U. Glaeser

• No toggling between edit/control and ink mode. Pen input inside the input method area is treated
as ink to be recognized by the recognizer; pen input outside this area is treated as mouse events,
e.g., selection, etc. Without this separation, special provisions, sometimes unnatural, have to be
taken to distinguish among the two pen modes.
• Better user control. Within the specially designated writing window it is possible to have additional
GUI elements that help the user with the input task. For instance, there might be buttons
for common edit keys such as backspace, newline, and delete. Similarly, a list of recognition
alternates can be easily displayed and selected from. This is particularly important because top-n
recognition accuracy—a measure of how often the correct answer is among the highest ranked
n results, is generally much higher than top-1 accuracy.
• Consistent UI metaphor. Despite its ergonomic limitations, an on-screen keyboard is generally
available as one of the text input methods on the device. Using a special input area for handwriting
makes the user interface of alternative text entry methods similar.
Modal Input. The possibilities of the user’s input are selectively limited in order to increase recognition
accuracy. Common modes include “digits,” “symbols,” “upper-case letters,” and “lower-case letters”
in English, or “traditional” versus “simplified” in Chinese. By limiting the number of characters
against which a given input ink is matched, the opportunities for confusion and mis-recognition
are decreased, and recognition accuracy is improved. Writing modes represent another tradeoff
between making life simpler for the system or simpler for the user.
Natural Character Set. It is possible to use any character writing style commonly used in the given
language, no need to learn a special alphabet. Characters can be multi-stroke,
i.e., written with
more than one pen trace.
Multi-boxed Input. When multi-stoke input is allowed, end of writing is generally detected by use of
a timer that is set after each stroke is completed; the input is deemed concluded if a set amount
of time elapses before any more input is received in the writing area. This “timeout” scheme is
sometimes confusing to users. Multiple boxes give better performance because a character in one
box can be concluded if input is received in another, removing the need to wait for the timer to
finish.
Of all the restrictions imposed on users by these character-based input methods, modality is the one
where user feedback has been strongest: people want modeless input. The challenge lies in that distinguishing
between letters which have very similar forms across modes is virtually impossible without
additional information. In English orthography, for instance, there are letters for which the lower case
version of the character is merely a smaller version of the upper case version; examples include “Cc,”
“Kk,” “Mm,” “Oo,” “Ss,” “Uu,” “Ww,” etc. Simple attempts at building modeless character recognizers can
result in a disconcerting user experience because upper case letters, or digits, might appear inserted into
the middle of lower case words. Such m1Xed CaSe w0rdS (mixed case words) look to users to be gibberish.
In usability studies, the authors have further found that as the text data entry needs on wireless PIA
devices shifts from short address book or calendar items to longer notes or e-mail messages, users deem
writing one letter at a time to be inconvenient and unnatural.
More Natural User Interfaces
One known way of dealing with the character confusion difficulties described in section “User Interfaces
on Mobile Devices” is to use contextual information in the recognition process. At the simplest level this
means recognizing characters in the context of their surrounding characters and taking advantage of
visual clues derived from word shape. At a higher level, contextual knowledge can be in the form of
lexical constraints, e.g., a dictionary of known words in the language is used to restrict interpretations
of the input ink. These ideas naturally lead to the notion of a word-based text input method. By “word”
we mean a string of characters which, if printed in text using normal conventions, would be surrounded
by white-space characters (see Fig. 42.38(a)).
© 2002 by CRC Press LLC