JPH0580713A - Video signal correcting circuit of liquid crystal display device - Google Patents

Abstract

PURPOSE:To properly correct a video signal and simplify the device by constituting video signal correcting circuits into table constitution which uses a digital memory and storing correction curve data as table contents. CONSTITUTION:The video signal correcting circuits 2R, 2G and 2B of the liquid crystal display device which performs inverse gamma correction inverse to gamma correction performed by an image pickup system and applies voltage-transmissivity correction corresponding to the applied voltage-transmissivity characteristics of a liquid crystal light valve are constituted into the table constitution using the digital memory. This memory stores with data (combination of input data DIN and output data DOUT) of the composite correction curve C3 of an inverse gammacorrection curve C1 and an applied voltage-transmissivity correction curve C2. Two memories are used for the digital memory; and data on the inverse gammacorrection curve C1 are stored in the front-side memory and composite correction curve data on the inverse gamma correction curve and applied voltage- transmissivity correction curve C2 are stored in the rear-side memory.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal correction circuit in a liquid crystal display device such as a liquid crystal display or a liquid crystal projector, and more particularly to correction of a video signal according to the applied voltage-transmittance characteristic of a liquid crystal light valve and image pickup. Γ done in the system
This is suitable for applying to the inverse γ correction of the video signal performed in the display system for the correction.

[0002]

2. Description of the Related Art In a liquid crystal display device, by making a video signal and a light transmittance (light transmittance) have a linear relationship,
The linear gradation of the video signal is maintained, and the display quality of the video signal can be made appropriate. However, in the liquid crystal light valve in the active matrix type liquid crystal panel, the applied voltage and the transmittance are not in a linear relationship. Therefore, it is necessary to correct the video signal in advance according to the applied voltage-transmittance characteristic of the liquid crystal light valve so that the video signal before correction and the transmittance have a linear relationship. Hereinafter, such correction will be referred to as applied voltage-transmittance correction.

Further, in the image pickup system, it is assumed that a cathode ray tube whose light emission luminance is proportional to the γth power of the input voltage (that is, the light emission luminance and the input voltage are non-linear) is applied to the video signal in the display system. On the other hand, 1 / γ power correction (so-called γ correction) is performed. However, since the γ correction is for the cathode ray tube, the γ correction is unnecessary in the liquid crystal display device. Therefore, in the liquid crystal display device, inverse correction (hereinafter referred to as inverse γ correction) to γ correction performed in the image pickup system is performed on the video signal.

Conventionally, as an applied voltage-transmittance correction circuit,
A function generating circuit with an analog circuit configuration was used. Also,
A function generating circuit having an analog circuit configuration was also used as the inverse γ correction circuit. In practice, an applied voltage-transmittance correction circuit is provided after the inverse γ correction circuit, the inverse γ correction is applied only to the γ correction, and the applied voltage-transmittance correction is applied only to the applied voltage-transmittance characteristic. I am trying to do it.

[0005]

However, the applied voltage-transmittance characteristic of the liquid crystal light valve has a curve which is difficult to be expressed by one function, and even if it is approximated, there are three or more curves and a straight line. It is expressed using a combination of. Therefore, the correction circuit that performs the applied voltage-transmittance correction becomes complicated, and it is difficult to obtain an appropriate correction curve for the applied voltage-transmittance characteristic. Further, the correction curve theoretically obtained has a steep shape, and in such a steep shape portion, the output voltage naturally changes greatly with a slight difference in the input voltage, and the correction curve There is a problem that it is difficult to obtain a suitable curve. Therefore, according to the conventional correction method using the analog circuit, the applied voltage-transmittance correction is insufficient and the display image quality is deteriorated.

On the other hand, the inverse γ correction curve can be expressed by one function. However, even if it can be represented by a single function, its shape is a non-linear shape, so it is difficult to properly realize it with a function generating circuit having an analog circuit configuration. There were some things that couldn't be done.

As described above, both corrections to the video signal are insufficient, and the video signals subjected to the both corrections are more inappropriate than the combination of the degrees of insufficiency due to the respective corrections, resulting in a large display image quality. The decline could not be avoided in the past.

Incidentally, the above-mentioned problems have not been so great because the requirement for gradation required by the liquid crystal display device has been low in the past, but recently, with the development of the technology of the liquid crystal display device, The key requirement is severe, and the problem that the correction cannot be completed becomes a serious problem.

The present invention has been made in consideration of the above points, and it is possible to appropriately execute the correction of the video signal required only for the liquid crystal display device, and further to simplify the device. It is an object of the present invention to provide a video signal correction circuit for a liquid crystal display device.

[0010]

In order to solve such a problem, the present invention responds to the inverse γ correction which is the inverse correction of the γ correction executed in the image pickup system and the applied voltage-transmittance characteristic of the liquid crystal light valve. In a video signal correction circuit of a liquid crystal display device that performs applied voltage-transmittance correction, the video signal correction circuit has a table configuration using a digital memory, and the table contents are correction curve data.

More specifically, two memories are used as the digital memory, the reverse γ correction curve data is stored in the front side memory, and the applied voltage-transmittance correction curve data is stored in the rear side memory. Is preferred.

Alternatively, one memory is used as the digital memory, and an inverse γ correction curve and an applied voltage
It is preferable to store the data of the correction curve obtained by combining the transmittance correction curves.

Here, the applied voltage-transmittance characteristic of the liquid crystal light valve is divided into three areas, and a function of a predetermined power of a variable whose differential coefficient gradually increases from the area having a smaller applied voltage. It is preferable to use data of an applied voltage-transmittance correction curve which is approximated by a linear function or a function of a variable which is a variable whose derivative coefficient is gradually reduced and which is determined by an inverse function of these functions.

Further, in the correction curve data stored in the digital memory, the data value of the black level is selected to a value larger than the minimum value thereof, and the data value of the white level is selected to a value smaller than the maximum value thereof. It is preferable that the data value smaller than the data value of the black level and the data value larger than the data value of the white level are determined according to the correction curve shape between the data value of the black level and the data value of the white level.

[0015]

In the present invention, the video signal correction circuit has a table structure using a digital memory, and the contents of the table are used as the correction curve data to realize the simplification of the structure and the accurate correction.

In this case, two memories are used as digital memories, the reverse γ correction curve data is stored in the front side memory, and the applied voltage-transmittance correction curve data is stored in the rear side memory. It is possible to easily respond to each modification of the γ correction curve data or the applied voltage-transmittance correction curve data.

On the other hand, one memory is used as the digital memory, and an inverse γ correction curve and an applied voltage − are applied to this memory.
By storing the correction curve data in which the transmittance correction curves are combined, the simplification of the configuration and the degree of realization of accurate correction become large.

Applied voltage-determination of the data of the transmittance correction curve is a difficult process, but the applied voltage of the liquid crystal light valve-
The transmittance characteristic is divided into three regions, and a function of a predetermined power of a variable whose linear coefficient is gradually increased, a linear function, and a differential coefficient are gradually reduced from the region where the applied voltage is smaller. It can be easily determined if it is approximated by a function of a predetermined power of a variable and is determined by using an inverse function of these functions.

In order to execute the correction accurately,
It is important to have a margin in the correction curve data,
It is preferable that data values smaller than the data value of the black level and data values larger than the data value of the white level are determined according to the correction curve shape and stored in the digital memory.

[0020]

【Example】

(1) First Embodiment The arrangement position of a video signal correction circuit according to the first embodiment of the present invention on a liquid crystal display device and its correction method will be described in detail with reference to the drawings.

FIG. 1A shows a main structure of a liquid crystal display device according to this embodiment. In FIG. 1A, the inverse matrix circuit 1 is provided with, for example, a luminance signal Y and two color difference signals RY and BY which are digital signals, and the three primary color signals R are subjected to matrix processing by these signals. , G, B are obtained and given to the video signal correction circuits 2R, 2G, 2B corresponding to the respective primary color signals. Each video signal correction circuit 2R, 2G, 2B is, for example, a ROM or RAM.
And the like, and each of the input primary color signal data DIN (R, G, B) is received as a read address and the corrected primary color signal data DOUT (R is received.
A so-called conversion table TBL as shown in FIG. 1B for outputting (A, GA, BA) is provided.

These video signal correction circuits 2R, 2G, 2
In FIG. 1C, the reverse γ correction curve C1 and the applied voltage-transmittance correction curve C2 are combined and determined as described below.
Data DIN and DO according to the correction curve C3 as shown in
A set of UTs is stored. Note that in FIG. 1C, the horizontal axis represents input data (read address) DIN and the vertical axis represents output data DOUT.

Each corrected primary color signal R which is a digital signal
A, GA, BA are given to the corresponding digital / analog conversion circuits 3R, 3G, 3B to be converted into analog signals, and these analog signals are supplied to the liquid crystal drive amplifiers 4R, 4G,
It is given to the liquid crystal driver 5 via 4B. Thus,
The liquid crystal driver 5 drives, for example, an active matrix type liquid crystal panel (not shown), and each liquid crystal light valve of the liquid crystal panel drives the corrected primary color signals RA, GA,
The transmittance is controlled according to BA. In the case of this embodiment, the case of a so-called normally black mode in which the transmittance increases as the applied voltage increases is considered, but the so-called normally white mode in which the transmittance decreases as the applied voltage increases. Even in the case of the mode, the same can be applied by changing the configuration of the liquid crystal drive amplifier.

Next, the inverse γ correction curve C in FIG.
A method for determining 1 will be described. FIG. 2 is a diagram provided for this description.

As is well known, a cathode ray tube has a voltage (normalized in FIG. 2) applied to the grid of the cathode ray tube.
Where x is the input x and the emission luminance (normalized in FIG. 2) due to the applied voltage is the output y, it has a non-linear characteristic as represented by the equation (1) and the curve C4 in FIG. Therefore, when the video signal demodulated by the display system is directly applied to the cathode ray tube, a linear relationship between the video signal obtained by imaging and the display brightness cannot be obtained due to this characteristic.

Y = x ^a (1) Then, in the imaging system, it is an inverse function of the function shown in the equation (1),
According to the equation (2) and the correction curve C5, the image signal related to the image pickup is corrected (γ-corrected), and when the image signal demodulated in the display system is applied to the cathode ray tube, the image signal related to the image pickup and the display brightness are Is a linear relationship C6.

Y = x ^{1 / a} (2) However, the liquid crystal light valve of the liquid crystal panel has a relationship between the applied voltage and the light emission luminance different from that of the cathode ray tube. Therefore, from the liquid crystal light valve's point of view, the γ correction shown in equation (2) is unnecessary, and the video signal is corrected (reverse γ) before the video signal voltage is applied to the liquid crystal panel.
It is necessary to correct it and restore it. γ correction is (2)
Since it is expressed by the equation, the inverse γ correction that restores this γ correction follows the equation (1). Therefore,
The inverse γ correction curve C4 (C1) may be obtained by the equation (1). Note that the multiplier a is actually about 2.2.

The relationship between the voltage applied to the grid of the cathode ray tube and the light emission luminance and the relationship between the input voltage and the output voltage in the inverse γ correction are different in the level and the unit system, but cannot be originally shown in the same drawing. For simplification of description, in FIGS. 1C and 2, each value is shown in the same drawing by being normalized. The values obtained by normalization are also shown in the following characteristic curve diagram and correction curve diagram.

Next, a method of determining the applied voltage-transmittance correction curve C2 in FIG. 1C will be described.

FIG. 3 shows a normalized applied voltage-transmittance characteristic curve of the liquid crystal light valve, and applied voltage-
It is explanatory drawing which shows the relationship with a transmittance correction curve. Between the applied voltage (horizontal axis x) and the transmittance (vertical axis y) at the applied voltage to the liquid crystal light valve, the curve C7 in FIG.
As shown in, there is a relationship on the S curve. Video signal voltage and transmittance (equal to luminance in normally black mode)
In order to have a linear relationship as shown by the dotted line C8 in FIG. 3, even if the characteristic shown in the curve C7 is applied to the corrected voltage (applied voltage), the original image is corrected. It is necessary to establish a linear relationship between the signal voltage and the transmittance as shown by the dotted line C8. Here, such a correction curve C9 is a line symmetrical to the curve C7 with respect to the dotted line C8 in the normalized coordinate system. Therefore, in order to obtain the correction curve C9, first, the applied voltage −
It suffices to obtain the transmittance characteristic curve C7 and then obtain the inverse characteristic of the curve C7.

The applied voltage-transmittance characteristic curve C7 can be obtained by actual measurement. However, such a curve C
It is difficult to immediately obtain the inverse characteristic of No. 7 from the actual measurement data, and therefore it is required to represent the curve C7 by a function. However, as described above, since the curve C7 is an S-shaped curve, it is difficult to represent it with one function. Therefore, in the case of this embodiment, the central portion of the curve C7 is approximated by a straight line, and the front and rear thereof are approximated by a curve. That is, the curve C7 is divided into three parts and each part is approximated by a predetermined function.

FIG. 4 is an explanatory diagram of each such approximate function. As shown in FIG. 4, the curve portion on the coordinate origin side is represented by the function y = f (x), the central portion is represented by the function y = g (x), and the curve portion having a larger value is represented by the function y = h. (X)
It is represented by. Further, the connection point coordinates of the function f (x) and the function g (x) are represented by A (P1, Q1), and the function g (x) and the function h
The coordinates of the connection point with (x) are represented by B (P2, Q2). Then, each function f (x), g (x), h (x) is
It was decided to approximate by Eqs. (3), (4), and (5).

Y = f (x) = a1.x ^b1 (3) (a1 and b1 are constants, and x and y are respectively 0 ≦
x = P1, 0 ≦ y <Q1) y = g (x) = a2.x + c2 (4) (a2 and c2 are constants, and x and y are P1 respectively.
Y = h (x) = a3 (1-x) ^b3 (5) (a3 and b3 are constants, and x and y are P2, respectively). ^≤x <P2, Q1 ≤y <Q2
.Ltoreq.x <1, Q2 .ltoreq.y <1.) As described above, the curve C7 of the applied voltage-transmittance characteristic is converted into the function f
When approximated using (x), g (x), and h (x), the applied voltage-transmittance correction curve C9 shows the inverse functions f ⁻¹ (x), g ^{− of} these as shown in FIG. It can be approximated by using ¹ (x) and h ⁻¹ (x). Each inverse function f ^-1 (x), g ^-1
(X) and h ⁻¹ (x) can be expressed by the equations (6), (7), and (8).

Y = f ⁻¹ (x) = (x / a1) ^{1 / b1} (6) (x and y are values in the range of 0 ≦ x <Q1 and 0 ≦ y <P1) y = g ^-1 (x) = (x-c2) / a2 (7) (where x and y are Q1≤x <Q2 and P1≤y <P, respectively)
Y = h ^-1 (x) = 1- (x-1 / a3) ^{1 / b3} (8) (x and y are in the range of Q2≤x <1 and P2≤y <1 respectively) Therefore, if the constants relating to the functions f (x), g (x), and h (x) that approximate the curve C7 of the applied voltage-transmittance characteristic are determined, the applied voltage-transmittance correction curve The inverse functions f ⁻¹ (x), g ⁻¹ (x), h ⁻¹ (x) that approximate C9 can be determined. In order to smoothly connect the parts formed by the respective functions f (x), g (x) and h (x), the connection point A (P1, Q
1), A (P2, Q2) should have the same differential coefficient. Also, the origin in the normalized coordinate system and (1,1)
Since it passes through the point A, the connection points A (P1, Q1), A (P2,
Q2) and coordinate values C on the functions f (x) and h (x)
Given (R1, S1) and D (R2, S2), the constants a1 to a3, b1, b3, c2 can be determined. Therefore, each constant may be calculated by applying the actual measurement value to the coordinates of the points A to D.

From equations (3) to (5), constants a1 to a3,
b1, b3 and c2 can be given by the equation (9).

[0036]

[Equation 1]

The applied voltage-transmittance correction curve C9 can be determined by substituting the constants thus determined in the equations (6) to (8).

FIG. 6 shows the inverse γ obtained as described above.
Correction curve C4 (C1) and applied voltage-transmittance correction curve C
It is explanatory drawing of the synthesis | combination of 9 (C2). After the video signal is returned to the video signal in the image pickup system by the inverse γ correction, the video signal is combined according to the applied voltage-transmittance characteristic. That is, from the normalized value (horizontal axis) VIN of the input voltage to each of the video signal correction circuits 2R, 2G, and 2B, according to the inverse γ correction curve C4, the normalized value V1 of the inverse γ correction voltage with respect to the value VIN (vertical axis). Ask for. Next, from the normalized value V1 (horizontal axis) after the inverse γ correction, the corrected normalized value VOUT (vertical axis) for the applied voltage-transmittance characteristic is obtained according to the applied voltage-transmittance correction curve C9. Then, with respect to the normalized value VIN of the input voltage in the video signal correction circuit, the obtained normalized value VOUT is set as the normalized value of the output voltage from the video signal correction circuit. Such processing is performed for all the normalized values of the input voltage, and the combined curve C10 (C3)
To get

The input voltage data DIN and the output voltage data D of the composite curve C10 are added to the video signal correction circuit having the table structure.
When OUT is stored, the normalized value is converted into any value of the quantization numbers determined by the number of bits of data.

Therefore, according to the above-described first embodiment, since the video signal correction circuit is composed of the conversion table using the digital memory, the data of the desired correction curve can be stored and the correction can be appropriately performed. It is possible to improve the display quality. Incidentally, in the video signal correction circuit having the analog circuit configuration, it is inevitable that the correction curve is slightly deviated from the original correction curve.

Further, even if the correction curve needs to be corrected by changing the liquid crystal panel or the like, it can be dealt with by rewriting the table contents or by exchanging the digital memory having new contents. Can be modified.

Further, since the video signal correction circuit is constituted by the digital memory and the inverse γ correction and the applied voltage-transmittance correction can be simultaneously performed by one access, the constitution is simpler than the conventional one. It can be anything.

Further, since the combined curve of the inverse γ correction curve and the applied voltage-transmittance correction curve is stored, the configuration shown in FIG.
As shown in (C), the stored curve C3 has a gradual change, and the error (noise) generated in the correction of the video signal can be suppressed to a small level. By the way, the reverse γ
Each of the correction curve and the applied voltage-transmittance correction curve has a steep change portion, and an error is likely to occur.

When the correction circuit storing the inverse γ correction curve and the correction circuit storing the applied voltage-transmittance correction curve are provided separately, the quantization error in each correction circuit affects each other, and However, the quantization error in the corrected data becomes large, but when only the correction circuit that stores the combined curve of the inverse γ correction curve and the applied voltage-transmittance correction curve is provided, the corrected quantization error Will be small.

Further, according to the above-mentioned embodiment, the applied voltage-transmittance characteristic curve is divided into three parts, each part is approximated by a simple function, and this approximate function is specified from the measured data and applied. Since the voltage-transmittance correction curve is determined, the determination work can be facilitated.
As mentioned above, since equation (9) has already been obtained, data of four points are extracted from the measured data, equation (9) is applied, and then equations (6) to (8) are applied. The applied voltage-transmittance correction curve can be determined.

(2) Second Embodiment Next, a second embodiment of the present invention will be described. In the case of the first embodiment described above, the correction curve data stored in the video signal correction circuits 2R, 2G, and 2B has the minimum value (normalized value 0) at the black level and the maximum value (normalized value). Although the value 1) indicates a white level, in the second embodiment, a value slightly larger than the minimum value is the black level, and a value slightly smaller than the maximum value is the white level. In practice, the video signal (which means a television signal here) is converted to analog /
When performing digital conversion, the pedestal level is often used as the reference, or the maximum digital value is set larger than the digital value of the white level.Therefore, the data input to the video signal correction circuit does not always have the black level. It is not always the value from the data to the white level data.

FIG. 7 is an explanatory view of the outline of the second embodiment. In the case of this embodiment, the combined correction curve (see curve C10 in FIG. 6) obtained as in the first embodiment is several% for the black level side and several% for the white level side.
To obtain curve C11. That is, the normalization value BP of the black level reference point is made slightly larger than 0, and
The normalized value WP of the white level reference point is made slightly smaller than 1. A straight line C12,
Interpolation is performed by C13. Although FIG. 7 shows the processing up to this point, a straight line C12 and a compression curve C are further added.
11 and the smoothing process of the connection between the compression curve C11 and the straight line C13 are performed to obtain a normalized curve to be stored in the table.

The outline of the second embodiment has been described above. In practice, the compression of the curve, the addition of the straight line portion, the smoothing of the connection between the curved line portion and the straight line portion are performed by using the inverse γ correction curve and the applied voltage-transmission It is often performed for each of the rate correction curves and then combined.

Since the compression of the curve of the inverse γ correction curve, the addition of the straight line portion, the smoothing process of the connection of the curve portion and the straight line portion, and the processing of the applied voltage-transmittance correction curve are substantially the same, In the following, although somewhat doubled from the above description, the process of compressing the curve, adding the straight line portion, and smoothing the connection of the curved line portion and the straight line portion of the inverse γ correction curve will be described with reference to FIG.

As shown in FIG. 8A, the inverse γ correction curve (see the curve C9 in FIG. 6) obtained as in the first embodiment is several% on the black level side and on the white level side. Also, compress only a few percent and normalize value B of the black level reference point.
Normalized value W of the reference point of white level, where P is slightly larger than 0
A curve C14 in which P is slightly smaller than 1 is obtained. Interpolation is performed by the straight lines C15 and C16 at both end portions vacated by the compression. This interpolation can be easily performed because it is a linear interpolation with an inclination of 1. Further, a smoothing process for connecting the straight line C15 and the compression curve C14 as shown in FIG. 8B, and a smoothing process for connecting the straight line C15 and the straight line C16 as shown in FIG. 8C. Get a normalized curve that defines the data to be stored and stored in the table. Since the smooth curve portions C17 and C18 are slight portions, they may be determined manually without using the approximation function.

As described above, such processing is also executed for the applied voltage-transmittance correction curve, and then both curves are combined to determine the final curve.

Therefore, according to the second embodiment as well, the same effect as that of the above-mentioned first embodiment can be obtained. In addition to this, even if data of a level lower than the black level is input or data of a level higher than the white level is input, the correction can be performed, that is, from the black level to the white level required as a video component. Since the margin is provided in addition to the space, the correction between the black level and the white level can be accurately executed. Incidentally, in the basic operation, data between the black level and the white level is input.

Further, the input data range can be easily changed due to the change of brightness or contrast.

It should be noted that the correction curve to be stored in the digital memory used as a table becomes a little more complicated than in the first embodiment.

(3) Third Embodiment A third embodiment of the present invention will be described below. The third embodiment differs from the second embodiment in the processing after compression.

FIG. 9 is an explanatory view of the outline of the third embodiment. In the case of the third embodiment, the differential coefficient gradually increases and passes through the black level reference point (x and y coordinates are BP) in the vacant portion on the black level side caused by the compression of the correction curve. , A function curve C20 of a predetermined power of x is interpolated. After that, a straight line portion C21 extending from the reference point of the black level and having a slope equal to the derivative of the function curve C20 at the reference point is provided until it intersects with the compression correction curve C22. Similarly, the white level reference point (x and y coordinates are W
Interpolate a function curve C23 that passes through P) and has a monotonically increasing differential coefficient and gradually increases to a predetermined power of x. Then, a straight line portion C24 extending from the reference point of the white level and having a slope equal to the derivative of the function curve C23 at the reference point
Are provided until they intersect the compression correction curve C22. And
Finally, the connection between the straight line portion C21 and the compression correction curve C22, and the connection between the compression correction curve C22 and the straight line portion C24 become continuous (smooth) in the differential coefficient.
The straight line portion C21 near the intersection and the compression correction curve C2
2. Correct the straight line portion C24 (the correction smoothing curve portion is represented by reference numerals C25 and C26).

Note that such processing may be performed after the reverse γ correction curve and the applied voltage-transmittance correction curve are combined, and the reverse γ correction curve and the applied voltage-transmittance correction curve may be respectively processed. It is also possible to combine them and then combine them. FIG. 9 shows a case where the above-described processing is performed on the applied voltage-transmittance correction curve.

According to the third embodiment, the same effect as the second embodiment can be obtained. Further, there is an effect that the reference values of the black level and the white level are accurately transferred between the input data and the output data. Incidentally, in the case of the second embodiment, even if the input data is the reference value of the black level,
The output data is not the reference value of the black level for smoothing the curve.

(4) Other Embodiments The present invention can be applied not only to the color liquid crystal display device described above, but also to a monochrome liquid crystal display device.

Further, in the above-described embodiment, the video signal correction circuit is constituted by the one-stage digital memory (table), but the two-stage digital memory (two tables).
Alternatively, the data of the inverse γ correction curve may be stored in the digital memory at the front stage, and the data of the applied voltage-transmittance correction curve may be stored in the digital memory at the rear stage. By doing so, as compared with the above-described embodiment, the configuration becomes large and the quantization error generated in the correction process as a whole becomes large, but on the other hand, each of the inverse γ correction curve or the applied voltage-transmittance correction curve is It has the advantage that another modification is easier.

Further, in the γ correction in the image pickup system, when the inclination is too large, the inclination is suppressed to about 2 to 3 and S /
Although the deterioration of the N ratio is prevented, the inverse γ correction curve may be modified so that the inclination is about 1/3 to 1/2.

[0062]

As described above, according to the present invention, the video signal correction circuit for performing the inverse γ correction and / or the applied voltage-transmittance correction according to the applied voltage-transmittance characteristic of the liquid crystal light valve is provided in the digital memory. Since it is realized by the table configuration using, the video signal can be appropriately corrected, and the device can be simplified.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment.

FIG. 2 is an explanatory diagram of an inverse γ correction curve according to the first embodiment.

FIG. 3 is an explanatory diagram of an applied voltage-transmittance correction curve of the first embodiment.

FIG. 4 is an explanatory diagram of a method of approximating an applied voltage-transmittance characteristic curve.

FIG. 5 is an explanatory diagram of a method of approximating an applied voltage-transmittance correction curve according to the first embodiment.

FIG. 6 is an explanatory diagram of a method of synthesizing an inverse γ correction curve and an applied voltage-transmittance correction curve according to the first embodiment.

FIG. 7 is an explanatory diagram of an outline of a second embodiment.

FIG. 8 is an explanatory diagram of an inverse γ correction curve according to the second embodiment.

FIG. 9 is an explanatory diagram of an outline of a third embodiment.

[Explanation of symbols]

2R, 2G, 2B ... Video signal correction circuit for each primary color signal R, G, B, 3R, 3G, 3B ... Digital / analog conversion circuit, 5 ... Liquid crystal driver, TBL ... Table, C1 ... Inverse .gamma. Correction curve, C2 ... Applied voltage to liquid crystal light valve −
Transmittance correction curve, C3 ... Combined curve of curves C1 and C2 (normalized curve of curve stored in table TBL).

Claims (5)

[Claims] 1. A video signal correction of a liquid crystal display device, which performs an inverse .gamma. Correction which is an inverse correction of .gamma. A video signal correction circuit for a liquid crystal display device, wherein the video signal correction circuit has a table structure using a digital memory, and the table contents are correction curve data. 2. The two memories are used as the digital memory, and the inverse γ correction curve data is stored in the front side memory,
The video signal correction circuit of the liquid crystal display device according to claim 1, wherein applied voltage-transmittance correction curve data is stored in a memory on the rear side. 3. A single memory is used as the digital memory, and data of a correction curve obtained by combining an inverse γ correction curve and an applied voltage-transmittance correction curve is stored in this memory. A video signal correction circuit of the described liquid crystal display device. 4. The applied voltage-transmittance characteristic of the liquid crystal light valve is divided into three regions, and a function of a predetermined power of a variable whose differential coefficient is gradually increased from the region of lower applied voltage, A linear function, which is approximated by a function of a predetermined power of a variable whose differential coefficient is gradually reduced, and data of an applied voltage-transmittance correction curve determined by an inverse function of these functions is used. Item 4. A video signal correction circuit for a liquid crystal display device according to any one of items 1 to 3. 5. The correction curve data stored in the digital memory has a black level data value selected to a value larger than the minimum value thereof and a white level data value selected to a value smaller than the maximum value thereof. The data value smaller than the data value of the black level and the data value larger than the data value of the white level are determined according to the correction curve shape between the data value of the black level and the data value of the white level. 1 to
5. A video signal correction circuit of the liquid crystal display device according to any one of 4 above.