Abstract:
A method and computer program product for reflowing a PDL page without using the original application used to create the PDL page. The method and computer program product include receiving a page represented in a page description language, the page including a plurality of page objects, and changing one or both of a size of the page and a size of one or more of the page objects, while maintaining spatial relationships between the page objects.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application and claims priority under 35 USC §120 to U.S. patent application Ser. No. 11/112,015 filed on Apr. 22, 2005, (U.S. Pat. No. 7,511,720 to be issued on Mar. 31, 2009), which is a divisional application of and claims priority to U.S. application Ser. No. 09/635,999, filed on Aug. 9, 2000 now U.S. Pat. No. 6,915,484, the contents of which are hereby incorporated. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a system and method for generating output for computer systems, and more particularly to a system and method for modifying the presentation of structured documents. 
     The rapid expansion of the World Wide Web—where dynamic, compelling images are crucial—has driven the demand for a document format that preserves all of the fonts, formatting, colors, and graphics of any source document, regardless of the application and platform used to create it. 
     One such format is referred to as the portable document format (PDF). PDF is a file format developed by Adobe Systems, Incorporated. PDF captures formatting information from a variety of desktop publishing applications, making it possible to send formatted documents and have them appear on the recipient&#39;s monitor or printer as they were intended. 
     A source document can be authored in a page description language (PDL). PDL is a language for describing the layout and contents of a printed page. One well-known PDL is PostScript™ by Adobe Systems, Inc. PostScript describes a page in terms of page objects including textual objects and graphical objects such as lines, arcs, and circles. Moreover, PDF is a PDL. 
     According to conventional methods, a PDL document is rendered by first defining a bounding box, such as a page, and then placing the textual and graphical objects defined for the page into the bounding box according to the definitions in the PDL document. Normally the size of a PDL page is chosen so that it is clearly legible on a standard full-sized display. For example, an 8-inch page width may be chosen for display on a 15-inch computer monitor. 
     However, a single page size may not be ideal for devices having non-standard display sizes, such as a hand-held personal digital assistant (PDA). To view a PDL page having an 8-inch page width on a 3-inch-wide display, the user has two alternatives. The user can change the zoom factor of the display to show the entire page on the 3-inch display. However, this approach will generally render the page too small to be legible. Alternatively, the user can simply show a portion of the page at full magnification, and scroll horizontally and vertically to view the rest of the page. This approach is inconvenient and time-consuming. 
     Another approach is for the author of the PDL page to generate a different PDL page for each display size using the application that created the PDL page. This approach is wasteful because multiple copies of each PDL page must be maintained. In addition, the user must select the copy that is appropriate for the display on which the PDL page will be viewed. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, the invention features a method and computer program product for reflowing a PDL page without using the original application used to create the PDL page. One use of the present invention is to resize a page for viewing on a display of a different size than the display to which the document was originally rendered, or to display at a different resolution, either because the inherent resolution of the display differs, or because the reader has demanded a larger, more visible representation. 
     In one aspect the method and computer program product include receiving a page represented in a page description language, the page including a plurality of page objects; and changing a size of the page to a changed size in a first dimension without changing the size of the page objects, while maintaining spatial relationships between the page objects in a second dimension. 
     Particular implementations can include one or more of the following features. The page objects can include textual and graphical elements, and the changing step includes maintaining spatial relationships between the textual and graphical elements in the second dimension. The changing step can further include creating one or more new pages having the changed size in the first dimension; and adding the textual and graphical elements to the one or more new pages. The adding step can include identifying distances in the second dimension between one or more textual elements and one or more graphical elements; adding the textual elements to the one or more new pages; and adding the graphical elements to the one or more new pages based on the distances in the second dimension and positions of the textual elements in the one or more new pages. The identifying step can include creating a map containing the positions of the textual elements in the page, and augmenting the map with the positions of the textual elements in the one or more new pages to produce a relationship for each textual element between the position of the textual element in the page and the position of the textual element in the one or more new pages; and the step of adding the graphical elements can include adding the graphical elements to the one or more new pages according to the map. The step of adding the graphical elements according to the map can include associating one or more particular textual elements with one or more particular graphical elements; determining distances in the second dimension between the particular textual elements and the particular graphical elements; and selecting positions in the one or more new pages for placement of the particular graphical elements based on the distances and the positions of the particular textual elements in the one or more new pages as listed in the map. The associating step can include associating a particular graphical element with a particular textual element that is nearest to the particular graphical element in the first dimension. The associating step can include associating a given graphical element with a plurality of given textual elements; and the selecting step can include scaling the given graphical element when a distance in the first dimension between the plurality of given textual elements in the page differs from a corresponding distance between the plurality of given textual elements in the one or more new pages. The textual elements can be organized as words. 
     In another aspect the method and computer program product include receiving a page represented in a page description language, the page including a plurality of page objects; and changing a size of the page objects without changing the size of the page, while maintaining spatial relationships between the page objects in a dimension of the page. The page objects can include textual and graphical elements, and the changing step can include maintaining spatial relationships between the textual and graphical elements in the dimension. The changing step can include creating one or more new pages having the same size as the page in a further dimension; scaling the textual and graphical elements, producing scaled textual and graphical elements; and adding the scaled textual and graphical elements to the one or more new pages. The adding step can include identifying distances in the dimension between one or more textual elements and one or more graphical elements; adding the scaled textual elements to the one or more new pages; and adding the scaled graphical elements to the one or more new pages based on the distances in the dimension and the positions of the scaled textual elements in the one or more new pages. The identifying step can include creating a map containing the positions of the textual elements in the page, and augmenting the map with the positions of the textual elements in the one or more new pages to produce a relationship for each textual element between the position of the textual element in the page and the position of the corresponding scaled textual element in the one or more new pages; and the step of adding the graphical elements can include adding the graphical elements to the one or more new pages according to the map. The step of adding the scaled graphical elements according to the map can include associating one or more particular textual elements with one or more particular graphical elements; determining distances in the dimension between the particular textual elements and the particular graphical elements; and selecting positions in the one or more new pages for placement of the scaled graphical elements corresponding to the particular graphical elements based on the distances and the positions of scaled textual elements corresponding to the particular textual elements in the one or more new pages as listed in the map. The associating step can include associating a particular graphical element with a particular textual element that is nearest to the particular graphical element in the further dimension. The associating step can include associating a given graphical element with a plurality of given textual elements; and the selecting step can include scaling the given graphical element in the dimension when a distance in the dimension between the plurality of given textual elements in the page differs from a corresponding distance in the one or more new pages between a plurality of scaled textual elements corresponding to the plurality of given textual elements. The textual elements can be organized as words. 
     In another aspect the method and computer program product include receiving a page represented in a page description language, the page including a plurality of page objects; and changing a size of the page to a changed size in a first dimension, and changing a size of one or more of the page objects, while maintaining spatial relationships between the page objects in a second dimension. The page objects include textual and graphical elements, and wherein the changing step can include maintaining spatial relationships between the textual and graphical elements in the second dimension. The changing step can include creating one or more new pages having the same size as the page in a further dimension; scaling the textual and graphical elements, producing scaled textual and graphical elements; and adding the scaled textual and graphical elements to the one or more new pages. The adding step can include identifying distances in the second dimension between one or more textual elements and one or more graphical elements; adding the scaled textual elements to the one or more new pages; and adding the scaled graphical elements to the one or more new pages based on the distances in the second dimension and positions of the textual elements in the one or more new pages. The identifying step can include creating a map containing the positions of the textual elements in the page, and augmenting the map with the positions of the textual elements in the one or more new pages to produce a relationship for each textual element between the position of the textual element in the page and the position of the corresponding scaled textual element in the one or more new pages; and the step of adding the graphical elements can include adding the graphical elements to the one or more new pages according to the map. The step of adding the graphical elements according to the map can include associating one or more particular textual elements with one or more particular graphical elements; determining distances in the second dimension between the particular textual elements and the particular graphical elements; and selecting positions in the one or more new pages for placement of the scaled graphical elements corresponding to the particular graphical elements based on the distances and the positions of scaled textual elements corresponding to the particular textual elements in the one or more new pages as listed in the map. The associating step can include associating a particular graphical element with a particular textual element that is nearest to the particular graphical element in the first dimension. The associating step can include associating a given graphical element with a plurality of given textual elements; and the selecting step can include scaling the given graphical element when a distance in the dimension between the plurality of given textual elements in the page differs from a corresponding distance in the one or more new pages between a plurality of scaled textual elements corresponding to the plurality of given textual elements. The textual elements can be organized as words. The amount of size change of a page object can depend on the type of the page object. 
     In general, in one aspect, the invention features a method and computer program product for forming illustrations in a page. It includes receiving a page represented in a page description language (PDL), the page including a plurality of page objects including line art elements, each page object associated with a PDL element range including at least one PDL element; repeatedly augmenting each PDL range with a PDL element that is adjacent to the PDL range and is not part of another PDL range when the bounding box of the PDL element overlaps the bounding box of the PDL object associated with the PDL range; such that the PDL elements in each PDL range define an illustration. Particular implementations can include combining two illustrations when their PDL ranges are adjacent and their bounding boxes overlap. 
     In another aspect the method and computer program product include receiving a page represented in a page description language (PDL), the page including a plurality of page objects including line art elements, each page object associated with a PDL element range including at least one PDL element; recursively coalescing line art elements having overlapping bounding boxes to form one or more illustrations; adding to each illustration each PDL element within the PDL range of the illustration that is not part of the illustration when the bounding box of the PDL element overlaps the bounding box of the illustration; and repeatedly augmenting the PDL range of each illustration with PDL elements that are adjacent to the PDL range and are not part of another illustration when the bounding box of the PDL elements overlap the bounding box of the illustration; such that the PDL elements in each PDL range define an illustration. Particular implementations can include combining two illustrations when their PDL ranges are adjacent and their bounding boxes overlap. The step of recursively coalescing can include combining two line art elements having overlapping bounding boxes, thereby forming an illustration; and creating a new bounding box containing the illustration. Particular implementations can include combining a line art element with the illustration when the bounding boxes of the line art element and the illustration overlap. 
     Advantages that can be seen in implementations of the invention include one or more of the following. PDL pages can be resized. A PDL page produced according to the invention can be legibly displayed on any size display. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a computing system for displaying a document. 
         FIG. 2  depicts a conventional PDL page. 
         FIG. 3  depicts a PDL page resulting from the operation of one implementation of the present invention. 
         FIG. 4  depicts a PDL page resulting from the operation of another implementation of the present invention. 
         FIG. 5  depicts a PDL page resulting from the operation of yet another implementation of the present invention. 
         FIG. 6  is a flowchart depicting a process for reflowing a PDL page. 
         FIGS. 7-10  show the results of the process of  FIG. 6  when applied to a PDL page containing eleven PDL elements. 
         FIG. 11  depicts a process for forming illustrations. 
         FIG. 12  is a flowchart depicting an alternative process for forming illustrations. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The present invention can be implemented in a raster image processor (RIP). This implementation is described with reference to  FIG. 1 . 
       FIG. 1  is a block diagram of a computing system  100  for displaying a document. In system  100 , an application  102 , such as a word processor, generates a request to display a page in response to a user selection. The request is sent to an operating system  104 , such as Windows™, using an operating system call. The operating system  104  in turn directs the request to a page description language (PDL) driver  106 . The driver  106  translates the operating system calls and generates a data stream that is sent to RIP  120 . RIP  120  operates to generate an encoded raster file  122 . The encoded raster file is sent to display device  130  for display. 
     The implementation described below changes only the page width, and not the size of the page objects. In another implementation, only the size of the page objects is changed. In yet another implementation, both the page width and the size of the page objects are changed. In variations of these implementations, it is the page length that is changed, rather than the page width. These variations are especially useful for languages that are written from top to bottom, rather than from left to right. The textual elements can be organized as characters, words and the like. 
       FIG. 2  shows a conventional PDL page  202 . The page includes textual elements  206  and graphical elements  208  and  210 . The page has a page width  220 . Each graphical element in a page is associated with one or more textual elements in the page. Graphical element  208  spans several lines of text. Therefore, it is associated with two textual elements  212  (“I”) and  214  (“desperate”). For convenience, textual elements  212  and  214 , referred to as “anchors,” are shown in bold type. Graphical element  210  spans only a single line. Therefore, it is associated with a single anchor  216  (“My”). 
       FIG. 3  shows a PDL page  302  after application of the reflow process of the present invention. The width of the original PDL page  202  is changed while the font size of a textual element  206  remains constant. Referring to  FIGS. 2 and 3 , the page width  320  of new page  302  is chosen to be narrower than the page width  220  of original page  202 . Accordingly, the length of the page increases. When referring to a PDL page, the horizontal dimension is referred to as its X-axis and the vertical dimension is referred to as the Y-axis. Thus, it is the distance in the Y-axis that increases. In this implementation, the graphical elements are moved and stretched to follow their anchors. 
     The Y-axis position of anchor  216  has also increased. Therefore, the Y-axis position of associated graphical element  210  is also increased so that anchor  216  and graphical element  210  are aligned on the Y-axis. In addition, the Y-axis distance between anchors  212  and  214  has increased. Therefore, corresponding graphical element  208  is stretched to span the distance between anchors  212  and  214 . 
       FIG. 4  shows a PDL page  402  resulting from the operation of another implementation of the present invention. In this implementation, the width of the PDL page remains constant while the font size of its textual elements is increased. Referring to  FIGS. 2 and 4 , the page width  420  of page  402  is the same as the page width  220  of page  202  ( FIG. 2 ). However, the font size of the textual elements  206  has been increased from 12 points to 14 points. Therefore, the length of the page  402  is greater than the length of page  202 . 
     The Y-axis position of anchor  216  has also increased. Therefore, the Y-axis position of associated graphical element  210  is increased so that anchor  216  and graphical element  210  are aligned on the Y-axis. In addition, the Y-axis distance between anchors  212  and  214  has increased. Therefore, corresponding graphical element  208  is stretched to span the distance between anchors  212  and  214 . 
       FIG. 5  shows a PDL page  502  resulting from the operation of another implementation of the present invention. According to this implementation, the width of the PDL page and the font size of its textual elements are increased. Referring to FIGS.  2  and  6 / 5 , the page width  520  of new page  502  is chosen to be narrower than the page width  220  of original page  202 . In addition, the font size of the textual elements  206  has been increased from 12 points to 14 points. Therefore, the length of the page  502  is greater than the length of page  202 . 
     The Y-axis position of anchor  216  has also increased. Therefore, the Y-axis position of associated graphical element  210  is increased so that anchor  216  and graphical element  210  are aligned on the Y-axis. In addition, the Y-axis distance between anchors  212  and  214  has increased. Therefore, corresponding graphical element  208  is stretched to span the distance between anchors  212  and  214 . 
       FIG. 6  is a flowchart depicting a process for reflowing a PDL page. According to this process, only the width of the PDL page is changed. The size of the textual elements within the PDL page remains constant. In another implementation, the size of the textual elements is increased while the page width is unchanged, as shown in  FIG. 4 . In another implementation, both the page width and the font size of the textual elements are changed, as shown in  FIG. 5 . 
     A PDL page is received in step  602 . The PDL page includes page objects and including textual and graphical elements. In step  604 , the process creates a new PDL page having a page width that differs from that of the received original PDL page. Note that all of the implementations maintain the spatial relationship between the textual and graphical elements. 
     In one implementation, two or more new PDL pages are created. The textual elements are added to the new PDL page in step  606 . Next sub-process  620  is repeated for each graphical element. 
     The graphical element is associated with one or more textual elements in step  608 . Then the process determines a Y-axis difference between the position of the graphical element and a position of each associated textual element, as shown in step  610 . This step is useful when a graphical element and its associated textual element do not have the same Y-axis position. 
     In one implementation, the Y-axis positions of each textual element in the original PDL page and the new PDL page are recorded in a “Y-map.” An exemplary Y-map is shown in Table 1. Table 1 is a Y-map between page  202  of  FIG. 2  and page  302  of  FIG. 3 . Table 1 presents the Y position in the old page (page  202 ) and the Y position in the new page (page  302 ) for the anchor textual elements. In another implementation, the Y-map records positions for each textual element. Referring to Table 1, it is seen that the textual element “I” (anchor  212 ) is at a Y-axis position of 0.25 in both the old and new pages. However, the word “desperate” (anchor  214 ) has moved by half an inch. Similarly, the word “My” (anchor  216 ) has moved by ¾ of an inch. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Textual Element 
                 Y Position in Old Page 
                 Y Position in New Page 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 0.25 
                 0.25 
               
               
                   
                 desperate 
                 1.75 
                 2.25 
               
               
                   
                 My 
                 2.00 
                 2.75 
               
               
                   
                   
               
             
          
         
       
     
     A position for the graphical element in the new page is then determined based on the Y-axis position of the associated textual element(s) in step  612 . For example, the position of graphical element  210  in page  302  is determined based on the Y-axis position of its associated textual elements (anchor  216 ) in page  302 . Referring to the Y-map of Table 1, it is seen that the Y-axis position of anchor  216  is 2.75 inches. Therefore, assuming that the Y-axis difference between graphical element  210  and anchor  216  is zero, the position for graphical element  210  in page  302  is determined to be 2.75 inches along the Y-axis. If necessary, the graphical element is scaled (that is, stretched) in step  614 . For example, referring to  FIG. 3 , graphical element  208  is stretched because its associated anchors  212  and  214  are further apart than in the original page. Finally, the graphical element is placed at the position determined in step  612 , as shown in step  616 . 
     The present invention is also useful in documents having multiple columns. Each column is simply treated according to the process of  FIG. 6  within its bounding box in the same way the PDL page  202  is treated within page  302 . Implementations of the present invention include three variations to handle different multi-column cases. For example, consider a two-column case with a vertical line-art element between the two columns. Each column has a Y-map, so there are two Y-maps. The vertical line-art element is associated with textual elements in both columns. When reflowing the line-art element, it must be decided which Y-map to use. In one implementation, the Y-map having the maximum Y value for the line-art element is used. Other implementations can be used, as would be apparent to one skilled in the relevant arts. 
     In a multiple column case, where a single text-line or line-art element intersects the X-axis extent of a set of columns, that intersection is considered to be a “fault line.” This fault line is used as a break, so that subsequent text (that is, text that has a greater Y-axis position than the fault line) is considered to be a new column. 
     An implementation of the present invention handles hyphenation and ligatures according to the following method. The process hyphenates a word at a line-end in the new page if the original word had a soft hyphen at that point. Similarly, such a word can be unhyphenated when it is no longer at a line-end in the new page. In implementations in which the font size of the text elements is changed, the positioning of the text lines is addressed. In one implementation, all vertical white space is retained. That is, the inter-paragraph vertical gap is retained, and within the paragraph, the inter-line vertical gap is retained. 
     In the implementation discussed above, the graphical elements can be simple line art elements, images, or combinations of line art elements, images and text, such as captions. PDF documents often contain complex illustrations including multiple graphical elements, such as strokes and fills, images, and even textual elements, such as captions. Humans are very good at identifying which components belong to a particular illustration. However, in order to successfully reflow a document containing a complex illustration, it is desirable to perform this process automatically. After an illustration is identified, it can be reflowed into the new page according to the process described above. 
       FIGS. 8-10  graphically depict combining page objects to form a single illustration.  FIG. 7  represents a PDL page containing eleven PDL elements. PDL elements E 1 , E 2 , E 3 , E 4 , E 5  and E 6  are line art elements forming a “stick man” standing on the ground. PDL elements E 7  and E 9  are line art elements representing balloon tethers. PDL elements E 8  and E 10  are images representing balloons. PDL element E 11  is a text element that is the caption for the drawing. 
     The process begins by coalescing line art elements to form illustrations. Each line art element is assigned a “bounding box.” In the described implementation, each bounding box is rectilinear having sides parallel to the edges of the PDL page. Referring to  FIG. 8 , PDL element E 7  is enclosed by bounding box  802 , and PDL element E 9  is enclosed by bounding box  804 . 
     According to the process, when line art elements have overlapping bounding boxes, they are combined to form a single illustration. This illustration, I 2 , contains the elements E 7  and E 9  and can be represented by
 
I2=E7, E9  (1)
 
     The drawing of  FIG. 7  is represented by a sequential collection of PDL elements given by equation 1. Assume that PDL elements forming the stickman standing on the ground have already been collected to form an illustration I 1  given by
 
I1=E1, E2, E3, E4, E5, E6  (2)
 
     The sequence of PDL elements, from first to last, associated with an illustration is referred to as its “range.” The PDL representation of the drawing of  FIG. 7  is given below with the range of illustrations I 1  and I 2  underlined.
 
PDL=E1, E2, E3, E4, E5, E6, E7, E8, E9, E10, E11  (3)
 
     Note that, although element E 8  is not part of illustration I 2 , it falls within the range of illustration I 2 . The treatment of such “gaps” in range is described below. 
     The process recursively joins line-art elements to form illustrations. Referring to  FIG. 9 , illustration I 2  has been enclosed in bounding box  902 , and illustration I 1  has been enclosed in bounding box  904 . Because bounding boxes  902  and  904  overlap, the process coalesces the contained line-art elements to form an illustration I 3  given by equation 6.
 
I3=E1, E2, E3, E4, E5, E6, E7, E9  (4)
 
     The PDL range of illustration I 3  then runs from E 1  to E 9 . The PDL sequence for  FIG. 9  is given below with the range of illustration I 3  underlined.
 
PDL= E1, E2, E3, E4, E5, E6, E7, E8, E9 , E10, E11  (5)
 
     The process next seeks to fill gaps in the range such as that represented by element E 8 . At this point, all of the line-art elements in the PDL page have been coalesced to form illustrations. Now the process seeks to combine those illustrations with other PDL elements such as images and text. The first step of this process is to fill the gaps in the PDL ranges of the line-art illustrations. Referring to  FIG. 10 , PDL element E 8  is an image that lies within the range of illustration I 3 . The process combines a PDL element with an illustration if it lies within the PDL range of that illustration and the bounding boxes of the illustration and the PDL element overlap. Referring to  FIG. 10 , illustration I 3  has been enclosed in a bounding box  1002 , and image E 8  has been enclosed within a bounding box  1004 . Bounding boxes  1002  and  1004  overlap. Therefore, element E 8  is combined with illustration I 3 . Illustration I 3  now combines all of the elements from E 1  to E 9  as shown below.
 
I3=E1, E2, E3, E4, E5, E6, E7, E8, E9  (6)
 
     The PDL representation of  FIG. 10  is given below, with the range of I 3  underlined.
 
PDL= E1, E2, E3, E4, E5, E6, E7, E8, E9 , E10, E11  (7)
 
     The process then seeks to combine PDL elements that are adjacent to the range of an illustration. A PDL element will be combined with an illustration when it is adjacent to the illustration in the PDL sequence and the bounding boxes of the illustration and the PDL element overlap. Referring to equation 9, we see that image E 10  is adjacent to the range of illustration I 3 . Referring to  FIG. 10 , we see the bounding box  1006  of image E 10  and the bounding box  1002  of illustration I 3  overlap. Therefore, image E 10  is combined with illustration I 3 . As a result, illustration I 3  is given by
 
I3=E1, E2, E3, E4, E5, E6, E7, E8, E9, E10  (8)
 
     The PDL representation of the drawing is then given by
 
PDL= E1, E2, E3, E4, E5, E6, E7, E8, E9, E10 , E11  (9)
 
     Referring to equation 11, it is seen that text element E 11  is adjacent to the range of illustration I 3 . Referring to  FIG. 10 , it is seen that the bounding box  1008  of element E 11  and bounding box  1002  illustration I 3  overlap. Therefore, text element E 11  is combined with illustration I 3 . Illustration I 3  has been given by
 
I3=E1, E2, E3, E4, E5, E6, E7, E8, E9, E10, E11  (10)
 
     The PDL range of the drawing has been given by
 
PDL= E1, E2, E3, E4, E5, E6, E7, E8, E9, E10, E11   (11)
 
     It is seen that all of the elements within the drawing have now been combined to form a single illustration. 
       FIG. 11  depicts a process for forming illustrations according to an implementation of the present invention. A PDL page is received at step  1102 . The PDL page includes page objects including line-art elements. The page objects can also include other sorts of PDL elements such as images and text elements. Each page object is associated with a PDL element range that includes at least one PDL element. It is possible that an illustration generated in this way is simply part of a background. Therefore, if a page element illustration is the same color as the background, it is discarded in step  1103 . 
     The line-art elements within the PDL page are recursively coalesced to form illustrations at step  1104 . The first recursion includes combining two line-art elements when their bounding boxes overlap to form an illustration. Following recursions include combining the illustration and a line-art element when their bounding boxes overlap to form the next illustration. 
     As described above, the range of an illustration may include PDL elements that are not part of the illustration. These PDL elements represent “gaps” in the PDL range. These “gaps” are located at step  1105 . Each such “gap” is tested to determine whether it should be joined with the illustration at step  1106 . A PDL element within the range of an illustration is combined with that illustration when the bounding boxes of the element and the illustration overlap. 
     The process then tests PDL elements that are adjacent to the ranges of the illustrations to determine whether they should be joined with those illustrations in step  1108 . In one implementation, only those elements that are not already a part of another illustration are tested. A PDL element that is adjacent to the range of an illustration is combined with that illustration when the bounding boxes of the element and illustration overlap. This step is also performed recursively to “grow” the illustrations as the range of each illustration increases. 
     The process then tests the illustrations to determine whether any of them should be joined to form a single illustration in step  1110 . Illustrations are combined when their PDL ranges are adjacent and their bounding boxes overlap. 
     Each PDL range that results from this process is a separate illustration. Each illustration is treated as a separate graphical element in the reflow process described above. 
       FIG. 12  is a flowchart depicting a process for forming illustrations according to another implementation of the present invention. A PDL page is received at step  1202 . The PDL page includes page objects including line-art elements. The page objects can also include other sorts of PDL elements such as images and text elements. Each page object is associated with a PDL element range that includes at least one PDL element. 
     The process then tests PDL elements that are adjacent to the ranges of the illustrations to determine whether they should be joined with those illustrations in step  1204 . In one implementation, only those elements that are not already a part of another illustration are tested. A PDL element that is adjacent to the range of an illustration is combined with that illustration when the bounding boxes of the element and illustration overlap. This step is also performed recursively to “grow” the illustrations as the range of each illustration increases. 
     According to one implementation, each illustration is classified for treatment during reflow. Illustrations that lie within one line of a paragraph are classified as character surrogates. A character surrogate is an illustration that functions as a text character. Character surrogates are treated as text elements during reflow. Illustrations that lie within the bounding box of a paragraph, and which vertically overlap with two or more initial lines, and which are to the left of all the characters in those lines, are classified as “illuminated letters.” Illuminated letters are reflowed at the upper left of the paragraph, with the text elements of the paragraph flowed to the right and below the illustration. 
     Illustrations that lie directly above (or below) a paragraph are reflowed to lie directly above (or below) that paragraph. Illustrations that do not fit within the reflow bounding box are scaled to fit within that bounding box. 
     The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired; and in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Generally, a computer will include one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits). 
     To provide for interaction with a user, the invention can be implemented on a computer system having a display device such as a monitor or LCD screen for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer system. The computer system can be programmed to provide a graphical user interface through which computer programs interact with users. 
     The invention has been described in terms of particular embodiments. Other embodiments are within the scope of the following claims. For example, the steps of the invention can be performed in a different order and still achieve desirable results.