JPH1145074A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with brightness approximately proportional to the brightness of a picked-up image and to obtain excellent image reproducibility by making γ value vary within a specific range in a region of a specific proportion or more of a whole gradation region. SOLUTION: In a gradation specified wherein brightness 1 is defined to correspond to a maximum of a gradation signal, γ value is arranged so that γ value may fall between γ=1.5 and γ=3.0 of a gradation-brightness characteristic of a liquid crystal display device to which RGB digital signals are inputted in a 60% or more of the whole gradation region. And in a reference voltage generation circuit of the liquid crystal display device, three kinds of ladder resister circuits 9-11 can be changed over by simultaneously changing over the ladder resistor switch 7 and the reference voltage change-over switches 8. The gradation-brightness characteristic thus obtained can be selected according to the image by a user, in order to clarify a gradation in the neighborhood of black and that in the neighborhood of white.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device having a luminance correcting means.

[0002]

2. Description of the Related Art Liquid crystal display devices have been used both as monitors for personal computers and as television receivers.
Is expected to replace. A CRT used for a receiver has a γ characteristic of γ = 2.2. For this reason, the imaging apparatus performs γ correction of γ = 0.45 so that the brightness of the captured image is proportional to the brightness of the screen projected by the receiver. In addition, the CRT is provided with a function of adjusting contrast and the like.

In a liquid crystal display device, the voltage-liquid crystal transmittance characteristic applied to a pixel electrode is non-linear, and C
Since it does not match the acceleration voltage-luminance characteristics of RT electrons,
The gradation-luminance characteristics of a liquid crystal display device are not unified among manufacturers (for example, Nikkei Micro Devices, November 1996, pp. 51-54).

In a liquid crystal display device for digitally inputting an RGB signal, a source driver IC uses RGB signals.
According to the signal, a voltage corresponding to the gradation is output to the pixel. The voltage for each gradation is generated by a ladder resistance circuit. If the image signal input is an 18-bit RGB signal, 6
There are four tones, and 128 voltage levels are generated inside the IC in combination with the positive polarity and the negative polarity. All of these voltage levels are not supplied from outside the IC, but a plurality of voltage levels are generated outside the IC by a ladder resistance circuit and input to the IC.

FIG. 4 shows a ladder resistance circuit of a conventional liquid crystal display device. In FIG.
2 is a source driver IC, 3 is a bus line, and 4 is a resistor. FIG. 4 shows a ladder resistance circuit in the case of dot inversion drive in which the polarity is opposite to that of the upper, lower, left and right pixels adjacent to each other on the liquid crystal display. In this ladder resistor circuit, a total of 12 voltages of positive and negative polarities, for example, 1, 8, 16, 32, 48, and 64 gradations are generated, and the source driver IC2
And the gradation voltage level between them is generated by a ladder resistor or the like inside the IC. The grayscale voltage generated outside the IC is called a reference voltage. These reference voltages are generated by a ladder resistance circuit in the liquid crystal display device.

[0006]

A conventional liquid crystal display device has only one ladder resistance circuit for generating a reference voltage. Depending on the image handled by the liquid crystal display and the environment of the display user, Although the brightness of the backlight can be changed, fine adjustment of contrast and the like cannot be performed to make the image more visible. For example, when an image mainly composed of white such as a snow surface is handled by a liquid crystal display, it is easier to see if the gradation-luminance change rate is large in an area where the luminance is high, while the black color such as a rock face of black rock is easy to see. When a display mainly handles an image, it is easier to see if the gradation-luminance change rate is large in a low luminance area. However, in the conventional liquid crystal display, an optimum gradation-luminance characteristic cannot be selected depending on an image to be handled.

If the gradation-luminance characteristic is γ = 2.2, an image having a brightness proportional to the brightness of the captured image can be obtained on the liquid crystal display. It is not 2.2.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and aims to obtain an image which is more easily viewable by making the gradation-luminance characteristics of a liquid crystal display device variable within a predetermined range. It is.

[0009]

In a liquid crystal display device according to the present invention, in a case where RGB signals are digitally inputted, a γ value is 1.5 or more and 3.0 or more in an area of 60% or more of all gradation areas. It is variable within the following range.

In the above configuration, at least two reference voltage setting ladder resistance circuits are provided, and the γ value is made variable by switching the ladder resistance circuits.

In the above configuration, the input signal is inverted γ.
It has a corrected luminance characteristic.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 shows gradation-luminance characteristics of the liquid crystal display device according to Embodiment 1 of the present invention. In FIG. 1, the luminance is standardized, and the luminance of 1 corresponds to the luminance when the gradation signal is the maximum. Curve 5 in FIG. 1 is a curve when γ = 1.5, and curve 6 is a curve when γ = 3.0. In the standardized gradation, the gradation-luminance characteristics of the liquid crystal display device for digitally inputting the RGB signals in an area of 60% or more of the entire gradation area indicate that γ = 1.5 and γ = 3.0 in FIG. So that it falls between the curves.

Embodiment 2 FIG. FIG. 2 shows a reference voltage generation circuit of a liquid crystal display device according to Embodiment 2 of the present invention. FIG. 2 shows a reference voltage generating circuit for performing dot inversion driving. In this figure, 7 is a ladder resistance changeover switch, 8 is a reference voltage changeover switch, 9 is a first ladder resistance, 10 is a second ladder resistance, and 11 is a third ladder resistance. In FIG. 2, three types of ladder resistance circuits can be switched by simultaneously switching the ladder resistance switch 7 and the reference voltage switch 8.

FIG. 3 shows an example of gradation-luminance characteristics obtained by switching the switches 7 and 8. In this figure, curve 1
2 is a curve of γ = 2.2 and corresponds to the ladder resistance 9, curve 13 is a curve of γ = 0 and corresponds to the ladder resistance 10, and curve 14 is a curve of γ = 4 and ladder resistance 11
It corresponds to. Curve 12 is a standard tone-luminance curve, curve 13 is for sharpening the tone near black, and curve 14 is for sharpening the tone near white. In this way, the user can select a gradation-luminance characteristic suitable for the image, depending on the image handled on the screen of the liquid crystal display device that digitally inputs the RGB signals.

[0015]

As described above, according to the present invention, it is possible to obtain an image having a brightness substantially proportional to the brightness of a captured image, and to obtain a liquid crystal display device having good image reproducibility.

Further, by providing a plurality of gradation-luminance characteristics and switching between the gradation-luminance characteristics, it is possible to select a gradation-luminance characteristic that makes it easy for a user to see an image.

[Brief description of the drawings]

FIG. 1 is a graph showing gradation-luminance characteristics of a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is a circuit diagram showing a reference voltage generation circuit of a liquid crystal display device according to Embodiment 2 of the present invention.

FIG. 3 is a graph illustrating an example of gradation-luminance characteristics of the liquid crystal display device according to the second embodiment.

FIG. 4 is a circuit diagram showing a reference voltage generation circuit of a conventional liquid crystal display device.

[Explanation of symbols]

1 DC power supply, 2 source driver IC, 3 bus line, 4 resistance, 7 ladder resistance switch, 8
Reference voltage switch, 9 first ladder resistor, 10 second ladder resistor, 11 third ladder resistor.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 9/69 H04N 9/69

Claims (3)

[Claims] 1. A liquid crystal display device to which RGB signals are digitally input, wherein a γ value is in a range of 1.5 or more and 3.0 or less in an area of 60% or more of a whole gradation area. Liquid crystal display device. 2. A liquid crystal display device to which an RGB signal is digitally input, has at least two ladder resistance circuits for setting a reference voltage, and switches over the ladder resistance circuits in an area of 60% or more of the entire gradation area. A liquid crystal display device wherein the γ value is variable within a range of 0 or more and 4.0 or less. 3. The liquid crystal display device according to claim 1, wherein the input signal has a luminance characteristic subjected to inverse γ correction.