structures are constrained by using a multi-scale pyramid. Subjective tests and objective metrics show that our proposed approach can effectively enhance the perceptual quality of the image after geometric attacks. The test of the attacking effects on two typical watermarking systems demonstrates that our approach does not degrade the attacking effects for Markov random field generated displacement field.     

Evaluation of stereoscopic visual fatigue in experts

Several objective or subjective measures have been employed to evaluate stereoscopic visual fatigue. Objective measures are more preferred for their capability to quantify the degree of human visual fatigue without being affected by individual variation. However, the combination of objective indicators, their sensibility in reflecting subjective fatigue and their applicability to different groups has rarely been studied. In our previous study based on non‐expert experiment, we proposed a method combining subjective assessment and objective measures to evaluate stereoscopic visual fatigue and an objective visual fatigue model (non‐expert model). In this study, we use the same procedure to conduct a contrast experiment in 2D and 3D conditions, but only with expert viewers. The results in 2D condition show that the two objective indicators are usable for visual fatigue evaluation. The difference between the results in 2D and 3D conditions shows that the stereo 3D can cause much more fatigue and the indicators can efficiently identify the extra fatigue with satisfactory accuracy. An objective visual fatigue model (expert‐only model) is developed based on the data obtained in the 3D condition and is evaluated with comparison to the non‐expert model. Both visual fatigue models show high correlation with the subjective data. The method we proposed is reasonably insusceptible to different viewer groups, and the results of repeated experiments are consistent. It is a promising approach to evaluate visual fatigue efficiently and objectively.     

A robust digital audio watermarking scheme based on DWT and Schur decomposition

The vulnerability of digital audio signals for different types of risks requires an imperceptible and robust digital audio watermarking scheme. In this research, we propose creating one such imperceptible and robust hybrid watermarking scheme based on a discrete wavelet transform (DWT) and Schur decomposition hybrid method. The proposed scheme embeds the foreground bits of the watermarking image into the least significant bit of the diagonal coefficients of the triangular matrix S generated from Schur decomposition. Schur decomposition is applied on the second sub-band HL₂ generated from applying a second-level 2D-Haar DWT on the first channel of the original audio signal. We analyze the proposed digital audio watermarking scheme’s performance in terms of signal to noise ratio (SNR), objective difference grades (ODG), and subjective difference grades (SDG) that resulting 81.43, 4.78 and 0.184, respectively. The resulting of payload capacity, NC, and BER are as high as 319.29 bps, 0.9911, and 0.0135, respectively. Experimental results confirm that the proposed scheme is inaudible and robust against common types of attacks such as Gaussian noise, re-quantization, re-sampling, low-pass filter, high-pass filter, echo, MP3 compression, and cropping. In comparison with state-of-the-art audio watermarking schemes, the proposed scheme’s performance is superior in term of imperceptibility, robustness, and data payload size.

     

DCT-based objective quality assessment metric of 2D/3D image

With the increasing growth of multimedia applications over the networking in recent years, users have put forward much higher requirements for multimedia quality of experience (QoE) than before. One of the representative requirements is the image quality. Therefore, the image quality assessment ranging from two-dimension (2D) image to three-dimension (3D) image has been getting much attention. In this paper, an efficient objective image quality assessment metric in block-based discrete cosine transform (DCT) coding is proposed. The metric incorporates properties of human visual system (HVS) to improve its validity and reliability in evaluating the quality of stereoscopic image. This is fulfilled by calculating the local pixel-based distortions in frequency domain, combining the simplified models of local visibility properties embodied in frequency domain, which consist of region of interest (ROI) mechanism (visual sensitivity), contrast sensitivity function (CSF) and contrast masking effect. The performance of the proposed metric is compared with other currently state-of-the-art objective image quality assessment metrics. The experimental results have demonstrated that the proposed metric is highly consistent with the subjective test scores. Moreover, the performance of the metric is also confirmed with the popular IRCCyN/IVC database. Therefore, the proposed metric is promising in term of the practical efficiency and reliability for real-life multimedia applications.     

基于表面粗糙度的三维模型质量评价研究

数字水印的嵌入会引起三维模型数据的失真,正确评价含水印三维模型的质量可以为三维水印算法的测评提供统一标准。提出了一种新的三维模型质量的评价方法,它首先利用网格模型中二面角为基本度量单位计算出整个原始三维模型的粗糙度,然后在嵌入水印以后用同样的方法计算出含水印三维模型的粗糙度,最后得到嵌入水印前后粗糙度的增量,并将其作为水印嵌入对三维模型造成的失真度的度量。大量实验结果表明,相比传统的质量评价方法,该方法更加适用于三维网格模型。该质量评价方法还可用于评价各种水印攻击对含水印三维模型造成损害的程度。     

Entropy based spatial domain image watermarking and its performance analysis

Digital image watermarking technique based on LSB Substitution and Hill Cipher is presented and examined in this paper. For better imperceptibility watermark is inserted in the spatial domain. Further the watermark is implanted in the Cover Image block having the highest entropy value. To improve the security of the watermark hill cipher encryption is used. Both subjective and objective image quality assessment technique has been used to evaluate the imperceptibility of the proposed scheme.Further, the perceptual perfection of the watermarked pictures accomplished in the proposed framework has been contrasted and some state-of-art watermarking strategies. Test results demonstrates that the displayed method is robust against different image processing attacks like Salt and Peppers, Gaussian filter attack, Median filter attacks, etc.

     

Robust multi bit and high quality audio watermarking using pseudo-random sequences

A robust multi bit and high quality audio watermarking technique in time domain is proposed in this paper. Watermarking is a technique used to label digital media by hiding copyright or other information into the underlying data. The watermark must be imperceptible and undetectable by the user and should be robust to various types of distortion. To enhance the robustness and taper-resistance of the embedded watermark, in this paper a multi bit technique is employed. Instead of embedding one bit into an audio frame, multiple bits can be embedded into each audio sub-frame. For attackers, since they do not know the parameters, this significantly reduces the possibility of unauthorized bit detection and removal of watermark. In real-time watermarking applications, robustness is not the only factor that plays an important role. The other factor that plays a very an important role is computational complexity. In general, audio file is transmitted in compressed form. Real-time watermark embedding must take into account this compressed form, because first decompressing the data, adding a watermark and then recompressing the data is computationally too demanding. In this paper, we propose robust and low complexity audio watermarking algorithm. To evaluate the performance of the proposed audio watermarking algorithm, subjective and objective quality tests including bit error rate (BER) and signal-to-noise ratio (SNR) were conducted. Compared to traditional one bit embedding algorithm, the proposed algorithm gives highly recovery rate after attack by commonly used audio data manipulations, such as low pass filtering, requantization, resampling, and MP3 compression.     

可见光与红外图像融合质量评价指标分析

目的 客观评价作为图像融合的重要研究领域,是评价融合算法性能的有力工具。目前,已有几十种不同类型的评价指标,但各应用领域包括可见光与红外图像融合,仍缺少统一的选择依据。为了方便比较不同融合算法性能,提出一种客观评价指标的通用分析方法并应用于可见光与红外图像融合。方法 将可见光与红外图像基准数据集中的客观评价指标分为两类,分别是基于融合图像的评价指标与基于源图像和融合图像的评价指标。采用Kendall相关系数分析融合指标间的相关性,聚类得到指标分组;采用Borda计数排序法统计算法的综合排序,分析单一指标排序和综合排序的相关性,得到一致性较高的指标集合;采用离散系数分析指标均值随不同算法的波动程度,选择充分体现不同算法间差异的指标;综合相关性分析、一致性分析及离散系数分析,总结具有代表性的建议指标集合。结果 在13对彩色可见光与红外和8对灰度可见光与红外两组图像源中,分别统计分析不同图像融合算法的客观评价数据,得到可见光与红外图像融合的建议指标集(标准差、边缘保持度),作为融合算法性能评估的重要参考。相较于现有方法,实验覆盖20种融合算法和13种客观评价指标,并且不依赖主观评价结果。结论...     

Fidelity-guaranteed robustness enhancement of blind-detection watermarking schemes

Watermarking performance enhancement has always been a difficult task since the performance metrics of watermarking systems, i.e., fidelity, robustness, and payload size, inherently conflict with each other. Nowadays, most watermarking schemes hide payloads according to predefined rules or empirical perceptual models. Therefore, the performance of digital watermarking schemes can be determined only passively. In this study, a genetic algorithm-based framework for watermarking performance enhancement is proposed. Watermarked results having better robustness, guaranteed fidelity, and fixed payload size can be obtained. Existing blind-detection watermarking schemes can be improved significantly by incorporating the proposed framework. In addition, the proposed framework has many desirable advantages such as asymmetric embedding/detection overhead, easy integration with existing data-hiding schemes, and direct control over fidelity and robustness.     

基于离散小波变换的QR二维条码防伪技术

基于数字水印的快速响应矩阵（QR）二维条码防伪技术的水印容量低、防伪效果差。为解决该问题,提出QR码二值图像Rand灰度化和背景图灰度化方法,以提高防伪水印容量。QR码二值图像灰度化的程度由灰度化阈值决定,并且可以根据实际应用需要灵活确定。在此基础上,设计基于离散小波变换的QR二维条码防伪水印方案,通过量化函数实现水印的嵌入和检测,利用混沌密钥生成的二维混沌序列控制水印嵌入和检测的位置。实验结果表明,该方案在确保条码信息可识别的条件下,提高了QR码防伪水印的性能。     

基于表面粗糙度的自适应三维模型盲水印算法

针对已有的三维模型盲水印算法在相同鲁棒性约束条件下模型失真度较大的问题,提出一种基于表面粗糙度的自适应三维模型盲水印算法。引入视觉掩盖的思想,通过计算三维模型表面粗糙度以及各顶点相对位置选择待嵌入顶点,使得水印嵌入强度自适应于模型表面粗糙度。实验证明此算法在保持鲁棒性约束条件下能够有效降低模型的失真度。     

软件质量的度量问题

度量的目的是为软件产品提供量化的测量结果，以避免主观论断的差错。软件度量是软件维护的基础。本文对软件度量的定义、度量的过程、面向对象软件的度量、度量与维护的关系等进行了讨论。