Abstract:
A method of displaying an electronic document on a digital handheld device first calculates a reduction ratio equal to a ratio of an original document width to the digital handheld device screen width. The method then calculates color values of pixels in a reduced document by processing color values of an array of pixels in the original document. The method builds the reduced document having a size related to the original document by the reduction ratio. Finally, the method displays the reduced electronic document on the digital handheld device screen, and allows a user to switch between the original and reduced documents.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for displaying an electronic document on a digital handheld device, and more specifically to a method for reducing the size of the electronic document to be displayed on the digital handheld device. 
   2. Description of the Prior Art 
   Currently, there is a wide variety of digital handheld devices available to consumers. One popular type of digital handheld device is a personal digital assistant (PDA). PDAs are portable and are commonly used to read electronic documents such as web pages. A user can store, manipulate, and access large amounts of information in the form of electronic documents with the aid of a PDA. 
   A large number of PDA users want to be able to view documents originating from a personal computer (PC) on their PDAs. For example, if a user downloads a web page from the Internet using his PC but wishes to read the web page while commuting, he can simply transfer the web page to his PDA. Then, while commuting, the user can browse the web page at his leisure. 
   The prior art method for displaying an electronic document on a PDA is illustrated in FIG.  1 . Shown in  FIG. 1  is a typical PDA  10  comprising a user interface  12  and a screen  14 . The screen  14  is made up of a plurality of pixels, and has a width of 240 pixels and height of 320 pixels. Displayed on the screen  14  are a horizontal scroll bar  16 , a vertical scroll bar  18 , and a portion of an electronic document  20 . The electronic document  20  originated from a PC and has a size larger than the size of the PDA screen  14 , for example 810 pixels wide by 1974 pixels high, and consequently cannot be displayed in entirety the screen  14 . As a result, the PDA screen  20  can only display a portion of the document  20  at a given time. 
   When a user views the document  20 , the user must control the scroll bars  16  and  18  by touching a stylus to the screen  14  to scroll the document to the desired portion. Alternatively, the user can employ the user interface  12  to scroll the document  20 . As the document  20  actually requires twenty-eight PDA screens to view entirely, the user may find this to be tiresome. Additionally, viewing a relatively small portion of the whole document  20  may cause difficulty for the user in understanding the document  20 . 
   The prior art method of displaying an electronic document on a handheld device is inconvenient and can lead to misunderstanding of the electronic document. 
   SUMMARY OF INVENTION 
   It is therefore a primary objective of the claimed invention to provide a method for displaying an electronic document on a handheld device in a reduced form to solve the problems of the prior art. 
   According to the claimed invention, a digital handheld device comprises a screen on which to view an electronic document, the screen having a plurality of pixels and having a width in pixels and a height in pixels. The method first provides an original document comprising a plurality of pixels, and a having a width in pixels and a height in pixels, then calculates a reduction ratio equal to a ratio of the original document width to the digital handheld device screen width. The method then processes color values of a two dimensional array of pixels of the original document, and builds a reduced document comprising a plurality of pixels. The reduced document has a width in pixels equal to the width of the original document divided by the reduction ratio and a height in pixels equal to the height of the original document divided by the reduction ratio, and a color value of each pixel determined by said processing. Finally, the method displays the reduced electronic document on the digital handheld device screen. 
   A color value of a pixel in the reduced document, resulting from the abovementioned processing of color values, can be a weighted arithmetic mean, a median value, or a numerical mode of the color values of the array of pixels of the original document. 
   According to the claimed invention, the method further comprises displaying a portion of the original document on the digital handheld device screen when a user selects a region of the reduced document. 
   It is an advantage of the claimed invention that the reduced document can be displayed on the screen of the digital handheld device such that a larger and more understandable portion of the original document can be viewed by a user, while the visual quality of the content of the original document is preserved. Furthermore, the claimed invention allows the user to access the original document in a convenient manner by selecting a portion of the reduced document. 
   These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a front view of a PDA displaying an electronic document on a screen according to the prior art. 
       FIG. 2  is a front view of a PDA displaying an electronic document on a screen according to the present invention. 
       FIG. 3A  is a schematic diagram of an original document according to the present invention. 
       FIG. 3B  is a schematic diagram of a reduced document according to the present invention. 
       FIG. 4A  is a schematic diagram of the pixel array shown in  FIG. 3A   
       FIG. 4B  is a schematic diagram of the pixel shown in FIG.  3 B. 
       FIG. 5  is a flowchart of the method according to the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention method will be described in an embodiment that utilizes an arithmetic mean function to reduce an electronic document so it can be displayed on a screen of a handheld device. The electronic document is reduced with reference to its width and the width of the handheld device screen. 
   Please refer to  FIG. 2 , which shows a digital handheld device  30 , in this case a PDA, displaying an electronic document  38 , such as a web page, on a screen  34  according to the present invention. The present invention is not limited to a PDA and can be applied to a cellular phone, tablet PC, or any other digital handheld device having a pixel-based screen. The PDA includes a user interface  32 , which includes a stylus that is not shown. The screen  34  also displays a vertical scroll bar  36 . The document  38  displayed has been reduced according to the present invention method. 
   The PDA screen  34  is a touch sensitive TFT matrix that comprises a plurality of pixels and has a width of 240 pixels and a height of 320 pixels. The size of the screen  34  does not limit the invention, and another readily available screen size is 160 pixels square. A user can manipulate what is displayed on the screen  34  by applying the stylus to the scroll bar  36 , or by using the user interface  32 . For example, the user can control the scroll bar  36  to cause the screen  34  to display the unseen portion of the reduced document  38 . 
   The reduced document  38  shown on the PDA screen  34  is a reduced copy of an original document. Referring to  FIG. 3A , the original document  40  has a width, ranging from x coordinates 0 to 809, of 810 pixels, and a height, ranging from y coordinates 0 to 1973, of 1974 pixels. Note that the local origin of the x-y coordinate system (0,0) is at the top-left of the original document  40 . An array of pixels  46  of the original document  40  is shown exaggerated in size. The original document  40  is displayed on a PC monitor having PC screen extents  42 . The screen extents  42  represent a typical PC screen size of 1024 pixels wide by 768 pixels high, and range from x and y coordinates 0 to 1023 and 0 to 767 respectively. The entire width of the original document  40  fits within PC screen extents  42  and can be fully displayed on a PC screen. The entire length of the document  40  does not entirely fit within the PC screen extents  42 , and can be scrolled to be fully displayed. According to this embodiment of the present invention, the width and height of the original document  40  can have any values provided that the width of the original document  40  is larger than the width of the PDA screen  34 . 
   The reduced document  38  is shown in FIG.  3 B and has a width of 203 pixels, ranging from 0 to 202, and a height of 494 pixels, ranging from 0 to 493. Note that the reduced document  38  also has a local x-y origin of (0,0) at the top-left corner. PDA screen extents  44  are illustrated representing the size of the PDA screen  34 , shown in  FIG. 2 , of 240 pixels wide by 320 pixels high. Accordingly, the PDA screen extents  44  range from x coordinates 0 to 239, and from y coordinates 0 to 319. A pixel  48 , corresponding to the pixel array  46 , is shown in the reduced document  38  exaggerated in size. 
   The method reduces the original document  40  by a factor of 4 to create the reduced document  38 . The reduction factor k of 4 is determined by dividing the original document width of 810 pixels by the PDA screen width of 240 pixels and rounding the result up to the nearest integer using a ceiling function. This approach to calculating the reduction factor k ensures that the entire width of the reduced document  38  can be displayed on the PDA screen extents  44 , and is described by the following formula: 
             k   =     ⌈       W   O       W   RS       ⌉             (       Eq   .           ⁢   1     -   1     )             
 
where,
 
   k is the reduction factor; note the ceiling function brackets; 
   W O  is the width of the original document in pixels; 
   W RS  is the width of the reduced screen in pixels, and in this case is the width of the PDA screen  34 ; 
   As previously mentioned the width of the reduced document  38  is 203 pixels. The value of 203 is attained by dividing the width of the original document  40 , which is 810 pixels, by the reduction factor of 4 and rounding the result up to the nearest pixel. Rounding this result down would result in information being lost. The height of the reduced document  38  of 493 pixels is attained by an identical operation. The reduction factor k can also be determined using the ratio of the height of the original document  40  to the height of the PDA screen  34 . In this embodiment however, the width is the dimension of importance. 
   Once the size of the reduced document  38  is determined, information of the original document  40  must be processed. The method uses pixel arrays to sample the pixels of the original document  40  in order to construct the reduced document  38 . The method relates the pixels of the reduced document to the pixel arrays in the original document according to the following equation: 
                 CV   R     ⁡     (     x   ,   y     )       =         ∑     j   =   0     J     ⁢     [       ∑     i   =   0     I     ⁢       CV   0     ⁡     (         k   ·   x     +   i     ,       k   ·   y     +   j       )         ]         k   2               (Eq.  1-2)             
 
where,
 
   CV R  is a color value of a pixel in the reduced document  38  at a coordinate (x,y) of the reduced document  38 ; 
   CV O  is a color value of a pixel in the original document  40  at a coordinate (k·x+i,k·y+j) of the original document  40 ; 
   k is the reduction ratio of the reduced document as determined by Eq. 1-1; 
   i is a an index of a pixel in the x direction of a pixel array of the original document under consideration; is an upper bound of the pixel array in the x direction; 
   j is an index of the pixel in the y direction of the pixel array; 
   J is an upper bound of the pixel array in the y direction; 
   The method applies equation 1-2 for all the pixels of the reduced document  38  by using all valid (x,y) coordinates. Please refer to FIG.  4 A and  FIG. 4B  showing enlargements of the pixel array  46  and the corresponding pixel  48  respectively. The width and height of the square pixel array  46  are both normally set equal to the reduction ratio k, in this example having a value of 4, by setting the upper bounds I and J to equal k-1, which is a value of 3. The pixel  48  is at an (x,y) coordinate of (8,7) in the reduced document. The corresponding pixel array  46  has an origin in the original document at an (x,y) coordinate of (32,28), and a pixel furthest from the origin with an (x,y) coordinate of (35,31). The various colors of pixels of the array  46  and of the pixel  48  are represented in FIG.  4 A and  FIG. 4B  by varying degrees of shading. 
   In practical application, the method applies Eq. 1-2 three times for each pixel in the reduced document, one application for each of the red, green, and blue (RGB) color components. The color values CV O  and CV R  represent a single component color for each application of Eq. 1-2 for a particular pixel in the reduced document  38 . In effect, the method utilizes Eq. 1-2 to calculate an arithmetic mean of the three color components, represented as RGB triplets, of the pixel array  46  to generate an RGB color value of the pixel  48 . 
   Throughout the bulk of the original document  40  the values of the upper bounds IJ of the array  46  are equal to the reduction factor k minus one, such that the size of the array  46  in both the x and y directions is equal to the reduction factor k. However, when the method reaches a pixel at the rightmost or bottommost position of the reduced document the values of I and J are accordingly reduced to accommodate the true size of the original document  40 , which is not constrained to be a multiple of the reduction factor k. Equations 1-3 and 1-4 illustrate how the values of I and J are generally determined. 
             I   =     {             k   -   1     ⁢                   x   &lt;       W   R     -   1                   W   R     -       ⌊       W   R     k     ⌋     ·   k             x   =       W   R     -   1                       (Eq.  1-3)               J   =     {             k   -   1     ⁢                   y   &lt;       H   R     -   1                   H   R     -       ⌊       H   R     k     ⌋     ·   k             y   =       H   R     -   1                       (Eq.  1-4)                                         
 
where,
 
   I is the upper bound of the pixel array in the x direction; note the floor function brackets; 
   k is the reduction ratio of the reduced document as determined in Eq. 1-1; 
   W R  is the width of the reduced document in pixels; 
   J is the upper bound of the pixel array in the y direction; again note the floor function brackets; 
   H R  is the height of the reduced document in pixels; 
   The terms W R −1 and H R −1 simply correspond to the rightmost column of pixels and the bottommost row of pixels in the reduced document  38 . The upper bounds I and J are always equal to or less than a value of k−1, and hence, the pixel array  46  is constrained to have a width and a height equal to or less than the reduction ratio k. 
   The PDA  30 , shown in  FIG. 2 , further comprises a processor and a memory, which are able to perform the above-described method. The memory stores the original document  40 . The processor then performs the method as described on the original document  40  utilizing a buffer portion of the memory to build the reduced document  38 . Finally, the reduced document  38  is stored in the memory and displayed on the screen  34  of the PDA  30 . 
   Please refer to  FIG. 5 , which shows a flowchart of the method according to the present invention. The flowchart shows the method beginning at a coordinate (0,0) and traversing through the entire reduced document referencing a coordinate (x,y). 
   Step  100 : Start; 
   Step  102 : Access the original document  40  stored in the memory of the PDA; 
   Step  104 : Generate and store in a buffer a bitmap image of the original document  40 ; 
   Step  106 : 
   Apply Eq. 1-1 to determine the reduction factor k referencing the size of the original document  40  and the width of the PDA screen  34 ; 
   Step  108 : Set the y coordinate to 0, which represents a first row of pixels in the reduced document  38 ; 
   Step  110 : 
   Set the x coordinate to 0, which represents a first column of pixels in the reduced document  38 ; 
   Step  112 : 
   Apply Eq. 1-3 and Eq. 1-4 to determine I and J, and the size of the pixel array based on the (x,y) coordinate of the pixel under consideration; 
   Step  114 : 
   Apply Eq. 1-2 for each RGB color component of the pixel at coordinate (x,y), and set the color of the pixel at (x,y) in the reduced document accordingly; 
   Step  116 : Increment the x coordinate i.e. move to the next pixel in the current row; 
   Step  118 : 
   Has the last valid x coordinate been exceeded? If it has, go to step  120 ; if it has not, go to step  112 ; 
   Step  120 : Increment the y coordinate i.e. move to the next row of pixels; 
   Step  122 : 
   Has the last valid y coordinate been exceeded? If it has, go to step  124 ; if it has not, go to step  110 ; 
   Step  124 : Display the reduced document  38  on the PDA screen  34 ; 
   Step  126 : End. 
   After the reduced document  48  has been built and is stored in the memory of the PDA  30  and displayed on the PDA screen  34 , a user can then view the reduced document  38  by scrolling vertically through it. If the user needs to see more detail, she can simply apply the user interface  32  to a part of the reduced document  38  to display the original document  40  on the PDA screen  34 . The original document  40  is centered on the PDA screen  34  at a location corresponding to a location selected by the user. This feature of the present invention ensures that no original information is lost. Moreover, if the original document  40  is so large that the user cannot easily understand the reduced copy  38 , the user can still utilize the reduced document  38  as a map of the original document  40 . When the user is finished viewing the detail of the original document  40 , she can then redisplay the reduced document  38  from the memory of the PDA without having to regenerate it. 
   The above-described method, in particular Eq. 1-2, generates a reduced document that contains pixels having arithmetically averaged RGB color values. Different averaging schemes can also be employed. The summation equation 1-2 can be readily modified to provide linear or nonlinear weightings, having a value other than unity, to the summed RGB color values. Alternatively, rather than a summation, a median value or a numerical mode of color values could be taken. Finally, the described method of generating color values for pixels of the reduced document is not limited to RGB values and can be made use of for grayscale and monochrome images as well. 
   Additionally, Eq. 1-2, 1-3, and 1-4 constrain each pixel in the reduced document to correspond to a unique array of pixels in the original document. This one-to-one relationship necessitates that each pixel in the original document is only a member of a single pixel array. This limitation could be modified to allow a pixel to be used in multiple arrays, however the slight increase in image quality of the reduced document may not justify the additional load on the processor of the PDA. This alternative embodiment would allow the reduction ratio k to be a real number. 
   Finally, if desired the original document can be reduced by setting the reduction ratio k equal to the larger of two ratios. The first ratio is the ratio of the original document width to the PDA screen width, and the second ratio is the ratio of the original document height to the PDA screen height. Using a reduction ratio k equal to the larger of these two ratios would ensure that the entire reduced document could be previewed on the PDA screen without any scrolling being required. In contrast to the prior art, the present invention allows an original electronic document to be displayed in reduced form on a screen of a digital handheld device. The present invention facilitates convenient viewing of a reduced document by a user, and ensures that the information in the document can be readily understood. The present invention can also display the original document when the user wishes, and can just as easily redisplay the reduced document. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.