Patent Publication Number: US-7719511-B2

Title: Display apparatus with dynamic blinking backlight and control method and device thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 94139396, filed on Nov. 10, 2005. All disclosure of the Taiwan application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a control method and device of a backlight. More particularly, the present invention relates to a control method and device of a dynamic blinking backlight. 
     2. Description of Related Art 
     As some types of display panels cannot emit light themselves, they need to be disposed with backlights. For example, liquid crystal displays (LCDs) need backlights for the aid of displaying frames. With considerable improvement of the viewing angle and significant reduction in price, the trend of LCDs replacing cathode ray tube (CRT) displays as computer screens has already developed. And its next ambition focuses on a broader market, the household television. To achieve dynamic image quality display rivaling the CRT display, various well-known LCD manufacturers have started exploring the improvement of the dynamic features of LCDs. Quality degradation of LCDs when displaying dynamic images includes: reduction in dynamic contrast, edge-blur, and stroboscopic motion. The main reason lies in that the response speed of the liquid crystal is slow and the so-called Hold-type data writing feature. 
     To reduce the influence of the Hold-type data writing feature, the applicable methods can be divided into two categories: image temporary interruption and non-image interruption. The former imitates the CRT display to temporarily interrupt the image, not being received by the visual system; while the later increases the data renewal speed or compensates the dynamic track. Though the blinking backlight is a basic method for improving the dynamic image quality, it causes worries about extra power consumption and decrease in the service life of the lamp. 
     U.S. Pat. No. 4,958,915 discloses a liquid crystal apparatus, including a method of making the low-level brightness of the blinking backlight synchronous with the period of writing data to the display panel. This conventional technology makes the backlight blink at a fixed frequency, so as to imitate the CRT display to temporarily interrupt the image, thereby improving the dynamic features of LCDs. However, keeping the backlight blinking at a fixed frequency will cause extra power consumption and shorten the service life of the lamp. 
     U.S. patent application Ser. No. 20020154088 discloses a transmissive-type liquid crystal display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp based on the parameters of dynamic images, so as to turn off all the cold cathode lamps in the vertical blank period of a frame period, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the cold cathode lamp. 
     U.S. patent application Ser. No. 20040246242 discloses a display apparatus. This conventional technology determines the on-and-off time of the cold cathode lamp in a frame period based on the parameters of dynamic images. In other words, the ratio of lightening time to darkening time of the cold cathode lamp in a frame period is determined by the movement amount of the dynamic images, thereby improving the dynamic features of LCDs. Therefore, as the cold cathode lamp is kept blinking at a fixed frequency, this conventional technology will also cause extra power consumption and shorten the service life of the lamp. 
     U.S. patent application Ser. No. 20040051692 discloses a liquid crystal display device. This conventional technology controls the brightness of the backlight by adjusting the time proportion of the lightening and the darkening period in accordance with the brightness information in the display signal. This conventional cold cathode lamp is kept blinking at a fixed frequency without the capability of dynamically adjusting the blinking frequency in accordance with the features of the displayed image. As the cold cathode lamp is kept blinking at a fixed frequency, it will cause extra power consumption and shorten the service life of the lamp. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a dynamic blinking backlight control method. In accordance with the motion condition of a frame, the method dynamically determines the scanning frequency of the backlight or even stops the backlight from blinking so as to keep the backlight lit without blinking; various requirements such as improving dynamic image quality, reducing power consumption, and prolonging the service life of the backlight can be fulfilled. 
     Another object of the invention is to provide a dynamic blinking backlight control device, which fulfills the above objects by hardware architecture. 
     Yet another object of the invention is to provide a display apparatus with a dynamic blinking backlight, which reduces power consumption and improves image quality by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlight. 
     Based on the above and other objects, the present invention provides a dynamic blinking backlight control method, used for controlling the lighting status of multiple backlights of a display panel. The dynamic blinking backlight control method includes the following steps. First, the motion condition of a frame to be displayed on the display panel is detected to obtain a motion detection result. Then, the scanning frequency is determined in accordance with the motion detection result. Also, the lighting status of the backlights is controlled sequentially and respectively in accordance with the determined scanning frequency. 
     From another point of view, the present invention provides a dynamic blinking backlight control device. The dynamic blinking backlight control device includes a motion detection circuit, a control circuit, multiple backlights and a light source driving circuit. The motion detection circuit detects the motion condition of a frame to output a motion detection result. The control circuit is electrically connected to the motion detection circuit to determine the scanning frequency in accordance with the motion detection result. The light source required for displaying images on the display panel is provided by various backlights. The light source driving circuit is electrically connected to the control circuit and various backlights, wherein the lighting status of the backlights is controlled sequentially and respectively by the light source driving circuit in accordance with the scanning frequency determined by the control circuit. 
     The present invention provides another display apparatus with dynamic blinking backlight, which includes a display panel, a display driver, a motion detection circuit, a control circuit, multiple backlights, and a light source driving circuit. The display panel is used for displaying images. The display driver is electrically connected to the display panel to scan the display panel in accordance with the scanning frequency, and to drive the display panel to display the corresponding images in accordance with a frame. The motion detection circuit detects the motion condition of a frame to output the motion detection result. The control circuit, electrically connected to the motion detection circuit and the display driver, is used for determining the scanning frequency in accordance with the motion detection result. The light source required for displaying images on the display panel is provided by various backlights. The light source driving circuit is electrically connected to the control circuit and various backlights, wherein the lighting status of the backlights is controlled sequentially and respectively by the light source driving circuit based on the scanning frequency determined by the control circuit. 
     By modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlights in accordance with the motion condition of a frame, and even by stopping blinking backlights and keeping the backlights lit without blinking, the present invention fulfills the various requirements of improving the dynamic image quality, reducing power consumption, and prolonging the service life of the backlight. 
     In order to the make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart illustrating a dynamic blinking backlight control method in accordance with an embodiment of the invention. 
         FIGS. 2A and 2B  are schematic views illustrating respectively a slow moving frame and a quick moving frame. 
         FIG. 3  is a schematic example illustrating the dynamic scanning backlight control in accordance with the invention. 
         FIG. 4  is a block view illustrating a display apparatus with dynamic blinking backlight in accordance with the embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a flow chart illustrating a dynamic blinking backlight control method in accordance with an embodiment of the invention. Referring to  FIG. 1 , this dynamic blinking backlight control method is used to control the lighting status of multiple backlights of a display panel (for example, a liquid crystal display panel). First, step S 105  is carried out, i.e., the motion condition of a frame to be displayed is detected to obtain a motion detection result. The aforementioned frame to be displayed will be displayed on a display panel. 
     Step S 105  can be implemented by those skilled in the art in any ways. For example, compare the pixel data in the corresponding positions in the previously displayed frame and the frame to be displayed presently, obtain a differential pixel percentage in accordance with the changing proportion between both data, and take the differential pixel percentage as the motion detection result. Or, the motion detecting is carried out for the provided previously displayed frame and the frame to be displayed presently to obtain a motion vector as the motion detection result. 
     Then step S 110  is carried out, wherein it is determined whether or not the frame is a static frame in accordance with the motion detection result. As the static frame does not need to imitate the CRT display to temporarily interrupt the image, the backlight is kept lit without blinking when the motion detection result shows that the frame is a static frame (step S 115 ), thereby reducing the power consumption and prolonging the service life of the backlight. 
     When the motion detection result shows that the frame is a dynamic frame, steps S 120  to S 135  are carried out to improve the power consumption and image quality by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlight modular. This embodiment uses the motion detection result to activate the dynamic blinking backlight control mechanism, but it is not limited to this. For example, a button can be disposed. A user can press the button to send a command to activate (or turn off) the dynamic blinking backlight control mechanism, so as to perform steps S 120  to S 135 . Or, the application (for example, a movie playing program) executed by a host (for example, a personal computer) generates a command when outputting (or stopping output) the dynamic images, so as to activate (or turn off) the dynamic blinking backlight control mechanism. 
     In step S 120 , the scanning frequency is determined in accordance with the motion detection result. Those skilled in the art can set a reference value to determine the scanning frequency in accordance with the relationship between the motion detection result and the reference value. To avoid an incorrect determination caused by the unexpected factors such as a few abruptly skipping images in the frame (for example, the quick motion of the mouse pointer), or to avoid the scanning frequency being switched too often, a hysteresis function can be added into step S 120 . For example, if the motion detection result is the above-mentioned differential pixel percentage, when the differential pixel percentage (i.e., the changing proportion of the frame) is larger than an upper limit value (for example, 10%) (showing that the frame is a quick moving frame, for example, as shown in  FIG. 2B ), the scanning frequency will be switched from a low frequency (for example, 60 Hz) to a high one (for example, 120 Hz) to improve the display quality of the frame. If the differential pixel percentage is smaller than a lower limit value (for example, 5%) (showing that the frame is a slow moving frame, for example, as shown in  FIG. 2A ), the scanning frequency will be switched from a high frequency back to a low one to reduce power consumption and to prolong the service life of the backlight. Or, when the number of successive times in which the differential pixel percentage is larger than an upper limit value reaches a predetermined number (for example, the differential pixel percentages of two successive frames are all larger than the upper limit value), the scanning frequency will be switched from a low frequency to a high one. And when the number of successive times in which the differential pixel percentage is smaller than a lower limit value reaches a predetermined number, the scanning frequency will be switched from a high frequency back to a low one. Furthermore, if the motion detection result is represented by the motion vector, its operating steps can also refer to the above description. 
     In this embodiment, the backlight is, for example, a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), with its manner of arrangement shown in  FIG. 3 . In  FIG. 3 , the backlights  301 - 306  are disposed at the back of the display panel along the direction of a scan line of the display panel. When the dynamic blinking backlight control mechanism is activated, the averaged brightness of the backlight will be reduced. In step S 125 , the brightness of every backlight when it is lit will be increased in accordance with the scanning frequency, so as to compensate the averaged brightness of the backlight. 
     In step S 130 , the lighting status of the backlights  301 - 306  is controlled respectively in accordance with the scanning frequency determined in step S 120  and the brightness determined in step S 125 . For example, when the scanning frequency is determined to be 60 Hz or 120 Hz, as shown in  FIG. 3 , at least one of the backlights  301 - 306  is lit in accordance with the determined scanning frequency and the other backlights are turned off. Of course, the backlights  301 - 306  can also be lit, turned off or kept blinking at the same time in accordance with the determined scanning frequency. 
     This embodiment continues to carry out step S 135  after finishing step S 125 , i.e., the scanning frequency determined by Step S 120  is used to scan the display panel, so as to make the display panel display the corresponding images in accordance with the frame. Therefore, the display panel and the backlights can be scanned synchronously to display the frame, thereby improving the frame display quality. 
       FIG. 4  is a block diagram illustrating a display apparatus with dynamic blinking backlight in accordance with the embodiment of the invention. Referring to  FIG. 4 , the display apparatus  400  includes a dynamic blinking backlight control device, a display driver  450 , a display panel  460 , a memory  470 , and a graphic unit  480 . The dynamic blinking backlight control device includes a motion detection circuit  410 , a control circuit  420 , a light source driving circuit  430 , and backlights  440 . In this embodiment, the display panel  460  is, for example, liquid crystal display panel, and the backlights  440  can be composed by CCFLs or LEDs. The backlights  440  can be disposed at the back of the display panel  460  in accordance with the arrangement as shown in  FIG. 3 . 
     A central processing unit (CPU)  490  is electrically connected to the memory  470  and the graphic unit  480 . The graphic unit  480  continuously outputs frames to carry out the graphic operation based on the control of the CPU  490 . The graphic unit  480  is not only transmitted to the motion detection circuit  410 , but is also stored in the memory  470  at the same time. The motion detection circuit  410  compares the presently displayed frame output by the graphic unit  480  and the previously displayed frame stored in the memory  470  to detect the motion condition of the frame, and accordingly outputs the motion detection result to the control circuit  420 . The control circuit determines the scanning frequency in accordance with the motion detection result output by the motion detection circuit  410 . 
     Those skilled in the art can implement the motion detection circuit  410  by any means. For example, the motion detection circuit  410  compares the pixel data in the corresponding positions in the previously displayed frame and the frame to be displayed presently to obtain a differential pixel percentage in accordance with the changing proportion between both data, and take the differential pixel percentage as the motion detection result. Or, the motion detection circuit  410  carries out the motion detection for the previously displayed frame and the frame to be displayed presently to obtain a motion vector as the motion detection result. 
     The control circuit  420  is electrically connected to the motion detection circuit  410 . The control circuit  420  determines whether the frame to be displayed on the display panel  460  is a static frame in accordance with the motion detection result output by the motion detection circuit  410 . As the static frame needs not to imitate the CRT display to temporarily interrupt the image, when the motion detection result shows that the frame is a static frame, the control circuit  420  keeps the backlights  440  lit without blinking via the light source driving circuit  430 , thereby reducing power consumption and prolonging the service life of the backlights. 
     When the motion detection result output by the motion detection circuit  410  shows that the frame is a dynamic frame, the power consumption can be reduced and image quality can be improved by modulating the light source of the display panel, i.e., the control circuit  420  dynamically changes the lighting frequency of the backlight  440  via the light source driving circuit  430 . This embodiment uses the motion detection result to activate the dynamic blinking backlight control mechanism, but it is not limited to this. For example, a button can be disposed. A user can press the button to send out a command to activate (or turn off) the mechanism, so as to carry out dynamic blinking backlight control. Or, the application (for example, a movie playing program) executed by a host (for example, a personal computer) generates a command when outputting (or stopping output) the dynamic images, so as to activate (or turn off) the dynamic blinking backlight control mechanism. 
     Then, the control circuit  420  determines the scanning frequency in accordance with the motion detection result. Those skilled in the art can set a reference value to determine the scanning frequency based on the relationship between the motion detection result and the reference value. To avoid the incorrect determination caused by the unexpected factors such as a few abruptly skipping images in the frame (for example, the quick motion of the mouse pointer), or to avoid the scanning frequency being switched too often, a hysteresis function can be added to the control circuit  420 . For example, if the motion detection result is the above-mentioned differential pixel percentage, when the differential pixel percentage (i.e., the changing proportion of the frame) is larger than an upper limit value (for example, 10%) (showing that the frame is a quick moving frame, for example, as shown in  FIG. 2B ), the scanning frequency will be switched from a low frequency (for example, 60 Hz) to a high one (for example, 120 Hz) to improve the display quality of the frame. If the differential pixel percentage is smaller than a lower limit value (for example, 5%) (showing that the frame is a slow moving frame, for example, as shown in  FIG. 2A ), the scanning frequency will be switched from a high frequency back to a low one, so as to reduce the power consumption and to prolong the service life of the backlights. Or, when the number of successive times in which the differential pixel percentage is larger than an upper limit value reaches a predetermined number (for example, the differential pixel percentages of two successive frames are larger than the upper limit value), the scanning frequency will be switched from a low frequency to a high one. And when the number of successive times in which the differential pixel percentage is smaller than a lower limit value reaches a predetermined number, the scanning frequency will be switched from a high frequency back to a low one. Furthermore, if the motion detection result is represented by a motion vector, its operating manner can also refer to the above description. 
     When the control circuit  420  activates the dynamic blinking backlight control mechanism, the averaged brightness of the backlights will be reduced. The control circuit  420  will raise the brightness of the backlights  440  when they are lit via the light source driving circuit  430  in accordance with the determined scanning frequency, so as to compensate the averaged brightness of the backlights. The control circuit  420  controls the lighting status of the backlights  440  respectively via the light source driving circuit  430  in accordance with the determined scanning frequency and brightness. For example, when the scanning frequency is 60 Hz or 120 Hz as shown in  FIG. 3 , at least one of the backlights  301 - 306  is lit in accordance with the determined scanning frequency and the other backlights are turned off. Of course, the backlights  301 - 306  (i.e., the backlights  440  in  FIG. 4 ) can also be lit, turned off, or kept blinking at the same time in accordance with the determined scanning frequency. 
     The display driver  450  is electrically connected to the display panel  460  to scan the display panel  460  based on the scanning frequency determined by the control circuit  420 , and to drive the display panel  460  to display the corresponding images in accordance with the frame. In this embodiment, the display driver  450  includes a timing controller  451 , a scanning driver  452  and a data driver  453 . The timing controller  451  is electrically connected to the graphic unit  480  to receive the frame to be displayed presently. The timing controller  451  is further electrically connected to the control circuit  420  to scan the display panel  460  via the scanning driver  452  based on the scanning frequency determined by the control circuit  420 . The data driver  453  cooperates with the scanning timing of the scanning driver  452  to transmit the scan line data to the display panel  460  to display the frame. 
     In sum, by modulating the light source of the display panel, especially by dynamically changing the lighting frequency of the backlights in accordance with the motion condition of a frame, and even by stopping blinking backlights and keeping the backlights lit without blinking, the present invention fulfils the various requirements of improving dynamic image quality, reducing power consumption and prolonging the service life of the backlights. 
     Though the present invention has been disclosed above by the preferred embodiments, it is not intended to limit the invention. Anybody skilled in the art can make some modifications and variations without departing from the spirit and scope of the invention. Therefore, the range of protection of the invention shall be defined by the appended claims.