JP5888930B2 - Image display apparatus and control method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display device and a control method thereof.

A liquid crystal display device is a display device that utilizes the light transmittance of a liquid crystal panel. In a liquid crystal display device, the display is controlled by the light emitted from the backlight installed on the back of the liquid crystal panel being transmitted through the liquid crystal panel and the light emitted from the backlight being blocked by the liquid crystal panel. Is done.
As the light source of the backlight, a plurality of light emitting diodes (hereinafter referred to as LEDs) are used. Examples of LEDs used for the light source include R (red), G (green), and B (blue) color LEDs.
There is PWM control as a method for adjusting the brightness and color of LEDs. In PWM control, desired brightness and white balance can be obtained by adjusting the length of the light emission period of each LED. However, in PWM control, since the length of the light emission period of each LED is different, the backlight instantaneously emits light in R, G, B, or a mixed color of two of them, so-called color breakage state Will occur.

FIG. 8 is a timing chart showing the operation of the backlight using color LEDs.
FIG. 8A shows a vertical synchronization signal, which is a signal that becomes L level for a predetermined time every frame period. For example, when the frequency of the vertical synchronization signal is 60 Hz, one frame period is about 16.7 msec. In one frame period, the vertical synchronization signal becomes H level in a period other than the predetermined time period.
FIGS. 8B to 8D show the light emission states of RLED (color LED that emits red light), GLED (color LED that emits green light), and BLED (color LED that emits blue light), respectively. ing. In the figure, the ON period indicates the LED light emission period, and the OFF period indicates the LED extinguishing period.
At this time, in the period when only RLED is lit (period from time t1 to t2), or during the period when RLED and GLED are lit and BLED is not lit (period from time t2 to t3), the observer (user) Color breakup may be perceived.

Conventional techniques for solving the above problems are disclosed in, for example, Patent Documents 1 to 3.
Specifically, Patent Document 1 discloses that each LED is blinked to shorten a period during which another LED is turned off while another LED is turned on.
Patent Document 2 discloses that white light is always synthesized by shifting phases between light source units (light source units including RLED, GLED, and BLED) that are periodically driven.
Patent Document 3 discloses that the deviation of the light emission period is shortened by aligning the central times of the light emission periods of RLED, GLED, and BLED.

JP 2008-191248 A JP 2006-164631 A JP-A-2005-208425

It has been found that the above-described color breakup is more easily perceived by the user as the luminance is higher. In the liquid crystal display device, the luminance visually recognized by the user varies depending on the transmittance of the liquid crystal panel.
However, in the techniques described in Patent Documents 1 to 3, since the transmittance of the liquid crystal panel is not taken into consideration at all, there is a possibility that color breakup may be perceived by the user.

  Therefore, the present invention controls the backlight in consideration of the transmittance of the liquid crystal panel, and thereby can more effectively suppress the perception of color breakage by the user than in the past. And it aims at providing the control method.

The image display device of the present invention is
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
The control means includes
When the determination means determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors are used. out so that only a portion of the light source is earlier than the period of time for emitting all of the light sources emits light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors from each other The light emission period of each light source within the period of the next frame to be displayed is set such that only a part of the light sources emits light after the period of light emission of all the light sources.
Moreover, the image display device of the present invention includes:
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
The control means includes
When the determination means determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors are used. The light emission period of each light source within the period of the next frame to be displayed is set so that a period during which only some of the light sources emit light precedes a period during which all the light sources emit light. .
Moreover, the image display device of the present invention includes:
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
The control means includes
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors from each other The light emission period of each light source within the period of the next frame to be displayed is set such that only a part of the light sources emits light after the period of light emission of all the light sources.

The control method of the image display device of the present invention includes:
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame , out so that only a portion of the light source is earlier than the period of time for emitting all of the light sources emits light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame , The light emission period of each light source within the period of the next frame to be displayed is set such that only a part of the light sources emits light after the period of light emission of all the light sources.
In addition, the control method of the image display device of the present invention includes:
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, The light emission period of each light source within the period of the next frame to be displayed is set so that the period during which only some of the light sources emit light precedes the period during which all light sources emit light.
It is characterized by that.
In addition, the control method of the image display device of the present invention includes:
A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, The light emission period of each light source within the period of the next frame to be displayed is set so that the period during which only some of the light sources emit light is after the period during which all the light sources emit light.
It is characterized by that.

  According to the present invention, by controlling the backlight in consideration of the transmittance of the liquid crystal panel, it is possible to more effectively prevent the user from perceiving color breakup than in the past.

1 is a block diagram showing an example of a functional configuration of a liquid crystal display device according to Embodiment 1. FIG. The figure which shows an example of a structure of the backlight which concerns on Example 1. FIG. 7 is a flowchart illustrating an example of the operation of the liquid crystal display device according to the first embodiment. FIG. 3 is a timing chart illustrating an example of the operation of the backlight according to the first embodiment. Timing chart showing an example of the operation of a conventional backlight 7 is a flowchart illustrating an example of the operation of the liquid crystal display device according to the second embodiment. Timing chart showing an example of operation of the backlight according to the second embodiment Timing chart showing an example of the operation of a conventional backlight

<Example 1>
Hereinafter, a liquid crystal display device and a control method thereof according to Embodiment 1 of the present invention will be described in detail with reference to the drawings. However, the functions, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified. The functions and shapes of the components and components once described in the following description are the same as those in the first description unless otherwise described.

FIG. 1 is a block diagram illustrating an example of a functional configuration of a liquid crystal display device according to Embodiment 1 of the present invention.
The CPU 101 is connected to a ROM and a RAM (not shown). The CPU 101 controls the overall operation of the display device 100 using the RAM as a work memory according to a program stored in the ROM.
The input unit 102 decodes image data input from an image output device (not shown) and outputs the decoded image data to the image processing unit 103.
The image processing unit 103 includes a gradation displacement analysis unit 104. The gradation displacement analysis unit 104 determines whether the gradation value of the image data of the next frame to be displayed (next frame) is higher than the gradation value of the image data of the currently displayed frame (current frame). To do. Specifically, the gradation displacement analysis unit 104 determines the displacement direction (gradation displacement direction) of the gradation value of the image data from the current frame to the next frame from the image data of the current frame and the image data of the next frame. To analyze. The analysis of the gradation displacement direction will be described later. The image processing unit 103 outputs the determination result (gradation displacement direction) of the gradation displacement analysis unit 104 to the backlight control unit 108.
In addition, the image processing unit 103 outputs the input image data to the liquid crystal panel 105 after applying desired signal processing such as high image quality processing.

The transmittance of the liquid crystal panel 105 is controlled according to the gradation value of the input image data so that the transmittance of light from the backlight 111 increases as the gradation value of the input image data increases. A plurality of liquid crystal elements. The liquid crystal panel 105 is, for example, an active matrix liquid crystal panel.
The backlight 111 has a plurality of light sources having different emission colors.
When the light from the backlight 111 passes through the liquid crystal panel 105, an image based on the image data is displayed on the screen.

The sensor 106 includes a color sensor and a temperature sensor. For example, the color sensor has a structure in which an optical filter of each color is combined with a photodiode.
The sensor control unit 107 can obtain the luminance and chromaticity of the backlight from the detection value acquired from the sensor 106. In addition, the sensor control unit 107 has a function of compensating temperature characteristics of other sensors and the light source of the backlight using the detection value of the temperature sensor.

The backlight control unit 108 and the light emission timing setting unit 110 control the light emission periods of a plurality of light sources (LEDs) included in the backlight based on the determination result of the gradation displacement analysis unit 104.
Specifically, the backlight control unit 108 sets each LED so that the detection value (backlight luminance and chromaticity) of the sensor 106 becomes the target value (target luminance and target chromaticity) stored in the memory 109. The length of the light emission period (PWM value) is calculated. Then, each LED is driven according to the PWM value and a setting result of a light emission timing setting unit 110 described later.
Further, the backlight control unit 108 calculates the difference between the target value and the detection value of the sensor 106, and feedback-controls the PWM value so that the detection value of the sensor 106 becomes the target value.
The light emission timing setting unit 110 sets the light emission period (specifically, the light emission start timing) of each LED based on the gradation displacement direction input from the image processing unit 103. The setting of the light emission start timing will be described later.

Note that the display device 100 includes at least one image quality mode, and has a configuration in which target luminance and target chromaticity are preset according to the image quality mode.
The backlight control unit 108 receives a vertical synchronization signal output when image data is output from the image processing unit 103 to the liquid crystal panel 105, and the PWM value is updated according to the vertical synchronization signal. That is, each LED is PWM controlled for each frame so that the luminance and chromaticity of the backlight coincide with the target values.

FIG. 2 is a diagram illustrating an example of the configuration of the backlight.
The backlight 111 includes a plurality of LED groups 201 arranged in a matrix. The LED group 201 has a plurality of LEDs (color LEDs of RLED 202, GLED 203, and BLED 204 in this embodiment). The RLED 202 is an LED that emits red light, the GLED 203 is green, and the BLED 204 is blue. Further, the RLED 202, the GLED 203, and the BLED 204 can be individually controlled by the backlight control unit 108.
In this embodiment, in order to obtain light of a desired color (for example, white), the lengths of the light emission periods of a plurality of light sources (RLED202, GLED203, BLED204) within one frame period are set to different lengths. Shall be.

Here, among a plurality of light sources (a plurality of light sources having different emission colors) included in the backlight, a color break may be perceived by the user during a period when only some of the light sources emit light. In the example of FIG. 2, a color break may be perceived by the user in a period in which only the RLED 202, the GLED 203, the BLED 204, or only two of them emit light. Specifically, human eyes are likely to perceive color breakup when the luminance is high. Therefore, if a period in which only one of the RLED 202, GLED 203, or BLED 204 emits light or a period in which only two of the three LEDs emit light is assigned to a period in which the luminance on the screen is high, the color breaks to the user. It becomes easy to perceive.
Therefore, in this embodiment, the period in which only some of the light sources (LEDs) emit light is assigned (set) to a period in which the transmittance of the liquid crystal panel is low, that is, a period in which the luminance on the screen is low. Makes it difficult to perceive.

The processing of the liquid crystal display device according to the first embodiment will be described with reference to the flowchart of FIG. 3 and the timing chart of FIG.
FIG. 3 is a flowchart illustrating an example of operations of the backlight control unit 108 and the light emission timing setting unit 110. The process of this flowchart is started in response to the input of the vertical synchronization signal.
First, the backlight control unit 108 calculates the length of the light emission period of each LED in the next frame from the target value (or the detection value acquired from the sensor control unit 107 and the target value acquired from the memory 109) (step S1). S301).
Next, the light emission timing setting unit 110 confirms the gradation displacement direction (the determination result of the gradation displacement analysis unit 104) input from the image processing unit 103 (step S302).
If the gradation displacement direction is a higher (plus) direction (the gradation value of the image data of the next frame is higher than the gradation value of the image data of the current frame) (step S303: Yes), the processing is performed. Is advanced to step S304. When the gradation displacement direction is a decreasing (minus) direction (the gradation value of the image data of the next frame is lower than the gradation value of the image data of the current frame) (step S303: No), the process is step. The process proceeds to S305.

Here, a method of determining the gradation displacement direction by the gradation displacement analysis unit 104 will be described.
For each pixel, the gradation displacement analysis unit 104 calculates gradation displacement from the difference between the gradation value of the current frame and the gradation value of the next frame (the value obtained by subtracting the gradation value of the current frame from the gradation value of the next frame). Calculate the direction. Specifically, the RGB value of each pixel is converted into a luminance value Y (grayscale gradation value), and the difference is calculated.
Then, the gradation displacement analysis unit 104 determines that the gradation value of the image data of the next frame is an image of the current frame when the number of pixels whose gradation displacement direction is positive is greater than the number of pixels whose gradation displacement direction is negative. It is determined that it is higher than the gradation value of the data.

For example, the gradation displacement direction VG of image data can be calculated using the following equation. In the following equation, Pij (t) is the gradation value of the pixel A (the horizontal position is i and the vertical position is j) in the current frame (tth frame). Pij (t + 1) is the gradation value of the pixel A of the next frame (t + 1th frame). Gij is a value obtained by subtracting the gradation value of the pixel A of the current frame from the gradation value of the pixel A of the next frame. VGij is the gradation displacement direction of the pixel A. As shown in the following equation, when the gradation value of the pixel A of the next frame is higher than the gradation value of the pixel A of the current frame (when the gradation displacement direction of the pixel A is a positive direction), The adjustment displacement direction VGij is set to +1. When the gradation value of the pixel A of the next frame is lower than the gradation value of the pixel A of the current frame (when the gradation displacement direction of the pixel A is a negative direction), the gradation displacement direction VGij is −1. Is done.
Then, the total sum of the gradation displacement directions VGij for each pixel is output as a determination result (gradation displacement direction VG). Specifically, when the sum of the gradation displacement directions VGij for each pixel is a positive value, it is determined that the gradation displacement direction of the image data is the plus direction, and the determination result (gradation displacement direction VG) is obtained. The sum is output. Further, when the total sum of the gradation displacement directions VGij for each pixel is a negative value, it is determined that the gradation displacement direction of the image data is a negative direction, and the sum is obtained as a determination result (gradation displacement direction VG). Is output.
In step S303, the light emission timing setting unit 110 determines that the gradation displacement direction is a positive direction if VG is a positive value, and determines that the gradation displacement direction is a negative direction if VG is a negative value. .

Gij = Pij (t + 1) −Pij (t)
If Gij> 0,
VGij = (+ 1)
If Gij (t) ≦ 0,
VGij = (-1)
VG = ΣVGij

The determination method is not limited to this. For example, as a determination result, not the sum but the sign of the sum may be output. Further, the gradation displacement analysis unit 104 determines that the gradation value of the image data of the next frame is the gradation value of the image data of the current frame when the total sum of the displacement amount of the gradation value of each pixel (Gij (t)) is positive. You may determine with it being higher than a gradation value.

In step S304, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the period during which only some LEDs emit light precedes the period during which all LEDs emit light. To do.
In step S305, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the period in which only some LEDs emit light is after the period in which all LEDs emit light. .
After step S304 or step S305, the backlight control unit 108 drives each LED so that it emits light for the time calculated in step S301 from the set light emission start timing in the period of the next frame (step S301). S306).
That is, in this embodiment, when the gradation value of the image data of the next frame is higher than the gradation value of the image data of the current frame, the period during which only some light sources emit light is longer than the period during which all light sources emit light. As before, the light emission period of each light source within the period of the next frame is set. Further, when the gradation value of the image data of the next frame is lower than the gradation value of the image data of the current frame, the period in which only some light sources emit light is after the period in which all light sources emit light. The light emission period of each light source within the period of the next frame is set.

4A to 4E are timing charts showing an example of a change in gradation (transmittance) of the liquid crystal panel according to this embodiment and a light emission period of each LED.
FIG. 4A shows a response waveform of the liquid crystal panel (liquid crystal response waveform; change in transmittance of the liquid crystal panel). FIG. 4B shows a vertical synchronization signal. 4C to 4E show the light emission states of RLED, GLED, and BLED, respectively.
4A to 4E, for the sake of simplicity, the display image is changed from a full screen black image (hereinafter, all black) to a full screen white image (hereinafter, all white) at time t0 at time t3. In the above example, the display image is switched from all white to all black. For example, all black is an image based on image data having a minimum gradation value of each pixel. For example, all white is an image based on image data having the maximum gradation value of each pixel.

  When the gradation value of the image data of the next frame is different from the gradation value of the image data of the current frame, the transmittance of the liquid crystal panel (liquid crystal element) is transmitted according to the gradation value of the next frame during the next frame period. Gradually change towards rate. Specifically, as shown in FIG. 4A, when the display image changes from all black to all white at time t0 (the tone value of the image data of the next frame is greater than the tone value of the image data of the current frame). If it is high), the transmittance increases slowly. Further, when the display image changes from all white to all black at time t3 (when the gradation value of the image data of the next frame is lower than the gradation value of the image data of the current frame), the transmittance gradually decreases. For example, in the IPS mode liquid crystal panel, when the temperature of the liquid crystal panel is 30 ° C., the time from the start of rise (time t1) to the end of rise (t2) is about 16 msec, and the time from the start of fall to the end of fall is also The same level.

When the display image is switched from all black to all white at time t0, the image processing unit 103 (gradation displacement analysis unit 104) determines that the gradation displacement direction of the image data is the plus direction. Therefore, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the period in which only some LEDs emit light is before the period in which all LEDs emit light. In this embodiment, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the end time of the light emission period of each LED becomes the same time. Specifically, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the end time of the light emission period of each LED matches the end time of the period of the next frame. Thereby, it is possible to set the light emission start timing of each LED within the period of the next frame so that the period in which only some LEDs emit light is before the period in which all LEDs emit light with simple control. it can.

  When the display image is switched from all white to all black at time t3, the image processing unit 103 (gradation displacement analysis unit 104) determines that the gradation displacement direction of the image data is the minus direction. Therefore, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the period during which only some LEDs emit light is later than the period during which all LEDs emit light. In this embodiment, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the start time of the light emission period of each LED becomes the same time. Specifically, the light emission timing setting unit 110 sets the light emission start timing of each LED within the period of the next frame so that the start time of the light emission period of each LED matches the start time of the period of the next frame. Thereby, with simple control, the light emission start timing of each LED within the period of the next frame can be set so that the period during which only some LEDs emit light is after the period during which all LEDs emit light. .

  As described above, the transmittance of the liquid crystal panel gradually changes from frame to frame according to the gradation value of the image data of the frame. Therefore, by performing the above-described control, it is possible to assign (set) a period during which only some of the light sources emit light to a period during which the transmittance of the liquid crystal panel is low, that is, a period during which the luminance on the screen is low.

  As described above, according to the present embodiment, the backlight is controlled in consideration of the transmittance of the liquid crystal panel. Specifically, a period in which only a part of the light sources emits light is assigned (set) to a period in which the transmittance of the liquid crystal panel is low, that is, a period in which the luminance on the screen is low. Thereby, compared with the past, it can suppress more effectively that a user breaks color perception.

  In this embodiment, it is assumed that the amount of current to each light source is constant (not changed). However, when calculating the length of the light emission period, the difference in the length of the light emission period of each light source is minimized. As such, the amount of current to each light source may be increased or decreased. For example, the amount of current supplied to the GLED in FIG. 4D may be reduced and the light emission period of the GLED may be extended so as to approach the light emission period of the RLED in FIG. However, if the amount of current is greatly increased or decreased, the wavelength spectrum characteristic of the light source changes, and a so-called color shift phenomenon occurs in which a desired color cannot be obtained. For this reason, it is desirable that the increase / decrease of the current amount is performed so that the increase / decrease amount is equal to or less than a predetermined threshold value (a threshold value determined so as not to cause a color shift phenomenon). In this way, by adjusting the light emission period by increasing / decreasing the amount of current, the period during which only some of the light sources emit light can be shortened.

  In addition, although the present Example demonstrated the case where a light source was LED, a light source is not restricted to LED. For example, the light source may be a cold cathode tube. In this embodiment, the case of using three color light sources of RGB has been described, but the emission color of the light source is not limited to RGB. For example, a light source that emits yellow (Y) or white (W) light may be used.

In this embodiment, when the gradation displacement direction of the image data is a plus direction, the end time of the light emission period of each light source is made to coincide with the end time of the period of the next frame. The period is not limited to this. If the period during which only some light sources emit light is later than the period during which all light sources emit light, the end time of the light emission period of each light source may not coincide with the end time of the period of the next frame. The same applies to the case where the gradation displacement direction of the image data is the minus direction.

  In this embodiment, the gradation displacement direction of the entire image data is determined and the light emission period of each LED is controlled according to the determination result. However, the present invention is not limited to this configuration. For example, when the backlight has a plurality of LEDs for each divided area obtained by dividing the screen area (that is, when the backlight has an LED group for each divided area as shown in FIG. 2). May determine the gradation displacement direction for each divided region. Then, for each divided region, the light emission periods of the plurality of LEDs may be set based on the determination result (gradation displacement direction) of the divided region. By setting the light emission periods of a plurality of LEDs for each divided region, it is possible to make it difficult to detect color breakup for each divided region. For this reason, it is possible to make it difficult to detect the color breakup, compared to the case where the gradation displacement direction of the entire image data is determined and the light emission period of each LED is controlled according to the determination result.

  In this embodiment, the luminance value (Y value) is calculated from the RGB values of the input image data and the gradation displacement direction of the Y value is calculated. However, the gradation displacement direction of the R value and the scale of the G value are calculated. The adjustment displacement direction and the gradation displacement direction of the B value may be calculated. At this time, among the calculated gradation displacement directions, by using the gradation displacement direction of the color having the largest displacement as the final gradation displacement direction, it is possible to effectively reduce color breakup.

<Example 2>
A liquid crystal display device and a control method thereof according to Embodiment 2 of the present invention will be described below with reference to the drawings. In the second embodiment, the description of the parts common to the above-described first embodiment will be omitted as appropriate.
In the first embodiment, the case where each LED is controlled every one frame period (1/60 sec) has been described. However, if each LED is controlled every 1/60 sec, flicker may be visually recognized. Therefore, each LED is often controlled every 1/240 sec. Therefore, in this embodiment, an example will be described in which the backlight (light emission period of a plurality of LEDs) is controlled for each subframe period obtained by dividing one frame period. Specifically, an example in which the backlight is controlled every 1/240 sec will be described.
One frame period is not limited to 1/60 sec. That is, the frame rate is not limited to 60 Hz. For example, the frame rate may be 120 Hz. One subframe period is not limited to 1/240 sec. One subframe period may be a period obtained by dividing one frame period.

FIG. 5 is a timing chart showing the operation of a conventional backlight when the frame rate is 60 Hz and the backlight is driven every 1/240 sec. As shown in FIG. 5, conventionally, a required light emission period (required light emission period) in one frame period is divided into four subframe periods (each of which has a length of 1/240 sec. Each sub-frame period) and each LED was controlled.
However, even with the method of FIG. 5, when a period in which only some LEDs emit light is assigned during a period when the luminance on the screen is high, color breakup is likely to be perceived by the user.
Therefore, in this embodiment, the frame period is divided into the necessary light emission period in one frame period so that the period during which only some LEDs emit light is assigned to the subframe period in which the transmittance of the liquid crystal panel is low. To be divided into a plurality of subframe periods obtained. As a result, color breakup is less perceived.

In the second embodiment, the operations of the backlight control unit 108 and the light emission timing setting unit 110 are different from those in the first embodiment.
FIG. 6 is a flowchart illustrating an example of operations of the backlight control unit 108 and the light emission timing setting unit 110 according to the second embodiment. The process of this flowchart is started in response to the input of the vertical synchronization signal.
First, the backlight control unit 108 calculates the length of the necessary light emission period of each LED in the next frame from the target value (or the detection value acquired from the sensor control unit 107 and the target value acquired from the memory 109) ( Step S601).
Next, the backlight control unit 108 equally divides the length of the necessary light emission period of each LED for each subframe period included in the period of the next frame (step S602). In the present embodiment, the required light emission period of each LED is divided into four subframe periods (periods each having a length of 1/240 sec) obtained by dividing the period of the next frame (period having a length of 1/60 sec). Are equally distributed. That is, for each LED, the required light emission period of the LED is assigned to each subframe period by a quarter.

Then, the light emission timing setting unit 110 checks the gradation displacement direction input from the image processing unit 103 (step S603).
Next, when the gradation displacement direction is the plus direction (step S604: Yes), the process proceeds to step S605, and when it is the minus direction (step S604: No), the process proceeds to step S606. It is done.

In step S605, the light emission timing setting unit 110 adjusts the length of the light emission period of each LED in the subframe period in order from the subframe period that is the latest in time among the subframe periods in the next frame period. Specifically, the light emission periods of the other LEDs are shortened so as to coincide with the LED having the shortest light emission period. At this time, the shortened light emission period is added to the light emission period in the earliest subframe period. Then, the light emission timing setting unit 110 sets the light emission start timing of each LED for each subframe period within the next frame period.
As a result of the addition, if the length of the light emission period exceeds the length of one subframe period, the light emission period to be added is the light emission period in the next subframe period in time. It is said. At this time, the entire light emission period corresponding to the shortened time may or may not be added to the light emission period in the temporally next subframe period. For example, a part of the light emission period corresponding to the shorter light emission period may be added to the light emission period in one subframe period so that the length of the light emission period becomes the length of one subframe period. The remaining light emission period may be added to the light emission period in the next subframe period after the one subframe period.

In step S606, the light emission timing setting unit 110 adjusts the light emission period of each LED in the subframe period in order from the earliest subframe period in the subframe period in the next frame period. Specifically, the lengths of the light emission periods of the other LEDs are shortened so as to coincide with the LED having the shortest light emission period. At this time, the shortened light emission period is added to the light emission period in the latest subframe period. Then, the light emission timing setting unit 110 sets the light emission start timing of each LED for each subframe period within the next frame period.
As a result of the above addition, if the length of the light emission period exceeds the length of one subframe period, the addition destination of the light emission period corresponding to the shortened time is the time in the subframe period immediately preceding in time. The light emission period. At this time, the entire light emission period corresponding to the shortened time may or may not be added to the light emission period in the subframe period immediately preceding in time. For example, a part of the light emission period corresponding to the shorter light emission period may be added to the light emission period in one subframe period so that the length of the light emission period becomes the length of one subframe period. Then, the remaining light emission period may be added to the light emission period in the subframe period immediately preceding the one subframe period.

After step S605 or step S606, the backlight control unit 108 emits light for the adjusted time (the adjusted light emission period length) from the set light emission start timing in the period of the next frame. Each LED is driven.
That is, in this embodiment, the light emission period of each LED within the period of the next frame is set as follows. When the gradation displacement direction is the plus direction, the next frame is assigned such that a period in which only some of the LEDs emit light within the earlier subframe period among the plurality of subframe periods within one frame period. The light emission period of each LED within the period is set. Further, when the gradation displacement direction is a negative direction, among the plurality of subframe periods in one frame period, a period in which only some LEDs emit light in a later subframe period is assigned. The light emission period of each LED within the period of the next frame is set.

7A to 7E are timing charts showing an example of a change in gradation (transmittance) of the liquid crystal panel according to the present embodiment and a light emission period of each LED.
FIG. 7A shows a response waveform of the liquid crystal panel (change in transmittance of the liquid crystal panel). FIG. 7B shows a vertical synchronization signal. FIGS. 7C to 7E show the light emission states of the RLED, GLED, and BLED, respectively. In the figure, periods 1 to 4 are four subframe periods obtained by dividing one frame period. Periods 5 to 8 are also four subframe periods obtained by dividing one frame period.
In FIGS. 7A to 7E, for the sake of simplicity, the display image is changed from a full screen black image (hereinafter, all black) to a full screen white image (hereinafter, all white) at time t0 at time t3. In the above example, the display image is switched from all white to all black.

When switching the display image from all black to all white at time t0, the image processing unit 103 determines that the gradation displacement direction of the image data is the plus direction. Therefore, the light emission timing setting unit 110 shortens the lengths of the RLED and GLED light emission periods in the periods 4, 3, and 2 so as to coincide with the BLED having the shortest light emission period. A process for adding the amount to the light emission period of period 1 is performed. However, as a result of the addition, when the length of the light emission period of period 1 exceeds the length of period 1, the process is performed with the light emission period of period 2 as the addition destination.
After determining the length of the light emission period in each subframe period, the image processing unit 103 sets the light emission start timing of each LED for each subframe period. Specifically, the light emission start timing of each LED is set within a subframe period in which a period during which only some LEDs emit light is set so that the end time of the light emission period of each LED becomes the same time. The light emission start timing of each LED within the other subframe period is set such that the light emission periods of the LEDs are the same. In the example of FIG. 7, the light emission start timing of each LED in the period 1 is set so that the end time of the light emission period of the period 1 coincides with the end time of the period 1 (reference numeral 703 in FIG. 7). Similarly, the light emission start timing of each LED in the periods 2, 3, and 4 is set so that the end time of the light emission period of each LED coincides with the end time of the corresponding subframe period.

When switching the display image from all white to all black at time t3, the image processing unit 103 determines that the gradation displacement direction of the image data is the minus direction. Therefore, the light emission timing setting unit 110 shortens the lengths of the light emitting periods of the RLED and the GLED in that period so as to coincide with the BLED having the shortest light emitting period. A process of adding the amount to the light emission period of period 8 is performed. However, if the length of the light emission period of period 8 exceeds the length of period 8 as a result of the addition, the process is performed with the light emission period of period 7 as the addition destination.
After determining the length of the light emission period in each subframe period, the image processing unit 103 sets the light emission start timing of each LED for each subframe period. Specifically, the light emission start timing of each LED is set within a subframe period in which a period during which only some LEDs emit light is set so that the start time of the light emission period of each LED is the same time. The light emission start timing of each LED within the other subframe period is set such that the light emission periods of the LEDs are the same. In the example of FIG. 7, the light emission start timing of each LED in the period 8 is set so that the start time of the light emission period of the period 8 coincides with the start time of the period 8 (reference numeral 704 in FIG. 7). The light emission start timing of each LED in the periods 5, 6, and 7 is set so that the end time of the light emission period of each LED coincides with the end time of the corresponding subframe period.

  By performing the above-described control, the light emission period required for one frame period is divided so that the period during which only some LEDs emit light is assigned to the subframe period in which the transmittance of the liquid crystal panel is low. Can be distributed over a plurality of subframe periods.

  As described above, according to the present embodiment, the light emission period necessary for one frame period is such that the period during which only some LEDs emit light is assigned to the subframe period in which the transmittance of the liquid crystal panel is low. The frame period is divided into a plurality of subframe periods obtained by dividing the frame period. Thereby, it can suppress more effectively that a user perceives a color break compared with the past, and can suppress that a flicker is visually recognized.

In this embodiment, when the gradation displacement direction of the image data is a plus direction, a sub-period in which only some LEDs emit light is assigned so that the end times of the light emission periods of the respective LEDs are the same time. The light emission period of each LED within the frame period is set. However, the light emission period of each LED is not limited to this. The subframe period in which only some LEDs emit light is a period in which the luminance on the screen is lower than in other subframe periods. Therefore, even if the end times of the light emission periods of the respective LEDs are different, it is possible to more effectively suppress the user from perceiving color breakup as compared with the conventional case. However, if the light emission period of each LED is set so that the end time of the light emission period of each LED is the same time, a period during which only some LEDs emit light is assigned to a period during which the transmittance of the liquid crystal panel is lower. Can do. The same applies to the case where the gradation displacement direction of the image data is the minus direction.
Note that the light emission periods of the LEDs in the subframe period other than the subframe period to which only some LEDs emit light may be equal to each other, and the start time and end time may be any time. . For example, the start time and end time of the light emission period of each LED may not coincide with the start time and end time of the corresponding subframe period.

DESCRIPTION OF SYMBOLS 100 Display apparatus 104 Gradation displacement analysis part 105 Liquid crystal panel 108 Backlight control part 110 Light emission timing setting part 111 Backlight

Claims (14)

A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
The control means includes
When the determination means determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors are used. out so that only a portion of the light source is earlier than the period of time for emitting all of the light sources emits light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors from each other out so that only a portion of the light source is later than the period of time for emitting all of the light sources emits light, the image and setting the light emission period of each light source in a period of a frame to be displayed on the next Display device. The control means includes
When the determination unit determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the end time of the light emission period of each light source is the same Set the light emission period of each light source within the period of the next displayed frame so as to be time,
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the start time of the light emission period of each light source is the same The image display device according to claim 1, wherein a light emission period of each light source within a period of the next frame to be displayed is set so as to be time. The control means includes
Controlling the light emission periods of the plurality of light sources for each subframe period obtained by dividing one frame period;
When the determination means determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, a plurality of subframe periods within one frame period of more so that only the portion of the light source in the previous sub-frame period is assigned the period for emitting light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, a plurality of subframe periods within one frame period among, so that only the portion of the light source in a more subframe period after being assigned a period for emitting a feature to set the emission period of each light source in a period of a frame to be displayed on the next The image display device according to claim 1. The control means includes
When the determination unit determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the end time of the light emission period of each light source is the same Set a light emission period of each light source within a subframe period to which a time period during which only some of the light sources emit light is set to be time,
When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the start time of the light emission period of each light source is the same The image display device according to claim 3, wherein a light emission period of each light source is set within a subframe period in which a period during which only some of the light sources emit light is set to be time. The light emitting unit has the plurality of light sources for each divided region obtained by dividing a region of the screen,
The determination means determines, for each of the divided areas, whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
The said control means sets the light emission period of these light sources for every said division area based on the determination result of the said determination means of the division area, The any one of Claims 1-4 characterized by the above-mentioned. The image display device described in 1.   A light emitting unit having a plurality of light sources having different emission colors;
  A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
  Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
  Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
    The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
  The control means includes
    When the determination means determines that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors are used. The light emission period of each light source within the period of the next frame to be displayed is set so that a period during which only some of the light sources emit light precedes a period during which all the light sources emit light. Image display device.   A light emitting unit having a plurality of light sources having different emission colors;
  A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
  Determining means for determining whether the gradation value of the image data of the frame to be displayed next is higher than the gradation value of the image data of the currently displayed frame;
  Control means for controlling the light emission periods of the plurality of light sources based on the determination result of the determination means;
Have
    The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
  The control means includes
    When the determination means determines that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the plurality of light sources having different emission colors from each other An image characterized in that a light emission period of each light source is set within a period of the next frame displayed so that a period during which only some of the light sources emit light is after a period during which all the light sources emit light. Display device. A light emitting unit having a plurality of light sources having different emission colors;
A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame , out so that only a portion of the light source is earlier than the period of time for emitting all of the light sources emits light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame , out so that only a portion of the light source is later than the period of time for emitting all of the light sources emits light, the image and setting the light emission period of each light source in a period of a frame to be displayed on the next Display device control method. In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the end time of the light emission period of each light source is the same Set the light emission period of each light source within the period of the next displayed frame so as to be time,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the start time of the light emission period of each light source is the same 9. The method of controlling an image display device according to claim 8 , wherein a light emission period of each light source within a period of the next frame to be displayed is set so as to be time. The control step is a step of controlling the light emission periods of the plurality of light sources for each subframe period obtained by dividing one frame period.
In the control step,
If it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, a plurality of subframe periods within one frame period of more so that only the portion of the light source in the previous sub-frame period is assigned the period for emitting light, to set the emission period of each light source in a period of a frame to be displayed on the next,
When it is determined in the determining step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, a plurality of subframe periods within one frame period among, so that only the portion of the light source in a more subframe period after being assigned a period for emitting a feature to set the emission period of each light source in a period of a frame to be displayed on the next The method for controlling an image display device according to claim 8 . In the control step,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, the end time of the light emission period of each light source is the same Set a light emission period of each light source within a subframe period to which a time period during which only some of the light sources emit light is set to be time,
When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, the start time of the light emission period of each light source is the same The method for controlling an image display device according to claim 10 , wherein a light emission period of each light source is set within a subframe period in which a period during which only some of the light sources emit light is set to be time. The light emitting unit has the plurality of light sources for each divided region obtained by dividing a region of the screen,
In the determination step, for each of the divided areas, it is determined whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
In the control step, the each divided area, based on a determination result of the determining step of the divided regions, any one of claims 8 to 11, characterized by setting the light emission period of the plurality of light sources The control method of the image display apparatus as described in any one of Claims 1-3.   A light emitting unit having a plurality of light sources having different emission colors;
  A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
  A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
  A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
    The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
  In the control step,
    When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame, The light emission period of each light source within the period of the next frame to be displayed is set so that the period during which only some of the light sources emit light precedes the period during which all light sources emit light.
And a control method for the image display device.   A light emitting unit having a plurality of light sources having different emission colors;
  A plurality of displays in which the transmittance is controlled in accordance with the gradation value of the input image data so that the transmittance of light from the light emitting unit increases as the gradation value of the input image data increases. A display panel having elements;
A method for controlling an image display device comprising:
  A determination step of determining whether or not the gradation value of the image data of the next frame to be displayed is higher than the gradation value of the image data of the currently displayed frame;
  A control step for controlling light emission periods of the plurality of light sources based on a determination result of the determination step;
Have
    The lengths of the light emission periods of the plurality of light sources having different emission colors within one frame period are different from each other,
  In the control step,
    When it is determined in the determination step that the gradation value of the image data of the next frame to be displayed is lower than the gradation value of the image data of the currently displayed frame, The light emission period of each light source within the period of the next frame to be displayed is set so that the period during which only some of the light sources emit light is after the period during which all the light sources emit light.
And a control method for the image display device.

Images