Sriganesh Madhvanath

The role of holistic paradigms in handwritten word recognition

The holistic paradigm in handwritten word recognition treats the word as a single, indivisible entity and attempts to recognize words from their overall shape, as opposed to their character contents. In this survey, we have attempted to take a fresh look at the potential role of the holistic paradigm in handwritten word recognition. The survey begins with an overview of studies of reading which provide evidence for the existence of a parallel holistic reading process,in both developing and skilled readers. In what we believe is a fresh perspective on handwriting recognition, approaches to recognition are characterized as forming a continuous spectrum based on the visual complexity of the unit of recognition employed and an attempt is made to interpret well-known paradigms of word recognition in this framework. An overview of features, methodologies, representations, and matching techniques employed by holistic approaches is presented.

Chaincode contour processing for handwritten word recognition

Contour representations of binary images of handwritten words afford considerable reduction in storage requirements while providing lossless representation. On the other hand, the one-dimensional nature of contours presents interesting challenges for processing images for handwritten word recognition. Our experiments indicate that significant gains are to be realized in both speed and recognition accuracy by using a contour representation in handwriting applications.

HMM-Based Lexicon-Driven and Lexicon-Free Word Recognition for Online Handwritten Indic Scripts

Research for recognizing online handwritten words in Indic scripts is at its early stages when compared to Latin and Oriental scripts. In this paper, we address this problem specifically for two major Indic scripts-Devanagari and Tamil. In contrast to previous approaches, the techniques we propose are largely data driven and script independent. We propose two different techniques for word recognition based on Hidden Markov Models (HMM): lexicon driven and lexicon free. The lexicon-driven technique models each word in the lexicon as a sequence of symbol HMMs according to a standard symbol writing order derived from the phonetic representation. The lexicon-free technique uses a novel Bag-of-Symbols representation of the handwritten word that is independent of symbol order and allows rapid pruning of the lexicon. On handwritten Devanagari word samples featuring both standard and nonstandard symbol writing orders, a combination of lexicon-driven and lexicon-free recognizers significantly outperforms either of them used in isolation. In contrast, most Tamil word samples feature the standard symbol order, and the lexicon-driven recognizer outperforms the lexicon free one as well as their combination. The best recognition accuracies obtained for 20,000 word lexicons are 87.13 percent for Devanagari when the two recognizers are combined, and 91.8 percent for Tamil using the lexicon-driven technique.

Holistic verification of handwritten phrases

In this paper, we describe a system for rapid verification of unconstrained off-line handwritten phrases using perceptual holistic features of the handwritten phrase image. The system is used to verify handwritten street names automatically extracted from live US mail against recognition results of analytical classifiers. Presented with a binary image of a street name and an ASCII street name, holistic features (reference lines, large gaps and local contour extrema) of the street name hypothesis are predicted from the expected features of the constituent characters using heuristic rules. A dynamic programming algorithm is used to match the predicted features with the extracted image features. Classes of holistic features are matched sequentially in increasing order of cost, allowing an ACCEPT/REJECT decision to be arrived at in a time-efficient manner. The system rejects errors with 98 percent accuracy at the 30 percent accept level, while consuming approximately 20/msec per image on the average on a 150 MHz SPARC 10.

Syntactic methodology of pruning large lexicons in cursive script recognition

Abstract In this paper, we present a holistic technique for pruning of large lexicons for recognition of off-line cursive script words. The technique involves extraction and representation of downward pen-strokes from the off-line cursive word to obtain a descriptor which provides a coarse characterization of word shape. Elastic matching is used to match the image descriptor with “ideal” descriptors corresponding to lexicon entries organized as a trie of stroke classes. On a set of 23,335 real cursive word images the reduction is about 70% with accuracy above 75%.

Serial classifier combination for handwritten word recognition

The performance of off-line handwritten word recognition algorithms declines with increasing lexicon size, but may be improved by serial combination of classifiers. The authors address some issues relevant to the design of serial classifier combinations. They present experimental results that show that the performance of a serial combination depends on not only the intrinsic recognition power of the classifiers but also the relative orthogonality of their features. A top-choice recognition rate of 83% is obtained for a lexicon of size 1700 by combining two analytical word classifiers that perform individually at 70%. Even higher recognition rates may be expected from a serial combination of two classifiers with less correlated features, such as a high-performance holistic classifier with an analytical classifier.

Reading handwritten US census forms

Commercial forms-reading systems for extraction of data from forms do not meet acceptable accuracy requirements on forms filled out by hand. In December 1993, NIST called industry and research organizations working in the area of handwriting recognition to participate in a test to determine the state of the art in the area. A database of form images containing actual responses received by the US Census Bureau was provided. The handwritten responses are very loosely constrained in terms of writing style, format of response and choice of text. The sizes of the lexicons provided are very large (about 50000 entries) and yet the coverage is incomplete (about 70%). In this paper we discuss the approach taken by CEDAR to automate the task of reading the census forms. The subtasks of field extraction and phrase recognition are described.

Contour-based image preprocessing for holistic handwritten word recognition

The one-dimensional nature of contour representations presents interesting challenges for processing of images for handwritten word recognition. In this paper, we discuss the issues of determination of upper and lower contours of the word, determination of significant focal extrema on the contour, and determination of reference lines from contour representations of handwritten words.

Local reference lines for handwritten phrase recognition

Reference line information has been used for diverse purposes in handwriting research, including word case classification, OCR, and holistic word recognition. In this paper, we argue that the commonly used global reference lines are inadequate for many handwritten phrase recognition applications. Individual words may be written at different orientations or vertically displaced with respect to one another. A function used to approximate the implicit baseline will not be differentiable or even continuous at some points. We have presented the case for local reference lines and illustrate its successful use in a system that verifies street name phrases in a postal application.

Pruning large lexicons using generalized word shape descriptors

We present a technique for pruning of large lexicons for recognition of cursive script words. The technique involves extraction and representation of downward pen-strokes from the cursive word (off-line or online) to obtain a generalized descriptor which provides a coarse characterization of word shape. The descriptor is matched with ideal descriptors of lexicon entries organized as a trie. When used with a static lexicon of 21,000 words, the accuracy of reduction to 1000 words exceeds 95%.