- Handwriting recognition
Handwriting recognition is the ability of a computer to receive and interpret intelligible handwritten input from sources such as paper documents, photographs, touch-screens and other devices. The image of the written text may be sensed "off line" from a piece of paper by optical scanning (optical character recognition) or intelligent word recognition. Alternatively, the movements of the pen tip may be sensed "on line", for example by a pen-based computer screen surface.
Handwriting recognition principally entails optical character recognition. However, a complete handwriting recognition system also handles formatting, performs correct segmentation into characters and finds the most plausible words.
Off-line handwriting recognition involves the automatic conversion of text in an image into letter codes which are usable within computer and text-processing applications. The data obtained by this form is regarded as a static representation of handwriting. Off-line handwriting recognition is comparatively difficult, as different people have different handwriting styles. And, as of today, OCR engines are primarily focused on machine printed text and ICR for hand "printed" (written in capital letters) text. There is no OCR/ICR engine that supports handwriting recognition as of today.
Problem domain reduction techniques
Narrowing the problem domain often helps increase the accuracy of handwriting recognition systems. A form field for a ZIP code for example, would contain only the characters 0-9. This fact would reduce the number of possible identifications.
- Specifying specific character ranges
- Utilization of specialized forms
Off-line character recognition often involves scanning a form or document written sometime in the past. This means the individual characters contained in the scanned image will need to be extracted. Tools exist that are capable of performing this step however, several common imperfections in this step. The most common being characters that are connected together are returned as a single sub-image containing both characters. This causes a major problem in the recognition stage. Yet many algorithms are available that reduce the risk of connected characters.
After the extraction of individual characters occurs a recognition engine is used to identify the corresponding computer character. Several different recognition techniques are currently available.
Neural network recognizers learn from an initial image training set. The trained network then makes the character identifications. Each neural network uniquely learns the properties that differentiate training images. It then looks for similar properties in the target image to be identified. Neural networks are quick to set up; however, they can be inaccurate if they learn properties that are not important in the target data.
Feature extraction works in a similar fashion to neural network recognizers however, programmers must manually determine the properties they feel are important.
Some example properties might be:
- Aspect Ratio
- Percent of pixels above horizontal half point
- Percent of pixels to right of vertical half point
- Number of strokes
- Average distance from image center
- Is reflected y axis
- Is reflected x axis
This approach gives the recognizer more control over the properties used in identification. Yet any system using this approach requires substantially more development time than a neural network because the properties are not learned automatically.
On-line handwriting recognition involves the automatic conversion of text as it is written on a special digitizer or PDA, where a sensor picks up the pen-tip movements as well as pen-up/pen-down switching. That kind of data is known as digital ink and can be regarded as a dynamic representation of handwriting. The obtained signal is converted into letter codes which are usable within computer and text-processing applications.
The elements of an on-line handwriting recognition interface typically include:
- a pen or stylus for the user to write with.
- a touch sensitive surface, which may be integrated with, or adjacent to, an output display.
- a software application which interprets the movements of the stylus across the writing surface, translating the resulting strokes into digital text.
Commercial products incorporating handwriting recognition as a replacement for keyboard input were introduced in the early 1980s. Examples include handwriting terminals such as the Pencept Penpad and the Inforite point-of-sale terminal. With the advent of the large consumer market for personal computers, several commercial products were introduced to replace the keyboard and mouse on a personal computer with a single pointing/handwriting system, such as those from PenCept, CIC and others. The first commercially available tablet-type portable computer was the GRiDPad from GRiD Systems, released in September 1989. Its operating system was based on MS-DOS.
In the early 1990s, hardware makers including NCR, IBM and EO released tablet computers running the PenPoint operating system developed by GO Corp.. PenPoint used handwriting recognition and gestures throughout and provided the facilities to third-party software. IBM's tablet computer was the first to use the ThinkPad name and used IBM's handwriting recognition. This recognition system was later ported to Microsoft Windows for Pen Computing, and IBM's Pen for OS/2. None of these were commercially successful.
Advancements in electronics allowed the computing power necessary for handwriting recognition to fit into a smaller form factor than tablet computers, and handwriting recognition is often used as an input method for hand-held PDAs. The first PDA to provide written input was the Apple Newton, which exposed the public to the advantage of a streamlined user interface. However, the device was not a commercial success, owing to the unreliability of the software, which tried to learn a user's writing patterns. By the time of the release of the Newton OS 2.0, wherein the handwriting recognition was greatly improved, including unique features still not found in current recognition systems such as modeless error correction, the largely negative first impression had been made. After discontinuation of Apple Newton, the feature has been ported to Mac OS X 10.2 or later in form of Inkwell (Macintosh).
Palm later launched a successful series of PDAs based on the Graffiti recognition system. Graffiti improved usability by defining a set of "unistrokes", or one-stroke forms, for each character. This narrowed the possibility for erroneous input, although memorization of the stroke patterns did increase the learning curve for the user. The Graffiti handwriting recognition was found to infringe on a patent held by Xerox, and Palm replaced Graffiti with a licensed version of the CIC handwriting recognition which, while also supporting unistroke forms, pre-dated the Xerox patent. The court finding of infringement was reversed on appeal, and then reversed again on a later appeal. The parties involved subsequently negotiated a settlement concerning this and other patents Graffiti (Palm OS).
A Tablet PC is a special notebook computer that is outfitted with a digitizer tablet and a stylus, and allows a user to handwrite text on the unit's screen. The operating system recognizes the handwriting and converts it into typewritten text. Windows Vista and Windows 7 include personalization features that learn a user's writing patterns and/or vocabulary for English, Japanese, Chinese Traditional, Chinese Simplified and Korean. The features include a "personalization wizard" that prompts for samples of a user's handwriting and uses them to retrain the system for higher accuracy recognition. This system is distinct from the less advanced handwriting recognition system employed in its Windows Mobile OS for PDAs.
In recent years, several attempts were made to produce ink pens that include digital elements, such that a person could write on paper, and have the resulting text stored digitally. The best known of these use technology developed by Anoto, which has had some success in the education market. The general success of these products is yet to be determined.
Although handwriting recognition is an input form that the public has become accustomed to, it has not achieved widespread use in either desktop computers or laptops. It is still generally accepted that keyboard input is both faster and more reliable. As of 2006[update], many PDAs offer handwriting input, sometimes even accepting natural cursive handwriting, but accuracy is still a problem, and some people still find even a simple on-screen keyboard more efficient.
Initial software modules could understand print handwriting where the characters were separated. Commercial examples came from companies such as Communications Intelligence Corporation and IBM. In the early 90s, two companies, ParaGraph International, and Lexicus came up with systems that could understand cursive handwriting recognition. ParaGraph was based in Russia and founded by computer scientist Stepan Pachikov while Lexicus was founded by Ronjon Nag and Chris Kortge who were students at Stanford University. The ParaGraph CalliGrapher system was deployed in the Apple Newton systems, and Lexicus Longhand system was made available commercially for the PenPoint and Windows operating system. Lexicus was acquired by Motorola in 1993 and went on to develop Chinese handwriting recognition and predictive text systems for Motorola. ParaGraph was acquired in 1997 by SGI and its handwriting recognition team formed a P&I division, later acquired from SGI by Vadem. Microsoft has acquired CalliGrapher handwriting recognition and other digital ink technologies developed by P&I from Vadem in 1999.
A modern handwriting recognition system can be seen in Microsoft's operating system running on Tablet PCs (notably Windows XP Tablet PC Edition, Windows Vista, and Windows 7). It is based on a Time delay neural network (TDNN) classifier, nicknamed "Inferno", built at Microsoft. Later on a version of CalliGrapher, a successor of the handwriting recognition software used on Newton OS 2.0, was integrated as a secondary recognizer with the TDNN. The new generation of CalliGrapher software is currently shipped for Windows Mobile by PhatWare Corp, which licensed ParaGraph's technologies from Vadem in 2001.
The "third generation" riteScript handwriting recognition technology, built by EverNote Corporation (the successor of Pen&Internet division of Parascript) in 2000-2008, is included in the ritePen and EverNote software. ritePen also includes fusion technology, which allows combining riteScript with the embedded handwriting recognition in Windows Vista and Windows 7 to improve recognition accuracy of each handwriting recognition engine. riteScript technology is available on Windows and Linux.
CellWriter is an Open Source handwriting recognition program written for Linux. It was developed primarily by Michael Levin, working under the University of Minnesota's Undergraduate Research Opportunity Program. CellWriter is designed to be writer-dependent, so input training is required prior to use. It includes an English word-recognition engine to aid recognition accuracy, an on-screen keyboard and the ability to fine tune or correct mistakes through a context menu. Unlike most recognition engines, the source code and algorithms are available and free to download.
MyScript Builder is a handwriting recognition SDK from VisionObjects  that is popular among companies developing software for digital pens based on Anoto technology.
Handwriting Recognition has an active community of academics studying it. The biggest conferences for handwriting recognition are the International Conference on Frontiers in Handwriting Recognition (ICFHR), held in even-numbered years, and the International Conference on Document Analysis and Recognition (ICDAR), held in odd-numbered years. Both of these conferences are scrutinized by the IEEE. Active areas of research include:
- Online Recognition
- Offline Recognition
- Signature Verification
- Postal-Address Interpretation
- Bank-Check Processing
- Writer Recognition
A survey of research on handwriting recognition is by R Plamondon and S. N. Srihari.
Brief historical notes
- 1915: U.S. Patent on handwriting recognition user interface with a stylus
- 1957: Stylator tablet: Tom Dimond demonstrates electronic tablet with pen for computer input and handwriting recognition
- 1961: RAND Tablet invented: better known than earlier Stylator system
- 1962: Computer recognition of connected/script handwriting
- 1969: GRAIL system: handwriting recognition with electronic ink display, gesture commands
- 1973: Applicon CAD/CAM computer system using the Ledeen recognizer for handwriting recognition
- 1980s: Retail handwriting-recognition systems: Pencept and CIC both offer PC computers for the consumer market using a tablet and handwriting recognition instead of a keyboard and mouse. Cadre System markets Inforite point-of-sale terminal using handwriting recognition and a small electronic tablet and pen.
- 1989: Portable handwriting recognition computer: GRiDPad from GRiD Systems.
- 1997: First handwritten address interpretation system(HWAI) deployed by United States Postal Service
- 2007: First automatic writer recognition system: CEDAR-FOX.
More extensive information on the history of handwriting recognition technology can be found in the article on Pen computing.
- Handwriting movement analysis
- Optical character recognition
- Pen computing
- Tablet PC
- Sketch recognition
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