JP2013222081A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction in quality of a display image caused by video blur, flicker, and the like without changing color hues of an image even with a simple constitution.SOLUTION: In this liquid crystal display device (A), a backlight controller (6) receives drive mode information from image discrimination means (4) and, on the basis of the drive mode, changes the drive frequency of a backlight (2) such that the proportion for the lighted period to the drive period for the backlight (2) does not change.

Description

  The present invention relates to a liquid crystal display device used for a thin television receiver or the like.

  The liquid crystal display device includes a liquid crystal panel and a backlight unit disposed on a back surface of the liquid crystal panel, and the liquid crystal panel adjusts a light transmittance (amount of transmission) from the backlight unit, and An image is displayed in front of the liquid crystal panel.

  When displaying a moving image in a liquid crystal display device, it is known that a so-called “moving image blur” occurs in which the contour of a moving part is blurred and recognized by an observer. This moving image blur in the moving image display is caused by a delay in the optical response time of the liquid crystal, but it is also considered that there is a cause in the driving method of the liquid crystal display device besides this.

  That is, in the liquid crystal display device, charges stored by applying an electric field to the liquid crystal are held at a relatively high rate until the next electric field is applied. In particular, in a TFT liquid crystal display device, a TFT switch is provided for each dot constituting a pixel, and moreover, since an auxiliary capacitor is usually provided for each pixel, the ability to hold the stored charge is increased. In this way, the liquid crystal display device keeps the charge of the pixel and continues to transmit light until it is rewritten with the image information of the next frame. Due to the transmission of this light, a moving image blur of the moving image occurs.

  In a liquid crystal display device, a method of emitting light from a backlight unit in a pulsed manner is employed in order to suppress the above-described motion blur. That is, by turning on the backlight only in the second half of each field period of the display image, the time for the light to reach the observer is limited, and moving image blur is suppressed.

  In the liquid crystal display device, when the light from the backlight is emitted in a pulse shape, the brightness of the backlight can be easily adjusted by adjusting the lighting time. However, in a liquid crystal display device, it is known that when the frequency of the backlight is low, the observer recognizes blinking of the backlight, so-called “flicker”. Therefore, in the liquid crystal display device, the backlight is driven in synchronization with the liquid crystal panel to suppress flickering.

  In addition, it is known that such moving image blur and flicker are likely to occur depending on the nature of the video to be displayed and those that are unlikely to occur.

  In order to suppress such blurring and flickering, the liquid crystal display device described in Japanese Patent No. 4540605 detects the amount of motion blur included in the transmitted image signal, and based on the amount of motion blur, While changing the ratio (impulse rate) of the image display period in one frame period and turning on the light source in synchronization with the impulse rate, the display quality of images such as moving image blur is improved.

  In the liquid crystal display device, the lighting period of the light source is changed in accordance with the impulse rate of the liquid crystal panel, and the light emission luminance of the light source is adjusted (when the impulse rate is low, the light emission luminance is increased). Reduces the brightness of the device.

Japanese Patent No. 4540605

  However, in recent years, it has been known that, in an LED widely used as a light source, the chromaticity of emitted light changes when the current value supplied to change the light emission luminance is changed. As in the liquid crystal display device described in Japanese Patent No. 4540605, when the lighting period of the light source is changed in accordance with the change of the video display time ratio (impulse rate), the emission luminance of the light source at that time is changed. As a result, the color tone of the image displayed on the liquid crystal panel fluctuates, which causes a reduction in image quality.

  Therefore, in the liquid crystal display device described in Japanese Patent No. 4540605, gamma correction is performed by adjusting the gradation of the input image signal to suppress the change in the color tone of the display image. In the case of such a configuration, it is necessary to always change the gradation of the input signal, and the configuration and control of the liquid crystal display device are complicated, and complicated processing is required in a short time. Or) It is necessary to provide a high-speed (high-grade) element for processing information.

  In addition, flicker often does not relate to the amount of motion blur, and if the adjustment impulse rate is adjusted only by the amount of motion blur, flicker may not be suppressed.

  SUMMARY OF THE INVENTION The present invention provides a liquid crystal display device having a simple configuration and capable of suppressing deterioration in display image quality caused by moving image blur, flicker, etc., without changing the color tone of the image. And

  In order to achieve the above object, the present invention relates to a liquid crystal panel, a backlight for supplying light to the liquid crystal panel in synchronization with the operation of the liquid crystal panel, and a backlight driving mode based on display image information. Video determining means for determining, and backlight driving means for changing the driving frequency of the backlight based on the driving mode, wherein the backlight driving means is a ratio of the lighting period to the driving period of the backlight There is provided a liquid crystal display device characterized in that the drive frequency of the backlight is changed so that the value does not change.

  According to this configuration, when displaying an image that is likely to cause flickering and moving image blur, the backlight drive frequency is changed, so that flickering and moving image blur caused by the image can be suppressed.

  By controlling the backlight in this way, it is possible to prevent the luminance and chromaticity from changing when the backlight is turned on. Accordingly, the quality of the liquid crystal display device is unlikely to deteriorate regardless of the backlight driving mode. In addition, since adjustment of the liquid crystal panel is not necessary to adjust the change in chromaticity of the backlight, the control is simplified.

  In the above-described configuration, brightness detection means for detecting brightness around the liquid crystal display device is provided, and the video determination means includes the brightness information from the brightness detection means, and the drive mode May be determined.

  In the above configuration, the backlight driving unit may divide the lighting period into a plurality of times when changing the driving frequency of the backlight, and provide a transition period in which the time between the lighting periods gradually changes to change the lighting period. Good.

  In the above configuration, the video determination unit may determine the drive mode based on an average luminance level (APL) value of the display video.

  In the above configuration, the video discriminating unit may determine the drive mode based on a motion blur amount of the display video.

  In the above configuration, the drive mode may include a normal drive mode that is completely synchronized with the operation of the liquid crystal panel, and a flicker prevention drive mode having a drive frequency higher than that of the normal drive mode.

  In the above configuration, the backlight is divided into a plurality of areas in the scanning direction of the liquid crystal panel, each area is lit independently, and the liquid crystal panel scans line-sequentially and writes an image. The backlight driving unit may drive the corresponding area to be driven in synchronization with the writing operation of the liquid crystal panel.

  In the above configuration, the backlight may be turned on simultaneously on the entire surface.

In the above configuration, the backlight may have a configuration in which a plurality of light sources are two-dimensionally arranged on a surface facing the liquid crystal panel.

  The said structure WHEREIN: The structure which has a light-guide plate may be sufficient as the said backlight.

  According to the present invention, it is possible to provide a liquid crystal display device that has a simple configuration and can suppress deterioration in the quality of a display image caused by moving image blur, flicker, etc. without changing the color tone of the image. .

It is a disassembled perspective view of the liquid crystal display device concerning this invention. It is a block diagram which shows the electrical connection of the liquid crystal display device concerning this invention. 6 is a timing chart showing backlight driving in a normal drive mode and a flicker prevention drive mode. It is a figure which shows the drive waveform of the backlight in normal drive mode and flicker prevention drive mode. It is a flowchart which shows switching of a drive mode. It is a block diagram which shows the electrical connection of the other example of the liquid crystal display device concerning this invention. It is a figure which shows the drive waveform of the backlight in the liquid crystal display device concerning this invention. It is a figure which shows the other example of the drive waveform of the backlight in the liquid crystal display device concerning this invention. It is a figure which shows the further another example of the drive waveform of the backlight in the liquid crystal display device concerning this invention. It is a disassembled perspective view of the further another example of the liquid crystal display device concerning this invention. It is a figure which shows the drive waveform of the liquid crystal panel and backlight of the liquid crystal display device shown in FIG. It is a block diagram which shows the electrical connection of the further another example of the liquid crystal display device concerning this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is an exploded perspective view of a liquid crystal display device according to the present invention. As shown in FIG. 1, the liquid crystal display device A includes a liquid crystal panel 1 and a backlight 2. In the following description, although it may be referred to as a vertical direction or a horizontal direction, or up and down or left and right, the direction in a state where an image displayed on the liquid crystal display device is viewed is shown.

  As shown in FIG. 1, the liquid crystal panel 1 is arranged with an array substrate 11 having pixel electrodes and TFTs (switching elements) (both not shown) arranged in an array on the surface, and facing the array substrate 11. The counter substrate 12 is provided with a common electrode and a color filter for coloring transmitted light (both not shown), and a liquid crystal layer 13 between the array substrate 11 and the counter substrate 12. The liquid crystal layer 13 is sealed with a sealing member so that liquid crystal having fluidity does not leak. A polarizing film (not shown) is attached to the light receiving surface side of the array substrate 11 and the light emitting surface side of the counter substrate 12. Details of the liquid crystal panel 1 will be described later.

  The backlight 2 is an illuminating device that is disposed on the back surface of the liquid crystal panel 1 that displays an image and includes a plurality of LEDs 21 that include white LEDs or RGB three-color LEDs as light sources. In the liquid crystal display device A, the backlight 2 is a direct type, and the LEDs 21 are two-dimensionally arranged on the surface facing the liquid crystal panel 1. The LED 21 arranged in the backlight 2 is controlled so as to be repeatedly turned on and off.

  Further, the backlight 2 includes an optical sheet 22. The optical sheet 22 has a configuration in which a plurality of optical sheet members are stacked. For example, in the optical sheet 22, as an optical sheet member, a diffusion sheet 221 that diffuses light emitted from the backlight 2, a brightness enhancement sheet (DBEF) 222 that improves luminance, and a direction of light emitted from the backlight 2 That is, a prism sheet 223 that changes the direction of light that has entered obliquely toward the liquid crystal panel 1. An optical sheet member having optical characteristics other than these may be used.

  Next, the electrical connection of the liquid crystal display device A will be described with reference to a new drawing. FIG. 2 is a block diagram showing electrical connection of the liquid crystal display device according to the present invention. As shown in FIG. 2, the liquid crystal display device A includes a liquid crystal panel 1, a backlight 2, a video signal processing circuit 3, a video discrimination circuit (video discrimination means) 4, a timing control circuit 5, and a backlight controller. (Backlight driving means) 6.

  On the array substrate 11 of the liquid crystal panel 1, a plurality of source lines 111 (also referred to as data lines) formed in the vertical direction as video signal lines and arranged in parallel in the horizontal direction, and a vertical extension as scanning signal lines in the horizontal direction. And a plurality of gate lines 112 formed in parallel to the direction. That is, the source line 111 and the gate line 112 are formed side by side in a lattice pattern, and a TFT is disposed at the intersection of the source line 111 and the gate line 112. The source line 111 is connected to the source of the TFT, and the gate line 112 is connected to the gate of the TFT. The drain of the TFT is connected to the pixel electrode. When a signal (voltage) is input to the gate of the TFT with a voltage applied to the source, a current flows between the source and the drain, and charge is accumulated (charged) in the pixel electrode.

  A plurality of source lines 111 are connected to the source driver 14, and a plurality of gate lines 112 are connected to the gate driver 15. The source driver 14 converts the liquid crystal drive signal Lcs received from the timing control circuit 5 into a voltage (referred to as a video voltage), and applies the video voltage to the source line 111 based on the source timing signal Sts received from the timing control circuit 5. Supply. Further, the gate driver 15 supplies pulse voltages (gate drive signals) for operating the TFTs to the plurality of gate lines 112 in order from the upper stage based on the gate timing signal Gts from the timing control circuit 5.

  In the liquid crystal panel 1, as described above, a pulse-like gate drive signal for driving is applied to the TFTs by the gate lines 112 extending in the horizontal direction, so that all the TFTs in the horizontal row are simultaneously turned on / off. In accordance with the on / off timing, a video voltage is applied from the source line 111, and a video is simultaneously written to all the pixels in a horizontal row. This operation is repeated a number of times corresponding to the number of pixels in the vertical direction to complete one frame of video. That is, the liquid crystal panel 1 is driven line-sequentially. Note that writing an image to a pixel means accumulating charge in the pixel electrode, and this charge is held until the next image is written. The liquid crystal display device A is a liquid crystal display device capable of full HD display, and the number of pixels in the vertical direction of the liquid crystal panel 1 is 1080. That is, the liquid crystal panel 1 has 1080 gate lines 112.

  In the liquid crystal panel 1, liquid crystal molecules are rotated by an electric field generated between the pixel electrode and the common electrode. The liquid crystal panel 1 displays an image using the change in transmittance caused by the inclination of the liquid crystal molecules. That is, the liquid crystal display device A performs video display based on the liquid crystal drive signal Lcs by modulating the light supplied from the backlight 2 with the liquid crystal corresponding to each pixel of the liquid crystal panel 1.

  The LED 21 provided in the backlight 2 is turned on when a pulse current is supplied. That is, the LED 21 is lit while the pulse current is supplied (in other words, while the high level pulse current is supplied). By supplying a pulse current from the backlight controller 6 to the LED 21, the lighting control of the backlight 2 is performed.

  As described above, the liquid crystal panel 1 is driven line-sequentially. Therefore, in the backlight 2, the LEDs 21 arranged in the horizontal direction are grouped into a plurality of groups in the vertical direction, and the LEDs 21 are synchronized with the writing of the portions corresponding to the respective stages of the liquid crystal panel 1. Lights up (scanning lighting method). By making the backlight 2 a scanning lighting system, it is possible to lengthen the lighting time of the LED 21. Note that the number of LEDs 21 is not large compared to the number of pixels of the liquid crystal panel 1. Therefore, in the scanning lighting of the backlight 2, the LED 21 corresponding to these stages is lit when the writing of a plurality of stages of the liquid crystal panel 1 is completed. Even with such a configuration, it is possible to lengthen the lighting period of the LED 21.

  In the backlight 2, the luminance is determined by the ratio of the lighting period. In the present embodiment, the backlight 2 is driven such that the ratio of the lighting period (hereinafter referred to as on-duty ratio: see FIG. 4 described later) to the driving cycle (the sum of the lighting period and the extinguishing period) is constant. Has been. Further, it is known that the chromaticity of the LED 21 changes when the current value of the supplied pulse current fluctuates. Therefore, in the liquid crystal display device A of the present invention, the current value of the pulse current supplied to the LED 21 is constant. Further, since the on-duty ratio of the backlight 2 is constant and the current value of the pulse current supplied to the LED 21 is constant, the backlight 2 irradiates the liquid crystal panel 1 with light with a small change in chromaticity and constant luminance. Yes.

  The video signal processing circuit 3 decodes a video signal Ims (for example, a transport stream) from an external device such as a tuner, BD, or DVD, generates video data Vid such as MPEG, and transmits the video data Vid to the timing control circuit 5. The video signal processing circuit 3 extracts content data Cid (content type, shooting conditions, frame rate, motion blur additional information, video APL value, etc.) included in the video data Vid and transmits the content data Cid to the video discrimination circuit 4. .

  The video discriminating circuit 4 determines whether to drive the backlight 2 in the normal drive mode or the flicker prevention drive mode (both will be described later) based on the content data Cid. Then, the video discriminating circuit 4 transmits drive information Did including drive mode information to the backlight controller 6.

  The timing control circuit 5 includes an arithmetic processing unit such as a CPU and a microcomputer. The timing control circuit 5 generates a liquid crystal drive signal Lcs including voltage information for driving the liquid crystal panel 1 based on the video data Vid and transmits the liquid crystal drive signal Lcs to the source driver 14. The source driver 14 converts the voltage applied to the liquid crystal in each pixel based on the liquid crystal drive signal Lcs. The timing control circuit 5 generates a source timing signal Sts indicating the driving timing of the source driver 14 and a gate timing signal Gts indicating the driving timing of the gate driver 15 from the video data Vid simultaneously with the liquid crystal driving signal Lcs. To the source driver 14 and the gate driver 15, respectively.

  The timing control circuit 5 may include a storage unit that stores the video data Vid sent from the video processing circuit 3 in time series. Then, the video data Vid is extracted from the storage unit in time series, converted into the liquid crystal drive signal Lcs in accordance with the video writing timing, sent to the source driver 14 together with the source timing signal Sts, and gate timing synchronized with the source timing signal Sts. The signal Gts may be sent to the gate driver 15.

  Further, the timing control circuit 5 generates a backlight timing signal Bts indicating the driving timing of the backlight 2 in synchronization with the source timing signal Sts and the gate timing signal Gts based on the video data Vid, and sends it to the backlight controller 6. .

  The backlight controller 6 drives the backlight 2 in accordance with the backlight timing signal Bts sent from the timing control circuit 5. The backlight timing signal Bts is provided with a timing signal for supplying a pulse current, and information on the driving frequency of the liquid crystal panel 1 is also described. The backlight controller 6 adjusts the on-duty ratio of the backlight 2 in one frame period based on the information about the driving frequency of the liquid crystal panel 1 of the backlight timing signal Bts.

  The backlight controller 6 can also drive the backlight 2 at a frequency higher than the driving frequency of the liquid crystal panel 1 based on the backlight timing signal Bts. The backlight controller 6 supplies a pulse current so that the on-duty ratio of the backlight 2 is constant even when the drive frequency of the backlight 2 is changed.

  Thereby, even when the drive frequency of the backlight 2 fluctuates, the on-duty ratio does not change, so the luminance of the backlight 2 does not change. Moreover, since the current value of the pulse current supplied to the LED 21 does not change, the chromaticity of the light emitted from the LED 21 does not change (is difficult to change).

  In general, when the light source is repeatedly turned on and off in a very short time (for example, 60 times or more per second: 60 Hz or more), it is difficult to recognize the switching between turning on and off (light source blinking). Yes, it is recognized as continuously lit. In the liquid crystal display device A, since the on-duty ratio of the backlight 2 and the current value of the pulse current supplied to the LED 21 are constant, flickering is prevented as the driving frequency of the backlight 2 increases.

  On the other hand, even if the driving frequency of the backlight 2 is the same, flicker may be easily recognized in a bright image. This is because there is a large difference between the brightness when the backlight 2 is turned on and the darkness when the backlight 2 is turned off (contrast is high), so that it may be recognized as turned on and turned off. In order to suppress such flickering due to video characteristics, the liquid crystal display device A according to the present invention includes a normal driving mode and a flicker prevention driving mode as driving modes of the backlight 2. The flicker prevention drive mode is set to have a higher frequency than the normal drive mode.

  Further, when a moving image is displayed on the liquid crystal display device A, moving image blur may occur. Next, moving image blur will be described. The liquid crystal display device A reproduces a moving image by displaying an image for each frame in time series. In such a moving picture, a motion blur that works to interpolate an intermediate time between frames may be added depending on the video.

  In the video with the motion blur added, the video representing the movement from the previous frame is added to the video of each frame. When displaying images of frames with motion blur added, if the percentage of time during which images are displayed in each frame (impulse rate) is large, the human eye clearly recognizes motion blur. , Video blur will be strong. For this reason, it is preferable that the impulse rate is small for an image with a large amount of motion blur.

  On the other hand, in the case of a video with no motion blur (small), if the impulse rate is reduced, the afterimage of the previous frame video is difficult to be recognized, and stroboscopic images in which the video appears to fly apart are likely to occur. Such stroboscopic is eliminated by increasing the impulse rate. In the liquid crystal display device A of the present invention, the on-duty ratio of the backlight 2 and the current value of the pulse current are constant, and it is difficult for the backlight 2 to change the actual impulse rate. Therefore, in the case of video with no motion blur (less), by increasing the drive frequency of the backlight 2, it can be recognized as if the lighting time of the backlight 2 has become longer, artificially increasing the impulse rate, Can be suppressed (flicker prevention mode).

  The normal drive mode and the flicker prevention drive mode will be described with reference to the drawings. FIG. 3 is a timing chart showing backlight driving in the normal driving mode and the flicker prevention driving mode, and FIG. 4 is a schematic diagram showing backlight driving waveforms in the normal driving mode and the flicker prevention driving mode. In FIG. 3, the vertical axis indicates the vertical position of the liquid crystal panel 1 and the backlight 2, and the horizontal axis indicates time, which is shaded to indicate the lighting of the backlight 2. Further, in the figure, oblique arrow lines described from the upper left to the lower right indicate switching of frame periods in each stage of the liquid crystal panel 1. For convenience, in FIGS. 3 and 4, the backlight 2 is turned on at the end of each frame.

  First, the normal drive mode will be described. In the liquid crystal display device A, the driving frequency of the liquid crystal panel 1 is often 60 Hz or more. In this case, flickering hardly occurs even when the backlight 2 is completely synchronized with the liquid crystal panel 1 except in the case of displaying a high-luminance video as described above (in normal video display). Therefore, as shown in FIG. 3, in the normal drive mode, the backlight 2 is driven in complete synchronization with the liquid crystal panel 1 (frame period). That is, since the liquid crystal panel 1 is written in a line-sequential manner from the upper stage, the backlight is also turned on sequentially from the upper group.

  In this normal drive mode, when an image with a large amount of motion blur is displayed, the on-duty ratio of the LED 21 and the current value of the pulse current are less likely to cause motion blur and the chromaticity of the displayed image does not decrease. (See FIG. 3). In the normal drive mode, the drive frequency of the backlight 2 is 60 Hz.

  In general, liquid crystal is an element that changes the degree of light transmission according to an applied electric field, and the response speed is not so high. For this reason, there are rising and falling portions where the degree of transmission changes at the beginning and end of the frame period. When the backlight 2 is turned on at this portion, an image different from the image that should originally be displayed is displayed. May be. Therefore, in practice, the backlight controller 6 is configured to light the backlight 2 (LED 21) so as not to overlap the falling portion in the latter half of the frame period of each stage.

  In addition, as shown in FIG. 3, when the image brightness is high and flicker occurs when displayed in the normal drive mode, or when strobes occur, the flicker prevention drive mode (with higher frequency than the normal drive mode ( Here, it is driven at 120 Hz). As shown in FIG. 3, in the flicker prevention driving mode, lighting is driven at a driving frequency of 120 Hz. In other words, the frame period of the liquid crystal panel 1 is divided into the first half and the second half, and the backlight 2 is once in the first half and the second half. It is the same as turning on once each.

  Here, the luminance and driving cycle of the backlight 2 will be described. As shown in FIG. 4, when the drive cycle of the backlight 2 in the normal drive mode is B1 and the lighting period is A1, the on-duty ratio Op1 of the backlight 2 in the normal drive mode is A1 / B1. Since the liquid crystal panel 1 and the backlight 2 are synchronized, the driving cycle B1 is the same length as one frame period. Further, as shown in FIG. 4, in the flicker prevention drive mode, the drive cycle is half that of the normal drive mode. When the drive cycle B2 in the flicker prevention drive mode and the lighting period are A2, the on-duty ratio Op2 in the flicker prevention drive mode is A2 / B2. Since the backlight controller 6 drives the backlight 2 so that the on-duty ratio is constant regardless of the driving frequency of the backlight 2, Op1 = Op2.

  As described above, since the current value of the pulse current sent to the LED 21 is constant in the backlight 2, the luminance is determined by the on-duty ratio. When the backlight controller 6 drives the backlight 2 in this way, the luminance of the backlight 2 does not change. In the flicker prevention mode, the backlight 2 is driven at a frequency higher than that in the normal drive mode. Therefore, even when the luminance of the image is high, it is difficult for human eyes to recognize whether the light is on or off, and flicker is suppressed. Furthermore, since the backlight 2 is driven in the flicker prevention drive mode, the lighting and extinguishing of the backlight 2 are not accurately recognized. Therefore, the human eye has the illusion that the backlight 2 is continuously lit. Is done. Therefore, it is possible to suppress the occurrence of stroboscopic copying even in an image having a pseudo-high impulse rate and no or little motion blur.

  Here, as an example of the flicker prevention driving mode, the backlight 2 is driven at a frequency twice the driving frequency of the liquid crystal panel 1, but the present invention is not limited to this and is not limited to this. A frequency that can reliably suppress flickering at a higher frequency than the mode can be widely adopted. Further, such a frequency can be arbitrarily set. However, if it is an integral multiple of the driving frequency of the liquid crystal panel 1, synchronization with the liquid crystal panel 1 is easy and preferable.

  A procedure for switching between the normal drive mode and the flicker prevention mode in the liquid crystal display device A according to the present invention will be described with reference to the drawings. FIG. 5 is a flowchart showing switching of drive modes. In the liquid crystal display device A, the average luminance value (APL value) is used to determine whether the image is likely to flicker.

  First, when the video signal Ims is sent to the video signal processing circuit 3, when the video signal processing circuit 3 generates the video data Vid from the video signal Ims, the APL value and the motion blur amount are detected, and the content data Cid is detected. Stored and transmitted to the video discriminating circuit 4 (step S11).

  Note that the motion blur amount may or may not be included in the video signal Ims. The amount of motion blur is determined to some extent by the type and content of the content and the shooting state.

  For example, in the case of CG (computer graphics), animation, game images, etc., only a discrete image (that is, a certain moment in each frame) is drawn in the continuous continuous time. In many cases, motion blur is not added.

  In addition, since an image captured by a storage type camera normally used as a television camera is an integral of continuous time when the shutter is open, the amount of motion blur varies depending on the shutter speed. For example, images shot indoors with strong lighting, such as movies and studios (for example, in the case of relay of indoor sports such as news programs and swimming) have a high shutter speed (shutter opening time is short). There is little motion blur added to moving images.

  Furthermore, in a dark outdoor shot such as a baseball game or a soccer night game, the shutter speed is often low (the shutter opening time is long), and a lot of motion blur is added to the moving image during shooting. In addition to these, a method that can accurately detect the amount of motion blur may be used.

  From the above contents, the video signal processing unit 3 can detect the amount of motion blur based on the type of content included in the video signal, shooting conditions (shooting time, shutter speed), and the like. The detection of the motion blur amount is not limited to this, and a method that can accurately detect the motion blur amount added to the video can be widely used.

  The video discriminating circuit 4 reads the data of the APL value of the video from the transmitted content data Cid, and determines whether or not it is larger than a predetermined specified value (step S12). This specified value is the lower limit value of the APL value at which flickering is likely to occur when the backlight 2 is driven with the determined on-duty ratio and the current value of the pulse current. If the APL value of the video is equal to or greater than the specified value (YES in step S12), the video discriminating circuit 4 determines that the video is likely to flicker and flickers as drive data Did to the backlight controller 6. Information indicating that the driving is performed in the prevention driving mode is transmitted (step S13).

  When the backlight controller 6 receives the drive data Did, it drives the backlight 2 in the flicker prevention drive mode (drive frequency 120 Hz) (step S14). If the APL value is smaller than the specified value (No in step S12), the video determination circuit 4 determines that the video is not likely to flicker, and determines whether the motion blur amount is larger than the specified value. (Step S15). When the amount of motion blur is less than the specified value (No in step S15), the video discriminating circuit 4 determines that the video is likely to generate strobes, and the backlight controller 6 uses the flicker prevention driving mode as the driving data Did. The information to drive is transmitted (step S13).

  If the amount of motion blur is greater than the specified value (Yes in step S15), the video discriminating circuit 4 determines that the video is less likely to cause stroboscopic copying, and the backlight controller 6 performs normal driving as drive data Did. Information to drive in the mode is transmitted (step S16). When receiving the drive data Did, the backlight controller 6 drives the backlight 2 in the normal drive mode (drive frequency 60 Hz) (step S17).

  As described above, in the liquid crystal display device A according to the present invention, occurrence of flickering and moving image blur is suppressed. Moreover, since the on-duty ratio of the backlight 2 and the current value of the pulse current supplied to the LED 21 are constant, the luminance of the backlight 2 is constant and the chromaticity does not change. For this reason, in the liquid crystal display device A according to the present invention, the display quality hardly changes even in a display with reduced moving image blur or a display with reduced flicker. Furthermore, since correction for suppressing the change in chromaticity is unnecessary, the configuration can be simplified and the control in the liquid crystal display device A is simplified.

  In the above-described embodiment, the mode switching of the backlight 2 is performed based on the APL value and the motion blur amount. However, the present invention is not limited to this. May be detected, and mode switching may be performed based on the numerical value. In the present embodiment, the determination based on the APL value is performed first (priority), but the determination based on the motion blur amount may be performed first. However, when the flicker is intense, there are observers who feel bad, so the discrimination based on the APL value is preferable.

  Furthermore, in the above-described embodiment, the on-duty ratio of the backlight 2 and the current value of the pulse current supplied to the LED 21 in the normal drive mode can suppress the occurrence of motion blur and stroboscopic copy regardless of the amount of motion blur. In the case of a small value, the determination based on the motion blur amount may be omitted.

  As described above, the characteristics (luminance, amount of motion blur, etc.) of moving images differ depending on the contents, shooting conditions, and the like. The liquid crystal display device A according to the present invention appropriately adjusts the lighting timing and supply current value of the LED 21 (the brightness of the LED at the time of lighting) according to the characteristics when displaying such a moving image. By doing so, the occurrence of flicker and video blur is suppressed.

(Second Embodiment)
Another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. FIG. 6 is a block diagram showing electrical connection of another example of the liquid crystal display device according to the present invention. The liquid crystal display device B shown in FIG. 6 further includes an illuminance sensor 7 compared to the liquid crystal display device A shown in FIG. Other portions have the same configuration as the liquid crystal display device A, and substantially the same portions are denoted by the same reference numerals and detailed description of the same portions is omitted.

  As described above, the flicker felt in the image displayed on the liquid crystal display device B is related to the luminance of the displayed video. However, even when an image with the same luminance is displayed on the liquid crystal display device B, the luminance may be felt high or low depending on the illuminance of the environment. Therefore, the liquid crystal display device B includes an illuminance sensor 7 that detects the brightness of the surroundings where the liquid crystal display device B is disposed.

  In the liquid crystal display device B, the illuminance information Lmd from the illuminance sensor 7 is input to the video discrimination circuit 4. When the video discriminating circuit 4 compares the APL value and discriminates the drive mode (for example, step S12 in FIG. 5), the video discriminating circuit 4 refers to the illuminance information Lmd from the illuminance sensor 7 and compares the specified value to be compared with the APL value of the video. Correction is performed based on the illuminance information Lmd from the luminance sensor 7.

  For example, when the surrounding environment is bright, even if an image with a high APL value is displayed, flicker is difficult to recognize. Therefore, the video discrimination circuit 4 adopts a higher value as the specified value. On the other hand, when the surrounding environment is dark, flicker is likely to be recognized even for an image with a low APL value. Therefore, the video discriminating circuit 4 adopts a lower value as the specified value.

  The adjustment of the specified value by the video discriminating circuit 4 may be calculated based on the illuminance information Lmd using a pre-given arithmetic expression, or by referring to a table or database provided in advance. Further, it may be finely set for each illuminance information Lmd. As described above, the image determination circuit 4 can further increase the flicker suppression effect by changing the specified value according to the ambient brightness.

  Note that the stroboscopic is also easy to recognize or difficult to recognize depending on the brightness of the surroundings. Therefore, the video discriminating circuit 4 may correct the prescribed value when comparing the motion blur amount (step S15 in FIG. 5) based on the illuminance information Lmd when determining the drive mode. The correction of the prescribed value of the motion blur amount may be calculated using a predetermined arithmetic expression, or may be determined using a database or a table.

(Third embodiment)
Another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. FIG. 7 is a diagram showing a driving waveform of the backlight in the liquid crystal display device according to the present invention. In the present embodiment, the backlight is driven in the same liquid crystal display device A as in the first embodiment, but the same operation is possible in the liquid crystal display device B in the second embodiment. The same applies to all the following embodiments.

  In the liquid crystal display device A, the backlight 2 is driven in two drive modes, a normal drive mode and a flicker prevention drive mode. As shown in FIG. 7, in the normal drive mode, the backlight 2 is driven at 60 Hz, the drive cycle is B1, and the lighting period of the backlight 2 is A1. In the flicker prevention driving mode, the backlight 2 is driven at 120 Hz, the driving cycle is B2, and the lighting period is A2. The driving period B2 is half of the driving period B, and the lighting period A2 is half of the lighting period A. When the backlight 2 is driven in these drive modes, the atmosphere of the displayed video is greatly different. When the driving mode of the backlight 2 is switched instantaneously, the video often feels uncomfortable.

  Therefore, the liquid crystal display device according to the present embodiment has a configuration in which the mode switching between the normal drive mode and the flicker prevention drive mode is gradually performed (a transition period is provided). A case where the backlight controller 6 switches the backlight 2 from the normal drive mode to the flicker prevention drive mode will be described.

  When the backlight 2 is driven in the normal driving mode, the lighting period is A1, and the driving frequency in the flicker prevention driving mode is twice that in the normal driving mode. Therefore, the lighting period A2 in the flicker prevention driving mode is the lighting period. Half of A1. That is, in the flicker prevention drive mode, the configuration is the same as the configuration in which the backlight 2 is lit twice in the lighting period A1.

  When the backlight controller 6 receives an instruction to switch from the normal drive mode to the flicker-preventing drive mode based on the drive information Did, the backlight controller 6 illuminates the backlight 2 in two steps. First, in the first frame period t1 after switching, the first lighting is started at the same timing as the lighting in the normal drive mode. Since the lighting period A2 after switching is half of the lighting period A1, it is extinguished in half the period. In the second frame period t1, the second lighting is performed after a time Bt1 shorter than the driving period B2. At this time, since the interval between the first lighting and the second lighting is short, it is recognized that the human eye keeps lighting during the first lighting and the second lighting.

  Then, in the second frame period t2 after switching, the first backlight 2 is turned on at the same timing as in the normal drive mode, and the second backlight is turned on with a time Bt2 longer than bt1. Similarly, the time Btm for the first lighting and the second lighting is gradually extended. Finally, the drive cycle B2 in the flicker prevention drive mode is set to be the same. Thus, by gradually increasing the interval until lighting, it is recognized by the human eye that the lighting period is gradually longer.

  In the liquid crystal display device A according to the present invention, the backlight controller 6 controls the backlight 2 so that the on-duty ratio is the same. Therefore, since the sum of the two lighting periods is the same as the lighting period in the normal prevention mode, and when driven in the flicker prevention driving mode, the on-duty ratio is the same as that in the normal driving mode, 2 The lighting period is the same.

  In this way, by gradually shifting the lighting of the second backlight, it is possible to suppress a sense of discomfort when shifting from the normal drive mode to the flicker prevention drive mode. Note that the reverse procedure can be used to switch from the flicker prevention drive mode to the normal drive mode while suppressing a sense of discomfort.

  Another example of switching the drive mode of the backlight 2 of the liquid crystal display device A according to the present invention will be described with reference to the drawings. FIG. 8 is a diagram showing another example of the driving waveform of the backlight in the liquid crystal display device according to the present invention, and FIG. 9 is a diagram showing still another example of the driving waveform of the backlight in the liquid crystal display device according to the present invention. It is.

  As shown in FIG. 8, the lighting end timing of the second backlight 2 is matched with the lighting end timing of the backlight 2 in the normal drive mode, and there is no sense of incompatibility even if the first lighting timing is shifted forward. The drive mode can be switched.

  In addition, as shown in FIG. 9, the second lighting 2 is turned on before the first lighting timing with the center of the lighting period of the backlight 2 in the normal driving mode. Even if it is shifted later, the drive mode can be switched without a sense of incongruity.

(Fourth embodiment)
Still another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. 10 is an exploded perspective view of still another example of the liquid crystal display device according to the present invention, and FIG. 11 is a diagram showing drive waveforms of the liquid crystal panel and the backlight of the liquid crystal display device shown in FIG. A liquid crystal display device C shown in FIG. 10 includes an edge light type backlight 8 instead of the backlight 2. Other parts are the same as those of the liquid crystal display device A, and substantially the same parts are denoted by the same reference numerals and detailed description of the same parts is omitted.

  As shown in FIG. 10, the backlight 8 includes a light guide plate 81 and LEDs 82 arranged to face the side surfaces of the light guide plate 81. The light guide plate 81 is a transparent plate-like member, and one main surface is formed on the light output surface 811 and the side surface is formed on the light receiving surface 812, and light from the LED 82 enters from the light receiving surface 812. Note that the edge-light type backlight has a well-known configuration, and details thereof are omitted. Further, in the edge light type backlight 8, since a part of the light guide plate 81 has the same effect as the optical sheet 22, the optical sheet 22 can be omitted.

  In the backlight 8 employing such a light guide plate 81, the entire surface is generally turned on simultaneously. For this reason, the backlight 8 is turned on entirely before the rewriting of the entire surface of the liquid crystal panel 1 is completed and writing of the next video is started (see FIG. 11).

  In the case of the liquid crystal display device C having such a configuration, the time during which the same frame image is written on the entire liquid crystal panel 1 is shortened. Therefore, the lighting period of the backlight is shortened. Lights when the same frame image is written in all stages of the liquid crystal panel 1 in the normal drive mode, so that the drive frequency is doubled and the flicker prevention drive mode is performed regardless of the image writing state. The backlight 8 is lit, and the backlight 8 is always lit in a pseudo manner.

  Even with such a configuration, it is possible to suppress blurring and flickering of video displayed on the liquid crystal display device C by appropriately driving the backlight 8. The switching between the normal drive mode and the flicker prevention drive mode may be instantaneously switched, or may be gradually changed as shown in the third embodiment.

  In the present embodiment, as an example of a backlight that is turned on simultaneously on the entire surface, an edge light type backlight including a light guide plate is shown. However, the present invention is not limited to this, and the direct type shown in FIG. The backlight may be used. Further, in the edge light type backlight, the LEDs 82 facing the light receiving surface 812 are sequentially turned on so that the scanning lighting can be performed in accordance with the writing of the liquid crystal panel 1.

(Fifth embodiment)
Still another example of the liquid crystal display device according to the present invention will be described with reference to the drawings. FIG. 12 is a block diagram showing electrical connection of still another example of the liquid crystal display device according to the present invention. As shown in FIG. 12, the liquid crystal display device D has the same configuration as the liquid crystal display device A shown in the first embodiment, except that the video discriminating circuit 4 includes a receiving unit 41. The same reference numerals are given to the same parts, and detailed description of the same parts is omitted.

  As described above, the flickering of the image is easy to feel or difficult to feel by the observer. Moreover, even if it is the same observer, it may change with the physical condition at the time of observation. Therefore, the liquid crystal display device D includes a receiving unit 41, and the receiving unit 41 receives an instruction from the user from the outside.

  When there is no special instruction from the user, the video discriminating circuit 4 transmits drive information Did to the backlight controller 6 so as to suppress flickering of the video to be displayed in the same procedure as the liquid crystal display device A (see FIG. 5). ).

  When the receiving unit 41 receives an instruction to weaken the flicker prevention function from the user, the specified value of the APL value is increased in step S12 of FIG. 5 to make it difficult to drive in the flicker prevention drive mode. On the contrary, when the user gives an instruction to strengthen the flicker prevention function, the specified value of the APL value in step S12 in FIG. 5 is decreased to facilitate driving in the flicker prevention drive mode.

  In this way, since the drive mode can be switched according to the user's preference, the display quality of the video can be improved.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this content. The embodiments of the present invention can be variously modified without departing from the spirit of the invention.

  The liquid crystal display device of the present invention can be used as a display device for devices that display three-dimensional images, such as thin television devices, thin display devices, and mobile phones.

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 11 Array substrate 111 Source electrode 112 Gate electrode 12 Opposite substrate 13 Liquid crystal layer 14 Source driver 15 Gate driver 2 Backlight 21 LED
3 Video signal processing circuit 4 Video discrimination circuit 5 Timing control circuit 6 Backlight controller 7 Illuminance sensor 8 Backlight 81 Light guide plate 82 LED

Claims (10)

LCD panel,
A backlight for supplying light to the liquid crystal panel in synchronization with the operation of the liquid crystal panel;
Video discriminating means for determining the drive mode of the backlight based on the information of the display video;
Backlight drive means for changing the drive frequency of the backlight based on the drive mode,
The liquid crystal display device, wherein the backlight driving unit changes a driving frequency of the backlight so that a ratio of a lighting period to a driving period of the backlight does not change. A brightness detecting means for detecting the brightness around the liquid crystal display device;
The liquid crystal display device according to claim 1, wherein the video determination unit determines the driving mode in consideration of brightness information from the brightness detection unit.   3. The liquid crystal display device according to claim 1, wherein the backlight driving unit is provided with a transition period in which the frequency gradually changes when the driving frequency of the backlight is changed.   4. The video display device according to claim 1, wherein the video discriminating unit determines the drive mode based on an average luminance level (APL) value of the display video. 5.   The video display device according to claim 1, wherein the video discriminating unit determines the drive mode based on a motion blur amount of the display video. The drive mode includes a normal drive mode that is completely synchronized with the operation of the liquid crystal panel, and
The video display device according to claim 1, further comprising a flicker prevention drive mode having a drive frequency higher than that of the normal drive mode. The backlight is divided into a plurality of areas in the scanning direction of the liquid crystal panel, and each area is lit independently.
The liquid crystal panel scans line-sequentially and writes an image,
The liquid crystal display device according to any one of claims 1 to 6, wherein the backlight driving unit drives and drives a corresponding region in synchronization with a writing operation of the liquid crystal panel. The liquid crystal display device according to claim 1, wherein the backlight is turned on simultaneously on the entire surface. The liquid crystal display device according to claim 7, wherein the backlight has a configuration in which a plurality of light sources are two-dimensionally arranged on a surface facing the liquid crystal panel.   The liquid crystal display device according to claim 7, wherein the backlight has a light guide plate.

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