Patent Publication Number: US-11663987-B2

Title: Display apparatus and driving method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 109139252, filed on Nov. 11, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to an electronic device and a driving method thereof, and more particularly, to a display apparatus and a driving method thereof. 
     Description of Related Art 
     In recent years, with the advantages of lightness/thinness, durability, and low power consumption which is in line with energy saving and environmental protection, the electronic paper display apparatus has been widely applied to e-readers (e.g., e-books, electronic newspapers) or other electronic components (e.g., electronic tags) on the market. However, taking the flexible electronic paper display apparatus as an example, after the flexible electronic paper display apparatus is folded or rolled for a long time or multiple times, the performance of its display panel may decrease due to the mechanical fatigue effect. Therefore, when the performance of the display panel decreases due to the mechanical fatigue effect, the difference in the gray level or color of the pixel as compared with the surrounding region may increase. The user may perceive this difference in the normal display state and perceive the disuniformity (mura) of the image frame, which thus undermines the user experience. 
     SUMMARY 
     The disclosure provides a display apparatus and a driving method thereof, in which the displayed image frame is uniform and a good user experience can be provided. 
     A display apparatus of the disclosure includes a display panel and a display driver. The display driver is coupled to the display panel. The display driver is configured to, in a first state, drive the display panel by at least one of a plurality of gray levels to display an image frame. The display driver is configured to, in a second state, drive the display panel by a predetermined gray level to display a standby frame. The display driver determines the predetermined gray level of the standby frame according to the gray levels of the image frame. 
     In an embodiment of the disclosure, the gray levels include a first gray level and a second gray level, and an arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The predetermined gray level is selected from the first gray level or the second gray level. 
     In an embodiment of the disclosure, the gray levels include a first gray level and a second gray level, and an arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The gray levels further include a lowest gray level. In the first state, the display driver drives the display panel by the lowest gray level to display a background part of the image frame. The first gray level and the second gray level are greater than the lowest gray level. The predetermined gray level is greater than or equal to the lowest gray level, and the predetermined gray level is less than the first gray level or the second gray level. 
     In an embodiment of the disclosure, the gray levels include a first gray level and a second gray level, and an arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The gray levels further include a highest gray level. In the first state, the display driver drives the display panel by the highest gray level to display a background part of the image frame. The first gray level and the second gray level are less than the highest gray level. The predetermined gray level is less than or equal to the highest gray level, and the predetermined gray level is greater than the first gray level or the second gray level. 
     In an embodiment of the disclosure, the display driver is further configured to calculate a gray level average of each pixel on the display panel, and determine the predetermined gray level according to the gray level average of each pixel. 
     In an embodiment of the disclosure, the standby frame includes a dot pattern. The dot pattern includes a plurality of pixel blocks. Each of the pixel blocks includes at least one pixel. The display driver drives a part of the pixel blocks by the predetermined gray level to display the standby frame. The pixel blocks driven by the predetermined gray level are not adjacent to each other in a horizontal direction and a vertical direction. 
     A driving method of a display apparatus of the disclosure includes the following steps. In a first state, a display panel is driven by at least one of a plurality of gray levels to display an image frame. A predetermined gray level is determined according to the gray levels of the image frame. In a second state, the display panel is driven by the predetermined gray level to display a standby frame. 
     In an embodiment of the disclosure, the gray levels include a first gray level and a second gray level, and an arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The predetermined gray level is selected from the first gray level or the second gray level. 
     In an embodiment of the disclosure, the driving method of the display apparatus further includes the following step. In the first state, the display panel is driven by a lowest gray level to display a background part of the image frame. The gray levels include a first gray level, a second gray level, and the lowest gray level. The first gray level and the second gray level are greater than the lowest gray level. An arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The predetermined gray level is greater than or equal to the lowest gray level, and the predetermined gray level is less than the first gray level or the second gray level. 
     In an embodiment of the disclosure, the driving method of the display apparatus further includes the following step. In the first state, the display panel is driven by a highest gray level to display a background part of the image frame. The gray levels include a first gray level, a second gray level, and the highest gray level. The first gray level and the second gray level are less than the highest gray level. An arithmetic mean of the first gray level and the second gray level is a median of the gray levels. The predetermined gray level is less than or equal to the highest gray level, and the predetermined gray level is greater than the first gray level or the second gray level. 
     In an embodiment of the disclosure, the standby frame includes a dot pattern. The dot pattern includes a plurality of pixel blocks. Each of the pixel blocks includes at least one pixel. The step of driving the display panel by the predetermined gray level to display the standby frame in the second state includes the following step. A part of the pixel blocks is driven by the predetermined gray level to display the standby frame. The pixel blocks driven by the predetermined gray level are not adjacent to each other in a horizontal direction and a vertical direction. 
     Based on the above, in the embodiments of the disclosure, the display driver drives the display panel by the predetermined gray level to display the standby frame in the second state, which can prevent the user from perceiving the disuniformity of the image frame in the first state. 
     To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view of a flexible electronic paper display apparatus according to an embodiment of the disclosure. 
         FIG.  2    is a schematic view showing a state change of the flexible electronic paper display apparatus and the corresponding displayed frames according to an embodiment of the disclosure. 
         FIG.  3    is a flowchart showing steps of a driving method of a display apparatus according to an embodiment of the disclosure. 
         FIG.  4    is a diagram showing the relationship between a fatigue cycle and gray level decay of a flexible electronic paper display apparatus according to an embodiment of the disclosure. 
         FIG.  5    is a schematic view showing a standby frame including a dot pattern according to an embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following, as an example of the display apparatus, a flexible electronic paper display apparatus will be described with reference to the accompanying drawings. However, the display apparatus of the disclosure is not limited to the flexible electronic paper display apparatus. 
       FIG.  1    is a schematic view of a flexible electronic paper display apparatus according to an embodiment of the disclosure. Referring to  FIG.  1   , a flexible electronic paper display apparatus  100  of this embodiment includes a display driver  110  and a flexible electronic paper display panel  120 . The display driver  110  is coupled to the flexible electronic paper display panel  120 . The display driver  110  outputs a driving signal S 1  to drive the flexible electronic paper display panel  120  to display an image frame. The flexible electronic paper display apparatus  100  may be a color electronic paper display apparatus or a black-and-white electronic paper display apparatus, which is not specifically limited herein. Therefore, the image frame displayed by the flexible electronic paper display panel  120  may include a color image or a gray level image, the image content is determined by an image data S 2  inputted to the display driver  110 , and may include plain text content or other non-text content. The flexible electronic paper display apparatus  100  of the embodiment of the disclosure may also be a flexible organic light-emitting diode display apparatus or other flexible display apparatuses. 
       FIG.  2    is a schematic view showing a state change of the flexible electronic paper display apparatus and the corresponding displayed frames according to an embodiment of the disclosure. Referring to  FIG.  1    and  FIG.  2   , the state change of the flexible electronic paper display apparatus  100  may include a change from an unfolding state (first state) S 100  to a folding state (second state) S 110 , then a change from the folding state S 110  back to an unfolding state S 120 . Correspondingly, the frames displayed by the flexible electronic paper display panel  120  are respectively an image frame M 100 , a standby frame M 110 , and an image frame M 120 . 
     The unfolding states S 100  and S 120  are a state in which a user is using the flexible electronic paper display apparatus for reading or viewing, so the unfolding states S 100  and S 120  may also be a slightly folding state, i.e., a first state which may allow normal use for reading or viewing. In the unfolding states S 100  and S 120 , the flexible electronic paper display panel  120  may be set to a flat, unfolded, or unrolled state. In the unfolding states S 100  and S 120 , the display driver  110  drives the flexible electronic paper display panel  120  by at least one of a plurality of gray levels to respectively display the image frames M 100  and M 120 . The image content of the image frames M 100  and M 120  may be the same or different, is determined by the image data S 2  inputted to the display driver  110 , and may include plain text content or other non-text content. The gray level range for driving the flexible electronic paper display panel  120  may be a gray level range of gray levels 0 to 15, 0 to 127, or 0 to 255. However, the disclosure is not limited to the above gray level ranges. 
     On the other hand, the folding state S 110  is a state in which the user is not using the flexible electronic paper display apparatus  100 , e.g., in a storage state, and the flexible electronic paper display apparatus  100  is in a standby state. In the folding state S 110 , the flexible electronic paper display panel  120  may be set to an uneven, folded, or rolled state. In the folding state S 110 , the display driver  110  drives the flexible electronic paper display panel  120  by a predetermined gray level to display the standby frame M 110 . The display driver  110  determines the predetermined gray level according to the gray levels 0 to 15, 0 to 127, or 0 to 255. The standby frame M 110  may be a gray frame with the same one gray level. Alternatively, the standby frame M 110  may include a dot pattern. 
       FIG.  3    is a flowchart showing steps of a driving method of a display apparatus according to an embodiment of the disclosure. Referring to  FIG.  1    and  FIG.  3   , the driving method of this embodiment is applicable to the display apparatus  100  of  FIG.  1   , for example. In step S 200 , in a first state, the display driver  110  drives the display panel  120  by at least one of a plurality of gray levels to display an image frame. In step S 210 , the display driver  110  determines a predetermined gray level according to the gray level. In step S 220 , in a second state, the display driver  110  drives the display panel  120  by the determined predetermined gray level to display a standby frame. 
     In addition, the driving method of the display apparatus of this embodiment may be sufficient taught, suggested, and described by the descriptions of the embodiment in  FIG.  1    to  FIG.  2   . 
     In the embodiments of  FIG.  1    to  FIG.  3   , the display driver  110  determines the predetermined gray level of the standby frame according to the gray level of the image frame. The following describes the different embodiments of determining the predetermined gray level of the standby frame. 
     First Embodiment 
     In the unfolding state, the display driver  110  drives the flexible electronic paper display panel  120  by gray levels 0 to 15, for example, to display the image frame. In this embodiment, in the folding state, the display driver  110  may select a first gray level 7 or a second gray level 8 to drive the flexible electronic paper display panel  120  to display the standby frame. In other words, the predetermined gray level is selected from the first gray level 7 or the second gray level 8, and the gray levels 0 to 15 include the first gray level 7 and the second gray level 8. The arithmetic mean “7.5” of the first gray level 7 and the second gray level 8 is the median of the gray levels 0 to 15. 
       FIG.  4    is a diagram showing the relationship between a fatigue cycle and gray level decay of a flexible electronic paper display apparatus according to an embodiment of the disclosure. Referring to  FIG.  4   , the vertical axis of  FIG.  4    indicates that the gray levels used to drive the flexible electronic paper display panel  120  to display the image frame are 0 to 15, and the predetermined gray level used to drive the flexible electronic paper display panel  120  to display the standby frame is, for example, 8. The horizontal axis of  FIG.  4    indicates the times of mechanical fatigue (i.e., fatigue cycle) experienced by the flexible electronic paper display apparatus  100  during repeated folding or rolling, which are respectively fifty thousand times (50k), one hundred thousand times (100k), and two hundred thousand times (200k). 
     In this embodiment, the 16-gray-level black-and-white flexible electronic paper display apparatus  100  uses a frame of the predetermined gray level 8 as the standby frame in the folding state. Therefore, the standby frame is a gray frame with the same one gray level. In this embodiment, the gray level 0 is defined as a black frame, and the gray level 15 is defined as a white frame. In an embodiment, a frame of the predetermined gray level 7 may also be used as the standby frame in the folding state. When the flexible electronic paper display apparatus  100  is subjected to the mechanical fatigue effect during repeated folding or rolling so that the performance of the flexible electronic paper display panel  120  decays and the driving capacity thus decreases, the performance decay is as shown by a curve  300 . Since the standby frame of the flexible electronic paper display apparatus  100  is a frame of the gray level 8, the maximum gray level difference from a black image frame (gray level 0) or a white image frame (gray level 15) is 7 to 8 gray levels. With the maximum gray level difference between the standby frame and the image frame being within 7 to 8 gray levels, it is possible to prevent the human visual perception from perceiving the disuniformity of the image frame in the unfolding state, and thus it is possible to provide a good user experience. In other words, when the display is in a folding or rolling state, it is on standby with a specific frame. After the performance of the electronic paper ink decays due to the mechanical fatigue effect, with the specific standby frame, the difference from the surrounding display elements is small, and it is difficult for the human eye to determine the difference. Therefore, it is possible to prevent the human visual perception from perceiving the disuniformity of the image frame in the unfolding state. 
     For example, the mechanical strength of the ink in the electronic ink layer exhibits a certain Gaussian distribution during the manufacturing process. Therefore, in a bending region, most of the electronic paper ink which is subjected to the fatigue effect but has driving capacity not yet impaired can be normally driven to the gray level 15 when driving for a white frame. In the bending region, a small part of the electronic paper ink which has decayed due to the fatigue effect can only be driven to the gray level 14 when driving for a white frame. Therefore, compared with the adjacent unimpaired electronic ink, there is a difference of only one gray level. Moreover, since its quantity is much smaller than that of the unimpaired electronic paper ink, it is possible to prevent the human visual perception from perceiving the disuniformity of the frame. The same also applies to the opposite scenario. When the electronic ink in the bending region is driven for a black frame, there is a difference of only one gray level between most of the electronic paper ink which is subjected to the fatigue effect but has driving capacity not yet impaired, and a small part of the adjacent electronic paper ink whose driving capacity has decayed due to the fatigue effect. Therefore, it is possible to prevent the human visual perception from perceiving the disuniformity of the frame. In an embodiment, a 128-gray-level black-and-white flexible electronic paper display apparatus  100  uses, for example, a frame of a predetermined gray level 63 or 64 as the standby frame in the folding state. In another embodiment, a 256-gray-level black-and-white flexible electronic paper display apparatus  100  uses, for example, a frame of a predetermined gray level 127 or 128 as the standby frame in the folding state. 
     Second Embodiment 
     In this embodiment, taking the 16-gray-level black-and-white flexible electronic paper display apparatus  100  as an example, when the use context of the flexible electronic paper display apparatus  100  is a dark background, the predetermined gray level of the standby frame of the flexible electronic paper display apparatus  100  in the folding state may be set to one of 0 to 8. For example, in the unfolding state, the display driver  110  drives the flexible electronic paper display panel  120  by the lowest gray level 0 to display the background part of the image frame (i.e., the gray level of the background part of the image frame is 0). In the folding state, the gray level of the standby frame may also be set to 0. Therefore, when the use context of the flexible electronic paper display apparatus  100  is a dark background, the predetermined gray level is greater than or equal to the lowest gray level 0, and the predetermined gray level is less than the second gray level 8. 
     In another embodiment, the predetermined gray level of the standby frame of the flexible electronic paper display apparatus  100  in the folding state may be set to one of 0 to 7. Therefore, when the use context of the flexible electronic paper display apparatus  100  is a dark background, the predetermined gray level is greater than or equal to the lowest gray level 0, and the predetermined gray level is less than the first gray level 7. 
     On the other hand, in this embodiment, when the use context of the flexible electronic paper display apparatus  100  is a light-color background, the predetermined gray level of the standby frame of the flexible electronic paper display apparatus  100  in the folding state may be set to one of 7 to 15. For example, in the unfolding state, the display driver  110  drives the flexible electronic paper display panel  120  by the highest gray level 15 to display the background part of the image frame (i.e., the gray level of the background part of the image frame is 15). In the folding state, the gray level of the standby frame may also be set to 15. Therefore, when the use context of the flexible electronic paper display apparatus  100  is a light-color background, the predetermined gray level is less than or equal to the highest gray level 15, and the predetermined gray level is greater than the first gray level 7. 
     In another embodiment, the predetermined gray level of the standby frame of the flexible electronic paper display apparatus  100  in the folding state may be set to one of 8 to 15. Therefore, when the use context of the flexible electronic paper display apparatus  100  is a light-color background, the predetermined gray level is less than or equal to the highest gray level 0, and the predetermined gray level is greater than the second gray level 8. 
     Third Embodiment 
     In this embodiment, the display driver  110  calculates a gray level average of each pixel on the flexible electronic paper display panel  120 , and determines the predetermined gray level according to the gray level average of each pixel. In other words, the display driver  110  counts the gray level or color displayed by each pixel during the use process according to the use condition of the flexible electronic paper display apparatus  100 , and calculates an average of the gray level displayed by each pixel to set this gray level average as the predetermined gray level of the standby frame. 
     For example, taking the 16-gray-level black-and-white flexible electronic paper display apparatus  100  as an example, in the application of an e-book reader, in the unfolding state, the peripheral region of the image frame mainly displays a white background, and the middle region mainly displays black texts on a white background. Therefore, in the folding state, the predetermined gray level of the peripheral region of the standby frame may be set to 15, and the predetermined gray level of the middle region may be set to 6 to 9. 
     Fourth Embodiment 
       FIG.  5    is a schematic view showing a standby frame including a dot pattern according to an embodiment of the disclosure. Referring to  FIG.  5   , the standby frame M 110  in this embodiment includes a dot pattern  400 . The dot pattern  400  includes a plurality of pixel blocks  410  and  420 . Each pixel block includes at least one pixel. For example, each pixel block includes 1 to 5 pixels. In this embodiment, the display driver  110  drives a part of the pixel blocks by a predetermined gray level to display the standby frame M 110 . For example, taking the 16-gray-level black-and-white flexible electronic paper display apparatus  100  as an example, the display driver  110  drives the pixel blocks  410  by a predetermined gray level 0 to display the darker blocks in the standby frame M 110 . The pixel blocks  410  driven by the predetermined gray level 0 are not adjacent to each other in the horizontal direction and the vertical direction. Similarly, the display driver  110  drives the pixel blocks  420  by a predetermined gray level 15 to display the lighter-color blocks in the standby frame M 110 . The pixel blocks  420  driven by the predetermined gray level 15 are not adjacent to each other in the horizontal direction and the vertical direction. Therefore, the pixel blocks  410  and  420  are evenly distributed on the standby frame M 110  to form the dot pattern  400 . 
     In this embodiment, since the flexible electronic paper display panel  120  is driven by the evenly distributed pixel blocks  410  and  420  as the standby frame M 110  in the folding state, even if the performance of the flexible electronic paper display panel  120  decreases due to the mechanical fatigue effect, the user&#39;s perception of disuniformity of the image frame in the unfolding state decreases, and thus a good user experience can be provided. For example, in the dot-patterned standby frame, there is respectively half probability for the electronic ink which is potentially impaired due to the fatigue effect to be distributed in the black pixel regions and in the white pixel regions. Therefore, the disuniformity of the image frame perceived by the user in normal use is half of that in the case of using a standby frame of the gray level 15 or the gray level 0. 
     Fifth Embodiment 
     Taking a color flexible electronic paper display apparatus as an example, the display driver  110  drives the flexible electronic paper display panel  120  by a light-gray gray level to display the standby frame in the folding state. In the gray level range of 0 to 15, the light-gray gray level is a gray level greater than 8. In the gray level range of 0 to 255, the light-gray gray level is a gray level greater than 128. 
     When the performance of the flexible electronic paper display panel  120  decreases due to the mechanical fatigue effect, the light-gray failed pixels may be easily rendered by the surrounding normal pixels, so that the user&#39;s perception of disuniformity of the image frame in the unfolding state is also reduced. For example, the human perception of color is limited by the effects of chromatic adaptation, luminance, the object area, etc. In terms of chromatic adaptation, white is most likely affected by surrounding colors. For example, when a small white dot is surrounded by red color, the human eye will determine it as lighter red instead of a white dot and multiple red dots, which is namely the rendering effect. In terms of luminance, when the luminance is insufficient, the human eye cannot perceive its existence. Therefore, light gray reduces the luminance and makes it less perceivable when the pixels gradually fail. In terms of the object area, when the object area is extremely small, the human eye cannot perceive the existence of the failed pixels. 
     Therefore, the display driver  110  may determine the predetermined gray level according to at least one method among the first embodiment to the fifth embodiment, but the disclosure is not limited to the above five methods. 
     In summary of the above, in the embodiments of the disclosure, the display driver determines the predetermined gray level according to the gray level of the image frame. In the folding state, the display driver drives the flexible electronic paper display panel by the determined predetermined gray level to display the standby frame. Accordingly, it is possible to prevent the user from perceiving the disuniformity of the image frame in the unfolding state. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.