WO2009125600A1

WO2009125600A1 - Liquid crystal image display unit

Info

Publication number: WO2009125600A1
Application number: PCT/JP2009/001658
Authority: WO
Inventors: 安部玲央; 西田保洋; 渡辺一幸
Original assignee: 株式会社ナナオ
Priority date: 2008-04-11
Filing date: 2009-04-09
Publication date: 2009-10-15
Also published as: JPWO2009125600A1; JP5132763B2

Abstract

At the time of display of a video picture (motion image) that is hard to sense flickering and at the time of display of a video picture (still image) that is easy to sense flickering, the liquid crystal image display unit controls modulated light pulses for a backlight by changing phases of pulses within a unit vertical synchronization period instead of changing the number of a plurality of modulated light pulses to be generated within the unit vertical synchronization period. At the time of display of the motion image, pulse intervals are reduced to combine a plurality of pulses into a single pseudo pulse. At the time of display of the still image, the pulse intervals are equalized. This generates, in a pseudo manner, the modulated light pulses different in frequency for display of the motion image and still image. In reality, any frequencies of the modulated light pulses are never changed, thus variations in chroma and luminance of the images at the time of display of the motion image and the still image can be constrained, and further blurring on the motion image and flickering on the still image can be constrained.

Description

Liquid crystal image display

The present invention relates to a liquid crystal image display device, and more particularly to a lighting method of a backlight, and relates to a technique for appropriately generating a light control signal of the backlight according to the movement of a video image.

As problems of liquid crystal image display, there are image outline blurring of a moving image and flicker of a still image (flickering of an image). Since a liquid crystal image display device is originally a hold type image display device, it is not suitable for displaying moving images as in a CRT which is an impulse type image display device. Therefore, in order to improve the image outline blurring of a moving image, the backlight of the impulse type is blinked (hereinafter referred to as intermittent lighting) to improve the image outline blurring of the moving image. The frequency of intermittent lighting of this backlight is synchronized to 60 Hz which is a vertical synchronization signal of the TV. In this intermittent lighting method, the batch intermittent lighting method in which all backlights are lit collectively and the backlight are divided into several phases, and the backlights of each phase are sequentially lit according to the writing of liquid crystal pixels. There is an intermittent lighting method sequentially. By these lighting methods, the image outline blurring of the moving image is greatly improved.

However, flickering that was not felt in moving pictures can be felt in still pictures when it is intermittently lit at 60 Hz. This is because, due to the characteristics of the human eye, when the frequency of intermittent lighting of the backlight is low, flicker is perceived in an image such as a still image where movement is poor. Therefore, if the frequency of intermittent lighting is increased, the flicker will not be felt. The frequency which does not feel this flicker at all is called critical fusion frequency (CFF).

It is known that this critical fusion frequency becomes high due to the conditions under which the liquid crystal display is viewed, the enlargement of the liquid crystal display and the increase in luminance. The critical fusion frequency was previously said to be lower than 60 Hz, but has recently exceeded 60 Hz. From this, flickering is felt when it is intermittently turned on in synchronization with the vertical sync signal of 60 Hz in a still image.

In order to solve this problem, in the technology disclosed in Patent Document 1, it is determined by the motion detection circuit whether the video image is a moving image or a still image. When it is determined to be a moving image, a first dimming pulse (60 Hz) having the same frequency as that of the vertical synchronization signal is generated. When it is determined that the image is a still image, a second dimming pulse (240 Hz) having a frequency higher than that of the vertical synchronization signal is generated. In this way, in the case of a moving image, the backlight is intermittently turned on to improve the blurring of the moving image image, and in the case of a still image, the backlight is turned on at a frequency exceeding the critical fusion frequency to reduce flicker.

However, in the technique of Patent Document 1, the following problems remain. That is, when switching from the light control pulse (60 Hz) at the time of moving image judgment to the light control pulse (240 Hz) at the still image judgment, and at the reverse switching, this switching is instantaneously performed by the selector circuit. For this reason, a momentary change in luminance (flashing phenomenon) can be felt by the human eye. This is caused by the nature of the photoreceptors of the human eye storing light as an integral quantity over a certain period of time. The integral amount of light in a fixed time accumulated in the eye changes rapidly by switching the frequency of the dimming pulse instantaneously, and this can be felt by the human eye as a momentary change in brightness.

More specifically, Weber's law in the field of psychophysics is known for its ability to sense changes in human eye brightness. According to this law, the human eye does not notice that the brightness has changed unless the brightness changes by a certain amount. In FIG. 11 (a), when a light amount S 'obtained by increasing the brightness further from the light amount S is given to the human eye, the minimum value of the difference between the light amounts S and S' at which the difference in brightness can be felt is It is called the discrimination threshold ΔS for brightness. That is, if the change in brightness is ΔS or more, the human can recognize the change in brightness, and if the change in brightness is less than ΔS, the human can not recognize this change in brightness. Then, according to FIG. 11B, the Weber's law in the discrimination of brightness is that the ratio of ΔS to S, ΔS / S, is constant. According to this law, when the frequency of the dimming pulse is instantaneously switched, the amount of change in the amount of light accumulated in the human eye becomes equal to or greater than ΔS along with the instantaneous change in luminance. Are felt.

This will be described with reference to FIG. In FIG. 12B, the solid line is the luminance emitted by the light source, and the broken line is a square wave of the dimming pulse. When switching from a dimming pulse with a high frequency to a dimming pulse with a low frequency, the pattern of luminance change greatly changes. Then, after switching, the same pattern of change in luminance continues thereafter. The graph of FIG. 12A shows, as the luminance at that time, the integral amount obtained by integrating the luminance emitted by the screen in a period of 16.6 ms going back from each point at an arbitrary time point of FIG. 12B. . The luminance felt by humans is also a value integrated over a period of about 16.6 ms in the past received by the eye. As a result, the amount of change in integral of the luminance at the transition of the pattern from high frequency to low frequency is equal to or greater than ΔS of Weber's law, and it can be perceived by the human eye as an instantaneous luminance change. For the above reasons, when the backlight is switched from the still image determination to the moving image determination, or vice versa, a flushing phenomenon occurs to cause an unpleasant feeling to the viewer of the liquid crystal display device.

Therefore, in the technique of Patent Document 2, the types of frequencies of dimming pulses are increased. From the moving image determination to the still image determination, and vice versa, the flashing phenomenon is suppressed by gradually increasing or decreasing the frequency of the dimming pulse. That is, by making the change of the integral of the light amount in a certain time stored in the human eye slow, the amount of change is suppressed to less than ΔS in Weber's rule, and the human eye does not feel an instantaneous luminance change.
JP 2002-287700 A JP, 2006-018200, A

However, the techniques disclosed in Patent Document 1 and Patent Document 2 still have the following unsolvable problems. This problem arises from the fact that the number of dimming pulses in a unit vertical synchronization period is different for each type of frequency because there are multiple types of frequencies of dimming pulses.

Since the frequency is different before and after the switching of the dimming pulse, the number of falling of the dimming pulse in the unit vertical synchronization period is different before and after the switching of the dimming pulse. That is, the number of fall of the dimming pulse in the unit vertical synchronization period is different between the moving image determination and the still image determination. According to Patent Document 1, when the light adjustment pulse at the time of moving image judgment is 60 Hz, the number of falling of the light adjustment pulse in the unit vertical synchronization period is one, and when the light adjustment pulse at the still image judgment is 240 Hz The number of falling of the dimming pulse in the unit vertical synchronization period is four. As a result of the difference in the number of falling edges of the dimming pulse, when the moving image determination and the still image determination are compared, chromaticity change and luminance change constantly occur on the screen.

The cause is as follows. A fluorescent tube is usually used as a backlight of a liquid crystal image display device. Red, green, and blue phosphors are applied to the inner surface of the glass of the fluorescent tube, and the green phosphor has an afterglow characteristic that the afterglow time is longer than that of other reds and blues. From this, every time the dimming pulse falls once, that is, every time the fluorescent tube is switched from the lighting state to the extinguishing state, a green afterglow occurs. That is, the number of times of occurrence of the green afterglow is different in each image judgment because the number of falling of the light adjustment pulse in the unit vertical synchronization period is different between the moving image determination and the still image determination. In a large number of states, that is, when the still image determination has a high dimming pulse frequency, the whole screen has a greenish chromaticity than the moving image determination.

Further, as a characteristic of the fluorescent tube, it can be raised that the luminance has a non-linear waveform. As shown in FIG. 12B, even if the dimming pulse is a rectangular wave, the luminance is a non-linear curvilinear wave. From this, even if the duty ratio per unit vertical synchronization period of each frequency is the same, the luminances do not match. Even if the duty ratio is the same, the luminance is not simply superimposed, so the screen with a high frequency is slightly lower in luminance than the screen with a low frequency. That is, the brightness of the screen at the still image determination with the narrow pulse width and the large pulse number is darker than that in the moving image determination with the wide pulse width and one pulse number, even if the duty ratio is the same. As a result, when the luminances of the moving image determination, the still image determination, and the screen are compared, the entire screen becomes slightly darker at the still image determination.

The present invention has been made in view of such circumstances, and the lighting mode of the backlight is instantaneously changed in luminance (flushing phenomenon) when switching between a moving image and a still image, and steady before and after the switching. It is an object of the present invention to provide a liquid crystal image display device which does not display image contour blurring at the time of moving image and flicker at the time of still image without causing any luminance change and chromaticity change.

The present invention has the following configuration in order to achieve such an object.
That is, in the liquid crystal image display device of the present invention, a light control signal consisting of a pulse train formed of a plurality of predetermined pulses and a video judgment means for transmitting a video judgment signal predetermined based on the video signal is vertical It comprises: a light control signal generating unit that generates each synchronization signal; a light emitting unit driven by the light control signal sent from the light control signal generating unit; and a liquid crystal image display unit that emits light by the light emitting unit. The light adjustment signal generation means, when the first image discrimination signal is sent from the image discrimination means, maintains the number of pulses constituting the light adjustment signal, and the pulse interval in the pulse train is maintained. Are gradually narrowed, and when the second image discrimination signal is sent from the image discrimination means, the pulse interval in the pulse train is set while maintaining the number of pulses constituting the light adjustment signal. Gradually Characterized by widely.

According to the liquid crystal image display device of the present invention, in order to shift the lighting method of the backlight to either the moving image mode or the still image mode by the video image discrimination signal sent based on the video signal, every vertical synchronization period The phase of each pulse generated in the same number is displaced. That is, the moving image mode and the still image mode are switched by adjusting the interval of each pulse in the pulse train. It is a feature of the present invention to adjust the intervals of a plurality of pulses generated in the same number in the unit vertical synchronization period.

Further, in the moving image mode and the still image mode, since the number of pulses in the unit vertical synchronization period is the same in both modes, the number of falling edges of the pulse in the unit vertical synchronization period is the same. Therefore, since the green afterglow characteristics of approximately the same amount appear in either mode, the change in chromaticity upon switching between the moving image mode and the still image mode is largely suppressed. In addition, since the number of falling edges of the pulse in the unit vertical synchronization period is the same, the non-linear waveform of the backlight is the same, and the steady luminance change at the time of switching between the moving image mode and the still image mode is significantly suppressed. . For these reasons, before and after the switching between the moving image mode and the still image mode, the chromaticity change and the luminance change are reduced to such an extent that a human does not feel a change by appropriately setting the pulse interval in the moving image mode. Moreover, in addition to adjusting the pulse interval in a stepwise manner to such an extent that the human eye can not notice the change of the mode switching, the progressive change described in claim 1 notices the change of the mode switching with the human eye. It also means adjusting the pulse interval steplessly to the extent that it can not

In addition, when the first image discrimination signal is sent from the image discrimination means, the dimming signal generation means gradually narrows the pulse interval in the pulse train while maintaining the number of pulses constituting the dimming signal. Thus, a pulse train formed by a plurality of pulses can be regarded as one pulse in a pseudo manner, and when the second image discrimination signal is sent from the image discrimination means, a light control signal is formed. The pulse train is equivalent to a pulse train represented by a frequency obtained by multiplying the number of pulses in the dimming signal by the number of pulses in the dimming signal by gradually widening the pulse interval in the pulse train while maintaining the number of pulses. It is desirable to make it

The adjustment of the pulse interval (displacement of the phase) will be described in detail below. By gradually narrowing the interval of the pulses in the pulse train based on the transmitted image discrimination signal, the pulse train formed from a plurality of pulses shifts to a moving image mode in which it is regarded as one pulse in a pseudo manner. Then, when an image discrimination signal different from the above is sent, the interval of the pulses in the pulse train is gradually extended, and the pseudo one pulse is shifted to the independent pulse. Then, in the still image mode, the phase of the pulse having the widest pulse interval in the dimming signal becomes the same phase as the pulse of the frequency obtained by multiplying the number of pulses in the unit vertical synchronization period by the vertical synchronization frequency. . From this, at the time of switching from the moving image mode to the still image mode, and at the reverse switching time, the instantaneous luminance change (flushing phenomenon) of the backlight is eliminated.

By narrowing the pulse interval in the pulse train by the transmitted image discrimination signal, the pulse train is virtually regarded as one pulse, and the lighting period and the lighting-off period of the fluorescent tube are approximately divided into two within the unit vertical synchronization period, The continuous black insertion period within the unit vertical synchronization period becomes long. Thereby, the image outline blurring of a moving image can be reduced. When displaying an image that is easy to sense flicker, it is the same as turning on the backlight at a frequency exceeding the critical fusion frequency, and therefore no flicker is felt.

Further, the video discrimination means discriminates whether the video is a video which is not likely to sense flicker or is a video which is likely to sense a flicker based on the video signal, and when it is determined that the video is unlikely to sense flicker, the first video discrimination signal The second image discrimination signal may be transmitted when it is determined that the image is transmitted and flicker is easy to feel. From this, the image discrimination means discriminates whether the image is an image which is easy to sense flicker or not so as to send each image discrimination signal, so that the image displayed on the liquid crystal image display device can be displayed. A suitable backlight can be lit.

In addition, the light adjustment signal generation unit may be provided with a screen brightness adjustment signal reception unit that adjusts the brightness of the liquid crystal screen by adjusting the pulse duty ratio of the light adjustment signal by receiving the screen brightness adjustment signal. Good. Since the adjustment of the brightness of the liquid crystal screen is performed by changing the duty ratio of the pulse forming the dimming signal, the switching between the moving image mode and the still image mode of the dimming signal and the adjustment of the brightness of the screen are performed. Can be performed by one dimming signal generation circuit.

The light emitting means may have a plurality of light sources, and the lighting method of the light sources may be an intermittent lighting method in sequence. Thus, by providing a plurality of light sources, it is possible to intermittently turn on the backlight sequentially according to the response speed of the liquid crystal. This further reduces blurring of the image outline of the moving image.

Also, the light emitting means may comprise a light source consisting of three or more layers. Since the liquid crystal display is controlled by the sequential intermittent lighting of three or more layers even in the case of a large screen, it is possible to efficiently reduce the image outline blurring of a moving image.

According to the liquid crystal image display device according to the present invention, instantaneous luminance change (flushing phenomenon) does not occur at the time of switching between the moving image mode and the still image mode of the backlight. In addition, it is possible to provide an image in which steady change in chromaticity and change in luminance before and after switching are significantly suppressed.

FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal image display device according to a first embodiment. FIG. 2 is a block diagram showing a schematic configuration of a video image discrimination circuit provided in the first embodiment. FIG. 2 is a block diagram showing a schematic configuration of a light adjustment signal generation circuit provided in the first embodiment. FIG. 2 is a block diagram showing a schematic configuration of a backlight module provided in the first embodiment. FIG. 5 is a schematic view showing a dimming signal generated in the dimming signal generation circuit of the first embodiment. 5 is a flowchart showing a process of calculating pulse intervals in a pulse interval calculation unit provided in the dimming signal generation circuit of the first embodiment. FIG. 7 is a diagram showing dimming signals generated in the moving image mode in the three dimming signal generation circuits of the first embodiment. It is the figure which compared the light control signal of the backlight in Example 1 and a prior art example, and the brightness perceived through a liquid crystal panel. FIG. 6 is a diagram showing luminance and chromaticity in a moving image mode and a still image mode of the first embodiment. It is a figure which shows the brightness | luminance and chromaticity in moving image mode in a prior art example, and still image mode. It is a figure which shows the Weber's law in discrimination of human brightness. It is a figure which shows the luminance sensed through the light control signal of a backlight, and a liquid crystal panel.

2 ... Image discrimination circuit 3 ... Dimming signal generation circuit 5 ... Backlight module 7 ... Liquid crystal panel

The first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the liquid crystal image display device according to the first embodiment. This device determines whether the image is a video that does not easily sense flicker or a flicker based on a video signal and sends out a video discrimination signal, and an optimal dimming according to the image based on a video discrimination signal. A light control signal generation circuit 3 for generating a signal, a backlight module 5 for emitting a backlight by the light control signal, and a liquid crystal panel 7 for emitting light by the backlight module 5 to display an image.

The configuration of each part will be described in more detail below.
<< Video discrimination circuit >>
The configuration of the video image discrimination circuit 2 will be described with reference to FIG. The image discrimination circuit 2 calculates the sum of image differences between the signal of the previous frame image 10 and the signal of the current frame image 8 based on the image signal branched from the image signal sent to the liquid crystal panel 7 It asks with the vessel 9. This operation is a function included in a general video processing IC, and this embodiment is also used. Next, by comparing the sum of the differences of the image signals with the threshold set in advance by the discriminator 11, it is determined whether the current frame image 8 is a video that is hard to sense flicker or a video that is prone to flicker Make a decision. Then, when it is determined that the video is hard to feel flicker, for example, a signal of '1' (moving image) is sent as a video discrimination signal, and when it is discriminated that the video is easy to feel flicker, '0' (still image Send a signal of). Thereby, the light control signal generation circuit 3 is instructed to determine whether the video image is a moving image or a still image. As well known, if the video is a moving image, it is difficult to sense flicker, and if it is a still image, flicker is likely to be felt. However, there are cases where moving pictures and still pictures are mixed in the display screen in practice, and if moving pictures are included in the display screen, it can not be immediately determined to be moving pictures. Therefore, a video that is hard to sense flicker means a video that is substantially moving. A substantially moving image refers to a moving image as a whole, even if a part of the screen includes a non-moving image. Similarly, an image that is susceptible to flicker means an image that is substantially motionless. A substantially motionless video refers to a video that has no motion as a whole, even if the portion of the screen includes a motional video.
This image discrimination method may be appropriately selected by the designer regardless of the above method, and a discrimination signal as to whether it is a moving image or a still image may be sent out.

Dimming signal generation circuit
Next, the configuration of the dimming signal generation circuit 3 will be described with reference to FIG. The dimming signal generation circuit 3 generates an optimal dimming signal according to the image in accordance with the image discrimination signal. Here, three parameters of pulse interval, duty ratio, and pulse generation timing are calculated to generate a dimming signal. In the present embodiment, a three-phase dimming signal is sent to the backlight module. The generation of the dimming signal will be described in detail later.

Backlight module
Next, the configuration of the backlight module 5 will be described with reference to FIG. The backlight module 5 includes

light sources

23a, 23b, 23c and

inverters IC

21a, 21b, 21c for controlling them. As a light source, in the present embodiment, two CCFL tubes are provided for each light source. That is, the backlight module 5 has a total of six CCFL (Cold Cathode Fluorescent Lamp) tubes. Depending on the dimming signal 1, the dimming signal 2, and the dimming signal 3 generated by the dimming signal generation circuit 3 two by two, the respective dimming frequencies are synchronized by the

respective inverters IC

21 a, 21 b and 21 c. Have control. As a result, the

light sources

23a, 23b, and 23c are intermittently turned on one after another to illuminate the liquid crystal panel 7. In addition to the above, the number of fluorescent tubes, the number of fluorescent tubes to be controlled by the inverter IC, and the like may be determined by a designer who is considered to be optimum.

"LCD panel"
In this embodiment, the liquid crystal panel 7 includes a drive circuit of the liquid crystal panel, and uses an active matrix liquid crystal display panel using thin film transistors (TFTs). The illumination of light from the backlight module 5 adapted to the video signal makes it possible for the viewer not to feel a momentary change in luminance when switching between the moving image mode and the still image mode. In addition, a comfortable video can be provided without the viewer being able to feel a steady change in chromaticity and a change in luminance before and after switching.

Dimming signal generation circuit
The operation of the dimming signal generation circuit 3 will be described below.
The video discrimination signal sent out by the video discrimination circuit 2 is taken into the pulse interval calculation unit 13, and the pulse interval of the pulse train in the dimming signal is calculated frame by frame by the vertical synchronization signal and the video discrimination signal. Here, as shown in FIG. 5 of this embodiment, the pulse interval means the interval between each pulse forming the pulse train within the unit vertical synchronization period.

Further, as shown in FIG. 5, in the present embodiment, the number of pulses of the pulse train of the dimming signal in the unit vertical synchronization period is three. Also, in the still image mode, the pulse train forming the dimming signal has the same phase as the pulse train generated at a frequency of 180 Hz. Thus, in the still image mode, since the frequency is higher than the critical fusion frequency in which flicker does not occur, the still image can be viewed comfortably. The vertical synchronization frequency is 60 Hz in the case of the NTSC signal standard.

The number of pulses of the pulse train in the unit vertical synchronization period is not limited to three and may be plural. The pulse train of the dimming signal in the still image mode is the same as the pulse train generated at the frequency of (number of pulses) × (vertical synchronization frequency). Furthermore, it is preferable that (number of pulses) × (vertical synchronization frequency) exceeds the critical fusion frequency.

The pulse interval calculation unit 13 has the smallest pulse interval, the most suitable moving image mode for moving image display (FIG. 5 (b)), and the largest pulse interval, the most suitable still image mode for still image display (FIG. 5). 5 (d) and the interval between the light control pulses of the four states of moving picture mode transition state from still picture mode to moving picture mode transition state and vice versa transition state from moving picture mode to still picture mode calculate.

The dimming signal having the smallest pulse interval can be regarded as pseudo in that a pulse train formed by three pulses is formed by one pulse. In other words, a pulse train with the same phase as three independent pulses at 180 Hz in still image mode can be regarded as one pulse of 60 Hz in a pseudo manner by reducing the pulse interval in the pulse train in moving image mode. it can. As a result, since the fluorescent tube lighting period and the light-off period are approximately divided into two in the unit vertical synchronization period in the moving image mode, backlight irradiation is optimal for moving image display.

<< Pulse interval calculation >>
The flow of pulse interval calculation performed by the pulse interval calculation unit 13 is shown in FIG. In this calculation flow, calculation of the pulse interval is started when the vertical synchronization signal is input. When a video discrimination signal is input from the video discrimination circuit 2, in step S1, video discrimination is performed to determine whether the signal is larger than '0'. If the video image discrimination signal is '1' (moving image), the process proceeds to step S2. If the video image discrimination signal is' 0 '(still image), the process proceeds to step S2'. First, the case where the video image discrimination signal is a moving image and the process proceeds to step S2 will be described.

In step S2, an operation to reduce the pulse interval is performed. Here, Space is a pulse interval, and ΔX is a pulse interval displacement amount in a unit vertical synchronization period. This ΔX is a value determined by the vertical synchronization frequency, the number of pulses, the duty ratio, and the number of frames applied to transition from the moving image mode to the still image mode.

The setting amount of the pulse interval displacement amount ΔX determines the speed of transition from the moving image mode to the still image mode or transition from the still image mode to the moving image mode. When the pulse interval displacement amount ΔX is made large, the switching of the mode becomes fast, so that the luminance change due to the instantaneous switching occurs. In addition, if the pulse interval displacement amount ΔX is made small, the mode switching is delayed, so there is a time difference until the flicker disappears while the image is switched from the moving image to the still image, and the image changes from the still image to the moving image Even though the image is switched to the above, there is a time difference until the image outline blurring of the moving image disappears. Therefore, as a result of searching for a pulse interval displacement amount ΔX that does not feel an instantaneous luminance change accompanying the transition between the modes, it is optimal in the present embodiment that switching between modes takes about 1 second (about 60 frames). It turned out to be. Since this pulse interval displacement amount ΔX is a value which changes depending on various conditions, an optimum value may be set, and accordingly, the switching time between modes may be set without being caught by one second.

Then, since the image discrimination is determined to be a moving image, in step S2, the pulse interval displacement amount ΔX is subtracted from the previous pulse interval.

Next, in step S3, the subtracted pulse interval is compared with a preset minimum value. If the subtracted pulse interval is greater than the minimum value, the subtracted pulse interval is output as the calculated result. As a result, the pulse interval is smaller than that of the previous pulse train, and the light adjustment signal closer to moving image display is approached.

However, if the subtracted pulse interval is equal to or less than the minimum value, the pulse interval subtracted in step S4 is reset to the minimum value, and the minimum value is output as the calculation result. In the process of S4, after reaching the most suitable pulse interval for moving image display, the smallest pulse interval most suitable for moving image display is output as long as the video discrimination signal continues to send '1' (moving image). It is a process to continue.

The minimum pulse interval in this moving picture mode differs depending on the frequency of the vertical synchronization signal of the NTSC system, PAL system or the like, the length of the fluorescent tube, and the color gamut. The upper limit is also determined by how much continuous black insertion time (fluorescent tube off time) in the vertical synchronization period is secured in the moving image mode, and the degree of chromaticity before and after switching between the moving image mode and the still image mode The lower limit value is determined depending on whether or not a change occurs, so it is necessary to set appropriately.

The upper limit value of the minimum pulse interval in the moving image mode can be determined as follows. When the number of pulses in the pulse train is three, if the continuous black insertion time in the unit vertical synchronization period is 50% of the unit vertical synchronization period and the dimming ratio is 10%, the remaining 40% Can be used as a pulse interval, so that 20% of the unit vertical synchronization period can be a pulse interval per pulse train. If the unit vertical synchronization period is 16.6 msec, 3.32 msec is the upper limit value of the minimum pulse interval. However, as described above, since the upper limit value of the minimum pulse interval is determined by the number of pulses in the pulse train, the black insertion time, and the dimming ratio, it can be set appropriately.

Further, the lower limit value of the minimum pulse interval in the moving image mode is a numerical value determined depending on how much chromaticity change is not generated before and after switching between the moving image mode and the still image mode, as described above. Then, it is 0.1 msec or more, more preferably 0.5 msec or more.

When the image discrimination signal '0' (still image) is input in step S1, the process proceeds to step S2 '. Here, contrary to step S2, the pulse interval displacement amount ΔX is added to the previous pulse interval. As a result, an operation to increase the pulse interval is performed.

Next, in step S3 ', the added pulse interval is compared with a preset maximum value. If the added pulse interval is smaller than the maximum value, the added pulse interval is output as the calculated result. As a result, the pulse interval is larger than that of the previous dimming pulse signal, and the dimming pulse closer to still image display is approached.

If the pulse interval added in step S3 'is equal to or greater than the maximum value, the added pulse interval is reset to the maximum value in step S4', and the maximum value is output as the calculation result. In the process of S4 ', after reaching the most suitable pulse interval for still image display, the widest pulse most suitable for still image display as long as the video discrimination signal continues to send' 0 '(still image). It is a process of continuing to output the interval.

The maximum value of the pulse interval in the still image mode is a value determined by the vertical synchronization frequency, the number of pulses, and the duty ratio.

Dimming signal generation
The pulse interval calculation unit 13 sends the pulse interval to the pulse generation timing control unit 15. The vertical synchronization signal and the duty ratio are sent to the pulse generation timing control unit 15 in addition to the pulse interval. The duty ratio is set by sending a screen brightness adjustment signal of the brightness setting value of the liquid crystal screen display device selected by the user to the screen brightness adjustment signal receiving unit 17.

In the pulse generation timing control unit 15, as shown in FIG. 3 and FIG. 7, each adjustment is performed such that the pulse phase of each of the light adjustment

signal generation circuits

19a, 19b, 19c is shifted by 1/3 period in the vertical synchronization period. The first pulse rise command for light signal generation, trigger 1, trigger 2, trigger 3 is sent out. Since the pulse phases to be sent to the respective dimming

signal generation circuits

19a, 19b and 19c are shifted by 1/3 each, the three light sources provided in the backlight module 5 are only driven by driving the fluorescent tubes in accordance with the sent dimming signal. Turns on and off three phases sequentially. The numeral 1/3 means that three-phase control is performed as the light source in the present embodiment, and when the light source is controlled with N phases, it is shifted by 1 / N.

The pulse rise timing is calculated using the pulse interval and the duty ratio as parameters after receiving the vertical synchronization signal, and the trigger command position of the first pulse rise is determined. Next, the first pulse generated by each of the dimming

signal generation circuits

19a, 19b, and 19c is shifted so that the phase of the pulse train of the dimming signal generated by each dimming signal generation circuit is shifted by 1/3 period. Calculate the startup timing.

Further, from the pulse generation timing calculation result, three timing data for raising the pulse in each light adjustment signal generation circuit are sent to a loop counter (not shown) in the pulse generation timing control unit 15. Then, when the loop counter reaches the determined three values, Trigger 1, Trigger 2, and Trigger 3 are sent as the first pulse rise signals to the respective dimming

signal generation circuits

19a, 19b, 19c.

As described above, the phases of the pulse trains generated in the respective light control signal generation circuits are shifted, and as the respective pulse trains shift to the moving image mode, the fluorescent tube lighting period and the light off period in the light control signal are substantially Since the intermittent lighting becomes more prominent sequentially by being divided into two, it becomes an image display which reduces the image outline blurring of a moving image.

In the dimming

signal generation circuits

19a, 19b and 19c, the width of the pulse is determined based on the duty ratio sent from the screen brightness adjustment signal receiving unit 17, and the pulse interval sent by the pulse interval calculation unit 13 is The pulse interval is determined, and three pulses are generated according to the trigger sent by the pulse generation timing control unit 15. Thus, the dimming signal is sent to the backlight module 5.

<< Effect of this embodiment >>
By the liquid crystal image display device described above, the luminance shown in FIG. 8 can be obtained from the liquid crystal image display device. FIG. 8A shows the luminance (solid line) emitted by the light source within the unit vertical synchronization period in the moving image mode obtainable from the present embodiment and the square wave (dashed line) of the dimming pulse. FIG. 8 (b) shows the luminance (solid line) emitted by the light source within the unit vertical synchronization period in the moving image mode obtainable from the conventional example and the square wave (broken line) of the dimming pulse. FIG. 8C shows the luminance (solid line) emitted by the light source in the still image mode within the unit vertical synchronization period and the square wave (dashed line) of the dimming pulse which can be obtained from this embodiment and the conventional example. According to this embodiment, even in the moving image mode, intervals are provided between the pulses, and the luminance generates a non-linear curved wave according to the number of pulses. Since this and the number of falling of the non-linear curvilinear wave of luminance in the still image mode are the same, steady-state luminance change and chromaticity change are suppressed.

On the other hand, as shown in FIG. 8 (b), in the conventional moving image mode, there is no interval between each pulse in the pulse train or no pulse interval because it falls below the lower limit of the above-mentioned minimum pulse interval. It is considered to be. In this case, since there is only one dimming pulse in the pulse train in the unit vertical synchronization period, the number of falling edges of the luminance curve wave is different from the number of falling edges of the luminance curve wave in the still image mode. The change and the change in chromaticity are larger than those in this embodiment.

Further, in the conventional example, since the transition between the moving image mode of FIG. 8B and the still image mode of FIG. 8C is performed by switching by the selector circuit, the flushing phenomenon occurs. However, in the present embodiment, since the mode switching is performed by gradually adjusting the transition between the moving image mode of FIG. 8A and the still image mode of FIG. 8C, the flushing phenomenon does not occur.

FIGS. 9 and 10 show the measurement results of luminance and chromaticity in the above-described moving image mode and still image mode. FIG. 9 shows the luminance and chromaticity of the moving image mode and the still image mode according to the present embodiment, and FIG. 9A is obtained through the dimming rate of the dimming pulse and the liquid crystal screen in the unit vertical synchronization period. 9B shows only the chromaticity information obtained by removing the lightness component Y of the xy Y color system of the CIE color system from the color space in the moving image mode and the still image mode. It is shown. The minimum pulse interval in the pulse train in FIG. 9 is set to 0.5 msec. On the other hand, in FIG. 10, the minimum pulse interval in the pulse train is set to 0.05 msec.

While there is almost no difference in luminance between the moving image mode (circle) and the still image mode (rhombic) in FIG. 9 (a), the moving image mode (circle) and still in FIG. 10 (a) There is a difference in luminance between the image mode (diamonds). That is, when the minimum pulse interval in the pulse train is 0.05 msec, it is considered that there is almost no pulse interval. Further, as shown from this figure, according to the configuration of the present application, it is possible to suppress a steady change in luminance in the moving image mode and the still image mode.

Moreover, when FIG.9 (b) and FIG.10 (b) are compared, the difference of the graph of FIG.9 (b) with the graph of each chromaticity of moving image mode and still image mode is narrower. That is, according to this embodiment, it is shown that the change in chromaticity is suppressed in the moving image mode and the still image mode.

As described above, according to this embodiment, the following effects can be obtained.
Based on the video signal sent, the video discrimination circuit 2 determines whether the video is a video that is hard to sense flicker or a video that is prone to flicker, and sends out a video discrimination signal of a moving image or a still image. By this image discrimination signal, at the time of moving image discrimination, the pulse interval in the pulse train is narrowed to make the pulse train virtually into one pulse. Then, at the time of still image discrimination, the pulse interval in the light control signal is made wide to evenly take the light off period of the fluorescent tube in the light control signal. As a result, since the lighting period and the extinguishing period of the fluorescent tube are divided into approximately two in the dimming signal when transitioning to the moving image mode, blurring of the image outline of the moving image is reduced, and the dimming signal is transitioned to the still image mode. Does not feel flicker on the liquid crystal screen because it has the same phase as the pulse train beyond the critical fusion frequency. Then, in the switching from the moving image mode to the still image mode, and also in the reverse switching, the brightness change is suppressed to less than ΔS in Weber's law by gradually adjusting the pulse interval. As a result, the viewer does not feel a momentary change in luminance, nor does it feel any steady change in chromaticity or change in luminance before and after switching.

Furthermore, even if the liquid crystal panel has a large screen, one inverter IC is made to correspond to a plurality of CCFL tubes and the light source is controlled in three phases to efficiently match intermittent lighting to the writing response of the liquid crystal Crowded. While simplifying the control of the backlight, the response to the image outline blurring of the moving image is efficiently improved.

Further, since the brightness adjustment of the liquid crystal screen and the pulse phase adjustment based on the image discrimination are performed in the same pulse generation circuit at the time of pulse generation, the configuration of the backlight control becomes simpler.

The present invention is not limited to the above embodiment, and can be modified as follows.
(1) In the first embodiment, six CCFL tubes are used for the backlight module, but any number of CCFL tubes may be used, and the number of dimming signal generation circuits 3 is not limited. It may be selected by the designer's appropriate judgment. Furthermore, even when the light source is one, the inverter IC is one, and the dimming pulse generation circuit is one as in a notebook personal computer, the effect of the present invention can be obtained. At the time of switching between the moving image mode and the still image mode, an instantaneous luminance difference does not occur, and neither a steady chromaticity change nor a luminance change occurs even before and after the mode switching.

(2) In the first embodiment, the intermittent lighting is controlled sequentially by the pulse generation timing control unit 15. However, the phases of the respective light adjustment signals may be shifted in the back light module and the intermittent lighting may be sequentially performed. In this case, only the dimming signal 1 is sent to the backlight module, and a pulse whose phase is shifted is generated based on this signal. Further, as means for shifting the phase in the backlight module, for example, although there is an inverter IC, it may not be limited to this. Further, the phase of the pulse may be shifted before the rewriting of the pixel signal according to the response speed of the liquid crystal, or the phase of the pulse may be shifted after the rewriting.

(3) In the first embodiment, the video discrimination circuit 2 performs video discrimination based on the video signal sent in real time, and transmits the video discrimination signal to the dimming signal generation circuit 3, but this is replaced by the video prediction circuit. May be Based on the video signal, the video prediction circuit predicts whether the video image will be a video that is not likely to sense flicker or is likely to be a flicker and the video prediction signal is sent to the dimming signal generation circuit 3. Therefore, it is possible to realize the lighting of the back light with high responsiveness to moving pictures and still pictures.

(4) In the first embodiment, a CCFL tube is used for the backlight module, but EL (electroluminescence) coated with a fluorescent paint may be used. Steady-state chromaticity changes can be suppressed.

Claims

Video discrimination means for transmitting a predetermined video discrimination signal based on the video signal;
Dimmer signal generating means for generating, for each vertical synchronization signal, a dimmer signal comprising a pulse train formed of a plurality of predetermined pulses;
Light emitting means driven by the dimming signal sent from the dimming signal generation means;
Liquid crystal image display means irradiated with light by the light emitting means;
The dimming signal generation means
When the first image discrimination signal is sent from the image discrimination means, the pulse interval in the pulse train is gradually narrowed while maintaining the number of pulses constituting the light adjustment signal,
When the second image discrimination signal is sent from the image discrimination means, the pulse interval in the pulse train is gradually widened while maintaining the number of pulses constituting the light adjustment signal. Liquid crystal image display device.
In the liquid crystal image display device according to claim 1,
The dimming signal generation means, when the first image discrimination signal is sent from the image discrimination means, sets the pulse interval in the pulse train while maintaining the number of pulses constituting the dimming signal. By gradually narrowing, the pulse train formed of a plurality of pulses is made to be regarded as one pulse in a pseudo manner, while
When the second image discrimination signal is sent from the image discrimination means, the pulse interval in the pulse train is gradually widened while maintaining the number of pulses constituting the light adjustment signal. A liquid crystal image display device in which a pulse train is in a state equivalent to a pulse train represented by a frequency obtained by multiplying a vertical synchronization frequency by the number of pulses in the dimming signal.
In the liquid crystal image display device according to claim 1 or 2,
The video judging means judges, based on the video signal, whether the video is a video which is hard to sense flicker or a video which is easy to feel flicker,
When it is determined that the video is hard to sense flicker, the first video discrimination signal is transmitted,
A liquid crystal image display device characterized in that the second video image discrimination signal is transmitted when it is discriminated as a video image in which flicker is easily felt.
The liquid crystal image display device according to any one of claims 1 to 3.
The light control signal generation unit is a liquid crystal having a screen brightness control signal receiving unit that adjusts the brightness of the liquid crystal screen by adjusting the pulse duty ratio of the light control signal by receiving the screen brightness control signal. Image display device.
The liquid crystal image display device according to any one of claims 1 to 4.
The liquid-crystal image display apparatus which has a several light source in the said light emission means, and the lighting system of the said light source is an intermittent lighting system one by one.
In the liquid crystal image display device according to claim 5,
The liquid crystal image display device, wherein the light emitting means comprises a light source consisting of three or more phases.