As the liquid crystal display (LCD) technology advances, LCD televisions are gradually replacing cathode ray tube televisions in the global market. However LCD televisions are less responsive to motion pictures than CRT televisions, thus motion blur often occurs at the edges of moving objects on LCD TVs. In order to reduce the motion blur, a clock multiplier factor has been used.
FIG. 1 shows two adjacent pixels 101, 102 displaying gray levels A and B in a time frame Tf. FIG. 2 shows the two adjacent pixels 101, 102 displaying gray levels A and B in the first half of the time frame Tf, and displaying black images (gray level 0) in the second half of the time frame Tf by doubling the clock multiplier factor. According to an eye-tracking model, this will effectively reduce the blur width of motion blur by roughly a half. However, since the known method displays the correct gray levels only in half a period instead of a full period, the luminance of the picture is reduced by half and the image quality is sacrificed.
To minimize the reduction of luminance, another method has been provide to reduce the blur width of motion blur while the luminance is rarely affected. In FIG. 3, when the pixels 101, 102 receive target gray levels A and B respectively, the pixel 101 displays substitute gray levels A′ and C in the time frame Tf sequentially, and the pixel 102 displays substitute gray levels B′ and D in the time frame Tf sequentially. The average luminance of the substitute gray levels A′ and C is similar to the luminance of the target gray level A. The average luminance of the substitute gray levels B′ and D is similar to the luminance of the target gray level B. FIG. 4 shows a table 40 listing the substitute gray levels for each target gray level for the method of FIG. 3. According to FIGS. 3 and 4, when a pixel receives, e.g., a target gray level of 150 for a time frame, the pixel will display substitute gray levels of 250 and 0 sequentially each for half a time frame. When a pixel receives, e.g., a target gray level of 151 for a time frame, the pixel will display substitute gray levels of 255 and 0 sequentially each for half a time frame. As shown in the table 40, when a received target gray level is smaller than 152, a black image with a gray level of 0 will substitute for half a time frame so that the luminance of the two substitute gray levels will be similar to the luminance of the received target gray level. When a received target gray level is greater than 150, a white image with a gray level of 255 will substitute for half a time frame so that the luminance of the two substitute gray levels will be similar to the luminance of the received target gray level. Frequently, gray levels of adjacent pixels are very close. Thus, if the received target gray levels of both of the pixels 101, 102 are smaller than 152, then the substitute gray levels C, D are both 0. If the received target gray levels of both of the pixels 101, 102 are greater than 150, then the substitute gray levels A′, B′ are both 255. In both situations, the blur width of the motion blur will be reduced approximately by half without impairing the overall luminance. FIG. 5 illustrates the table 40 in a coordinate format. When a received target gray level is not smaller than g51, the first substitute gray level is 255. When a received gray level is not greater than g51, the second substitute gray level is 0. Further in the known method, the sequence of the first and second substitute gray levels can be reversed as long as the sequence is consistent throughout the picture being displayed on the LCD TV. Moreover, g51 can be 151 or another number.
FIGS. 2 and 3 disclose two common methods for reducing the blur width of motion blur. Both methods display a large amount of black images, which may cause problems to the pixel luminance. In particular, after a pixel displays a black image, if a following image has a high grey level, the pixel is likely to display the following image at a luminance lower than the expected luminance. After a pixel displays a high grey level image, if a following image is supposed to be a black image, the pixel is likely to display the following image at a luminance higher than the expected luminance.
FIG. 6 shows the luminance displayed by a pixel during several time frames from t60 to t69 as implemented by the method of FIG. 4. During the time frames from t60 to t64, the pixel receives a target grey level 100 twice. According to the table 40, the pixel should display images at substitute grey levels 150, 0, 150, 0 sequentially. During the time frames from t65 to t69, the pixel receives a target grey level 151 twice. According to the table 40, the pixel should display images at substitute grey levels 255, 0, 255, 0 sequentially. However due to the slow response of the liquid crystal material, the luminance L1 at t62, t64 (corresponding to the substitute grey level of zero) is lower than the luminance L2 at t67, t69 (also corresponding to the substitute grey level of zero) by Δy1.
FIG. 7 shows the luminance displayed by the pixel during several time frames from t70 to t79 as implemented by the method of FIG. 4. During the frames from time t70 to t74, the pixel receives a target grey level 151 twice. According to the table 40, the pixel should display images at substitute grey levels 255, 0, 255, 0 sequentially. During the frames from time t75 to t79, the pixel receives a target grey level 200 twice. According to the table 40, the pixel should display images at substitute grey levels 255, 100, 255, 100 sequentially. However due to the slow response of the liquid crystal material, the luminance L4 at t71, t73 (corresponding to the substitute grey level of 255) is lower than the luminance L5 at t76, t78(also corresponding to the substitute grey level of 255) by Δy2.
FIGS. 6 and 7 show that the slow response of the liquid crystal material is one reason why the LCD's pixels are unable to display images at the desired luminance. For example, the luminance at t67, t69 fails to reach the desired level of L1, and the luminance at t71, t73 fails to reach the desired level of L5. This has caused distortion to the images displayed by the pixel since the pixel is unable to display the images both without motion blur and with the desired luminance.