Huaigu Cao

Gabor features for offline Arabic handwriting recognition

Many feature extraction approaches for off-line handwriting recognition (OHR) rely on accurate binarization of gray-level images. However, high-quality binarization of most real-world documents is extremely difficult due to varying characteristics of noises artifacts common in such documents. Unlike most of these features, Gabor features do not require binarization of the document images, and thus are likely to be more robust to noises in document images. To demonstrate the efficacy of our proposed Gabor features, we perform subword recognition for off-line Arabic handwritten images using Support Vector Machines (SVM). We also compare the recognition performance with other binarization based features which have been proven to be effective in capturing shape characteristics of handwritten Arabic subwords, such as GSC (a set of gradient, structure, and concavity features) and skeleton based Graph features. Our preliminary experimental results show that Gabor features outperform Graph features and are slightly better than GSC features for Arabic subword recognition. In addition, by combining Gabor and GSC features, we obtain a significant reduction in classification error rate over using GSC or Gabor features alone.

Improvements in BBN's HMM-Based Offline Arabic Handwriting Recognition System

Offline handwriting recognition of free-flowing Arabic text is a challenging task due to the plethora of factors that contribute to the variability in the data. In this paper, we address some of these sources of variability, and present experimental results on a large corpus of handwritten documents. Specific techniques such as the application of context-dependent Hidden Markov Models (HMMs) for the cursive Arabic script, unsupervised adaptation to account for the stylistic variations across scribes, and image pre-processing to remove ruled-lines are explored. In particular, we proposed a novel integration of structural features in the HMM framework which exclusively results in a 9% relative improvement in performance. Overall, we demonstrate a relative reduction of 17% in word error rate over our baseline Arabic handwriting recognition system.

Preprocessing of Low-Quality Handwritten Documents Using Markov Random Fields

This paper presents a statistical approach to the preprocessing of degraded handwritten forms including the steps of binarization and form line removal. The degraded image is modeled by a Markov random field (MRF) where the hidden-layer prior probability is learned from a training set of high-quality binarized images and the observation probability density is learned on-the-fly from the gray-level histogram of the input image. We have modified the MRF model to drop the preprinted ruling lines from the image. We use the patch-based topology of the MRF and belief propagation (BP) for efficiency in processing. To further improve the processing speed, we prune unlikely solutions from the search space while solving the MRF. Experimental results show higher accuracy on two data sets of degraded handwritten images than previously used methods.

Handwritten Carbon Form Preprocessing Based on Markov Random Field

This paper proposes a statistical approach to degraded handwritten form image preprocessing including binarization and form line removal. The degraded image is modeled by a Markov random field (MRF) where the prior is learnt from a training set of high quality binarized images, and the probabilistic density is learnt on-the-fly from the gray-level histogram of input image. We also modified the MRF model to implement form line removal. Test results of our approach show excellent performance on the data set of handwritten carbon form images.

Automated image quality assessment for camera-captured OCR

Camera-captured optical character recognition (OCR) is a challenging area because of artifacts introduced during image acquisition with consumer-domain hand-held and Smart phone cameras. Critical information is lost if the user does not get immediate feedback on whether the acquired image meets the quality requirements for OCR. To avoid such information loss, we propose a novel automated image quality assessment method that predicts the degree of degradation on OCR. Unlike other image quality assessment algorithms which only deal with blurring, the proposed method quantifies image quality degradation across several artifacts and accurately predicts the impact on OCR error rate. We present evaluation results on a set of machine-printed document images which have been captured using digital cameras with different degradations.

A stroke regeneration method for cleaning rule-lines in handwritten document images

We describe a rule-line removal algorithm for handwritten document images in this paper. Compared to the existing approaches, our algorithm obtains more scalability to higher-resolution images and thicker rule-lines. Derived from the simple gap-filling methods using line-drawing algorithms, we present a novel approach to regenerating the missing portions of text strokes. Using this approach, the deformed text can be restored to its original shape. We also explore the noise filtering method for binarized document images, in particular by choosing the morphological operator in accordance with the noise power of the input image. Our approach has proven to be effective by experiments on both real and synthetic handwritten document images.

Text Extraction from Video Using Conditional Random Fields

In this paper, we describe an approach to extract text from broadcast videos. Candidate blocks are detected based on edge extraction results. Corners and geometrical features are used for the purpose of initial classification which is carried out by using a support vector machine (SVM). Considering the spatial inter-dependencies of different regions in the image, we propose a novel conditional random field (CRF) based framework which integrates the outputs of SVM into the system to improve the accuracy of labeling for blocks. The experimental results show that the proposed system achieves reliable performance for text detection/extraction from videos.

Graph Clustering-Based Ensemble Method for Handwritten Text Line Segmentation

Handwritten text line segmentation on real-world data presents significant challenges that cannot be overcome by any single technique. Given the diversity of approaches and the recent advances in ensemble-based combination for pattern recognition problems, it is possible to improve the segmentation performance by combining the outputs from different line finding methods. In this paper, we propose a novel graph clustering-based approach to combine the output of an ensemble of text line segmentation algorithms. A weighted undirected graph is constructed with nodes corresponding to connected components and edge connecting pairs of connected components. Text line segmentation is then posed as the problem of minimum cost partitioning of the nodes in the graph such that each cluster corresponds to a unique line in the document image. Experimental results on a challenging Arabic field dataset using the ensemble method shows a relative gain of 18% in the F1 score over the best individual method within the ensemble.

Vector Model Based Indexing and Retrieval of Handwritten Medical Forms

A vector model based information retrieval of handwritten medical forms is presented in this paper. In order to improve the IR performance on the erroneous output of handwriting recognition (HR) systems, a variation of the vector model is made to estimate the number of occurrences of terms from word segmentation and recognition probabilities. IR Tests show that our approach outperforms the retrieval of ordinary HR text in terms of mean average precision (MAP), R-Precision, and interpolated 11-point precisions.

Handwritten and Typewritten Text Identification and Recognition Using Hidden Markov Models

We present a system for identification and recognition of handwritten and typewritten text from document images using hidden Markov models (HMMs) in this paper. Our text type identification uses OCR decoding to generate word boundaries followed by word-level handwritten/typewritten identification using HMMs. We show that the contextual constraints from the HMM significantly improves the identification performance over the conventional Gaussian mixture model (GMM)-based method. Type identification is then used to estimate the frame sample rates and frame width of feature sequences for HMM OCR system for each type independently. This type-dependent approach to computing the frame sample rate and frame width shows significant improvement in OCR accuracy over type-independent approaches.