Patent Publication Number: US-2012026203-A1

Title: Image compensation apparatus and method thereof and field sequential color liquid crystal display using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 99124786, filed on Jul. 27, 2010. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND 
     1. Field of the Invention 
     The invention relates to a flat panel display technique, more particularly to, an image compensation apparatus and a method thereof for a field sequential color liquid crystal display. 
     2. Description of Related Art 
     With development of photoelectric technology and semiconductor technology, flat panel displays are quickly developed, and in various flat panel displays, a liquid crystal display (LCD) becomes popular in the market due to its advantages of high space utilization rate, low power consumption, no irradiation and low electromagnetic interference, etc. It is known that an LCD includes an LCD panel and a backlight module, and since the LCD panel has no luminescent function itself, the backlight module is required to be disposed under the LCD panel for providing a planar light source to the LCD panel. In this way, the LCD can display images to a user. 
     In a conventional LCD, a design principle of the backlight module used for providing the planar light source to the LCD panel is to provide a white light, and then the white light is transmitted to color filters on each pixel position within the LCD panel for displaying a color of each pixel. Generally, three color filters, i.e. a red (R) filter, a green (G) filter and a blue (B) filter are required to be disposed on each pixel position to achieve a full color effect. However, such method is not only expensive, but also leads to a low transmittance of each pixel after the white light being processed by the color filters. 
     Accordingly, in a lately designed LCD, the backlight source of light-emitting diodes (LEDs) is applied for substituting the conventional white light backlight source. Namely, the conventional method of mixing colors of the color filters on a spatial axis, i.e. mixing colors of the red (R), green (G) and blue (B) sub-pixels on the spatial axis within a viewing range of human eyes now may be substituted by mixing colors of the LED backlight source on a time axis. Namely, based on a visual staying principle of the human eyes, images of the three colors red, green and blue are switched swiftly on the time axis, so as to achieve a color mixing effect. 
     For example, if the images are dynamically displayed for 60 frames per second, and the images of the three colors red, green and blue are switched swiftly on the time axis, a refresh frequency of the images of the three colors red, green and blue is then at least 180 images per second, i.e. an image refresh period is 5.56 ms ( 1/180 second), and this method is the so-called field color sequential method. Accordingly, disposing of the color filters on each pixel position of the LCD panel is unnecessary, and the transmittance of each of the pixels is then improved. 
     Since the human eyes have the visual staying phenomenon when receiving external images, the LCD driven by the field color sequential method may switch the color images by using a high frequency, so as to cope with the visual staying phenomenon of the human eyes to display full color images. However, since the field sequential color liquid crystal display (FSC-LCD) may probably have a color breakup phenomenon when displaying motion images or static images, a display quality of the FSC-LCD is greatly decreased. 
     Therefore, to effectively mitigate/resolve the color breakup problem has become one of the major subjects to various manufacturers. 
     SUMMARY OF THE INVENTION 
     Accordingly, the invention is directed to an image compensation apparatus and a method thereof for a field sequential color liquid crystal display (FSC-LCD), which can effectively mitigate/resolve a color breakup phenomenon occurred when the FSC-LCD displays motion/static images. 
     The invention provides an image compensation apparatus of an FSC-LCD, which includes a motion estimation unit, a decomposition unit, a motion compensation unit and an adjustment unit. Wherein, the motion estimation unit receives a first color image information, and performs a motion estimation to the first color image information to obtain a motion vector. The decomposition unit receives the first color image information, and performs a color decomposition to the first color image information to obtain a first sub-color-field and a residual color image information. 
     The motion compensation unit is coupled to the motion estimation unit and the decomposition unit, and is used for receiving the residual color image information and the motion vector, and performing a motion compensation to the residual color image information according to the motion vector, so as to obtain a second, a third and a fourth sub-color-fields. The adjustment unit is coupled to the decomposition unit and the motion compensation unit, and is used for receiving the first to the fourth sub-color-fields, and separating a white component from the second, the third and the fourth sub-color-fields into the first sub-color-field, so as to make a color component corresponding to one of the second, the third and the fourth sub-color-fields to be zero, and accordingly output and provide a second color image information to the FSC-LCD to display a frame. 
     The invention provides an image compensation method of an FSC-LCD. The method can be described as follows. A motion estimation is performed to a first color image information, so as to obtain a motion vector. A color decomposition is performed to the first color image information, so as to obtain a first sub-color-field and a residual color image information. A motion compensation is performed to the residual color image information according to the motion vector, so as to obtain a second, a third and a fourth sub-color-fields. A white component is separated from the second, the third and the fourth sub-color-fields into the first sub-color-field, so as to make a color component corresponding to one of the second, the third and the fourth sub-color-fields to be zero, and accordingly output a second color image information to the FSC-LCD to display a frame. 
     The invention further provides an FSC-LCD, which includes the aforementioned image compensation apparatus and a display module. Wherein, the display module displays frames in response to a second color image information output by the image compensation apparatus. 
     According to the above descriptions, based on processing of the first color image information performed by the image compensation apparatus of the invention, regardless whether the frames displayed by the display module of the FSC-LCD in response to the second color image information are motion frames or static frames, the color breakup phenomenon is avoided. In this way, the display quality of the FSC-LCD can be greatly improved. 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       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 block diagram illustrating a field sequential color liquid crystal display (FSC-LCD) according to an embodiment of the invention. 
         FIG. 2  is a block diagram illustrating an image compensation apparatus according to an embodiment of the invention. 
         FIG. 3  is a schematic diagram illustrating a red (R), a green (G) and a blue (B) image information of a pixel according to an embodiment of the invention. 
         FIGS. 4A-4E ,  FIG. 5  and  FIGS. 6A-6D  are explanation schematic diagrams of an FSC-LCD according to an embodiment of the invention. 
         FIG. 7  is a block diagram illustrating a display module according to an embodiment of the invention. 
         FIG. 8  is a flowchart illustrating an image compensation method of an FSC-LCD according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED 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 block diagram illustrating a field sequential color liquid crystal display (FSC-LCD)  100  according to an embodiment of the invention. Referring to  FIG. 1 , the FSC-LCD  100  includes an image compensation apparatus  101  and a display module  103 . Wherein, the image compensation apparatus  10  is used for processing an inputted color image information RGB, so as to output a color image information WRGB to the display module  103  for displaying a motion/static frame. Here, the color image information RGB may include a red (R), a green (G) and a blue (B) color image information, though the invention is not limited thereto. The color image information WRGB may include a white (W), a red (R), a green (G) and a blue (B) color image information, though the invention is not limited thereto. 
     In the present embodiment, based on the processing of the color image information RGB performed by the image compensation apparatus  101 , regardless whether the frames displayed by the display module  103  in response to the color image information WRGB are motion frames or static frames, the color breakup phenomenon is avoided. In this way, the display quality of the FSC-LCD  100  can be greatly improved, so that the problem of the conventional technique can be effectively mitigated/resolved. 
     In detail,  FIG. 2  is a block diagram illustrating the image compensation apparatus  101  according to an embodiment of the invention. Referring to  FIG. 2 , the image compensation apparatus  101  includes a motion estimation unit  201 , a decomposition unit  203 , a motion compensation unit  205  and an adjustment unit  207 . The motion estimation unit  201  receives the color image information RGB, and performs a motion estimation to the color image information RGB to obtain a motion vector MV. 
     The decomposition unit  203  receives the color image information RGB, and performs a color decomposition to the color image information RGB to obtain a first sub-color-field (for example, a white sub-color-field) WF and a residual color image information RGB′. In the present embodiment, the first sub-color-field WF relates to a white component in the color image information RGB, and the residual color image information RGB′ relates to color components other than the white component in the color mage information RGB. 
     Taking the color image information RGB of a single pixel as an example, and assuming a relationship of a red (R), a green (G) and a blue (B) color image information of the pixel are as that shown in  FIG. 3 , i.e. a red pixel value is the minimum, a blue pixel value is the secondary, and a green pixel value is the maximum. In this way, the white component in the color image information RGB is W, and the color components other than the white component W in the color image information RGB are the green (G) and the blue (B) color image information. 
     The motion compensation unit  205  is coupled to the motion estimation unit  201  and the decomposition unit  203 . The motion compensation unit  205  receives the residual color image information RGB′ and the motion vector MV, and performs a motion compensation to the residual color image information RGB′ according to the motion vector MV (the motion compensation is not directly performed to the original inputted color image information RGB), so as to obtain a second sub-color-field (for example, a red sub-color-field) RF, a third sub-color-field (for example, a green sub-color-field) GF and a fourth sub-color-field (for example, a blue sub-color-field) BF. 
     The adjustment unit  207  is coupled to the decomposition unit  203  and the motion compensation unit  205 . The adjustment unit  207  receives the first to the fourth sub-color-fields WF, RF, GF and BF, and separates a white component from the second, the third and the fourth sub-color-fields RF, GF and BF into the first sub-color-field WF, so as to make a color component corresponding to one of the second to the fourth sub-color-fields RF, GF and BF to be zero, and accordingly output the color image information WRGB to the display module  103  for displaying a motion/static frame. 
     According to the above descriptions, during a process that the optically compensated bend (OCB) FSC-LCD  100  sequentially lights up a red backlight source R T , a green backlight source G T  and a blue backlight source B T  (as that shown in  FIG. 4A ), a period of time K T  has to be maintained to display a fully black frame (i.e. the red, the green and the blue backlight sources are all turned off), which is equivalent to insert a single-color (i.e. black) field frame. Then, a red field frame, a green field frame and a blue field frame are sequentially displayed. Wherein, Rv, Gv and By shown in  FIG. 4A  can be regarded as a color image information RGB of a single pixel. Therefore, a situation that the green pixel value is the minimum, the blue pixel value is the secondary and the red pixel value is the maximum is taken as an example for description. 
     In this way, the decomposition unit  203  is used to perform the color decomposition to the color image information RGB, so that the FSC-LCD  100  is changed to sequentially lights up a white backlight source W T  (i.e. the red, the green and the blue backlight sources are all turned on), a black backlight source K T  (i.e. the red, the green and the blue backlight sources are all turned off), the red backlight source R T , the green backlight source G T  and the blue backlight source B T  (as that shown in  FIG. 4B ). Therefore, the FSC-LCD  100  sequentially displays a white field frame, the black field frame, the red field frame, the green field frame and the blue field frame. According to  FIG. 4B , the color components other than the white component in the color image information RGB are only the red and the blue color image information, i.e. the residual color image information RGB′. 
     Then, when the motion compensation unit  205  performs the motion compensation to the residual color image information RGB′ in a RGB domain according to the motion vector MV, since obtained positions are generally not on the same pixel points, i.e. as that shown in  FIG. 5 , positions of sub pixels R, G and B are not on the same positions in two adjacent frames O 1  and O 2 , the second to the fourth sub-color-fields RF, GF and BF (i.e. the red, the green and the blue sub-color-fields) obtained after the motion compensation unit  205  performs the motion compensation to the residual color image information RGB′ in the RGB domain according to the motion vector MV may all have values (as that shown in  FIG. 4C ), and now the red pixel value is the minimum, the blue pixel value is the secondary, and the green pixel value is the maximum. 
     Accordingly, the adjustment unit  207  has to be used to separate the white component from the second to the fourth sub-color-fields RF, GF and BF (i.e. the red, the green and the blue sub-color-fields) into the first sub-color-field WF (i.e. the white sub-color-field), so as to make a color component corresponding to one of the second to the fourth sub-color-fields RF, GF and BF to be zero, i.e. the color component corresponding to the second sub-color-field RF is zero (as that shown in  FIG. 4D ). 
     In the present embodiment, since the second to the fourth sub-color-fields RF, GF and BF (i.e. the red, the green and the blue sub-color-fields) obtained after the motion compensation unit  205  performs the motion compensation to the residual color image information RGB′ in the RGB domain according to the motion vector MV, and the first sub-color-field WF (i.e. the white sub-color-field) obtained after the decomposition unit  203  performs the color decomposition to the color image information RGB are again adjusted (i.e. color decomposition) by the adjustment unit  207 , one of the red (R), the green (G) and the blue (B) color image information in the color image information RGB of the pixel is zero. 
     Therefore, the feature of inserting a fully black field frame to the OCB FSC-LCD  100  can be satisfied by one of the red (R), the green (G) and the blue (B) color image information in the color image information WRGB (since one of the red (R), the green (G) and the blue (B) color image information is zero). In this way, the FSC-LCD  100  of the present embodiment is unnecessary to add a display time for the black field frame (as that shown in  FIG. 4E ), so that the adjustment unit  207  is only required to output the color image information WRGB having the white (W), the red (R), the green (G) and the blue (B) color image information to the display module  103 , and thus the display module  103  can display the motion/static frame without the color breakup phenomenon. 
     According to another aspect, referring to  FIGS. 6A-6D , in which a horizontal axis represents pixel positions, a vertical axis represents time, and diagonal arrows represent the motion vector MV. According to  FIG. 6A , it is known that the green pixel value is 50, the blue pixel value is 75 and the red pixel value is 100. Wherein, the three color pixel values relate to the red (R), the green (G) and the blue (B) color image information in the color image information RGB of the pixel, i.e. the red (R), the green (G) and the blue (B) color image information in the original inputted color image information RGB. 
     Moreover, according to  FIG. 6B , it is known that in case of the same pixel positions, according to a result that the decomposition unit  203  performs the color decomposition to the color image information RGB, the first sub-color-field WF related to the white component W of the color image information RGB is obtained, and the residual color image information RGB′ related to the color components other than the white component W in the color image information RGB is obtained. In this way, the pixel value corresponding to the white component W in the color image information RGB is 50, the pixel values corresponding to the red (R) and the blue (B) color image information of the same pixel positions are respectively 50 and 25 (i.e. the residual color image information RGB′), and the pixel values corresponding to the green (G) and the blue (B) color image information of different pixel positions are respectively 50 and 75. 
     Moreover, since the motion compensation unit  205  may perform the motion compensation to the residual color image information RGB′ according to the motion vector MV, an object traced by human eyes is moved rightwards. Now, according to  FIG. 6C , it is known that the second to the fourth sub-color-fields RF, GF and BF (i.e. the red, the green and the blue sub-color-fields) obtained after the motion compensation unit  205  performs the motion compensation to the residual color image information RGB′ in the RGB domain according to the motion vector MV may all have values (since the obtained positions are not on the same pixel points). Therefore, in case of the same pixel positions, the second to the fourth sub-color-fields RF, GF and BF may still have the white component W, and the corresponding pixel values thereof are 50. 
     Therefore, according to  FIG. 6D , after the adjustment unit  207  separates the white component W from the second to the fourth sub-color-fields RF, GF and BF (i.e. the red, the green and the blue sub-color-fields) into the first sub-color-field WF (i.e. the white sub-color-field), not only the pixel value of the white component W corresponding to the red (R), the green (G) and the blue (B) color image information of the same pixel positions is changed to 100, but also the pixel value corresponding to the blue (B) color image information of the same pixel position is also changed to 25, and thus the color component corresponding to one of the second to the fourth sub-color-fields RF, GF and BF is changed to zero (i.e. the color component corresponding to the third sub-color-field GF is zero). 
     Therefore, the feature of inserting a fully black field frame to the OCB FSC-LCD  100  can be satisfied by one of the red (R), the green (G) and the blue (B) color image information in the color image information WRGB (since one of the red (R), the green (G) and the blue (B) color image information is zero). In this way, the FSC-LCD  100  of the present embodiment is unnecessary to add a display time for the black field frame, so that the adjustment unit  207  is only required to output the color image information WRGB having the white (W), the red (R), the green (G) and the blue (B) color image information to the display module  103 , and the display module  103  can display the motion/static frame without the color breakup phenomenon. 
     In the present embodiment, once the adjustment unit  207  outputs the color image information WRGB having the white (W), the red (R), the green (G) and the blue (B) color image information to the display module  103 , the display module  103  may accordingly display the motion/static frame without the color breakup phenomenon. In detail,  FIG. 7  is a block diagram illustrating the display module  103  according to an embodiment of the invention. Referring to  FIG. 7 , the display module  103  includes a timing controller (T-con)  701 , a gate driver  703 , a source driver  705 , a light emitting diode (LED) backlight module  707  and a display panel  709  with a resolution of M*N (wherein M and N are positive integers), though the invention is not limited thereto. 
     In the present embodiment, when the timing controller  701  receives the color image information WRGB output by the adjustment unit  207 , the timing controller  701  may generate some related operation signals for controlling operations of the gate driver  703 , the source driver  705  and the LED backlight module  707 , so that the gate driver  703  and the source driver  705  may generate scan signals and data signals to drive the display panel  709 , and the LED backlight module  707  may sequentially provide backlight sources of corresponding colors (i.e. white, red, green and blue). 
     In this way, the display module  103  may display the motion/static frame without the color breakup phenomenon in response to the color image information WRGB output by the adjustment unit  207 . However, since a method that the timing controller  701  controls the operations of the gate driver  703 , the source driver  705  and the LED backlight module  707  is known by those skilled in the art, detailed descriptions thereof are not repeated. 
       FIG. 8  is a flowchart illustrating an image compensation method of an FSC-LCD according to an embodiment of the invention. Referring to  FIG. 8 , the image compensation method of the FSC-LCD may include following steps, and a sequence of the following steps can be suitably adjusted according to an actual requirement. 
     A motion estimation is performed to a first color image information (which may include a red (R), a green (G) and a blue (B) color image information, though the invention is not limited thereto), so as to obtain a motion vector (step S 801 ). 
     A color decomposition is performed to the first color image information, so as to obtain a first sub-color-field (for example, a white sub-color-field, which relates to a white component of the first color image information) and a residual color image information (which relates to color components other than the white component in the first color image information) (step S 803 ). 
     A motion compensation is performed to the residual color image information according to the motion vector, so as to obtain a second, a third and a fourth sub-color-fields (which are, for example, a red, a green and a blue sub-color-field) (step S 805 ). 
     A white component is separated from the second, the third and the fourth sub-color-fields into the first sub-color-field, so as to make a color component corresponding to one of the second, the third and the fourth sub-color-fields to be zero, and accordingly output a second color image information (which may include a white (W), a red (R), a green (G) and a blue (B) color image information, though the invention is not limited thereto) to the FSC-LCD to display a frame (step S 807 ). 
     In summary, based on processing of the first color image information performed by the image compensation apparatus of the invention, regardless whether the frames displayed by the display module of the FSC-LCD in response to the second color image information are motion frames or static frames, the color breakup phenomenon is avoided. In this way, the display quality of the FSC-LCD can be greatly improved. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.