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Dehooking Procedure for Handwriting on a Tablet

IP.com Disclosure Number: IPCOM000043979D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Tappert, CC: AUTHOR

Abstract

An earlier article [*] describes a system for recognizing discretely written characters based on elastic matching of an unknown character against a set of character prototypes. The input to the system is point data produced by the dynamic trace of a stylus on an electronic tablet. Writing with a special stylus on an electronic tablet is not quite like writing with pen or pencil on paper. For most electronic tablets the stylus is equipped with a ball-point pen so that by mounting a piece of paper on the tablet one sees the ink appear on the paper as one writes. However, the correspondence between the ink traces on the paper and the data points electronically recorded is not always very precise.

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Dehooking Procedure for Handwriting on a Tablet

An earlier article [*] describes a system for recognizing discretely written characters based on elastic matching of an unknown character against a set of character prototypes. The input to the system is point data produced by the dynamic trace of a stylus on an electronic tablet. Writing with a special stylus on an electronic tablet is not quite like writing with pen or pencil on paper. For most electronic tablets the stylus is equipped with a ball-point pen so that by mounting a piece of paper on the tablet one sees the ink appear on the paper as one writes. However, the correspondence between the ink traces on the paper and the data points electronically recorded is not always very precise. Apart from inaccuracies due to tablet resolution and sampling rate, the most prevalent inaccuracy is generally that occasionally extra data are recorded having the appearance of "hooks." A hook can occur at the beginning and/or end of a stroke, and is due to inaccuracy of pen up-down detection in the hardware. It is important to eliminate these extraneous hooks for later display of handwriting or for recognition procedures where their presence can cause recognition errors. An example of an extraneous hook at the beginning of a stroke is shown in Fig. 1, and one at the end of a stroke in Fig. 2. Two procedures are described herein (Figs. 3 and 4), which, when used together, have been found to eliminate most extraneous hooks without eliminating true data. The first procedure searches the beginning and end of a stroke for a steady state, that is, a sequence of x-y coordinate data in which little movement occurs. Since such steady states generally occur between the hook and what is considered the stroke data itself, a hook can be deleted by locating a steady state near the edge of a stroke and deleting the data points up to the steady state. The first procedure is invoked before filtering since it depends on actual timing to detect a steady state. The second procedure was designed to eliminate any remaining hooks at stroke ends. Hooks at stroke ends are more frequent then those at stroke beginnings and require this additional procedure to ensure their elimination. The second procedure, invoked after filtering, looks for a big direction change close to the end of a stroke and eliminates the points from the direction change to the stroke end. A flowchart o...