This claims priority under 35 U.S.C. §119 to Taiwan Application No. 095138282, filed Oct. 17, 2006, which is hereby incorporated by reference.
The invention relates to a liquid crystal display (LCD) device and a driving method thereof, and, in particular, to a LCD device and an image display method applying black/gray insertion technology.
In order to enhance the display quality of a liquid crystal display (LCD) device, a display duty cycle may be shortened by adding a sub-frame. This method is sometimes referred to as impulse-like LCD technology. Specifically, a normally black sub-frame is often added and the technology is referred to as black insertion or gray insertion technology.
In the conventional image display method of a LCD device, pixels on a display surface in the same frame are commonly driven by either a dynamic mode (e.g., pixel data changes in sequential frames) or static mode (e.g., pixel data does not change in sequential frames) according to a dynamic or static property of the frame. The black/gray frame inserting method is used when the pixels are to be driven by the dynamic mode. Black/gray frame insertion helps avoid blurring that may be associated with dynamic modes and LCDs, as is commonly understood by those of ordinary skill in the art. Such blurring is not typical with impulse devices such as cathode ray tubes (CRTs). No dark frame is inserted when pixels are driven by the static mode, in contrast to dynamic mode, because blurring is typically not an issue with motionless situations (e.g., when there is little difference between successive frames).
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To avoid this reduction of frame luminance, a second conventional image display technology for impulse-like LCD devices has been implemented. As shown in
As shown in
In the second conventional technology when the image is continuously in the moving situation, replacing the black frame insertion with the gray frame insertion can indeed improve the flicker of the moving frame. However, when the image is changed from the moving situation to the motionless situation instantaneously, all the pixels originally driven by the dynamic mode are driven by the static mode. Consequently, the luminance of the whole image suddenly increases because no gray frame is inserted after the image is converted into the static one, and the viewer may notice the luminance surge in the generated image. Thus, the image display quality of the LCD device may be lessened.
An embodiment of the invention includes a method of driving pixels of a liquid crystal display (LCD) device when displaying a first frame and a second frame in sequence. The method includes: (a) detecting a gray-scale difference between the first frame and the second frame; (b) determining a driving mode change between the first frame and the second frame based on the detected gray-scale difference; (c) adjusting a ratio of first pixels, which are driven by a dynamic mode and are included in the plurality of pixels, to second pixels, which are driven by a static mode and are included in the plurality of pixels, in the second frame based on the determined driving mode change; and (d) outputting gray-scale data based on the adjusted ratio. Other embodiments are included herein.
The accompanying drawings, incorporated in and constituting a part of this specification, may illustrate one or more implementations consistent with the principles of the invention and, together with the description of the invention, explain such implementations. The drawings are not necessarily to scale, the emphasis instead being placed upon illustrating the principles of the invention.
The following description refers to the accompanying drawings. Among the various drawings the same reference numbers may be used to identify the same or similar elements. While the following description provides a thorough understanding of the various aspects of the claimed invention by setting forth specific details such as particular structures, architectures, interfaces, and techniques, such details are provided for purposes of explanation and should not be viewed as limiting. Moreover, those of skill in the art will, in light of the present disclosure, appreciate that various aspects of the invention claimed may be practiced in other examples or implementations that depart from these specific details. At certain junctures in the following disclosure descriptions of well known devices, circuits, and methods have been omitted to avoid clouding the description of the present invention with unnecessary detail.
With reference to
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In step S01, a gray-scale difference between the first frame and the second frame is detected to determine a driving mode variation between the first frame and the second frame.
In step S02, the number of pixels driven by a dynamic mode and the number of pixels driven by a static mode in the second frame is adjusted according to the driving mode variation.
In step S03, gray-scale data corresponding to the pixels in the second frame is output.
In step S04, a liquid crystal display panel is driven according to the gray-scale data corresponding to the pixels in the second frame.
The following operation is made in order to eliminate or reduce the surge that results from frame driving mode variation and the sudden change of the frame luminance that may be sensed by the viewer. Driving mode variation includes switching, in either direction, between static mode and dynamic mode. When the frame driving mode is changed, the image display method of an embodiment of the invention adjusts the number of pixels driven by the dynamic mode and the number of pixels driven by the static mode in the next frame, or adjusts the ratio of the number of pixels driven by the dynamic mode to the number of pixels driven by the static mode in the next frame. In one embodiment of the present invention, the driving mode of all the pixels in the whole frame is gradually switched from the dynamic mode to static mode or from static mode to dynamic mode, instead of suddenly switching the driving mode of all the pixels in the whole frame to dynamic mode or static mode as practiced in conventional methods. For instance, according to some embodiments, the driving modes of certain pixels in the frame may be different from the driving modes of other pixels in the frame. A pixel driven by the dynamic mode may use the conventional gray insertion technology to display the image signal, and a pixel driven by the static mode may not use the gray insertion technology to display the image signal. Thus, when the frame driving mode is changed, the sudden change of the frame luminance may be eliminated or reduced, and the generated luminance surge can be reduced.
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In the example of
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The order of appearance for the frames from
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In addition, when each pixel in the block is not completely driven by the static mode or the dynamic mode and the ratio is adjusted due to the frame driving mode being changed, the dynamic/static pixel ratio only has to be adjusted in a reverse direction.
For example, the frame driving mode may be changed from the dynamic mode to the static mode, and then changed back to the dynamic mode in, for example, the third frame (
According to an embodiment of the invention as shown in
The frame buffer controller 21, electrically connected to the input buffer 22, may store frame data received by the input buffer 22 and/or frame buffer 20. The frame buffer controller 21 may provide frame data from the frame buffer 20 to the detecting circuit 24 and the gray-scale converting circuit 26.
The detecting circuit 24 may detect a gray-scale difference between successive frames (between frames Fm−1 and Fm) to determine a driving mode variation between the frames Fm−1 and Fm. Detecting circuit 24 may output a driving mode conversion determining signal SD/S. The adjusting circuit 25, electrically connected to detecting circuit 24, may adjust the number of pixels driven by a dynamic mode and the number of pixels driven by a static mode in the frame Fm (or a ratio of the number of pixels driven by a dynamic mode to the number of pixels driven by a static mode in the frame Fm) according to the driving mode conversion determining signal SD/S. The gray-scale converting circuit 26, electrically connected to the adjusting circuit 25, may output the gray-scale data corresponding to each pixel.
When the gray-scale converting circuit 26 processes the frame Fm, the detecting circuit 24 and the adjusting circuit 25 may adjust the ratio of the number of pixels driven by the dynamic mode to the number of pixels driven by the static mode in the frame Fm or adjust the number of pixels driven by the dynamic mode and the number of pixels driven by the static mode in the frame Fm according to the driving mode variation between the frames Fm−1 and Fm.
The frame data may be input from the input buffer 22 and then output to a data line driving circuit (not shown) from the output buffer 23. The data line driving circuit may output the frame data to a storage capacitor of each pixel on a liquid crystal display panel so as to control the tilting angle of the corresponding liquid crystal molecules.
In one embodiment of the invention, the detecting circuit 24 may subtract the values of the gray-scale data of the pixel in the frame Fm−1 from the values of the gray-scale data of the pixel in the frame Fm to obtain a plurality of gray-scale differences, sum the gray-scale differences, or, for example, the absolute values of the gray-scale differences, to obtain a summed difference, and compare the summed difference with a threshold value such as, for example, (maximum gray level)×(resolution of the display)×3×( 1/20), to generate the driving mode conversion determining signal SD/S to determine whether the driving mode between the frames Fm−1 and Fm is different.
When the frame Fm−1 is driven by the dynamic mode and the frame Fm is driven by the static mode, the driving mode conversion determining signal SD/S may be at a first level. When the frame Fm−1 is driven by the static mode and the frame Fm is driven by the dynamic mode, the driving mode conversion determining signal SD/S may be at a second level.
Referring to
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The driving mode tables 252 and the block may have the same size in one embodiment of the invention. For example, if the block is a 2×2 square matrix, the adjusting circuit 25 may have four driving mode tables 252 and information recorded in each driving mode table 252 as shown in
The multiplexer 253 may select one of the driving mode tables 252 according to the count value Val, and output the values of the reference marks of the driving mode tables 252 in a column-by-column and row-by-row manner to serve as the pixel driving mode switching signal Smux.
When the driving mode is converted from the dynamic frame Fm−1 into the static frame Fm, the count value Val may be increased, and the count values Val in the following frames Fm+1 and Fm+2 may be gradually increased. Thus, the multiplexer 253 may select, frame-by-frame, the driving mode table 252 with increasingly larger number of reference marks “1” as the output so as to increase the number of the pixels driven by the static mode gradually. When the count value Val reaches the maximum, it may represent that all the pixels are driven by the static mode.
On the other hand, when the driving mode is converted from the static frame Fm−1 into the dynamic frame Fm, the count value Val may be decreased, and the count values Val in the following frames Fm+1 and Fm+2 may be gradually decreased. Thus, the multiplexer 253 may select, frame-by-frame, the driving mode table 252 with the larger number of the reference marks “0” as the output so as to decrease the number of the pixels driven by the static mode gradually. When the count value Val reaches the minimum, it may represent that all the pixels are driven by the dynamic mode.
In addition, as will be discussed further below, the other frame counter 254 may continuously switch a level of a sub-frame switching signal SH/L during two sub-frames of one frame.
In one embodiment of the invention, the adjusting circuit 25 may have eight driving tables 252 and information recorded in each driving mode table 252 as shown respectively in, for example,
Furthermore, the contents of the driving mode table 252 corresponding to each pixel may change once every frame in one embodiment of the invention. Taking the driving mode table of square matrix for example, the matrix may be rotated by 90 degrees to change the contents of the driving mode table (i.e., position of each pixel driven by different methods in the block) and to prevent a fixed pattern from being generated when the image is being displayed. When the driving mode table 252 is composed of plural columns of pixels, the positions of the columns may be arbitrarily or sequentially changed to change the contents of the driving mode table (i.e., position of each pixel driven by different methods in the block). In addition, the driving mode table 252 may also be replaced with a random number generating table. That is, the contents of the driving mode table (i.e., positions of the pixels driven by the static/dynamic mode in the block) are not fixed.
Referring again to
The multiplexer 261 may select the gray-scale data determined by one of the static gray-scale table 264, the dynamic high gray-scale table 262 and the dynamic low gray-scale table 263 as the output according to the pixel driving mode switching signal Smux output from the driving mode table 252. When the pixel at some position in the block is driven by the static mode, the multiplexer 261 selects the gray-scale data from the static gray-scale table 264 as the output in one frame period. When the pixel at some position in the block is driven by the dynamic mode, the multiplexer 261 sequentially selects the gray-scale data from the dynamic high gray-scale table 262 and the dynamic low gray-scale table 263 as the output in successive sub-frames of one frame period according to the sub-frame switching signal SH/L. The output may be provided to the data line driving circuit so that the liquid crystal display panel can show the image normally. Thus, a portion of the pixels is driven by the dynamic mode, and the other portion of the pixels is driven by the static mode simultaneously.
In another embodiment of the invention, as shown in
In another embodiment of the invention, the detecting circuit 24 may compare the value of the gray-scale data of the pixel in the frame Fm−1 and the value of the gray-scale data of the pixel in the frame Fm to determine if the pixel changes the gray-scale data in successive frames, accumulate the number of pixels changing the gray-scale data to obtain a total number, and compare the total number with a threshold value such as, for example, (resolution of the display)×3×( 1/20), to determine whether the driving mode between the frames Fm−1 and Fm is different.
Therefore, in one embodiment of the invention, the LCD device and the image display method may adjust the number of pixels driven by the dynamic mode and the number of pixels driven by the static mode (or the ratio of the number of pixels driven by the dynamic mode to the number of pixels driven by the static mode) in the second frame instead of driving all pixels in the second frame by the dynamic mode or the static mode when the driving mode is changed between the first frame and the second frame. Consequently, it is possible to prevent the sudden change of the luminance of the image when the driving mode is changed. Thus, the viewer may not easily sense the surge generated in the image.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons or ordinary skill in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.
Number | Date | Country | Kind |
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95138282 A | Oct 2006 | TW | national |
Number | Name | Date | Kind |
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20060238552 | Chuang et al. | Oct 2006 | A1 |
20070063947 | Kang | Mar 2007 | A1 |
20070165051 | Yamada | Jul 2007 | A1 |
Number | Date | Country | |
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20080088650 A1 | Apr 2008 | US |