cvpr cvpr2013 cvpr2013-382 knowledge-graph by maker-knowledge-mining

382 cvpr-2013-Scene Text Recognition Using Part-Based Tree-Structured Character Detection


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Author: Cunzhao Shi, Chunheng Wang, Baihua Xiao, Yang Zhang, Song Gao, Zhong Zhang

Abstract: Scene text recognition has inspired great interests from the computer vision community in recent years. In this paper, we propose a novel scene text recognition method using part-based tree-structured character detection. Different from conventional multi-scale sliding window character detection strategy, which does not make use of the character-specific structure information, we use part-based tree-structure to model each type of character so as to detect and recognize the characters at the same time. While for word recognition, we build a Conditional Random Field model on the potential character locations to incorporate the detection scores, spatial constraints and linguistic knowledge into one framework. The final word recognition result is obtained by minimizing the cost function defined on the random field. Experimental results on a range of challenging public datasets (ICDAR 2003, ICDAR 2011, SVT) demonstrate that the proposed method outperforms stateof-the-art methods significantly bothfor character detection and word recognition.

Reference: text


Summary: the most important sentenses genereted by tfidf model

sentIndex sentText sentNum sentScore

1 In this paper, we propose a novel scene text recognition method using part-based tree-structured character detection. [sent-10, score-0.94]

2 Different from conventional multi-scale sliding window character detection strategy, which does not make use of the character-specific structure information, we use part-based tree-structure to model each type of character so as to detect and recognize the characters at the same time. [sent-11, score-2.069]

3 While for word recognition, we build a Conditional Random Field model on the potential character locations to incorporate the detection scores, spatial constraints and linguistic knowledge into one framework. [sent-12, score-1.177]

4 The final word recognition result is obtained by minimizing the cost function defined on the random field. [sent-13, score-0.302]

5 Experimental results on a range of challenging public datasets (ICDAR 2003, ICDAR 2011, SVT) demonstrate that the proposed method outperforms stateof-the-art methods significantly bothfor character detection and word recognition. [sent-14, score-0.97]

6 [7], given an image containing text and other objects, viewers tend to fixate on text, suggesting the importance of text to human. [sent-19, score-0.288]

7 In fact, text recognition is indispensable for a lot of applications such as automatic sign reading, language translation, navigation and so on. [sent-20, score-0.337]

8 Most of the previous work on scene text recognition could be roughly classified into two categories: tradition- Figure 1. [sent-22, score-0.265]

9 Given a text image, we first use tree-structured models to get the character detection results, based on which we get the potential character locations. [sent-24, score-1.703]

10 Character detection scores are used to define the unary cost and language model is used to define the pairwise cost. [sent-26, score-0.393]

11 We finally infer each label of the node and the word by minimizing the cost function. [sent-27, score-0.291]

12 However, since text in natural images differs from text in traditional scanned document in terms of resolution, illumination condition, size and font style, the binarization result is usually unsatisfactory. [sent-30, score-0.43]

13 Moreover, the loss of information during the binarization process is almost unrecoverable, which means if the binarization result is poor, the chance of correctly recognizing the text is quite small. [sent-31, score-0.387]

14 On the other hand, object recognition based methods assume that scene character recognition is quite simi222999556199 Figure 2. [sent-33, score-0.872]

15 For scene character recognition, these methods [4, 13, 19, 18] directly extract features from original image and use various classifiers to recognize the character. [sent-37, score-0.839]

16 While for scene text recognition, since there are no binarization and segmentation stages, most existing methods [19, 18, 11, 10] adopt multi-scale sliding window strategy to get the candidate character detection results. [sent-38, score-1.255]

17 Thus, these methods heavily rely on the postprocessing methods such as pictorial structures [19, 18] or CRF [11, 10] to choose the final word from piles of candidate detections. [sent-40, score-0.348]

18 When humans try to recognize scene characters with distortions and complex background, the detection of the character from complex background and the recognition of the character are somehow interdependent. [sent-41, score-1.925]

19 On one hand, the unique structure of each character helps us to detect the characters from complex background and on the other hand, detecting the character-specific structure from complex background also helps us to recognize the character. [sent-42, score-1.198]

20 In other words, humans naturally combine detection and recognition together when recognizing characters from scene images. [sent-43, score-0.423]

21 Thus, in this paper, we try to imitate human perceptual ability and propose to recognize characters by detecting character-specific part-based structures, which seamlessly combine detection and recognition together. [sent-44, score-0.523]

22 To recognize the scene text, we build the CRF model on the potential character locations. [sent-46, score-0.926]

23 Character detection scores, spatial constraints and linguistic knowledge are used to define the unary and pairwise cost function. [sent-47, score-0.32]

24 The final word recognition result is acquired by minimizing the cost function. [sent-48, score-0.32]

25 Section 2 details the proposed method, including the model for character detection and word recognition. [sent-52, score-0.988]

26 First, we use part-based tree-structured models to detect characters, based on which we get the potential character locations. [sent-58, score-0.8]

27 We use character detection scores, spatial constraints and language model to define the unary and pairwise cost function. [sent-60, score-1.074]

28 Finally we get the word recognition result by minimizing the cost function. [sent-61, score-0.32]

29 Next, we will detail the character detection method and word recognition model. [sent-62, score-1.027]

30 Structure information is even more important to characters, since characters are designed by human and each type of character has unique structure representing itself. [sent-68, score-1.039]

31 To utilize the unique structure information of characters, we model each character as a tree whose nodes correspond to parts of the character. [sent-69, score-0.84]

32 Each rectangle corresponds to a part-based filter of the character and the red lines illustrate the topological relations of the parts. [sent-76, score-0.759]

33 Model for each character: We represent each character by a tree Tk = (Vk , Ek), where k is the index of the model for different structures, Vk represents the nodes and Ek specifies the topological relations of nodes [20]. [sent-77, score-0.864]

34 By incorporating the elastic structure information, the model could detect characters − − with contamination or deformation as shown in Figure 4(a). [sent-99, score-0.397]

35 The character in the green rectangle labels the type of the sturcture. [sent-103, score-0.758]

36 (a) Detection results of characters with contamination and deformation. [sent-104, score-0.282]

37 Re-scoring: Apart from unique structure, different parts of a character tend to have similar intensity, which we could utilize to further improve the performance. [sent-112, score-0.746]

38 To learn the model, we assume a fully-supervised paradigm, where we are provided positive images with characters as well as part labels, and negative images with- 222999666311 out characters. [sent-125, score-0.253]

39 We design the tree-structure for each type of character by our experience and the experimental results show that they perform quite well. [sent-128, score-0.75]

40 The Word Recognition Model Although the character detection step provides us with a set of windows containing characters with high confidence as shown in Figure 4(b), inevitably it also produces some false positives and ambiguities between similar characters. [sent-143, score-1.095]

41 We make use of character detection scores, spatial constraints, and linguistic knowledge to define the cost function. [sent-146, score-0.909]

42 Finally, the word recognition result is acquired by minimizing the cost function. [sent-147, score-0.32]

43 For a given scene text image, there are several potential character locations. [sent-148, score-0.929]

44 Each position, which might have several character detection results, is represented by a random variable Xi. [sent-150, score-0.776]

45 1 Graph Construction After applying Non-Maximum Suppression (NMS) [20] on the original character detection results, the left detection windows constitute the potential locations. [sent-176, score-0.924]

46 Then, for each location, we choose those detection windows which are close to this location as the candidate characters for this location. [sent-179, score-0.409]

47 2 Cost Function The unary cost E(xi) represents the penalty of assigning label cj to node xi. [sent-186, score-0.235]

48 In this case, if the detection score for a certain type of character model cj is very high, the cost of labeling the node cj should be small and vise versa. [sent-187, score-1.11]

49 (1,0) where P(ci, cj) r⎩⎪efers to the bi-gram language model learnt from the lexicon, Dij is the relative distance of the two nodes, Si and Sj represent the maximum character detection scores at the corresponding locations, Si,j is the larger one of Si and Sj, and μ is set to 1. [sent-205, score-0.967]

50 We use the SRI Language Modeling Toolkit [17] to learn the probability of joint occurrences of characters in a large English dictionary with around 0. [sent-207, score-0.253]

51 The pairwise cost function means that if the probability of joint occurrence of a character pair (ci , cj) is large, the cost of nodes (xi, xj) taking labels (ci, cj) should be small. [sent-209, score-0.887]

52 Moreover, if the relative distance of the two nodes is small, and the maximum score of the node is low, the cost of the node taking a null label should be small. [sent-210, score-0.22]

53 3 Inference After computing the unary and pairwise cost, we use the sequential tree-reweighted message passing (TRW-S) algorithm [8] to minimize the cost function in (8), due to its efficiency and accuracy on our recognition problem. [sent-213, score-0.224]

54 Experimental Results In this section, we give detailed evaluation of the proposed character detection and word recognition method. [sent-219, score-1.027]

55 We compare the detection based character recognition method with conventional HOG+NN. [sent-220, score-0.858]

56 We also compare the proposed character detection method with conventional sliding window strategy, SYNTH+FERNS proposed by Wang et al. [sent-221, score-0.896]

57 For word recognition task, we compare our results with state-of-the-art methods [19, 18, 10, 11] as well as commercial OCR engines ABBYY FineReader 9. [sent-223, score-0.251]

58 To evaluate the performance of the proposed detection based character recog- nition method, we test the recognition rate on two public datasets: Chars74k [4] and ICDAR 2003 robust character recognition dataset (ICDAR03-CH) [9]. [sent-228, score-1.614]

59 However, since we focus on detecting and recognizing characters with certain structures, characters with similar structures such as, ’0’, ’O’ and ’o’, ’P’ and ’p’, ’K’ and ’k’, ’X’ and ’x’, should belong to the same class. [sent-229, score-0.572]

60 We use the challenging public datasets Street View Text (SVT) [19], ICDAR 2003 robust word recognition [9] and ICDAR 2011word recognition datasets [16] to evaluate the performance of the overall word recognition method. [sent-238, score-0.559]

61 Since we focus on the word recognition task, we use the SVT-WORD dataset following × the experimental protocol of [19, 18]. [sent-240, score-0.251]

62 For ICDAR 2003 and ICDAR 2011datasets, similar to [18], we ignore words with less than two characters or with non-alphanumeric characters. [sent-241, score-0.298]

63 Detection Based Character Recognition To recognize characters using the detection model, we apply each character-specific tree-structured model (TSM) on the image and choose the structure with the highest score as the recognition result. [sent-244, score-0.587]

64 Since we focus on detecting characters with unique structures, we only train 49 types of character model whose structures are different from each other. [sent-252, score-1.057]

65 The great improvement suggests (1) the effectiveness of the tree-structured models, as they tend to detect and recognize characters with certain structures, and thus (2) the high possibility of achieving better recognition result if we postprocess the result to deal with similar structures. [sent-255, score-0.445]

66 Character Detection To evaluate the superiority of the proposed character detection method over conventional multi-scale sliding window detection strategy for word recognition, we test the word recognition result using the word spotting strategy PLEX from [18]. [sent-263, score-1.762]

67 In this case, based on the character detection results of the proposed TSM and the SYNTH+FERNS proposed by Wang et al. [sent-264, score-0.776]

68 In the SVT-WD case, a lexicon of about 50 words is provided with each image as part of the dataset. [sent-267, score-0.236]

69 The word recognition results are shown in Table 1. [sent-268, score-0.251]

70 Since we use the same word spotting strategy PLEX, the only difference between the two methods lies in the character detection method. [sent-270, score-1.085]

71 For FERNS+PLEX, multi-scale sliding window strategy is used to detect characters and FERNS classifier is used to recognize the characters. [sent-275, score-0.52]

72 While for TSM, tree-structured models are used to detect and recognize the characters at the same time. [sent-276, score-0.388]

73 strategy to detect and recognize characters, which does not make use of the character-specific global structure informa- tion. [sent-278, score-0.208]

74 Thus, there are many false positives, which would disturb the word spotting stage. [sent-279, score-0.293]

75 While for the proposed character detection method, since we make use of both global structure information and local appearance information, the detection results are more reliable and representative. [sent-280, score-0.907]

76 Word Recognition To recognize the word, we build the CRF model on the character detection results as discussed in Section 2. [sent-283, score-0.917]

77 We use ICDAR 2003, ICDAR 2011 and SVT datasets to evaluate the proposed word recognition method. [sent-286, score-0.251]

78 Same bigram language model learnt from the lexicon with 0. [sent-287, score-0.344]

79 Similar to the evaluation scheme in [18] and [11], we use the inferred result to retrieve the word with the smallest edit distance in the lexicon. [sent-289, score-0.218]

80 For ICDAR datasets, we measure performance using a lexicon created from all the words in the test set (ICDAR03(FULL), ICDAR1 1(FULL)), and with lexicon consisting of the ground truth words plus 50 random words from the test set (ICDAR03(50), ICDAR1 1(50)). [sent-290, score-0.517]

81 he results on ICDAR03(50), ICDAR1 1(50), SVT are acquired by retrieving the ones with the smallest edit distance in the lexicon of 50 words whereas for ICDAR03(FULL) and ICDAR1 1(FULL), the lexicon contains all the ground truth words in the test set. [sent-302, score-0.514]

82 The proposed method outperforms TSM+PLEX by 6%-9%, showing the effectiveness of the CRF model which incorporates detection scores, linguistic knowledge and spatial constraints, since both methods adopt the same character detection method. [sent-305, score-0.951]

83 also used the CRF model to encode character detection results and language model. [sent-309, score-0.911]

84 However, they used the multi-scale sliding window strategy to get the candidate character locations and SVM to classify these characters. [sent-310, score-0.906]

85 The detection method is not as good as the proposed tree-structured character detection method which makes use of the intrinsic global structure information. [sent-311, score-0.887]

86 Furthermore, they built the CRF model on all the detection windows as long as their spatial distance and overlap ratio satisfy a certain condition, which makes the CRF model more complex than ours since we only use the potential character locations to define the nodes. [sent-312, score-0.905]

87 [11] computed the node-specific lexicon prior for each text image from their corresponding lexicon, which means (1) the lexicon priors heavily rely on the lexicon for that image and (2) the computation cost is increased since the lexicon prior should be recomputed for each image. [sent-314, score-0.959]

88 Compared to [11], the recognition rates on SVT do not improve a lot, mainly because some of the scene text images in SVT are difficult to recognize even for human as shown in Figure 7. [sent-320, score-0.339]

89 As we can see, our method could recognize scene text with low resolution, different fonts and distortions. [sent-323, score-0.343]

90 Both the character detection and word recognition are implemented in Matlab. [sent-325, score-1.027]

91 The average processing time to recognize a scene text image is about 3 seconds on an In222999666755 tel(R) Core(TM) i7-2600 CPU 3. [sent-326, score-0.282]

92 Since the character detectors are independent from each other, the implementation could be much faster using parallel processing. [sent-328, score-0.727]

93 Conclusion In this paper, we propose an effective scene text recognition method using the CRF model to incorporate treestructure based character detection and linguistic knowl- edge into one framework. [sent-330, score-1.115]

94 Different from the conventional multi-scale sliding window character detection strategy, which does not make use of the intrinsic global structure information, we propose to learn a part-based tree-structured model for each type of character to detect and recognize the characters simultaneously. [sent-331, score-2.069]

95 Based on these detection results, we build a CRF model on the potential character locations to integrate detection scores, spatial constraints and language model. [sent-332, score-1.093]

96 The experimental results show that our method could recognize text in unconstrained scene images with a high accuracy. [sent-335, score-0.308]

97 Multiscale histogram of oriented gradient descriptors for robust character recognition. [sent-420, score-0.701]

98 Icdar 2011 robust reading competition challenge 2: Reading text in scene images. [sent-435, score-0.25]

99 In Proceedings of the international conference on spoken language processing, volume 2, pages 901–904, 2002. [sent-441, score-0.211]

100 Segmentation and recognition of characters in scene images using selective binarization in color space and gat correlation. [sent-467, score-0.46]


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