Abstract:
A page display system is provided for improving an intuitive visibility of letters and lines of letters as patterns by increasing the time for displaying each page. 
     A formatter  13  of the page display system interprets and arrange the structured text  11  into page units, a rasterizer expands letters of the structured text  11  into fonts to form image patterns and generate each page image by synthesizing with images of attached data  12  and the like, and the image buffer  15  temporarily stores the thus produced page images. The image composer  16  acquires page images from the image buffer and composes a plurality of images upon necessity, the display device  17  displays page images. The page scroll controller  19  adjust the composition of images by the image composer  16 . The timer  20  transmits information indicating the passage of time.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a page display system, a method of displaying pages, and a recording medium containing a program for displaying pages, and particularly relates to a page display system, a method therefor, and a recording medium containing a program for indicating pages, utilizing after-images. 
     This application is based on Patent Application No. Hei.9-302896 filed in Japan, the content of which is incorporated herein by reference. 
     2. Background Art 
     Four million years have passed since the birth of human beings. The invention of paper brought a great progress in accumulation of information. The invention of the typography by Gutenberg in the fifteenth century has further produced remarkable progress in the transmission and accumulation of information. Until recent years, paper has been widely used as a recording medium due to its fine visibility. Paper is thin, supple, and elastic. These characteristics of paper enable reading of printed papers by handling papers and turning pages such that parcels of necessary information are extracted by identifying letters as a pattern from many pages in a bundle of papers within a short time. 
     Recently, as computerization advances with the progress of electronics, called the second industrial revolution, information is often displayed by display devices such as cathode-ray tubes and LCDs (Liquid Crystal Display). However, since such devices are self-luminous and inferior in resolution, letters or lines of letters as patterns displayed in such display devices are inferior in high speed and intuitive visibility than those on paper. This constitutes a basic reason for obstruction of the spread of electronic apparatuses for displaying lengthy documents such as, for example, electronic books, and obstruction of the arrival of the paperless age. 
     Japanese Patent Application, First Publication No. Sho 62-18595 discloses a display device which is capable of improving visibility by utilizing after-images. This device displays a sum of both multiplication products, one of which is a multiplication product of an output of a first frame buffer by an output from a display control circuit and another is a multiplication product of an output of a second frame buffer by a compliment of an output of a display control circuit. 
     The first problem of the hereinabove described conventional device is in that it is not possible for the device to control the timing of the displayed after-image at any time on request of a user. The problem is due to the fact that the time to display the after-image is not alterable, since an output from the display control circuit is constantly being generated. 
     The second problem is that the conventional device cannot perform processing of structured text. This is because the device is not provided with means to convert the structured text into picture images. 
     The third problem is that the device cannnot send or scroll pages in the opposite direction (that is, return to the previous images). This is because the device is not provided with a means to send pages in the opposite direction. 
     It is therefore the object of the present invention to provide a system which is capable of improving the visibility of letters or lines of letters as patterns by increasing an information content displayed at a time point by composing the after-image of the previous page on the presently displayed page as well as by increasing the total time for displaying one page. 
     SUMMARY OF THE INVENTION 
     A page display system according to the first embodiment of the present invention is provided for inspecting a plurality of pages of a structured text, which can not be displayed on one page, by scrolling pages either in forward or backward directions, in order to improve the intuitive visibility of letters and lines of letters as image patterns. This system is provided with a means to determine a waiting time for replacing a page by a user&#39;s direction, and a means for increasing an information content of the display and for automatically increasing a total time of displaying a page by composing the previous image as an after-image on the present page being displayed on a display, while controlling a brightness of the after-image by comparing the display start time of the previous page with that of the present image. 
     A page display system according to the second embodiment of the present invention is provided with, 
     (a) a formatter for interpreting a structured text, arranging the structured text into a page unit, and for preparing the form of the page; 
     (b) a rasterizer for expanding letters into fonts to transform them into a pattern, and for generating a page image as a unit page with an attached data image, when the attached data is directed by the structured text so as to be incorporated into the page; 
     (c) an image buffer for storing unit page images corresponding to two pages generated by said rasterizer; 
     (d) an image composer for synthesizing said unit page images corresponding to two pages stored in said image buffer; 
     (e) a display device for displaying said composed image formed by said image composer; 
     (f) a page scroll controller having a slider to be controlled by a user for scrolling pages in the backward direction when a cursor is moved to a left side region from the center of the slider, for scrolling pages in the forward direction when the cursor is moved to the right side region of the slider, and the page scrolling speed is proportional to an angular displacement of the cursor from the center; 
     (g) a timer for generating a time; 
     (h) a composition controller for controlling a degree of composition based on both input from said page scroll controller and a time from said timer. 
     A page display system according to the third embodiment of the present invention is the same system as the system according to the second embodiment and the image composer outputs a brightness value of each pixel of the composed image by calculating a sum of both multiplication products, one is a multiplication product of a brightness value of each pixel of the previous page image stored in said image buffer by f (t), and another is a multiplication product of a brightness values of each pixel of the present image by 1-f(t). 
     A first method of displaying pages for inspecting a plurality of pages of structured text, which can not be displayed in one page, by scrolling pages in either forward or backward directions, comprising the steps of: 
     determining a waiting time for replacing pages by a user&#39;s direction; 
     increasing an amount of displayed information and automatically increasing a time of displaying a page by superposing the previous image as an after-image on the present displayed page, after controlling a brightness of the after-image by comparison with that of the present image, which results in improving the intuitive visibility of letters and lines of letters as pattern images. 
     The second method of displaying pages comprises: 
     (a) a first step to make a formatter interpret a structured text, arrange the structured text into unit pages, and prepare a form of page; 
     (b) a second step to make a rasterizer expand letters into fonts to transform them into a pattern, and generate a page image as a unit page with an attached data, when the attached data is directed by the structured text so as to be incorporated in the page; 
     (c) a third step to make an image buffer store unit page images corresponding to two pages generated by said rasterizer; 
     (d) a fourth step to make an image composer compose said unit page images corresponding to two pages stored in said image buffer; 
     (e) a fifth step to make a display device display said composed image formed by said image composer; 
     (f) a sixth step to make a page scroll controller having a slider to be controlled by a user send pages in the backward direction when a cursor is moved to a left side region from the center of the slider, send pages in the forward direction when the cursor is moved to the right side region of the slider, and the page scroll speed is proportional to an angular displacement of the cursor from the center; 
     (g) a seventh step to make a timer generate a time; and 
     (h) an eighth step to make a composition controller control a degree of composition based on both input from said page scroll controller and a time from said timer. 
     The third method of displaying pages is the same as the method by the second embodiment except that the fourth step makes the image composer output a brightness value of each pixel of the composed image by calculating a sum of a multiplication of a brightness value of each pixel of the previous page image stored in said image buffer by f (t), and a multiplication of a brightness values of each pixel of the present image by 1-f(t). 
     The first recording medium containing a program for inspecting a plurality of pages of a structured text, which can not be displayed in one page, by scrolling pages in either forward or backward directions, comprising: 
     a means to determine a waiting time for replacing pages by a user&#39;s direction; 
     a means for increasing an amount of displayed information and for automatically increasing a time of displaying a page by superposing the previous image as an after-image on the present displayed page, after controlling a brightness of the after-image by comparison with that of the present image for improving the intuitive visibility of letters and lines of letters as a pattern, 
     The second recording medium containing a program for making computer execute: 
     (a) a first step to make a formatter interpret a structured text, arrange the structured text into unit pages, and prepare a form of page; 
     (b) a second step to make a rasterizer expand letters into fonts to transform them into a pattern, and generate a page image as a unit page with an attached data, when the attached data is directed by the structured text so as to be incorporated in the page; 
     (c) a third step to make an image buffer store unit page images corresponding to two pages generated by said rasterizer; 
     (d) a fourth step to make an image composer compose said unit page images corresponding to two pages stored in said image buffer; 
     (e) a fifth step to make a display device display said composed image formed by said image composer; 
     (f) a sixth step to make a page scroll controller having a slider to be controlled by a user send pages in the backward direction when a cursor is moved to a left side region from the center of the slider, send pages in the forward direction when the cursor is moved to the right side region of the slider, and the page scroll speed is proportional to an angular displacement of the cursor from the center; 
     (g) a seventh step to make a timer generate a time; and 
     (h) an eighth step to make a composition controller control a degree of composition based on both input from said page scroll controller and a time from said timer. 
     A third recording medium containing a program which is the same as the second program, in which said fourth step makes the image composer output a brightness value of each pixel of the composed image by calculating a sum of a multiplication of a brightness value of each pixel of the previous page image stored in said image buffer by f (t), and a multiplication of a brightness values of each pixel of the present image with by 1-f(t). 
     A fourth page display system which is the same as the second system further comprises an image buffer which is able to store page images corresponding to more than 3 pages. 
     A fifth page display system, which is the same as the first system, and having LCDs as the display device and the fifth system comprises a plurality of LCDs in piles so as to be able to display a plurality of pages simultaneously. 
     A sixth page display system which is the same as the first page display system, and having projector type display devices as the display device and this sixth system is capable of displaying a plurality of pages on a screen simultaneously by the use of said plurality of projectors. 
     These embodiments can be used alone or in combinations of two or more. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a block diagram showing an embodiment of the present invention. 
     FIG. 2 is a flow-chart showing the initialization operation. 
     FIG. 3 show a flow-chart showing operations at the waiting state for an input. 
     FIG. 4 is a flow-chart showing a flow of scroll pages in a sequential direction. 
     FIG. 5 is a flow-chart showing a flow of scroll pages in an opposite direction. 
     FIG. 6 shows a computer and a recording medium. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A system according to the first embodiment of the present invention is described hereinafter referring to FIG.  1 . FIG. 1 shows a system according to the first embodiment of the present invention. As shown in FIG. 1, the present system of this embodiment comprises a structured text  11 , attached data  12 , a formatter  13 , a rasterizer  14 , a page-image buffer  15 , an image composer  16 , a display device  17 , a page scroll controller  18 , a composition controller  19 , and a timer  20 . 
     The structured text  11 , which is represented by HTML (Hyper Text Markup Language) or SGML (Standard Generalized Markup Language), is a text file expressed by the embodiment of the present invention. The attached data  12  are a data file excluding the structured text and including images and voices for complimenting the structured text  11 . The attached data  12  are referred to from the structured text  11 . 
     The formatter  13  arranges the structured text  11  into page units by the interpretation of the structured text  11 . The rasterizer  14  expands letter information into fonts for conversion into images, and generates page images per unit page by incorporating the attached data  12  with the page image. The page-image buffer  15  is a buffer for storing page-images per unit page temporarily which are generated by the rasterizer  14 . The page-image buffer has an area corresponding to 2 pages. 
     The image composer  16  acquires page-images from the page-image buffer  15  and composes a plurality of page-images in accordance with necessary. The display device  17  displays the page image generated by the image composer  16 . 
     The page scroll controller  18  is a controller by which a user controls a speed of image scrolling. For the preferred embodiments of the present invention, “scrolling” includes fading, dissolving or diminishing persistence of pages into or out of view. In order to perform stepless control of the image scrolling speed, the controller is designed such that, after setting a slider at a center position at first, when the user moves the cursor to the left side, the page scrolls back to the previous page, when the user moves the cursor to the right, then the page scrolls forward, and the speed of the page scroll is proportional to the distance of the cursor from the center position. 
     The composition controller  19  receives an input from the page scroll controller  18  and controls a degree of composition of images by the image composer  16 . The timer is used for transmitting information indicating the passage of time to the composition controller  19 . 
     An operation of the system of the present embodiment will be described hereinafter referring to FIG. 2 to FIG.  5 . An initialization operation is first described referring to FIG. 2, which illustrates a flow-chart of the initialization operation. As shown in FIG. 2, the composition controller  19  directs the formatter  13  to read data corresponding to one page from the top of the structured text  11 , and to prepare a form as a page after laying out the attached data, if the attached data are directed by the structured text  11  so as to be incorporated in the page (Step S 1  in FIG.  2 ). After completion of the page form, the rasterizer  14  expands letters of the structured text  11  into images using fonts and produces a page image of a page. The thus produced page image is stored in one side of the page image buffer  15  (Step S 2  in FIG.  2 ). 
     After the page image is stored in one side of the page image buffer  15 , the composition controller  19  directs output to and display of the as-produced page image on the display device (Step S 3  in FIG. 2) The program proceeds to an input-waiting state. 
     An operation at an input waiting state is described referring to FIG.  3 . FIG. 3 shows a flow-chart showing an operation at the input wait state. As shown in FIG. 3, the composition controller  19  always monitors the page scroll controller  18 , and when the cursor is slid into a region of the forward direction by the user (“yes” at Step S 11  in FIG.  3 ), then the controller  19  proceeds to scroll in the forward direction (Step S 12  in FIG.  3 ). If the user moves the cursor into the opposite region (“yes” at Step S 13  in FIG.  3 ), the controller  19  proceeds to scroll pages in the opposite or backward direction (Step S 14  in FIG.  3 ). 
     If the answers at Steps S 11  and S 13  are neither yes nor no, or when the page scrolling process is completed, a waiting time is calculated which corresponds to a time interval until the state of the page scroll controller  18  is monitored next time (Step S 15  in FIG.  3 ). The waiting time is set such that the larger the displacement of the cursor from the center position of the slide, the shorter the waiting time. Thus, if the displacement of the cursor from the zero position is larger, the controller  19  directs execution of the scroll operation more frequently. Once the waiting time is calculated, the process waits for a time corresponding to the waiting time (Step S 16  in FIG.  3 ), and the process in the waiting state is repeated from the start. 
     Next, an operation of a scroll processing in the forward direction is described hereinafter. FIG. 4 is a flow-chart showing the operation of scroll processing in the forward direction. As shown in FIG. 4, the composition controller  19  acquires the time at present from the timer  20 , and store the time of this processing (Step S 21  in FIG.  4 ). Subsequently, the composition controller  19  directs the formatter  13  to make the formatter  13  judge whether or not there are data in the structured text  11  below the previously processed position, that is, whether or not there are data for the next page (Step S 22  in FIG.  4 ). 
     If there is data, the processing continues, and if not, the processing proceeds to the step S 27 . The composition controller  19  makes the formatter  13  read data corresponding to one page after the end of the previous reading. If the structured text has a direction to incorporate the attached data into a page, the page form is prepared by incorporating and arranging the attached data in the page (Step S 23  in FIG.  4 ). Once the form of the page is arranged, the rasterizer  14  receives an output of the formatter  14  and produces a page image using fonts of letters, and the page image is stored in a remaining page of the memory which is not used in the previous storage (Step S 24  in FIG.  4 ). 
     Next, based on the time difference between the previous time and the present time, the composition controller  19  performs a calculation as to a degree of composition, that is, a ratio of superposition of the previous page image on the present page image (Step S 25  in FIG.  4 ). 
     When the time difference is represented by t, and the degree of the superposition is represented by f(t), the function f(t) attenuates from “1” at t=0 to “0” at t=T. Here, T represents a time within which the after-image disappears. T and f(t) are prescribed by a preference of the user. And, f(t) is 0≦f(t)≦1. 
     The image composer  16  outputs values to the display device  17  as brightness values for respective pixels of a composed page image by calculating a sum of both values obtained by a multiplication of brightness values of pixels of the previous page image by f(t) and a multiplication of a brightness values of pixels of the present page image by 1-f(t) (Step S 26  in FIG.  4 ). 
     For example, assume each brightness value of each pixel of the previous image is P, and each brightness value of each pixel of the present page image is N, and each brightness value of each pixel of the composed image is C, the relation of these brightness values are: 
     
       
         CP*f(t)+N*(1−f(t))  equation(1) 
       
     
     The ending time of the present processing is then stored as the time of the previous processing (Step S 27  in FIG. 4) and the present processing is completed. 
     The page scroll operation in the backward direction is described referring to FIG.  5 . FIG. 5 is a flow chart showing processes for backward scrolling. As shown in FIG. 5, the composition controller  19  acquires the present time from the timer  20  and stores it as the time of the present time (Step S 31  in FIG.  5 ). The composition controller  19  controls the formatter  13  and make the formatter  13  judge whether there are data corresponding to two pages in the structured text  11  before the present reading position (Step S 32  in FIG.  5 ). If there are data, processing continues and, if not, the process proceeds to Step  37 . The composition controller  19  directs the formatter  13  to shift the reading position by two pages before the present reading position, and directs it to read data for one page, and, if a direction is attached to incorporate the attached data in the page, to layout an attached data and prepare a form for one page (Step S 33  in FIG.  5 ). 
     Once the form is completed, the rasterizer  14  receives an output from the formatter  13 , produces a page image using fonts of letters. The page image corresponding to one page is stored in the page image buffer  15  in an area which is not used by the previous processing (Step S 34  in FIG.  5 ). 
     Subsequently, the composition controller  19  calculates a degree of composition as to the degree of superposition of the previous page image on the present page image based on the difference between the previous time and the present time (Step S 35  in FIG.  5 ). 
     The image composer  16  receives an instruction from the composition controller  19  and outputs to the display device  17  a brightness value of each pixel of a composed image based on the above equation (1) (Step S 36  in FIG.  5 ). 
     The composition controller  19  resets and stores the present time as the previous time, and complete processing. 
     The above description is given as to a system having a single image buffer. However, it is possible to improve the visibility of images even during high speed scrolling by providing a plurality of image buffers  15  and by indicating more than two after-images simultaneously. 
     Furthermore, when LCDs (Liquid Crystal Display) are used as display devices, it is also possible to construct a system to display a plurality of pages at the same time by providing a plurality of LCDs. 
     Moreover, when projection-type display devices are used, it is also possible to display a plurality of pages simultaneously by providing a plurality of projectors for a single screen. 
     The above descriptions are given in terms of the system. However, it is also possible to describe the present invention from a point of view of the method. As shown in FIG. 6, it is further possible to execute the above method by loading a series of programs of the present invention on a hard disc of a computer from a recording medium containing these programs for realizing the above method. 
     Examples of the recording medium include floppy-discs, CD-ROMs, and other digital recording mediums. 
     The first effect of the present invention is in that a plurality of pages can be displayed simultaneously on a single screen so that a relatively long period of time can be assigned for perception of pages, while the conventional system requires perception of pages within a far shorter period of time during scrolling. 
     The above effect is obtained because of the following reasons. That is, assume a document is lengthy and cannot be displayed as a single picture on electric display devices such as a CRTs or LCDs. When a plurality of pages of such document is inspected at high speed by either one of forward or backward scrolling, the system and the method provided by the present system remarkably improves the intuitive visibility of a letter or lines of letters, because the information contents of page images are increased and a period of time for displaying one page is increased due to artificial superposition of the previous page image as an after-image on the image of the present page. 
     The second effect of the present invention is that an automatic arrangement is provided to display the after-image at any time when the user requires. The effect of the present system is obtained because the user can move the cursor of the slider to change the waiting time for switching a page. 
     The third effect is that the present system can process a structured text. That is because the present system is provided with a formatter which is a means for transforming the structured text to an picture image. 
     The fourth effect is the present system can perform scrolling in the backward direction. This is because the present system is provided with an image composer.