Abstract:
To reduce the image sticking, a first number of frames outputted from the multimedia signal source are successively received. The first number of frames are processed to obtain a plurality of corresponding gray-level characteristic. A predefined frame is inserted into a plurality of incoming frame with a specified ratio if the plurality gray-level characteristic is qualified to a specified predefined condition.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and a system of reducing the image sticking, and more particularly to a method and a system of reducing the image sticking resulted from a liquid crystal display (LCD). 
       BACKGROUND OF THE INVENTION 
       [0002]      FIG. 1  depicts a functional block diagram illustrating a LCD system. Conventionally, the LCD system includes an analog-to-digital converter (ADC)  102 , a scaler  104 , a timing controller (TCON)  122 , a driving circuit  124 , and a LCD panel  126 . The ADC  102  and the scaler  104  together constitute an image processing unit  10 . Furthermore, the TCON  122 , the driving circuit  124 , and the LCD panel  126  together constitute a LCD panel module  12 . 
         [0003]    The ADC  12  is used for receiving an analog frame, and then converting the analog frame into a digital frame; where the analog frame can be outputted from a multimedia device, such as a computer, a television set, or a media player (not shown). Because the resolution of the LCD panel  126  is fixed before released to the market but the resolution of the received frame is various, the pixels in the received frame must be zoom-in or zoom-out first by the scaler  104  to make the size, the light intensity, and the color of the frame to fit the specification of the LCD panel  126 . Afterwards, the modified pixels of the received frame are then outputted to the TCON  122 . The TCON  122  is used to modify the sequence and the timing of showing the pixels of the received frame. The driving circuit  124  then outputs the driving voltages to the LCD panel  126  according to the pixels of the received frame. Then, the corresponding image of the received frame can be shown by the LCD panel  126  via modifying the arrangement of the liquid-crystal molecules in the LCD panel  126  according to the received driving voltages. 
         [0004]      FIG. 2  is a scheme illustrating an internal structure of the LCD panel  126 . The LCD panel  126  includes a polarizer  1262 , a glass substrate  1264 , an indium tin oxide (ITO) film  1266 , an alignment film  1268 , a color filter  1270 , a thin film transistor (TFT)  1272 , and a plurality of liquid-crystal molecule  1274 . The driving voltages, derived from the driving circuit  124  depicted in  FIG. 1  and for the driving of the liquid-crystal molecule  1274 , are outputted to the TFT  1272  and the ITO  1266 . The alignment film  1268  is used for fixing the liquid-crystal molecule  1274  to a specific direction. The color filter  1270  is used for filtering the light  14  to red, green, blue lights that are named as a RGB, where the light  14  is emitted from a back-light source (not shown). The polarizer  1262  is used for guaranteeing all the lights in the LCD panel  126  are outputting to or incoming from a specific direction. 
         [0005]    The driving of the LCD panel  126  is based on the optical activity of the liquid-crystal molecule  1274 . When the driving voltages, derived from the TFT  1272  and the ITO  1266 , are applied to the liquid-crystal molecule  1274 , the liquid-crystal molecule  1274  is accordingly rotated to a corresponding angle, so as partial of the light  14  can emit through the liquid-crystal molecule  1274  and partial of the light  14  cannot emit through the liquid-crystal molecule  1274 . In other words, via controlling the value of the driving voltages applied to the liquid-crystal molecule  1274 , the amount (or light intensity) of the light  14  capable of emitting through the liquid-crystal molecule  1274  is accordingly controlled. Also, the light intensity of the light  14  capable of emitting through the liquid-crystal molecule  1274  is named as a gray level. 
         [0006]    Basically, the LCD can be categorized to a normal-white LCD or a normal-black LCD based on the corresponding angle of the liquid-crystal molecule  1274  after the LCD panel is applied by the driving voltages. The LCD panel  126  is categorized to a normal-white LCD, such as the twisted nematic (TN) LCD, if the light  14  can be fully emitted through the liquid-crystal molecule  1274  applied with zero driving voltage, so as the image shown by the normal-white LCD panel  126  has a highest light intensity. Accordingly, the image shown by the normal-white LCD panel  126  has a lowest light intensity if the normal-white LCD panel  126  is applied by a highest driving voltage. That is to say, the light intensity of the image shown by the normal-white LCD is related to the value of the driving voltage. On the other hand, the LCD panel  126  is categorized to a normal-black LCD, such as the in-plane switching (IPS) LCD or the multi-domain vertical alignment (MVA) LCD, if no light  14  can be emitted through the liquid-crystal molecule  1274  applied with highest driving voltages, so as the image shown by the normal-black LCD panel  126  has a lowest light intensity. Accordingly, the image shown by the normal-black LCD panel  126  has a highest light intensity if the normal-black LCD panel  126  is applied by zero driving voltage. That is to say, the light intensity of the image shown by the normal-black LCD panel is related to the value of the driving voltage. 
         [0007]    An internal electric field, so as an internal electric capacity, is generated after the two glass substrates  1264  located on the two ends of the LCD panel  126  adsorbing the charged ions in the liquid-crystal molecule  1274  when the driving voltages are applied to the LCD panel  126  for a relatively long period. Once the charged ions cannot be released from the internal electric capacity when the LCD panel  126  shows a next image, so as the liquid-crystal molecule  1274  cannot be rotated to a specified angle corresponding to the image, the image sticking is resulted in. 
         [0008]    The image sticking can be illustrated by the  FIGS. 3A and 3B .  FIG. 3A  is a scheme illustrating a LCD showing an image with a plurality of black block  301 . If the LCD suddenly turns to show a white image after a long-term showing the image depicted in  FIG. 3A , the image-sticking block  303  depicted in  FIG. 3B  is resulted in. The image-sticking block  303  has a lower gray level compared to the black block  301 . 
         [0009]    Please refer to  FIG. 2  again. Not only the image sticking is resulted in when the liquid-crystal molecule  1274  is applied under a relatively high driving voltage, the quality of the image shown by the LCD panel  126  or the life of LCD panel  126  may be also reduced. Because the ion or the impurity are also appeared in the liquid-crystal molecule  1274  and the alignment film  1268 , the residual DC voltage is accordingly increased if the liquid-crystal molecule  1274  is applied under a relatively high driving voltage, so as the quality of the image shown by the LCD panel  126  and the life of LCD panel  126  is reduced. 
         [0010]    Conventionally, the screen saver is introduced in the LCD system to avoid the image sticking. If an image is shown on a LCD panel for a relatively long period, the execution of the screen saver can prevent the LCD panel to be operated under a relatively high driving voltage. In other words, via the execution of the screen saver, the frame inputted to the LCD panel is changed. Accordingly the intensity of the driving voltage applied to the LCD panel is changed. However, once the screen saver is performed, the user cannot operate the multimedia device, such as the computer, the television set, or the media player, via the LCD panel. 
       SUMMARY OF THE INVENTION 
       [0011]    Therefore, the present invention provides a method and a system of reducing the image sticking without performing the screen saver, and the user can still operate the multimedia device via the LCD panel. 
         [0012]    The present invention relates to a method of reducing image sticking, applied between a liquid crystal display system and a multimedia signal source, comprising steps of: successively receiving a first number of frames outputted from the multimedia signal source; correspondingly computing a plurality of gray-level characteristic according to a RGB of a plurality of pixel in the received frames; and inserting a predefined frame into a plurality of incoming frame with a first ratio and then outputting the inserted frame if the plurality of gray-level characteristic is qualified to a first predefined condition. 
         [0013]    The present invention relates to a liquid crystal display system with a function of reducing image sticking, comprising: a scaler for successively receiving a plurality of digital frame, and outputting the plurality of digital frame after modifying the light intensity and the color of a plurality of pixel in the plurality of digital frame; and a liquid crystal display panel connected to the scaler, for showing a plurality of corresponding image according to the plurality of digital frame; wherein the scaler further comprises a gray-level extraction and analysis unit, for correspondingly computing a plurality of gray-level characteristic according to a RGB of a plurality of pixel in the plurality of received digital frames, and notifying the scaler to insert a predefined frame into a plurality of incoming digital frame with a first ratio and then outputting the predefined frames if the plurality of gray-level characteristic is qualified to a predefined condition. 
         [0014]    The present invention relates to a liquid crystal display system with a function of reducing image sticking, comprising: a timing controller for successively receiving a plurality of digital frame, and outputting the plurality of digital frame after modifying the sequence and the timing of a plurality of pixel in the plurality of digital frame; and a liquid crystal display panel connected to the timing controller, for showing a plurality of corresponding image according to the plurality of digital frame; wherein the timing controller further comprises a gray-level extraction and analysis unit, for correspondingly computing a plurality of gray-level characteristic according to a RGB of the plurality of pixel in the plurality of received digital frames, and notifying the timing controller to insert a predefined frame into a plurality of incoming digital frame with a first ratio and then outputting the predefined frames if the plurality of gray-level characteristic is qualified to a predefined condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
           [0016]      FIG. 1  is a functional block diagram illustrating a conventional LCD system; 
           [0017]      FIG. 2  is a scheme illustrating an internal structure of the LCD panel; 
           [0018]      FIG. 3A  is a scheme illustrating a LCD showing an image with a plurality of black block; 
           [0019]      FIG. 3B  is a scheme illustrating the image sticking is resulted in after a long-term period showing the image depicted in  FIG. 3A ; 
           [0020]      FIG. 4A  is a histogram illustrating a gray-level distribution of a frame; 
           [0021]      FIG. 4B  is another histogram illustrating a gray-level distribution of a frame; 
           [0022]      FIG. 5A  is a flowchart illustrating the present invention of the method of reducing the image sticking; 
           [0023]      FIG. 5B  is a scheme illustrating an example of inserting a mid-gray frame to a plurality of normal frame based on the weight of the high-gray levels to the whole gray levels; 
           [0024]      FIG. 5C  is another flowchart illustrating the present invention of the method of reducing the image sticking; 
           [0025]      FIG. 5D  is another flowchart illustrating the present invention of the method of reducing the image sticking; and 
           [0026]      FIGS. 6A and 6B  are functional block diagrams illustrating the present invention of a system of reducing the image sticking. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0027]    Each frame is constructed by pixels with different value of RGB. That is to say, the pixel (0, 0, 0), also defined as a zero-gray level, has a lowest light intensity; contrarily, the pixel (255, 255, 255), also defined as a 255-gray level, has a highest light intensity. Therefore, each frame can be regarded as constructed by many gray levels, and each gray level is in the range from the zero-gray level to the 255-gray level. Besides, for the convenience, the gray level having a relatively low value is defined as a low-gray level (having a relatively low light intensity); contrarily, the gray level having a relatively high value is defined as a high-gray level (having a relatively high light intensity) in the embodiment of the present invention. 
         [0028]      FIG. 4A  depicts a histogram illustrating a gray-level distribution of a frame, and the frame is assumed to be shown by a normal-black LCD. As described above, a relatively high driving voltage must be applied to the normal-black LCD to show a high-gray level (high light intensity). In other words, the driving voltage is increasing with the increasing value of the gray level in a normal-black LCD. Therefore, the gray levels with values greater than a specified value (e.g., 192-gray level) can be regarded as operated in a high-voltage zone, as depicted in  FIG. 4A . Contrarily,  FIG. 4B  depicts a histogram illustrating a gray-level distribution of another frame, and the frame is assumed to be shown by a normal-white LCD. As described above, a relatively high driving voltage must be applied to the normal-white LCD to show a low-gray level (low light intensity). In other words, the driving voltage is decreasing with the decreasing value of the gray level in a normal-white LCD. Therefore, the gray levels with values less than a specified value (e.g., 64-gray level) can be regarded as operated in a high-voltage zone, as depicted in  FIG. 4B . 
         [0029]    A gray-level extraction and analysis, for calculating the gray-level distribution of a received frame, is implemented in the present invention. If a first number of gray-levels in a received frame is determined in the high-voltage zone and the first number is greater then a specified number, the received frame is regard as a high-voltage frame. According to the present invention, when a number of the high voltage frames received by the LCD is greater then a predetermined frame count, a mid-gray frame will be inserted into the incoming frame for reducing the image sticking. 
         [0030]      FIG. 5A  is a flowchart illustrating the present invention of the method of reducing the image sticking. First, the method of the present invention receives a frame (step S 501 ) outputted from a multimedia device (e.g., computers, television sets, or media players). After the gray-level extraction and analysis of the received frame is performed (step S 503 ), the gray-level distribution of the received frame is obtained. If the ratio of the high-gray levels (e.g., above 192-gray level) to the whole gray levels of the received frame is over a specified ratio (e.g., 70%) and the frame is shown by a normal-black LCD, accordingly the frame is defined as a high-voltage frame. Similarly, if the ratio of the low-gray levels (e.g., below 64-gray level) to the whole gray levels of the received frame is over a specified ratio (e.g., 70%) and the frame is shown by a normal-white LCD, accordingly the frame is defined as a high-voltage frame. 
         [0031]    If the received frame is not a high-voltage frame based on the result of the gray-level extraction and analysis, the method of the present invention moves to the step of receiving the next incoming frame (step S 501 ). On the other hand, accumulate the count of the high-voltage frames (step S 507 ) if the received frame is a high-voltage frame (step S 505 ). If the high-voltage frames are continuously sent from the multimedia device but the accumulating count of the received high-voltage frames is not over a predetermined frame count (step S 509 ), the method of the present invention moves to the step of receiving the next incoming frame (step S 501 ). However, if the accumulating count of the received high-voltage frames is over the predetermined frame count (step S 509 ), the image sticking may happen and a mid-gray frame is inserted into the incoming frames with a ratio of N:1 (step S 511 ). The mid-gray frame is constructed by pixels with middle values of RGB, and the mid-gray frame accordingly can be shown by a LCD panel applied by a driving voltage ranged between a relatively high driving voltage and a relatively low driving voltage. Also, the ratio of N:1 means that one mid-gray frame is inserted into every N received frames (normal frames). That is to say, once the method of the present invention determines the LCD panel is in the risk of occurring the image sticking, one mid-gray frame is inserted into the incoming N frames (N normal frames) outputted from the multimedia device, so as the image sticking can be avoid. 
         [0032]    To a normal-black LCD, it is understood that inserting a low-gray frame into a plurality of high-gray frame can get a better performance to avoid image sticking. However, the inserted low-gray frame may also bring an obvious contrast between the relatively high and the relatively low light intensities, so as the quality of the outputting image is poor. Therefore, for the balance between the anti of the high driving voltage and the maintaining of the image quality, the mid-gray frame is considered in the embodiment of the present invention. Similarly, to a normal-white LCD, even inserting a high-gray frame into a plurality of low-gray frames can get a better performance to avoid image sticking, the mid-gray frame is still considered in the embodiment of the present invention. 
         [0033]    Furthermore, in the present invention of the method of reducing image sticking (only the normal-black LCD is took for the example), the ratio of the normal frames to the mid-gray frame can be dynamically adjusted based on ratio of the weight of the high-gray levels to the whole gray levels of the received frame. For example, after the gray-level extraction and analysis is done to the received frame and calculating the ratio of the high-gray levels (e.g., above 192-gray level) to the whole gray levels in the frame is over to 70%, and this type of frames are continuously outputted from the multimedia device over a predetermined frame count, a mid-gray frame will be inserted into the incoming normal frames with a ratio of N:1. For example, every 50 incoming normal frames will be inserted with a mid-gray frame. On the other hand, after the gray-level extraction and analysis is done to the received frame and calculating the ratio of the high-gray levels (e.g., above 192-gray level) to the whole gray levels in the frame is over to 80%, and this type of frames are continuously outputted from the multimedia device over the predetermined frame count, a mid-gray frame will be inserted in the incoming normal frames with a ratio of M:1. For example, every 30 incoming normal frames will be inserted with a mid-gray frame. By using the dynamically adjustment of the ratio of the mid-gray frames to the normal frames, a better performance of anti the high electric field is obtained. 
         [0034]      FIG. 5B  depicts a scheme illustrating an example of inserting a mid-gray frame to a plurality of normal frame based on the weight of the high-gray levels to the whole gray levels. The left side of the  FIG. 5B  illustrates sequentially displaying a plurality of frame with many black blocks without adopting the present invention of the method of reducing the image sticking. If these frames are sequentially displayed by a LCD for a relatively long time, the LCD is in the risk of resulting in the image sticking. The middle side of the  FIG. 5B  illustrates sequentially displaying a plurality of frame with many black blocks by adopting the present invention of the method of reducing the image sticking; where the ratio of the high-gray levels (e.g., above 192-gray level) to the whole gray levels in each frame is over 70% and the ratio of the normal frames to the mid-gray frames is N:1. The right side of the  FIG. 5B  illustrates sequentially displaying a plurality of frame with many black blocks by adopting the present invention of the method of reducing the image sticking; where the ratio of the high-gray levels (e.g., above 192-gray level) to the whole gray levels in each frame is over 80%, and the ratio of the normal frames to the mid-gray frames is M:1. 
         [0035]    Furthermore, the present invention of the method for reducing the image sticking can be adopted with the conventional screen saver or other monitor power saving mechanism.  FIG. 5C  is another flowchart illustrating the present invention of the method of reducing the image sticking. The steps before S 509  are already described above in the flowchart depicted in  FIG. 5A . If the accumulating count of the received high-voltage frames is not only over a first predetermined frame count (step S 509 ) but also over a second predetermined frame count (step S 510 ), then the method of the present invention assumes the LCD showing this type of frames over a reasonable period, accordingly, the LCD will be switched to the screen saver or the LCD will be directly shut down (step S 512 ). 
         [0036]    Furthermore, the present invention of the method of reducing the image sticking can be adopted with image-capture devices such as the CCD camera. The image-capture device is used for detecting whether the user is appeared in front of the LCD or not, and whether inserting the mid-gray frame is based on the detected result.  FIG. 5D  is another flowchart illustrating the present invention of the method of reducing the image sticking. The steps before S 509  are already described above in the flowchart depicted in  FIG. 5A . If the accumulating count of the received high-voltage frames is over a predetermined frame count (step S 509 ), a present image captured by the image-capture device is compared with another image of the user in front of the LCD (step S 510 - 1 ). If the comparing result indicates the user is in front of the LCD (step S 510 - 2 ), then the method of the present invention inserts the mid-gray frame into the plurality of incoming normal frame with a ratio of N:1 (step S 511 ). On the other hand, if no user is detected in front of the LCD, the LCD will be switched to the screen saver or the LCD will be directly shut down (step S 512 ) due to no need to insert the mid-gray frame for reducing the image sticking. 
         [0037]    The above-described gray-level extraction and analysis and the determination of inserting the mid-gray frame can be implemented by a gray-level extraction and analysis unit. As described above, the scaler in the LCD system can output a gray frame via the controlling of the light intensity and the color of the outputting image, it is reasonable to integrate the gray-level extraction and analysis unit of the present invention into the scaler.  FIG. 6A  is a functional block diagram illustrating the present invention of a system of reducing the image sticking (only the normal-black LCD is took as an example). The system includes an ADC  102 , a scaler  604 , a TCON  122 , a driving circuit  124 , and a LCD panel  126 . The scaler  604  further includes a gray-level extraction and analysis unit  6042 . In the gray-level extraction and analysis unit  6042 , a high-gray level standard value (HS), a high-gray ratio standard value (HR), and an insert-mid-gray-frame count (HT) are predefined. Also, the high-gray level standard value (HS), the high-gray ratio standard value (HR), and the insert-mid-gray-frame count (HT) can be stored in a register  6044  of the gray-level extraction and analysis unit  6042 . 
         [0038]    First, a frame is outputted from the multimedia device (e.g., computers, television sets, or media players) to the scaler  604  via the ADC  12 . After the gray-level extraction and analysis is done to the received frame by the gray-level extraction and analysis  6042 , the gray-level distribution of the received frame is obtained. Afterwards, the computed gray-level distribution of the received frame is compared to the high-gray level standard value (HS) and the high-gray ratio standard value (HR) stored in the register  6044 . If the ratio of some specified gray levels equal/or greater than the high-gray level standard value (HS, e.g., 192) to the whole gray levels of the frame is over the high-gray ratio standard value (HR, e.g., 70%), the received frame is defined as a high-voltage frame, and a counter (not shown) adds the count of the high-voltage frames by one. If the high-voltage frames are continuously sent from the multimedia device and the accumulating count of the received high-voltage frames is up to the insert-mid-gray-frame count (HT), a mid-gray frame is inserted into the incoming frames with a ratio of N:1 by the scaler  604 . In other words, via the scaler  604  capable of controlling the light intensive and the color of the received frame, the gray-level extraction and analysis  6042  can inform the scaler  604  to insert a gray frame after every receiving N normal frames if the accumulating count of the received high-voltage frames is up to the insert-mid-gray-frame count (HT). Afterwards, the inserted gray frame is sent to the TCON  122 . Because the functions of the ADC  102 , the TCON  122 , the driving circuit  124 , the LCD panel  126  already explained in  FIG. 1 , no further describing of the above devices here. 
         [0039]    Furthermore, the TCON in the LCD system can output a gray frame via the controlling of the sequence and the timing of the outputting pixels; it is reasonable to integrate the gray-level extraction and analysis unit of the present invention into the TCON.  FIG. 6B  is another functional block diagram illustrating the present invention of a system of reducing the image sticking. Because the only difference to the system depicted in  FIG. 6A  is that inserting the gray frame is performed by the TCON  122 , no further describing of other devices here. 
         [0040]    To sum up, according to the present invention, once the LCD is in the risk of occurring the image sticking, a mid-gray frame is inserted into the incoming frames to anti the high electric field, so as the image sticking can be avoid. Furthermore, because the anti of the image sticking is not via the screen saver, the user still can operate the multimedia device (e.g., computers, television sets, or media players) via the LCD. 
         [0041]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.