JPH10340069A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of automatically adjusting contrast in accordance with the content of image data. SOLUTION: A counter 16 outputs a reset signal at the point of time when the number of frame signals becomes a previously set numerical value. When the reset signal is inputted, a memory circuit 15 outputs the total value of the picture elements of image data till then and restores the total value of the picture elements to '0'. A contrast control circuit 14 compares a stored value in the memory circuit 15 at the point of time when the reset signal is inputted with a threshold equivalent to the half of the number of all the dots and outputs a control signal after judging in accordance with the compared result whether the contrast should be made higher or lower. A contrast adjusting circuit 13 generates the driving voltage of a level in accordance with the inputted control signal and controls the contrast of a liquid crystal display 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having an automatic contrast adjustment function, which is used in a personal computer or other information processing device.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device, a device having a contrast adjusting function is used for the purpose of automatically adjusting contrast (Japanese Patent Laid-Open No. 5-12760).
No. 9). FIG. 3 is a block diagram showing an example of the conventional liquid crystal display device. In the figure, the manual adjustment mechanism 21
Is an adjustment mechanism using a variable resistor or the like so that the user can adjust the contrast to an arbitrary value. The data storage circuit 22 stores the latest correction value V _OP manually adjusted according to the gradation mode.
Is stored, and the correction data is selected and sent to the automatic contrast adjustment circuit 23 so as to be the same as the contrast used in the previous adjustment when the same gradation mode is used next time.

The voltage for driving the liquid crystal display 25 is:
The contrast is automatically calculated by the automatic adjustment circuit 23 on the basis of the manual adjustment mechanism 21 and the data storage circuit 22, and the driver circuit 24
Given by The display control circuit 26 is a control circuit for displaying characters and pictures on the liquid crystal display 25, and transmits the currently used gradation mode to the data storage circuit 22. As described above, in the conventional liquid crystal display device, the next time the same gradation mode is used, the contrast can be automatically adjusted to the previously adjusted contrast.

[0004]

However, in the above-mentioned conventional liquid crystal display device, since there is no means for detecting the contents of image data, even if the gradation mode of the personal computer is the same, the display of the application to be used is performed. If the image to be displayed is an overall dark image that is close to a negative display such as a white character display on a black background, to make it easier to see, the background black that occupies most of the screen is darker, and white characters are more white.
Adjustments must be made to increase the contrast. On the other hand, when an overall bright image close to a positive display such as black character display is displayed on a white background, the contrast is adjusted so as to reduce the contrast in order to make it easy to see the background white which occupies most of the screen. There is a need.

[0005] The present invention has been made in view of the above points,
It is an object of the present invention to provide a liquid crystal display device capable of automatically adjusting contrast according to the content of image data.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a signal generating means for generating image data and a frame signal in synchronization with each other, and receiving image data and a frame signal as input signals, A liquid crystal display that performs image display of image data with a contrast corresponding to the driving voltage of the image data, and a predetermined number of pixels of the image data are summed for each predetermined number of frames, and the sum is compared with a threshold value. And a contrast control means for controlling the contrast of the liquid crystal display by generating a drive voltage at a level corresponding to the obtained comparison result.

According to the present invention, by comparing the total value of image data within a predetermined frame number unit period with a threshold value, a comparison result indicating whether the entire light / dark display content of an image by image data is bright or dark is obtained. Thus, the contrast of the screen can be adjusted according to the comparison result.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of the liquid crystal display device according to the present invention. The liquid crystal display of this embodiment includes a liquid crystal display 11, a display control circuit 12, a contrast adjustment circuit 13, a contrast control circuit 14, a memory circuit 15, and a counter 16.

The liquid crystal display 11 has a display control circuit 1
2 is driven by the image data generated by 2 and a frame signal indicating a break of data for one screen, and a driving voltage of the liquid crystal display 11 is given by a contrast adjusting circuit 13 to adjust the contrast. The voltage value of the drive voltage output from the contrast adjustment circuit 13 is
Controlled by the contrast control circuit 14.

The counter 16 is connected to the display control circuit 12, and generates a reset signal when the number of frame signals reaches a predetermined number. The reset signal is supplied to the contrast control circuit 14 and the memory circuit 15. The memory circuit 15 is connected to the display control circuit 12, the counter 16, and the contrast control circuit 14, and outputs a total value of image data according to a reset signal.

The contrast control circuit 14 calculates an appropriate contrast value according to the total value of image data input from the memory circuit 15 in response to the reset signal, and outputs it to the contrast adjustment circuit 13 as a control signal. The contrast adjusting circuit 13 generates a driving voltage having a level corresponding to the input control signal and applies the driving voltage to the liquid crystal display 11.

Next, the operation of this embodiment will be described with reference to the timing chart of FIG. Display control circuit 12
Generates image data corresponding to the image to be displayed. This image data is, for example, binary data shown in FIG. Further, the display control circuit 12 generates a frame signal shown in FIG. 2B in synchronization with the output interval of the image data for one screen together with the image data.

The memory circuit 15 has, for example, a value of “1” (white) in the image data output from the display control circuit 12.
, And adding the value to the total value up to the previous pixel is repeated (that is, cumulatively added). On the other hand, the counter 16 counts the number of frame signals output from the display control circuit 12, and outputs a reset signal when the number reaches a predetermined value (specified value). The predetermined value in the counter 16 is 6 per second.
When displaying 0 frames worth of image data, in order to avoid the effect of halftone display realized by frame rate control, it is necessary to have a relatively long time, and not to delay the response too much so that the operability becomes worse. For example, it is preferable to set it to about 30 frames.

The reset signal is a signal as shown in FIG. 2C and is supplied to the memory circuit 15 and the contrast control circuit 14, respectively. When the reset signal is input, the memory circuit 15 outputs the stored white pixel total value of the image data up to that point, as schematically shown in FIG. Change the value back to 0.

The contrast control circuit 14 fetches the memory value of the memory circuit 15 (ie, the total value of white pixels of the image data up to that time) at the time when the reset signal is input, and stores the memory value. Is compared with a threshold value corresponding to half of the total number of dots, and it is determined whether to increase or decrease the contrast according to the comparison result, and a control signal is output to the contrast adjustment circuit 13.
The contrast adjusting circuit 13 generates a driving voltage of a level corresponding to the input control signal, supplies the driving voltage to the liquid crystal display 11, and controls the contrast.

For example, 100 × 100 pixels, counter 1
In the case of a monochrome liquid crystal display device having a prescribed value of 30, the contrast control circuit 14 sets the threshold value to 150,000, which is half of the total number of pixels in 30 frames, and the output value (total value of white pixels) of the memory circuit 15 becomes If it is larger than this threshold, the screen is considered bright and the contrast is lowered,
If it is smaller, it is determined that the screen is dark, and a control signal for increasing the contrast is output to the contrast adjustment circuit 13. The contrast adjusting circuit 13 generates a driving voltage based on the control signal and supplies the driving voltage to the liquid crystal display 11.
Adjust the contrast. Thereby, contrast adjustment is performed according to the content of the image data.

In the case of color display, three primary color signal data of red (R), green (G) and blue (B) are stored in the memory circuit 1.
In step 5, it is sufficient to simply add all of them. Also,
As another embodiment, the contrast is not continuously controlled by a half value as in the above-described embodiment when the contrast is determined by the contrast control circuit 14, but the contrast is continuously adjusted according to the output of the memory circuit 15. May be variable.

As another embodiment, instead of adding all image data in the memory circuit 15, white data,
Only the number of black data may be added, and the contrast control circuit 14 may determine which data is larger.

[0019]

As described above, according to the present invention,
The threshold value is compared with the total value of the number of pixels of the predetermined value of the image data within the predetermined frame number unit period, and a comparison result indicating whether the entire display content of the image by the image data is bright or dark is obtained, Since the contrast of the screen is adjusted according to the comparison result, the contrast can be automatically adjusted according to the content of the image data, and the user does not need to adjust the contrast when the display state of the image data changes. In both cases, optimal contrast adjustment can be performed, and complicated operation can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of FIG. 1;

FIG. 3 is a block diagram of an example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Liquid crystal display 12 Display control circuit 13 Contrast adjustment circuit 14 Contrast control circuit 15 Memory circuit 16 Counter

Claims (3)

[Claims] 1. A signal generating means for generating image data and a frame signal in synchronization with each other, receiving the image data and the frame signal as input signals, and displaying an image of the image data with a contrast according to an external driving voltage. And a drive voltage of a level according to a comparison result obtained by summing a predetermined number of pixels of the image data for each predetermined number of frames and comparing the sum with a threshold value And a contrast control means for controlling the contrast of the liquid crystal display by generating the liquid crystal display. 2. The contrast control means counts the frame signal and outputs a reset signal for each of the predetermined number of frames, and receives the image data and the reset signal as input signals. A storage circuit that outputs a total value of the predetermined number of pixels of the image data for each predetermined frame number unit, and compares the total value and the threshold value from the storage circuit with each other, and according to the comparison result. A control circuit for outputting a control signal; and a contrast adjusting circuit for adjusting a contrast of the liquid crystal display by generating a drive voltage of a level corresponding to the comparison result based on an output control signal of the control circuit. The liquid crystal display device according to claim 1, wherein 3. The contrast adjustment circuit decreases the contrast when the control signal is determined to be bright as a result of the comparison between the total value and the threshold value in the contrast control circuit, and determines that the screen is dark. 3. The liquid crystal display device according to claim 2, wherein when the control signal is input, a drive voltage for increasing the contrast is generated.