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Inter-Office Memorandum

To Spline Aficionados Date November 20, 1973

From Ad rienne Payne Location Palo Alto

Subject Spline Function Representation Organization PARC/CSt
of Chinese Characters


Attached is a working draft of a paper by Bob Flegal; Bob .told me to tell
you all that held be around to talk to you individually about the paper.
Or, you can stop by the Graphics Lab and chat,with him.

Patrick Baudelaire
Danny Bobrow
Alan Kay
But 1er Lampson
Dick Shoup
Bob Sproull
Bob Taylor
Adele Goldberg
Diana Jones (archive files)
Dan Swi nehart
David Liddle

Working Draft / August 15, 1973

Robert Flegal


In using computers to represent and manipulate Chinese characters,
much effort to date has quite properly been devoted to the primary problems
of compactness of coding, storage and retrieval, and character- recognition
[References I through 5]. Aesthetic problems in matters of typography and
call igraphy have necessari ly played a lesser role. Yet looking ahead to
the time when the aesthetic quality of computer generated output may be
allowed to assume a greater significance, it is clear that much work
remains to be done. Our purpose in this paper is to call attention to the
possibilities inherent in the use of spline functions to represent
arbitrary graphical figures In general, and Chinese characters in
particular. Although t'he techniques have quite wide appl icabtl ity, we have
chosen to illustrate their use in the treatment of hand-written characters
input to a small computer system in real time.

Cubic spline functions have properties that make them particularly
suitable for approximating hand-drawn curves for which relatively few
sample points are available. Most importantly they are the mathematical
analog of splines used by draftsmen. A mechanical spline is a thin strip
Robert Flegal I Working Draft I August 15, 1973 I Page 2

of plastic or metal that can be constrained to a particular shape wi,th lead
weights (called "dogs") that hold the strip In place.

As a consequence of behaving like mechanical splines, cubic spline
functions are smooth, and furthermore, a change In the position of one of
the dogs does not radically change the shape of the whole curve --
properties not shared, for example, by interpolatory polynomials.

Outline of the method

Characters are written on a digitizing tablet which is interfaced to a
small computer system.* [Footnote: The sy