JP2008292704A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is reduced in capacity of a memory for an LUT during overshoot driving. <P>SOLUTION: The liquid crystal display device has the LUT 4 in which coefficients of cubic functions when an overshoot grayscale is represented with the cubic functions of a first grayscale are stored correspondingly for every multiple predetermined second grayscales, and a first operation unit which finds an overshoot grayscale as an output grayscale from a first grayscale of a current frame by using a cubic function whose coefficient is determined with a second grayscale one frame before the current frame among the cubic functions whose coefficients are stored in the LUT 4. Respective relationships between first grayscales predetermined with respective cubic functions of the plurality of predetermined second grayscales determined by the respective second grayscales and overshoot grayscales approximate respective relationships between first grayscales and overshoot grayscales when the overshoot grayscales suitable to a module 5 are determined using the second grayscales predetermining those relationships and the first grayscales. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including a display module, and more particularly to a liquid crystal display device display device that performs overshoot driving.

  In recent years, progress in flat panel displays (FPDs) has been remarkable, and CRT monitors are being replaced by various FPDs. In particular, Liquid Crystal Display (LCD), the pioneer of FPD, has made remarkable progress in technology and has been used in various scenes of daily life. It is growing.

  However, LCD still has some major weaknesses. One of the typical examples is that it is not good at displaying moving images. That is, the response speed is slower than that of CRT, and afterimage and image blurring in moving image display are problems. The response speed of the liquid crystal is often considered to be a black and white switching speed, but with the replacement of the cathode ray tube monitor as described above, the switching between halftone and halftone accounts for a large proportion, and the liquid crystal in this state The response speed must be taken into account. Moreover, in general, the response speed is slower in switching between halftones and halftones than in monochrome switching, which is a problem. In particular, a liquid crystal display device in the VA (vertical alignment) mode has a slow response from an intermediate gradation.

  For this reason, increasing the response speed is an unavoidable problem when replacing a TV with a CRT, and how to increase the response speed of liquid crystal between all gradations is significant. It has become a challenge. One of the means for solving the above problems is an overshoot drive. An example of this driving method is shown in FIG. When the liquid crystal switches from the gradation level (gradation) A of one frame to the gradation B of the next frame, generally, the larger the difference in gradation level between gradation A and gradation B, the larger The liquid crystal performs high-speed switching.

  Accordingly, if the rise response is A <B as shown in FIG. 17, by inputting the target gradation level B after instantaneously inputting the overshoot gradation C having the gradation level satisfying B <C, It becomes possible to switch the liquid crystal at a higher speed than the normal switching speed from A to B. If the decay response is A> B, the target gradation level B is input after the overshoot gradation C having the gradation level B> C is input, so that the normal A is changed to B. The liquid crystal can be switched at a higher speed than the switching speed.

  Actually, during full gradation switching (for example, switching from 0 gradation to 255 gradation), the liquid crystal switches at the highest speed, so the response speed of the liquid crystal by overshoot drive is theoretically between all gradations. In this switching, the response speed of full gradation switching can be increased. Therefore, by using overshoot drive in the liquid crystal display mode in which full gradation switching has a sufficiently high speed response, it is possible to obtain an LCD capable of a sufficiently high speed response in switching between all gradations.

  One of the important factors in overshoot driving is how to determine the gradation C described above.

  To determine the gradation C, an LUT-ROM (Lookup Table-Read Only Memory) having a lookup table is used. That is, the gradation C can be determined by comparing the gradation A of a certain frame with the gradation B of the next frame by referring to the lookup table.

  In Patent Document 1, the upper 4 bits of 8-bit input data and the upper 4 bits of 8-bit previous frame data are input to a lookup table, and the lower 4 bits of the input data are added to the output of the lookup table. It is disclosed. According to this configuration, the step of the output data can be reduced as much as possible while reducing the memory capacity of the lookup table.

  In recent years, there has been a tendency for moving picture reproduction on mobile devices to increase, and accordingly, it is required to realize overshoot driving with a small circuit.

Patent Documents 2 and 5 disclose a technique for determining an output gradation in consideration of additional conditions such as temperature. Patent Document 3 discloses a technique for comparing the current frame with the gradation of the previous frame and determining the output gradation based on the comparison result. Patent Document 4 discloses a technique for compressing data by encoding / decoding.
JP 2006-126256 A (published May 18, 2006) JP 2004-4629 A (published January 8, 2004) JP 2005-326633 A (published November 24, 2005) JP 2006-47993 A (published February 16, 2006) JP 2006-195231 A (released July 27, 2006)

  However, as described in Patent Document 1 above, when 4 bits of 8 bits are used, the remaining 4 bits are not taken into account, so that the accuracy for obtaining the output gradation is reduced (that is, the input gradation is smoother). And a problem that the memory stored in the LUT is still large and expensive. Further, Patent Documents 2 to 5 similarly have a problem that the memory of the LUT is large.

  The present invention has been made in view of the above problems, and its purpose is to reduce the memory of the look-up table without degrading the accuracy of obtaining the output gradation when performing overshoot driving. Another object of the present invention is to provide a liquid crystal display device that eliminates the look-up table and reduces costs.

  In order to solve the above problems, the liquid crystal display device of the present invention has a display module that displays an image processed by overshoot driving, and when the image is divided into frames, A liquid crystal display device that obtains an overshoot gradation to be output to a display module as an output gradation from a second gradation one frame before the current frame, and for each of a plurality of predetermined second gradations, Of the first look-up table in which the coefficient of the cubic function when the shoot gradation is expressed by the cubic function of the first gradation is stored in association with each other, and the cubic function in which the coefficient is stored in the first look-up table, A first calculation unit that obtains an overshoot gray level as an output gray level from the first gray level of the current frame using a cubic function in which a coefficient is determined by the second gray level one frame before the frame; Each relationship between the first gradation and the overshoot gradation defined by each cubic function determined by each second gradation of a plurality of second gradations determined in advance is each second defining these relationships. It is characterized in that it approximates the relationship between the first gradation and the overshoot gradation when the overshoot gradation suitable for the display module is determined using the gradation and the first gradation.

  In general, in order to perform overshoot driving, when a look-up table in which an optimum output gradation is determined from the gradation of the current frame and the gradation one frame before the current frame is used, When the relationship between the gradation of the current frame and the output gradation is represented in a graph for each key, the curve has a maximum of two inflection points.

  Focusing on this point, in the above configuration, the overshoot gradation (corresponding to the output gradation) is set to the first floor for each of a plurality of predetermined second gradations (corresponding to the gradation one frame before the current frame). This is expressed by a cubic function (corresponding to the gradation of the current frame), and the coefficient of this cubic function is stored in the lookup table for each second gradation, and the first gradation and the second floor are stored using this cubic function. A first calculation unit for obtaining an overshoot tone as an output tone from the tone is provided.

  Furthermore, in the present invention, each relationship between the first tone and the overshoot tone defined by each cubic function determined by each second tone of a plurality of second tones determined in advance is the relationship between each of these relationships. It is approximated to the relationship between the first gradation and the overshoot gradation when the overshoot gradation suitable for the display module is determined in accordance with each of the second gradation and the first gradation. Yes. In addition, how to obtain the overshoot gradation suitable for the display module according to the second gradation and the first gradation can be obtained by various conventional methods.

  Therefore, it is not necessary to store a large number of overshoot gradations corresponding to the first gradation and the second gradation in the lookup table as in the prior art, and the lookup table has a number of second predetermined values to be determined in advance. It is only necessary to store a coefficient of a cubic function for each gradation. Among these cubic functions, an overshoot gradation as an output gradation corresponding to the first gradation is obtained using a cubic function determined by the second gradation. Since the cubic function is determined so as to approximate the relationship between the first gradation and the overshoot gradation, the amount of memory stored in the lookup table can be reduced without degrading the accuracy of the output gradation. The cost can be greatly reduced and the cost can be reduced.

  In the liquid crystal display device of the present invention, when the second gradation one frame before the current frame is not any of the plurality of predetermined second gradations, it corresponds to any of the plurality of predetermined second gradations. It is preferable to have a first linear interpolation unit that obtains a coefficient of a cubic function corresponding to the second gradation one frame before the current frame by linear interpolation using the obtained coefficient.

  According to the above configuration, even if the second gradation one frame before the current frame is not stored in advance in the lookup table, the coefficient corresponding to any of the second gradations stored in advance. Is linearly interpolated to obtain a coefficient corresponding to the second gradation one frame before the current frame. Therefore, even when the second gradation is not stored in the lookup table in advance, the overshoot gradation as the output gradation can be obtained from the first gradation of the current frame.

  In the liquid crystal display device of the present invention, when the second gradation one frame before the current frame is not any of the plurality of predetermined second gradations, it corresponds to any of the plurality of predetermined second gradations. It is preferable to have a second linear interpolation unit that obtains an overshoot gradation as an output gradation by linear interpolation using the overshoot gradation obtained by the first calculation unit using the calculated coefficient.

  According to the above configuration, even if the second gradation one frame before the current frame is not stored in the lookup table in advance, the coefficient corresponding to one of the second gradations stored in the lookup table Is used to linearly interpolate the overshoot tone obtained by the first calculation unit to obtain an overshoot tone as an output tone. Therefore, even when the second gradation is not stored in the lookup table in advance, the overshoot gradation as the output gradation can be obtained from the first gradation of the current frame.

  In order to solve the above problems, the liquid crystal display device of the present invention has a display module that displays an image processed by overshoot driving, and when the image is divided into frames, A liquid crystal display device that obtains an overshoot gradation to be output to the display module as an output gradation from the second gradation one frame before the current frame. An overshoot gradation suitable for a display module when one gradation is the minimum gradation, an overshoot gradation suitable for the display module when one gradation is the maximum gradation, and an intermediate floor between the minimum gradation and the maximum gradation. Overshoot gradation suitable for the display module when the predetermined gradation a is smaller than the tone, and display module when the predetermined gradation b is larger than the intermediate gradation between the minimum gradation and the maximum gradation. It is characterized by having a second look-up table with four overshoot grayscale overshoot Gradation for a Le stored in association with each of the first gradation.

  In general, in order to perform overshoot driving, when a look-up table in which an optimum output gradation is determined from the gradation of the current frame and the gradation one frame before the current frame is used, When the relationship between the gradation of the current frame and the output gradation is represented in a graph for each key, a curve having a maximum of two inflection points is obtained. An inflection point is obtained when the gray level of the current frame is equal to the gray level one frame before the current frame.

  Focusing on this point, in the above configuration, when the first gradation becomes the minimum gradation, the overshoot gradation and the maximum gradation suitable for the display module are obtained for each second gradation determined in advance. Overshoot gradation suitable for the display module, overshoot gradation suitable for the display module when the predetermined gradation a is smaller than the intermediate gradation between the minimum gradation and maximum gradation, and the minimum gradation and maximum A second look in which four overshoot gradations, which are suitable for the display module in the case of a predetermined gradation b greater than the intermediate gradation, are stored in association with each first gradation. Has an up table.

  When the first gradation is an intermediate gradation between the minimum gradation and the maximum gradation (for example, 128 gradations if 256 gradations), the average of inflection points of gradations one frame before It becomes. According to the above configuration, an appropriate overshoot tone value in the case where the first tone is smaller than the average (intermediate tone) of the inflection points, i.e., the larger tone b and the second look is used. Stored in the uptable. It should be noted that the convexity on the first gradation-overshoot gradation graph and the convexity on the bottom are exchanged at least once in each of the places where the first gradation is larger and smaller than the intermediate gradation. .

  Therefore, from these overshoot gradations, the relationship between the first gradation and the overshoot gradation can be approximated to a linear function. Therefore, it is not necessary to store overshoot gradations corresponding to the first gradation and the second gradation in the lookup table as in the prior art, and the lookup table has a predetermined second gradation for each predetermined gradation. In addition, since only the overshoot gradation corresponding to the predetermined first gradation is stored, the amount of memory stored in the lookup table can be greatly reduced. In addition, since the overshoot gradation suitable for the predetermined gradation “a” larger than the intermediate gradation and the gradation “b” smaller than the intermediate gradation is obtained, it is possible to prevent the deterioration of the accuracy.

  In the liquid crystal display device of the present invention, the gradation a is an intermediate gradation between the second gradation and the minimum gradation, and the gradation b is an intermediate gradation between the second gradation and the maximum gradation. It is preferable that

  According to the above configuration, the gradation a is an intermediate gradation between the second gradation and the minimum gradation, and the gradation b is an intermediate gradation between the second gradation and the maximum gradation. That is, appropriate overshooting in two cases, the first gradation being an intermediate gradation between the second gradation and the minimum gradation and the intermediate gradation between the second gradation and the maximum gradation. We are looking for shoot gradation.

  When the first gradation is equal to the second gradation, that is, when the gradation of the current frame is the same as that of the previous frame, it becomes an inflection point in the first gradation-overshoot gradation graph. According to the above configuration, the overshoot gradation value for the first gradation in the middle of the inflection point, the minimum gradation, and the maximum gradation is obtained. In the vicinity of the midpoint between the inflection point and the minimum gradation and the maximum gradation, there is a high possibility that there is a switching between an upward convex and a downward convex in the graph representing the relationship between the first gradation and the overshoot gradation. Accordingly, by obtaining the overshoot gradation for the first gradation in this portion, it is possible to obtain the overshoot gradation for all the first gradations using linear interpolation. Therefore, it is not necessary to store the overshoot gradation corresponding to the first gradation and the second gradation in the lookup table as in the prior art, and the second lookup table has some second floors to be determined in advance. For each key, it is only necessary to obtain the relationship between the first gradation and the overshoot gradation, and the amount of memory stored in the lookup table can be greatly reduced.

  In the liquid crystal display device of the present invention, the second gradation one frame before the current frame is not any of the plurality of second gradations determined in advance, and the first gradation of the current frame is the lowest floor. If the tone is equal to one of the tone, maximum tone, tone a, or tone b, an overshoot tone corresponding to one of a plurality of predetermined second tones is linearly interpolated to output an overtone as an output tone. It is preferable to have a third linear interpolation unit for obtaining a shoot gradation.

  According to the above configuration, even if the second gradation one frame before the current frame is not stored in the second lookup table in advance, it corresponds to one of the second gradations stored in advance. A third linear interpolation unit that obtains an overshoot gradation corresponding to the second gradation one frame before the current frame by linearly interpolating the overshoot gradation is provided. Therefore, even when the second gradation is not stored in the second lookup table in advance, the overshoot gradation as the output gradation can be obtained from the first gradation of the current frame.

  In the liquid crystal display device of the present invention, the second gradation one frame before the current frame is equal to any of a plurality of predetermined second gradations, and the first gradation of the current frame is the current frame. When the first gradation is not equal to any of the minimum gradation, maximum gradation, gradation a, or gradation b, the first gradation that becomes the minimum gradation, maximum gradation, gradation a, or gradation b It is preferable to have a fourth linear interpolation unit that linearly interpolates an overshoot gradation corresponding to any of the gradations to obtain an overshoot gradation as an output gradation.

  According to the above configuration, the first gradation of the current frame is the minimum gradation, the maximum gradation, the intermediate gradation between the second gradation and the minimum gradation, or the intermediate between the second gradation and the maximum gradation. Even if it is not equal to any of the gradations, the fourth linear interpolation unit for obtaining an overshoot gradation corresponding to any of the second gradations stored in advance is provided. Therefore, the first gradation of the current frame, in which the first gradation is stored in the lookup table in advance, is the minimum gradation, the maximum gradation, the intermediate gradation a between the second gradation and the minimum gradation, or the second gradation. Even if the gradation b is not intermediate between the tone and the maximum gradation, the overshoot gradation as the output gradation can be obtained from the first gradation of the current frame.

  In the liquid crystal display device of the present invention, the second gradation one frame before the current frame is not any of the plurality of second gradations determined in advance, and the first gradation of the current frame is the lowest floor. If the tone, the maximum tone, the tone a, or the tone b are not equal, the first frame of the current frame is calculated from the overshoot tone corresponding to any second tone stored in the second look-up table. A third linear interpolation unit for obtaining an overshoot gradation corresponding to the case where the gradation is the minimum gradation, the maximum gradation, the gradation a, and the gradation b, and the overshoot obtained by the first linear interpolation unit. It is preferable to have a fourth linear interpolation unit for linearly interpolating the gradation to obtain an overshoot gradation as an output gradation.

  According to the above configuration, the second gradation one frame before the current frame is not stored in the second lookup table in advance, and the first gradation of the current frame is the first gradation of the current frame. The minimum gradation, the maximum gradation, the intermediate gradation “a” between the second gradation and the minimum gradation, or the intermediate gradation “b” between the second gradation and the maximum gradation. Also, from the overshoot gradation corresponding to any of the second gradations stored in the second lookup table, the first gradation of the current frame becomes the minimum gradation, maximum gradation, second gradation and minimum gradation. A third linear interpolation unit for obtaining an overshoot gray level corresponding to a gray level a intermediate between the key and a gray level b between the second gray level and the maximum gray level; The overshoot gradation obtained as described above is linearly interpolated to obtain the overshoot gradation as the output gradation. And a mel fourth linear interpolation unit. Therefore, the overshoot gradation as the output gradation can be obtained from the first gradation of the current frame.

In order to solve the above problem, the liquid crystal display device of the present invention has a display module for displaying an image processed by overshoot driving, and when the image is divided into frames, the first floor of the current frame is displayed. A liquid crystal display device that obtains an overshoot gradation to be output to a display module as an output gradation from a tone and a second gradation one frame before the current frame;
A comparison unit that compares the first gradation of the current frame with the second gradation one frame before the current frame;
When the first gradation of the current frame is larger than the second gradation one frame before the current frame, a predetermined quadratic function whose constant changes in accordance with the second gradation, A second calculation unit that obtains an overshoot gradation from the first gradation of the current frame as an output gradation using a quadratic function; and the first gradation of the current frame is greater than the second gradation one frame before the current frame Is constant, the constant changes according to the second gradation, but is a predetermined quadratic function different from the quadratic function, and the first function of the current frame using the quadratic function of the first gradation. A third arithmetic unit that obtains an overshoot gradation from the gradation as an output gradation, and a first gradation when an overshoot gradation suitable for the display module is determined using an arbitrary second gradation The constant is determined by the relationship between the overshoot tone and the second tone that defines this relationship. Two of the first gradation and the overshoot grayscale defined by a quadratic function relationship and is characterized in that mutually similar that.

  In general, in order to perform overshoot driving, when a look-up table in which an optimum output gradation is determined from the gradation of the current frame and the gradation one frame before the current frame is used, When the relationship between the gradation of the current frame and the output gradation is represented in a graph for each key, a curve having a maximum of two inflection points is obtained. Further, by combining two quadratic functions, a curve having an inflection point can be approximated. Further, an inflection point is obtained when the gradation of the current frame is equal to the gradation one frame before the current frame.

  Focusing on this point, in the above configuration, the comparison unit that compares the first gradation of the current frame with the second gradation one frame before the current frame, and the first gradation of the current frame is the current frame A predetermined quadratic function whose constant changes in accordance with the second gradation when the second gradation is larger than the second gradation one frame before, and using the quadratic function of the first gradation, A second arithmetic unit that obtains an overshoot gradation as an output gradation from the gradation and the second gradation one frame before the current frame; and a second gradation that the first gradation of the current frame is one frame before the current frame The constant changes according to the second gradation, but is a predetermined quadratic function that is different from the quadratic function, and the second Output gradation from one gradation and overshoot gradation from the second gradation one frame before the current frame And the relationship between the first gradation and the overshoot gradation when an overshoot gradation suitable for the display module is determined using an arbitrary second gradation. The relationship between the first gradation and the overshoot gradation defined by two quadratic functions whose constants are determined by the second gradation that defines the relationship is approximated to each other.

  That is, by expressing the relationship between the first gradation and the overshoot gradation with two quadratic functions with the inflection point as a boundary, the second calculation unit and the third calculation that calculate using these two relationships By providing the unit, a look-up table becomes unnecessary, the memory can be greatly reduced, and the cost can be reduced. Furthermore, when an overshoot gradation suitable for the display module is determined using an arbitrary second gradation, the relationship between the first gradation and the overshoot gradation and a constant at the second gradation that defines this relationship Since the relationship between the first gradation and the overshoot gradation defined by the two quadratic functions for which is determined is approximated, the output gradation can be obtained without reducing the accuracy.

  In the liquid crystal display device of the present invention, a third function that stores at least one of the coefficient of the quadratic function used for the calculation of the second calculation unit and the coefficient of the quadratic function used for the calculation of the third calculation unit is stored. Preferably, a lookup table is provided.

  According to the above configuration, at least one of the coefficient of the quadratic function used for the calculation of the second calculation unit and the coefficient of the quadratic function used for the calculation of the third calculation unit is stored in the third lookup table. Has been.

  Thereby, the precision of approximation can be further improved by appropriately adjusting the coefficient stored in the third lookup table.

  As described above, the liquid crystal display device of the present invention has a display module that displays an image processed by overshoot driving, and the first gradation of the current frame and the current frame when the image is divided into frames. A liquid crystal display device that obtains an overshoot gradation to be output to the display module as an output gradation from the second gradation one frame before the overshoot gradation for each of a plurality of predetermined second gradations Of the current frame among the first look-up table in which the coefficients of the cubic function are stored in association with each other and the cubic function in which the coefficients are stored in the first look-up table. A first arithmetic unit that obtains an overshoot gray level as an output gray level from the first gray level of the current frame using a cubic function whose coefficient is determined by the second gray level before the frame. Each relationship between the first gradation and the overshoot gradation defined by each cubic function determined by each of the second gradations of the number of second gradations is the second gradation that defines these relationships, and This approximates the relationship between the first gradation and the overshoot gradation when the overshoot gradation suitable for the display module is determined using the first gradation.

  In addition, the liquid crystal display device of the present invention has a display module for displaying an image processed by overshoot driving. When the image is divided into frames, the first gradation of the current frame and one frame of the current frame are displayed. A liquid crystal display device that obtains an overshoot gradation to be output to a display module as an output gradation from a previous second gradation, wherein the first gradation is the smallest for each of a plurality of predetermined second gradations Overshoot gradation suitable for the display module when the gradation is reached, overshoot gradation suitable for the display module when the gradation is maximum, a predetermined smaller than the intermediate gradation between the minimum gradation and the maximum gradation An overshoot gradation suitable for the display module when the gradation a is reached, and an overshoot suitable for the display module when the predetermined gradation b is greater than the intermediate gradation between the minimum gradation and the maximum gradation. Four overshoot gradation chute tone has a second lookup table storing in association with each of the first gradation.

In addition, the liquid crystal display device of the present invention has a display module for displaying an image processed by overshoot driving. When the image is divided into frames, the first gradation of the current frame and one frame of the current frame are displayed. A liquid crystal display device that obtains an overshoot gradation output to a display module as an output gradation from the previous second gradation,
A comparison unit that compares the first gradation of the current frame with the second gradation one frame before the current frame;
When the first gradation of the current frame is larger than the second gradation one frame before the current frame, a predetermined quadratic function whose constant changes in accordance with the second gradation, A second calculation unit that obtains an overshoot gradation from the first gradation of the current frame as an output gradation using a quadratic function;
Unlike the above quadratic function, when the first gray level of the current frame is smaller than the second gray level one frame before the current frame, it is a predetermined quadratic function whose constant changes according to the second gray level. A third arithmetic unit that obtains an overshoot gradation from the first gradation of the current frame as an output gradation using a quadratic function of the first gradation, and uses an arbitrary second gradation The relationship between the first gradation and the overshoot gradation when the overshoot gradation suitable for the display module is determined, and two quadratic functions whose constants are determined by the second gradation that defines this relationship. The relationship between the first gradation and the overshoot gradation is approximate to each other.

  Accordingly, when overshoot driving is performed, the memory for the look-up table is reduced or the look-up table is eliminated without reducing the accuracy for obtaining the output gradation, and the liquid crystal display device is designed to reduce the cost. Can be provided.

  The present invention obtains the output gradation y for overshoot driving by a predetermined calculation when determining the gradation (arrival gradation) x of the current frame and the gradation k one frame before. As a result, the memory amount of the lookup table for overshoot driving can be greatly reduced, or the cost can be reduced by eliminating the lookup table itself.

[Embodiment 1]
In the present embodiment, in overshoot driving, the current frame gradation (reaching gradation; corresponding to “first gradation” described in claims) x and output gradation (described in claims) (Corresponding to “Overshoot tone”) A case of approximating a graph showing a relationship with y by a cubic function will be described.

  Note that the cubic function can be approximated in this way in the VA mode liquid crystal module, in the normally black method, the response from the low gradation to the low gradation is slow and the response from the low gradation to the high gradation is The reason is that in the fast, normally white system, the opposite is true, and the response speed increases between gradations. Even in the IPS mode, there is a difference in response speed between gradations, but this is particularly noticeable in the VA mode. The difference in response speed depends on the type of liquid crystal display device and is difficult to calculate theoretically. Therefore, as shown below, the cubic function parameters (coefficients) ).

[Configuration of liquid crystal display device]
An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a liquid crystal display device of the present embodiment.

  This liquid crystal display device is a device that performs so-called overshoot driving. Here, “overshoot driving” is a driving method in which an excessive signal voltage is applied to the liquid crystal cell in a short time, and this overshoot driving accelerates the change in the molecular arrangement of the liquid crystal substance, thereby expressing moving images. Can be improved.

  As shown in FIG. 1, the liquid crystal display device includes an external signal source (signal source) 1, a frame memory 2, a first calculation unit (corresponding to “first calculation unit” recited in the claims) 3, a look An up table (LUT; corresponding to “first look-up table” described in claims) 4 and a module (corresponding to “display module” described in claims) 5 are provided.

  The signal source 1 converts the reached gradation (the current frame gradation) x into the frame memory 2 and the first calculation unit 3, more specifically, the first output gradation calculation unit of the first calculation unit 3. 7 (described later).

  The frame memory 2 is a FIFO (First-in First-out) type memory capable of storing gradation data for one frame. Therefore, the frame memory 2 can perform simultaneous processing of data input / output. The frame memory 2 can generate a gradation k that is delayed by one frame (a gradation one frame before; corresponding to the “second gradation” recited in the claims). The frame memory 2 calculates the gradation k of one frame before by the first calculation unit 3, more specifically, a first linear interpolation unit 6 (described later) and a first output calculation unit 7 of the first calculation unit 3. Send to.

  The module 5 includes an active matrix type liquid crystal panel (panel) including a thin film transistor (TFT) as a switching element, and drivers (source driver and gate driver; not shown) for driving the liquid crystal panel. The liquid crystal panel has a plurality of source bus lines (not shown) arranged in parallel with each other in the vertical direction of the screen and a plurality of scanning lines (not shown) arranged in parallel with each other in the horizontal direction of the screen. On the outside of the liquid crystal panel, the source bus line is connected to the source driver, while the scanning line is connected to the gate driver. The source bus lines and the scanning lines are orthogonal to each other, and pixels (not shown) are formed corresponding to the intersections. In these pixels, a TFT (Thin Film Transistor; not shown) and a liquid crystal cell (not shown) are arranged. In order to display an image on this liquid crystal panel, the TFT connected to each scanning line is sequentially turned on for each scanning line by a gate driver, and according to the gradation data (image data) corresponding to each scanning line by a source driver. The gradation voltage thus written is written to the pixel corresponding to each scanning line.

  Next, it is the most important part of the present invention. The LUT 4 and the first calculation unit 3 will be described.

[About LUT4]
The LUT 4 will be described. More specifically, data stored in advance in the LUT 4 will be described.

  When the gradation k one frame before is 0, 32, 64, 96, 128, 160, 192, 224, 255, the ideal relationship between the reached gradation x and the output gradation y is As shown in FIG. That is, FIG. 2 is a graph showing the relationship between the reached gradation x and the output gradation y, which is an approximation target in the present invention, and is an experimental value (measured value).

  The inventors of the present invention have determined a cubic function (a cubic function indicating the relationship between the reached gradation x and the output gradation y) shown in FIG. 2 in a plurality of gradations k (0, 32, 64, 96, 128, 160, 192, 224, 255).

  By the way, all the cubic functions can be expressed by the following general formula.

Y = a * X3 + b * X2 + c * X + d (Formula 1)
For convenience of explanation, normalization is performed as Y = y / 255 (y: output gradation) and X = x / 255 (x: arrival gradation). Further, a, b, c, and d are variable parameters that change depending on the gradation k one frame before. If a, b, c, and d corresponding to the gradation k one frame before are determined, the output gradation y can be obtained from the arrival gradation x based on the above (Equation 1).

  From FIG. 2, the following (A) to (C) hold.

  (A) The xy curve corresponding to the gradation k one frame before passes through (0, 0) and (1, 1) regardless of the value of the gradation k one frame before.

  (B) When the gradation k and the arrival gradation x that are one frame before are the same gradation, the output gradation y is equal to the arrival gradation x.

  (C) The above-described (B) is established at an inflection point when the xy curve is approximated to a cubic function.

  From (A), (Equation 1) becomes d = 0 and c = 1−ab. Therefore, (Expression 1) can be rewritten as the following (Expression 2).

Y = a * X3 + bX2 + (1-ab) * X (Formula 2)
Further, from (C), the cubic function has a second derivative (second derivative) of 0 at the inflection point. Further, at the inflection point, the condition of (B) is satisfied, that is, the gradation k one frame before and the reaching gradation x are the same gradation, so that (Equation 3) below is 0, x = k holds (the gradation k one frame before and the arrival gradation x are equal).

d2Y / dX2 = 3a × X + 2b (Formula 3)
Therefore, if K = k / 255 (k: gradation before one frame), (Expression 2) can be further rewritten as the following (Expression 4).

Y = a * X3- (3a / 2) * X2 + (1-a + (3a / 2) K) * X (Formula 4)
The variable parameter a is determined according to the value of the gradation k one frame before. Therefore, the variable parameter a in (Equation 4) can also be written as a (K).

  Further, it is ideal to obtain the value of the variable parameter a corresponding to all the gradations k one frame before, that is, to obtain a (K), but in practice it is very difficult to obtain this. Therefore, in the present embodiment, the value of a in (Expression 4) is obtained for a discrete tone k before one frame as follows. That is, assuming that the gradation k of one frame before is 0, the graph of the cubic function drawn by (Expression 4), and the xy curve corresponding to 0 of the gradation k of 1 frame before in FIG. Determine the value of a (K) that is more approximate. The value of a obtained here is, for example, k0.

  Next, assuming that k is 32, the variable parameter a in which the graph of the cubic function drawn by (Expression 4) and the graph corresponding to the gradation k of 32 in the previous frame in FIG. Determine the value of. The value of a thus obtained is set to k32, for example. Thereafter, k64, k96, k128, k160, k192, k224, and k255 are obtained in the same manner.

  K0 to k255 obtained in this way are stored in the LUT 4 as the variable parameter a in the above (Equation 4). The variable parameter a is a value unique to the module 5.

[About the first arithmetic unit 3]
As shown in FIG. 1, the first calculation unit 3 includes a first linear interpolation unit (corresponding to the “first linear interpolation unit” recited in the claims) 6, and a first output gradation calculation unit. 7.

  Whether the first linear interpolation unit 6 selects the value of the variable parameter a from the values (k0 to k255) stored in the LUT 4 based on the gradation k one frame before received from the frame memory 2 Or by linear interpolation.

  The first linear interpolation unit 6 receives the gradation k one frame before from the frame memory 2, and the gradation k is 0, 32, 64, 96, 128, 160, 192, 224, or 255. Determine if it exists. When the gradation k one frame before is one of 0, 32, 64, 96, 128, 160, 192, 224, or 255, the first linear interpolation unit 6 sets the variable parameter a corresponding to each of them. Is selected from the LUT 4 and sent to the first output gradation calculation unit 7.

  On the other hand, when the gradation k one frame before is not any of 0, 32, 64, 96, 128, 160, 192, 224, and 255, the first linear interpolation unit 6 performs as follows. Thus, the value of the variable parameter a is determined. That is, the first linear interpolation unit 6 calculates (k0 + k32) / 2, for example, when the gradation k one frame before is 16, and uses this value as the variable parameter a, the first output gradation in the subsequent stage. This is sent to the calculation unit 7. That is, the first linear interpolation unit 6 obtains the value of the variable parameter a in (Expression 4) by linear interpolation. Furthermore, in other words, the first linear interpolation unit 6 outputs 0 if the gradation k one frame before is not 0, 32, 64, 96, 128, 160, 192, 224, or 255. , 32, 64, 96, 128, 160, 192, 224, and 255, the variable parameter a stored in the LUT 4 corresponding to any two gradations is received from the LUT 4, and the value of the variable parameter a is obtained by linear interpolation. Ask for.

  The first output gradation calculation unit 7 receives the arrival gradation x from the signal source 1, receives the value of the variable parameter a from the first linear interpolation unit 6, and the gradation one frame before from the frame memory 2. k is received, the output gradation y is obtained from these values based on the above (Equation 4), and sent to the module 5. Note that the first output gradation calculation unit 7 may receive the reached gradation x and the gradation k one frame before through the first linear interpolation unit 6.

[Operation of liquid crystal display device]
First, the signal source 1 sends the reached gradation x to the frame memory 2 and the first calculation unit 3. More specifically, the data is sent to the first output gradation calculation unit 7 of the first calculation unit 3. The frame memory 2 that has received the reached gradation x sends the gradation k one frame before to the first linear interpolation unit 6 and the first output gradation calculation unit 7 of the first calculation unit 3.

  The first linear interpolation unit 6 that has received the gradation k one frame before determines whether or not the value of the variable parameter a corresponding to this gradation is stored in the LUT 4, that is, the first first interpolation unit 6. The first linear interpolation unit 6 determines whether the gradation k one frame before is any of 0, 32, 64, 96, 128, 160, 192, 224, or 255.

  When the gradation k one frame before is 0, 32, 64, 96, 128, 160, 192, 224, or 255, the first linear interpolation unit 6 corresponds to these gradations k. The value of the variable parameter a to be received is received from the LUT 4 and sent to the first output gradation calculation unit 7.

  On the other hand, when the gradation k one frame before is not 0, 32, 64, 96, 128, 160, 192, 224, or 255, the first linear interpolation unit 6 sets the variable parameter a to LUT4. The value of the variable parameter a corresponding to any two gradations k one frame before stored is received from the LUT 4, and the variable parameter a corresponding to the gradation k one frame before is obtained by linear interpolation. The value is obtained by calculation and sent to the first output gradation calculation unit 7.

  The first output gradation calculation unit 7 receives the value of the variable parameter a received from the first linear interpolation unit 6, the value of the reached gradation x received from the signal source 1, and one frame received from the frame memory 2. Based on the value of the previous gradation k and the above (Equation 4), the output gradation y is obtained and output to the module 5.

  As described above, in the liquid crystal display device according to the present embodiment, the LUT 4 has the gradation k (0, 32, 64, 96, 128, 160, 192, 224, or 255) one frame before as the variable parameter a. The overshoot drive can be performed by storing only nine values (k0 to k255) corresponding to. Therefore, the memory can be significantly reduced as compared with the conventional case where 81 memories are stored in the LUT, and the cost can be reduced. Further, since it is not necessary to perform linear interpolation between the reached gradation x and the output gradation y, a continuous value can be obtained. Note that the variable parameter a may be input from the outside with the LUT 4 externally attached.

(Variation 1 of Embodiment 1)
In the first calculation unit 3 described above, when the gradation k one frame before is not any of 0, 32, 64, 96, 128, 160, 192, 224, and 255, After obtaining the variable parameter a corresponding to the gradation k by linear interpolation, the output gradation y is obtained. However, the present invention is not limited to this, and the output gradation y may be linearly interpolated instead of linearly interpolating the variable parameter a. For example, when the gradation k of the previous frame is 16 gradations, the output gradation y is, for example, when the gradation k of the previous frame is 0 and 32 (that is, when the variable parameters are k0 and k32). The respective output gradations y are obtained, and these output gradations y are linearly interpolated to obtain the output gradation y when the gradation k one frame before is 16 gradations.

  In this case, the first linear interpolation unit 6 in FIG. 1 does not linearly interpolate a, and one or two values (variable parameter a) received from the LUT 4 are sent to the first output tone calculation unit 7. send. Thereafter, when the first output gradation calculation unit 7 receives one value from the first linear interpolation unit 6, the first output gradation calculation unit 7 sets this as the output gradation y as a module. Send to 5. On the other hand, when the first output gradation calculation unit 7 receives two values from the first linear interpolation unit 6, the first output gradation calculation unit 7 is provided in a first stage (not shown) provided after the first output gradation calculation unit 7. The output gradation y is linearly interpolated according to the value of the gradation k one frame before by a linear interpolation part (corresponding to the “second linear interpolation part” recited in the claims) different from the linear interpolation part As a result, an output gradation y corresponding to the gradation k one frame before received from the frame memory 2 is obtained and sent to the module 5.

(Variation 2 of Embodiment 1)
The data stored in (Equation 4) and the LUT 4 are not limited to the above, and the following may be used.

  Instead of the above (formula 4), the following (formula 5) may be used.

Y = b × (X−1) ³ + b (X−1) ² + (1−b−c) × (X−1) +1 (Formula 5)
That is, in the above (Equation 4), the variable parameter a is set to one according to the gradation k one frame before. However, as shown in (Equation 5), the variable parameter is set to two of b and c. Also good. This (Equation 5) is also obtained based on the above (A) to (C).

  In this case, two variable parameters b and c are stored in the LUT 4 in accordance with the gradation k (0, 32, 64, 96, 128, 160, 192, 224, or 255) one frame before. Has been.

  As an example of the relationship between the variable parameters b and c and the gradation k one frame before, the one shown in FIG. 3 can be used. These variable parameters b and c are obtained by approximating with the graph shown in FIG. 2 for each gradation k one frame before as in the case of a.

  FIG. 4 shows the relationship between the reached gradation x and the output gradation y for each gradation k one frame before using FIG. Also in this case, the amount of memory in the LUT can be significantly reduced compared to the conventional case, and the cost can be reduced.

[Embodiment 2]
In the present embodiment, a case will be described in which a graph indicating the relationship between the gradation (arrival gradation) x of the current frame and the output gradation y in overshoot driving is approximated by a linear function. That is, in this embodiment, a method for approximating the curve shown in FIG. 2 with a plurality of straight lines (linear functions) will be described. Only parts different from the first embodiment will be described, and the description of the same parts will be omitted.

  A block diagram of a liquid crystal display device in the case of approximating a linear function will be described.

  As shown in FIG. 5, the liquid crystal display device according to the present embodiment includes an external signal source (signal source) 11, a frame memory 12, a second arithmetic unit 13, and a lookup table (LUT). “Corresponding to“ second look-up table ”) 14 and module (corresponding to“ display module ”described in claims) 15. In the present embodiment, the second linear interpolation unit 16 (described later) receives the reached gradation x from the signal source 11 and the gradation k one frame before from the frame memory 12. Yes.

  Since the difference from the first embodiment described above is the data stored in the LUT 14 and the second calculation unit 13, these two points will be described, and description of other members will be omitted.

[About LUT14]
Based on FIG. 2, when the gradation k one frame before is 0, 32, 64, 96, 128, 160, 192, 224 and 255, the arrival gradation x is 64 gradations (claims) Output gradation y in the case of “gradation a” described in the above, and output gradation y in the case of 160 gradation (corresponding to “gradation b” described in claims). Ask. Data of these output gradations y is written in the LUT 14 in advance. Further, in the LUT 14, the reached gradation x is 0 gradation (corresponding to the “minimum gradation” recited in the claims), 255 gradation (corresponding to the “maximum gradation” recited in the claims) The output gradation y is also stored. FIG. 6 is a diagram describing the contents of the LUT 14 thus obtained. The reason why the output gradation y when the arrival gradation x is 64 gradations and the output gradation y when the arrival gradation x is 160 gradations will be described later.

[About the second arithmetic unit 13]
As shown in FIG. 5, the second calculation unit 13 includes a second linear interpolation unit (corresponding to “third linear interpolation unit” recited in the claims) 16 and a third linear interpolation unit (patent (Corresponding to “fourth linear interpolation unit” recited in the claims). Hereinafter, each of the second linear interpolation unit 16 and the third linear interpolation unit 17 will be described.

[About the second linear interpolation unit 16]
The second linear interpolation unit 16 determines whether the gradation k one frame before corresponds to any of 0, 32, 64, 96, 128, 160, 192, 224, or 255.

  When the second linear interpolation unit 16 determines that the gradation k one frame before corresponds to one of 0, 32, 64, 96, 128, 160, 192, 224, or 255, the second linear interpolation unit 16 further determines whether the reached gradation x corresponds to any one of 0, 64, 160, and 255.

  (D) When the second linear interpolation unit 16 determines that the reached gradation x corresponds to any one of 0, 64, 160, or 255, the second linear interpolation unit 16 outputs from the LUT 14. The data of the gradation y is received, and this is sent as it is to the module 15 as the output gradation y. For example, based on FIG. 6, when the gradation k one frame before is 32 and the arrival gradation x is 160, 225 is sent to the module 15 as the output gradation y.

  (E) On the other hand, if the second linear interpolation unit 16 determines that the reached gradation x is not any of 0, 64, 160, or 255, the second linear interpolation unit 16 sets 0, 64, Out of 160 and 255, the data of the output gradation y corresponding to each of the two gradations before and after the reached gradation x is received from the LUT 14 and sent to the third linear interpolation unit 17. For example, the second linear interpolation unit 16 may output data 207 (output gradation y when the arrival gradation x is 160, for example, when the gradation k of one frame before is 64 and the arrival gradation x is 224. ) And 255 (data of the output gradation y when the arrival gradation x is 255) are sent to the third linear interpolation unit 17.

  On the other hand, when the second linear interpolation unit 16 determines that the gradation k one frame before is not 0, 32, 64, 96, 128, 160, 192, 224, or 255, the second linear interpolation The unit 16 selects the arrival gradation (0, 64, 160, 255) x of the gradation k one frame before any two of 0, 32, 64, 96, 128, 160, 192, 224, or 255. The data of the output gradation y corresponding to is received from the LUT 14.

  For example, if the gradation k one frame before is 16 gradations, the second linear interpolation unit 16 outputs the output gradation y (when the gradation k one frame before is 0 and 32. 0, 203, 249, 255; 0, 117, 225, 255) are received from the LUT 14.

After that, the second linear interpolation unit 16 outputs corresponding to each reached gradation x (0, 64, 160, 255) in the case of gradation k (16 gradations) one frame before by linear interpolation. The data of gradation y is obtained. For convenience of explanation, it is assumed that the data of the obtained output gradation y is Y ₀ , Y ₆₄ , Y ₁₆₀ , Y ₂₅₅ .

  Further, the second linear interpolation unit 16 determines whether the reached gradation x is 0, 64, 160, or 255.

(F) If the second linear interpolation unit 16 determines that the reached gradation x corresponds to one of 0, 64, 160, or 255, the second linear interpolation unit 16 performs the linear operation as described above. The data of the output gradation y obtained by interpolation, that is, any one of Y ₀ , Y ₆₄ , Y ₁₆₀ , or Y ₂₅₅ is sent to the module 15. For example, when the reached gradation x is 64, the second linear interpolation unit 16 sends Y ₆₄ of the output gradation y data to the module 15 as the output gradation y data.

(G) On the other hand, if the second linear interpolation unit 16 determines that the reached gradation x is not 0, 64, 160, or 255, the second linear interpolation unit 16 determines that Y ₀ , Y Out of ₆₄ , Y ₁₆₀ , and Y ₂₅₅ , data of output gradation y corresponding to any two gradations of the gradation of the current frame is sent to the third linear interpolation unit 17. For example, when the reached gradation x is 96, the second linear interpolation unit 16 sends Y ₆₄ and Y ₁₆₀ to the third linear interpolation unit 17.

[About the third linear interpolation unit 17]
In the case of (E), the third linear interpolation unit 17 receives data of two output gradations y from the second linear interpolation unit 16, and performs linear interpolation from the data of these output gradations y by 1 An output gradation y corresponding to the gradation k before the frame and the arrival gradation x is obtained. For example, when the gradation k of one frame before is 192 and the arrival gradation x is 112, the output gradation y is set to 226 and sent to the module 15.

  The third linear interpolation unit 17 receives data of two output gradations y from the second linear interpolation unit 16 and performs linear interpolation from the data of these output gradations y in the case of (G) above. The output gradation y corresponding to the gradation k one frame before and the arrival gradation x is obtained, and the obtained output gradation y is sent to the module 15. For example, when the reached gradation x is 112, “Y64 + (Y160−Y64 / 2)” is sent to the module 15 as the output gradation y.

  By approximating the curve shown in FIG. 2 with a linear function as in the present embodiment, the data stored in the LUT becomes 36 as shown in FIG. 6, which is less accurate than in the first embodiment. Compared to the above, the memory of the LUT can be reduced. FIG. 7 is a graph showing the relationship between the gradation x and the output gradation y of the current frame when overshoot driving is performed using the LUT 14 shown in FIG.

  Note that the 64 gradation and the 160 gradation are merely examples, and any one may be used as long as one is a gradation smaller than the 128 gradation and the other is a gradation larger than the 128 gradation.

  Here, in the above description, the output gradation y when the arrival gradation x is 64 gradations and the output gradation y when the arrival gradation x is 160 gradations are obtained. This is because the error is minimized by setting. In other words, the average of the inflection points in the gradation k (0, 32, 64, 96, 128, 160, 192, 224 and 255) one frame before is 64 gradations (current frame) and 160 gradations (current frame). ), The error can be reduced.

  This reason is considered to be due to the vertical alignment (VA) mode. That is, in the VA mode liquid crystal module, the rise of liquid crystal molecules from a low gradation is very slow in the normally black method, while the rise from a high gradation is fast, and vice versa in the normally white method. For this reason, the LUT used for rising from a low gradation is a large parameter, and conversely, it is a relatively small parameter when rising from a high gradation. FIG. 8 is a diagram illustrating an example in which the response speed is measured in the VA mode liquid crystal alignment.

  The response speed differs depending on the gradation, and the LUT has a characteristic shape due to the property that it becomes the slowest when changing from a low gradation to a low gradation. Further, when the start gradation and the arrival gradation are the same, the LUT becomes the same as the arrival gradation, and thus the inflection point of the LUT is this point. As described above, in the case of approximating the linear function, the reached gradation is set to 64 gradation and 160 gradation because the most consistent with the original shape can be obtained by selecting these two places. . Since the inflection point changes according to the gradation k one frame before, selecting the point farthest from the inflection point approximates the original shape. FIG. 8 shows the case of a normally black module. In the case of normally white, the gradation is reversed, so that the peak position is changed from a high gradation to a high gradation.

  Further, according to the second embodiment, since the output gradation y can be obtained by a simple calculation, the scale of the arithmetic circuit can be made smaller than that in the first embodiment.

(Variation 1 of Embodiment 2)
In the second embodiment, the value of the LUT 14 is set assuming that the reached gradation x is 64 gradations and 160 gradations.

  However, for each gradation k one frame before, the intermediate gradation between the inflection point where the gradation k of the previous frame and the gradation x of the current frame are equal, and the minimum gradation, and the inflection point and the maximum The output gradation y in the intermediate gradation with the gradation may be obtained and stored in a lookup table instead of FIG. Thus, the linear interpolation can be used to approximate the graph of FIG.

(Variation 2 of Embodiment 2)
A modification of the second embodiment, that is, a modification in the case of approximating the curve shown in FIG. 2 with a linear function will be described. In the modification of the second embodiment, the second calculation unit 13 in the liquid crystal display device includes a fourth linear interpolation unit (not shown) and a second output tone calculation unit (not shown).

  In the second embodiment, the value of the LUT 14 is set assuming that the reached gradation x is 64 gradations and 160 gradations. However, the present invention is not limited to the above method, and the following method may be used. In the following description, it is assumed that there are two inflection points.

  From the obtained inflection points, three straight lines “Y = aX (0 ≦ X ≦ f), Y = bX + c (f ≦ X ≦ g), Y = dX + e (g ≦ X ≦ 255) ”. The LUT 14 stores a to g corresponding to the gradation k obtained one frame before in advance.

  When the gradation k one frame before is not 0, 32, 64, 96, 128, 160, 192, 224, or 255, the fourth linear interpolation unit linearly changes the values of a to g. When it is obtained by interpolation and sent to the second output gradation calculation unit, while the gradation k one frame before is 0, 32, 64, 96, 128, 160, 192, 224, or 255, The fourth linear interpolation unit sends the values of a to g corresponding to the gradation k one frame before stored in the LUT 14 to the second output gradation calculation unit.

  The second output gradation calculation unit outputs the output scale based on the above-mentioned “Y = aX (0 ≦ X ≦ f), Y = bX + c (f ≦ X ≦ g), Y = dX + e (g ≦ X ≦ 255)”. The key is obtained and the obtained output gradation is sent to the module 15.

  Further, the above-mentioned f is preferably near the middle between the origin and the inflection point, g is preferably near the middle between the inflection point and (255, 255), and h always takes 255, so three straight lines Therefore, the number of variables can be reduced by setting c = a × f and e = b × g + a × f.

[Embodiment 3]
In the present embodiment, a case will be described in which a graph indicating the relationship between the gradation (arrival gradation) x of the current frame and the output gradation y in overshoot driving is approximated by a quadratic function. That is, in the present embodiment, a method for approximating the curve shown in FIG. 2 to a quadratic function will be described. Only parts different from the first and second embodiments will be described, and the description of the same parts will be omitted.

  A block diagram of a liquid crystal display device in the case of approximating a quadratic function will be described.

  As shown in FIG. 9, the liquid crystal display device according to the present embodiment includes an external signal source (signal source) 21, a frame memory 22, and a third arithmetic unit (the “second arithmetic unit” recited in the claims). Corresponding) 23, fourth computing unit (corresponding to “third computing unit” described in claims) 24, module (corresponding to “display module” described in claims) 25, and comparing unit 26 It has.

  Unlike the above-described first and second embodiments, the liquid crystal display device of the present embodiment does not include an LUT. In addition, the liquid crystal display device of the present embodiment includes two calculation units 23 and 24, and includes a comparison unit 26 as a further configuration.

  In general, since the quadratic function can express the change of the slope only once, the present inventors have found that the inflection point is divided into cases. Furthermore, when the gradation k and the arrival gradation x are the same as one frame before, the output gradation y is always equal to the arrival gradation x, and the point in the graph of the arrival gradation x−output gradation y at this time Therefore, the present inventors have found that K (k / 255) = X (x / 255) is used as a boundary to classify cases. Based on this concept, a configuration unique to the present embodiment will be described below. Note that the boundary is not limited to one boundary for the gradation k one frame before, and may have a plurality of boundaries.

[Comparator 26]
The comparator 26 receives the reached gradation x from the signal source 21 and also receives the gradation k one frame before from the frame memory 22. The comparison unit 26 compares these reached gradations x with the gradation k one frame before, and determines the magnitude relationship.

  When the comparison unit 26 determines that the arrival gradation x and the gradation k one frame before are equal to each other, the comparison unit 26 outputs the arrival gradation x to the module 25 as the output gradation y.

  When the comparison unit 26 determines that the gradation k one frame before the arrival gradation x is larger, the comparison unit 26 sends the gradation k and the arrival gradation x one frame before to the third calculation unit 23.

  When the comparison unit 26 determines that the gradation k one frame before the arrival gradation x is smaller, the comparison unit 26 transmits the gradation k and the arrival gradation x one frame before to the fourth calculation unit 24.

[About the third arithmetic unit 23]
Third arithmetic unit 23 receives the gradation k and reached gradation x of the preceding frame from the comparator 26, (1 / K) of the calculated X ^2, it outputs a value 255 times the value obtained gradation y To the module 25. As in the first embodiment, K = k / 255 and X = x / 255.

That is, the third calculation unit 23
Y = (1 / K) X ²
Is used to calculate the output gradation y.

  Note that X = x / 255, Y = y / 255, and K = k / 255 (the same applies in the present embodiment).

[About the fourth arithmetic unit 24]
The fourth calculation unit 24 receives the gradation k and the arrival gradation x one frame before from the comparison unit 26, obtains 1-{(X-1) ² } / K, and is a value obtained by multiplying the obtained value by 255. Is output to the module 25 as an output gradation y. That is, the fourth calculation unit 24
Y = 1 − {(X−1) ² } / K
Is used to calculate the output gradation y.

  FIG. 10 is a graph showing the relationship between the reached gradation and the output gradation determined using the liquid crystal display device of the third embodiment.

  As a result, overshoot driving can be performed without providing a lookup table, and a significant cost reduction can be achieved.

  In each of the above embodiments, the display of 8 bits, that is, 256 gradations is described. However, the display is not limited to this, and display with other gradations such as 6 bits may be used.

  However, when approximated by a quadratic function, as shown in FIG. 11, a lookup table (third lookup table; LUT) 30 may be provided in the liquid crystal display device.

  As shown below, a quadratic function different from the above may be used, and the coefficient of this quadratic function may be stored in the lookup table in advance.

  The liquid crystal display device shown in FIG. 11 is simply provided with the LUT 30 that stores the coefficients of the quadratic function used for the calculations performed by the third calculation unit 23 and the fourth calculation unit 24 in the liquid crystal display device shown in FIG. It ’s just that.

  Data stored in the LUT 30 shown in FIG. 11 will be described. The LUT 30 stores a first coefficient of a quadratic function used for calculation by the third calculation unit 23 and a second coefficient of a quadratic function used for calculation by the fourth calculation unit 24.

Even when the LUT 30 is provided, as in the case where the LUT 30 is not provided, the approximation is performed by the least square method by dividing before and after the inflection point for each gradation one frame before. (In other words, the determination is made depending on whether the gradation of the current frame is larger or smaller than the gradation one frame before.)
Coefficients a2, b2, c2 of quadratic functions when the third calculation unit 23 performs calculation (that is, the gradation of the current frame is smaller than the gradation of the previous frame, in the case of decay response), And the coefficients a1, b1, c1 of the quadratic function when the calculation is performed in the fourth calculation unit 24 (that is, the gradation of the current frame is larger than the gradation of the previous frame, in the case of a rise response). Is as shown in the following [Table 1].

  That is, in the LUT 30, the data shown in [Table 1] is stored in advance as a coefficient of a quadratic function in accordance with the gradation one frame before. Where a1 and a2 are quadratic coefficients of a quadratic function, b1 and b2 are quadratic coefficients of the quadratic function, and c1 and c2 are zeroth-order coefficients of the quadratic function. is there.

  FIG. 12 is a graph showing the relationship between the gradation of the current frame and the output gradation when the liquid crystal display device shown in FIG. 11 is used, that is, when approximated to a quadratic function.

  As described above, by providing the LUT 30 also in this embodiment, the accuracy of approximation can be improved as compared with the graph of FIG. 10 by adjusting the curve of the intercept and the function curve in FIG.

  How to actually obtain the output gradation from the general formula will be briefly described. A structure having a logic operation unit in addition to a memory area for storing a frame memory and a look-up table inside an IC for overshoot driving. The logic operation unit is a logic circuit formed from logical operators such as AND, OR, and NOT. It is possible to calculate the output gradation by forming a logic circuit with an approximate function such as a cubic function in the present invention in this logic operation unit.

[Supplementary explanation]
Here, as a supplementary explanation, a specific approximation method to a cubic function, a quadratic function, and a linear function will be described.

  FIG. 13 is a graph showing experimental values (actually measured values), and is a graph showing the relationship between the ideal output gradation and the gradation of the current frame for each gradation one frame before, as in FIG. is there.

  The graph shown in FIG. 2 is slightly different from the graph shown in FIG. This is because it depends on experimental conditions such as characteristics and temperature of the liquid crystal display panel to be used.

  In order to approximate this graph with a cubic function, the data is rotated 90 degrees. FIG. 14 is a graph rotated 90 degrees. In this way, the reason for rotating 90 degrees is that the gradation one frame before is a function of the output gradation, but the output gradation is not a function of the gradation one frame before, so This is because the approximation by the polynomial cannot be performed.

  Fitting by the least square method is performed on each of the gradations one frame before the graph shown in FIG.

  Table 2 is calculated by approximation. By using Table 1, the graph shown in FIG. 15 can be generated.

  Finally, by rotating FIG. 15 by 90 degrees, as shown in FIG. 16, an approximate graph representing the gradation of the current frame with respect to the output gradation can be created.

  If the value of y is uniquely determined when x has a certain value with respect to certain x and y, y is called a function of x. In other words, if one output is always made for a certain input, it can be approximated by some form of function. What is important when performing approximation is how to improve the accuracy of the target to be approximated. In general, when approximation is performed using a polynomial, 1 is added to the number of inflection points. A good approximation can be performed using the order. In this case, we want to approximate a LUT with up to two inflection points, so we try to approximate it with a cubic polynomial. Of course, higher-order approximation can be performed with higher accuracy, but since the merit of the memory reduction effect is lost due to the complexity of the logic unit, the maximum is third-order. In addition, the accuracy is reduced by reducing the secondary, the primary, and the order, but the approximation itself can be performed.

  Moreover, since the output gradation is not a function with respect to the gradation of the current frame as in the case where approximation by a cubic function is performed using the least square method as described above, the calculation is theoretically performed. It has become difficult. This also applies to approximation by a quadratic function. However, since the quadratic function is divided into cases in the above, the output gradation is a function of the 1/2 power of the current frame as a result. Therefore, by performing an approximation such as a least square method, a mathematical expression can be obtained using the output gradation as a function of the current frame, and the output gradation can be theoretically calculated. In the case of a linear function, when x is a function of y, y is always a function of x, so that it is easy to calculate the output gradation.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The liquid crystal display device of the present invention can be used for a liquid crystal display device mounted on a mobile device.

It is a block diagram which shows the liquid crystal display device of Embodiment 1 of this invention. It is a graph which shows the ideal (approximation target) reached gradation-output gradation relationship with respect to a predetermined gradation one frame before. 6 is a table in which two variable parameters are determined for each predetermined gradation one frame before in the first embodiment. FIG. 4 is a graph showing the relationship between reached gradation and output gradation using a cubic function determined by the table shown in FIG. 3. It is a block diagram which shows the liquid crystal display device of Embodiment 2 of this invention. 10 is a table that defines output gradations that are determined with respect to a predetermined gradation one frame before and a predetermined current frame gradation in the second embodiment. It is the graph which showed the relationship of an arrival gradation-output gradation using the cubic function defined by the table shown in FIG. It is a figure which shows the example which measured the response speed in the liquid crystal alignment of VA mode. It is a block diagram which shows the liquid crystal display device of Embodiment 3 of this invention. 14 is a graph showing the relationship between the reached gradation and the output gradation determined using the liquid crystal display device of the third embodiment. FIG. 10 is a block diagram showing a liquid crystal display device different from FIG. 9 in Embodiment 3. 12 is a graph showing the relationship between the reached gradation and the output gradation determined using the liquid crystal display device shown in FIG. 11. 3 is a graph showing an ideal (approximation target) reached gradation-output gradation relationship with respect to a predetermined gradation one frame before that different from FIG. 2. 12 is a graph obtained by rotating the graph of FIG. 11 by 90 degrees. FIG. 13 is an approximate graph of FIG. 12 in which fitting by the least square method is performed on the gray level one frame before. 14 is a graph obtained by rotating the graph of FIG. 13 by 90 degrees. It is a figure explaining overshoot drive.

Explanation of symbols

3 1st operation part (1st operation part)
6 1st linear interpolation part (1st linear interpolation part)
4 LUT (first lookup table)
5 modules (display modules)
14 LUT (second lookup table)
15 modules (display modules)
16 2nd linear interpolation part (3rd linear interpolation part)
17 3rd linear interpolation part (4th linear interpolation part)
23 3rd operation part (2nd operation part)
24 4th operation part (3rd operation part)
25 modules (display modules)
26 comparison unit 30 LUT (third lookup table)

Claims (10)

A display module that displays an image processed by overshoot driving, and when an image is divided into frames, display is performed from the first gradation of the current frame and the second gradation one frame before the current frame. A liquid crystal display device that obtains an overshoot gradation output to a module as an output gradation,
A first look-up table in which a coefficient of a cubic function in a case where the overshoot gradation is expressed by a cubic function of the first gradation is stored in association with each other for a plurality of predetermined second gradations;
Of the cubic functions whose coefficients are stored in the first look-up table, the overshoot gradation is calculated from the first gradation of the current frame using a cubic function in which the coefficient is determined by the second gradation one frame before the current frame. A first calculation unit for obtaining output gradation,
Each relationship between the first gradation and the overshoot gradation defined by each cubic function determined by each second gradation of a plurality of second gradations determined in advance is each second defining these relationships. A liquid crystal display device characterized by approximating each relationship between a first gradation and an overshoot gradation when an overshoot gradation suitable for a display module is determined using the gradation and the first gradation. When the second gradation one frame before the current frame is not any of a plurality of predetermined second gradations,
A first linear interpolation unit that obtains a coefficient of a cubic function corresponding to the second gradation one frame before the current frame by linear interpolation using a coefficient corresponding to any of a plurality of predetermined second gradations; The liquid crystal display device according to claim 1. When the second gradation one frame before the current frame is not any of a plurality of predetermined second gradations,
Second to obtain an overshoot gradation as an output gradation by linear interpolation using an overshoot gradation obtained by the first calculation unit using a coefficient corresponding to one of a plurality of predetermined second gradations. The liquid crystal display device according to claim 1, further comprising a linear interpolation unit. A display module that displays an image processed by overshoot driving, and when an image is divided into frames, display is performed from the first gradation of the current frame and the second gradation one frame before the current frame. A liquid crystal display device that obtains an overshoot gradation output to a module as an output gradation,
For each of a plurality of predetermined second gradations, an overshoot gradation suitable for the display module when the first gradation is the minimum gradation, and an overshoot scale suitable for the display module when the first gradation is the maximum gradation. Overshoot gradation suitable for a display module and intermediate gradation between the minimum gradation and the maximum gradation when the gradation a is smaller than the intermediate gradation between the minimum gradation and the maximum gradation. And a second lookup table that stores four overshoot gradations that are suitable for the display module in association with each first gradation when the predetermined gradation b is larger than the predetermined gradation b. Liquid crystal display device.   The gradation a is an intermediate gradation between the second gradation and the minimum gradation, and the gradation b is an intermediate gradation between the second gradation and the maximum gradation. 5. A liquid crystal display device according to 4. The second gradation one frame before the current frame is not any of a plurality of predetermined second gradations, and the first gradation of the current frame is the minimum gradation, maximum gradation, gradation If it is equal to either a or gradation b
5. A third linear interpolation unit that linearly interpolates an overshoot gradation corresponding to any of a plurality of predetermined second gradations to obtain an overshoot gradation as an output gradation. Or 5. The liquid crystal display device according to 5. The second gradation one frame before the current frame is equal to any of a plurality of predetermined second gradations, and the first gradation of the current frame is the minimum of the first gradation of the current frame. If it is not equal to any of the gradation, maximum gradation, gradation a, or gradation b,
Fourth to obtain an overshoot gradation as an output gradation by linearly interpolating an overshoot gradation corresponding to any of the first gradation that is the minimum gradation, maximum gradation, gradation a, or gradation b 6. The liquid crystal display device according to claim 4, further comprising a linear interpolation unit. The second gradation one frame before the current frame is not any of a plurality of predetermined second gradations, and the first gradation of the current frame is the minimum gradation, maximum gradation, gradation If it is not equal to either a or gradation b
From the overshoot gradation corresponding to any of the second gradations stored in the second lookup table, the first gradation of the current frame is the minimum gradation, maximum gradation, gradation a, and gradation b. A third linear interpolation unit for obtaining an overshoot gradation corresponding to
6. The liquid crystal according to claim 4, further comprising a fourth linear interpolation unit that linearly interpolates the overshoot gradation obtained by the first linear interpolation unit to obtain an overshoot gradation as an output gradation. Display device. A display module that displays an image processed by overshoot driving, and when an image is divided into frames, display is performed from the first gradation of the current frame and the second gradation one frame before the current frame. A liquid crystal display device that obtains an overshoot gradation output to a module as an output gradation,
A comparison unit that compares the first gradation of the current frame with the second gradation one frame before the current frame;
When the first gradation of the current frame is larger than the second gradation one frame before the current frame, a predetermined quadratic function whose constant changes in accordance with the second gradation, A second calculation unit that obtains an overshoot gradation from the first gradation of the current frame as an output gradation using a quadratic function;
When the first gray level of the current frame is smaller than the second gray level one frame before the current frame, the constant changes according to the second gray level, but a predetermined quadratic function different from the above quadratic function A third arithmetic unit that obtains an overshoot gradation as an output gradation from the first gradation of the current frame using a quadratic function of the first gradation;
A constant is determined by the relationship between the first gradation and the overshoot gradation when the overshoot gradation suitable for the display module is determined using an arbitrary second gradation, and the second gradation that defines this relationship. A liquid crystal display device characterized in that the first gradation and the overshoot gradation defined by two quadratic functions approximate each other.   A third look-up table storing at least one of a coefficient of a quadratic function used for calculation of the second calculation unit and a coefficient of a quadratic function used for calculation of the third calculation unit is provided. The liquid crystal display device according to claim 9.

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