视频和图像文本提取方法综述

文本提取在视频和图像中具有重要的应用价值。近年来,大数据时代带来了海量信息检索的迫切需求,大量视频和图像中文本的提取方法涌现出来。回顾了视频和图像中文本提取的算法,从文本提取流程出发,将其分为文本区域检测定位和文本分割两大步骤。在每个步骤中,分析并比较了现有算法的使用范围及相对优缺点,讨论了图像公用数据库,列举了近些年来图像中文本提取的重要应用,指出了当前研究中存在的问题,展望了视频和场景图像文本提取方法的发展趋势。     

图像文本分析技术及其应用

文本是计算机视觉的许多应用中的一项重要特征。大量复杂图像文本的应用,使图像文本分析技术成为研究的新方向。图像文本分析技术和通常的文档图像分析技术之间有着紧密的联系;但是图像文本其自身所具有的特性,又使得图像文本分析技术具有不同于一般的文档图像分析的更加丰富的内容。我们将图像文本分析技术划分为三大组成部分：图像文本定位、图像文本的预处理和图像文本的识别进行讨论。最后,本文也对图像文本分析技术的应用进行了讨论。     

图像中的文本定位技术研究综述

介绍了图像中文本定位技术的研究现状,依据定位所利用的特征进行分类,分析了其中几种典型算法,并对文本定位算法的性能评价标准进行了深入讨论。     

表格文本图像中文字的提取算法

提出了一种从含有表格的文本图像的页面中提取文字的算法。该算法通过模板扫描形成包围图像前景像素的矩形框。从而提取出前景像素，进而组合矩形框形成模式链。利用模式的最大黑游程、长、宽三个统计特征实现对模式的分类。实验结果表明，该算法不仅对普通的表格有效，而且还可以从倾斜的表格及流程图中成功地提取出文字。本算法只适用于二值图像。     

基于目标区域和相关反馈的图像检索

提出了一种基于目标区域和相关反馈的图像检索方法,首先采用改进的K均值无监督分割方法将图像分割成区域,然后提取每个区域的颜色、位置、形状特征进行相似度计算;最后采用基于支持向量机（SVM）的相关反馈算法提高检索精度。实验结果表明,方法具有良好的检索性能。     

基于TextRank算法和互信息相似度的维吾尔文关键词提取及文本分类

针对维吾尔语文本的分类问题,提出一种基于TextRank算法和互信息相似度的维吾尔文关键词提取及文本分类方法。首先,对输入文本进行预处理,滤除非维吾尔语的字符和停用词;然后,利用词语语义相似度、词语位置和词频重要性加权的TextRank算法提取文本关键词集合;最后,根据互信息相似度度量,计算输入文本关键词集和各类关键词集的相似度,最终实现文本的分类。实验结果表明,该方案能够 提取出具有较高识别度的关键词,当关键词集大小为1250时,平均分类率达到了91.2%。     

基于边缘提取的无人机图像定位方法研究

无人机航拍图像具有很高分辨率,如何提取主要特征并降低计算代价是无人机图像匹配辅助导航的主要问题.提出了一种新的基于边缘梯度幅值和相位的边缘提取方法,对Canny算子进行改进,保留强阈值边缘,同时提取弱阚值下的直线特征,在保持主要边缘特征的同时,减少了边缘的数量,降低了匹配计算量,提高了图像匹配的精度.实验证明该方法是有效可行的.     

面向彩色图像和视频的文本提取新方法

随着基于内容检索技术的发展，人们逐渐意识到包含在彩色图像和视频中的文本具有重要的语义作用，并需要采用有效的方法来提取这些文本，文中提出一个全面作用在RGB颜色空间3个分量上的彩色图像边缘检测新算子和一种利用空间频率特征，结合彩色边缘检测与基于区域图像分割方法的彩色图像和视频文本提取新算法。实验表明在彩色图像和视频的文本提取中，文中算子形成的二值边缘图像的文本区域轮廓清晰完整，有利于下一步文本区域与背景的剥离，该算法具有较高的广西区域提取准确率和较好的对于文本字符在尺寸和颜色方面的适应性。     

考虑视觉显著性的部分相似图像检索

当前流行的图像检索系统普遍采用词袋(Bag-of-Words)模型表示图像视觉内容.由于传统的视觉词袋模型忽略了局部特征间的几何关系,考虑几何约束的后处理方法明显地提高了检索准确率.这些方法认为每个局部特征点是平等的,然而在实际情况中,图像中的局部特征点对于部分相似图像检索任务的重要性是不同的,比如位于相似图像区域上的特征点要比位于背景图像区域的特征点重要.鉴于此,提出考虑图像特征点重要性的部分相似图像检索算法.首先用视觉显著性算法来计算图像每个像素点的显著性(即重要性),然后在几何验证计算图像间匹配分数中考虑匹配局部特征点的重要性,最后在广泛使用的相似图像检索数据集上对提出的算法进行验证.实验结果表明了本方法的优越性.     

视频文本的自动提取方法

提出一种基于彩色边缘检测和游程平滑的视频文本提取方法，首先用彩色边缘检测算子检测出图像中的边缘。然后用多次水平和垂直的游程平滑操作使得文字边缘形成连通区域，并去掉部分孤立的噪声，再通过对连通域的分析和分解定位出文本区域的边界，最后对文本区进行确认．实验表明，本文的视频文本自动提取方法具有较高的文本提取率和较准确的边界定位。     

基于二值化聚类的图像文字提取算法

为解决渐变色给文字提取聚类算法带来的问题,研究与实现了基于二值化聚类的图像文字提取算法。图像通过一系列预处理后,得到了利于聚类的二值图像,根据背景图像区域特征,对图像进行聚类分块,再利用文字图像区域特征,聚类识别出文字区域。实验表明,该算法在各类图像上取得了理想的效果。     

基于内容的图像检索技术与医学图像检索

在分析基于内容的图像检索技术特点的基础上,提出了4种基于内容的图像检索方法,并对每种方法的实现特别是特征抽取进行了一定的研究。根据医学图像的使用特点,对基于内容的医学图像检索技术进行了初步的研究;对医学图像特征的抽取,应将重点放在形状特征和纹理特征的抽取上;同时,对医学图像进行检索,还可以使用颜色空间分布特征,来进一步进行相似匹配。     

基于多特征抽取的商标图像检索

提出了一种多特征抽取方法进行商标图像检索。首先根据图像的连通性把图像分割成多个独立的单元子图像,然后对各个单元子图像提取特征;同时提出多对多特征匹配方法对商标图像进行检索。实验结果表明,应用该方法得到的检索结果是有效的,能够很好地满足人的视觉感受。     

Multiple representations, similarity matching, and results fusion for content-based image retrieval

In this paper, we show how the use of multiple content representations and their fusion can improve the performance of content-based image retrieval systems. We consider the case of texture and propose a new algorithm for texture retrieval based on multiple representations and their results fusion. Texture content is modeled using two different models: the well-known autoregressive model and a perceptual model based on perceptual features such as coarseness and directionality. In the case of the perceptual model, two viewpoints are considered: perceptual features are computed based on the original images viewpoint and on the autocovariance function viewpoint (corresponding to original images). So we consider a total of three content representations. The similarity measure used is based on Gower's index of similarity. Simple results of the fusion models are used to merge search results returned by different representations. Experimentations and benchmarking carried out on the well-known Brodatz database show a drastic improvement in search effectiveness with the fused model without necessarily altering their efficiency in an important way.     

Learning similarity measure for natural image retrieval with relevance feedback

A new scheme of learning similarity measure is proposed for content-based image retrieval (CBIR). It learns a boundary that separates the images in the database into two clusters. Images inside the boundary are ranked by their Euclidean distances to the query. The scheme is called constrained similarity measure (CSM), which not only takes into consideration the perceptual similarity between images, but also significantly improves the retrieval performance of the Euclidean distance measure. Two techniques, support vector machine (SVM) and AdaBoost from machine learning, are utilized to learn the boundary. They are compared to see their differences in boundary learning. The positive and negative examples used to learn the boundary are provided by the user with relevance feedback. The CSM metric is evaluated in a large database of 10009 natural images with an accurate ground truth. Experimental results demonstrate the usefulness and effectiveness of the proposed similarity measure for image retrieval.     

Adaptive tree similarity learning for image retrieval

Learning-enhanced relevance feedback is one of the most promising and active research directions in content-based image retrieval in recent years. However, the existing approaches either require prior knowledge of the data or converge slowly and are thus not coneffective. Motivated by the successful history of optimal adaptive filters, we present a new approach to interactive image retrieval based on an adaptive tree similarity model to solve these difficulties. The proposed tree model is a hierarchical nonlinear Boolean representation of a user query concept. Each path of the tree is a clustering pattern of the feedback samples, which is small enough and local in the feature space that it can be approximated by a linear model nicely. Because of the linearity, the parameters of the similartiy model are better learned by the optimal adaptive filter, which does not require any prior knowledge of the data and supports incremental learning with a fast convergence rate. The proposed approach is simple to implement and achieves better performance than most approaches. To illustrate the performance of the proposed approach, extensive experiments have been carried out on a large heterogeneous image collection with 17,000 images, which render promising results on a wide variety of queries.An early version of part of the system was reported in Proceedings of the IEEE International Conference on Computer Vision and Pattern Recognition 2001.     

基于模糊决策树的文本分类规则抽取

提出一种合并分枝的模糊决策树文本分类方法对相似文本类进行分类,并可抽取出分类精度较高的模糊分类规则。首先研究改进了的χ²统计量,并根据改进的χ²统计量对文本的特征词条进行聚合,有效地降低了文本向量空间的维数。然后使用一种合并分枝的模糊决策树进行分类,大大减少了抽取的规则数量。从而既保证了决策树分类的精度和速度,又可抽取出可理解的模糊分类规则。     

Color indexing for efficient image retrieval

Content based image retrieval is an active area of research. Many approaches have been proposed to retrieve images based on matching of some features derived from the image content. Color is an important feature of image content. The problem with many traditional matching-based retrieval methods is that the search time for retrieving similar images for a given query image increases linearly with the size of the image database. We present an efficient color indexing scheme for similarity-based retrieval which has a search time that increases logarithmically with the database size.In our approach, the color features are extracted automatically using a color clustering algorithm. Then the cluster centroids are used as representatives of the images in 3-dimensional color space and are indexed using a spatial indexing method that usesR-tree. The worst case search time complexity of this approach isOn _q log(N^* n_avg)), whereN is the number of images in the database, andn _q andn _avg are the number of colors in the query image and the average number of colors per image in the database respectively. We present the experimental results for the proposed approach on two databases consisting of 337 Trademark images and 200 Flag images.     

基于虚拟关联反馈与聚类的图像检索技术研究

基于虚拟相关反馈(PRF)技术,提出了一种新的自动关联反馈检索方法--外部自动相关反馈(OARF).该方法基于图像内容特征距离,应用K-均值聚类,自动扩展查询图像特征,从而提高检索性能.试验结果表明,OARF能够降低用户负担,显著提高原始检索算法的性能,缩小"语义鸿沟".