During the last few years many document recognition methods have been developed to determine whether a
handwriting specimen can be attributed to a known writer. However, in practice, the work-flow of the document
examiner continues to be manual-intensive. Before a systematic or computational, approach can be developed, an
articulation of the steps involved in handwriting comparison is needed. We describe the work flow of handwritten
questioned document examination, as described in a standards manual, and the steps where existing automation
tools can be used. A well-known ransom note case is considered as an example, where one encounters testing for
multiple writers of the same document, determining whether the writing is disguised, known writing is formal
while questioned writing is informal, etc. The findings for the particular ransom note case using the tools are
given. Also observations are made for developing a more fully automated approach to handwriting examination.
Forensic individualization is the task of associating observed evidence with a specific source. The likelihood ratio
(LR) is a quantitative measure that expresses the degree of uncertainty in individualization, where the numerator
represents the likelihood that the evidence corresponds to the known and the denominator the likelihood that
it does not correspond to the known. Since the number of parameters needed to compute the LR is exponential
with the number of feature measurements, a commonly used simplification is the use of likelihoods based on
distance (or similarity) given the two alternative hypotheses. This paper proposes an intermediate method
which decomposes the LR as the product of two factors, one based on distance and the other on rarity. It was
evaluated using a data set of handwriting samples, by determining whether two writing samples were written
by the same/different writer(s). The accuracy of the distance and rarity method, as measured by error rates, is
significantly better than the distance method.
Line segmentation is the first and the most critical pre-processing step for a document recognition/analysis task.
Complex handwritten documents with lines running into each other impose a great challenge for the line segmentation
problem due to the absence of online stroke information. This paper describes a method to disentangle
lines running into each other, by splitting and associating the correct character strokes to the appropriate lines.
The proposed method can be used along with the existing algorithm1 that identifies such overlapping lines in
documents. A stroke tracing method is used to intelligently segment the overlapping components. The method
uses slope and curvature information of the stroke to disambiguate the course of the stroke at cross points. Once
the overlapping components are segmented into strokes, a statistical method is used to associate the strokes with
appropriate lines.
Matching of partial fingerprints has important applications in both biometrics and forensics. It is well-known that
the accuracy of minutiae-based matching algorithms dramatically decrease as the number of available minutiae
decreases. When singular structures such as core and delta are unavailable, general ridges can be utilized. Some
existing highly accurate minutiae matchers do use local ridge similarity for fingerprint alignment. However, ridges
cover relatively larger regions, and therefore ridge similarity models are sensitive to non-linear deformation. An
algorithm is proposed here to utilize ridges more effectively- by utilizing representative ridge points. These points
are represented similar to minutiae and used together with minutiae in existing minutiae matchers with simple
modification. Algorithm effectiveness is demonstrated using both full and partial fingerprints. The performance
is compared against two minutiae-only matchers (Bozorth and k-minutiae). Effectiveness with full fingerprint
matching is demonstrated using the four databases of FVC2002- where the error rate decreases by 0.2-0.7% using
the best matching algorithm. The effectiveness is more significant in the case of partial fingerprint matching-
which is demonstrated with sixty partial fingerprint databases generated from FVC2002 (with five levels of numbers
of minutiae available). When only 15 minutiae are available the error rate decreases 5-7.5%. Thus the method,
which involves selecting representative ridge points, minutiae matcher modification, and a group of minutiae
matchers, demonstrates improved performance on full and especially partial fingerprint matching.
A new technique to segment a handwritten document into distinct lines of text is presented. Line segmentation
is the first and the most critical pre-processing step for a document recognition/analysis task. The proposed
algorithm starts, by obtaining an initial set of candidate lines from the piece-wise projection profile of the
document. The lines traverse around any obstructing handwritten connected component by associating it to the
line above or below. A decision of associating such a component is made by (i) modeling the lines as bivariate
Gaussian densities and evaluating the probability of the component under each Gaussian or (ii)the probability
obtained from a distance metric. The proposed method is robust to handle skewed documents and those with
lines running into each other. Experimental results show that on 720 documents (which includes English, Arabic
and children's handwriting) containing a total of 11, 581 lines, 97.31% of the lines were segmented correctly. On
an experiment over 200 handwritten images with 78, 902 connected components, 98.81% of them were associated
to the correct lines.
The paper describes the use of Conditional Random Fields(CRF) utilizing contextual information in automatically
labeling extracted segments of scanned documents as Machine-print, Handwriting and Noise. The result of
such a labeling can serve as an indexing step for a context-based image retrieval system or a bio-metric signature
verification system. A simple region growing algorithm is first used to segment the document into a number of
patches. A label for each such segmented patch is inferred using a CRF model. The model is flexible enough
to include signatures as a type of handwriting and isolate it from machine-print and noise. The robustness of
the model is due to the inherent nature of modeling neighboring spatial dependencies in the labels as well as
the observed data using CRF. Maximum pseudo-likelihood estimates for the parameters of the CRF model are
learnt using conjugate gradient descent. Inference of labels is done by computing the probability of the labels
under the model with Gibbs sampling. Experimental results show that this approach provides for 95.75% of the
data being assigned correct labels. The CRF based model is shown to be superior to Neural Networks and Naive
Bayes.
The fingerprint verification task answers the question of whether or not two fingerprints belongs to the same finger. The paper focuses on the classification aspect of fingerprint verification. Classification is the third and final step after after the two earlier steps of feature extraction, where a known set of features (minutiae points) have been extracted from each fingerprint, and scoring, where a matcher has determined a degree of match between the two sets of features. Since this is a binary classification problem involving a single variable, the commonly used threshold method is related to the so-called receiver operating characteristics (ROC). In the ROC approach the optimal threshold on the score is determined so as to determine match or non-match. Such a method works well when there is a well-registered fingerprint image. On the other hand more sophisticated methods are needed when there exists a partial imprint of a finger- as in the case of latent prints in forensics or due to limitations of the biometric device. In such situations it is useful to consider classification methods based on computing the likelihood ratio of match/non-match. Such methods are commonly used in some biometric and forensic domains such as speaker verification where there is a much higher degree of uncertainty. This paper compares the two approaches empirically for the fingerprint classification task when the number of available minutiae are varied. In both ROC-based and likelihood ratio methods, learning is from a general population of ensemble of pairs, each of which is labeled as being from the same finger or from different fingers. In the ROC-based method the best operating point is derived from the ROC curve. In the likelihood method the distributions of same finger and different finger scores are modeled using Gaussian and Gamma distributions. The performances of the two methods are compared for varying numbers of minutiae points available. Results show that the likelihood method performs better than the ROC-based method when fewer minutiae points are available. Both methods converge to the same accuracy as more minutiae points are available.
The design and performance of a system for spotting handwritten Arabic words in scanned document images is presented. Three main components of the system are a word segmenter, a shape based matcher for words and a search interface. The user types in a query in English within a search window, the system finds the equivalent Arabic word, e.g., by dictionary look-up, locates word images in an indexed (segmented) set of documents. A two-step approach is employed in performing the search: (1) prototype selection: the query is used to obtain a set of handwritten samples of that word from a known set of writers (these are the prototypes), and (2) word matching: the prototypes are used to spot each occurrence of those words in the indexed document database. A ranking is performed on the entire set of test word images-- where the ranking criterion is a similarity score between each prototype word and the candidate words based on global word shape features. A database of 20,000 word images contained in 100 scanned handwritten Arabic documents written by 10 different writers was used to study retrieval performance. Using five writers for providing prototypes and the other five for testing, using manually segmented documents, 55% precision is obtained at 50% recall. Performance increases as more writers are used for training.
New machine learning strategies are proposed for person identification which can be used in several biometric
modalities such as friction ridges, handwriting, signatures and speech. The biometric or forensic performance
task answers the question of whether or not a sample belongs to a known person. Two different learning paradigms
are discussed: person-independent (or general learning) and person-dependent (or person-specific learning). In
the first paradigm, learning is from a general population of ensemble of pairs, each of which is labelled as being
from the same person or from different persons- the learning process determines the range of variations for given
persons and between different persons. In the second paradigm the identity of a person is learnt when presented
with multiple known samples of that person- where the variation and similarities within a particular person are
learnt. The person-specific learning strategy is seen to perform better than general learning (5% higher performace
with signatures). Improvement of person-specific performance with increasing number of samples is also
observed.
Search aspects of a system for analyzing handwritten documents are described. Documents are indexed using global image features, e.g., stroke width, slant as well as local features that describe the shapes of words and characters. Image indexing is done automatically using page analysis, page segmentation, line separation, word segmentation and recognition of words and characters. Two types of search are permitted: search based on global features of entire document and search using features at local level. For the second type of search, i.e., local, all the words in the document are characterized and indexed by various features and it forms the basis of different search techniques. The paper focuses on local search and describes four tasks: word/phrase spotting, text to image, image to text and plain text. Performance in terms of precision/recall and word ranking is reported on a database of handwriting samples from about 1,000 individuals.
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