Abstract:
A dynamic control method for controlling backlight module of liquid crystal display (LCD) comprises steps of: receiving a frame data which is transferred to the LCD and consists a plurality of raw grayscale level; processing a statistical analysis for distribution of the plurality of raw grayscale level; and transferring a plurality of corrected grayscale level which is resulted from the statistical analysis corresponding to the raw grayscale level to the backlight control unit and a data modification simultaneously, wherein the backlight control unit uses the plurality of corrected grayscale level to modify brightness of backlight module and the data modification uses the plurality of corrected grayscale level to compare with the plurality of raw grayscale level for accurate display performance, so that the electrical power consumption is reduced and image quality is enhanced.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a driving method of an LCD device having a backlight module with dynamic backlight control unit, and more particularly for controlling backlight module of LCD which dynamically adjusts backlight brightness from grayscale level distribution of the display by frame data analysis. Due to dynamically adjusting backlight brightness, electric power consumption can be diminished and display quality can be enhanced. 
         [0003]    2. Description of the Prior Art 
         [0004]    Conventional backlight module of LCD is illustrated as  FIG. 1 . A backlight module  9  as shown on  FIG. 1  includes a diffuser  91 , a reflector  92  and a plurality of light source  93 , wherein the reflector and plurality of light source are on the side of the diffuser and the plurality of light source is distributed between the reflector and diffuser regularly. Reflecting side  921  of the reflector comprises transverse concaves which have the plurality of light source on their focus and reflects light to the diffuser. Light from the plurality of light source can directly go through the diffuser and can be reflected by the reflector to the diffuser. Intensity or brightness of light source is controlled by a controller (not shown on  FIG. 1 ). In general, the light source can be cold cathode fluorescent lamp (CCFL) as cylinders  93  on  FIG. 1 . The controller for CCFL is inverter controller (not shown on  FIG. 1 ) which controls brightness of CCFL by pulse width modulation (PWM). As LCD developing, strip lamp  94  formed by light emitting diodes  941  (LEDs) in serial on strip board  942  can be the light source of LCD instead of CCFL. The PWM of strip lamp is controlled by LED driver controller (not shown on  FIG. 1 ). 
         [0005]    As increasing size of LCD, number and intensity of the light source (CCFL  93  or strip LED lamp  94 ) increase too. Electric power consumption increases also. In an exemplary LCD with 65-inch panel, electric power consumption for turning on the backlight module  9  is greater than 700 W as well as an operating heater. The worse is only two stages for backlight module operation, on or off. Event in a dark scent, brightness of backlight module is in full intensity and dark scene is made by controlling rotation angle of liquid crystal molecule. In a long term, electric power consumption is substantial. How to lower down electric power consumption becomes therefore an important issue for saving power as LCD developing. 
         [0006]    Thus, inventors depending on their abundant experience on LCD design and producing figure out the present invention for solving mentioned problems after many cycles of consideration, produce, and modification. 
       SUMMARY OF THE INVENTION 
       [0007]    An object of the present invention is to provide a dynamic control method for controlling backlight module of LCD, wherein electric power consumption by backlight module can be lower down to save money and power. 
         [0008]    Another object of the present invention is to provide a dynamic control method for controlling backlight module of LCD, wherein brightness of backlight module is dynamically adjusted with grayscale level distribution in different frame data to lower down electric power consumption. 
         [0009]    Another object of the present invention is to provide a dynamic control method for controlling backlight module of LCD, wherein scene contrast is improved and display quality is improved as well. 
         [0010]    In order to achieve the above objects in the present invention, the method of driving a liquid crystal panel according to one aspect of the present invention having backlight of the LCD is provided by a plurality of light source of backlight module and controlled by a backlight control unit. And, the dynamic control method for controlling backlight module of LCD according to the present invention comprises the following steps: receiving a frame data which is transferred to the LCD and consists a plurality of raw grayscale level; processing a statistical analysis for distribution of the plurality of raw grayscale level; and transferring a plurality of corrected grayscale level which is resulted from the statistical analysis corresponding to the raw grayscale level, wherein the backlight control unit uses the plurality of corrected grayscale level to modify brightness of backlight module. 
         [0011]    Furthermore, a weighted-average grayscale level can be a consequence of the step of processing statistical analysis for uses of further analysis and determinant conditions. Additionally, a most significant bit (MSB) of the plurality of raw grayscale level resulted from a manner of bit truncation can be used to reduce data processing during the step of processing statistical analysis. 
         [0012]    In the present invention, all the brightness of light source of backlight module can be changed by the same amount for whole brightness modification. The brightness of light source of backlight module on the same strip board can be changed by the same amount for strip-wise brightness modification. The brightness of light source of backlight module on the same area board can be changed by the same amount for area-wise brightness modification. 
         [0013]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the following description taken in conjunction with accompanying drawings, in which 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates a prior art to show structure diagram of backlight module. 
           [0015]      FIG. 2  shows a flowchart of timing controller according to the present invention. 
           [0016]      FIG. 3  is an exemplary histogram diagram of raw grayscale level according to the present invention. 
           [0017]      FIG. 4  is a schematic diagram of bit truncation according to the present invention. 
           [0018]      FIGS. 5A and 5B  shows relations between corrected grayscale level and raw grayscale level in a first embodiment according to the present invention. 
           [0019]      FIG. 6  shows relations between corrected grayscale level and raw grayscale level in a second embodiment according to the present invention. 
           [0020]      FIG. 7  shows relations between corrected grayscale level and raw grayscale level in a third embodiment according to the present invention. 
           [0021]      FIG. 7A  shows a detail diagram for  FIG. 7  at small input values. 
           [0022]      FIG. 8  shows relations between corrected grayscale level and raw grayscale level in a fourth embodiment according to the present invention. 
           [0023]      FIG. 9  shows a flowchart of an embodiment according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims. 
         [0025]    A color image can be performed by RGB additive primaries. Different grayscale level of primary represents different primary brightness. In the following embodiment description, a single grayscale level with 8-bit resolution, i.e. using digits 0˜255 to present different brightness between full dark to full white, is used for clear understanding. 
         [0026]    Generally, a LCD consists of a backlight module and a backlight control unit to drive the backlight and control the operation of the backlight so that it emits light always at a specified level of brightness. The backlight module consists of a plurality of light source, which are provided by CCFL, LCD or other operable illumination devices, for backlight of LCD. 
         [0027]    Based on an operation for a timing controller  1  of LCD, an embodiment according to the present invention is shown on  FIG. 2 . As a frame data is received by the LCD through the timing controller, a plurality of raw grayscale level in the frame data is transferred to a brightness calculation  11  and a data modification  12  respectively. The brightness calculation gathers all the raw grayscale level to do a statistics of brightness distribution. According to the results from statistics of brightness distribution, the following statistic analysis and determinant operations can generate a plurality of corrected grayscale level corresponding to the raw grayscale level. 
         [0028]    The plurality of corrected grayscale level is further transferred to data modification  12  and backlight control unit  14  at the same time for synchronization. In the data modification  12 , the plurality of corrected grayscale level is compared with the plurality of raw grayscale level and a plurality of optimized grayscale level is generated and sent to a timing controller  13  for image optimization. Finally, the timing controller sends the plurality of optimized grayscale level and control signal to LCD panel for controlling rotation of liquid crystal molecule and panel brightness. 
         [0029]    When the plurality of corrected grayscale level is transferred to the backlight control unit, an inverter or a LED driver controller (as mark  15  on  FIG. 2 ) is used to control the intensity of light source in backlight module. According to the corrected grayscale level, brightness of backlight module can be modified for different purposes. In an exemplary dark image, i.e. grayscale level distribution in low level, brightness of backlight module is modified to a lower intensity for saving electrical energy. 
         [0030]    As an exemplary histogram of brightness distribution on  FIG. 3 , X represents grayscale level 0˜255 and Y represents number distribution in the frame data. Brightness distribution and weighting is easy to show on the histogram. According to the histogram, a weighted-average grayscale level can be a consequence of the step of processing statistical analysis for uses of further analysis and determinant conditions. 
         [0031]    Before gathering brightness histogram, the bits of raw grayscale level can be truncated and represented as most significant bit (MSB) through a manner of bit truncation for reducing data process. As shown on  FIG. 4 , the 8 bits of raw grayscale level is truncated as 5 bits, wherein 3 least significant bits (LSBs) is truncated and 5 MSBs is left to represent raw grayscale level. Although there are 7-digits resolution is sacrificed for dropping 3-bit LSB, amount of processing information is dramatically reduced from 8-bit to 5-bit. Seven-digit sacrifice in image quality is hard to tell by human&#39;s eyes, so the huge reduction of processing time is worth. 
         [0032]    In the present invention, there are several ways to transfer the raw grayscale level to the corrected grayscale level. The followings are some exemplary relations between the raw and corrected grayscale levels: 
         [0033]    The first embodiment of relations between the raw and corrected grayscale levels is shown on FIGS  5 A and  5 B. X variable is denoted as “input” and responded to the raw grayscale level. Y variable is denoted as “output” and responded to the corrected grayscale level. Before any correction, the relation between input and output looks like a straight line as line  51  on Cartesian coordinate shown in  FIG. 5A . A straight line as line  52  shown in  FIG. 5B  shows one of relations when maximum value (Max. code) of input is less 255. After correction, the maximum value (Max. code) of input is corresponded to value 255 for output. The relation can be represented as a following formula: 
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         [0034]    By following the formula, the relation between input and output is a straight line as line  52  shown in  FIG. 5B . In order to prevent useless correction, a downlimit  53  of grayscale level replaces the maximum of raw grayscale level when the maximum value of raw grayscale level is less than the downlimit of grayscale level. By following the formula and the downlimit of raw grayscale level, the relation between input and output is a straight line as line  54  shown in  FIG. 5B . 
         [0035]    Besides the straight-line relations, there are other relation curves for input and output as follows: 
         [0036]    As well as line  52 , a smooth curve as curve  55  also has a starting point at (0,0) and an end point at (maximum value of raw grayscale level, maximum value of corrected grayscale level) ((Max. code, maximum value of corrected grayscale level)). The difference is output value following curve  55  is greater than or equal to the one following line  52  at the same input value. One of smooth curves is negative gamma curve corresponding to light response of human&#39;s eyes. The maximum value of raw grayscale level is a variable of negative gamma function in order to fit different needs. 
         [0037]    In order to prevent useless correction, a downlimit  53  of grayscale level replaces the maximum of raw grayscale level when the maximum value of raw grayscale level is less than the downlimit of grayscale level. The relation between input and output becomes a smooth curve as curve  56  shown in  FIG. 5B . 
         [0038]    Further,  FIG. 6  shows the second embodiment of relation between input and output. As well as curve  55 , the relation between input and output is a smooth curve through Cartesian coordinate (0,0) and (maximum value of raw grayscale level, maximum value of corrected grayscale level) ((Max. code, maximum value of corrected grayscale level)) marked as denotation  61 . The difference is curve  61  is always lower than denotation  62 . One of smooth curves is positive gamma curve corresponding to light response of human&#39;s eyes. The maximum value of raw grayscale level is a variable of positive gamma function in order to fit different needs. In order to prevent useless correction for too small maximum value of input, a downlimit  63  of grayscale level replaces the maximum of raw grayscale level when the maximum value of raw grayscale level is less than the downlimit of grayscale level. The relation between input and output becomes a smooth curve as curve  64  on  FIG. 6 . 
         [0039]    Further, the third embodiment of relation between input and output is shown on  FIG. 7 . Changes of output and input at large values keep the same ratio as line  72  which is as well as the equal line  71  but with a horizontal shift on X axis. The maximum value of raw grayscale level (Max. code) is also corresponded to the maximum value of corrected grayscale level.  FIG. 7A  shows relation between input and output at small values is corrected to a concave curve for matching coordinate (0,0) at zero input. With the different maximum values of raw grayscale level, the concave curve near small values is different for matching coordinate (0,0). 
         [0040]    In order to prevent useless correction, a downlimit  73  of grayscale level replaces the maximum of raw grayscale level when the maximum value of raw grayscale level is less than the downlimit of grayscale level. The relation between input and output becomes a smooth curve as curve  74  on  FIG. 7 . 
         [0041]    Further, the fourth embodiment of relation between input and output is shown on  FIG. 8 . Curve  81  is one of exemplary curves for fifth embodiment. As well as other embodiments, curve  81  is a smooth curve linking between Cartesian coordinate (0,0) and (maximum value of raw grayscale level (Max. code), maximum value of corrected grayscale level). The difference is curve  81  is convex near large values and concave near small values as an S shape curve. As using curve  81  correction, it not only reduces backlight intensity and electrical power consumption but also enhance image contrast at the same time. In addition to curve  81 , other curves with experimental facts can be used to enhance image quality for grayscale level correction. 
         [0042]    No matter what correction is used for relation between the raw grayscale level and the corrected grayscale level, backlight brightness is changed to a lower intensity or higher intensity by backlight control unit depending on the corrected grayscale level. With the different light source and different needs of brightness control, the backlight control unit has many ways for brightness control as follows: 
         [0043]    First way of the backlight control unit is to change all the brightness of light source of backlight module by the same amount for modification of whole panel brightness. 
         [0044]    Second way of backlight control unit is to change the brightness of light source of backlight module on the same strip board by the same amount for strip-wise brightness modification. 
         [0045]    Third way of backlight control unit is to change the brightness of light source of backlight module on the same area board by the same amount for area-wise brightness modification. The whole light source of backlight module can be divided into several rectangular areas. The third way of backlight control unit can control those different areas independently based on their corrected grayscale level. Because change of brightness is gradual in smaller region (i.e. the rectangular areas), brightness difference is harder to tell by human&#39;s eyes. 
         [0046]    Those three ways of backlight control unit have their own advantages and disadvantages. Using one of them or combination of them can reduce electrical power consumption of backlight module and enhance image quality. 
         [0047]    An operation embodiment according to the present invention is shown as a flowchart on  FIG. 9 . When a frame data is input (denotation 101 ), it is passed to do statistical analysis (denotation 102 ). Next, a static scene verification (denotation 103 ) excuses command of brightness keeping or changing time reduction (denotation 104 ) and returns the step of fame data inputting for static scene. 
         [0048]    If the scene is not static, the dynamic backlight control is not necessary for every changed scene. For the present embodiment, the maximum value of raw grayscale level (Max) and the average value of raw grayscale level (Ave) are compared (denotation 105 ) to verify the need of dynamic backlight control. When the difference is small, there is no need of the dynamic backlight control (denotation 106 ) and maximum backlight intensity is remained (denotation 107 ). Then, flowchart processing jumps to the starting step for waiting next frame data (denotation 105 ). 
         [0049]    When the difference is large, processing steps forward to verify the need of grayscale level correction (denotation 109 ). As the maximum value of raw grayscale level is 255, there is no need of grayscale level correction (denotation 111 ) and maximum backlight intensity is remained (denotation 111 ). As the maximum value of raw grayscale level is less 255, processing steps forward to compute the corrected grayscale level from the correction relation (denotation 112 ). According to the corrected grayscale level, backlight intensity can be modified to a lower intensity (denotation 113 ) for power reduction. Then, flowchart processing jumps to the starting step for waiting next frame data (denotation 108 ). In the present embodiment, any modification and change on the steps and verification is probably made from general knowledge in related technology field. 
         [0050]    From an experimental test result, electrical power consumption of LCD backlight module can be save up to 25% and image quality can be enhanced too by using the present invention. 
         [0051]    Accordingly, the objectives for electrical power saving, power consumption reduction and environment protection can be made successfully and image contrast and quality are also enhanced too by using the present invention. However, the present invention is not limited in the sequence of the present embodiments and reference diagrams, e.g. distribution statistics, relation between raw grayscale level and corrected level, backlight control unit. 
         [0052]    Accordingly, as disclosed by the above description and accompanying drawings, the present invention surely can accomplish its objectives, and may be put into industrial use especially for mass product. 
         [0053]    It should be understood that various modifications, variations, and appliance such as organic light-emitting diode (OLED) or plasma display panel (PDP) could be made from the teaching disclosed above by the person familiar in the art, without departing the spirit of the present invention.