doi:10.1016/S0167-8655(03)00057-6
Copyright © 2003 Elsevier B.V. All rights reserved.
A nearest-neighbor chain based approach to skew estimation in document images
Yue Lu
,
and Chew Lim Tan
Department of Computer Science, School of Computing, National University of Singapore, 3 Science Drive 2, Kent Ridge, Singapore 117543, Singapore
Received 16 September 2002;
revised 13 March 2003.
Available online 1 May 2003.
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Abstract
A nearest-neighbor chain (NNC) based approach is proposed in this paper to develop a skew estimation method with a high accuracy and with language-independent capability. Size restriction is introduced to the detection of nearest-neighbors (NN). Then NNCs are extracted from the adjacent NN pairs, in which the slopes of the NNCs with a largest possible number of components are computed to give the skew angle of document image. Experimental results on various types of documents containing different linguistic scripts and diverse layouts show that the proposed approach has achieved an improved accuracy for estimating document image skew angle and has an advantage of being language independent.
Author Keywords: Skew estimation; Document analysis; Nearest-neighbor chain
Fig. 1. NN pairs and NNCs: (a) English, (b) Chinese.
Fig. 2. Skew angles: (a) Δ
x>Δ
y, (b) Δ
x<Δ
y.
Fig. 3. Document images in which connected components have been bounded: (a) English document, (b) Chinese document.
Fig. 4. NNCs of
Fig. 3(a): (a)
K=2, (b)
K=3, (c)
K
4, (d) connection lines for
K=2, (e) connection lines for
K=3, (f) connection lines for
K
4.
Fig. 5. NNCs of
Fig. 3(b): (a)
K=2, (b)
K=3, (c)
K
4, (d) connection lines for
K=2, (e) connection lines for
K=3, (f) connection lines for
K
4.
Fig. 6. Examples: (a) Document with dominant graphics (estimated skew angle is 24.13° while actual skew is 24°). (b) Document with tables (estimated skew angle is −17.78° while actual skew is −18°). (c) Document with English and Chinese, horizontal and vertical text orientations (estimated skew angle is −10.18° while actual skew is −10°). (d) Tamil document (estimated skew angle is 7.92° while actual skew is 8°).
Table 1. Statistic results of PL and NPL with respect to K

Table 2. Some typical results of estimated skew angles (all in degree)

A: Hashizume’s method.
B: Jiang’s method.
C: The proposed method using mean value.
D: The proposed method using median value.
Table 3. Mean and maximum of absolute error obtained by different methods (all in degree)

Table 4. Typical time required for the skew angle estimation
