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Correction of Wild Points Within an Electronic Tablet Data

IP.com Disclosure Number: IPCOM000038665D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 64K

Publishing Venue

IBM

Related People

Kim, J: AUTHOR [+2]

Abstract

Electronic tablets are used to record images of handwriting and drawings. This is done by recording periodically the x-y coordinate points obtained from the dynamic trace of a stylus moving over the tablet. An indication of pen up-down is also recorded and the coordinate points are generally recorded only when the pen is down. Thus, information is obtained of the strokes used in the writing or drawing. A stroke is the data from pen down to pen up. Writing with a special stylus on an electronic tablet has some differences from writing with pen or pencil on paper. The correspondence between the shape of the writing or drawing and the data points electronically recorded is not always precise. Apart from inaccuracies due to tablet resolution and sampling rate, data are sometimes poorly recorded due to tablet error.

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Correction of Wild Points Within an Electronic Tablet Data

Electronic tablets are used to record images of handwriting and drawings. This is done by recording periodically the x-y coordinate points obtained from the dynamic trace of a stylus moving over the tablet. An indication of pen up-down is also recorded and the coordinate points are generally recorded only when the pen is down. Thus, information is obtained of the strokes used in the writing or drawing. A stroke is the data from pen down to pen up. Writing with a special stylus on an electronic tablet has some differences from writing with pen or pencil on paper. The correspondence between the shape of the writing or drawing and the data points electronically recorded is not always precise. Apart from inaccuracies due to tablet resolution and sampling rate, data are sometimes poorly recorded due to tablet error. Tablet error can be due to problems with tablet linearity or with the occasional erroneous generation of coordinate points referred to as "wild" points.

(Image Omitted)

A method is described herein for effecting the detection and correction of wild points. A wild point generally appears as a discontinuity in the writing, and the discontinuity is usually in either the x or y coordinate value and not in both simultaneously. Examples of wild points are shown in Fig. 1 which shows 3 samples: Writer 1 on tablet 1; Writer 1 on tablet 2, and Writer 2 on tablet 1. The correction of wild points is necessary to increase the fidelity of the recorded information relative to the input writing. This increased fidelity has been found advantageous, for example, in the display and recognition of handwriting. The present method for detecting a wild point is based on a calculation of the acceleration of the movement of the stylus tip. The algorithm is described in broad terms here and in more detail below.

Basically, if the magnitude of the acceleration exceeds a threshold, a wild point is detected. Acceleration was found to be a useful criterion for several reasons. First, in the middle of a stroke where relatively high velocities can occur, the acceleration (change of velocity) is generally stable and does not falsely detect a true point as being wild. Second, a wild point is generally characterized by an abrupt velocity reversal which is well captured by the acceleration measurement. Third, the acceleration of the hand and/or arm during writing is limited by its mass and the muscular forces driving the pen motion, as well as by other factors. Other measurements, such as velocity and velocity ratios, were found to be less accurate for detecting wild points. Because samples are generally not recorded when the pen is up between strokes, causing discontinuity in time between pen up and pen down, each stroke is processed separately. In order to simplify the computation and also because the discontinuity of a wild point is generally in either only the x or y direction, the acceleration i...