This paper presents an original solution for flexible hand-written text
division into rows. Unlike the standard procedure, the proposed method avoids
the isolated characters extensions amputation and reduces the recognition error
rate in the final stage.Comment: 6 pages, exposed on 5th International Conference "Actualities and
  Perspectives on Hardware and Software" - APHS2009, Timisoara, Romani

Lacrama, Dan L.

Snep, Ioan

English

arXiv

This paper presents an original solution for flexible hand-written text division into rows. Unlike the standard procedure, the proposed method avoids the isolated characters extensions amputation and reduces the recognition error rate in the final stage

Dan L. Lacrămă

Ioan Şnep

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     Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    199                F Fl le ex xi ib bl le e   f fr ro on nt ti ie er rs s   f fo or r   t te ex xt t   d di iv vi is si io on n   i in nt to o   r ro ow ws s        D Da an n   L L. .   L La ac cr ră ăm mă ă1 1, ,   I Io oa an n   Ş Şn ne ep p2 2   1 ”Tibiscus” University of Timişoara, Romania 2 NMS Institute, Paris, France   ABSTRACT:  This  paper  presents  an  original  solution  for  flexible hand-written text division into rows. Unlike the standard procedure, the  proposed  method  avoids  the  isolated  characters  extensions amputation and reduces the recognition error rate in the final stage. KEYWORDS: pattern recognition, image processing   Introduction  The  standard  methodology  for  any  automatic  reading  systems  contains  a multiple segmentation procedure before the character recognition stage. The text  body  is  first  divided  into  rows,  than  each  word  inside  the  row  is detached  and  finally  word’s  letters  are  isolated.  Sometimes,  this decomposition is continued, and even the characters are cleaved in their sub-components  in  order  to  detect  lines  loops  and  breaks  in  their  structure [SGS93]. The cutting of the text body into rows is traditionally done by straight line borders, and this proves to be highly efficient for printed text samples as it is shown in Figure 1.1.a. This procedure is also adequate if the text is carefully hand-written in order to avoid any partial superposition between the  descendant  zone  of  the  upper  row  and  the  ascendant  of  its  lower neighbour. Unfortunately  this  is  not  the  case  for  the  most  of  the  hand-written samples and consequently there is no chance for the frontier to bypass one or more  of  the  ascending  or  descending  extensions present  in  the  inter-row region as it can be seen in the Figure 1.1.b.      Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    200 These amputations usually do not affect the recognition of the cleaved character but create a great error hazard in the classification of the neighbour to which the cut “tail” is appended. For example the little part cleaved from the letter ‘p’ in word “pt.” is likely to cause the wrong classification of the first loop of the ‘m’ in the word “imagini” as an ‘i’ and consequently a non-word label (recognition fail) for the resulting “iinagini” at the end of the reading [Gil96]. This peril is bigger when texts are written in a language where the alphabet contains letters with accents or other isolated upper or lower extensions (e.g. Romanian specific characters ‘ă’, ’â’ ‘ş’, and ‘ţ’).  Figure 1.1. Straight line borders text segmentation into rows  Bottom edge following borders segmentation is a second methodology recommended in the literature. The basic idea is the construction of frontiers point by point nearby the base edge of the words. The link between two consecutive  words  is  done  usually  by  a  straight  line.  After  this  first construction step, the border is redrawn with straight line segments in order to reduce its complexity (i.e. contour relaxation) [LF95].  Figure 1.2. Bottom edge following borders method for text segmentation into rows  The algorithm performs a very good segmentation into rows for texts in  English  but  constantly  amputates  the  descending  isolated  parts  (i.e. diacritic signs) of special characters in other national languages alphabets. This problem is illustrated in Figure 1.2. where the word “animaţie” letter ‘ţ’ low part is cut off from the upper row and will be appended to the lower one a. Printed text  b. Hand-written text      Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    201 causing latter a great amount of problems in the recognition of character ‘r’ from “iar”. Another  disadvantage  of  this  procedure  is  the  fact  that  it  is  time consuming because it does the edge following point by point all over the given document and this affect the speed for all the segmentation process. The contour relaxation in the end solve the problem of simplifying the text image division into individual rows images, but it also need some extra time to be done. Therefore  this  paper  propose  a  technique  able  to  avoid  both  the amputation of the linked and isolated ascending or descending extensions of the characters in the process of row segmentation of the text body.   1 Flexible frontiers segmentation method  The flexible borders are usually straight line segments which link together short edge following curve segments existing only in the neighbourhood of a character  -  frontier  intersection  point.  Hence  the  row  dividing  border contains: * line segments extending until a letter edge is reached * contour following curves extending until a new line segment can be started *      Figure 2.1. Rows splitting in a partially Figure 2.1. Rows splitting in a partially superposed zone  The contour pursuing method used for the algorithm implementation was  the  “Hand  on  the  wall  following”  standard  procedure  described  in [GW93]  and  it  proved  to  be  an  efficient  and  low  time  consuming.  A comparison between the results of the classic straight line border method and the method proposed by this paper is given in Figure 2.1 for a case that is quite frequent in hand-written texts. The Logic flow chart of the flexible border procedure routine is given in Figure 2.2. a. Straight line segmentation technique   b. Flexible frontier segmentation technique  a. Straight line segmentation technique       Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    202 Because  it  was  very  important  to  avoid  amputation  of  isolated character’s  parts,  every  time  when  such  an  extension  is  met  the  border detour realised by the pursuing curve was orientated firstly to the exterior of the  row.  Only  if  it  arrives  to  the  central  part  of  the  adjacent  row  the procedure is taken from its begging with a detour to the interior. Figure 2.3 illustrates this kind of behaviour and its importance for a correct separation of the rows in a Romanian text.    Figure 2.2. Logic flow chart of the flexible border procedure routine   Figure 2.3. Avoiding amputation with exterior detour  It  has  to  be  stressed  here  that  every  straight  line  segment  of  the flexible border has the same direction given by the medium row angle. This is necessary because usually hand-written rows are not exactly parallel with      Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    203 the document image horizontal. This is due both to the human error and the impossibility of exact alignment in the acquisition process [LSO95]. The  routine  waits  for  an  intersection  point  to  occur  and  starts  the contour tracking by looking for a neighbouring pixel that is a background - letter edge pixel. When such a pixel is found, it is declared point of the frontier and a new border pixel is searched in its own neighbourhood. First the contour following direction is oriented to the outside of the row. The “Next row median zone?” if block controls the frontier in order to avoid its entrance in the middle zone of the nearby row. If this happens the direction  is  reversed  and  a  new  tracking  procedure  is  started  from  the beginning intersection point. This  point  by  point  construction,  similar  to  the  one  in  the  second method described in the paragraph above, ends in the point where a line segment with the medium row angle can be started. This point is detected in the “Straight border direction?” if block. If it encounters another intersection the pursuing is repeated with the same algorithm, if not the line goes until the right end of the image. During each curved segment the border is drawn by  the  above  routine,  during  line  segment  the  border  is  established  and designed by the main programme.  Figure 3.1. Flexible frontiers segmentation results   2 Experimental results  The Figure 3.1.a. and b. show the test of the Flexible frontier segmentation technique over the same samples as the two classic methods presented in the first paragraph. There are no errors and the text body is correctly cut into rows in both cases. This remarkable adaptability to quite different situations is an important and useful feature of the proposed procedure. a. Printed text   b. Hand-writting text       Anale. Seria Informatică. Vol. VII fasc. 1 – 2009 Annals. Computer Science Series. 7th Tome 1st Fasc. – 2009    204 Extending experiments to a set of 24 test samples it was proved that the  method  was  able  to  reduce  segmentation  errors  with:  63.7%  in comparison with the Straight line border method and 12.2% in comparison with the Bottom edge following borders method. Another important gain of the proposed procedure is the fact that it preserves the speed of the straight line border method in samples where no partial  superposition  occurs  (sample  from  Figure  3.1.  is  segmented  in practically the same time with both straight and flexible frontiers method). This  is  possible  because  the  contour  following  procedure  is  a  routine becoming active only when it is needed, in the moment of meting a border - character intersection.   References  [Gil96]  M. Gilloux – Research Into A New Generation Of Character And Mailing Address Recognition Systems At The French Post Office  Research  Centre  Pattern  Recognition  Letters,  North Holland, vol.17, Nr. 4, April 1996, pp. 267-276  [GW93]  R.  Gonzales,  P.  Wintz  –  Digital  Image  Processing,  Adison-Wesley 1993  [LSO95]  L. D. Lacrămă, I. Şnep, V. Oaie – Segmentarea textelor scrise de mână, Revista Facultăţii de economie, Timişoara 1995, vol XVI, pp. 23-31   [LF95]  G.L. Likforman-Sulem, C. Faure – Une methode de resolution des conflits d’alignements pour la segmentation des documents manuscrits, Traitement du signal, vol.12, No 4-6 Avril 1995  [SGS93]  V. Shapiro, G. Glutchev, V. Sgurev – Hand-written document image segmentation and Analysis, Pattern Recognition Letters, North Holland, vol.14, Nr. 1, January 1993, pp. 71-78  

Flexible frontiers for text division into rows

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