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Machine Printed Handwritten Text Discrimination


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  • 1. Machine Printed Handwritten Text Discrimination Using Radon Transform and SVM Classifier ET-Tahir Zemouri1 and Youcef Chibani 2 Signal Processing Laboratory, Faculty of Electronic and Computer Sciences University of Sciences and Technology Houari Boumediene USTHB, EL-Alia, B.P. 32, 16111, Algiers, Algeria 1 tzemouri, 2 ychibani@usthb.dzAbstract—Discrimination of machine printed and handwritten lines in Bangla script. Guo and Ma [3] proposedhandwritten text is deemed as major problem in the an approach based on the vertical projection profile of therecognition of the mixed texts. In this paper, we address the segmented words, which used a Hidden Markov Modelproblem of identifying each type by using the Radon transform (HMM) as the classifier. Zheng et al. [4] reported on printedand Support Vector Machines, which is conducted at three and handwritten text segmentation using k-NN, Supportsteps: preprocessing, feature generation and classification. New Vector Machines (SVM) and Fisher classifier with featuresset of features is generated from each word using the Radon like pixel density, aspect ratio and Gabor features. Kandan ettransform. Classification is used to distinguish printed text al. [5] used invariant moments, which are insensitive tofrom handwritten. The proposed system is tested on IAM translation, scale, mirroring and rotation as the feature fordatabases. The recognition rate of the proposed method is distinguishing the printed and handwritten elements and thecalculated to be over 98%. SVM classifier. We propose in this paper a new method for text Keywords-document analysis; machine printed and discrimination by using the Radon transform and Supporthandwritten text discrimination; Radon transform; Support Vector Machines.Vector Machines (SVM). The Radon transform is adapted for detecting linear features. Hence, printed words generate Radon coefficients I. INTRODUCTION more regular comparatively to handwritten words. This Machine printed and handwritten text are often met in property can be used for distinguishing between printed andapplication forms, question papers, mail as well as notes, handwritten words. While, the SVM is well adapted for acorrections and instructions in printed documents. robust separation of two classes. In all mentioned cases it is crucial to detect, distinguish The paper is organized as follows. In section 2, weand process differently the areas of handwritten and printed describe the proposed system. Experiments and conclusionstext (OCR for machine printed text and ICR for handwritten are discussed in Sections 3 and 4, respectively.annotations) for obvious reasons such as: (a) retrieval ofimportant information (identification of handwriting in II. THE PROPOSED SYSTEMapplication forms), (b) removal of unnecessary information The system for the discrimination between machine(removal of handwritten notes from official documents), and printed and handwritten text can be decomposed into three(c) application of different recognition algorithms in each stages [1], as shown in Fig. 1. The first stage is thecase. preprocessing stage, in which the document is cleaned of all The main difference between machine printed and the noise components present such as spurious dots andhandwritten text is their shape structure. Characters in lines. In the second stage, features are generated based onmachine printed text have a uniform shape. Whereas Radon transform, for which the elements are classified intohandwritten text are of arbitrary curly allograph styles. This printed or handwritten using SVM classifiers.difference can be exploited for generating features byexploring the regularity of the machine printed words A. Preprocessing stagecomparatively of the handwritten words. Due to large variations in image data, preprocessing, There exist a few papers on the discrimination of which is used to reduce variations and produce a moremachine printed and handwritten text. Kuhnke et al. [1] consistent set of data, is essential for accurate characterproposed a neural network-based approach with straightness recognition. In our system, preprocessing includes theand symmetry as features. Pal and Chaudhuri [2] have used filtering, binarization, skew angle correction, smoothing, andhorizontal projection profiles for separating the printed and word segmentation.
  • 2. characters is more or less stable within a text word. On the Document image other hand, the distribution of the shape of handwritten characters is quite diverse. The Radon transform has been used in many pattern Preprocessing recognition applications as shape recognition [11]. In our approach, the Radon transform is used as a tool for Filtering Binarization Skew correction generating a feature vector. Hence, we briefly review its main properties. 1) Radon Transform Segmentation Smoothing The Radon transform computes projections of an image along specified directions. A projection of a two-dimensional function I ( x, y ) is a set of line integrals. The Radon Feature generation transform computes the line integrals from multiple sources along parallel paths in a certain direction. To represent an image, the Radon transform takes multiple and parallel Classification projections of the image from different angles by rotating the source around the center of the image. Formally, the Radon transform of an image is defined as [12]: Machine printed Handwritten TRI ( ρ ,θ ) = ∫x ∫y I ( x, y )δ ( x cosθ + y sin θ − ρ )dxdy (1) Figure 1. Block-diagram of the classification system. 1) Image filtering: Generally, the image acquired from where δ is the Dirac function, θ ∈]0,180°] anda scanner contains the noise, which can be reduced using a ρ ∈] - ∞,+∞] . In other words, TRI is the integral of I ( x, y )3x3 Wiener filter [6]. over the line defined by ρ = x cos θ + y sin θ . 2) Binarization: the text is separated from background The Radon transform has several useful properties, asby automatic thresholding. The Wolf approach [7] is used to periodicity, symmetry, translation invariance, rotationthe binary image. invariance and scaling invariance. 3) Skew angle correction: The skew estimation and In our approach, we only are interested on periodicitycorrection is an important step in any document analysis and and symmetry. Fig. 2 shows an example of the Radonrecognition system. Hence, we use the projection profile for transform computed on the printed and handwritten words.estimating the skew angle [8], which can be performed fordifferent angles and the largest magnitude variationscorrespond to the skew angle. 4) Smoothing: For smoothing binary document images,four filters [9] can be used to smooth the edges and removingthe small pieces of noise. 5) Segmentation: Segmentation aims to extract thewords from the document. Segmentation is performed in twoconsecutive steps: line segmentation and word segmentation.Both steps make use of the projection profiles [10].B. Feature Generation Many kinds of features can be generated for distinguishthe printed from handwritten text, Kuhnke et al. [1] proposeda straightness of vertically/horizontally oriented lines andsymmetry relative to different points as features. Pal andChaudhuri [2] used the distinctive structural and statisticalfeatures. Guo and Ma [3] evaluated their scheme using thevertical projection profile. Zheng et al. [4] used features like (a) (b)Gabor filter, Run length histogram features etc. Kandan et al. Figure 2. A shape (a) and its Radon transform (b).[5] used the invariant moments that are invariant undertranslation, scaling, rotation and reflection. We can easily see that the Radon transform generates The main idea of our approach is to take advantage of the more coefficients of the handwritten word comparatively tostructural properties that help to discriminate printed from the printed word.handwritten text. More precisely, the shape of the printed
  • 3. 2) Feature vector generation We can see that the energy based-Radon transform To generate features of printed and handwritten words, generates more energy of the handwritten wordwe fix the angular direction number denoted by Nθ comparatively to the printed word.( θ ∈]0,360°] ). Since, the Radon transform generates 3) Feature vector normalizationredundant coefficients (Fig 2.b), hence, in our approach, we In many practical situations, a designer is confrontedselect the positive radial projections and taking all directions with features whose values lie within different dynamicfrom 0 to 360°. The feature vector is then generated by ranges. Thus, features with large values may have a largercomputing for a given column in positive space of the Radon influence in the cost function than features with small values,transform, the sum of the square coefficient by setting the although this does not necessarily reflect their respectivenumber of angular direction Nθ . The feature values E I (θ ) significance in the design of the classifier. The problem isare defined as: overcome by normalizing the features so that their values lie within similar ranges. This is achieved by using nonlinear transformation [13]. 1 E I (θ ) = ∑ N ρ TR ( ρ ,θ ) I 2 (2) Nρ C. Classification SVM are supervised learning methods, which have beenFig. 3 illustrates an example of feature generation values widely and successfully used for pattern recognition inwhich include the Radon transform energy for each angle θ . different applications as digit recognition [14]. The main concept of SVM lies to find a hyperplane that allows separating two classes, leaving the largest margin between the vectors of the two classes [14]. However, in real life, problems can be linearly non separable. To deal with this problem, a nonlinear decision surface is obtained by lifting the feature space into a higher dimensional space. A linear separating hyperplane is found in the higher dimensional space that gives a nonlinear decision surface in the original feature space. The decision function of the SVM can be expressed as follows: (a) f ( x) = ∑ α i yi K ( x, xi ) + b (3) i Where ( xi , yi ) ∈ ℜ d X{± 1} are the feature vectors and labels, respectively. In our case, the feature vectors and labels correspond to the Radon energy {xi } , printed words {+1} and handwritten words {-1}, respectively. Parameters α i and b are found by maximizing a quadratic function subject to some constraints [14]. K ( x, xi ) is the kernel function, which allows mapping the feature vectors into a (b) higher dimension inner product space. In our case, we use the RBF kernel (Radial Function Basis) since it offers better discrimination than other kernels. The RBF kernel is defined as: d ( x, xi ) K ( x, xi ) = exp(− ) (4) 2σ 2 2 d ( x, xi ) = x − xi (5) σ is user defined. (c) The optimization algorithm adopted for training SVMs is the Sequential Minimal Optimization (SMO) which provides Figure 3. Feature vector generation, (a) Printed word and its Radon transform, (b) handwritten word and its Radon transform, (b) Radon practical advantages [15]. transform, (c) Radon energy versus angle.
  • 4. III. EXPERIMENTAL RESULTS B. System validation In order to validate our system various experiments areA. Data set conducted for finding the SVM regularization parameter For evaluating the performances of the proposed method, (fixed at 10), kernel parameter ( σ ) and the best angularwe use the IAM database (Institut für Informatik und direction number ( Nθ ). Fig. 5 shows the recognition rateangewandte Mathematik) [16]. They are scanned withresolution of 300 dpi, 8 bits/pixel, gray-scale and converted obtained on the validation set for each angular directioninto binary images using the Wolf binarization method. This number. We can note that the RR is not very sensitive to thedatabase is formed for more than 1500 documents containing number of the angular direction. However, the bestprinted and handwritten text. An example of a document can performances (RR=77.06%) are obtained for Nθ =20 andbe seen in Fig. 4. Regions of printed and handwritten words σ =2.1.are easily separable. They present no auxiliary lines to fill orto supply with written texts. This characteristic facilitates theidentification and classification of each type of words. For testing the performances of our system, 21 imagesare chosen and preprocessed. The set of words are dividedinto three subsets for training (1/3), validating (1/3) andtesting (1/3), respectively. Table 1 summaries the data set. For each word, a vector with the energy based-RadonTransform is calculated. We use the recognition rate (RR) asa metric to evaluate the performances of our system, which isdefined as: # of words correctly classified RR = (%) (7) Figure 5. Recognition rate using Radon transform # total of words for the system validation. In order to improve the recognition rate, we add by concatenation statistical features to the energy based-Radon transform, which are mean, variance, variance of projection profile (vertical and horizontal) and entropy. Fig. 6 shows the recognition rate versus the number of the angular direction. Figure 6. Recognition rate using Radon transform and statistical features. We can see that statistical feature sets are very suitable Figure 4. IAM Database form. information for the discrimination between machine printed and handwritten text since the RR has been improved to 92.8% for Nθ =10 and σ =2 using validation set. This TABLE I. DATA SET constitutes an additional advantage when adding the Data set Training Validation Testing statistical features. Machine printed 447 447 438 C. System testing Handwritten 525 525 484 After the validation of the system, the testing set is used Total 972 972 922 for evaluating its performances. Hence, the optimal values of
  • 5. the system validation are used for computing the recognition [6] B. Gatos, I. Pratikakis and S. J. Perantonis, “Adaptive degradedrate. The obtained results are 98.32%, which constitutes document image binarization,” Pattern Recognition, vol. 39, pp. 317- 327, 2006.encouraging performances compared to other works [1-5]. [7] C. Wolf, and J.M. Jolion, “Extraction and recognition of artificial textD. Comparaison with other similar works in multimedia documents,” Pattern Analysis and Applications, vol. 6, n. 4, pp. 309-326, 2003. We compare our results with some other published [8] T. Akiyama, and N. Hagita, “Automatic entry system for printedresearch works in terms of RR. Hence, Kuhnke et al. [1] documents,” Pattern Recognition, vol. 23, n. 11, pp. 1141-1154, 1990.proposed a neural network-based approach with straightness [9] M. Cheriet, N. Kharma, C. L. Liu, and C. Suen, “Characterof vertically/horizontally oriented lines and symmetry Recognition Systems: A Guide for Students and Practitioners,”relative to different points as features. The system reached a Wiley-Interscience editor, p 321, 2007.RR of 78.5%. Pal and Chaudhuri [2] approach based on the [10] E. Ataer, and P. Duygulu, “Retrieval of Ottoman Documents,” Proc 8th ACM international workshop on Multimedia informationdistinctive structural and statistical features of machine retrieval, pp. 155-162, 2006.printed and handwritten text lines in Bangla script. The [11] S. Tabbone ,L. Wendling, and J. P. Salmon, “A new shape descriptorclassification scheme has a RR of 98.3%. Guo and Ma [3] defined on the Radon transform,” Computer Vision and Imageevaluated their scheme using the vertical projection profile of Understanding, vol.102, n. 1, pp. 42–51, 2006.the segmented word and obtained a 92.86% from their [12] S. R. Deans, “The Radon Transform and Some of Its Applications. New York: Wiley, 1983.scheme using HMM. Zheng et al. [4] got a RR of 96% using [13] S. Theodoridis, and K. Koutroumbas, “Pattern Recognition,” 4th Ed,SVM classifier and features like Gabor filter, Run length Elsevier Inc, 2009.histogram features etc. Kandan et al. [5] obtained a RR of [14] H. Nemmour, Y. Chibani, “Handwritten digit recognition based on a93.22% using the invariant moments that are invariant under neural-SVM combination”, Int journal of computers and applicationstranslation, scaling, rotation and reflection as features and (Acta Press Editor), vol. 32, n.1, pp. 104-109, 2010.SVM classifier. [15] H. Nemmour, Y. Chibani, “Integrating class-dependant tangent Our proposed method obtains a RR of 98.32% by using vectors into SVMs for handwritten digit recognition,” Int Conf on Signals, Circuits and Systems (ICSCS), pp. 1-4, 2009.Radon transform and statistical features and SVM classifier, [16] U.V. Marti, and H. Bunke, “The IAM-Database: an english sentencewhich constitutes encouraging performances compared to database for offline handwriting recognition,” International Journalother works. on Document Analysis and Recognition, vol. 5, n. 1, pp. 39-46, 2002. IV. CONCLUSION In this paper, we proposed a new method fordiscriminating printed and handwritten text in documentimages using the Radon transform and SVM classifiers. Thesystem was implemented and tested in IAM databases. Our approach presents encouraging results by combiningRadon energy and statistical features using SVM classifierswith the RBF kernel. In the future, we plane to implement our methodology todistinguish machine printed/handwritten with Arabic andLatin texts. REFERENCES[1] K. Kuhnke, L. Simoncini, and Z.M. Kovacs-V, “A System for Machine-Written and Hand-Written Character Distinction,” Proc. 3rd International Conference on Document Analysis and Recognition, vol. 2, pp 811-814, 1995.[2] U. Pal, and B. B. Chaudhuri, “Machine-printed and Hand-written Text Line Identification,” Pattern Recognition Letters, vol. 22, n. 3-4, pp. 431-441, 2001.[3] J. K. Guo, and M. Y. Ma, “Separating Handwritten Material from Machine Printed Text Using Hidden Markov Models,” Proc. 6th International Conference on Document Analysis and Recognition, pp. 439-443, 2001.[4] Y. Zheng, H. Li, and D. Doermann, “Machine Printed Text and Handwriting Identification in Noisy Document Images,” IEEE Trans on Pattern Analysis and Machine Intelligence, vol. 26, n. 3, pp. 337- 353, 2004.[5] R. Kandan, N. K. Reddy, K. R. Arvind, and A. G. Ramakrishnan, “A Robust Two Level Classification Algorithm for Text Localization in Documents,” Advances in Visual Computing, 3rd Int Symp, (ISVC 07), Part II, LNCS 4842, pp. 96–105, 2007.