WO2011042396A1

WO2011042396A1 - Display device having improved operation speed

Info

Publication number: WO2011042396A1
Application number: PCT/EP2010/064760
Authority: WO
Inventors: Johannes Petrus Van De Kamer
Original assignee: Irex Technologies B.V.; Irx Innovations B.V.
Priority date: 2009-10-05
Filing date: 2010-10-04
Publication date: 2011-04-14

Abstract

The invention relates to a method of displaying an electronic document on a display device (100) comprising a display panel (50). The method comprises: i) receiving (200) the electronic document in a first format, such as a PDF-file, not suitable for being displayed as images on the display panel (50), wherein the electronic document comprises a plurality of pages; ii) processing (210) a first one of the plurality of pages to obtain a first rendered page; iii) displaying (220) the first rendered page on the display panel (50), and iv) pre-processing (230) a second one of the plurality of pages upon starting the displaying of the first rendered page to obtain a second rendered page for future display on the display panel (50). The invention also relates to a computer program product comprising instructions for causing a processor to perform such method. The invention further relates to a display device comprising a display panel (50), wherein the display device is configured for carrying out the method. The method and the display device in accordance with the invention provide for an increased operation speed, i.e. a faster document opening and/or faster page turning.

Description

Display device having improved operation speed

FIELD OF THE INVENTION

The invention relates to a method of displaying an electronic document on a display device comprising a display panel. The invention further relates to a computer program product comprising instructions for causing a processor to carry out such method. The invention also relates to a display device comprising a display panel which is configured for carrying out such method. The invention further relates to applications of such display device. The invention relates in particular to the field of portable devices in which power consumption is the most critical performance indicator, i.e. a low power consumption is desired to increase battery life-time. In such portable devices, the processing power is kept relatively low in order to meet the power consumption constraints. Examples of such portable devices are smart-phones, PDA's, and E-readers with LCD displays. Such devices typically have processors running at a several hundreds of megahertz. In contrast with this, in desktops CPU's typically run at several gigahertz, or multi-processor architectures, running at somewhat lower clock speeds, are used for obtaining high processing power. The power consumption of such desktops is very high, which is not acceptable in portable devices, because of the battery life-time. Embodiments of the invention relate to bi-stable display devices which have even lower power consumption figures and thus even longer battery lifetime than LCD display devices. BACKGROUND OF THE INVENTION

A display device of the type mentioned in the opening paragraph is known from the international patent application US2006/0227196. This patent application discloses an electronic ink display which comprises two substrates. One of the substrates is transparent and is provided with a single electrode which is referred to as the counter electrode. This counter electrode is in other literature also referred to as common electrode or backplane electrode. The other substrate is provided with picture electrodes which comprise row and column electrodes. A display element or pixel is associated with an intersection of a row electrode and a column electrode. A pixel electrode of the display element is coupled to the column electrode via a thin film transistor (further referred to as TFT), the gate of which is coupled to the row electrode. This arrangement of display elements, TFT transistors and row and column electrodes together forms an active matrix. A row driver sequentially selects rows of display elements and the column driver supplies data signals to the selected row of display elements via the column electrodes and the TFT transistors. The data signals correspond to graphic data to be displayed.

An electronic ink is provided between the pixel electrode and the common electrode. The electronic ink comprises multiple microcapsules of about 10 to 50 microns. Each microcapsule comprises positively charged white particles and negative charge black particles suspended in a fluid. When a positive voltage is applied to the pixel electrode with respect to the common electrode, the positively charged white particles move to the side of the micro capsule directed to the transparent substrate on which the common electrode is present and a viewer will see a white display element. Simultaneously, the black particles move to the pixel electrode at the opposite side of the microcapsule where they are hidden to the viewer. By applying a negative voltage to the pixel electrode with respect to the common electrode, the black particles move to the common electrode at the side of the micro capsule directed to the transparent substrate and the display element appears dark to a viewer. When the voltage is removed, the display device remains in the acquired state and thus exhibits a bi-stable character. The electronic ink display with its black and white particles is particularly useful as an electronic book.

Grey scales are created in the display device by controlling the amount of particles that move to the common electrode at the top of the

microcapsules. For example, the energy of the positive or negative electric field in the pixel caused by the voltage difference between the pixel and common electrodes, defined as the product of field strength and time of application, controls the amount of particles moving to the top of the microcapsules.

A multi-level drive of the pixel electrodes enables to more closely reach a desired light output of a pixel because it is possible to more accurately control the movement of the particles at a lower value of the drive voltage. However, such a multi-level drive of the pixel electrodes requires complex display drivers.

GB2454030A discloses an electronic document reading device that is a device such as an electronic book which presents a document to a user on a display to enable the user to read the document. In particular, a display device is disclosed for displaying an electronic document page comprising a central rewritable portion, a non-rewritable border with external lateral physical dimensions defined by the display edges, wherein said border is colored to substantially match a background color of said central rewritable portion such that when a foreground part of said document page is displayed on said central rewritable portion the appearance of margins of said document page is provided by said background colored border. As a consequence, in use, said displayed electronic document page appears to extend up to said display edges, and wherein the surface of the display is substantially flat over the lateral physical dimensions from the central rewritable portion across the border to the display edges. The device may be controlled via a touch sensitive interface.

A problem of the known electronic document reading device is that, because of the reasons set out in the opening paragraph, its operation (such as opening documents and turning pages) speed is relatively slow. For example, when having selected an electronic document to be opened it may take a relative long time before the document shows up. Furthermore, when a next page is requested, i.e. by pressing a button or activating a flip bar, it may take a relative long time before the next page shows up. Both situations may be experienced as a bit inconvenient by the user. SUMMARY OF THE INVENTION

It is a first object of the invention to provide a method of displaying an electronic document on a display device comprising a display panel wherein the operation speed is increased. It is a second objection of the invention to provide a display device comprising a display panel which is configured for carrying out such method.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

In a first aspect, in accordance with the first object, the invention relates to a method as claimed in claim 1.

The effect of the features of the invention is as follows. The electronic document is received in a format which cannot be displayed as images on the display panel. An example format which is typically used is the Portable Document Format (PDF) as created by Adobe Systems in 1993. PDF is used for representing two-dimensional documents in a manner independent of the application software, hardware, and operating system. Each PDF file encapsulates a complete description of a fixed-layout 2D document (and, with Acrobat 3D, embedded 3D documents) that includes the text, fonts, images, and 2D vector graphics which compose the documents. Other examples of files which cannot be directly displayed are page description languages such as postscript. The non-displayable electronic documents typically comprise a plurality of pages. Before a first one of the plurality of pages can be displayed the respective page of the document must be rendered, i.e. converted into a rendered page or page image. Such rendering takes a certain amount of time. Thus, in the method of the prior art, once a second one of the plurality of pages has been selected it takes some time before it can be displayed, i.e. page flipping is relatively slow. In the method of the invention this processing (such as rendering) is performed upon starting the displaying of the first rendered page, i.e. the second rendered page to be displayed is pre-processed. As a consequence of this, once the second rendered page is selected it can be immediately displayed which takes less time, i.e. typically the display time may be in the order of a second. In this way the method of the invention provides for faster page turning than the method of the prior art.

In view of the invention pre-processing means pre-rendering or prefetching in accordance with embodiments of the invention. Pre-rendering a page means creating a page image (rendered page) of one of the pages of an electronic document file, such as a PDF-file. Such electronic document files are not displayable as images but need to be converted into displayable page images of the respective pages. The rendered page (page image) may be stored into part of the main memory which is reserved for acting as a render memory. Pre-fetching means retrieving a rendered page (which has been rendered at an earlier opening of the electronic document) from a render memory (which may be volatile or non-volatile in accordance with embodiments of the invention).

An embodiment of the method in accordance with the invention further comprises, after the pre-processing of the second one of the plurality of pages, displaying the second rendered page on the display panel. In an embodiment such displaying is triggered by a user. In another embodiment such event is triggered by a timer, eye-tracking, or any other event.

In an embodiment of the method in accordance with the invention the processing of the first one of the plurality of pages comprises: rendering the first one of the plurality of pages to obtain the first rendered page. This embodiment is advantageous in case the first one of the plurality of pages has not yet been rendered before, or in case it has been rendered before but not been saved.

In an embodiment of the method in accordance with the invention the pre-processing of the second one of the plurality of pages comprises: rendering the second one of the plurality of pages to obtain the second rendered page. This embodiment is advantageous in case the second one of the plurality of pages has not yet been rendered before, or in case it has been rendered before but not been saved. An embodiment of the method in accordance with the invention further comprises: storing said respective rendered pages in a render memory. Storing the rendered page is advantageous, because it renders the rendering of said pages superfluous.

In an embodiment of the method in accordance with the invention the processing of the first one of the plurality of pages comprises: searching the first rendered page in the render memory, and, if the first rendered page is found in the render memory, retrieving said first rendered page from the render memory. This embodiment is advantageous, because the first one of the plurality of pages does not need to be rendered. Instead, it is simply retrieved from the render memory, which can be easily achieved faster than rendering said page from the electronic document, i.e. the operation speed is further increased, and the user experiences a faster method of displaying.

In an embodiment of the method in accordance with the invention the processing of the second one of the plurality of pages comprises: searching the second rendered page in the render memory, and, if the second rendered page is found in the render memory, retrieving said second rendered page from the render memory. This embodiment is advantageous, because the second one of the plurality of pages does not need to be rendered. Instead, it is simply retrieved from the render memory, which can be easily achieved faster than rendering said page from the electronic document, i.e. the operation speed is further increased, and the user experiences a faster method of displaying.

In an embodiment of the method in accordance with the invention the display device further comprises a main memory, a microprocessor coupled to the main memory and the display panel and being configured for performing operations on data in the main memory, and a non-volatile document storage medium for prolonged storage of the electronic document. In this embodiment the receiving of the electronic document in the first format comprises: loading the electronic document from the non-volatile document storage medium into the main memory. Using a configuration as in described this embodiment constitutes a convenient implementation for carrying out the method of the invention.

In embodiments having the render memory it is advantageous to implement the render memory in the main memory, or expressed differently, to allocate part of the main memory for storing rendered pages. Generally, such main memories are fast memories, because the microprocessor uses this memory as operational memory. Therefore, using part of the main memory as render memory provides for a higher operation speed. Alternatively, the render memory may be a separate memory.

In an embodiment of the method in accordance with the invention the loading of the electronic document is carried out after starting the displaying of the first rendered page provided that the first rendered page has been found in and retrieved from the render memory. The advantage of this embodiment is that the time period for loading the electronic document into the main memory is shifted to after the displaying of the first rendered page. The time required for such action generally takes a relatively large amount of time, depending on the size of the electronic document this may typically be between 1 and 5 seconds. Moving this action to after the moment on which the first rendered page is displayed provides on the one hand for fast electronic document opening, i.e. the first page is displayed quickly after selecting the electronic document. On the other hand the time normally required for loading this document is now masked because it occurs right after starting the displaying of the first rendered page. The action of loading the document may be finished before the user has read the page and selects the next page.

It must be noted that this fast document opening effect may also be applied separate from the pre-processing for fast page turning effect of claim 1 . Both effects may be applied individually or in combination as in this embodiment. In any case the effect of both is that the user experiences an increased operation speed, i.e. a faster method of displaying.

In an embodiment of the method in accordance with the invention the loading of the electronic document is carried out after starting the displaying of the second rendered page provided that the second rendered page has also been found in and retrieved from the render memory. In view of the previous mentioned embodiment this embodiment provides not only for a fast document opening effect, but also for a fast second page viewing effect. Both the first rendered page and the second rendered page are taken from the render memory and the relatively lengthy document load operation is shifted to after starting of the displaying of the second rendered page.

In an embodiment of the method in accordance with the invention the storing of the respective rendered pages comprises storing at least a number of said respective rendered pages on a non-volatile page storage medium. Such storing may be carried out for all rendered pages, but also for a certain number/selection of pages. In case of a selection of pages it is possible to choose only the older pages in the render memory having a predefined minimum age. Instead of throwing pages away (which may be required because the render memory is full) it is advantageous to store those pages on a non-volatile page storage medium, such as a memory card. Using a non-volatile storage medium for the rendered pages has the advantage that the rendered pages are also available after switching of the display device, i.e. fast document opening and fast page turning are still possible on the next power on of the device. Here it must be noted that in case rendered pages are stored on both a main memory and the non-volatile memory, steps are needed to check both memories when searching for rendered pages. This is all considered to fall within the scope of the invention as claimed.

In an embodiment of the method in accordance with the invention the non-volatile page storage medium is the non-volatile document storage medium. This embodiment is an efficient solution, because a display device may already comprise a non-volatile storage medium for storing the electronic documents.

In an embodiment of the method in accordance with the invention the storing of the respective rendered pages in the render memory is carried out upon closing of the electronic document. This embodiment is advantageous, because in this time-slot (right after choosing closing of the document) the user will not notice the time required for writing the non-volatile page storage medium, or at least to a lesser extent. The user experience is further enhanced in this embodiment of the method.

In an embodiment of the method in accordance with the invention a page number of the second rendered page complies with at least one of the following formulas: N+1 , N+2, N+3, N+4, N+5, N-1 , N-2, N-3, N-4, and N-5, wherein N denotes the page number of the first rendered page. The pages nearest to the current page being displayed are often the most likely candidates to be displayed. This embodiment conveniently ensures that at least a selection of those pages are pre-processed for enhancing page turning to those pages.

In an embodiment of the method in accordance with the invention a page number of the second rendered page complies with at least one of the following formulas: N+C, wherein N denotes the page number of the first rendered page, and wherein C is a variable integer. This embodiment facilitates more flexible pre-processing. In case C is chosen to be very large ultra-fast page turning is provided. C may be a fixed value. Alternatively, C may be varied in accordance with variable requirements during operation.

In an embodiment of the method in accordance with the invention a sign of C is determined from a page turning direction such that C is positive when said pages are turned with increasing page number and C is negative when said pages are turned with decreasing page number. The pre-processing in this embodiment is carried out in a more clever manner, which reduces the number of rendered pages that require being stored in the render memory.

In an embodiment of the method in accordance with the invention C is specified by a user. In certain application a user may decide for himself what value C needs to have.

In an embodiment of the method in accordance with the invention C is determined such that the second rendered page comprises a starting page of a specific chapter of the electronic document. This embodiment provides for a fast document-scan feature, i.e. the user may quickly scan through the starting pages of the chapters of the electronic document.

In an embodiment of the method in accordance with the invention C is determined from hyperlinks, if present, on the first rendered page being displayed such that the second rendered page comprises a specific page referred to in the hyperlinks. In this embodiment the content of the page (for example a table of contents page) being displayed is examined and pages referred to in the hyperlinks contained in the respective pages are pre-processed. In an advantageous embodiment all referred pages are pre-processed.

In an embodiment of the method in accordance with the invention the display panel, on which the electronic document is displayed, is selected from a group comprising: an LCD display panel, a bi-stable LCD display panel, an electrowetting display panel, a bi-stable electrowetting display panel, and an electrophoretic display panel.

In a second aspect, the invention relates to a computer program product comprising instructions for causing a processor to perform the method in accordance with the invention.

In a third aspect, in accordance with the second object, the invention relates to a display device as claimed in claim 21 . The display device is configured for carrying out the method of the invention and has therefore corresponding embodiments having similar advantages as the method. In the description of the figures an example of a display device is further discussed. It will be apparent for the person skilled in the art that in particular for the display device many variations are possible. Different functions may be shifted amongst different blocks, or intentionally merged into one block.

An embodiment of the display device in accordance with the invention further comprises the non-volatile page storage medium. This non-volatile page storage medium may form part of the non-volatile document storage medium (which may be a memory card), but it may also be a separate non-volatile memory, i.e. a second memory card.

In an embodiment of the display device in accordance with the invention the display panel is selected from a group comprising: an LCD display panel, a bi-stable LCD display panel, an electrowetting display panel, a bi-stable electrowetting display panel, and an electrophoretic display panel.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 shows a display device in accordance with an embodiment of the invention;

Fig. 2 shows a block diagram of the display device of Fig. 1 ;

Fig. 3 shows a flow diagram of the method in accordance with an embodiment of the invention;

Fig. 4 shows diagrammatically a cross-section of a portion of an electrophoretic display device, and

Fig. 5 shows diagrammatically an equivalent circuit diagram of a portion of the electrophoretic display device.

List of reference numerals:

1 electrophoretic matrix display panel

2 base substrate

3 transparent substrate

4 transparent substrate

5, 5' transparent picture electrodes

6 common electrode

7 micro capsule

8 white particles

9 black particles

10 row driver

1 1 column or data electrodes

12 drive lines

13 (incoming) display data

15 processor

16 column driver 17 row or select electrodes

18 display element

19 active switching elements

20 gate electrodes

21 source electrodes

22 pixel electrodes

23 capacitor

24 storage capacitor lines

25 backplane driver

26 control signals

29 polymeric binder

VD data signal

VG gate electrode voltage

VP voltage from backplane driver

50 display panel

60 microprocessor

70 non-volatile document storage medium (memory card)

80 main memory (SDRAM)

99 device control buttons of display device

100 display device

200 document receiving step of method of invention

210 1 ^st pre-processing step of method of invention

220 1 ^st displaying step of method of invention

230 2^nd pre-processing step of method of invention

240 2^nd displaying step of method of invention

250 3^rd pre-processing step of method of invention

S1 step of reading an electronic document

S2 step of (pre-)rendering a page to be displayed

S2' step of (prefetching a page to be displayed

S3 step of transfer the rendered page from memory to the display panel

S4 step of displaying the rendered page on the display panel

S5 step of writing the rendered page back onto the non-volatile storage

S6 step of reading the rendered page from the non-volatile storage

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In order to facilitate the discussion of the detailed embodiments a few expressions are defined hereinafter. Fig. 1 shows a display device in accordance with an embodiment of the invention. The figure is purely schematic in order to explain important aspects of the invention. The display device 100 comprises a bi-stable display panel, such as an electrophoretic display panel (E-ink, E-paper). It must be stressed that the invention is broader applicable than in the field of bi-stable display panel; the invention is applicable in any display device where the processing power is kept low for power consumption reasons, for example in a portable device running on a battery. The display device 100 further comprises device control buttons 99, in this example located at the left side and the bottom side of the device (but this is not essential to the invention). The bi-stable display panel is divided into a display panel 50 located in the middle of the device.

Fig. 2 shows a block diagram of the display device of Fig.1. The display device 100 comprises the bi-stable display panel 50, a main memory 80 and a microprocessor 60 coupled to the main memory 80 and the display panel 50. The display device 100 further comprises a non-volatile document storage medium 70 (such as a memory card) that is also coupled to the microprocessor 60. The coupling of the respective blocks in Fig. 2 has been schematically illustrated by bold arrows. The display device 100 operates as follows. The microprocessor plays a central role in the displaying as it performs and triggers many operations.

In a first sub-step S1 an electronic document, such as a PDF-file or an html-file, is read from the non-volatile memory 70 into the main memory 80 (such as a DDR SDRAM). This step typically takes a second up to several seconds, depending on the size of the electronic document. The electronic document comprises a plurality of pages, which document is, as such, not displayable in images (instead it is displayable in some sort of document code, wherein the layout of the pages is not recognizable).

In a second sub-step S2 a first one of the plurality of pages is selected and rendered from the electronic document so that a first rendered page is obtained. The rendering is carried out by the microprocessor and the resulting rendered page is stored in the main memory 80. Such rendering step may typically take 800ms for a text page in an electrophoretic display device. In practical documents, it may take several hundreds of milliseconds up to a few seconds or even more than 10 seconds, depending on the complexity of the data of the page to be displayed. In an alternative sub-step S2' the first one of the plurality of pages is obtained from a render memory (not shown, but it may be comprised in the main memory in an embodiment). Such retrieval is only possible in case the respective page has been rendered before (at an earlier reading of the electronic document) and saved into the main memory 80. Retrieving a rendered page from the main memory can be done very fast, e.g. in just a few milliseconds up to several tens of milliseconds. Page turning speed is thereby significantly increased.

In a third sub-step S3 the first rendered page is transferred to the display panel 50, which may typically take about 20ms for an electrophoretic display device. In Fig. 2 this transfer has been illustrated by an arrow through the microprocessor. This is not essential, however, as in some embodiments the main memory 80 may have direct connections with the bi-stable display panel 50, wherein said transfer is triggered by the microprocessor but not through the microprocessor.

In a fourth sub-step S4 the first rendered page is displayed on the bistable display panel 50, which may typically take about 800ms for an electrophoretic display panel. Right after start of the displaying of the first rendered page a second one of the plurality of pages is pre-rendered, i.e. the second sub-step S2, or its alternative sub-step S2', are repeated. Which page is to be pre-processed depends on what specific features are desired. Several embodiments thereof have already been discussed in the summary of the invention and are not repeated here. Once the second one of the plurality of pages has been pre-processed it may be displayed, taking about 800ms.

Thus, once the electronic document has been loaded, in an electrophoretic display device it may typically take between about 0.8s (in case the second rendered page is available in the render memory) and 1 .6 seconds (in case the second rendered page is not available in the render memory) to display the second rendered page right after the first rendered page.

In a further embodiment the pre-processing of the second one of the plurality of pages is started right after processing of the first one of the plurality of pages. By doing so the display of the first-rendered page and the pre-processing of the second one of the plurality of pages may be done simultaneously, which effectively saves another 800ms (for the rendering of the second page), thus reducing the maximum delay between first page and the second page (and to subsequent pages) to about 820ms, i.e. 800ms for displaying plus 20ms for the transfer to the display. It can also be stated that the pre-rendering may be masked by the display time.

Fig. 2 also illustrates a fifth sub-step S5 in accordance with an embodiment of the invention. In this sub-step the respective rendered pages in the render memory are stored in the non-volatile document storage medium 70 (but it could be any non-volatile storage medium, such as a second, additional, non-volatile page storage memory). In this way the rendered pages remain available even after power down of the display device 100. The rendered pages on the non-volatile memory 70 may form a mirror database of the database of rendered pages in the main memory 80. However, they may also be a sub-set of said database. In yet another embodiment, wherein the render memory (in the main memory 80) has a limited size, the non-volatile memory 70 is configured for containing the largest database of rendered pages. In an embodiment, in case the render memory in the main memory is full, older pages in the render memory (having a predefined minimum age) may be stored in the non-volatile memory. From the above it will be apparent that there are many variations possible in as far as the render memory in the main memory 80 and the non-volatile page memory 70 are concerned. The databases may be complementary, but they may also overlap. One database may be leading, or both databases may be mirrors of each other.

An advantageous embodiment concerns one where the render memory in the main memory 80 is written to the non-volatile memory 70 upon closing of the electronic document. In this way, the relatively time-consuming step is shifted to a moment where it is not noticed by the user, or at least to a lesser extent.

Fig. 2 further illustrates a sixth sub-step S6, wherein a rendered page is read from the non-volatile memory 70. It must be noted that this step can be carried out much faster, typically a few milliseconds up to a few tens of milliseconds, than the step of reading the electronic document into the main memory, and subsequently rendering a page thereof.

Fig. 3 shows a flow diagram of the method in accordance with an embodiment of the invention. The figure serves to illustrate the main invention, rather than all its embodiments. For a more elaborate discussion of the embodiments, the reader is referred to the introductory part of this description.

In a first step 200 the electronic document is received in a first format, such as a PDF-file, not suitable for being displayed as images on the bi-stable display panel 50, wherein the electronic document comprises a plurality of pages.

In a second step 210 a first one of the plurality of pages is processed to obtain a first rendered page. The first rendered page may be rendered from the respective page of the electronic document, or it may be fetched from a render memory, in case the respective page has been rendered before during an earlier opening of the electronic document.

In a third step 220 the first rendered page is displayed on the bi-stable display panel 50.

In a fourth step 230 a second one of the plurality of pages is pre- processed upon starting the displaying of the first rendered page to obtain a second rendered page for future display on the bi-stable display panel 50. The second rendered page may be rendered from the respective page of the electronic document, or it may be fetched from a render memory, in case the respective page has been rendered before during an earlier opening of the electronic document.

As already mentioned earlier, the fourth step 230 and the third step

220 may be performed simultaneously, that is there is no need to wait until the displaying of the first rendered page is completed, before starting the pre-processing of the second page.

From the above it will be apparent that the method can be continued for further displaying of further pages. An example embodiment of such method is further discussed below.

In a fifth step 240, after the pre-processing of the second one of the plurality of pages, displaying the second rendered page on the bi-stable display panel 50.

In a sixth step 250 a third one of the plurality of pages is pre- processed upon starting the displaying of the second rendered page to obtain a third rendered page for future display on the bi-stable display panel (50).

In view of what has been mentioned earlier, the sixth step 250 and the fifth step 240 may be performed simultaneously, that is there is no need to wait until the displaying of the second rendered page is completed, before starting the preprocessing of the third page.

As already mentioned earlier in an embodiment the first step 200, i.e. the loading of the electronic document into the main memory 80, may be delayed to a moment after the displaying of the first rendered page or even to a moment after the displaying of the second rendered page, provided that such pages are available in the render memory (or on the non-volatile memory storage medium). This has been illustrated by the hollow arrows in Fig. 3. The advantage of this embodiment is that the document appears to open much faster, i.e. the first page is displayed quicker upon opening the electronic document. The first page that is displayed may be the first page of the electronic document, but also the last-page viewed upon closing of the document the previous time.

Fig. 4 diagrammatically shows a cross-section of a few display elements of an electrophoretic matrix display panel 1 , i.e. an example of a bi-stable display panel device 50. The display panel 1 comprises a base substrate 2, an electrophoretic film with an electronic ink which is present between two transparent substrates 3 and 4 which, for example, are of polyethylene. The substrate 3 is provided with transparent picture electrodes 5, 5' and the other substrate 4 with a transparent common electrode 6. The electronic ink comprises multiple micro capsules 7, of about 10 to 50 microns. Each micro capsule 7 comprises positively charged white particles 8 and negatively charged black particles 9. The particles 8 and 9 are suspended in a fluid. The dashed material 29 is a polymeric binder. The layer 3 is not necessary and could alternatively be a glue layer. When a negative voltage is applied to the common electrode 6 with respect to the picture electrodes 5, an electric field is generated which moves the white particles 8 to the side of the micro capsule 7 directed to the common electrode 6 and the display element will appear white to a viewer. Simultaneously, the black particles 9 move to the opposite side of the microcapsule 7 where they are hidden to the viewer. By applying a positive field between the common electrode 6 and the picture electrodes 5, the black particles 9 move to the side of the micro capsule 7 directed to the common electrode 6 and the display element will appear dark to a viewer (not shown). When the electric field is removed the particles 7 remain in the acquired state and the display exhibits a bi-stable character and consumes substantially no power. Instead of white and black the particles may have any desired color.

Fig. 5 shows diagrammatically an equivalent circuit of the matrix display device 1 which comprises an electrophoretic film laminated on the base substrate 2 provided with active switching elements 19, a row driver 16 and a column driver 10. For the second driver circuit 45 and the border region 55 similar techniques can be used as for the first driver circuit 40 and the display region 50. Preferably, the common electrode 6 is provided on the film comprising the encapsulated electrophoretic ink. Alternatively, the common electrode 6 could be provided on a base substrate if the operation of the display is based on in-plane electric fields. The display panel 1 is driven by active switching elements, for example, thin film transistors 19. The display device 1 comprises a matrix of display elements at the area of intersecting row or select electrodes 17 and column or data electrodes 1 1. The row driver 16 consecutively selects the row electrodes 17, while a column driver 10 provides data signals to the column electrodes 1 1 for the selected row electrode 17. Preferably, a processor 15 firstly processes incoming data 13 into the data signals to be supplied by the column electrodes 1 1.

The drive lines 12 carry signals which control the mutual synchronization between the column driver 10 and the row driver 16. Select signals VG from the row driver 16 which are electrically connected to the row electrodes 17 select the pixel electrodes 22 via the gate electrodes 20 of the thin film transistors 19. The source electrodes 21 of the thin film transistors 19 are electrically connected to the column electrodes 1 1. A data signal VD present at the column electrode 1 1 is transferred to the pixel electrode 22 of the display element 18 (also referred to as pixel) coupled to the drain electrode of the TFT if the associated TFT is conductive. In the embodiment shown, the display device of Fig.1 further comprises an additional capacitor 23 at the location of each display element 18. This additional capacitor 23 is connected between the pixel electrodes 22 of the associated pixel 18 and one or more storage capacitor lines 24. Instead of a TFT other switching elements can be applied such as diodes, MIM's, etc.

The common electrode 6 receives the voltage VB from a backplane driver 25. The backplane driver 25 supplies a sequence of voltages comprising non- zero voltages. The column driver 10 and the row driver 16 may be commonly used drivers. The processor 15 provides control signals 26 to the backplane driver 25 to coordinate the operation of the backplane driver 25 with the column driver 10 and the row driver 16.

If applicable, the processor 15 may comprise a memory 80 for storing previous drive voltages of the pixels 18 required for a transition drive scheme.

Alternatively, the memory 80 may be used to store the levels of the correction pulses required for each optical state.

Various variations of the display device in accordance with the invention are possible and do not depart from the scope of the invention as claimed. For example, the invention may also be implemented in a full color bi-stable display.

The invention thus provides a method of displaying an electronic document on a display device 100 comprising a bi-stable display panel 50. The method comprises: i) receiving 200 the electronic document in a first format, such as a PDF-file, not suitable for being displayed as images on the bi-stable display panel 50, wherein the electronic document comprises a plurality of pages; ii) processing 210 a first one of the plurality of pages to obtain a first rendered page; iii) displaying 220 the first rendered page on the bi-stable display panel 50, and iv) pre-processing 230 a second one of the plurality of pages upon starting the displaying of the first rendered page to obtain a second rendered page for future display on the bi-stable display panel 50. The invention also provides a computer program product comprising instructions for causing a processor to perform such method. The invention further provides a display device comprising a bi-stable display panel 50, wherein the display device is configured for carrying out the method. The method and the display device in accordance with the invention provide for an increased operation speed, i.e. a faster document opening and/or faster page turning. The invention may be applied in various application areas. For example, the invention may be applied in E-paper applications, electronic

readers/writers, laptops, PDA's, hand-held, multimedia players, cell phones, etc. The invention is particularly useful in the field of portable devices in which power consumption is the most critical performance indicator, i.e. a low power consumption is desired to increase battery life-time. In such portable devices, the processing power is kept relatively low in order to meet the power consumption constraints. Examples of such portable devices are smart-phones, PDA's, and E-readers with LCD displays. Such devices typically have processors running at a several hundreds of megahertz. In contrast with this, in desktops CPU's typically run at several gigahertz, or multi-processor architectures, running at somewhat lower clock speeds, are used for obtaining high processing power. The power consumption of such desktops is very high, which is not acceptable in portable devices, because of the battery life-time. Embodiments of the invention relate to bi-stable display devices which have even lower power consumption figures and thus even longer battery lifetime than LCD display devices.

It will be appreciated that the invention also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as partially compiled form, or in any other form suitable for use in the implementation of the method according to the invention. It will also be appreciated that such a program may have many different architectural designs. For example, a program code implementing the functionality of the method or system according to the invention may be subdivided into one or more subroutines. Many different ways to distribute the functionality among these subroutines will be apparent to the skilled person. The subroutines may be stored together in one executable file to form a self-contained program. Such an executable file may comprise computer executable instructions, for example processor instructions and/or interpreter instructions (e.g. Java interpreter instructions).

Alternatively, one or more or all of the subroutines may be stored in at least one external library file and linked with a main program either statically or dynamically, e.g. at run-time. The main program contains at least one call to at least one of the subroutines. Also, the subroutines may comprise function calls to each other. An embodiment relating to a computer program product comprises computer executable instructions corresponding to each of the processing steps of at least one of the methods set forth. These instructions may be subdivided into subroutines and/or be stored in one or more files that may be linked statically or dynamically. Another embodiment relating to a computer program product comprises computer executable instructions corresponding to each of the means of at least one of the systems and/or products set forth. These instructions may be subdivided into subroutines and/or be stored in one or more files that may be linked statically or dynamically.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Throughout the Figures, similar or corresponding features are indicated by same reference numerals or labels.

Claims

CLAIMS:

1 . A method of displaying an electronic document on a display device

(100) comprising a display panel (50), the method comprising:

- receiving (200) the electronic document in a first format, such as a

PDF-file, not suitable for being displayed as images on the display panel (50), wherein the electronic document comprises a plurality of pages;

processing (210) a first one of the plurality of pages to obtain a first rendered page;

- displaying (220) the first rendered page on the display panel (50), and pre-processing (230) a second one of the plurality of pages upon starting the displaying of the first rendered page to obtain a second rendered page for future display on the display panel (50).

2. The method as claimed in claim 1 , the method further comprising, after the pre-processing of the second one of the plurality of pages, displaying (240) the second rendered page on the display panel (50).

3. The method as claimed in any one of the preceding claims, wherein the processing of the first one of the plurality of pages comprises:

rendering the first one of the plurality of pages to obtain the first rendered page.

4. The method as claimed in any one of the preceding claims, wherein the pre-processing of the second one of the plurality of pages comprises:

rendering the second one of the plurality of pages to obtain the second rendered page.

5. The method as claimed in any one of the preceding claims, further comprising:

storing said respective rendered pages in a render memory.

6. The method as claimed in claim 5, wherein the processing of the first one of the plurality of pages comprises:

- searching the first rendered page in the render memory, and, if the first rendered page is found in the render memory, retrieving said first rendered page from the render memory.

7. The method as claimed in claim 5 or 6, wherein the processing of the second one of the plurality of pages comprises:

searching the second rendered page in the render memory, and, if the second rendered page is found in the render memory, retrieving said second rendered page from the render memory.

8. The method as claimed in any one of the preceding claims, wherein the display device (100) further comprises a main memory (80), a microprocessor (60) coupled to the main memory (80) and the display panel (50) and being configured for performing operations on data in the main memory (80), and a nonvolatile document storage medium (70) for prolonged storage of the electronic document, wherein the receiving of the electronic document in the first format comprises:

- loading the electronic document from the non-volatile document storage medium (70) into the main memory (80).

9. The method as claimed in any one of the preceding claims, wherein the loading of the electronic document is carried out after starting the displaying of the first rendered page provided that the first rendered page has been found in and retrieved from the render memory.

10. The method as claimed claim 9, wherein the loading of the electronic document is carried out after starting the displaying of the second rendered page provided that the second rendered page has also been found in and retrieved from the render memory.

1 1 . The method as claimed in any one of claims 5 to 10 in as far as dependent on claim 5, wherein the storing of the respective rendered pages comprises storing at least a number of said respective rendered pages on a nonvolatile page storage medium (70).

12. The method as claimed in claim 1 1 , wherein the storing of the respective rendered pages in the render memory is carried out upon closing of the electronic document.

13. The method as claimed in any one of the preceding claims, wherein a page number of the second rendered page complies with at least one of the following formulas: N+1 , N+2, N+3, N+4, N+5, N-1 , N-2, N-3, N-4, and N-5, wherein N denotes the page number of the first rendered page.

14. The method as claimed in any one of the preceding claims, wherein a page number of the second rendered page complies with at least one of the following formulas: N+C, wherein N denotes the page number of the first rendered page, and wherein C is a variable integer.

15. The method as claimed in claim 14, wherein a sign of C is determined from a page turning direction such that C is positive when said pages are turned with increasing page number and C is negative when said pages are turned with decreasing page number.

16. The method as claimed in claim 14 or 15, wherein C is specified by a user.

17. The method as claimed in any one of claims 14 to 16, wherein C is determined such that the second rendered page comprises a starting page of a specific chapter of the electronic document.

18. The method as claimed in any one of claims 14 to 16, wherein C is determined from hyperlinks, if present, on the first rendered page being displayed such that the second rendered page comprises a specific page referred to in the hyperlinks.

19. The method as claimed in any one of the preceding claims, wherein the display panel (50), on which the electronic document is displayed, is selected from a group comprising: an LCD display panel, a bi-stable LCD display panel, an electrowetting display panel, a bi-stable electrowetting display panel, and an electrophoretic display panel.

20. A computer program product comprising instructions for causing a processor to perform the method as claimed in any one of the preceding claims.

21 . A display device comprising: i) a main memory (80), ii) a display panel (50), iii) a microprocessor (60) coupled to the main memory (80) and the display panel (50) and being configured for performing operations on data in the main memory (80), and iv) a non-volatile document storage medium (70) for prolonged storage of the electronic document, the display device being configured for carrying out the method as claimed in any one of the preceding claims.

22. The display device as claimed in claim 21 , further comprising the nonvolatile page storage medium (70).

23. The display device as claimed in claim 21 or 22, wherein the display panel (50) is selected from a group comprising: an LCD display panel, a bi-stable LCD display panel, an electrowetting display panel, a bi-stable electrowetting display panel, and an electrophoretic display panel.