Handwritten Chinese text line segmentation by clustering with distance metric learning

Separating text lines in unconstrained handwritten documents remains a challenge because the handwritten text lines are often un-uniformly skewed and curved, and the space between lines is not obvious. In this paper, we propose a novel text line segmentation algorithm based on minimal spanning tree (MST) clustering with distance metric learning. Given a distance metric, the connected components (CCs) of document image are grouped into a tree structure, from which text lines are extracted by dynamically cutting the edges using a new hypervolume reduction criterion and a straightness measure. By learning the distance metric in supervised learning on a dataset of pairs of CCs, the proposed algorithm is made robust to handle various documents with multi-skewed and curved text lines. In experiments on a database with 803 unconstrained handwritten Chinese document images containing a total of 8,169 lines, the proposed algorithm achieved a correct rate 98.02% of line detection, and compared favorably to other competitive algorithms.     

Text line and word segmentation of handwritten documents

In this paper, we present a segmentation methodology of handwritten documents in their distinct entities, namely, text lines and words. Text line segmentation is achieved by applying Hough transform on a subset of the document image connected components. A post-processing step includes the correction of possible false alarms, the detection of text lines that Hough transform failed to create and finally the efficient separation of vertically connected characters using a novel method based on skeletonization. Word segmentation is addressed as a two class problem. The distances between adjacent overlapped components in a text line are calculated using the combination of two distance metrics and each of them is categorized either as an inter- or an intra-word distance in a Gaussian mixture modeling framework. The performance of the proposed methodology is based on a consistent and concrete evaluation methodology that uses suitable performance measures in order to compare the text line segmentation and word segmentation results against the corresponding ground truth annotation. The efficiency of the proposed methodology is demonstrated by experimentation conducted on two different datasets: (a) on the test set of the ICDAR2007 handwriting segmentation competition and (b) on a set of historical handwritten documents.     

古代汉字文献切分研究

针对古代汉字文档的特点,提出了适合于古文档的列切分方法和字切分方法。提出的列切分方法直接对文档的笔画投影进行分析,采用一种基于分层投影过滤和变长间隙阈值的递归切分算法。该算法在列间隔较小、列与格线存在粘连、文档具有一定程度的倾斜的情况下,也能准确地抽取出列,尤其对短列的切分达到了较好的效果。提出的字切分方法分为两步,进行粗切分确定大致的切分位置,采用基于连通域分析与粘连点判断的方法做进一步的细切分。该算法对具有较多粘连和重叠汉字的列,也能较好地切分出完整的单字。实验结果表明,提出的方法用于古代汉字文档切分能够获得较好的效果。     

朝汉混排古籍的文字切分方法

为解决朝鲜语古籍数字化中朝汉文种混排字符切分困难的问题,提出一种朝鲜语古籍图像的文字切分算法。针对古籍列与列之间存在不连续间隔线、倾斜或者粘连等问题,提出一种基于连通域投影的列切分方法。利用连通域的删除、合并、拆分等操作对文字进行切分。使用一种多步切分法完成了具有文字大小不一,横向、纵向混合排版特点图像的字符切分工作。对于粘连字,采用改进的滴水算法进行有效切分。实验结果表明所提出的算法能够很好地完成朝、汉文种混排,文字大小不一,排版情况复杂的朝鲜语古籍图像的文字切分工作。该算法的列切分准确率为97.69%,字切分准确率为87.79%。     

基于连通域特征的维吾尔手写文本行分割

针对维吾尔文手写体文本中行分割问题,基于连通域大小将图像中文字分为三类,提出了自适应涂抹细化算法,对主体文本行进行定位;并对第三类连通域中相邻两文本行间粘连的字符进行切割;此外,利用重心范围内的邻域搜索算法,解决了剩余笔画的文本行归附问题。实验结果表明,该方法与常见的水平投影法,分段投影法,及涂抹方法相比具有更好的分割效果。     

回归—聚类联合框架下的手写文本行提取

目的 手写文本行提取是文档图像处理中的重要基础步骤,对于无约束手写文本图像,文本行都会有不同程度的倾斜、弯曲、交叉、粘连等问题。利用传统的几何分割或聚类的方法往往无法保证文本行边缘的精确分割。针对这些问题提出一种基于文本行回归-聚类联合框架的手写文本行提取方法。方法 首先,采用各向异性高斯滤波器组对图像进行多尺度、多方向分析,利用拖尾效应检测脊形结构提取文本行主体区域,并对其骨架化得到文本行回归模型。然后,以连通域为基本图像单元建立超像素表示,为实现超像素的聚类,建立了像素-超像素-文本行关联层级随机场模型,利用能量函数优化的方法实现超像素的聚类与所属文本行标注。在此基础上,检测出所有的行间粘连字符块,采用基于回归线的k-means聚类算法由回归模型引导粘连字符像素聚类,实现粘连字符分割与所属文本行标注。最后,利用文本行标签开关实现了文本行像素的操控显示与定向提取,而不再需要几何分割。结果 在HIT-MW脱机手写中文文档数据集上进行文本行提取测试,检测率DR为99.83%,识别准确率RA为99.92%。结论 实验表明,提出的文本行回归-聚类联合分析框架相比于传统的分段投影分析、最小生成树聚类、Seam Carving等方法提高了文本行边缘的可控性与分割精度。在高效手写文本行提取的同时,最大程度地避免了相邻文本行的干扰,具有较高的准确率和鲁棒性。     

东巴象形文字文档图像的文本行自动分割算法研究

以卷积神经网络(CNN)为代表的深度学习技术在图像分类和识别领域表现出了非常优异的性能。但东巴象形文字未有标准、公开的数据集,无法借鉴或使用已有的深度学习算法。为了快速建立权威、有效的东巴文字库,分析已出版东巴文档的版面结构,从文档中提取文本行、东巴字成为了当前的首要任务。因此,结合东巴象形文字文档图像的结构特点,给出了东巴文档图像的文本行自动分割算法。首先利用基于密度和距离的k-均值聚类算法确定了文本行的分类数量和分类标准;然后,通过文字块的二次处理矫正了分割中的错误结果,提高了算法的准确率。在充分利用东巴字文档结构特征的同时,保留了机器学习模型客观、无主观经验影响的优势。通过实验表明,该算法可用于东巴文档图像、脱机手写汉字、东巴经的文本行分割,以及文本行中东巴字和汉字的分割,具有实现简单、准确性高、适应性强的特点,从而为东巴文字库的建立奠定基础。     

基于汉字连通分量的印刷图像版面分割方法

针对彩色印刷图像背景色彩丰富和汉字存在多个连通分量,连通域文字分割算法不能精确提取文字,提出基于汉字连通分量的彩色印刷图像版面分割方法。利用金字塔变换逆半调算法对图像进行预处理,通过颜色采样和均值偏移分割图像颜色,标记文字连通分量,根据汉字结构和连通分量特性重建汉字连通分量,分析文字连通分量连接关系确定文字排列方向实现文字分割。实验结果表明,该方法能够有效地重建汉字连通分量,在彩色印刷图像中实现对不同字体、字号、颜色的文字分割。     

改进的基于连通域的版面分割方法

版面分割是版面分析的重要组成部分,经过大量的研究,如今已到了一个比较成熟的阶段。对基于连通域的版面分割算法进行了改进,能有效快速地分割较为复杂的版面图像,同时有效减少原有算法中阈值引起的分割错误的情况。先对文本图像进行单个字体的区域扩充,使后续的连通间距统计更为准确和方便,再通过连通间距的统计对图像进行模糊整合,进行文本图像的连通区域分割。实验结果表明,改进的基于连通域的算法分割版面准确,速度快,适用范围广,对于较为复杂的版面分割更具有优越性。     

A new scheme for unconstrained handwritten text-line segmentation

Variations in inter-line gaps and skewed or curled text-lines are some of the challenging issues in segmentation of handwritten text-lines. Moreover, overlapping and touching text-lines that frequently appear in unconstrained handwritten text documents significantly increase segmentation complexities. In this paper, we propose a novel approach for unconstrained handwritten text-line segmentation. A new painting technique is employed to smear the foreground portion of the document image. The painting technique enhances the separability between the foreground and background portions enabling easy detection of text-lines. A dilation operation is employed on the foreground portion of the painted image to obtain a single component for each text-line. Thinning of the background portion of the dilated image and subsequently some trimming operations are performed to obtain a number of separating lines, called candidate line separators. By using the starting and ending points of the candidate line separators and analyzing the distances among them, related candidate line separators are connected to obtain segmented text-lines. Furthermore, the problems of overlapping and touching components are addressed using some novel techniques. We tested the proposed scheme on text-pages of English, French, German, Greek, Persian, Oriya and Bangla and remarkable results were obtained.     

Layout extraction of mixed mode documents

Proper processing and efficient representation of the digitized images of printed documents require the separation of the various information types: text, graphics, and image elements. For most applications it is sufficient to separate text and nontext, because text contains the most information. This paper describes the implementation and performance of a robust algorithm for text extraction and segmentation that is completely independent of text orientation and can deal with text in various font styles and sizes. Text objects can be nested in nontext areas, and inverse printing can also be analyzed. It should be mentioned that the classification is based only on rough image features, and individual characters are not recognized. The three main processing steps of the system are the generation of connected components, neighborhood analysis, and generation of text lines and blocks. As output, connected components are classified as text or nontext. Text components are grouped as characters, words, lines, and blocks. Nontext objects are accumulated as a separate nontext block.     

综合最大匹配和歧义检测的中文分词粗分方法

中文分词是中文文本信息处理的重要预处理。针对目前中文分词中存在的准确率低和粗分结果集大的问题,在最大匹配算法基础上,采用文本切分时的组合歧义检测和交叉歧义检测以及全切分算法,提高了文本粗分的准确率,并减小了粗分结果集的规模,为进一步正确分词奠定基础。通过公共语料库数据集的实验对比,取得很好的效果。     

深度学习的图像实例分割方法综述

实例分割是一项具有挑战性的任务,需要同时进行实例级和像素级的预测,在自动驾驶、视频分析、场景理解等方面应用广泛.近年来,基于深度学习的实例分割方法迅速发展,如两阶段检测器Faster R-CNN扩展出的聚焦于网络的精度而非速度的强大实例分割基准Mask R-CNN,一度成为实例分割的标杆.利用高速检测的单阶段检测器延伸出的实例分割算法YOLACT填补了实时实例分割模型的空白,具有较高的研究和应用价值.本文首先对实例分割算法进行了类别划分,然后对一些代表性的算法及其改进算法进行了深入分析,并阐述了相关算法的优缺点,最后对实例分割方法未来的发展进行了展望.     

A genetic framework using contextual knowledge for segmentation and recognition of handwritten numeral strings

For the first time, a genetic framework using contextual knowledge is proposed for segmentation and recognition of unconstrained handwritten numeral strings. New algorithms have been developed to locate feature points on the string image, and to generate possible segmentation hypotheses. A genetic representation scheme is utilized to show the space of all segmentation hypotheses (chromosomes). For the evaluation of segmentation hypotheses, a novel evaluation scheme is introduced, in order to improve the outlier resistance of the system. Our genetic algorithm tries to search and evolve the population of segmentation hypotheses, and to find the one with the highest segmentation/recognition confidence. The NIST NSTRING SD19 and CENPARMI databases were used to evaluate the performance of our proposed method. Our experiments showed that proper use of contextual knowledge in segmentation, evaluation and search greatly improves the overall performance of the system. On average, our system was able to obtain correct recognition rates of 95.28% and 96.42% on handwritten numeral strings using neural network and support vector classifiers, respectively. These results compare favorably with the ones reported in the literature.     

小波融合技术在图像分割算法中的应用研究

针对图像分割出现一些重要信息丢失与过分割的问题,提出了将小波融合技术应用到图像分割算法中,并对其进行实验验证。首先将图像分别进行Canny分割与迭代阈值分割;然后将这两种分割后的图像进行小波融合,得到融合图像。实验验证结果表明,与传统的Canny分割、迭代阈值分割相比,该算法能结合这两种分割算法的优点,互相弥补各自的一些不足之处并具有一定的抗噪声能力。     

连通区的页面分割与分类方法

页面分割与分类是文档处理的关键步骤，但目前多数方法对页面的块和倾斜进行了限制，文中提出一种新的基于连通区的页面分割与分类方法，首行采用快速算法抽取页面内的连通区，然后利用改进的PLSA算法分割页面，并根据连通区的分布情况以及块的特征对块进行分类，该方法页面分割与分类紧密结合，充分考虑到块的局部特征，保证块分类的正确性，大大提高了算法效率。     

Text line detection in handwritten documents

In this paper, we present a new text line detection method for handwritten documents. The proposed technique is based on a strategy that consists of three distinct steps. The first step includes image binarization and enhancement, connected component extraction, partitioning of the connected component domain into three spatial sub-domains and average character height estimation. In the second step, a block-based Hough transform is used for the detection of potential text lines while a third step is used to correct possible splitting, to detect text lines that the previous step did not reveal and, finally, to separate vertically connected characters and assign them to text lines. The performance evaluation of the proposed approach is based on a consistent and concrete evaluation methodology.     

印刷维吾尔文本切割

我国新疆地区使用的维吾尔文借用阿拉伯文字母书写。因为阿拉伯文字母自身书写的特点,造成维文文本的切割和识别极其困难。本文在连通体分类的基础上,结合水平投影和连通体分析的方法实现维文文本的文字行切分和单词切分。然后定位单词基线位置,计算单词轮廓和基线的距离,寻找所有可能的切点实现维文单词过切割,最后利用规则合并过切分字符。实验结果表明,字符切割准确率达到99 %以上。