Patent Publication Number: US-9412318-B2

Title: Display device for adjusting gray-level of image frame depending on environment illumination

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a Divisional of co-pending application Ser. No. 13/204,880, filed on Aug. 8, 2011, for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 100113770 filed in Taiwan, R.O.C. on Apr. 20, 2011 under 35 U.S.C. §119, the entire contents of all of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This disclosure relates to a display device reflecting ambient light, and in particular, to a display device and a method for adjusting a gray-level of an image frame depending on environment illumination. 
     2. Related Art 
     When environment illumination varies, a backlight brightness of a display device with an active backlight module, such as a liquid crystal display device, can be adjusted so that the brightness of image frame suits the environment illumination. In this way, the brightness of the image frame can be adjusted to the most suitable visual state for a user. For example, in ROC Invention Patent No. I336458 and ROC Invention Patent Publication No. TW201020606, technical features for adjusting a brightness of a display depending on environment illumination are proposed. 
     However, a display device reflecting ambient light, such as an electrophoretic display (e-paper), or a reflective liquid crystal display, reflects the ambient light to make image frame become visible. It is difficult for a display device reflecting ambient light to change the brightness of the external ambient light, and the display device reflecting ambient light can only reflect the ambient light passively. 
     Further, since the ambient light is reflected by the display device, the brightness of the reflected light is also affected by the displayed image frame. For example, under the illumination of ambient light with high brightness, if the displayed image frame has large blocks of low gray-level pixels, the brightness of the reflected light is high, so that the user feels dazzling when viewing the displayed image frame; similarly, under the irradiation of ambient light with high brightness, if the displayed image frame has large blocks of high gray-level pixels, the brightness of the reflected light generated after the ambient light is reflected is reduced, so that the user feels comfortable when viewing the display image frame. 
     Conversely, if the environment illumination is low and the display image frame has large blocks of high gray-level pixels, the brightness of the reflected light generated after the display-panel reflects the ambient light is reduced, so that the user cannot view the content of the display image frame clearly. Similarly, when the environment illumination is low, if the display image frame has large blocks of low gray-level pixels, the display-panel can still provide the relatively high brightness of the reflected light, so that the user views the display image frame clearly. 
     However, the environment illumination is an external factor and cannot be easily adjusted by the user or the display device, so that the visual effect of the display device reflecting the ambient light is easily affected by environment illumination. 
     SUMMARY 
     In the related art, the visual effect of the display device reflecting the ambient light is easily affected by the environment illumination, and the environment illumination is the external factor and cannot be controlled by the display device reflecting the ambient light. Embodiments of this disclosure are directed to a display device and a method for adjusting a gray-level of an image frame depending on environment illumination, capable of enhancing the visual effect by adjusting gray-levels of partial or all pixels. 
     One or more embodiment of this disclosure provides a display device for adjusting a gray-level of an image frame depending on environment illumination. The display device includes a display-panel, an optical-sensor, a controller, and an adjusting module. The display-panel is used to display an image frame with a plurality of pixels. The optical-sensor is used to obtain the environment illumination. The controller is used to drive the display-panel to display the image frame. The adjusting module is used to adjust gray-levels of partial or all pixels in the image frame according to the environment illumination. 
     A reference illumination range is designated to the adjusting module, and the adjusting module determines whether the environment illumination is within the reference illumination range. When the environment illumination is higher than the reference illumination range, the adjusting module raises the gray-levels of partial or all pixels in the image frame according to the environment illumination, so that the image frame viewed by a user becomes dim. When the environment illumination is lower than the reference illumination range, the adjusting module reduces the gray-levels of partial or all pixels in the image frame, so that the image frame viewed by the user becomes bright. 
     This disclosure further provides a method for adjusting a gray-level of an image frame depending on environment illumination, which is used to adjust the gray-level of at least one partial image frame in the image frame, in which the partial image frame has a plurality of pixels. 
     According to this method, firstly the environment illumination is obtained; and the a reference illumination range is set to determine whether the environment illumination is higher than the reference illumination range or is lower than the reference illumination range. 
     If the environment illumination is higher than the reference illumination range, gray-levels of partial or all pixels in the partial image frame are raised according to the environment illumination, and the adjusted image frame is displayed, so that the image frame viewed by the user becomes dim. 
     If the environment illumination is lower than the reference illumination range, the gray-levels of partial or all pixels in the partial image frame are reduced according to the environment illumination, and the adjusted image frame is displayed, so that the image frame viewed by the user becomes bright. 
     In this manner, no matter how the environment illumination varies, when the display-panel displays an image frame the user always experiences the suitable gray-level of the image frame, so as to improve the visual effect for the user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a circuit block diagram according to an embodiment; 
         FIG. 2  is a schematic diagram of a reference illumination range according to the embodiment; 
         FIG. 3  is a flow chart of a method for adjusting a gray-level of an image frame depending on environment illumination according to the embodiment; 
         FIG. 4A  and  FIG. 4B  are schematic diagrams of increasing gray-levels of partial or all pixels in an image frame according to the embodiment; 
         FIG. 5  is a flow chart of increasing gray-levels of partial or all pixels in an image frame according to the embodiment; 
         FIG. 6A  and  FIG. 6B  are schematic diagrams of reducing gray-levels of partial or all pixels in an image frame according to the embodiment; 
         FIG. 7  is a flow chart of reducing gray-levels of partial or all pixels in an image frame according to the embodiment; 
         FIG. 8  is a schematic diagram of a gray-level median interval according to the embodiment; 
         FIG. 9A  and  FIG. 9B  are schematic diagrams of performing an image inverse process on an image frame according to the embodiment; 
         FIG. 10  and  FIG. 11  are flow charts of performing an image inverse process on an image frame according to the embodiment; and 
         FIG. 12  is a circuit block diagram according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 , in which an embodiment of this disclosure provides a display device  100  for adjusting a gray-level of an image frame depending on environment illumination, which executes a method for adjusting a gray-level of an image frame depending on environment illumination. The display device  100  includes a display-panel  110 , an optical-sensor  120 , a controller  130 , a memory module  140 , and an adjusting module  150 . 
     As in  FIG. 1 , the display-panel  110  displays an image frame with a plurality of pixels. The display-panel  110  is a display-panel reflecting the ambient light, and allows a user to view a displayed image frame in a manner of reflecting the ambient light. Examples of the display-panel  110  include, but are not limited to, an electrophoretic display-panel, a reflective liquid crystal display-panel, etc. 
     As shown in  FIG. 1 , the optical-sensor  120  is used to detect the ambient light, so as to obtain the environment illumination. The optical-sensor  120  transforms the environment illumination to a brightness value signal, and sends the brightness value signal to the controller  130  or the adjusting module  150 , so that the controller  130  or the adjusting module  150  obtains the environment illumination from the optical-sensor  120 . 
     In order to enable the environment illumination obtained by the optical-sensor  120  to approach the environment illumination actually irradiating on the display-panel  110 , a preferred position of the optical-sensor  120  is close to the display-panel  110 , and the optical-sensor  120  and the display-panel  110  are located on the same side surface of the display device  100 ; for example, the optical-sensor  120  and the display-panel  110  are disposed on a front bezel of the display device  100 . 
     As shown in  FIG. 1 , the display-panel  110  and the optical-sensor  120  are electrically connected to the controller  130 . The controller  130  receives the environment illumination obtained by the optical-sensor  120 , and generates an image frame to drive the display-panel  110  to display the image frame. 
     As in  FIG. 1 , the memory module  140  is electrically connected to the controller  130  for storing operating systems, application programs, data, and image files. An example of the memory module  140  is, but not limited to, a flash memory, a magnetic disk, a random access memory, or a combination of the preceding storage devices. 
     An example of the adjusting module  150  is an independent electronic device electrically connected to the controller  130 ; an alternative example of the adjusting module  150  is a program code stored in the memory module  140 , and loaded and executed by the controller  130 . 
     As shown in  FIG. 1 , the adjusting module  150  obtains the environment illumination, and adjusts gray-levels of partial or all pixels in an image frame according to the environment illumination, so as to change the brightness of the image frame viewed by the user. 
     In the present embodiment, the adjusting module  150  achieved by that the controller  130  loads the program code. After the display device  100  is turned on, the controller  130  loads the program code serving as the adjusting module  150  from the memory module  140  and executes the program code, so that the controller  130  additionally has a function of the adjusting module  150 . 
     A gray-level variation range of each pixel forming the image frame is N scales of gray-levels. N is an integer; the 1st scale of gray-level is the lowest gray-level, which provides a white or bright visual effect for the user; and the Nth scale of gray-level is the highest, which provides a visual effect for the user which is either dim or black. Generally, N is 4, 8, 16, or 32, but is not limited to these numbers. 
     As shown in  FIG. 2 , a reference illumination range is designated to the adjusting module  150 , for use as a reference standard to determine whether the environment illumination is normal, too bright, or too dim. When the environment illumination is within the reference illumination range, the environment illumination is determined as normal, and the gray-level of the image frame is not required to be adjusted. When the environment illumination is outside the reference illumination range and is higher than the reference illumination range, the environment illumination is determined as too bright; when the environment illumination is outside the reference illumination range and is lower than the reference illumination range, the environment illumination is determined as too dim. When the environment illumination is too bright or too dim, the gray-level of the image frame has to be adjusted, so as to improve the visual effect for the user. 
     Please refer to  FIG. 1  to  FIG. 3 , in which an embodiment of the present disclosure provides a method for adjusting a gray-level of an image frame depending on environment illumination, which is used to adjust the gray-level of at least one partial image frame in the image frame, in which the partial image frame has a plurality of pixels. 
     As shown in  FIG. 1  and  FIG. 3 , after the optical-sensor  120  detects the environment illumination, the adjusting module  150  obtains the environment illumination through the optical-sensor  120 , as shown in Step  110 . 
     Then, the adjusting module  150  determines whether the obtained environment illumination is within the reference illumination range, so as to determine whether to adjust the gray-level of the image frame. 
     Determining process are that a reference illumination range is designated to the adjusting module  150 , and the adjusting module  150  determines whether the environment illumination is higher than the reference illumination range, so as to determine whether the environment illumination is too bright, as shown in Step  120 . 
     Then, the adjusting module  150  determines whether the environment illumination is lower than the reference illumination range, so as to determine whether the environment illumination is too dim, as shown in Step  130 . 
     The sequence of the preceding Step  120  and Step  130  is not limited to the preceding description; Step  120  and Step  130  are mainly used to determine whether the environment illumination is within the reference illumination range and to determine whether the environment illumination is higher than or lower than the reference illumination range; therefore, the sequence of implementing the two steps is not limited to the preceding description. 
     If the environment illumination is neither not higher than nor lower than the reference illumination range, the environment illumination is within the reference illumination range. At this time, the adjusting module  150  does not adjust the gray-level of the image frame, and the controller  130  directly drives the display-panel  110  to display the image frame, as shown in Step  140 ; and the controller  130  returns to Step  110 , so as to obtain the environment illumination again. 
     When the environment illumination is higher than the reference illumination range, the adjusting module  150  determines that the environment illumination is too bright. At this time, the adjusting module  150  raises the gray-levels of partial or all pixels in the image frame according to the environment illumination, as shown in Step  150 . The controller  130  drives the display-panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . As the gray-levels of partial or all pixels in the image frame are raised, the luminance of ambient light reflected by the display-panel is reduced, so that the image frame viewed by the user becomes dim, thereby avoiding the influence of the over-bright image frame on the visual effect. 
     To adjust the gray-levels of partial pixels or to adjust the all pixels in the image frame is determined to types of display content of the image frame. When the display content of the image frame is text data, since the adjustment of the gray-levels of the pixels has little influence on the reading of the text data, the adjusting module  150  adjusts the gray-levels of all pixels in the image frame according to the environment illumination. When the display content of the image frame is text data and graphs, since the adjustment of the gray-levels of the pixels has a great influence on the graphs, the adjusting module  150  adjusts the gray-levels of partial pixels corresponding to the text data in the image frame, but does not adjust the gray-levels of the pixels of the graphs. In another scenario, the gray-levels of the some adjusted pixels reach an upper limit value or a lower limit value, and cannot be raised or reduced any more, at this time, the adjusting module  150  does not adjust the gray-levels of the pixels, so that the gray-levels of only partial pixels are adjusted by the adjusting module  150 . 
     When the environment illumination is lower than the reference illumination range, the adjusting module  150  determines that the environment illumination is too dim. At this time, the adjusting module  150  reduces the gray-levels of partial or all pixels in the image frame according to the environment illumination, as shown in Step  170 . The controller  130  drives the display-panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . As the gray-levels of partial or all pixels in the image frame are reduced, the luminance of ambient light reflected by the display-panel is raised, so that the image frame viewed by the user becomes bright, thereby avoiding the influence of the overly dim image frame on the visual effect. 
     In this manner, no matter how the environment illumination varies, when the display-panel  110  displays an image frame the user always experiences the suitable gray-level of the image frame, so as to improve the visual effect for the user. 
     The preceding adjustment of the gray-level of the image frame is not limited to adjusting the whole image frame. In the preceding steps, the adjustment of the gray-level is performed on the partial image frame; that is to say, whether to adjust the gray-level of each pixel is determined only within the partial image frame. The partial image frame is a part of the image frame, and can also be expanded to the whole image frame. 
     The details of Step  150  are further described as follows. 
     Please refer to  FIG. 4A  and  FIG. 5 , when the environment illumination is higher than the reference illumination range, the adjusting module  150  raises the gray-levels of partial or all pixels, so as to generate the adjusted image frame. 
     In order to enable the image frame viewed by the user to become dim, the adjusting module  150  determines a first gray-level Y according to the environment illumination to serve as the lowest gray-level in the adjusted image frame, as shown in Step  151 . 
     Next, the adjusting module  150  determines a gray-level added value A required when the lowest gray-level i is adjusted to the first gray-level Y in the image frame, as shown in Step  152 . 
     Afterwards, the adjusting module  150  adds the gray-level added value A to the gray-level of each pixel in the image frame, as shown in Step  153 . 
     The adjusting module  150  then determines whether the highest gray-level A+j in the adjusted image frame is higher than the Nth scale of gray-level, that is to say, whether the highest gray-level A+j in the adjusted image frame is outside the gray-level variation range of the image frame, as shown in Step  154 . 
     If the adjusted highest gray-level A+j is within the gray-level variation range of the image frame, the gray-level values of all pixels are increased. The adjusting module  150  generates the adjusted image frame according to an adjustment result, as shown in Step  155 ; the controller  130  then drives the display panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     The preceding adjustment result is shown in  FIG. 4A , in which an adjustment method is that the gray-level value of each pixel in the image frame is panned, as shown in  FIG. 4A , the gray-level value is panned to the right, so that the gray-level value of each pixel is increased. 
     As shown in  FIG. 4B  and  FIG. 5 , if the highest gray-level A+j in the adjusted image frame is outside the gray-level variation range of the image frame, the adjusting module  150  adjusts the highest gray-level A+j in the adjusted image frame to the Nth scale of gray-level (the upper limit of the gray-level variation range), so as to reduce the gray-level variation range, as shown in Step  156 . The adjusting module  150  performs linear adjustment on the gray-level of each pixel in the image frame, so as to map each gray-level to the reduced gray-level variation range, as shown in Step  157 . At this time, only the gray-levels of partial pixels are raised; the pixel with the original gray-level being close to the Nth scale of gray-level are not required to be adjusted. The adjusting module  150  generates the adjusted image frame within the reduced gray-level variation range; and then the controller  130  drives the display-panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     The details of Step  170  are further described as follows. 
     Please refer to  FIG. 6A  and  FIG. 7 , when the environment illumination is lower than the reference illumination range, the adjusting module  150  reduces the gray-level of each pixel, so as to generate the adjusted image frame. 
     In order to enable the image frame viewed by the user to become bright, the adjusting module  150  determines a second gray-level X, according to the environment illumination, as the highest gray-level in the adjusted image frame, as shown in Step  171 . 
     Next, the adjusting module  150  determines a gray-level reduced value M required when the highest gray-level j is adjusted to the second gray-level X in the image frame, as shown in Step  172 . 
     Afterwards, the adjusting module  150  subtracts the gray-level reduced value M from the gray-level of each pixel in the image frame, as shown in Step  173 . 
     Then, the adjusting module  150  determines whether the lowest gray-level in the adjusted image frame i-M is lower than the 1st scale of gray-level, that is to say, whether the lowest gray-level in the adjusted image frame i-M is outside the gray-level variation range of the image frame, as shown in Step  174 . 
     If the lowest gray-level in the adjusted image frame i-M is within the gray-level variation range of the image frame, the gray-levels of all pixels are reduced. The adjusting module  150  generates the adjusted image frame according to the adjustment result, as shown in Step  175 ; the controller  130  then drives the display-panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     The adjustment result is shown in  FIG. 6A , in which an adjustment method is that the gray-level of each pixel in the image frame is panned, as shown in  FIG. 6A , the gray-level is panned to the left, so that the gray-level of each pixel is reduced. 
     As shown in  FIG. 6B  and  FIG. 7 , if the lowest gray-level in the adjusted image frame i-M is outside the gray-level variation range of the image frame, the adjusting module  150  adjusts the lowest gray-level in the adjusted image frame i-M to the 1st scale of gray-level (the lower limit of gray-level variation range), so as to reduce the gray-level variation range, as shown in Step  176 . The adjusting module  150  performs linear adjustment on the gray-level of each pixel in the image frame, so as to map each gray-level to the reduced gray-level variation range, as shown in Step  177 . At this time, only the gray-levels of partial pixels are reduced, the pixel with the original gray-level being close to the 1st scale of gray-level are not required to be adjusted. The adjusting module  150  generates the adjusted image frame within the reduced gray-level variation range; and then the controller  130  drives the display-panel  110  using the adjusted image frame, the controller  130  then drives the display-panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     In addition, when the user feels that an image frame is too dim or too bright, and increasing or reducing the gray-level still cannot enable the user to view the image frame clearly, Step  150  and Step  170  can be modified as follows. 
     As shown in  FIG. 8 , a gray-level median interval is further designated to the adjusting module  150 . The gray-level median interval is between the 1st scale of gray-level and the Nth scale of gray-level. When an average gray-level of the image frame is lower than the gray-level median interval, the image frame is defined as a white image frame; when the average gray-level of the image frame is higher than the gray-level median interval, the image frame is defined as a black image frame; and when the average gray-level of an image frame is within the gray-level median interval, the image frame is defined as a normal image frame. The gray-level median interval may be a single gray-level or a combination of a plurality of consecutive gray-levels. 
     Please refer to  FIG. 9A  and  FIG. 10 , when the environment illumination is higher than the reference illumination range, the adjusting module  150  further determines whether the average gray-level of the image frame is lower than the gray-level median interval (whether the image frame is a white image frame), as shown in Step  150   a.    
     If the average gray-level of the image frame is not lower than the gray-level median interval, the adjusting module  150  executes the adjustment process as shown in Step  151  to Step  157 . 
     If the brightness of ambient light is higher than the reference brightness interval, and at the same time, the average gray-level value of the image frame is lower than the gray-level median interval (the image frame is too white), the adjusting module  150  performs an inverse process on the image frame, so as to generate the adjusted image frame, as shown in Step  150   b.    
     As shown in  FIG. 9A , during the operation of the image inverse process, the adjusting module  150  defines each gray-level value as a complement of N+1, and obtains the adjusted gray-level value, so as to generate the adjusted image frame; for example, the original gray-level values of the pixels are distributed between the ith scale and the jth scale, but after the image inverse process, the ith scale becomes the (N−j+1)th scale and the j scale becomes the (N−i+1)th scale. Then, the controller  130  drives the display panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     Please refer to  FIG. 9B  and  FIG. 11 , when the environment illumination is lower than the reference illumination range, the adjusting module  150  further determines whether the average gray-level of the image frame is higher than the gray-level median interval (the image frame is too black). If the average gray-level of the image frame is not higher than the gray-level median interval, the adjusting module  150  executes the adjustment operation as shown in Step  171  to Step  177 . 
     If the brightness of ambient light is lower than the reference brightness interval, and at the same time the average gray-level value of the image frame is higher than the gray-level median interval (the image frame is too black), the adjusting module  150  performs the image inverse process on the image frame, so as to generate the adjusted image frame, as shown in Step  170   b . As shown in  FIG. 9B , during the operation of the image inverse process the adjusting module  150  defines each gray-level value as the complement of N+1, makes the ith scale become the (N−j+1)th scale and the j scale become the (N−i+1)th scale, and obtains the adjusted gray-level value, so as to generate the adjusted image frame; and then the controller  130  drives the display panel  110  using the adjusted image frame, so as to display the adjusted image frame, as shown in Step  160 . 
     In the embodiments described previously the display device  100  automatically loads the program code and executes the method for adjusting the gray-level of the image frame according to the environment illumination. However, the adjustment of the gray-level of the image frame may be executed manually. 
     As shown in  FIG. 12 , another embodiment of the present disclosure provides a display device  200  for adjusting a gray-level of an image frame depending on environment illumination. The display device  200  includes a display-panel  210 , a controller  230 , a memory module  240 , an adjusting module  250 , and an operation interface  260 . 
     The display-panel  210  displays an image frame with a plurality of pixels. The controller  230  is used to drive the display-panel  210  to display the image frame. 
     The operation interface  260  is operated by a user to send an image frame brightening command, an image frame dimming command, or an image inverse command to the controller  230 . 
     After receiving the image frame brightening command, the controller  230  starts the adjusting module  250  to reduce gray-levels of partial or all pixels, so as to generate the adjusted image frame. The controller  230  drives the display-panel  210  using the adjusted image frame, so as to display the adjusted image frame. 
     After receiving the image frame dimming command, the controller  230  starts the adjusting module  250 , to raise the gray-levels of partial or all pixels, so as to generate the adjusted image frame. The controller  230  drives the display-panel  210  using the adjusted image frame, so as to display the adjusted image frame. 
     After receiving the image inverse command, the controller  230  starts the adjusting module  250  to perform an image inverse process on the image frame, so as to generate the adjusted image frame. The controller  230  drives the display-panel  210  by the adjusted image frame, so as to display the adjusted image frame. 
     In addition, in the embodiments described previously the adjustment of the gray-level may be performed on the whole image frame or on the partial image frame. For example, in an image frame with both text data and graphs, the controller  130  first marks the partial image frame with the text data, and the adjusting module  150  then performs the adjustment of the gray-level on the partial image frame, but adjusting module  150  does not perform the adjustment of the gray-level on other parts of the image frame including the graphs. 
     While the present invention has been described by the way of example and in terms of the preferred embodiments, it is to be understood that the invention need not to be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.