Wacef Guerfali

The generation of handwriting with delta-lognormal synergies

Abstract. This paper presents a handwriting generation model that takes advantage of the asymptotic impulse response of neuromuscular networks to produce and control complex two-dimensional synergistic movements. A parametric definition of a ballistic stroke in the context of the kinematic theory of rapid human movements is given. Two types of parameters are used: command and system parameters. The first group provides a representation of the action plan while the second takes into account the temporal properties of the neuromuscular systems executing that plan. Handwriting is described as the time superimposition of basic discontinuous strokes that results in a continuous summation of delta-lognormal velocity vectors. The model leads to trajectory reconstruction, both in the spatial and in the kinematic domain. According to this new paradigm, the angular velocity does not have to be controlled independently and continuously; it naturally emerges from the vectorial summation process. Several psychophysical phenomena related to two-dimensional movements are explained and analyzed in the context of the model: the speed/accuracy trade-offs, spatial scaling, the isochrony principle, the two-thirds power law, effector independence, etc. The overall approach also shows how basic handwriting characteristics (dimension, slant, baseline, shape, etc.) are affected and controlled using an action plan made up of virtual targets fed into a neuromuscular synergy that is governed by a delta-lognormal law.

Normalizing and restoring on-line handwriting

Abstract Preprocessing and normalization techniques for on-line handwriting analysis are crucial steps that usually compromise the success of recognition algorithms. These steps are often neglected and presented as solved problems, but this is far from the truth. An overview is presented of the principal on-line techniques for handwriting preprocessing and word normalization, covering the major difficulties encountered and the various approaches usually used to resolve these problems. Some measurable definitions for handwriting characteristics are proposed, such as baseline orientation, character slant and handwriting zones. These definitions are used to measure and quantify the performance of the normalization algorithms. An approach to enhancing and restoring handwriting text is also presented, and an objective evaluation of all the processing results.

The Delta LogNormal theory for the generation and modeling of cursive characters

We exploit the Delta LogNormal theory, a powerful tool for the generation and modeling of rapid movements to generate curvilinear strokes and constituting letters that respect both the dynamics and the appearance of movements made by a human. A theoretical analysis of the effects of the various parameters of the model is carried out: first, to reduce the size of the representation space of the letter models; and second, to select the parameters that constitute the optimal conditions for representing various symbols.

Learning handwriting with pen-based systems: computational issues

This paper introduces the theoretical foundation for the development of a pen-based system dedicated to helping to teach handwriting in primary schools. Knowledge given by a kinematic theory of rapid human movements is used. The system proposed includes a letter model generator which is used to create letter shapes with a human-like kinematics. The system generates feedback to pupils after a multilevel analysis of the handwriting. The analysis presented deals with shape conformity, shape error identification, fluency analysis and kinematic parameter evaluation. Discussion on how fluency measurement and error quantification can be useful in developing a learning metric is also presented.

The 2/3 power law: when and why?

This paper presents the origin of some reported observations, which links the kinematics of handwriting with a movement trajectory, best known as the 2/3 power law. Using computer simulations, it is shown that the vectorial delta-lognormal model recently proposed to describe 2D movements can successfully simulate these phenomena. Although the power law has been found to be a good predictor in many experimental conditions, a few experiments have shown that the law does not apply to all graphic movements. Using the vectorial delta-lognormal model, the conditions under which a 2/3 power relationship can be observed are presented and the reasons why it does not seem to be verified for more general handwritten patterns are highlighted.

Why handwriting segmentation can be misleading

This paper presents a handwriting generation model based on a kinematic theory of rapid human movements. Handwriting is described as the vectorial sum of formal strokes. These strokes are characterized by a velocity profile that can be described by a delta-lognormal equation. The segmentation algorithm that results from this model allows a comparison of this formal approach with some operational and simpler segmentation methods, in the context of the unicity of the allograph representation.

A new method for the analysis of simple and complex planar rapid movements

Recent developments in the field of simple human movement modelling provide new ways in which to view complete models for analysing and understanding complex movements. Based on a kinematic theory and a vectorial delta-lognormal model recently proposed by Plamondon (1993a); Plamondon (1995a); Plamondon (1995b); Plamondon (1995c) and Plamondon (1998), a new method for exploring and understanding the inherent mechanisms that govern planar movement generation and predict human behaviour is presented here. This paper describes an approach for analysing simple as well as complex movements such as cursive handwriting. It highlights some difficulties encountered in the analysis of complex movements. Problems such as the development of robust approaches to solve the reverse engineering problem of automatic parameter extraction of a succession of time-overlapped nonlinear functions are discussed. The analysis of natural cursive handwriting shows many interesting properties of the model and proposes new ways to study perturbed movement phenomena.

The Generation of Oriental Characters: New Perspectives for Automatic Handwriting Processing

We recently developed a general theory of rapid human movements and applied it to the generation of western handwriting. The goal of this paper is to summarize the key concepts behind the so-called vectorial delta-lognormal model that results from this theory and to show how this model could be used for Chinese character analysis and processing.

Effect of Variability on Letters Generation with the Vectorial Delta-Lognormal Model

One of the primary goals of handwriting modeling is to understand how humans represent, control and generate compex movements. Moreover handwriting modeling has been also used for practical applications such as handwriting analysis and recognition. Numerous models used to date were not strong enough to explain and support some fundamental results about biomechanical or neurophysiological systems and neither practical enough to be used for accurate handwriting generation in the kinematic and the spatial domains. The vectorial delta lognormal model has been shown, in the past few years, to answer to these two paradigms showing accuracy for simple movements simulation and flexibility for letters and cursive handwriting generation. In this paper we show how this model can help to study handwriting variability, particulartly, the effects of the fluctuations of the commands and of the neuromuscular effectors, on the movement generated. Some characters models are proposed with examples of the variability effects. A parametric representation of allographs can then be used to represent basic shapes and some models of distortion, to generate a variety of prototypes.

The Generation of Oriental Characters

We recently developed a general theory of rapid human movements and applied it to the generation of western handwriting. The goal of this paper is to summarize the key concepts behind the so-called vectorial delta-lognormal model that results from this theory and to show how this model could be used for Chinese character analysis and processing.