JPH0662423A - Gamma correcting circuit for liquid crystal display - Google Patents

Abstract

PURPOSE:To prevent the loss of white balance caused by the conversion of brightness with the gamma correcting circuit of a liquid crystal display. CONSTITUTION:The gamma correcting circuit of a liquid crystal display controls the driving signal in response to the corresponding contrast and brightness for displaying the images formed by the input video signals on a liquid crystal display. In such conditions, the control voltage of the corresponding brightness is converted into a digital signal by an A/D converting part 8. Then the gamma correction data corresponding to the gamma characteristic of the liquid crystal display are read out of a ROM 7 with the preceding digital signal and the signal obtained by digitizing the input video signal used as the addresses. As the same time, the correction coefficient of the gamma correction data can be adaptably varied by the control voltage of the corresponding brightness. Then the driving signal is obtained for the liquid crystal display with the gamma correction carried out by the varied gamma correction data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit for a liquid crystal display used in a liquid crystal projector (television) or the like, and more specifically to a gamma correction circuit for a liquid crystal display which prevents white balance from being lost even when the brightness is changed. The present invention relates to a correction circuit.

[0002]

2. Description of the Related Art Conventionally, a gamma correction circuit of this type of liquid crystal display has a structure shown in FIG. 2, for example, and an A / D converter 1 for digitally converting an input video signal and a gamma characteristic of a liquid crystal display in advance. A memory (ROM) 2 that stores the corresponding gamma correction data and uses the digital signal from the A / D conversion unit 1 as an address, and a D / A conversion unit 3 that converts the data read from the ROM 2 into an analog signal.
An amplifying unit 4 and a clamp unit 5 for adjusting the analog-converted signal according to the contrast and bright control voltage; and a signal adjusted by the amplifying unit 4 and the clamp unit 5 for a drive signal of a liquid crystal display ( And an alternating voltage circuit 6 for controlling the applied voltage).

As described above, since the gamma correction data of the liquid crystal display is stored in the ROM 2,
It is possible to obtain a drive signal in which the gradation characteristic of the liquid crystal display is corrected.

[0004]

By the way, the transmittance characteristic of the above liquid crystal display is as shown in FIG.
When the drive signal (driving voltage) is different, the gamma characteristic of the liquid crystal display used is different from the correction value by the gamma correction data of the ROM 2.

When the bright control voltage in the clamp section 5 changes, the drive voltage changes, and for example, the drive voltage of the liquid crystal display changes from arrow a to arrow b in FIG. There is a problem in that the use position (gamma characteristic) of the transmittance curve is different and, as a result, the white balance of the display image on the liquid crystal display is lost.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display capable of preventing the white balance from being destroyed even by adjusting the brightness and adding a simple circuit. It is to provide a gamma correction circuit.

[0007]

To achieve the above object, the present invention relates to a memory when a drive signal for displaying an image by an input image signal on a liquid crystal display is adjusted according to the contrast and the brightness. A gamma correction circuit for a liquid crystal display that corrects the drive signal based on the stored gamma correction data for the liquid crystal display, which includes an A / D conversion unit that digitally converts the control voltage of the bright, and a gamma of the liquid crystal display in advance. The correction data is stored, and the gamma correction data that is different according to the bright control voltage is stored. The digital signal by the input video signal is set to an address of a predetermined number of bits, and the digital signal by the A / D conversion unit is stored. A memory having an address of a predetermined number of bits, The correction coefficient of the adaptive gamma correction data by a control voltage is variable possible, and gist that to obtain a drive signal corrected by the variable gamma correction data.

[0008]

With the above configuration, when the control voltage of the bright is changed, the driver signal (applied voltage) of the liquid crystal display changes, and the gamma characteristic of the liquid crystal transmittance characteristic curve also changes accordingly. The digital conversion value of the control voltage causes the gamma correction data read from the memory to have correction coefficients corresponding to the different gamma characteristics.

As described above, since the correction value is adaptively changed by the brightness, correct gamma correction can be performed according to the gamma characteristic of the liquid crystal display, and the gamma-corrected drive signal (applied voltage) of the liquid crystal display. Can be obtained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A gamma correction circuit for a liquid crystal display according to the present invention stores gamma correction data corresponding to the gamma characteristic of a liquid crystal display in a memory (conversion ROM) that uses a digital signal of an input video signal as an address, and the bright Different gamma correction data is stored according to the control voltage, and the digital signal of the input video signal is used as an address (for example, lower address) of a predetermined number of bits of the conversion ROM, and the digital signal of the bright control voltage is stored. Is an address of a predetermined number of bits of the conversion ROM (for example, an upper address), and an adaptive gamma correction value is obtained by the control voltage of the bright.

Therefore, the gamma correction circuit of the liquid crystal display of the present invention stores the gamma correction data in which the coefficient of the gamma correction value corresponding to the digital signal by the input video signal changes according to the control voltage of the bright ( ROM) 7 and an A / D converter 8 for digitally converting the control voltage of the bright, the lower address of the ROM 7 is used as a digital signal according to the input video signal, and the upper address thereof is a digital signal with the control voltage for the bright. I am trying. In FIG. 1, the same parts as those in FIG. 2 are designated by the same reference numerals, and duplicate description will be omitted.

That is, the ROM 7 has, for example, 4-bit A / A for a bright control voltage (1V to 2V).
In the case of D conversion, 16 kinds of gamma correction data, which is 2 to the 4th power, are written. Of the addresses of the ROM 7, the lower 8 bits are assigned with the digital signal of the input video signal, and the higher 4 bits are concerned with the relevant bright signal. A digital signal is assigned by the control voltage of.

The operation of the gamma correction circuit of the liquid crystal display having the above structure will be described. When displaying an image based on an input video signal on the liquid crystal display, the input video signal is converted into a digital signal by the A / D converter 1, The gamma correction data in the ROM 7 is read by this digital signal. At this time, the predetermined value of the brightness of the display image (bright control voltage) is input to the clamp section 5 and the A / D conversion section 8, and the digital signal from the A / D conversion section 8 is stored in the upper address of the ROM 7. To be done. Therefore, the gamma correction value of the liquid crystal display read from the ROM 7 is the correction coefficient adapted to the bright. If the brightness is changed, the correction value is adaptively changed by the brightness.

The data read from the ROM 7 is D
A / A section 3 digitally converts the converted digital signal by an amplifying section 4 and a clamp section 5 in the same manner as in the prior art, and the contrast and bright adjusted signal is converted by an AC circuit 6 into a liquid crystal display. Drive signal (applied voltage).

Here, by changing the control voltage of the bright,
When the drive signal (applied voltage) is changed from the arrow a in FIG. 2 to the arrow b, the gamma characteristic is different as shown by the liquid crystal transmittance characteristic curve in FIG. However, since the gamma correction data read from the ROM 7 is different depending on the control voltage of the bright and the gamma correction data corresponds to the different gamma characteristics, the display image of the liquid crystal display driven by the drive signal is changed. The white balance will not be lost.

As described above, a plurality of types of gamma correction data (data corresponding to the gamma characteristic of the liquid crystal display) are stored in the ROM 7 according to the control voltage of the bright, and the gamma correction value corresponding to the bright is read. hand,
Since the drive signal in which the gradation characteristic of the liquid crystal display is corrected is obtained, even if the brightness is changed, a good image can be obtained without losing the white balance of the image displayed on the liquid crystal display, and the capacity can be improved. Since a memory with a large size is used and only an A / D conversion circuit is added, a simple circuit can be used.

[0017]

As described above, according to the present invention, the drive signal for displaying the image by the input image signal on the liquid crystal display is stored in the memory when the drive signal is adjusted according to the contrast and the brightness. A gamma correction circuit for a liquid crystal display, which corrects the drive signal according to the gamma correction data of the liquid crystal display, which stores A / D conversion means for digitally converting the control voltage of the bright and gamma correction data of the liquid crystal display in advance. Further, different gamma correction data is stored according to the bright control voltage, the digital signal by the input video signal is set to an address (lower address) of a predetermined number of bits, and the digital signal by the A / D conversion means is stored. A memo with an address (upper address) of a specified number of bits (ROM), the correction coefficient of the gamma correction data can be adaptively changed by the control voltage of the bright, and the drive signal corrected by the changed gamma correction data is obtained. Even if is changed, the gamma correction data corresponding to the gamma characteristic of the liquid crystal display can be obtained, and the drive signal of the liquid crystal display corrected by this gamma correction data can be obtained. It is possible to solve the problem that the white balance of the image is lost and to add the A / D conversion means to increase the capacity of the ROM. Therefore, a simple circuit can be used.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a gamma correction circuit of a liquid crystal display showing an embodiment of the present invention.

FIG. 2 is a schematic block diagram of a gamma correction circuit of a conventional liquid crystal display.

FIG. 3 is a schematic transmittance characteristic curve diagram of a liquid crystal display.

[Explanation of symbols]

 1,8 A / D converter 3 D / A converter 4 Amplifier 5 Clamp 7 Memory (ROM)

Claims (1)

[Claims] 1. When adjusting a drive signal for displaying an image based on an input video signal on a liquid crystal display according to the contrast and brightness, the drive signal is adjusted according to gamma correction data of the liquid crystal display stored in a memory. A gamma correction circuit of a liquid crystal display for correcting, wherein A / D conversion means for digitally converting the control voltage of the bright, gamma correction data of the liquid crystal display is stored in advance, and varies depending on the control voltage of the bright. The gamma correction data is stored, and a memory for storing the digital signal by the input video signal as an address of a predetermined number of bits and the digital signal by the A / D conversion means as an address of a predetermined number of bits is provided. Gamma correction data is adaptively corrected by voltage A gamma correction circuit for a liquid crystal display, wherein a coefficient is made variable and a drive signal of the liquid crystal display corrected by the changed gamma correction data is obtained.