Patent Publication Number: US-2010117949-A1

Title: Control method for backlight module of lcd and application thereof

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 97143421, filed Nov. 10, 2008, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to a control method for a backlight module of a liquid crystal display (LCD) of an electrical device. More particularly, the present invention relates to a power saving method through controlling the backlight module of the LCD of the electrical device. 
     2. Description of Related Art 
     Nowadays, several low power chips and low power techniques for laptop computers have been developed to extend battery life of laptop computers by reducing power consumption. Power consumption of a LCD of a laptop computer is about 20%˜40% of the total power consumption of the laptop computer. Therefore, reducing the power consumption of the LCD can extend the battery life of the laptop computer significantly. 
     In the prior art, when the laptop computer is not operating for a period of time, which may imply that the user leaves the laptop computer and doesn&#39;t need the LCD to display, the laptop computer shuts down the LCD of the laptop computer. Therefore, the power consumption of the laptop computer is saved through shutting down the LCD. However, when the user utilizes the laptop computer to watch a movie, the user won&#39;t use any other operations on the laptop computer. Thus, when the user utilizes the laptop computer to watch a movie without using any other operations on the laptop computer for a period of time, the LCD of the laptop computer may be shut down, which may disturb the user. 
     Above all, a control method for the LCD is needed to prevent shutting down the LCD when the user is still utilizing the LCD without any other operation for a period of time, such as utilizing the LCD to watch movie. 
     SUMMARY 
     According to one embodiment of this invention, a control method for a backlight module of a LCD includes following steps: Capture an image in front of the LCD by a camera periodically. When there is no human face detected in the image, record the time at which the image is captured. Next, calculate the elapsed time, which there has been no human face detected in the image for, according to the recorded times. When the elapsed time is longer than the turn-off time for backlight, turn off the backlight module of the LCD. 
     According to another embodiment of this invention, an electrical device includes a camera, a LCD, a display control unit, a detect instruction database and a processing unit. The camera captures an image of the objects in front of the LCD periodically. The LCD includes a backlight module. The display control unit controls the LCD. The detect instruction database stores at least one detect instruction. The processing unit includes a detecting module, a time module and a turning-off module. The detecting module detects if there is a human face in the image with the detect instruction. When there is no human face detected in the image, the time module records the time at which the camera captures the image and calculates the elapsed time, which there has been no human face detected in the image for, according to the recorded times. When the elapsed time is longer than the preset turn-off time for backlight, the turning-off module turns off the backlight module of the LCD through the display control unit. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims. It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a flow diagram of a control method for a backlight module of a LCD according to an embodiment of this invention; 
         FIG. 2  is an embodiment of step  180  and step  190  in  FIG. 1 ; and 
         FIG. 3  is a block diagram of an electrical device according to another embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present 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 flow diagram of a control method for a backlight module of a liquid crystal display (LCD) according to an embodiment of this invention. The control method detects if there is any user in front of the LCD. When no user face is detected for a period of time, the backlight module of the LCD is turned off. The control method for the backlight module of the LCD  100  includes following steps: 
     Initialize a camera (step  110 ) and periodically capture an image in front of a LCD by a camera (step  120 ). In step  130 , detect if there is a human face in the image to determine if there is any user in front of the LCD. The detection in step  130  may be accomplished through utilizing face detection software to determine if there is any human facial features, such as eyebrows, nose, mouth or any other human facial features, in the image. 
     If a human face is detected in the image, the system assumes that there is a user in front of the LCD, and that the user may be utilizing the LCD. Therefore, when a human face is detected in the image, an image in front of the LCD is captured periodically (step  120 ) to detect if a human face is in the images (step  130 ) without turning off the backlight module of the LCD. Thus, when the user is still utilizing the LCD without any other operations, such as utilizing the LCD to watch a movie, the backlight module of the LCD would not be shut down. 
     If no human face is detected in the image, there may be no user in front of the LCD, which implies that there is no user utilizing the LCD. When there has been no user in front of the LCD for a period of time, the user may have left the front of the LCD for a long time, which implies that the backlight module of the LCD can be turned off to save power consumption without disturbing the user. Therefore, in step  140 , record the time at which the image is captured when no human face is detected in the image. In step  150 , calculate the elapsed time, which there has been no human face detected in the image for, according to the recorded times. In other words, there has been no user&#39;s face feature in front of the LCD for the elapsed time. The elapsed time can be calculated according to continuous count number of the recorded times or continuous accumulated value of the recorded times. In step  160 , determine if the elapsed time is longer than turn-off time for backlight. The turn-off time for backlight can be set through a user interface. When the elapsed time is shorter than the turn-off time for backlight, keep capturing an image periodically (step  120 ). Otherwise, turn off the backlight module of the LCD when the elapsed time is longer than the turn-off time for backlight (step  170 ). In other words, the backlight module of the LCD is turned off when no human face feature is detected in the image for a period longer than the turn-off time for backlight. 
     Since the backlight module consumes more power than other elements of the LCD, turning off the backlight module can significantly reduce the power consumption of the LCD. In addition, power consumed by a normal camera, such as a WEBCAM, is much less than power saved by turning off the backlight module. Therefore, applying the control method for the backlight module of the LCD  100  can still reduce power consumption of the LCD significantly with the camera periodically capturing an image in front of the LCD. Thus, when using a battery to supply power to the LCD, the battery life can be extended by applying the control method for the backlight module of the LCD  100 . 
     The control method for the backlight module of the LCD  100  may include the step of turning on the backlight module of the LCD when there is a present user detected in the image (step  180 ). In addition, the control method for the backlight module of the LCD  100  may further include the step of shutting down the camera when there has been no user detected in the image for a long time (step  190 ).  FIG. 2  is an embodiment of step  180  and step  190  in  FIG. 1 . Step  180  and step  190  may include following steps: 
     In step  210 , keep capturing an image in front of a LCD by a camera periodically when a backlight module of the LCD is turned off. In step  220 , detect if there is a human face in the image to determine if there is any user in front of the LCD. 
     In step  230 , record the time at which the image is captured when there is no human face detected in the image. In step  240 , calculate the elapsed time, which there has been no human face detected in the image for, according to the recorded times. In other words, there has been no user in front of the LCD for the elapsed time calculated by step  240 . 
     In step  250 , determine if the elapsed time is longer than shutting-down time. The shutting-down time can be set through a user interface, and the shutting-down time may be set longer than the turn-off time for backlight. 
     When the elapsed time is shorter than the shutting-down time, keep capturing an image in front of the LCD periodically (step  210 ). On the other hand, when the elapsed time is longer than the shutting-down time, shut down the camera (step  260 ). Therefore, when no user is detected in front of the LCD for a long time, power consumption can be further saved by shutting down the camera. 
     In addition, when there is a human face detected in the image by detection of the step  220 , turn on the backlight module of the LCD (step  280 ). In other words, when there is a human face of a user detected in front of the LCD, the backlight module of the LCD can be turned on to provide light to a panel of the LCD for display. 
     Before step  280 , determine if a present user in front of the LCD is the same as a previous user (step  270 ). The backlight module of the LCD is turned on only when the present user in front of the LCD is the same as the previous user (step  280 ). Therefore, the content displayed on the LCD wouldn&#39;t be shown to others after the previous user leaves. 
     In addition, step  270  can be accomplished through determining if the face in the image is the same as the face in the previous image. When the backlight module of the LCD was turned on previously and there was a human face detected in the image, the image was stored as the previous image. 
     Furthermore, step  270  can be also accomplished through capturing the present user&#39;s facial feature from the image, and comparing the present user&#39;s facial feature with the previous user&#39;s facial feature. Wherein the present user is determined to be the same as the previous user when the present user&#39;s facial feature is the same as the previous user&#39;s facial feature. When the backlight module of the LCD was turned on previously and there was a human face detected in the image, a feature of the human face was captured from the image, and the captured feature of the human face was stored as the previous user&#39;s facial feature. In addition, several facial features of the present user can be captured from the image for comparison in other embodiments. 
       FIG. 3  is a block diagram of an electrical device according to another embodiment of this invention. The electrical device detects if there is any user in front of a LCD of the electrical device. When there has been no user in front of the LCD for a period of time, turn off a backlight module of the LCD of the electrical device. The electrical device  300  includes a camera  310 , a LCD  320 , a display control unit  330 , a detect instruction database  340  and a processing unit  350 . The camera  310  is a WEBCAM or any other camera for capturing an image in front of the LCD  320  periodically. The LCD  320  includes a backlight module  321 . Light source of the backlight module  321  may be at least a cold cathode fluorescent lamp (CCFL), at least a light-emitting diode (LED), or any other light source. The display control unit  330  controls the LCD  320 . The detect instruction database  340  stores at least a detect instruction. The processing unit  350  includes a detecting module  351 , a time module  352  and a turning-off module  353 . The detecting module  351  detects if there is a human face in the image with the detect instruction. The detection instruction utilized by the detecting module  351  may detect if there is any human facial features, such as eyebrows, nose, mouth or any other facial features, in the image to determine if there is a human face in the image. When no human face is detected in the image, the time module  352  records time at which the image is captured by the camera  310  and calculates elapsed time, which there has been no human face detected in the image for, according to the recorded times. When the elapsed time is longer than turn-off time for backlight, the turning-off module  353  turns off the backlight module  321  of the LCD  320  through the display control unit  330 . Users may set value of the turn-off time for backlight through a user interface  360  of the electrical device  300 . 
     In practice, the LCD  320  consumes much more power than other elements of the electrical device  300  does, and the backlight module  321  of the LCD  320  consumes more power than other elements of the LCD  320  does. For example, when light source of the backlight module  321  is at least a CCFL, the power consumption of the backlight module  321  is 70%˜80% of the power consumption of the LCD  320 . Therefore, when there is no user in front of the LCD  320 , turning off the backlight module  321  can significantly reduce the power consumption of the LCD  320 . 
     In addition, power consumed by the camera  310 , is much less than power saved by turning off the backlight module  321 . Therefore, compared with other normal electrical devices, the electrical device  300  can still reduce power consumption significantly when the camera  310  continues to capture an image. Thus, when the electrical device  300  consumes power from a battery, the battery life can be extended. 
     The processing unit  350  may further include a turning-on module  354 . When the backlight module  321  is turned off and there is a human face detected in the image, the turning-on module  354  turns on the backlight module  321  through the display control unit  330 . In other words, the backlight module  321  is turned on when a present user detected in front of the LCD  320  to provide light to a panel of the LCD  320  for display. 
     In addition, when the backlight module  321  is turned off and there is a present user detected in front of the LCD  320 , the electrical device  300  may determine if the present user detected in front of the LCD  320  is the same as a previous user. Only when the present user detected in front of the LCD  320  is the same as the previous user, the electrical device  300  turns on the backlight module  321 . Therefore, the processing unit  350  of the electrical device  300  further includes a determining module  356  for determining if the present user in front of the LCD  320  is the same as the previous user. The turning-on module  354  turns on the backlight module  321  through the display control unit  330  only when the present user is the same as the previous user. Therefore, the content displayed on the LCD  320  wouldn&#39;t be shown to others after the previous user leaves the LCD  320  of the electrical device  300 . 
     In detail, when the backlight module  321  is turned off and there is a human face detected in the image, determining module  356  may determine if the face in the image is the same as the face in a previous image to determine if the present user in front of the LCD  320  is the same as the previous user. The turning-on module  354  turns on the backlight module  321  through the display control unit  330  only when the face in the image is the same as the face in the previous image. When the backlight module  321  was turned on previously and there was a human face detected in the image, the detecting module  351  stored the image as the previous image. 
     Furthermore, when the backlight module  321  is turned off and a human face is detected in the image, the determining module  356  may capture a present user&#39;s facial feature from the image. Then, the determining module  356  compares the present user&#39;s facial feature with the previous user&#39;s facial feature to determine if the present user is the same as the previous user. The turning-on module  354  turns on the backlight module  321  through the display control unit  330  only when the present user is the same as the previous user. When the backlight module  321  of the LCD  320  is turned on previously and there was at least a human face detected in the image, the detecting module  351  captured a facial feature from the front image and stored the captured facial feature as the previous user&#39;s facial feature. In addition, the determining module  356  may capture several facial features of the present user from the image for comparison in other embodiments. 
     The processing unit  350  may further include a shutting-down module  355 . When the elapsed time is longer than shutting-down time, shutting-down module  355  shuts down the camera  310 . Value of the shutting-down time can be set through a user interface  360 , and may be set to larger than the value of the turn-off time for backlight. Therefore, when there has been no user detected in front of the LCD  320  for a period of time, the camera  310  may be shut down for further saving power consumption. 
     Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, their spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.