Structural feature-based evaluation method of binarization techniques for word retrieval in the degraded Arabic document images

One of the most important and necessary steps in the process of document analysis and recognition is the binarization, which allows extracting the foreground from the background. Several binarization techniques have been proposed in the literature, but none of them was reliable for all image types. This makes the selection of one method to apply in a given application very difficult. Thus, performance evaluation of binarization algorithms becomes therefore vital. In this paper, we are interested in the evaluation of binarization techniques for the purpose of retrieving words from the images of degraded Arabic documents. A new evaluation methodology is proposed. The proposed evaluation methodology is based on the comparison of the visual features extracted from the binarized document images with ground truth features instead of comparing images between themselves. The most appropriate thresholding method for each image is the one for which the visual features of the identified words in the image are “closer” to the features of the reference words. The proposed technique was used here to assess the performances of eleven algorithms based on different approaches on a collection of real and synthetic images.     

基于图像分块的局部阈值二值化方法

针对目前局部阈值二值化结果存在目标虚假或断裂的缺陷,提出了一种基于图像分块的局部阈值二值化方法。首先,将图像分成若干子块并分析每个子块像素灰度变化情况;接着,取一定大小的局部窗口在图像中移动,比较该局部窗口内与包含窗口自身且比窗口更大区域内的像素灰度变化情况,更大区域由窗口模板当前覆盖的所有子块组成,以此判断窗口内是否为灰度变化平坦（或剧烈）区域;最后,根据不同的区域,给出具体的二值化方案。利用7种不同算法对4种不同类型的4组图像进行了二值化实验。实验结果表明该算法在屏蔽背景噪声和保留目标细节方面表现最优,特别地通过对车牌图像的二值化结果进行定量分析后发现该算法能够得到最高召回率和准确率。     

一种区域收缩及分类的车牌二值化方法

对车牌区域进行二值化一直是车牌识别系统的一个关键问题。针对车牌区域的特征,提出了一种基于分类思想的二值化方法。该算法从统计判别分析的思想出发,将二值化问题看成是一个分类问题。首先对区域进行收缩取样,然后进行分类。为了提高二值化精度,其中还使用了迭代分类技术。另外为了评价车牌二值化效果,从车牌二值化应用角度出发提出了粘连度、字符断裂度、噪声颗粒数、运行消耗时间的指标体系,用来评价车牌二值化的效果。有了这套指标体系,就可以方便地对各种车牌二值化技术进行评价。实验结果表明,该二值化算法简单有效。     

Adaptive binarization method for degraded document images based on surface contrast variation

Document binarization is an important technique in document image analysis and recognition. Generally, binarization methods are ineffective for degraded images. Several binarization methods have been proposed; however, none of them are effective for historical and degraded document images. In this paper, a new binarization method is proposed for degraded document images. The proposed method based on the variance between pixel contrast, it consists of four stages: pre-processing, geometrical feature extraction, feature selection, and post-processing. The proposed method was evaluated based on several visual and statistical experiments. The experiments were conducted using five International Document Image Binarization Contest benchmark datasets specialized for binarization testing. The results compared with five adaptive binarization methods: Niblack, Sauvola thresholding, Sauvola compound algorithm, NICK, and Bataineh. The results show that the proposed method performs better than other methods in all binarization cases.     

A binarization method with learning-built rules for document images produced by cameras

In this paper, we propose a novel binarization method for document images produced by cameras. Such images often have varying degrees of brightness and require more careful treatment than merely applying a statistical method to obtain a threshold value. To resolve the problem, the proposed method divides an image into several regions and decides how to binarize each region. The decision rules are derived from a learning process that takes training images as input. Tests on images produced under normal and inadequate illumination conditions show that our method yields better visual quality and better OCR performance than three global binarization methods and four locally adaptive binarization methods.     

Adaptive degraded document image binarization

This paper presents a new adaptive approach for the binarization and enhancement of degraded documents. The proposed method does not require any parameter tuning by the user and can deal with degradations which occur due to shadows, non-uniform illumination, low contrast, large signal-dependent noise, smear and strain. We follow several distinct steps: a pre-processing procedure using a low-pass Wiener filter, a rough estimation of foreground regions, a background surface calculation by interpolating neighboring background intensities, a thresholding by combining the calculated background surface with the original image while incorporating image up-sampling and finally a post-processing step in order to improve the quality of text regions and preserve stroke connectivity. After extensive experiments, our method demonstrated superior performance against four (4) well-known techniques on numerous degraded document images.     

Parameter-free based two-stage method for binarizing degraded document images

Binarization plays an important role in document image processing, especially in degraded documents. For degraded document images, adaptive binarization methods often incorporate local information to determine the binarization threshold for each individual pixel in the document image. We propose a two-stage parameter-free window-based method to binarize the degraded document images. In the first stage, an incremental scheme is used to determine a proper window size beyond which no substantial increase in the local variation of pixel intensities is observed. In the second stage, based on the determined window size, a noise-suppressing scheme delivers the final binarized image by contrasting two binarized images which are produced by two adaptive thresholding schemes which incorporate the local mean gray and gradient values. Empirical results demonstrate that the proposed method is competitive when compared to the existing adaptive binarization methods and achieves better performance in precision, accuracy, and F-measure.     

图谱理论在文本图像二值化算法中的应用

常用的阈值二值化方法不能很有效地分割出文本图像,而利用图谱理论的思想可以清晰有效地对文本图像进行二值化分割。针对传统的图谱理论分割图像算法计算量大、空间复杂度高的不足,提出了利用直方图灰度等级代替像素级,在此基础上近似计算了权函数的参数,算法的计算量和复杂度都有所降低。实验结果表明,该方法大大降低了计算的复杂性,在速度上优于传统的图谱理论分割方法,质量上优于常用的二值化分割方法。     

时空混沌二值化方法研究

针对耦合映像格子模型产生的时空混沌序列的特点,在符号函数二值化法的基础上,给出了一种新的二值化方法。随机性能和相关性检验的结果表明按这种方法得到的二值序列具有优良的伪随机性能及相关特性,说明提出的方法是有效的,而且简单实用。     

改进的谱聚类图像分割方法

图像分割作为图像识别的一个重要处理步骤,但存在效果不理想或者计算复杂度过高的问题。提出一种新的灰度图像二值化的方法。该方法将Ncut作为谱聚类的量度,在计算该值时使用基于图像灰度级的权重矩阵,而非普通基于图像像素的权重矩阵。这样,计算复杂度和空间复杂度都明显降低。通过对实际场景中文本图像的实验,数据表明此方法在时间和系统开销方面比传统基于阈值的分割方法具有更优的性能。     

Sugeno integral generalization applied to improve adaptive image binarization

Classic adaptive binarization methodologies threshold pixels intensity with respect to adjacent pixels exploiting integral images. In turn, integral images are generally computed optimally by using the summed-area-table algorithm (SAT). This document presents a new adaptive binarization technique based on fuzzy integral images. Which, in turn, this technique is supported by an efficient design of a modified SAT for generalized Sugeno fuzzy integrals. We define this methodology as FLAT (Fuzzy Local Adaptive Thresholding). Experimental results show that the proposed methodology produced a better image quality thresholding than well-known global and local thresholding algorithms. We proposed new generalizations of different fuzzy integrals to improve existing results and reaching an accuracy $\approx 0.94$ on a wide dataset. Moreover, due to high performances, these new generalized Sugeno fuzzy integrals created ad hoc for adaptive binarization, can be used as tools for grayscale processing and more complex real-time thresholding applications.     

多窗口图像二值化算法研究

常用的全局二值法和局部二值法算法存在细节丢失、噪声引入、运算时间过长等弊端。为此提出了一种多窗口图像二值化算法,采用多窗口模板分别对图像进行简单二值化处理,对不同窗口处理下获得的二值图进行综合判断,最终确定每个像素点的逻辑值。通过MATLAB仿真,与常用二值化算法进行比较,验证提出的多窗口图像二值化算法具有处理简单、运算速度快、鲁棒性较好等优点。     

一种针对较厚书籍扫描图像的二值化方法

摘 要: 对较厚的书籍进行扫描时,由于中缝难以压平,常使扫描后的图像出现黑边,因而采用常规的算法对其进行阈值化结果很不理想,进而严重影响到文字识别的效果。针对这一问题,提出了一种基于纹理分析的图像二值化方法。该方法在动态阈值的基础上,通过对分块后子图像的纹理特性进行分析,将子图像分成不同的类型,进而对不同类型的子图像进行不同的处理,很好地消除了图像黑边和背景亮度变化对二值化结果的影响。     

A noise attribute thresholding method for document image binarization

A new thresholding method, called the noise attribute thresholding method (NAT), for document image binarization is presented in this paper. This method utilizes the noise attribute features extracted from the images to make the selection of threshold values for image thresholding. These features are based on the properties of noise in the images and are independent of the strength of the signals (objects and background) in the image. A simple noise model is given to explain these noise properties. The NAT method has been applied to the problem of removing text and figures printed on the back of the paper. Conventional global thresholding methods cannot solve this kind of problem satisfactorily. Experimental results show that the NAT method is very effective. Received July 05, 1999 / Revised July 07, 2000     

A novel image thresholding method based on Parzen window estimate

Image segmentation is one of the most important and fundamental tasks in image processing and techniques based on image thresholding are typically simple and computationally efficient. However, the image segmentation results depend heavily on the chosen image thresholding methods. In this paper, histogram is integrated with the Parzen window technique to estimate the spatial probability distribution of gray-level image values, and a novel criterion function is designed. By optimizing the criterion function, an optimal global threshold is obtained. The experimental results for synthetic real-world and images demonstrate the success of the proposed image thresholding method, as compared with the OTSU method, the MET method and the entropy-based method.     

Goal-directed evaluation of binarization methods

This paper presents a methodology for evaluation of low-level image analysis methods, using binarization (two-level thresholding) as an example. Binarization of scanned gray scale images is the first step in most document image analysis systems. Selection of an appropriate binarization method for an input image domain is a difficult problem. Typically, a human expert evaluates the binarized images according to his/her visual criteria. However, to conduct an objective evaluation, one needs to investigate how well the subsequent image analysis steps will perform on the binarized image. We call this approach goal-directed evaluation, and it can be used to evaluate other low-level image processing methods as well. Our evaluation of binarization methods is in the context of digit recognition, so we define the performance of the character recognition module as the objective measure. Eleven different locally adaptive binarization methods were evaluated, and Niblack's method gave the best performance     

自适应最小误差阈值分割算法

对二维最小误差法进行三维推广, 并结合三维直方图重建和降维思想提出了一种鲁 棒的最小误差阈值分割算法. 但该方法为全局算法, 仅适用于分割均匀光照图像. 为 提高其自适应性, 本文采用Water flow模型对非均匀光照图像进行背景估计, 以此获 得原始图像与背景图像的差值图像, 达到降低非均匀光照对图像分割造成干扰的目的. 为进 一步提高分割性能, 本文对差值图像采用γ 矫正进行增强, 然后采用鲁棒最小误差 法进行全局分割, 从而完成目标提取. 最后本文对均匀光照下以及非均匀光照下图像进行了 实验, 并与一维最小误差法、二维最小误差法、三维直方图重建和降维的Otsu阈值分割 算法、灰度波动变换自适应阈值方法以及一种改进的FCM方法在错误分割率和运行时间上进 行了对比. 实验结果表明, 相对于以上方法, 本算法的分割性能均有明显提升.     

Intelligent region-based thresholding for color document images with highlighted regions

The study applies an intelligent region-based thresholding method for the binarization of color document images with highlighted regions. The results also indicate that the proposed method can threshold simultaneously when the background is gradually changing, reversed, or inseparable from the foreground, with efficient binarization results. Rather than the traditional method of scanning the entire document at least once, this method intelligently divides a document image into several foreground regions and decides the background range for each foreground region, in order to effectively process the detected document regions. Experimental results demonstrate the high effectiveness of the proposed method in providing promising binarization results with low computational cost. Furthermore, the results of the proposed method are more accurate than global, region-based, local, and hybrid methods. Images were analyzed using MODI OCR measurement data such as recall rate and precision rate. In particular, when test images produced under inadequate illumination are processed using the proposed method, the binarization results of this method have better visual quality and better measurable OCR performance than compared global, region-based, local, and hybrid methods. Moreover, the proposed algorithm can be run in an embedded system due to its simplicity and efficiency.     

多相Chan-Vese模型的直接对偶方法

多相图像分割的变分模型采用水平集函数定义不同区域的特征函数,其极值问题需要迭代求解一系列动态演化方程,计算效率低。较快的方法是对离散的二值标记函数凸松弛后设计对偶方法或Split Bregman方法,并结合阈值化技术得到分割结果。提出一种无需凸松弛和阈值化的快速分割方法—直接对偶方法(DDM)。DDM利用二值标记函数的二值特性,并根据KKT条件得到原变量的二值解析解和对偶变量的简单迭代格式。该方法首先应用到两相Chan-Vese模型,然后拓展到多相Chan-Vese模型。实验结果表明,DDM比梯度降方法、对偶方法和Split Bregman方法分割效果好、计算效率高。