基于图像内容视觉感知的图像质量客观评价方法

图像质量客观评价在图像和视频传输、编解码以及服务质量中起着非常重要的作用.然而现有的方法往往没有考虑图像内容特征及其视觉感知,使得其质量客观评价与主观感知结果存在一定的差距.基于此,本文结合图像内容的复杂性特征和人眼的掩蔽特性、对比敏感度特性以及亮度感知的非线性特性,提出了一种基于人眼对图像内容感知的图像质量客观评价方法.该方法首先结合亮度感知的非线性模型将图像进行转换,得到人眼感知强度图;再分别以人眼对比敏感度值和图像局部平均对比度值作为权重因子对强度求和,以求和的数据信息作为人眼感知图像的内容,并构建图像感知模型;最后以此模型分别模拟人眼感知参考图像和失真图像,并计算二者的强度差,以强度差为评价分数的基础构建图像质量客观评价模型.采用LIVE,TID2008和CSIQ三个数据库中的共47幅参考图像和1549幅测试图像进行仿真实验,且与SSIM,VSNR,FSIM和PSNRHVS等典型的图像质量客观评价模型进行对比分析,同时探讨影响图像质量评价的因素.结果表明:所提方法的评价分数与主观评价分数的Pearson线性相关性系数和Spearman秩相关系数值比SSIM的评价结果均有一定程度的提高,提高幅度分别平均为9.5402%和3.2852%,比PSNRHVS和VSNR提高幅度更大.综合以上表明:所提方法是一种有效可行的图像质量客观评价方法;同时,在图像质量客观评价中,考虑人眼对图像内容的感知和复杂度的分析有助于提高图像质量主客观评价的一致性,评价精度可得到进一步的提高.

Objective assessment method of image quality based on visual perception of image content

Objective image quality assessment (IQA) plays a very important role in transmission, encoding, and quality of service (QoS) of the image and video data. However, the existing IQA methods often do not consider image content features and their visual perception, so there is a certain gap between the objective IQA sores and the subjective perception. To solve this problem, in the study, we propose an objective IQA method based on the visual perception of image content, which combines the complexity characteristics of image content, and the properties of masking, contrast sensitivity and luminance perception nonlinearity of human visual system (HVS). In the proposed method, the image is first transformed using a nonlinear model of luminance perception to obtain the intensity perception image. Then, the intensity information is summed using the contrast sensitivity values of HVS and the average contrast values of the local image as a weighting factor of the intensity. The summed data information is taken as the content of human perceiving image, and an image perception model is constructed. Finally, the reference images and distorted images are perceived by simulating the HVS with this model. Moreover, the difference in intensity between two perceived images is calculated. Based on the intensity difference and peak signal-to -noise ratio model, an objective IQA model is constructed. Further, the simulation with 47 reference images and 1549 test images in the LIVE, TID2008, and CSIQ databases is conducted. Moreover, the experimental results are compared with those of four typical objective IQA models, namely SSIM, VSNR, FSIM, and PSNRHVS. In addition, we explore the factors that affect the IQA accuracy and a way to improve assessment accuracy by combining HVS characteristics, through analyzing the correlation between IQA results of the proposed model and the subjective mean opinion scores (MOSs) provided in the three image databases from the following two aspects. Namely, (1) all reference images in three image databases are distorted by multiple types, and the distorted images of each reference image are taken as a test sequence. Then, the proposed model is used to evaluate each test sequence to obtain the IQA scores. By analyzing the correlation between the IQA scores of each test sequence and the subjective MOSs and comparing them with the assessment results of SSIM, we explore the influence of the image content complexity on the objective IQA accuracy. (2) The test images which are distorted by each type and many distortion degrees are used as another sequence, and they are evaluated by the proposed IQA model. By analyzing the correlation between the subjective MOSs and the IQA results of each test sequence, and comparing them with assessment results of SSIM, we discuss the influence of image distortion mode on the IQA accuracy. The experimental results show that the coefficient values of Pearson linear correlation and Spearman rank order correlation between the objective IQA scores obtained by the proposed method and the subjective MOSs have been averagely improved by 9.5402% and 3.2852%, respectively, in comparison with IQA results from the SSIM method. Also, they are enhanced more significantly than those fom the PSNRHVS and VSNR methods. In summary, it is shown that the proposed IQA method is an effective and feasible method of objectively assessing the image quality; moreover, it is shown that in the objective assessment of image quality it is very helpful to improve the consistency of subjective and objective assessment of image quality by considering the content perception and complexity analysis of the images.