【作者】 吕轶超；

【导师】 印勇；

【作者基本信息】 重庆大学 ， 信号与信息处理， 2011， 硕士

【摘要】 随着计算机技术和多媒体技术的快速发展,多媒体图像的数量也以得到了极大地增长,如何从海量的图像库中快速、准确的检索到所需求的图像成为了当今多媒体技术中研究的热点问题。传统的基于文本的图像检索技术需要管理员手工对图像进行标注,不仅消耗了大量的人力,而且人工标注图像的主观性很大,对于不同的管理员,标注的结果可能不同。基于内容的图像检索技术是依靠图像的低层视觉特征(颜色、纹理、形状等)来进行检索的,但是人对图像的认识是一个利用自己的先验知识推理图像语义的过程,这样导致了图像的底层视觉特征和图像语义之间的“语义鸿沟”。为了减小“语义鸿沟”,本文将图像的高层语义和底层视觉特征结合起来,利用支持向量机(SVM)将图像的底层特征映射为高层语义。本文首先对语义的层次模型进行了分析,并且介绍了提取图像语义的一些常用方法。在分析了图像颜色、纹理、形状等特征提取方法的基础上,提出采用结合图像边缘和角点信息的低层特征提取方法,分别用不变矩和环形颜色直方图来表示图像的边缘和角点信息。本文重点研究了支持向量机的多分类技术,针对一些传统方法支持向量机多分类的缺点,例如:正负样本分布不均匀、识别率低、训练时间长等,提出了一种新的二叉树结构的SVM分类方法。以样本的空间分布为切入点,利用K-Mean聚类分析样本语义类之间的空间分布,采用聚类中心的欧氏距离作为量度,在树形结构SVM的根节点中首先确定空间距离最大的两个类别,将这两个类别分别确定为SVM正类和负类的中心,其他类根据它们与此两类的距离被分配到其对应的SVM类别中。对其他结点SVM类别,再按照根节点同样方式进行分类,直到最后得到单一的类别。以这种分配SVM正负类别的方式训练树形SVM,正负类别比较均匀,先分离开距离较远的类别,避免了它们对后续分类的干扰,提高了分类的准确率,而且除了根节点之外的节点中SVM所有数据量比其他树形结构方法都有很大减少,缩短了SVM的训练时间。实验结果表明,该方法在保证准确率的同时可以在较大程度上缩短图像检索时间。更多还原

【Abstract】 With the rapid development of computer and multimedia technology, the number of multimedia image mushrooms. How to retrieval the image you want quickly and accurately in a gigantic image database is a crucial problem of the multimedia technology research. Traditional keywords-based image retrieval technology need manager annotate images by hand, so it not only cost so much human labors, but also have subjectivity, different manager maybe have different label for the same image. The content-based image retrieval technology mainly searches image by visual contents (color, texture, shape and so no). But people understands a image is a process that he uses his knowledge to speculate semantics of the image, thus, it lead a“semantics gap”between low level features and image semantics.To reduce“semantics gap”, a method that combines the high level semantic and low level feature is proposed. It utilizes support vector machine (SVM) to transform low level features that are extracted from an image into high level semantics.In this paper, the semantic hierarchy of an image is analyzed and some classical methods of image semantic extracting are presented. On the basis of analysis some methods of extracting color feature, texture feature and shape feature propose, a low level feature extracting method that combines image edges and corners is proposed. It uses moment invariants express image edge and ring-shaped color histogram to express information of corners.This paper focuses on the multi-classification of SVM. In order to overcome the faults of traditional multi-classification of SVM, such as positive sample and negative sample are not balanceable, low recognition rate, train time so long, etc. a new tree structure SVM is proposed. Based on space distribution of the sample images, K-mean clustering is used to analyze space distribution among sample images semantic classification, and Euclidean distances among each clustering center are used as a tool to separate the classes. Firstly, two classes are classified, which have biggest distance of positive sample and negative sample of SVM in the root node of tree structure SVM. Then, the other classes will be classified to the corresponding SVM node if their distances are shorter to the one of two classes. For the other nodes, the classes are classified to two classes again. This step is repeated until only one class in the node. This distribution of positive sample and negative sample of SVM keep the balance of positive sample and negative sample. It classifies the two classes that have biggest distance to avoid disturbing other classification and increases the accuracy of classification. Moreover, it decreases the number of nodes of SVM and the training time of SVM. The experimental results show that the proposed method not only can improve image retrieval accuracy, but also reduce retrieval time.更多还原