JP2007010699A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly improve response performance of liquid crystal while reducing a capacity of a frame memory. <P>SOLUTION: The luminance variation in a horizontal direction of an input image signal is detected, and its feature quantity is calculated. The input image signal is subjected to signal processing of reducing the luminance variation causing a trouble of flicker, in accordance with the detected feature quantity. Pixel data of half a line in the horizontal direction, which has been subjected to signal processing is recorded and is delayed by one frame, and a correction value for improving the response performance is obtained from delayed data and pixel data of half a line in the horizontal direction of a present frame. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device for improving response performance of liquid crystal.

  In general, there are two factors that affect the response performance of a liquid crystal display device. One is based on the hold type driving method of the liquid crystal, and one is based on the response performance of the liquid crystal itself. The liquid crystal panel writes display data once per frame using data lines and address lines to pixels arranged in a matrix. Each pixel continues to hold display data for one frame period. That is, the same image is continuously displayed for one frame period. When a moving image is displayed by such a hold-type display method, a phenomenon that the contour of a moving object is blurred occurs. This is due to the influence of the hold-type display method and human visual characteristics. The detailed explanation of the phenomenon is omitted because it is explained in “Ichiro Kurita: Image quality of moving image display on hold type display, IEICE Tech. Bulletin, EID99-10 (1999-06)”.

  Another factor is that the response performance of the liquid crystal itself is slow and does not reach the gradation that should be displayed within one frame, so that the contour of the image is blurred. Generally, the liquid crystal response performance improvement method is improved by improving the liquid crystal material itself or overdriving. Overdrive is a display that compares the display gradation of the current frame with the display gradation of the previous frame for an arbitrary pixel so that the luminance level of the display gradation of the current frame is reached within one frame period. This is a method of correcting the gradation to be performed. The method of improving the response performance by overdrive can be realized by a simple circuit, and is currently the most frequently used method.

  However, this method requires a frame memory for recording pixel data of pixels in the immediately preceding frame. The resolution of liquid crystals currently used for televisions and monitors varies, but for example, liquid crystal panels such as WXGA (1366 x 768) must record pixel data for three RGB colors for 1366 x 768 pixels. A large-capacity memory is required.

  As a method for reducing the capacity, there is one disclosed in Japanese Patent Laid-Open No. 2003-330435. In this method, pixel data to be recorded in the memory is overdriven by recording only half the pixel data of one screen. A simple example will be described with reference to FIG. 8 for explaining the correction amount calculation method.

  FIG. 8A shows an enlarged part of the display screen, and the pixel to which overdrive is applied is a half-pixel of one screen in a portion painted in black. An overdrive correction method will be described with reference to FIG. The waveform in FIG. 8B represents the change in luminance of the liquid crystal. Normally, when response performance is improved by overdrive, adjustment is generally made so that the target luminance is reached in one frame, and adjustment is made so that the luminance change shown in c of FIG. Is done.

However, in the conventional example, the number of pixels to which overdrive is applied is half, so that the average value of the luminance change between the pixels to which overdrive is applied and the pixels to which overdrive is not applied becomes the change shown in c of FIG. Adjustments are being made. That is, the pixel to which overdrive is applied is corrected more strongly than in the past, and is adjusted so as to have a luminance change as shown in b of FIG. In this way, the pixel data recorded in the memory is halved to reduce the memory capacity and improve the response performance.
JP 2003-330435 A

  However, in the overdrive adjustment method shown in the conventional example, the pixels to be recorded are thinned out and the resolution of the image is reduced. For example, when displaying a moving image in which the luminance changes for each pixel, the moving image Cannot be displayed properly.

  Details will be described with reference to FIG. 9 for explaining the circuit operation. FIG. 9 shows a part of an image in which a defect occurs in the conventional example, and is a stripe image in which gradation is periodically repeated. Further, a pixel painted black is a pixel A that is subjected to correction processing for improving the response, and is a pixel A, and a white pixel is a pixel B that is not subjected to the correction processing. Consider a case where such an image that changes every pixel moves, for example, one pixel or an odd number of pixels every frame in the left direction.

  At this time, the gradation change displayed by the pixels A and B in FIG. 9 is shown in FIG. The state of the change in gradation displayed on the pixels A and B is shown for each frame from the top. In the pixel A, 0 → 128 → 0 → 128, and in the pixel B, 128 → 0 → 128 → 0. FIG. 10B shows the gradation actually displayed in the pixels A and B after the overdrive correction according to the conventional example when the video signal shown in FIG. 10A is input.

  In this case, since correction is performed in the pixel A, the gradation displayed as 128 + α → 0 → 128 + α → 0 (α: correction value) changes for each frame. Since pixel B is not corrected, 0 → 128 → 0 → 128 is displayed for each frame. For this reason, the gradation for displaying white (128 gradations) of the stripe image in two adjacent pixels is different from 128 + α for pixel A and 128 for pixel B. Considering the case where the stripe image of FIG. 9 is actually moved by one pixel or an odd number of pixels, paying attention to the white (128 gradations) of the stripe image, the white portion of the stripe image is corrected every frame. Pixels A that are applied and pixels B that are not applied are displayed alternately.

  Therefore, the gradation change in the white part of the stripe image is displayed in different gradations for each frame of 128 → 128 + α → 128 → 128 + α. Therefore, since the luminance changes every frame, it is recognized as flicker. That is, when the pixels to be recorded are thinned out, it is not possible to properly correct the video signal that changes in a cycle shorter than the cycle of the thinned pixels.

  In order to solve this problem, the present invention records one-phase / two-phase conversion means for outputting pixel data of one half of one horizontal line from an input video signal, and pixel data output from the one-phase / two-phase conversion means. Delay means for delaying one frame period; correction value calculation means for calculating a correction value for improving response performance from the data delayed by the delay means and the pixel data output from the one-phase to two-phase conversion means; In a liquid crystal display device comprising: a correcting unit that corrects the input video signal based on the correction value calculated by the correction knowledge calculating unit; and a liquid crystal panel that displays the video signal corrected by the correcting unit. By providing video signal processing means for removing high-frequency components of the video signal input to the one-phase to two-phase conversion means, video signal processing is performed in advance on the input video signal, and a flicker or the like is disabled. To eliminate the cause of generating.

  By using the liquid crystal display device according to the present invention, even when the memory capacity is reduced and the number of pixels for recording video signals is reduced, the response performance of the liquid crystal can be improved without any problems.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to a block diagram 1 showing a configuration of a liquid crystal display device 100. In the liquid crystal display device 100 shown in FIG. 1, the video signal processing circuit 20 performs signal processing for removing high frequency components of the input video signal I0. The signal-processed video signal Is is input to the one-phase / two-phase conversion circuit 30. The one-phase / two-phase conversion circuit 30 outputs half of the pixel data of one line in the horizontal direction of the input video signal Is. The delay circuit 40 records the pixel data output from the one-phase / two-phase conversion circuit 30 and delays it by one frame period. The correction value calculation circuit 50 calculates a correction value for improving response performance from the pixel data delayed by the delay circuit 40 and the pixel data output by the one-phase / two-phase conversion means. Based on the calculated correction value, the correction circuit 60 corrects the input video signal I0 for improving the response performance, and outputs the corrected video signal I1 to the liquid crystal panel 70.

  Detailed operation will be described. The operation of the liquid crystal display device of the present invention will be described by taking, as an example, a case where a stripe image whose display tone changes for each pixel shown in FIG. 9 is input and one pixel or an odd number of pixels moves in the horizontal direction every frame. As described with reference to FIG. 10, the operation state of the conventional liquid crystal display device cannot be corrected properly for a finely changing image when pixel information for calculating a correction value is thinned out, and flickers. Such problems occur.

  On the other hand, when the image shown in FIG. 9 is input to the liquid crystal display device 100 of the present invention, the image signal processing circuit 20 is like a low-pass filter (hereinafter referred to as LPF) that removes high-frequency components of gradation change in the horizontal direction. Video signal processing. Here, for simplicity, the characteristic of the LPF is Y = (X−1 + 2X0 + X + 1) / 4 (1). X-1 is the display gradation of the pixel on the left, X0 is the display gradation of the pixel of interest, and X1 is the display gradation of the pixel on the right. That is, display gradation is performed based on not only one pixel but also a plurality of pixels.

  By this LPF, the video signal Is output from the video processing circuit 20 is removed from the high frequency components, and becomes a constant video signal having no change shown in FIG. The video signal Is subjected to signal processing in this way is output to the one-phase / two-phase conversion circuit 30. The one-phase / two-phase conversion circuit 30 outputs pixel data S that is half of one line in the horizontal direction of the input video signal Is to the delay circuit 40. Here, it is assumed that data for each pixel is output in the horizontal direction, and data for pixel A shown in FIG. 2 is output. In the delay circuit 40, the pixel data S thinned out by the one-phase / two-phase conversion circuit 30 is recorded, delayed by one frame period, and output to the correction value calculation circuit 50.

  The correction value calculation circuit 50 calculates a correction value h for improving response performance from the pixel data dS delayed by one frame and the pixel data S thinned out by the one-phase / two-phase conversion circuit 30. The manner in which the correction value h is calculated will be described with reference to FIG. 3 for explaining the correction amount calculation method. FIG. 3 (a) shows a part of pixel data of the input video signal I0. When the frame changes, the pixel data of the pixels A and B change when moving horizontally by one pixel. Is shown. FIG. 3B shows how the video signal processed by the video signal processing circuit 20 changes for each frame.

  As shown in FIG. 2, the video signal changing for each pixel is output as a constant video signal without change by the video signal processing circuit 20, so that the pixels A and B output from the video signal processing circuit 20 are output. Pixel data does not change even if the frame changes. Since the correction value calculation circuit 50 calculates the correction value based on the difference between the pixel data of the current frame and the pixel data of the previous frame, the correction value is always 0 because the pixel data does not change even if the frame changes. FIG. 3C shows a change in the video signal corrected by the correction circuit 60 based on the correction value obtained. Since the correction value is always 0, the input video signal is output as it is.

  That is, for a video signal that changes for each pixel, a defect such as flicker occurs by performing correction for improving response performance by the method shown in the conventional example. By providing a video signal processing circuit 20 that removes high-frequency components by performing gradation expression specifying the amount of change, when such a video signal is input, correction for improving response performance is not performed. To. In practice, the filter characteristics of the video signal processing circuit 20 are designed to remove only frequency components that cause flicker. By doing so, even when the memory capacity is reduced, it is possible to appropriately improve the response performance without any problems.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to a block diagram 4 showing a configuration of a video display device. Further, the operation of the circuit of the present invention is the circuit described in the first embodiment provided with the feature amount detection circuit 10, and here, the details of the operation of the part related thereto will be described and the same as in the first embodiment. Description of the parts that operate is omitted.

  In the liquid crystal display device 101 shown in FIG. 4, the feature amount detection circuit 10 calculates the feature amount of the input video signal I0 based on the luminance information of the video signal. The obtained feature amount is output to the video signal processing circuit 20, and the video signal processing circuit 20 performs a correction process on the input video signal based on the feature amount. Subsequent functions of the one-phase / two-phase conversion circuit 30, the delay circuit 40, the correction value calculation circuit 50, the correction circuit 60, and the liquid crystal panel 70 are the same as those described in the first embodiment, and will not be described.

  Detailed operations will be described with specific examples. First, in the circuit of the invention of the first embodiment, when a video signal including an image as shown in FIG. 9 is input and the image moves one pixel or an odd number of pixels in the horizontal direction for each frame, the video signal processing circuit 20 The image that periodically changes is removed, and a correction value for improving the response performance is calculated based on the image. For this reason, when the image shown in FIG. 9 described in the first embodiment is input, correction for improving response performance is not performed, and response performance is improved without causing problems such as flicker. .

  Here, a case is considered where an image that changes periodically as shown in FIG. 5 but whose luminance change is small is input. In this case as well, in the liquid crystal display device according to the invention of the first embodiment, since the image that periodically changes is removed by the video signal processing circuit 20, correction for improving the response performance is not performed.

  However, in the case of an image in which the luminance periodically changes as shown in FIG. 5 but the luminance change is small, the correction is not performed by the video signal processing circuit 20 and the correction processing for improving the response performance is performed as usual. However, since the change in luminance is small, flicker does not occur so much that it can be recognized by the eyes.

  FIG. 6 shows a state of correction processing for improving response performance in the conventional example when the image shown in FIG. 5 is input. First, FIG. 6 (a) shows a change state when the input display image is moved by one pixel or several pixels for each frame in the horizontal direction. Here, when attention is paid to the pixels A and B, it changes repeatedly from 0 to 32 to 0 to 32 for each frame. FIG. 6B shows an output value after the correction process for improving the response is performed. In the pixel A, the output value changes from 32 + β → 0 → 32 + β → 0, and the pixel B is not corrected. 32 → 0 → 32 In this case, the display gradation of white (32 gradations) of the stripe image is different between the pixel A and the pixel B by β.

  In general, the correction amount for improving the response is obtained from the difference between the current frame pixel data of the pixel of interest and the pixel data of the previous frame, and the correction amount increases as the difference increases. In this case, since the difference between the pixel A and the pixel B is not so large, the obtained correction amount β is not so large. In general, since the liquid crystal panel shows a characteristic that the luminance change with respect to the gradation change is smaller as the gradation is lower, the luminance change due to the difference β is also reduced. For these reasons, even if the image changes periodically, the luminance difference is small, and in the case of a low gradation stripe image, the video signal processing circuit 20 does not need to remove the periodically changing image. Flicker does not occur so much that it can be recognized by the eyes.

  That is, in the liquid crystal display device shown in Embodiment 1, even if the image does not generate flicker, if the image changes periodically, the video signal processing circuit 20 removes the periodically changing image, so that the response In some cases, correction for performance improvement is not performed.

  As a means for solving this, the feature amount detection circuit 10 is used in the liquid crystal display circuit of the present invention. This method will be described as a simple example when an image as shown in FIG. 7 is input. First, here, the feature amount calculated by the feature amount detection circuit 10 is an amount indicating a degree of occurrence of a defect such as flicker when the input image is scrolled or moved to perform a correction for improving the response. It is assumed that the larger the amount, the stronger the flicker occurs, and the smaller the amount, the less the flicker occurs.

  Here, as a simple example of calculating the feature amount, a case will be described where the luminance difference between the pixel of interest and its left and right pixels (or several pixels) is calculated and the average is used as the feature amount. It should be noted that this feature amount can be obtained by calculating the gradation difference between the pixel of interest and its left and right pixels (or several pixels) and using the average as the feature amount. FIG. 7A shows the input image, which is repeated as 0, 32, 032 in the ABAB pixel portion and 0, 128, 0, 128 as the A′B′A′B ′ pixel portion. Assume that an image is input. At this time, the average value of the luminance difference between the left and right pixels of each pixel is shown in FIG. This is a feature value. Assuming that the gradation of the input image changes from 0 to 255, the feature value changes from 0 to 255. Based on this value, the video signal processing circuit 20 corrects the input video signal.

  Since flicker is recognized more strongly as the luminance change is larger, correction processing is performed to increase the degree of removal of periodic changes in the input image as the feature amount increases, and the input image remains as it is as the feature amount decreases. A correction process to output is performed. That is, the filter characteristics of the video signal processing circuit 20 are changed according to the feature amount.

  Here, for the sake of simple explanation, it is assumed that, as a predetermined amount, processing using the filter of the above-described expression (1) is performed when the feature amount is 100 or more, and when it is 100 or less, the processing is performed without performing processing. The output from the video signal processing circuit at that time is shown in FIG. Since the feature amount is small in the pixel repeating ABAB, the input image is output as it is, and the pixel repeating A′B′A′B ′ has a large feature amount. Therefore, the image processed by the equation (1) is output and displayed. The key is constant at 64. If the input video signal in FIG. 7A moves by one pixel or odd number of pixels for each frame, an output from the video signal processing circuit 20 shown in FIG. 7C is used to calculate a correction value for improving the response. Since the data is used, the correction value is calculated as usual in the ABAB pixel portion and the response performance is improved, and the correction value becomes 0 in the A′B′A′B pixel portion and the correction for improving the response is not performed. Prevent flicker. As a result, when the pixels to be recorded are thinned out for cost reduction, it is possible to appropriately correct for improving the response for all images.

  It should be noted that the feature amount detection method of the feature amount detection circuit 10 described in the second embodiment can be detected by using the luminance change amount in the horizontal direction as a feature amount. Thereby, the circuit configuration can be simplified. The basic operation is the same as that described in the second embodiment, and a description thereof will be omitted.

  By using the liquid crystal display device according to the present invention, even when the memory capacity is reduced and the number of pixels for recording video signals is reduced, it is possible to improve the response performance of the liquid crystal without any problem, and as a response performance improvement device of the liquid crystal Useful.

1 is a block diagram showing a liquid crystal display device in Embodiment 1 of the present invention. The figure which shows the video signal output from the video signal processing circuit in Embodiment 1 of this invention The figure which shows the change of the display gradation of the input and output video signal in the video signal processing circuit in Embodiment 1 of this invention FIG. 6 is a block diagram showing a liquid crystal display device according to Embodiment 2 of the present invention. The figure which shows the video signal output from the video signal processing circuit in Embodiment 2 of this invention The figure which shows the change of the display gradation of the input and output video signal in the video signal processing circuit in Embodiment 2 of this invention The figure which shows the display gradation of the input and output video signal in the video signal processing circuit in Embodiment 2 of this invention The figure which shows the luminance level correct | amended by the correction method of the conventional overdrive The figure which shows the display gradation of the video signal input into the conventional liquid crystal display device The figure which shows the change of the display gradation of the input and output video signal of the conventional frame unit

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Feature amount detection circuit 20 Video signal processing circuit 30 1 phase 2 phase conversion circuit 40 Delay circuit 50 Correction value calculation circuit 60 Correction circuit 70 Liquid crystal panel

Claims (3)

A one-phase / two-phase conversion unit that outputs pixel data of half of one line in the horizontal direction from an input video signal; a delay unit that records the pixel data output from the one-phase / two-phase conversion unit and delays it for one frame period; Based on the correction value calculated from the pixel data delayed by the delay means and the pixel data output from the one-phase to two-phase conversion means, and the correction value calculated by the correction value calculation means In a liquid crystal display device including a correction unit that corrects the input video signal and a liquid crystal panel that displays the video signal corrected by the correction unit, a high-frequency component of the video signal input to the one-phase to two-phase conversion unit is obtained. A liquid crystal display device comprising a video signal processing means to be removed. Video signal processing means for removing high-frequency components of the input video signal, and one-phase to two-phase conversion means for outputting half of one horizontal line of pixel data from the video signal corrected by the video signal processing means Correction means for improving response performance is calculated from delay means for recording pixel data and delaying it for one frame period, pixel data delayed by the delay means, and pixel data output from the one-phase to two-phase conversion means. In a liquid crystal display device comprising a correction value calculating means, a correcting means for correcting the input video signal based on the calculated correction value, and a liquid crystal panel for displaying the corrected video signal, the brightness of the input video signal A feature amount detection circuit for calculating a feature amount from the signal, and the video signal processing means removes a high-frequency component of the input video signal based on the feature amount calculated by the feature amount detection circuit. The liquid crystal display device, characterized in that. The liquid crystal display device according to claim 2, wherein the feature amount detection circuit uses a horizontal luminance change amount as a feature amount.

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