Weihua Huang

Imaged document text retrieval without OCR

We propose a method for text retrieval from document images without the use of OCR. Documents are segmented into character objects. Image features, namely the vertical traverse density (VTD) and horizontal traverse density (HTD), are extracted. An n-gram-based document vector is constructed for each document based on these features. Text similarity between documents is then measured by calculating the dot product of the document vectors. Testing with seven corpora of imaged textual documents in English and Chinese as well as images from the UW1 (University of Washington 1) database confirms the validity of the proposed method.

Accurate video text detection through classification of low and high contrast images

Detection of both scene text and graphic text in video images is gaining popularity in the area of information retrieval for efficient indexing and understanding the video. In this paper, we explore a new idea of classifying low contrast and high contrast video images in order to detect accurate boundary of the text lines in video images. In this work, high contrast refers to sharpness while low contrast refers to dim intensity values in the video images. The method introduces heuristic rules based on combination of filters and edge analysis for the classification purpose. The heuristic rules are derived based on the fact that the number of Sobel edge components is more than the number of Canny edge components in the case of high contrast video images, and vice versa for low contrast video images. In order to demonstrate the use of this classification on video text detection, we implement a method based on Sobel edges and texture features for detecting text in video images. Experiments are conducted using video images containing both graphic text and scene text with different fonts, sizes, languages, backgrounds. The results show that the proposed method outperforms existing methods in terms of detection rate, false alarm rate, misdetection rate and inaccurate boundary rate.

An approach to word image matching based on weighted Hausdorff distance

An approach to word image matching based on weighted Hausdorff distance (WHD) is proposed in this paper to facilitate the detection and location of the user-specified words in the document images. Preprocessing such as eliminating the space between adjacent characters in the word images and scale normalization is first done before the WHD is utilized to measure the distance between the template image and the word image extracted from the document image. Experimental results in the application of detecting the user-specified words from both English and Chinese document images show that it is a promising approach for word image matching.

An Efficient Edge Based Technique for Text Detection in Video Frames

Both graphic text and scene text detection in video images with complex background and low resolution is still a challenging and interesting problem for researchers in the field of image processing and computer vision. In this paper, we present a novel technique for detecting both graphic text and scene text in video images by finding segments containing text in an input image and then using statistical features such as vertical and horizontal bars for edges in the segments for detecting true text blocks efficiently. To identify a segment containing text, heuristic rules are formed based on combination of filters and edge analysis. Furthermore, the same rules are extended to grow the boundaries of a candidate segment in order to include complete text in the input image. The experimental results of the proposed method show that the technique performs better than existing methods in terms of a number of metrics.

Efficient video text detection using edge features

In this paper, we explore new edge features such as straightness for the elimination of non significant edges from the segmented text portion of a video frame to detect accurate boundary of the text lines in video images. To segment the complete text portions, the method introduces candidate text block selection from a given image. Heuristic rules are formed based on combination of filters and edge analysis for identifying a candidate text block in the image. Furthermore, the same rules are extended to grow boundary of candidate text block in order to segment complete text portions in the image. The experimental results of the proposed method show that the method outperforms an existing method in terms of a number of metrics.

Model-Based Chart Image Recognition

In this paper, we introduce a system that aims at recognizing chart images using a model-based approach. First of all, basic chart models are designed for four different chart types based on their characteristics. In a chart model, basic object features and constraints between objects are defined. During the chart recognition, there are two levels of matching: feature level matching to locate basic objects and object level matching to fit in an existing chart model. After the type of a chart is determined, the next step is to do data interpretation and recover the electronic form of the chart image by examining the object attributes. Experiments were done using a set of testing images downloaded from the internet or scanned from books and papers. The results of type determination and the accuracies of the recovered data are reported.

A system for understanding imaged infographics and its applications

Information graphics, or infographics, are visual representations of information, data or knowledge. Understanding of infographics in documents is a relatively new research problem, which becomes more challenging when infographics appear as raster images. This paper describes technical details and practical applications of the system we built for recognizing and understanding imaged infographics located in document pages. To recognize infographics in raster form, both graphical symbol extraction and text recognition need to be performed. The two kinds of information are then auto-associated to capture and store the semantic information carried by the infographics. Two practical applications of the system are introduced in this paper, including supplement to traditional optical character recognition (OCR) system and providing enriched information for question answering (QA). To test the performance of our system, we conducted experiments using a collection of downloaded and scanned infographic images. Another set of scanned document pages from the University of Washington document image database were used to demonstrate how the system output can be used by other applications. The results obtained confirm the practical value of the system.

Semi-automatic ground truth generation for chart image recognition

While research on scientific chart recognition is being carried out, there is no suitable standard that can be used to evaluate the overall performance of the chart recognition results. In this paper, a system for semi-automatic chart ground truth generation is introduced. Using the system, the user is able to extract multiple levels of ground truth data. The role of the user is to perform verification and correction and to input values where necessary. The system carries out automatic tasks such as text blocks detection and line detection etc. It can effectively reduce the time to generate ground truth data, comparing to full manual processing. We experimented the system using 115 images. The images and ground truth data generated are available to the public.

Text Retrieval from Document Images Based on Word Shape Analysis

In this paper, we propose a method of text retrieval from document images using a similarity measure based on word shape analysis. We directly extract image features instead of using optical character recognition. Document images are segmented into word units and then features called vertical bar patterns are extracted from these word units through local extrema points detection. All vertical bar patterns are used to build document vectors. Lastly, we obtain the pair-wise similarity of document images by means of the scalar product of the document vectors. Four corpora of news articles were used to test the validity of our method. During the test, the similarity of document images using this method was compared with the result of ASCII version of those documents based on the N-gram algorithm for text documents.

Chart Image Classification Using Multiple-Instance Learning

An important step in chart image understanding is to identify the type of the input image so that corresponding interpretation can be performed. In this paper, we model the chart image classification as a multiple-instance learning problem. A chart image is treated as a bag containing a set of instances that are graphical symbols. For both training and recognition, shape detection is performed and general shape descriptors are used to form feature vectors. For the training images, the correlation factor (CF) of each shape is calculated for each chart type. The learnt CFs are then used to estimate the type of a new input image. Comparing with traditional multiple-instance learning algorithms, we allow negative examples to be less restrictive and hence easier to provide. Using our method, both the type and the data components of the chart image can be obtained in one-pass. The experimental results show that our approach works reasonably well