JP2021056268A - Liquid crystal display device - Google Patents

Abstract

To provide a liquid crystal display device that can suppress a disclination phenomenon due to digital driving of a liquid crystal display element.SOLUTION: A liquid crystal driving device that drives a liquid crystal display element including a plurality of pixels on the basis of an input image includes gradation setting means that sets the driving gradation on the basis of an input gradation that is the gradation of the input image, driving means that controls the voltage to be applied to each pixel to be a first voltage and a second voltage lower than the first voltage in each of a plurality of subframe periods included in one frame period for which the liquid crystal display element displays one frame image in accordance with the driving gradation. The gradation setting means and the driving means are more than one. The plural gradation setting means and driving means are switched for each frame.SELECTED DRAWING: Figure 13

Description

The present invention relates to a discrete generated by digitally driving a liquid crystal display element.

In recent years, various digital drive methods for liquid crystal display elements have been proposed due to problems such as the inability to configure a drive circuit on a backplane due to the miniaturization and high definition of liquid crystal display elements. As a digital drive of the liquid crystal display element, a drive method generally called PWM (Pulse Width Modulation) is used.

FIG. 1 shows a general PWM drive method.

As shown in FIG. 1, in a general PWM drive system, gradation is controlled by controlling ON / OFF of a time when one frame is divided into a plurality of periods, which is called SF (subframe) as shown in 101 in the figure. It is a method of expression.

When this digital drive method is performed using a liquid crystal display element, discrimination (adjacent gradation discrimination) may occur in adjacent gradation.

Adjacent gradation discrimination will be described with reference to FIG.

The relationship between the ON / OFF period when 8 tones and 7 tones are displayed on the adjacent pixels 201 and 202 using the PWM drive waveform of FIG. 1, respectively, is shown. In FIG. 2, in the period shown in 203, 7 tones are ON and 8 tones are OFF. On the other hand, in FIG. 2, in the period shown in 204, 8 tones are ON and 7 tones are OFF. In a normally black digital drive type liquid crystal display element, a high voltage is usually applied during the ON period, and a low voltage is applied during the OFF period. Therefore, during the period of 204, a transverse electric field is generated between adjacent pixels as shown in 301 in FIG. 3, and the orientation of the liquid crystal is disturbed (discretion) as shown in 302.

In the analog drive type liquid crystal display element, the voltage that can be applied differs depending on the gradation to be displayed, so when images with significantly different voltages such as white and black are displayed on adjacent pixels, a transverse electric field is generated and dispersion occurs. Therefore, the images in which dispersion occurs are limited. On the other hand, in the digital drive system, even when a specific adjacent gradation is displayed as described above, a lateral electric field is generated and dispersion is generated, so that a smooth gradation expression such as a human skin or an image of the sky is performed. In many images, the image quality is disturbed by the dispersion, and it is visually recognized as a streak-like dark line, and the image quality quality is significantly deteriorated.

Conventionally, for such adjacent gradation discrimination, gain is applied to the input signal for each frame to change the PWM drive gradation for each frame, and the discrimination is reduced by shifting the generation position of the discrimination. Measures have been taken (see Patent Document 1).

This method will be described with reference to FIG.

FIG. 4 shows the PWM drive gradation and the position where the discrete occurs and the disk when the input signal of the first frame is gained 1.0 times and the input signal of the second frame is gained 0.9 times. It is a figure which shows the improvement effect of a relation.

As shown in 401 of FIG. 4, it is illustrated that adjacent gradation discrimination occurs when straddling 5 tones, 6 tones, and 7 tones and 8 tones in the first frame. On the other hand, in the second frame, the PWM drive gradation for the input signal is different from that in the first frame due to the 0.9 times gain applied, and the position 402 where the adjacent gradation discrimination occurs is different from that in the first frame. .. In this way, by applying a gain to the input signal for each frame to shift the PWM drive gradation and different the discreteation generation position, the discrimination generation position can be shifted on the image, and the streak-shaped disc can be shifted. Nation interference is reduced. In addition, by increasing the amount of gain that can be applied for each frame (for example, 0.8 times), the position where the discrimination occurs can be greatly shifted even in an image whose brightness changes slowly. An improvement effect can be obtained.

In FIG. 4, an example in which a gain of 1.0 times is applied to the first frame and a gain of 0.9 times is applied to the second frame has been described. Nation interference will be further improved.

JP-A-2017-53945

However, as described above, if the amount of gain applied is increased or the amount of gain is different over a plurality of frames, the discreteness is improved, but the gain for the input signal causes a change in brightness for each frame, which interferes with flicker. There is a problem that it is visually recognized as.

An object of the present invention is to provide a liquid crystal display device capable of suppressing a dispersion phenomenon due to digital drive of a liquid crystal display element.

In order to achieve the above object, the liquid crystal display device according to the present invention
A liquid crystal driving device that drives a liquid crystal display element having a plurality of pixels based on an input image, and a gradation setting means for setting a driving gradation based on an input gradation that is the gradation of the input image, and the driving. Depending on the gradation, the voltage applied to each pixel in each of the plurality of subframe periods included in the one frame period in which the liquid crystal display element displays the one frame image is calculated from the first voltage and the first voltage. It has a driving means for controlling to a low second voltage, has the gradation setting means and a plurality of the driving means, and switches between the plurality of gradation setting means and the driving means for each frame. ..

According to the liquid crystal display device according to the present invention, it is possible to provide an image in which flicker is not visually recognized while suppressing the dispersion generated in the adjacent gradation of the digitally driven liquid crystal display element.

Explanatory drawing of PWM drive Explanatory drawing of adjacent gradation discretion generation Explanatory diagram of discination Explanatory drawing of the conventional adjacent gradation discrete improvement method Explanatory drawing of liquid crystal display device in Example 1 Configuration diagram of the liquid crystal projector of Example 1 Explanatory drawing of PWM drive waveform for each frame in Example 1. Explanatory drawing of PWM drive gradation vs. brightness for each frame in Example 1. Explanatory drawing of a table set by the drive tone setting means in Example 1 for each frame. Explanatory drawing of brightness for each frame with respect to input gradation in Example 1. Explanatory drawing of discrimination improvement effect in Example 1 Explanatory drawing of PWM drive waveform for each frame in Example 2. Explanatory drawing of PWM drive gradation vs. brightness for each frame in Example 2. Explanatory drawing of a table set by the drive tone setting means in Example 2 for each frame. Explanatory drawing of brightness for each frame with respect to input gradation in Example 2. Explanatory drawing of discrimination improvement effect in Example 2

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

FIG. 5 shows a liquid crystal projector 501 as a liquid crystal display device according to a first embodiment of the present invention.

In this embodiment and the examples described later, a liquid crystal projector will be described as an example of a display device using a liquid crystal display element, but the adjacent gradation discrimination suppression method (video signal generation method) described below is a direct-view type. It can also be applied to other display devices using a liquid crystal display element such as a monitor.

The video signal (external video signal) output from the video player 502 is input to the liquid crystal projector 501 via the video cable 503. The liquid crystal projector 501 generates an output video signal suitable for display from the input external video signal, and projects the video 505 corresponding to the output video signal onto a projected surface 504 such as a screen.

FIG. 6 shows the configuration of the liquid crystal projector 501.

The video signal input to the liquid crystal projector 501 is subjected to brightness correction, contrast correction, gamma conversion, color conversion, and the like by the video processing unit 601. The tone setting means 609 included in the video processing unit changes the input / output characteristics for each frame. The signal output from the video processing unit is input to the liquid crystal drive unit 603. The drive means 602 included in the liquid crystal drive unit generates a different PWM drive waveform for each frame, generates a drive ON / OFF PWM pattern according to each output gradation for each frame, and generates a drive ON / OFF PWM pattern for each frame to generate a liquid crystal display element 604. Enter in.

One liquid crystal display element 604 is provided for each of the RGB colors, and each color image (continuous frame image) is displayed. The light from the light source 605 is decomposed into three color lights of RGB by the illumination optical system 606 and incident on the three liquid crystal display elements 604, and the image is modulated by the liquid crystal display element 604. The three image-modulated colored lights are combined into one light and projected by the projection optical system 607.

The CPU 608 as the main controller controls the processing of the video processing unit 601 and the delay circuit unit 602, controls the drive of the light source 606, and controls the drive of the liquid crystal display element 604 by the liquid crystal drive unit 603.

FIG. 7 shows an example of a PWM drive waveform that the drive means 602 inputs to the liquid crystal display element for each frame. FIG. 7A shows the relationship between the PWM drive gradation of the first frame and ON / OFF per frame, and FIG. 7B shows the relationship between the PWM drive gradation of the second frame and ON / OFF per frame. ing.

In FIG. 7, 701 and 702 show the total ON period of each of the first and second frames when the PWM drive gradation is 8 gradations. Here, the drive means is set so that the ON period of 702 is longer than that of 701. Therefore, when 8 gradations are displayed, a brighter display can be obtained when the PWM drive waveform of the second frame is used than when the PWM drive waveform of the first frame is used. The relationship between the total PWM drive gradation and the brightness in the first frame is shown in FIGS. 8,801, and the relationship between the total PWM drive gradation and the brightness in the second frame is shown in FIGS. 8,802. By providing the driving means for changing the PWM drive waveform between the first frame and the second frame in this way, it is possible to make a difference in the brightness of each frame.

Next, FIG. 9 shows an example of a table of input gradation vs. PWM drive gradation generated for each frame by the gradation setting means 609.

This input gradation vs. drive gradation table is set so as to reverse-correct the relationship between the drive gradation and the brightness for each frame shown in FIG. That is, when a drive means having a characteristic that the first frame is darker and the second frame is brighter for the same drive tone as shown in FIG. 8 is set, for the same input tone as shown in FIG. , A high drive tone is output in the first frame (901), and a low drive tone is output in the second frame (902). This drive gradation setting means may be generated by measuring the relationship between the drive gradation and the brightness, or may be generated by a predetermined function or the like. FIG. 10 shows the relationship between the input gradation and the brightness in this embodiment for each frame. By using the drive gradation setting means of FIG. 9 as shown in 1001 and 1002, it is possible to bring the difference in brightness caused by changing the PWM drive waveform for each frame closer. As described above, it is possible to suppress the change in brightness for each frame and reduce flicker interference while having a PWM drive gradation that is different for each frame with respect to the input gradation.

Next, the effect of improving the dispersion in this embodiment will be described with reference to FIGS. 11 (a) and 11 (b).

FIG. 11A is a diagram schematically showing the discrete generation generation positions in the PWM drive gradation of the first frame and the second frame.

Reference numerals 1101 and 1102 indicate the dispersion generation gradation of the first frame and the second frame, and here, an example is shown in which the dispersion generation position with respect to the PWM drive gradation is generated in the same gradation.

FIG. 11B shows the discretion generation positions in the input tone of the first frame and the second frame.

Since the drive gradation with respect to the input gradation is different between the first frame and the second frame due to the drive gradation setting means described above, the discrete generation position with respect to the input gradation is different for each frame such as 1103 and 1104. Therefore, when the first frame and the second frame are combined as shown in 1105, the generation positions can be scattered and the dispersion can be improved.

In this embodiment, the components common to those in the first embodiment are designated by the same reference numerals as those in the first embodiment.

12 (a), (b), (c), and (d) show the PWM drive gradation setting means for each frame set in this embodiment, and FIG. 13 shows the relationship between the drive gradation and the brightness for each frame, FIG. The relationship between the input gradation and the driving gradation table for each frame is shown in FIG. 15, and the relationship between the input gradation and the brightness for each frame is shown in FIG.

12 (a) is a PWM drive waveform set in the first frame, FIG. 12 (b) is a PWM drive waveform set in the second frame, and FIG. 12 (c) is a PWM drive waveform set in the third frame. (D) shows the PWM drive waveform set in the fourth frame.

The ON periods 1201 to 1204 in the same drive gradation (here, 8 gradations are exemplified) are set so that 1204> 1202> 1201> 1203. Therefore, as shown in FIG. 13, there is a relationship between drive gradation and brightness for each frame. The input gradation vs. brightness table set in FIG. 14 as in the first embodiment is such that the brightness difference for each frame in FIG. 13 caused by setting the PWM drive gradation setting for each frame (FIG. 12) is reversely corrected. It is set. Therefore, as shown in FIG. 15, as in the first embodiment, it is possible to suppress the change in brightness for each frame and reduce flicker interference while having a PWM drive gradation that is different for each frame with respect to the input gradation.

FIG. 16 shows the effect of improving dispersion in this example.

Disclosure generation with respect to the input gradation As shown in 1609, the discrimination can be scattered in a plurality of frames, and the discretion can be scattered more effectively than in the first embodiment.

In this embodiment, the PWM drive gradation setting means is different from the first frame to the fourth frame, but the present invention may be used over a plurality of frames.

The present invention relates to adjacent gradation discrimination that occurs when a liquid crystal display element is digitally driven. By switching between the drive gradation setting means and the drive means for each frame, it is possible to provide an image with less flicker interference while suppressing adjacent gradation dispersion.

101 PWM ON period example (1535/4095),
201, 202 pixels, 2037 tone ON period,
2048 gradation ON period, 301 lateral electric field,
302 Disorientation,
401 Discrimination occurrence position of the first frame,
402 Discrimination occurrence position of the second frame,
403 Disrelation occurrence position of the first and second frames,
501 projector, 502 video player,
503 video cable, 504 projected surface, 505 projected video,
601 Video processing unit, 602 drive means, 603 liquid crystal drive circuit,
604 liquid crystal display element, 605 light source, 606 illumination optical system,
607 Projection optics, 608 CPU, 609 gradation setting means,
701 First frame 8 gradation ON period,
702 Second frame 8 gradation ON period,
801 First frame drive gradation vs. brightness characteristics,
802 Second frame drive gradation vs. brightness characteristics,
901 First frame input gradation vs. drive gradation setting,
902 Second frame input gradation vs. drive gradation setting,
1001 First frame input gradation vs. brightness characteristics,
1002 Second frame input gradation vs. brightness characteristics,
1101 First frame drive gradation vs. discretion generation position,
1102 Drive gradation vs. discretion generation position of the second frame,
1103 Input gradation vs. discretion generation position of the first frame,
1104 Input gradation vs. discretion generation position of the second frame,
1105 Discrimination improvement effect,
1201 1st frame 8 gradation ON period,
1202 Second frame 8 gradation ON period,
1203 3rd frame 8 gradation ON period,
1204 4th frame 8 gradation ON period,
1301 First frame drive gradation vs. brightness characteristics,
1302 Second frame drive gradation vs. brightness characteristics,
1303 Third frame drive gradation vs. brightness characteristics,
1304 4th frame drive gradation vs. brightness characteristics,
1401 Input gradation vs. drive gradation setting of the first frame,
1402 Second frame input gradation vs. drive gradation setting,
1403 Input gradation vs. drive gradation setting of the third frame,
1404 4th frame input gradation vs. drive gradation setting,
1501 First frame input gradation vs. brightness characteristics,
1502 Second frame input gradation vs. brightness characteristics,
1503 Input gradation vs. brightness characteristics of the third frame,
1504 4th frame input gradation vs. brightness characteristics,
1601 First frame drive gradation vs. discretion generation position,
1602 Second frame drive gradation vs. discretion generation position,
1603 Drive gradation vs. discretion generation position of the third frame,
1604 Drive gradation vs. discretion generation position of the 4th frame,
1605 Input gradation vs. discretion generation position of the first frame,
1606 Input gradation vs. discretion generation position of the second frame,
1607 Input gradation vs. discretion generation position of the third frame,
1608 Input gradation vs. discretion generation position in the 4th frame,
1609 Discretion improvement effect

Claims (4)

A liquid crystal driving device that drives a liquid crystal display element having a plurality of pixels based on an input image, and a gradation setting means for setting a driving gradation based on an input gradation that is the gradation of the input image, and the driving. Depending on the gradation, the voltage applied to each pixel in each of the plurality of subframe periods included in the one frame period in which the liquid crystal display element displays the one frame image is calculated from the first voltage and the first voltage. It has a driving means for controlling to a low second voltage, has the gradation setting means and a plurality of the driving means, and switches between the plurality of gradation setting means and the driving means for each frame. LCD display device. The input tone input for each frame is A, the drive tone set by the tone setting means based on the input tone is Bn (A), and the total period of the first voltage set by the drive means is Cn (Bn (A)). ), The relationship between the drive gradations in the n-frame and the m-frame in at least one input gradation A is Bn (A)> Bm (A), and the total period of the first voltage set by the drive means is Cn. The liquid crystal display device according to claim 1, wherein (Bn (A)) <Cm (Bm (A)). The input tone input for each frame is A, the drive tone set by the tone setting means based on the input tone is Bn (A), and the total period of the first voltage set by the drive means is Cn (Bn (A)). ), The relationship between the drive gradations in the n-frame and the m-frame in at least one input gradation A is Bn (A) <Bm (A), and the total period of the first voltage set by the drive means is Cn (. The liquid crystal display device according to claim 1, wherein Bn (A))> Cm (Bm (A)). The projection type liquid crystal display device according to any one of claims 1 to 3.

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