Textline information extraction from grayscale camera-captured document images

Cameras offer flexible document imaging, but with uneven shading and non-planar page shape. Therefore cameracaptured documents need to go through dewarping before being processed by traditional text recognition methods. Curled textline detection is an important step of dewarping. Previous approaches of curled textline detection use binarization as a pre-processing step, which can negatively affect the detection results under uneven shading. Furthermore, these approaches are sensitive to high degrees of curl and estimate x-line1 and baseline pairs using regression which may result in inaccurate estimation. We introduce a novel curled textline detection approach for grayscale document images. First, the textline structure is enhanced by using match filter bank smoothing and then central lines of textlines are detected using ridges. Then, x-line and baseline pairs are estimated by adapting active contours (snakes) over ridges. Unlike other approaches, our approach does not use binarization and applies directly on grayscale images. We achieved 91% of detection accuracy with good estimation of x-line and baseline pairs on the dataset of CBDAR 2007 document image dewarping contest.

[1]  Wenxin Li,et al.  A Model-based Book Dewarping Method Using Text Line Detection , 2007 .

[2]  Berthold K. P. Horn.  SHAPE FROM SHADING: A METHOD FOR OBTAINING THE SHAPE OF A SMOOTH OPAQUE OBJECT FROM ONE VIEW , 1970 .

[3]  Yi Li,et al.  Script-Independent Text Line Segmentation in Freestyle Handwritten Documents , 2008, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[4]  Thomas M. Breuel,et al.  Performance Evaluation and Benchmarking of Six-Page Segmentation Algorithms , 2008, IEEE Transactions on Pattern Analysis and Machine Intelligence.

[5]  L. O'Gorman,et al.  Matched filter design for fingerprint image enhancement , 1988, ICASSP-88., International Conference on Acoustics, Speech, and Signal Processing.

[6]  M. Goldbaum,et al.  Detection of blood vessels in retinal images using two-dimensional matched filters. , 1989, IEEE transactions on medical imaging.

[7]  Syed Saqib Bukhari,et al.  Segmentation of Curled Textlines Using Active Contours , 2008, 2008 The Eighth IAPR International Workshop on Document Analysis Systems.

[8]  Ioannis Pratikakis,et al.  Segmentation Based Recovery of Arbitrarily Warped Document Images , 2007 .

[9]  Syed Saqib Bukhari,et al.  Ridges Based Curled Textline Region Detection from Grayscale Camera-Captured Document Images , 2009, CAIP.

[10]  Thomas M. Breuel,et al.  Pixel-Accurate Representation and Evaluation of Page Segmentation in Document Images , 2006, 18th International Conference on Pattern Recognition (ICPR'06).

[11]  Demetri Terzopoulos,et al.  Snakes: Active contour models , 2004, International Journal of Computer Vision.

[12]  Christoph H. Lampert,et al.  Document image dewarping using robust estimation of curled text lines , 2005, Eighth International Conference on Document Analysis and Recognition (ICDAR'05).

[13]  Thomas M. Breuel,et al.  Efficient implementation of local adaptive thresholding techniques using integral images , 2008, Electronic Imaging.

[14]  Syed Saqib Bukhari,et al.  Script-Independent Handwritten Textlines Segmentation Using Active Contours , 2009, 2009 10th International Conference on Document Analysis and Recognition.

[15]  Ioannis Pratikakis,et al.  A Two-Step Dewarping of Camera Document Images , 2008, 2008 The Eighth IAPR International Workshop on Document Analysis Systems.

[16]  Chew Lim Tan,et al.  Correcting document image warping based on regression of curved text lines , 2003, Seventh International Conference on Document Analysis and Recognition, 2003. Proceedings..

[17]  Syed Saqib Bukhari,et al.  Coupled Snakelet Model for Curled Textline Segmentation of Camera-Captured Document Images , 2009, 2009 10th International Conference on Document Analysis and Recognition.

[18]  Apostolos Antonacopoulos,et al.  Handwriting Segmentation Contest , 2007, ICDAR.

[19]  Basilios Gatos,et al.  Handwriting Segmentation Contest , 2007, ICDAR.

[20]  Junaed Sattar.  Snakes , Shapes and Gradient Vector Flow , 2022 .

[21]  Shijian Lu,et al.  The Restoration of Camera Documents Through Image Segmentation , 2006, Document Analysis Systems.

[22]  M. Riley,et al.  Time-Frequency Representations for Speech Signals , 1987 .

[23]  Thomas M. Breuel,et al.  Document cleanup using page frame detection , 2008, International Journal of Document Analysis and Recognition (IJDAR).

[24]  Faisal Shafait.  Document Image Dewarping Contest , 2007 .