Abstract:
In the case where a screen divided display is performed on a liquid crystal panel, a change in brightness or chromaticity between sub regions divided may be reduced. A display includes: a display panel; a backlight arranged corresponding to each of sub regions, and selectively illuminating the corresponding sub region, the sub regions being defined by dividing a display region of the display panel into a plurality of parts; a monitoring means for monitoring the light emission state of the backlight corresponding to each of the sub regions; and a display control means for determining a sub region on which an image is to be displayed, on the basis of the monitoring result of the monitoring means, to fit the image into the determined sub region, and controlling a backlight corresponding to the determined sub region to emit light.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present invention contains subject matter related to Japanese Patent Application JP 2007-104018 filed in the Japanese Patent Office on Apr. 11, 2007, the entire contents of which being incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a liquid crystal display displaying an image on a liquid crystal panel through the use of a backlight, and a display control method for the liquid crystal display. 
         [0004]    2. Description of the Related Art 
         [0005]    Large-screen liquid crystal televisions has steadily become popular at home according to advances in liquid crystal panel technology and cost reduction. In particular, in the case of watching a program such as a movie program or a sports program, a higher level of realism may be obtained with such a large-screen liquid crystal television. On the other hand, there is an issue that such a large-screen television consumes a large amount of power. Typically, the liquid crystal television uses a backlight for illuminating a liquid crystal panel, so when the size of the liquid crystal panel is increased, the power consumption of the backlight is increased accordingly. 
         [0006]    To overcome the issue, for example, Japanese Unexamined Patent Application Publication No. 2001-142409 discloses a technique in which driving of a light emission means is controlled in each of divided regions so that illuminating light is applied to at least a screen region which is necessary to be irradiated with the illuminating light in accordance with a video signal. According to the technique, it is possible not to apply the illuminating light to a screen region which is not necessary to be irradiated with the illuminating light, so the power consumption necessary for illumination may be reduced. 
         [0007]    In addition, Japanese Unexamined Patent Application Publication No. 2006-330222 discloses a technique in which a liquid crystal display screen is divided into a plurality of display areas, and time degradation in brightness of each display area is corrected. 
       SUMMARY OF THE INVENTION 
       [0008]    In contrast with categories such as a movie program or a sports program which are suitable to be watched with a large screen, TV programs include contents which are not necessarily watched with a large screen (for example, a news program, an educational program or the like). On the basis of the concept of Japanese Unexamined Patent Application Publication No. 2001-142409, a method in which in the case of contents of this kind, an image is downsized, and the downsized image is displayed on a part of a screen, and a backlight illuminating the other part is turned off is considered. Thereby, power consumption may be reduced. 
         [0009]    However, in this method, the cumulative value of the backlight lighting time in a screen region used for displaying the downsized image is different from that in the other screen region. As a result, light emission characteristics of a backlight for a region where the lighting time is long decline over time, compared to a backlight for a region where the lighting time is short, so degradation in image quality such as a decline in the brightness of an image or color unevenness occurs accordingly. 
         [0010]    In view of the foregoing, it is desirable to provide a liquid crystal display capable of reducing power consumption without time degradation in image quality by partial screen display through the use of a part of a large screen, and a display control method for the liquid crystal display. 
         [0011]    According to an embodiment of the invention, there is provided a display including: a display panel; a backlight arranged corresponding to each of sub regions, and selectively illuminating the corresponding sub region, the sub regions being defined by dividing a display region of the display panel into a plurality of parts; a monitoring means for monitoring the light emission state of the backlight corresponding to each of the sub regions; and a display control means for determining a sub region on which an image is to be displayed, on the basis of the monitoring result of the monitoring means, to fit the image into the determined sub region, and controlling a backlight corresponding to the determined sub region to emit light. 
         [0012]    According to an embodiment of the invention, there is provided a display control method for a display, the display including a display panel and a backlight arranged corresponding to each of sub regions and selectively illuminating the corresponding sub region, the sub region being defined by dividing a display region of the display panel into a plurality of parts, the method comprising the steps of: monitoring the light emission state of the backlight corresponding to each of the sub regions; and determining a sub region on which an image is to be displayed, on the basis of the monitoring result of the light emission state of the backlight, to fit the image into the determined sub region, and controlling a backlight corresponding to the determined sub region to emit light. 
         [0013]    In the display and the display control method for a display according to the embodiment of the invention, a sub region which is supposed to be used for image display is determined on the basis of the monitoring result of the light emission state of the backlight for each of the sub regions, and an image is fitted into the determined sub region, and a backlight corresponding to the determined sub region is controlled so as to emit light. Therefore, depending on the light emission state of the backlight, switching between the sub regions on which an image is displayed is able to be performed. 
         [0014]    In the display according to the embodiment of the invention, as a mode of monitoring the light emission state by the monitoring means, for example, a method of monitoring the cumulative light emission time of the backlight for each of the sub regions is considered. Time degradation in the backlight for each of the sub regions is able to be indirectly detected by the cumulative light emission time. Alternatively, a detecting means for detecting the brightness level of the backlight for each of the sub regions may be arranged so as to directly detect time degradation in the light emission state. 
         [0015]    In the display and the display control method for a display according to the embodiment of the invention, the light emission state of the backlight arranged corresponding to each of the sub regions is monitored, and a sub region on which an image is to be displayed is determined on the basis of the monitoring result, and the image is fitted into the determined sub region, and a backlight corresponding to the determined sub region emits light, so when partial drive display on the display panel is performed, the light emission characteristics of the backlight is able to be controlled so as to be uniform on the full screen. As a result, the power consumption by partial screen display may be reduced without time degradation in image quality. 
         [0016]    In particular, in the case where the cumulative light emission time of the backlight for each of the sub regions is monitored as a mode of monitoring the light emission state by the monitoring means, time degradation in the backlight for each of the sub regions is able to be indirectly detected through the use of the cumulative light emission time. In this case, it is not necessary to specifically arrange a brightness sensor, so an increase in the number of parts may be prevented. 
         [0017]    Moreover, in the case where a display switching operation from the current sub region to another sub region is performed in synchronization with an operation to the input section, the sense of discomfort associated with switching may be reduced. 
         [0018]    Further, in the case where a program determining means is arranged, and switches between the normal display mode and the downsized display mode depending on the category of a selected program on the basis of a program content determining result by the program determining means, mode switching may be automatically performed, so it is convenient for viewers. 
         [0019]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a block diagram showing the configuration of a liquid crystal display according to an embodiment of the invention; 
           [0021]      FIG. 2  is a flowchart for describing the operation of the liquid crystal display shown in  FIG. 1 ; 
           [0022]      FIGS. 3A ,  3 B and  3 C are illustrations showing examples of screen display in the liquid crystal display shown in  FIG. 1 ; 
           [0023]      FIG. 4  is a block diagram showing a modification of the liquid crystal display shown in  FIG. 1 ; and 
           [0024]      FIGS. 5A and 5B  are illustrations showing other examples of screen display in the liquid crystal display shown in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    A best mode for carrying out the invention (hereinafter simply referred to embodiment) will be described in detail below referring to the accompanying drawings. 
         [0026]      FIG. 1  schematically shows the configuration of a liquid crystal display according to an embodiment of the invention. A liquid crystal display  1  is configured as a television receiver, and includes a tuner  12  for channel tuning which is connected to an image receiving antenna  11 , a decoder  13  connected to the tuner  12 , and an IP converter  14  connected to the decoder  13 . The decoder  13  decodes an encoded signal selected by the tuner  12  to capture a video signal, an audio signal and associated data. The IP converter  14  converts the video signal which is an interlaced signal into a progressive signal (a non-interlaced signal). 
         [0027]    The liquid crystal display  1  further includes a scaler  15  connected to the IP converter  14 , a panel interface (I/F) section  16  connected to the scaler  15 , and a liquid crystal cell array  17  connected to the panel I/F section  16 . The scaler  15  is an image processor converting the video signal outputted from the IP converter  14  into a video signal in accordance with an actual display region (a sub region which will be described later or the whole region) in the liquid crystal cell array  17 . The panel I/F section  16  converts the video signal outputted from the scaler  15  into a signal which meets specifications of the liquid crystal cell array  17  to supply the signal to the liquid crystal cell array  17 . 
         [0028]    The liquid crystal display  1  further includes a control section  18  connected to the scaler  15 , a backlight driver (BL driver)  19  connected to the control section  18 , and a backlight  20  connected to the BL driver  19 . The control section  18  controls each block of the liquid crystal display  1 , and corresponds to a specific example of a monitoring means, a display control means and a mode switching means in the invention. The control section  18  monitors, for example, the cumulative light emission time of a backlight for each sub region which will be described later of the liquid crystal cell array  17 , or provides a scaling instruction which instructs the necessity or the kind of image scaling to the scaler  15 , or a backlight control instruction to the BL driver  19 . The control section  18  includes an IR receiver section  18 A receiving various IR (infrared ray) instructions provided from a remote control unit (remote control)  21 , and a memory  18 B storing various control data. As will be described later, data stored in the memory  18 B includes data showing the cumulative light emission time in each sub region of the backlight  20 . The IR receiver section  18 A corresponds to a specific example of an input section in the invention. 
         [0029]    The BL driver  19  includes an upper driver  19 A and a lower driver  19 B, and the backlight  20  includes an upper backlight  20 A and a lower backlight  20 B. The upper backlight  20 A is arranged corresponding to an upper half region of the liquid crystal cell array  17  on the back of the upper half region, and selectively illuminates the upper half region. On the other hand, the lower backlight  20 B is arranged corresponding to a lower half region of the liquid crystal cell array  17  on the back of the lower half region, and selectively illuminates the lower half region. The upper driver  19 A controls the light emission of the upper backlight  20 A, and the lower driver  19 B controls the light emission of the lower backlight  20 B. The upper backlight  20 A includes, for example, a plurality of CCFLs (cold cathode fluorescent tubes) which extend in a horizontal direction and are arranged in a vertical direction; however, instead of the CCFLs, the upper backlight  20 A may include, for example, a large number of LEDs (light-emitting diodes) arranged in a matrix form, or an organic EL (electro-luminescence) device. The lower backlight  20 B has the same configuration as that of the upper backlight  20 A. 
         [0030]    Next, referring to  FIG. 2 , the operation of the liquid crystal display  1  with the above-described configuration will be described below. 
         [0031]    The tuner  12  selects a signal of a channel from signals over airwaves received by the image receiving antenna  11  to input the signal into the decoder  13 . The decoder  13  decodes an encoded signal selected by the tuner  12  to capture a video signal, an audio signal and associated data. The video signal outputted from the decoder  13  is converted from an interlaced signal to a progressive signal by the IP converter  14 , and the video signal is inputted into the scaler  15 . 
         [0032]    The control section  18  monitors the light emission states of the upper backlight  20 A and the lower backlight  20 B to store the cumulative light emission time T U  of the upper backlight  20 A and the cumulative light emission time T L  of the lower backlight  20 B in the memory  18 B. The cumulative light emission time T U  is a cumulative value of the light emission time of the upper backlight  20 A from when the liquid crystal display  1  is manufactured to the current time, and the cumulative light emission time T L  is a cumulative value of the light emission time of the lower backlight  20 B from when the liquid crystal display  1  is manufactured to the current time. 
         [0033]    When a viewer (not shown) operates the remote control  21  to provide a mode selection instruction for selecting a display mode, the instruction is captured by the control section  18  through the IR receiver section  18 A. In the case where the mode selection instruction is to select a normal display mode (a full screen display mode) (step S 101 ), the control section  18  provides a full screen display instruction (step S 102 ). The upper driver  19 A and the lower driver  19 B of the BL driver  19  which receives the full screen display instruction turn the upper backlight  20 A and the lower backlight  20 B on, respectively to change into a full screen illumination state (step S 103 ). At the same time, the scaler  15  fits the video signal into the full screen of the liquid crystal cell array  17  (step S 104 ). Thereby, as shown in  FIG. 3A , an image is displayed on the full screen of the liquid crystal panel. Therefore, for example, in the case where a program to be watched is a movie program, a sports program or the like, dynamic and realistic images is possible to be watched. 
         [0034]    In the case where a program that a viewer is watching is a program which is not necessary to be displayed on a large screen such as a news program or an education program, and the mode selection instruction is to select a partial screen display mode (a downsized display mode) (step S 201 ), the control section  18  determines a difference between the cumulative light emission time T U  of the upper backlight  20 A and the cumulative light emission time T L  of the lower backlight  20 B with reference to the memory  18 B. As a result, if the cumulative light emission time T L  is longer than the cumulative light emission time T U , and the difference between them is larger than a predetermined threshold value T TL  (step S 202 ; Y), an upper-side display instruction is provided (step S 204 ). The upper driver  19 A of the BL driver  19  which receives the upper-side display instruction turns the upper backlight  20 A on to illuminate the upper-side sub region of the liquid crystal cell array  17  (step S 205 ), and the lower driver  19 B turns the lower backlight  20 B off. At the same time, the scaler  15  performs scaling (upper-side scaling) which downsizes an image so as to match the upper-side sub region, and fits the video signal into the upper-side sub region of the liquid crystal cell array  17  (step S 206 ). Thereby, as shown in  FIG. 3B , an image is displayed on the upper-side sub region of the liquid crystal panel. In this case, the lower backlight  20 B is turned off, so the power consumption may be saved. 
         [0035]    On the other hand, if the cumulative light emission time T U  is longer than the cumulative light emission time T L , and the difference between them is larger than the threshold value T TL  (step S 202 ; N, step S 203 ; Y), a lower-side display instruction is provided (step S 207 ). The lower driver  19 B of the BL driver  19  which receives the lower-side display instruction turns the lower backlight  20 B on to illuminate a lower-side sub region of the liquid crystal cell array  17  (step S 208 ), and the upper driver  19 A turns the upper backlight  20 A off. At the same time, the scaler  15  performs scaling (lower-side scaling) which downsizes an image so as to match the lower-side sub region, and fits the video signal into the lower-side sub region of the liquid crystal cell array  17  (step S 209 ). Thereby, as shown in  FIG. 3C , an image is displayed on the lower-side sub region of the liquid crystal panel. In this case, the upper backlight  20 A is turned off, so the power consumption may be saved. 
         [0036]    When the difference between the cumulative light emission time T U  and the cumulative light emission time T L  does not exceed the threshold value T TL  (step S 202 ; N, step S 203 ; N), display switching between the upper-side sub region and the lower-side sub region is not performed. 
         [0037]    Thus, in the liquid crystal display  1 , when a comparison between the cumulative light emission time T U  of the upper backlight  20 A and the cumulative light emission time T L  of the lower backlight  20 B is performed, and the difference between them is larger than the threshold value T TL , switching is performed so that an image is displayed on a sub region with a shorter cumulative light emission time. As a result, the difference between the cumulative light emission times of the upper backlight  20 A and the lower backlight  20 B is controlled to be equal to or lower than the threshold value T TL , so a difference in time degradation in light emission characteristics between the upper backlight  20 A and the lower backlight  20 B is maintained to be small. Therefore, it is difficult to cause uneven brightness or color unevenness due to brightness degradation or a chromaticity change between the upper-side sub region and the lower-side sub region of the liquid crystal panel, and degradation in image quality on the whole liquid crystal panel may be prevented. 
         [0038]    Although the present invention is described referring to some embodiments, the invention is not limited to them, and may be variously modified. For example, in the embodiment, when a difference between the upper-side and lower-side cumulative light emission times exceeds the threshold value T TL , image display is immediately switched to a sub region with a shorter cumulative light emission time; however, the invention is not limited to such control. For example, when the difference between the upper-side and the lower-side cumulative light emission times exceeds the threshold value T TL , and after that, a viewer conducts an operation (for example, changes a channel or turns the power on after turning the power off), switching between sub regions used for display may be performed in synchronization with the operation. In this case, the sense of discomfort associated with switching between the sub regions may be reduced. 
         [0039]    Moreover, in the embodiment, mode switching between the full screen display mode and the partial screen display mode is performed by a remote control operation by the viewer; however, the mode switching may be automatically performed depending on program category. In this case, for example, as shown in  FIG. 4 , as a program determining means, an EPG (Electric Program Guide) control section  22  is arranged to determine the content of a program selected by the tuner  12 . As a result, the selected program falls in a category such as, for example, a movie program or a sports program, the EPG control section  22  provides a full screen display mode selection instruction to the scaler  15 . On the other hand, when the selected program falls in a category such as, for example, a news program or an education program, the EPG control section  22  provides a partial screen display mode selection instruction to the scaler  15 . Operations after this are the same as those in the above-described case (refer to  FIG. 2 ). A liquid crystal display  1 A shown in  FIG. 4  has the same configuration as that of the liquid crystal display  1  shown in  FIG. 1 , except that the liquid crystal display  1 A includes the EPG control section  22 . 
         [0040]    Further, in the embodiment, the case where the full screen of the liquid crystal panel is divided into two sub regions, that is, the upper-side sub region and the lower-side sub region is described; however, the invention is not limited to the case, and, for example, as shown in  FIG. 5A , the full screen of the liquid crystal panel is divided into four sub regions, that is, an upper right sub region, an upper left sub region, a lower right sub region and a lower left sub region, and a backlight may be arranged corresponding to each sub region on the back of the sub region. Alternatively, for example, as shown in  FIG. 5B , the full screen of the liquid crystal panel may be divided into three sub regions in a vertical direction, and a backlight may be arranged corresponding to each sub region on the back of the sub region. In these cases, when a difference of the cumulative light emission time between a backlight with the shortest cumulative light emission time and a backlight with the longest cumulative light emission time is monitored, and the difference exceeds the threshold value, the backlight with the shortest cumulative light emission time is turned on to display an image on a corresponding sub region. Thereby, a difference of the cumulative light emission time between a backlight with the shortest cumulative light emission time and a backlight with the longest cumulative light emission time out of four (three) backlights corresponding to four (three) sub regions is controlled so as to be equal to or lower than the threshold value. As a result, a difference in time degradation in light emission characteristics may be reduced, and degradation in the image quality on the whole liquid crystal panel may be prevented. Moreover, in this case, the cumulative light emission time of the backlight for each sub region may be reduced more than the case shown in  FIGS. 3A to 3C , so the operating life of the whole backlight  20  is increased. In the case where the backlight is also divided in a vertical direction as in these cases, a plurality of LEDs are suitably arranged to form the backlight for each sub region. It is because in the case of an LED array, compared to the case where CCFLs are used, a boundary between the sub regions in the vertical direction is less noticeable. 
         [0041]    In the embodiment, the degradation state of each backlight is indirectly detected by monitoring the cumulative light emission time of the backlight for each sub region; however, instead of this, a sensor detecting the light emission state (brightness or spectroscopic characteristics) of a backlight corresponding to each sub region is arranged to directly detect the degradation state of each backlight on the basis of a sensor output. In this case, the time degradation state of each backlight is able to be monitored with higher precision, so uneven image quality on the whole liquid crystal panel may be reduced. 
         [0042]    In the embodiment, in the case where the partial screen display mode is selected, down-scaling is executed, thereby a downsized image obtained by the down-scaling is displayed on a sub region; however, the invention is not limited to the case, and, for example, a part of the whole image may be cut out without reducing its size to be displayed on a sub region. 
         [0043]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.