基于超完备字典的图像稀疏表示因其具有稀疏性、特征保持性、可分性等特点而被广泛应用于图像处理.本文提出一种超完备字典学习算法并应用于图像去噪.将字典学习等价于一个二次规划问题,并提出适合于大规模运算的投影梯度算法.学习所得字典能有效描述图像特征.基于此超完备学习字典,获得图像的稀疏表示,并恢复原始图像.实验结果表明,与小波类去噪方法相比,本文的学习算法能更好地去除图像噪声,保留图像细节信息,获得更高的PSNR值.
Images' sparse representations over over-complete dictionaries have a wide application in image processing due to the properties of sparsity,integrity and separability.This paper proposes a dictionary learning algorithm which is applied to image de-noising.The dictionary learning problem is expressed as a box-constrained quadratic program and a fast projected gradient method is introduced to solve it.The learned dictionary describes the image content effectively.Experimental results show that:in comparison with the wavelet-based de-noising methods,our learning-based algorithm has better de-noising ability,keep more detail image information and improve the peak signal-to-noise ratio.