Patent Publication Number: US-8537102-B2

Title: Backlight control apparatus and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 99103026, filed on Feb. 2, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a backlight control apparatus and the control method thereof, and more particularly, to a backlight control apparatus and a backlight control method of a backlight panel of a display panel. 
     2. Description of Related Art 
     In a display apparatus with passively light-emitting (for example, a liquid crystal display apparatus, i.e., LCD apparatus), it&#39;s a well known technique to deploy a backlight panel serving as the light-emitting source thereof. Along with the durably increasing demand of users on the display quality of a display apparatus, now the backlight panel is not meant to provide a pure light source only. In fact, the luminance of a modern backlight panel needs to be adjusted depending on different display conditions and the electrical consumption, so that the efficiency of the display apparatus can be effectively advanced. 
     In this regard, a recently launched content adaptive backlight control (CABC) technique is a technical effort, where the content of displayed image is used to adjust the luminance of backlight panel. The CABC technique is used to correspondingly adjust the luminance of backlight panel according to different frame modes of a display apparatus, i.e., according to a static frame mode or a dynamic frame mode. Adopting the CABC scheme makes a display apparatus have the optimal display effect under the most effective power management to achieve the minimum power consumption. However, in the conventional CABC embodiments, during switching the luminance of backlight panel, due to an incorrect switching time-point, the displayed frame of the display apparatus produces flashing phenomena so as to downgrade the display quality. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a backlight control apparatus and the control method thereof for automatically judging an image displayed by a display panel is a dynamic image or a static image and thereby adjusting the luminance of the backlight panel. 
     The present invention provides a backlight control apparatus for controlling the luminance of the backlight panel. The backlight control apparatus includes an image information memory and a detection and automatic switching circuit. The image information memory is for storing the image information. The detection and automatic switching circuit is coupled to the image information memory for detecting the updated frequency of the updated image information and then sets a displaying mode for adjusting the luminance of the backlight panel according to the updated frequency. 
     In an embodiment of the present invention, the above-mentioned detection and automatic switching circuit includes a detection counter and a mode switch, wherein the detection counter detects the updated status of the image information every a predetermined time period and further changes a counting result according to the updated status. The mode switch is coupled to the detection counter for setting the displaying model as an animated model or a static model according to the counting result. 
     In an embodiment of the present invention, when the above-mentioned detection counter detects out the image information is not updated yet within a predetermined time, the counting result is descended; when the detection counter detects out the image information is updated already within a predetermined time, the counting result is ascended. 
     In an embodiment of the present invention, when the counting result is greater than or equal to an upper limit value, the above-mentioned mode switch switches the displaying model to the animated model; when the counting result is less than or equal to a lower limit value, the above-mentioned mode switch switches the displaying model to the static model. 
     The present invention further provides a backlight control method for controlling the luminance of the backlight panel. The method includes: detecting the updated frequency of the image information stored in an image information memory; setting a displaying mode for adjusting the luminance of the backlight panel according to the updated frequency. 
     Based on the depiction above, the present invention detects the updated frequency of the image information stored in the image information memory and thereby judges whether the image displayed by the display panel is a dynamic image or a static image so as to accordingly set the displaying mode. Then, the set displaying mode is used to adjust the luminance of the backlight panel so that the optimal switching time-point for the luminance of the backlight panel can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a diagram of a backlight control apparatus  100  according to an embodiment of the present invention. 
         FIG. 1A  is an implement diagram of a detection and automatic switching circuit  120  according to an embodiment of the present invention. 
         FIGS. 2A and 2B  are operation flowcharts of the detection and automatic switching circuit according to the differences of the gray levels of a plurality of pixels corresponding to a same display position between the present frame information and the last frame information. 
         FIG. 3  is a flowchart of a backlight control method according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a diagram of a backlight control apparatus  100  according to an embodiment of the present invention. Referring to  FIG. 1 , the backlight control apparatus  100  is for controlling the luminance of a backlight panel  102 . The backlight control apparatus  100  includes an output/input interface  110 , a detection and automatic switching circuit  120 , a control register  130 , an image information memory  140 , an image analyzer  150 , an image processor  160  and a backlight adjuster  170 . The output/input interface  110  receives a information DATA come from a host terminal  101  and transmits the information DATA respectively to the control register  130  and the detection and automatic switching circuit  120 , wherein the information DATA sent by the host terminal  101  usually includes an image information IM provided to the display panel and a control command for controlling the operation of the backlight control apparatus  100 . The image information IM is transmitted to the image information memory  140  through the detection and automatic switching circuit  120  for storing and the control command is transmitted to the control register  130  for being registered. 
     Since the image information IM is saved in the image information memory  140  through the detection and automatic switching circuit  120 , so that the detection and automatic switching circuit  120  is able to know the updated status of the image information IM in the image information memory  140  and further obtain the updated frequency of the image information IM. In short, the detection and automatic switching circuit  120  records the counting number for the image information IM in the image information memory  140  to be updated within a certain predetermined time period (i.e., accumulating the new counting number for the image information IM to be transmitted to the detection and automatic switching circuit  120  within the predetermined time period) so as to obtain the updated frequency of the updated image information IM. 
     It should be noted that when the display panel  103  displays static frames, the image information IM is not durably to be necessarily updated, instead, the image information IM is updated only within a longer time period. In contrast, when the display panel  103  displays dynamic frames, the display panel  103  continuously displays a plurality of different images so that the image information IM is durably updated. In other words, when the detection and automatic switching circuit  120  detects out the updated frequency of the image information IM in the image information memory  140  is higher, it can be concluded that the display panel  103  is displaying dynamic frames and thereby the displaying mode MODE is set as the animated model. In contrast, when the detection and automatic switching circuit  120  detects out the updated frequency of the image information IM in the image information memory  140  is lower, it can be concluded that the display panel  103  is displaying static frames and thereby the displaying mode MODE is set as the static model. 
     In addition, the above-mentioned judgment about a higher or lower updated frequency can be implemented by setting a threshold value. Whenever the updated frequency is greater than the threshold value, the updated frequency is judged as a higher one, and whenever the updated frequency is not greater than the threshold value, the updated frequency is judged as a lower one. 
     The detection and automatic switching circuit  120  transmits the set displaying mode MODE to the control register  130  and further to the backlight adjuster  170  through the control register  130 , where the backlight adjuster  170  adjusts the luminance of the backlight panel  102  according to the received displaying mode MODE. In general speaking, when the displaying mode MODE received by the backlight adjuster  170  is the animated mode, the luminance of the backlight panel  102  is adjusted down; when the displaying mode MODE received by the backlight adjuster  170  is the static mode, the luminance of the backlight panel  102  is adjusted up. 
     It should be noted that the displaying mode MODE set by the detection and automatic switching circuit  120  can also be directly transmitted to the backlight adjuster  170  to make the backlight adjuster  170  adjust the luminance of the backlight panel  102  accordingly. The reason to mention the displaying mode MODE in the embodiment is transmitted to the backlight adjuster  170  through the control register  130  rests with that the user or the designer can also send out a control command through the host terminal  101  for adjusting the luminance of the backlight panel  102 . As a result, the control register  130  is able to integrate the commands of adjusting the luminance of the backlight panel  102  come from two different sources (one is the displaying mode MODE and another is the control command sent out by the host terminal  101 ), so that an appropriate command can reach the backlight adjuster  170  for adjusting the optimal luminance of the backlight panel  102 . 
     For example, when the control register  130  simultaneously receives the commands of adjusting the luminance of the backlight panel respectively come both from the detection and automatic switching circuit  120  and the host terminal  101 , the luminance of the backlight panel  102  specified by the host terminal  101  serves as the base to adjust the luminance, wherein for example, when the displaying mode MODE is the static mode, the luminance of the backlight panel  102  specified by the user is used as the luminance of the backlight panel  102  and when the displaying mode MODE is the animated mode, the luminance of the backlight panel  102  specified by the user must be multiplied by a factor less than  1  (for example, 80%) and the result is used as the luminance of the backlight panel  102 . 
       FIG. 1A  is an implement diagram of a detection and automatic switching circuit  120  according to an embodiment of the present invention. Referring to  FIG. 1A , in the embodiment, the detection and automatic switching circuit  120  includes a detection counter  121  and a mode switch  122 . The detection counter  121  is for detecting the updated status of the image information IM every a predetermined time period and then changing and producing the counting result CNT according to the detected updated status. The mode switch  122  is coupled to the detection counter  121  for setting the displaying mode MODE as an animated model or a static model according to the counting result CNT. 
     To depict the detection way of the updated frequency of the image information IM and the setting method of the displaying mode in the embodiment of the present invention more clearly, another embodiment is explained in following, so that anyone skilled in the art can better understand the unique feature of the present invention. 
       FIGS. 2A and 2B  are operation flowcharts of the detection and automatic switching circuit according to the differences of the gray levels of a plurality of pixels corresponding to a same display position between the present frame information and the last frame information. Referring to  FIG. 2A , firstly, the detection and automatic switching circuit  120  detects the updated status of the image information in the image information memory  140  within a predetermined time period (step S 210 ), which means the detection task includes whether or not the image information memory  140  has a writing action within the predetermined time period or furthermore whether or not the image information in the image information memory  140  gets changed within the predetermined time period. In particular, in step S 210 , the updated counting number of the image information within the predetermined time period is ignored, but only the event whether or not the image information is updated is logged. 
     The detection and automatic switching circuit  120  further judges whether or not the image information is updated within the predetermined time period (step S 220 ). If the detection and automatic switching circuit  120  judges out the image information is not updated within the predetermined time period, the counting result is descended (step S 230 ), followed by executing step S 210  again. On the other hand, if the detection and automatic switching circuit  120  judges out the image information is updated within the predetermined time period, the detection and automatic switching circuit  120  further judges whether or not the counting result is greater than or equal to the predetermined upper limit value (step S 240 ). At the time, if the detection and automatic switching circuit  120  judges out the counting result is less than the upper limit value, the counting result is ascended. During executing steps S 220  and S 230 , the detection and automatic switching circuit  120  keeps detecting whether or not the counting result is less than or equal to the predetermined lower limit value (step S 270 ). Once the detected counting result is less than or equal to the predetermined lower limit value, the detection and automatic switching circuit  120  switches the displaying mode to the static model (step S 280 ). 
     Referring to  FIG. 2B , steps S 240  and S 250  in  FIG. 2B  are the same as steps S 240  and S 250  in  FIG. 2A  and herein they are repeated for better showing only. When step S 240  judges out the counting result is greater than the predetermined upper limit value, the detection and automatic switching circuit  120  switches the displaying mode to the animated model (step S 260 ). 
     When the detection and automatic switching circuit  120  judges out the counting result is greater than or equal to the upper limit value and the displaying mode has been switched to the animated model, the counting number is stopped to be ascended. In contrast, when the detection and automatic switching circuit  120  judges out the counting result is less than or equal to the lower limit value and the displaying mode has been switched to the static model, the counting number is stopped to be descended. In this way, the present invention can effectively avoid overflow or underflow phenomena of the counting number value. 
     Referring to  FIGS. 1 ,  2 A and  2 B, the operation flow of the detection and automatic switching circuit  120  can also prevent switching the displaying mode MODE immediately after the detection and automatic switching circuit  120  detects out an excessive updated frequency of the image information IM in the image information memory  140 . In this way, the detection and automatic switching circuit  120  of the embodiment can effectively avoid continuously switching the displaying mode MODE sourced by the host terminal  101  which non-uniformly writes the image information into the image information memory  140  under a limited bandwidth condition with the image information memory  140 . 
       FIG. 3  is a flowchart of a backlight control method according to an embodiment of the present invention. Referring to  FIG. 3 , the steps include: firstly, detecting the updated frequency of the image information stored in the image information memory (step S 310 ); next, setting the displaying mode for adjusting the luminance of the backlight panel according to the updated frequency (step S 320 ). The detection of the updated frequency and the switching operation of the displaying mode are depicted in details in the above-mentioned embodiment of the backlight control apparatus  100 , so that they are omitted to describe. 
     In summary, the present invention detects the updated frequency of the image information in the image information memory to judge the displayed image by the display panel is a dynamic image or a static image. Thereby, the displaying mode is set accordingly so as to dynamically adjust the luminance of the backlight panel. The present invention is advantageous in saving the electric consumption of the backlight panel and considering to keep good display quality. 
     It will be apparent to those skilled in the art that the descriptions above are several preferred embodiments of the present invention only, which does not limit the implementing range of the present invention. Various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention.