Fractional-order derivative is attracting more and more interest from researchers working on image processing because it helps to preserve more texture than total variation when noise is removed.In the existing works,...Fractional-order derivative is attracting more and more interest from researchers working on image processing because it helps to preserve more texture than total variation when noise is removed.In the existing works,the Grunwald–Letnikov fractional-order derivative is usually used,where the Dirichlet homogeneous boundary condition can only be considered and therefore the full lower triangular Toeplitz matrix is generated as the discrete partial fractional-order derivative operator.In this paper,a modified truncation is considered in generating the discrete fractional-order partial derivative operator and a truncated fractional-order total variation(tFoTV)model is proposed for image restoration.Hopefully,first any boundary condition can be used in the numerical experiments.Second,the accuracy of the reconstructed images by the tFoTV model can be improved.The alternating directional method of multiplier is applied to solve the tFoTV model.Its convergence is also analyzed briefly.In the numerical experiments,we apply the tFoTV model to recover images that are corrupted by blur and noise.The numerical results show that the tFoTV model provides better reconstruction in peak signal-to-noise ratio(PSNR)than the full fractional-order variation and total variation models.From the numerical results,we can also see that the tFoTV model is comparable with the total generalized variation(TGV)model in accuracy.In addition,we can roughly fix a fractional order according to the structure of the image,and therefore,there is only one parameter left to determine in the tFoTV model,while there are always two parameters to be fixed in TGV model.展开更多
针对自适应广义整体变分(AGTV)图像降噪模型对图像边缘信息定位精度不高及提取不足的问题,为提高图像降噪效果和峰值信噪比,提出了改进的AGTV(IAGTV)图像降噪模型.一方面,该算法换用精度更高的梯度计算方法,相对于AGTV更精确地定位图像...针对自适应广义整体变分(AGTV)图像降噪模型对图像边缘信息定位精度不高及提取不足的问题,为提高图像降噪效果和峰值信噪比,提出了改进的AGTV(IAGTV)图像降噪模型.一方面,该算法换用精度更高的梯度计算方法,相对于AGTV更精确地定位图像边缘;另一方面,为优化图像预处理的滤波过程,用高斯-拉普拉斯联合变换替代高斯平滑滤波,更有利于检测图像边缘信息,在实现降噪的同时防止边缘信息弱化.数值仿真实验得出,IAGTV模型的复原图像峰值信噪比相对于固定p值的GTV模型提高了大约1.0 d B,比AGTV模型提高了至少0.2 d B.实验结果表明IAGTV具有良好的图像降噪能力.展开更多
图像修复是图像处理领域的基础问题,变分方法是实现图像修复的主要方法之一。经典的一阶变分模型存在阶梯效应,不能有效修复大破损区域。二阶变分模型为克服上述问题做出了改进,但修复后的图像会出现破损区域对比度降低、边界模糊现象...图像修复是图像处理领域的基础问题,变分方法是实现图像修复的主要方法之一。经典的一阶变分模型存在阶梯效应,不能有效修复大破损区域。二阶变分模型为克服上述问题做出了改进,但修复后的图像会出现破损区域对比度降低、边界模糊现象。以经典二阶总广义变差模型(Total Generalized Variation,TGV)为基础,提出了一种基于法矢量雅可比的总广义变差模型(Total Generalized Variation Model with Jacobian of Normal,TGVJN)以修复更多破损图像区域信息。该模型通过引入一系列辅助变量、拉格朗日乘子和惩罚参数设计相应的交替方向乘子算法。实验结果表明,本文模型在保持对比度和边缘方面有明显优势,同时能够有效修复大尺度破损图像,缩小边界模糊区域。展开更多
基金Raymond Honfu Chan’s research was supported in part by Hong Kong Research Grants Council(HKRGC)General Research Fund(No.CityU12500915,CityU14306316)HKRGC Collaborative Research Fund(No.C1007-15G)+2 种基金HKRGC Areas of Excellence(No.AoE/M-05/12)Hai-Xia Liang’s research was supported partly by the Natural Science Foundation of Jiangsu Province(No.BK20150373)partly by Xi’an Jiaotong-Liverpool University Research Enhancement Fund(No.17-01-08).
文摘Fractional-order derivative is attracting more and more interest from researchers working on image processing because it helps to preserve more texture than total variation when noise is removed.In the existing works,the Grunwald–Letnikov fractional-order derivative is usually used,where the Dirichlet homogeneous boundary condition can only be considered and therefore the full lower triangular Toeplitz matrix is generated as the discrete partial fractional-order derivative operator.In this paper,a modified truncation is considered in generating the discrete fractional-order partial derivative operator and a truncated fractional-order total variation(tFoTV)model is proposed for image restoration.Hopefully,first any boundary condition can be used in the numerical experiments.Second,the accuracy of the reconstructed images by the tFoTV model can be improved.The alternating directional method of multiplier is applied to solve the tFoTV model.Its convergence is also analyzed briefly.In the numerical experiments,we apply the tFoTV model to recover images that are corrupted by blur and noise.The numerical results show that the tFoTV model provides better reconstruction in peak signal-to-noise ratio(PSNR)than the full fractional-order variation and total variation models.From the numerical results,we can also see that the tFoTV model is comparable with the total generalized variation(TGV)model in accuracy.In addition,we can roughly fix a fractional order according to the structure of the image,and therefore,there is only one parameter left to determine in the tFoTV model,while there are always two parameters to be fixed in TGV model.
文摘针对自适应广义整体变分(AGTV)图像降噪模型对图像边缘信息定位精度不高及提取不足的问题,为提高图像降噪效果和峰值信噪比,提出了改进的AGTV(IAGTV)图像降噪模型.一方面,该算法换用精度更高的梯度计算方法,相对于AGTV更精确地定位图像边缘;另一方面,为优化图像预处理的滤波过程,用高斯-拉普拉斯联合变换替代高斯平滑滤波,更有利于检测图像边缘信息,在实现降噪的同时防止边缘信息弱化.数值仿真实验得出,IAGTV模型的复原图像峰值信噪比相对于固定p值的GTV模型提高了大约1.0 d B,比AGTV模型提高了至少0.2 d B.实验结果表明IAGTV具有良好的图像降噪能力.
文摘图像修复是图像处理领域的基础问题,变分方法是实现图像修复的主要方法之一。经典的一阶变分模型存在阶梯效应,不能有效修复大破损区域。二阶变分模型为克服上述问题做出了改进,但修复后的图像会出现破损区域对比度降低、边界模糊现象。以经典二阶总广义变差模型(Total Generalized Variation,TGV)为基础,提出了一种基于法矢量雅可比的总广义变差模型(Total Generalized Variation Model with Jacobian of Normal,TGVJN)以修复更多破损图像区域信息。该模型通过引入一系列辅助变量、拉格朗日乘子和惩罚参数设计相应的交替方向乘子算法。实验结果表明,本文模型在保持对比度和边缘方面有明显优势,同时能够有效修复大尺度破损图像,缩小边界模糊区域。
