Abstract:
The present invention overcomes the deficiencies of the prior art with a system for varying hand-drawn line width as a function of geometric or temporal properties such as curvature or time of the strokes as the user draws them. In one embodiment, the system of the present invention includes a stroke control module, a velocity adjustment module, a curvature adjustment module, a smoothing module, an adjacency verification module and a stroke dominance module. A stroke control module is operable on a processor to modify the width of input strokes and adjust them based on their curvature and/or the velocity at which they were received. The stroke control module cooperates with and controls the velocity adjustment module, a curvature adjustment module, the smoothing module and the other modules to provide overall width adjustment of strokes input by the user automatically to reflect the needs and intentions of the user and provide a natural-feeling drawing experience similar to that provided by paper.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to techniques for displaying hand-drawn lines by a display device. More particularly, the present invention relates to systems and method for varying the size of strokes displayed by a computing device to reflect the needs and intentions of the user. 
         [0002]    There have been a number of attempts in recent years to increase the adoption rate for pen-based computing devices. A number of laptop computers now include a stylus and displays that allows users to interact with the computer using the stylus in place of the mouse for cursor control and stroke capture. Recently, handheld computing devices such as smart phones and personal digital assistants (PDA) have also started to incorporate stylus/tablet type interfaces. 
         [0003]    One consistent problem with stylus-based tablets is that the user experience with the stylus and tablet does not match the experience one has when interacting with a writing instrument and paper. In particular, the strokes captured by the tablet and presented back to the user typically do not have any dimensions. In contrast, when a user writes on paper, the user employs pressure and a pencil angle to affect the width of the strokes drawn. But detecting angled pressure in a stylus-based tablet system is difficult and expensive. It requires both a complicated stylus and a complicated detection and reporting system. Such requirements for sophisticated stylus and reporting systems make such systems cost prohibitive. 
         [0004]    The inability of the prior art systems to be able to render strokes that have an appropriate width has significantly diminished the user experience and the adoption rate of such stylus-based tablets. Users tend to feel a need to write in larger strokes than they would like to in order to preserve readability, including the usual ratios of ink-filled space to empty space within and between characters and lines and this is due in part to the inability of the prior art to render lines with varying widths. Especially when taking notes, it is frustrating for the user to be unable to write characters as small as they can on paper. In contrast, when drawing circles, arrows and boxes, the user wants them to be easily viewed from a distance and desires fairly broad strokes. However, the prior art does not provide an ability to manage and modify stroke width to reflect user intentions. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention overcomes the deficiencies of the prior art with a system for varying hand-drawn line width as a function of geometric or temporal properties such as curvature or speed of the strokes as the user draws them. In one embodiment, the system of the present invention includes a stroke control module, a velocity adjustment module, a curvature adjustment module, a smoothing module, an adjacency identification module and a stroke dominance module. A stroke control module is operable on a processor to modify the width of input strokes and adjust them based on their curvature and/or the velocity at which they were received. The stroke control module cooperates with and controls the velocity adjustment module, a curvature adjustment module, the smoothing module and the other modules to provide overall width adjustment of strokes input by the user automatically to reflect the needs and intentions of the user and provide a natural-feeling drawing experience much more like that provided by paper. 
         [0006]    The present invention also includes a number of novel methods including: a method for varying hand-drawn line widths, a method for adjusting line width for curvature, a method for adjusting line width for velocity, a method for smoothing line segments, a method for computing dominance of the group in an area and a method for determining adjacency groups. 
         [0007]    The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the figures and description. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention is illustrated by way of example, and not by way of limitation in the figures of the accompanying drawings in which like reference numerals are used to refer to similar elements. 
           [0009]      FIG. 1  illustrates an embodiment of a system including stylus and digitizing tablet of the present invention. 
           [0010]      FIG. 2  illustrates a block diagram of a system configured in accordance with an embodiment of the present invention. 
           [0011]      FIG. 3  illustrates a block diagram of a memory of the computer of  FIG. 2  configured in accordance with an embodiment of the present invention. 
           [0012]      FIG. 4A  is a graphical representation of a display of a stroke unmodified as in the prior art. 
           [0013]      FIG. 4B  is graphical representation of a display of a stroke adjusted for velocity in accordance with an embodiment of the present invention. 
           [0014]      FIG. 5A  is graphical representation of a display of a stroke unmodified as in the prior art. 
           [0015]      FIG. 5B  is graphical representation of a display of a stroke adjusted for curvature in accordance with an embodiment of the present invention. 
           [0016]      FIGS. 6A and 6B  are a flowchart of an embodiment of a method for varying hand-drawn line width for display in accordance with the present invention. 
           [0017]      FIG. 7  is a flow chart of an embodiment of a method for varying line width based on velocity in accordance with the present invention. 
           [0018]      FIG. 8  is a flow chart of an embodiment of a method for varying line width based on curvature in accordance with the present invention. 
           [0019]      FIG. 9A  is a flowchart of an embodiment of a method for smoothing interior segments in accordance with the present invention. 
           [0020]      FIG. 9B  is a flowchart of an embodiment of a method for smoothing end segments in accordance with the present invention. 
           [0021]      FIG. 10  is a flowchart of an embodiment of a method for computing dominance of a group in an area in accordance with the present invention. 
           [0022]      FIG. 11  is a flowchart of an embodiment of a method for partitioning short strokes into adjacency groups in accordance with the present invention. 
           [0023]      FIG. 12  is a flowchart of an embodiment of a method for computing nearness of a stroke to a short stroke in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    A system and methods for varying hand-drawn line width for display are described. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention. For example, the present invention is described primarily with reference to a stylus and tablet computing device. However, the present invention applies to any type of pen-based computing device regardless of portability or size. 
         [0025]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0026]    Some portions of the detailed descriptions that follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
         [0027]    It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
         [0028]    The present invention also relates to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, each coupled to a computer system bus. 
         [0029]    Finally, the algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these systems will appear from the description below. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. 
       System 
       [0030]      FIG. 1  shows an example of a system  100  including a stylus  102  and a tablet or computing device  104  upon which an embodiment of the present invention is operable. The tablet or computing device  104  includes a display  210  for presenting images, text, data including representation of strokes to the user. The tablet or computing device  104  also includes a touch screen or digitizer  214  for determining the position of a finger or stylus, respectively. The digitizer  214  may be active or passive or similar technology as will be understood by those skilled in the art. 
         [0031]    Referring now also to  FIG. 2 , a functional block diagram of the system  100  configured in accordance with an embodiment of the present invention is shown. The system  100  preferably comprises a control unit  250 , a display device  210  and a digitizer  214 . The system  100  may optionally include a keyboard &amp; cursor control  212 , a network controller  216  and one or more input/output (I/O) devices  218 . 
         [0032]    The control unit  250  comprises an arithmetic logic unit, a microprocessor, a general purpose computer or some other information appliance equipped to provide electronic display signals to display device  210 . In one embodiment, the control unit  250  comprises a general purpose computer having a graphical user interface, which may be generated by, for example, a program written in Java running on top of an operating system like WINDOWS® or UNIX® based operating systems. In one embodiment, one or more application programs are executed by control unit  250  including, without limitation, graffiti, drawing applications, note pad applications, word processing applications, electronic mail applications, financial applications and web browser applications. 
         [0033]    Still referring to  FIG. 2 , the control unit  250  is shown including processor  202 , main memory  204 , and data storage device  206 , all of which are communicatively coupled to system bus  208 . 
         [0034]    Processor  202  processes data signals and may comprise various computing architectures including a complex instruction set computer (CISC) architecture, a reduced instruction set computer (RISC) architecture, or an architecture implementing a combination of instruction sets. Although only a single processor is shown in  FIG. 2 , multiple processors may be included. 
         [0035]    Main memory  204  stores instructions and/or data that may be executed by processor  202 . The instructions and/or data may comprise code for performing any and/or all of the techniques described herein. Main memory  204  may be a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, or some other memory device known in the art. The memory  204  is described in more detail below with reference to  FIG. 3 . 
         [0036]    Data storage device  206  stores data and instructions for processor  202  and comprises one or more devices including a hard disk drive, a floppy disk drive, a CD-ROM device, a DVD-ROM device, a DVD-RAM device, a DVD-RW device, a flash memory device, or some other mass storage device known in the art. 
         [0037]    System bus  208  represents a shared bus for communicating information and data throughout control unit  250 . System bus  208  may represent one or more buses including an industry standard architecture (ISA) bus, a peripheral component interconnect (PCI) bus, a universal serial bus (USB), or some other bus known in the art to provide similar functionality. Additional components coupled to control unit  250  through system bus  208  include the display device  210 , the keyboard &amp; cursor control device  212 , the digitizer  214 , the network controller  216  and the I/O device(s)  218 . 
         [0038]    Display device  210  represents any device equipped to display electronic images and data as described herein. Display device  210  may be, for example, a liquid crystal display (LCD), a cathode ray tube (CRT) or any other similarly equipped display device, screen or monitor. In one embodiment, display device  210  is equipped with a touch screen and/or includes a digitizer  214  in which a touch-sensitive, transparent panel covers the screen of display device  210 . 
         [0039]    The digitizer  214  or graphics tablet is a conventional type of device that consists of a flat surface upon which the user may “draw” an image using a pen-like drawing apparatus and which produces signals that can be decoded to be coordinate information. The digitizer  214  or graphics tablet can any one of the conventional types present included as part of tablet personal computers and other devices. 
         [0040]    As denoted by dashed lines, the system  100  may optionally include the keyboard &amp; cursor control device  214 , the network controller  216  and one or more input/output (I/O) devices  218  such as described below. 
         [0041]    Keyboard  212  represents an alphanumeric input device coupled to control unit  250  to communicate information and command selections to processor  202 . The Keyboard  212  can be a QWERTY keyboard, a key pad, or representations of such created on a touch screen. Cursor control  212  represents a user input device equipped to communicate positional data as well as command selections to processor  202 . Cursor control  212  may include a mouse, a trackball, a stylus, a pen, a touch screen, cursor direction keys or other mechanisms to cause movement of a cursor. 
         [0042]    Network controller  216  links control unit  250  to a network  220  that may include multiple processing systems. The network of processing systems may comprise a local area network (LAN), a wide area network (WAN) (e.g., the Internet), and/or any other interconnected data path across which multiple devices may communicate. The control unit  250  also has other conventional connections to other systems such as a network for distribution of files (media objects) using standard network protocols such as TCP/IP, http, https, and SMTP as will be understood to those skilled in the art. 
         [0043]    One or more I/O devices  218  are coupled to the system bus  208 . These I/O devices may be part of system  100  in one embodiment and in another embodiment are part of the other systems (not shown). For example, the I/O device  218  can include an image scanner for capturing an image of a document. The I/O device  218  also includes a printer for generating documents. The I/O device  218  may also include audio input/output device equipped to receive audio input via a microphone and transmit audio output via speakers. In one embodiment, audio device is a general purpose; audio add-in/expansion card designed for use within a general purpose computer system. Optionally, I/O audio device may contain one or more analog-to-digital or digital-to-analog converters, and/or one or more digital signal processors to facilitate audio processing. 
         [0044]    It should be apparent to one skilled in the art that system  100  may include more or fewer components than those shown in  FIG. 2  without departing from the spirit and scope of the present invention. For example, system  100  may include additional memory, such as, for example, a first or second level cache, or one or more application specific integrated circuits (ASICs). Similarly, additional components input/output devices  218  may be coupled to control unit  250  including, for example, an RFID tag reader, digital still or video cameras, or other devices that may or may not be equipped to capture and/or download electronic data to control unit  250 . One or more components could also be eliminated such as the keyboard &amp; cursor control  212 . 
         [0045]      FIG. 3  is a block diagram of one embodiment of the memory unit  204  for the system  100 . The memory unit  204  preferably comprises: an operating system  302 , a stroke control module  304 , a velocity adjustment module  306 , a curvature adjustment module  308 , a smoothing module  310 , an adjacency identification module  312  and a stroke dominance module  314 . Those skilled in the art will recognize that the memory  204  also includes buffers for storing stroke, segment and capture data although not specifically shown. As noted above, the memory unit  204  stores instructions and/or data that may be executed by processor  202 . The instructions and/or data comprise code for performing any and/or all of the techniques described herein. These modules  202 - 214  are coupled by bus  208  to the processor  202  for communication and cooperation to system  100 . Those skilled in the art will recognized that while the present invention will now be described as modules or portions of a memory unit  204  of a computer system  100 , the modules or portions thereof may also be stored in other media such as permanent data storage device  206  and may be distributed across a network  104  having a plurality of different computers such as in a client/server environment. 
         [0046]    The operating system  302  is preferably one of a conventional type such as, WINDOWS®, SOLARIS® or LINUX® based operating systems. Although not shown, the memory unit  204  may also include one or more application programs including, without limitation, drawing applications, word processing applications, electronic mail applications, financial applications and web browser applications. 
         [0047]    The stroke control module  304  is used to control the other modules of the memory  204 . The stroke control module  304  is adapted for communication with the velocity adjustment module  306 , the curvature adjustment module  308 , the smoothing module  310 , the adjacency identification module  312  and the stroke dominance module  314 . The operation of the stroke control module  304  will be apparent from the description of  FIGS. 6A and 6B  below. Once the processing by the other modules is complete, the stroke control module  304  also generates and cause the modified stroke to by presented on the display device  210 . While the stroke control module  304  is shown as a separate module of the memory  204 , those skilled in the art will recognize that the stroke control module  304  in another embodiment may be distributed as routines in the other modules  204 - 212 . 
         [0048]    The velocity adjustment module  306  is software and routines for modifying the stroke width to account for the velocity at which the user drew the stroke. In one embodiment, the velocity that the stylus  102  was traveling when it laid down the segment is used as the measure of stroke or segment velocity. The operation of the velocity adjustment module  306  is described in more detail below with reference to  FIG. 7 . In general, the velocity adjustment module  306  modifies the width of the stroke such that the greater its velocity the greater its width. 
         [0049]    The curvature adjustment module  308  is software and routines for modifying the stroke width to account for the curvature of the stroke or segment. In one embodiment, the curvature of a segment and the segments near it are used to modify the width of the line. The operation of the curvature adjustment module  308  is described in more detail below with reference to  FIG. 8 . In general, the curvature adjustment module  308  modifies the width of the stroke such that the less the curvature the greater its width. 
         [0050]    The smoothing module  310  is software and routines for modifying the stroke width to smooth the entire stroke. In one embodiment, all the strokes and segment are passed through smoothing routines during and initial phase so that artifacts introduced during the detection process are minimized. This is typically pre processing of the stroke data before it is processed by the other modules  304 - 314  of the memory. In another embodiment, the smoothing module  310  smoothes the end segments and the interior segments. This smoothing is accomplished by ensuring the width of adjacent segments does not vary greatly by enforcing maximum changes between the widths of adjacent segments. This eliminates the visual impact of transitions between segments. The operation of the smoothing module  310  is described in more detail below with reference to  FIGS. 9A and 9B . 
         [0051]    The adjacency identification module  312  is software and routines for identifying short strokes and their adjacency to other strokes and adjusting their width because of their adjacency to other strokes. In general, to make the appearance of the strokes as close to conventional handwriting as possible this module ensures that strokes in a predefined proximity to each other will have a widths that are sized consistent with the other strokes. The operation of the adjacency identification module  312  is described in more detail below with reference to  FIG. 10 . 
         [0052]    The stroke dominance module  314  is software and routines for determining areas that have a high number of strokes. In such high density areas, the stroke width is modified in a different manner consistent with the stroke dominance. The stroke dominance module  314  identifies such areas and determines what strokes fall within such areas, and how they are processed differently or additionally. The operation of the stroke dominance module  314  is described in more detail below with reference to  FIGS. 11 and 12 . 
       Sample Strokes 
       [0053]    Referring now to  FIG. 4A , an example stroke  400  unmodified as in the prior art is shown. Using the data captured by the digitizer  214  produces the line  400  with a consistent width. As can be seen, there is no variance whatsoever in the line width. Referring now also to Table 1 below, the data generated by the digitizer  214  and processed in a conventional manner is shown in the columns denoted “Event,” “X,” “Y” and “Time.” 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 SPEED ADJUSTED 
               
             
          
           
               
                   
                 Event 
                 X 
                 Y 
                 Time 
                 D 
                 D/T 
               
               
                   
                   
               
             
          
           
               
                   
                 MouseDown 
                 100 
                 300 
                 0 
                   
                   
               
               
                   
                 MouseDrag 
                 106 
                 296 
                 80 
                 7.50 
                 94 
               
               
                   
                 MouseDrag 
                 112 
                 293 
                 160 
                 6.50 
                 31 
               
               
                   
                 MouseDrag 
                 117 
                 291 
                 240 
                 5.15 
                 64 
               
               
                   
                 MouseDrag 
                 121 
                 289 
                 320 
                 4.47 
                 56 
               
               
                   
                 MouseDrag 
                 127 
                 286 
                 400 
                 7.16 
                 89 
               
               
                   
                 MouseDrag 
                 135 
                 283 
                 280 
                 8.54 
                 107 
               
               
                   
                 MouseDrag 
                 145 
                 278 
                 560 
                 10.51 
                 131 
               
               
                   
                 MouseDrag 
                 158 
                 272 
                 640 
                 14.32 
                 179 
               
               
                   
                 MouseDrag 
                 171 
                 266 
                 720 
                 14.32 
                 179 
               
               
                   
                 MouseDrag 
                 185 
                 258 
                 800 
                 16.56 
                 219 
               
               
                   
                 MouseDrag 
                 200 
                 249 
                 880 
                 17.49 
                 219 
               
               
                   
                 MouseDrag 
                 240 
                 225 
                 960 
                 46.91 
                 586 
               
               
                   
                 MouseDrag 
                 307 
                 175 
                 1040 
                 82.90 
                 1036 
               
               
                   
                 MouseDrag 
                 333 
                 135 
                 1120 
                 47.98 
                 600 
               
               
                   
                 MouseUP 
                 379 
                 100 
                 1200 
                 57.40 
                 718 
               
               
                   
                   
               
             
          
         
       
     
         [0054]    Referring now to  FIG. 4B , a stroke  402  generated by the system  100  of the present invention is shown. In addition to the parameters used by the prior art, the present invention also used the velocity, for example as provided in column denoted “D/T” to modify the stroke width. As shown, the width of the stroke  402  is modified to a greater thickness at a point  408  where velocity is the greatest.  FIG. 4B  also illustrates how the system  100  and methods of the present invention taper the ends  404 ,  406  of the stroke in additional processing based on stroke velocity as will be described below with reference to  FIGS. 6A and 6B . 
         [0055]      FIG. 5A  is graphical representation of a display of another example stroke unmodified as in the prior art. Using the data captured by the digitizer  214  produces the line  502  with a consistent width. As can be seen, there is no variance whatsoever in the line width whether it be at the ends  504 ,  406  of the stroke  502  or in a highly curved section  508 . Referring now also to Table 2 below, the data generated by the digitizer  214  and processed in a conventional manner is shown in the columns denoted “Event,” “X,” “Y” and “T(ms).” 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 CURVE ADJUSTED 
               
             
          
           
               
                   
                 Event 
                 X 
                 Y 
                 T(ms) 
               
               
                   
                   
               
             
          
           
               
                   
                 MouseDown 
                 100 
                 100 
                 0 
               
               
                   
                 MouseDrag 
                 99 
                 116 
                 80 
               
               
                   
                 MouseDrag 
                 102 
                 134 
                 160 
               
               
                   
                 MouseDrag 
                 110 
                 163 
                 240 
               
               
                   
                 MouseDrag 
                 116 
                 181 
                 320 
               
               
                   
                 MouseDrag 
                 124 
                 203 
                 400 
               
               
                   
                 MouseDrag 
                 134 
                 226 
                 480 
               
               
                   
                 MouseDrag 
                 149 
                 246 
                 560 
               
               
                   
                 MouseDrag 
                 174 
                 259 
                 640 
               
               
                   
                 MouseDrag 
                 200 
                 266 
                 720 
               
               
                   
                 MouseDrag 
                 221 
                 270 
                 800 
               
               
                   
                 MouseDrag 
                 243 
                 262 
                 880 
               
               
                   
                 MouseDrag 
                 252 
                 249 
                 960 
               
               
                   
                 MouseDrag 
                 242 
                 226 
                 1040 
               
               
                   
                 MouseDrag 
                 223 
                 226 
                 1120 
               
               
                   
                 MouseDrag 
                 219 
                 242 
                 1200 
               
               
                   
                 MouseDrag 
                 216 
                 260 
                 1280 
               
               
                   
                 MouseDrag 
                 223 
                 282 
                 1360 
               
               
                   
                 MouseDrag 
                 237 
                 296 
                 1440 
               
               
                   
                 MouseDrag 
                 256 
                 302 
                 1520 
               
               
                   
                 MouseDrag 
                 285 
                 302 
                 1600 
               
               
                   
                 MouseRelease 
                 300 
                 300 
                 1680 
               
               
                   
                   
               
             
          
         
       
     
         [0056]      FIG. 5B  is graphical representation of a display of a stroke  520  adjusted for curvature in accordance with an embodiment of the present invention. As can be seen the width of the stroke  520  varies greatly depending on the curvature of the segment. The more curved section  526  of the line has reduced width, and the ends  522 ,  524  are tapered by the system  100  and method of the present invention. 
       Methods 
       [0057]    Referring now to  FIGS. 6A and 6B , an embodiment of a method for varying hand-drawn line width for display in accordance with the present invention will be described. The process begins by partitioning  602  strokes into short strokes and long strokes. In one embodiment, the strokes are separated into long and short strokes based on length and time. In one embodiment short strokes are those that take less than 0.4 seconds to draw or cover less than twenty pixels in distance. Next, the method determines  604  whether processing of the long strokes is complete. If so the method continues in a process that will be described below in conjunction with  FIG. 6B . If there are additional long strokes to process, the method then selects  606  the next long stroke. Each long stroke is analyzed by processing the segments that comprise the long stroke in sequence. The method determines  608  whether all the segments of the selected stroke had been processed. If so, the method proceeds to step  624  to smooth the interior segments. This process will be described below in more detail with reference to  FIG. 9A . The method then smoothes  626  the end segments. This process will be described below with reference to  FIG. 9B . After step  626 , the method returns to step  604  to determine whether additional long strokes that need to be processed. 
         [0058]    If in step  608 , the method was not finished processing segments then a next segment is selected  610 . The method then tests  612  whether the selected segment is an end segment. If so, the method sets  614  the segment width to be the minimum width, and then returns to step  608  to determine whether there are any additional segments to process. On the other hand, if the segment is determined not to be an end segment in step  612 , the method determines  616  whether the segment is near the end. If the segment is near the end, the process does not assign the segment a width at this point. This will be handled by a later smoothing step  624 ,  626 . The process returns to step  608  to determine whether there are any additional segments to process. If the segment is not near the end, the method determines  618  an adjusted segment width based on velocity. The process for modifying segment width based on velocity will be described in more detail below with reference to  FIG. 7 . Then the method determines  620  an adjusted segment width based on curvature. The process for modifying segment width based on curvature will be described in more detail below with reference to  FIG. 8 . Once the appropriate adjustments for velocity and curvature have been determined, the process modifies  622  the segment width. In one embodiment, the segment width is modified based on velocity. In another embodiment, the segment width is modified based on curvature. In yet another embodiment the segment width is modified based on both velocity and curvature. For example, the width for the segment could be set to be a value of a width modified for velocity times a weight plus a width modified for curvature times one minus the weight. After the width of the segment has been modified  622  for velocity and/or curvature, the method continues in step  608  to determine whether it is finished processing the segments of the current stroke. 
         [0059]    Referring now to  FIG. 6B , the method for processing short strokes will be described. The method transitions from step  604  to step  630  where the processing of short strokes to begins. The method first partitions  630  the short strokes into “adjacency groups.” The present invention advantageously sets the width of strokes that are temporally or physically nearby other strokes to have similar widths. This is accomplished in part by dividing the short strokes into adjacency groups and processing them together. This process will be described in more detail below with reference to  FIG. 11 . For example, if the stroke is especially short, it is handled specially. The dot over the “i” should have approximately the same width as does the “i” itself. The method next determines  632  whether it is finished processing the adjacency groups. If so, the method is complete and ends. If not however, the method selects  634  the next group for processing. Then the method determines  636  the “dominance” of a group in an area. The “dominance” of a group in an area provides input as to how much weight the width of strokes in this area should be given in setting the width for this selected group of strokes. A method for determining stroke dominance is described below with reference to  FIG. 10 . The method then determines whether the selected group of strokes is “dominant” in its area. In essence, the method determines whether there are a lot of short strokes in a given area. If not, the method is going to adjust the width of the short strokes to match the long strokes in the area. The method accomplishes this by computing  644  the width of long strokes in the area and assigning  646  the average of those widths as a segment width for each of the short strokes that is a member of the group. If it is determined that this group of short strokes is dominant in the area in step  638 , the method transitions to compute  640  the average length of the short strokes in the group &amp; sets  642  the segment width for the short strokes in the group to be a function of this average length. After step  646  or  642 , the method continues to step  648  where minimal tapering on the short strokes is performed. The present invention advantageously slightly tapers the start and the end of the stroke, simulating the effect of a gradual application and release of pressure when the user starts or stops writing. In one embodiment, the tapering use of time delta for tapering at the beginning and end of strokes. After step  648  the method returns to step  632  to determine whether it is finished processing groups of short strokes. 
         [0060]    Referring now to  FIG. 7 , an embodiment of a method for varying line width based on velocity at which the stroke was input will be described. The method begins by computing  702  the velocity of this and the immediately adjacent segments. In one embodiment, this calculation is performed in real time as the input is received from the user. In such a case, only the segments preceding the segment for which the velocity is being calculated can be used in the velocity calculation. However, if the processing is done after (whether it is immediately after or significantly later) the strokes have been captured, then the segments preceding and following the selected segment can be used in the velocity calculation. In one embodiment, velocity calculation is simply the length of the segment divided by the time from the beginning of the segment to the end of the segment. Once the velocity has been calculated, the method proceeds to determine  704  whether the velocity for this segment is less than the “stall out” velocity. If so the adjusted width is set  706  to be the minimum width for the segment since there is a predetermined default threshold thickness below which no segment can fall. After the adjusted width the set to be the minimum width, the method proceeds to step  712  and assigns velocity weight of 1.0. If the velocity for this segment is determined to be greater than the stall out velocity in step  704 , the method proceeds to step  708 . In step  708 , the method determines whether the velocity for this segment is greater than the “escape velocity.” If so the velocity is beyond an amount for which the width of the stroke will be increased, and the method sets  710  the adjusted width for the stroke segment equal to the maximum width. After step  710  the method continues in step  712  to set the velocity weight equal to one. The present invention advantageously provides both a width value and a level of confidence (velocity weight) for that width value. In an embodiment, the confidence value ranges between zero and 1. Since in both step  706  and step  710  the velocity has either exceeded the maximum or is below the minimum, the velocity weight or confidence level is set to one. 
         [0061]    If the velocity of the segment is not greater than the escape velocity in step  708 , the stroke velocity is within a range which can be adjusted according to a function that makes the width greater in proportion to the velocity. More specifically, if the stroke was rapidly drawn, it&#39;s velocity will be greater than if it was slowly drawn. Thus in general, the method of the present invention will make segments that are rapidly drawn wider than segments that are slowly drawn. The method proceeds to step  714  in which the adjusted width is set to be a function of the velocity and the velocity weight is also set to be a function of the velocity. The example provided above in which a more rapidly drawn stroke produces a wider line is just one example of how the line width may be varied according to the velocity at which the segment was captured. Those skilled in the art will recognize that there could be a variety of different functions for calculating the adjusted width and the velocity weight. A system that was interested in simulating a calligraphic brush might behave just the opposite, drawing a thin line for a rapid stroke and a thick one to simulate the bleeding due to slow brush movement. After either step  714  or  712  to the method is complete and ends. 
         [0062]    Referring now to  FIG. 8 , a method for adjusting the line width based on the curvature of the segments will be described. The method begins by computing  802  the curvature of this and immediately adjacent segments. In one embodiment the curvature is given by the “radius of curvature,” which is found by determining the perpendicular bisector of adjacent segments and calculating its distance from the segments. In one embodiment the segments used in determining the radius of curvature are not actually the segments of the stroke, but the segments between stroke segments midpoints, thus somewhat smoothing out the stroke. The curvature computation in one embodiment includes a low pass filtering that reduces the effect of very short segments introduced by the styles position sampling system. In one embodiment, the radius of curvature of a given region of a stroke is averaged over several adjacent segments, further reducing sampling artifacts. As has been noted above for velocity, the curvature adjustment may also be calculated on a real-time basis or after all the segments have been captured. Depending on when the processing takes place, the method may use only prior segments in addition to the current segment, or both preceding and following segments in addition to the current segment in the curvature adjustment calculation. After the curvature for this and the adjacent segments has been determined, the method determines  804  whether the curvature is greater than the maximum radius (e.g., the line is relatively straight). If so the adjusted width is set  806  to the maximum width and the method is complete. If not the method continues to determine  808  whether the curvature is less than the minimum radius (e.g., the region is highly inflected, i.e. very kinky). If so the adjusted width is set  810  to the minimum width for a segment, and the method is complete and ends. In general, this method makes highly inflected portions of line segments thinner. If the curvature computed for this segment is between the maximum radius and the minimum radius then the method proceeds to step  812  and calculates as a function of the curvature, a width somewhere between the minimum and the maximum. One such function would simply map the curvature values between the minimum radius of curvature and the maximum radius of curvature linearly into the width values between the minimum segment width and the maximum segment width. Others might employ a smoother curve function. 
         [0063]    The process for smoothing segments includes both the smoothing of interior segments and the smoothing of end segments. In general, the present invention smoothes the strokes by adjusting the width of each segment to not vary too greatly from that of adjacent segments. Referring now to  FIG. 9A , an embodiment of a method for smoothing interior segments in accordance with the present invention will be described. The process begins by determining  902  whether the processing of interior segments is complete. If so the method is complete and ends. If there are additional interior segments to smooth, the method continues by selecting  904  a next pair of segments. The method then determines  906  whether the width difference between the segments is less than or equal to the maximum width difference between segments allowed by the present invention. If that is the case, no additional smoothing needs to be undertaken between these two segments and a method returns to step  902  to determine whether there are any additional interior segments that need to be smoothed. On the other hand, if the width difference between the two segments is greater than the maximum allowed width difference, we would like to carve these two segments into three for the purpose of smoothing out the width transition. Thus the method determines  908  whether the sum of the lengths of the selected pair of segments is greater than three times the minimum segment size for width smoothing. If so the method of the present invention divides  910  the two segments into three segments, and the middle segment has its width sets halfway between the widths of the other two segments or as different as the maximum width difference. If the sum of the segment lengths is not greater than three times the minimum segment size, the method modifies  912  the second to fall within the maximum width difference of the first. After either step  910  and  912 , the method returns to step  902  to determine whether there remain additional interior segments to process. 
         [0064]    Referring now to  FIG. 9B , an embodiment of a method for smoothing end segments in accordance with the present invention will be described. In general, the end segments are smoothed by dividing the end segment into smaller sub-segments. The process begins by computing  950  at each end segment the distance from the end to the inner segment. The method then determines  952  the maximum number of sub-segments due to length. The maximum number of sub-segments due to length is determined by dividing the end distance by the minimum sub-segment length for smoothing. The end distance was calculated in step  950 . Within the end smoothing process there is a minimum sub-segment length that each sub-segment must have. Therefore, the segment is limited as to the maximum number of sub-segments into which it can be divided. Next, the method determines  954  the maximum number of sub-segments into which we would like to divide the segment in order to do the necessary amount of smoothing. There is a “width delta” equal to the difference between the width of the first interior segment and the minimum segment width. Using this width delta, the maximum number of sub-segments due to the delta can be determined by dividing the width delta by the maximum inter-segment width delta. This gives an indication of how many sub-segments we want to divide the segment into in order to smooth out the width differences between segments. The method continues to determine  956  a number, n, of sub-segments into which the segment will be divided. In one embodiment, the number n is set to be the minimum of the maximum number of sub-segments due to length and the maximum number of sub-segments due to delta. The method continues by dividing  958  up the end region into n sub-segments and smoothly ramping the widths of the n sub-segments from the minimum width to the width of the first interior segment. 
         [0065]    Referring now to  FIG. 10 , an embodiment of a method for computing “dominance” of a group of strokes in an area in accordance with the present invention will be described. The process begins in step  1002  by computing the total length of all those short strokes in the area. The method then determines  1000  the set of long strokes that are “near” any of the short strokes in the area. A method for determining whether strokes are “near” other strokes is shown in  FIG. 12  and will be described below. The length of the set of long strokes determined in step  1004  are then summed  1006 . Next method determines  1008  whether the sum of the lengths of the short strokes from step  1002  is greater than the sum of the lengths of the long strokes from step  1006 . If so the method determines that the short strokes are dominant and outputs TRUE in step  1012 . If not, the method has determined that the short strokes are not dominant and outputs FALSE in step  1010 . 
         [0066]    Referring now to  FIG. 11 , an embodiment of a method for partitioning short strokes into adjacency groups in accordance with the present invention will be described. The method begins by determining  1102  whether all the short strokes have been sorted. If so, the process is complete and ends. If not, the method continues and selects  1104  an unsorted short stroke and creates a group for it. Next the method expands  1106  this group by recursively adding short strokes that are “near” any member of it. Once step  1106  has been completed, the process continues to step  1102  to determine whether of all strokes of the sorted. 
         [0067]    Referring now to  FIG. 12 , an embodiment of a method for computing nearness of a stroke to another stroke in accordance with the present invention will be described. The process begins by computing  1202  the center point of a short stroke. The method then computes a circle with that point at the center and a radius equal to the adjacency cut off distance. The adjacency cut off distance is a predetermined threshold that indicates whether strokes will be considered to be “near” each other or not. The method of the present invention assumes that strokes are near each other if they are within a predefined distance of each other. Next the method determines  1206  whether a given stroke intersects the circle defined in step  1204 . If so, the strokes are considered to be “near” each other, and TRUE  1214  is output. If the stroke does not intersect the circle defined in step  1204 , the method computes  1208  the minimum time delta between strokes. Then the method determines  1210  whether the time delta calculated in step  1208  is less than or equal to the adjacency time cut off. In addition to considering strokes to be near each other based on distance, the present invention also considers strokes to be near each other if they were input at about the same time. The adjacency time cut off provides the threshold by which strokes will be determined to be “near” each other in time. If the time delta of step  1208  is less than or equal to the adjacency time cut off, the strokes are near each other and the method continues and outputs TRUE  1214 . On the other hand if the time delta of step  1208  is greater than the time adjacency cut off the strokes are not considered to be near each other and the method continues to output FALSE  1212 . 
         [0068]    The foregoing description of the embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the present invention be limited not by this detailed description, but rather by the claims of this application. As will be understood by those familiar with the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Likewise, the particular naming and division of the modules, routines, features, attributes, methodologies and other aspects are not mandatory or significant, and the mechanisms that implement the present invention or its features may have different names, divisions and/or formats. Furthermore, as will be apparent to one of ordinary skill in the relevant art, the modules, routines, features, attributes, methodologies and other aspects of the present invention can be implemented as software, hardware, firmware or any combination of the three. Also, wherever a component, an example of which is a module, of the present invention is implemented as software, the component can be implemented as a standalone program, as part of a larger program, as a plurality of separate programs, as a statically or dynamically linked library, as a kernel loadable module, as a device driver, and/or in every and any other way known now or in the future to those of ordinary skill in the art of computer programming. Additionally, the present invention is in no way limited to implementation in any specific programming language, or for any specific operating system or environment. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the present invention, which is set forth in the following claims.