JP2013210508A - Liquid crystal display device and calibration method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the power consumption relating to the execution of calibration in a liquid crystal display device which performs local dimming control.SOLUTION: A liquid crystal display device is switchable between a normal mode and a power saving mode and includes calibration means capable of calibration based on a comparison result between a photometric value of the liquid crystal display device, which is acquired from photometric means, and a target value, and the calibration includes first calibration to be performed in the case of the liquid crystal display device being in the normal mode and second calibration to be performed in the case of switching from the normal mode to the power saving mode of the liquid crystal display device. In the case of the absence of a history that the first calibration was performed during non-execution of local dimming control, local dimming control is stopped to perform the second calibration in response to a request for switching from the normal mode to the power saving mode.

Description

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

2. Description of the Related Art Conventionally, a technique has been proposed in which an optical sensor that measures the light displayed on a liquid crystal display device is provided and fluctuations in luminance and chromaticity of the liquid crystal panel and backlight of the liquid crystal display device are suppressed based on the color measurement results. (Patent Document 1).
Furthermore, a colorimetric pattern is displayed at the light receiving position of the photosensor on the liquid crystal panel, and a colorimetric measurement is performed by the photosensor during normal work while displaying an image for normal work in the part other than the colorimetric pattern. It has been proposed to do this (Patent Document 2).

In addition, the backlight is divided into a plurality of regions, and the light emission amount of each region can be independently controlled according to the feature amount of the input image signal (this control is hereinafter referred to as local dimming control). Has been proposed (Patent Document 3).
Using such a conventional technique, it is possible to measure the colorimetric pattern with an optical sensor while performing local dimming control.
In addition, a technique is disclosed in which a display that can be opened and closed is calibrated when the display is closed, and then set to a power saving mode (Patent Document 4).

JP 2010-169990 A JP 2007-156284 A JP 2008-90076 A JP 2011-180383 A

By combining the techniques of Patent Document 1, Patent Document 2, and Patent Document 3 described above, color measurement can be performed while performing local dimming control during normal work, and display characteristics of the display can be calibrated (calibration). it can.
However, when local dimming control is performed, for example, if the input image changes during colorimetry by the optical sensor, the amount of backlight emission for each region may also change. In that case, the calibration accuracy may be lowered due to the influence of the change in the light emission amount of the backlight around the optical sensor.

In order to suppress such a decrease in calibration accuracy in a display that performs local dimming control, it is conceivable to perform calibration before the display enters the power saving mode as in Patent Document 4.
However, if calibration is always performed before entering the power saving mode, there is a problem that power consumption related to the calibration increases.

  An object of the present invention is to provide a technique for suppressing power consumption related to calibration in a liquid crystal display device that performs local dimming control.

The present invention includes a liquid crystal panel,
A backlight that irradiates the liquid crystal panel from the back, is divided into a plurality of light emitting blocks, and the amount of light emission can be independently controlled for each light emitting block;
A liquid crystal display device comprising:
Backlight control means capable of performing local dimming control for controlling the amount of light emission for each light emission block according to an input image signal;
As the operation mode of the liquid crystal display device, a power supply control means capable of switching between a normal mode for displaying an image based on an input image signal and a power saving mode for stopping a predetermined function to reduce power consumption,
Calibration of a liquid crystal display device based on a comparison result between a colorimetric value acquired from a colorimetric means for measuring the transmitted light from the liquid crystal panel and a predetermined target value, wherein the liquid crystal display device is in a normal mode Calibration means capable of performing a first calibration that is sometimes performed and a second calibration that is performed when the liquid crystal display device shifts from the normal mode to the power saving mode;
Storage means for storing a calibration execution history including information on whether or not the local dimming control was performed on the backlight when the calibration means performed the first calibration;
Have
When there is no execution history of the first calibration when the local dimming control is not performed, when the calibration means has a request to shift from the normal mode to the power saving mode of the liquid crystal display device The liquid crystal display device performs the second calibration by stopping the local dimming control.

The present invention includes a liquid crystal panel,
A backlight that irradiates the liquid crystal panel from the back, is divided into a plurality of light emitting blocks, and the amount of light emission can be independently controlled for each light emitting block;
A liquid crystal display device calibration method comprising:
A backlight control step for performing local dimming control for controlling the amount of light emission for each light emission block according to the input image signal;
As an operation mode of the liquid crystal display device, a power supply control step of switching between a normal mode for displaying an image based on an input image signal and a power saving mode for stopping a predetermined function to reduce power consumption,
Calibration of a liquid crystal display device based on a comparison result between a colorimetric value acquired from a colorimetric means for measuring the transmitted light from the liquid crystal panel and a predetermined target value, wherein the liquid crystal display device is in a normal mode A calibration process for performing a first calibration sometimes performed and a second calibration performed when the liquid crystal display device shifts from the normal mode to the power saving mode;
A step of reading from the storage means a calibration execution history including information on whether or not the local dimming control has been performed on the backlight when the first calibration is performed in the calibration step;
Have
When there is no execution history of the first calibration when the local dimming control is not performed, in the calibration step, when there is a request to shift from the normal mode to the power saving mode of the liquid crystal display device It is a calibration method for a liquid crystal display device that performs the second calibration by stopping the local dimming control.

  ADVANTAGE OF THE INVENTION According to this invention, in the liquid crystal display device which performs local dimming control, the technique which suppresses the power consumption which concerns on implementation of a calibration can be provided.

1 is a block diagram illustrating a configuration of a liquid crystal display device according to Embodiment 1. FIG. 2 is a part of a flowchart showing the operation of the first embodiment. 2 is a part of a flowchart showing the operation of the first embodiment. 2 is a part of a flowchart showing the operation of the first embodiment. 9 is a part of a flowchart showing the operation of the second embodiment. FIG. 9 is a part of a flowchart showing the operation of the third embodiment.

Example 1
FIG. 1 is a block diagram illustrating a configuration of a liquid crystal display device according to Embodiment 1 of the present invention.
In FIG. 1, the liquid crystal display device 1 includes a backlight 2 and a liquid crystal panel 3 capable of independently controlling the light emission amount for each of a plurality of regions. The light emitted from the back surface of the liquid crystal panel 3 by the backlight 2 passes through the liquid crystal panel 3 so that an image is displayed. Each region in which the light emission amount in the backlight 2 can be independently controlled is hereinafter referred to as a “light emission block”.

In FIG. 1, the image signal is input to the dimming unit 4.
The dimming unit 4 divides an image based on the input image signal into a plurality of regions (divided regions). Each of the plurality of divided regions corresponds to each of the plurality of light emitting blocks of the backlight 2. The dimming unit 4 determines the light emission amount of each light emission block of the backlight 2 in accordance with the feature amount of the image signal corresponding to each of the divided regions, and transmits a backlight control signal including information on the light emission amount to the backlight. Output to 2.

Further, the dimming unit 4 performs image processing on the input image signal for each divided region according to the feature amount of the image signal corresponding to each divided region, and outputs the processed image signal as a dimmed image signal.
As an example of the feature amount, the maximum gradation value of the image signal for each divided region can be used.

  The dimming unit 4 performs image processing for reducing the light emission amount of the light emission block corresponding to the divided area having a small maximum gradation value and multiplying the image signal of the divided area by a gain value larger than 1. As a result, it is possible to increase the display contrast of the image by lowering the brightness of the dark part, and to reduce the power consumption.

A calibration unit 5 surrounded by a broken line in FIG. 1 includes an image correction unit 6, a pattern generation unit 7, and a synthesis unit 8, and performs calibration.
The dimming image signal output from the dimming unit 4 is input to the image correction unit 6, corrected based on the correction information stored in the storage unit 9, and output as a corrected image signal.
The correction information includes a look-up table indicating the relationship between the gradation value of the dimming image signal input to the image correction unit 6 and the gradation value of the correction image signal output.

In the image correction unit 6, for example, the gradation value and the luminance of the display image are ITU-R BT. The dimming image signal is corrected so that the relationship as defined in 709 is obtained.
In addition, the liquid crystal display device 1 has a control unit 10 and records correction information in the storage unit 9.
Further, the control unit 10 controls the operation of the optical sensor 11, the pattern generation unit 7, and the power supply unit 12, and switches between valid / invalid operation of the dimming unit 4.

The optical sensor 11 is installed on the surface of the liquid crystal panel 3 with the light receiving surface facing the liquid crystal panel 3 side. The optical sensor 11 measures the light emitted from the backlight 2 and transmitted through the liquid crystal panel 3.
When a sensor control signal is output from the control unit 10 to the optical sensor 11, the optical sensor 11 performs a color measurement operation of the transmitted light of the liquid crystal panel 3 and returns a color measurement result to the control unit 10.
When performing color measurement with the optical sensor 11, the control unit 10 displays the color measurement pattern at the color measurement position of the optical sensor 11 on the liquid crystal panel 3, and the gradation value to be displayed. Is output to the pattern generation unit 7.

The pattern generation unit 7 generates a colorimetric pattern for the position and gradation value specified by the pattern control signal.
The colorimetric pattern generated by the pattern generator 7 is combined with the corrected image signal by the combiner 8 and output to the liquid crystal panel 3 as an output image signal. An image based on the output image signal is displayed on the liquid crystal panel 3. The
The control unit 10 performs correction by the image correction unit 6 based on the color measurement value (color measurement result) obtained by measuring the display of the color measurement pattern combined with the corrected image signal by the optical sensor 11. Correction information is obtained and recorded in the storage unit 9.

  In the present embodiment, calibration means that the colorimetric pattern is measured by the optical sensor 11 and is corrected by the control unit 10 based on the comparison result between the colorimetric value acquired from the optical sensor 11 and a predetermined target value. It is assumed that a series of operations for obtaining information and recording correction information in the storage unit 9 are represented.

The power supply unit 12 supplies power to each unit of the liquid crystal display device 1. Operations such as switching power supply to each unit and switching off, shifting to the power saving mode, and returning to the normal mode are controlled based on a power control signal from the control unit 10.
The control unit 10 outputs a power supply control signal to the power supply unit 12 according to a user operation, a timer count, or the like.

  The power saving mode is started, for example, when an image signal is not input for a certain period of time or when a user operates a switch to instruct a transition to the power saving mode. In the power saving mode, the liquid crystal display device stops a predetermined function and suppresses power consumption. For example, an operation of stopping the transmittance control of the liquid crystal panel based on the input image signal, reducing the brightness of the backlight, or turning off the backlight is performed. The power saving mode is canceled and the normal mode is restored when an image signal is input or when the user performs a switch operation for instructing the return from the power saving mode. In the normal mode, the liquid crystal display device 1 displays an image based on the input image signal.

In the liquid crystal display device 1 configured as described above, the operation of the first embodiment will be described with reference to the flowcharts of FIGS. The processes shown in these flowcharts are executed by the control unit 10.
2, in the liquid crystal display device 1 according to the first embodiment, when the power is turned on and the operation is started, an execution flag indicating whether or not calibration is performed is first set to 0 (step S1). .

  The calibration execution flag takes a value of 0, 1, or 2. When the execution flag value is 0, it indicates that the calibration is not performed. The case where the value of the execution flag is another value will be described later. The calibration execution flag is information on the history of calibration performed when the liquid crystal display device 1 is operating in the normal mode, and is stored in a storage unit inside the control unit 10. The storage unit 9 may store a calibration execution flag.

Next, a process for displaying a colorimetric pattern on the liquid crystal display device 1 and measuring the current display characteristics with the optical sensor 11 is performed (step S2).
Then, the difference between the colorimetric result in step S2 and the specified (target) display characteristic, that is, the target value (theoretical value) of the display characteristic when the colorimetric pattern is displayed on the liquid crystal display device 1 is calculated. (Step S3).
After calculation of the difference in step S3, the process proceeds to the flow shown in FIG. 3, and the difference is compared with a preset threshold value (step S4).

If the difference is equal to or smaller than the threshold value as a result of the comparison (step S4: No), the process proceeds to the flow shown in FIG. 4, and step S9 described later is executed.
When the difference is larger than the threshold value (step S4: Yes), calibration is performed (step S5). This calibration executed while the liquid crystal display device 1 is operating in the normal mode is referred to as a “first calibration”.
The calibration is executed at a predetermined time interval or at a timing designated by the user or the like while displaying a normal work screen.

Next, it is determined whether the local dimming control by the dimming unit 4 is valid or invalid (step S6).
When the local dimming control of the dimming unit 4 is invalid (step S6: No), the calibration execution flag is set to 1 (step S7).
When the local dimming control of the dimming unit 4 is valid (step S6: Yes), the calibration execution flag is set to 2 (step S8).

  When the value of the calibration execution flag is 1, it indicates that the local dimming control of the dimming unit 4 is invalid when the first calibration is performed. When the value of the calibration execution flag is 2, it indicates that the local dimming control of the dimming unit 4 was effective when the first calibration was performed. That is, the calibration execution flag includes a calibration execution history including information on whether or not the local dimming control was performed when the first calibration was performed while the liquid crystal display device 1 was operating in the normal mode. Show.

Next, the process moves to the flow of FIG. 4, and it is determined whether or not there is a request to shift to the power saving mode based on a user instruction or the like (step S <b> 9).
If there is no request for shifting to the power saving mode (step S9: No), the process returns to step S2 after a predetermined time wait (step S10).
When there is a request for shifting to the power saving mode (step S9: Yes), it is determined whether or not the value of the calibration execution flag is 2 (local dimming control by the dimming unit 4 is valid) (step S11). . If the value of the calibration execution flag is not 2 (step S11: No), the process proceeds to step S14.

When the value of the calibration execution flag is 2 (step S11: Yes), the local dimming control of the dimming unit 4 is invalidated (step S12), and calibration is performed (step S13). This calibration executed when the liquid crystal display device 1 switches from the normal mode to the power saving mode is referred to as a “second calibration”.
Then, the operation mode shifts to the power saving mode (step S14), and the process of the flowchart ends.

  In this embodiment, even if the local dimming control of the dimming unit 4 is valid or invalid, if the difference between the color measurement result and the theoretical value is equal to or greater than the threshold value, the first calibration is performed in step S5. The

When the local dimming control of the dimming unit 4 is effective, the light emission amount of each light emission block of the backlight 2 changes according to the feature amount of the image signal input to the dimming unit 4. Therefore, the accuracy of the first calibration may be lower than when the local dimming control of the dimming unit 4 is invalid.

  In the present embodiment, when the first calibration is performed in a state where the local dimming control is enabled, the local dimming control of the dimming unit 4 is disabled before shifting to the power saving mode, and the second calibration is performed. Calibration is performed. As a result, the calibration is performed in a state where the local dimming control is disabled, so that it is possible to perform calibration with high accuracy.

  However, if the local dimming control of the dimming unit 4 is invalid at the time of the first calibration in step S5, it is considered that the first calibration performed in step S5 is sufficiently accurate. For this reason, in this embodiment, when there is a history of calibration performed in a state where the local dimming control is invalid, the second calibration at the time of shifting to the power saving mode is not performed.

  Therefore, the execution of the second calibration in step S13 is limited to a case where there is no history in which the local dimming control of the dimming unit 4 at the time of the first calibration is invalid. As a result, since the number of times the second calibration is performed is reduced, it is possible to suppress power consumption related to the calibration.

  Note that black may be displayed on the entire screen before the local dimming control of the dimming unit 4 is disabled in step S12. Thereby, the display change when the local dimming control of the dimming unit 4 is switched from valid to invalid can be made difficult to be visually recognized.

(Example 2)
In the first embodiment, regardless of whether the local dimming control of the dimming unit 4 is valid or invalid, the difference between the color measurement result and the target value is compared with one threshold value, and the first difference is obtained when the difference is larger than the threshold value. It is configured to perform calibration.

In the second embodiment, the frequency at which the first calibration is performed is changed by changing the threshold value depending on whether the local dimming control of the dimming unit 4 is valid or invalid.
In the second embodiment, the operations in steps S1 to S3 and steps S9 to S14 in the first embodiment are the same as those in the first embodiment, and thus description thereof is omitted.

FIG. 5 is a flowchart illustrating processing of the part corresponding to FIG. 3 (step S4 to step S8) of the first embodiment in the second embodiment.
After the difference between the colorimetric result and the theoretical value is calculated in step S3, it is determined in step S15 whether the local dimming control of the dimming unit 4 is valid or invalid.

When the local dimming control of the dimming unit 4 is invalid (step S15: No), the difference between the color measurement result and the theoretical value is compared with a preset second threshold value (step S16).
As a result of the comparison, if the difference is equal to or smaller than the second threshold (step S16: No), the process proceeds to step S9 in FIG.
As a result of the comparison, when the difference is larger than the second threshold (step S16: Yes), the first calibration is performed (step S17), the calibration execution flag is set to 1 (step S18), and the process is performed. The process proceeds to step S9 and subsequent steps.

If it is determined in step S15 that the local dimming control of the dimming unit 4 is valid (step S15: Yes), the difference between the colorimetric result and the target value is compared with a preset third threshold value ( Step S19).
Different values can be set for the second threshold and the third threshold.
For example, by making the third threshold value larger than the second threshold value, the frequency with which the first calibration is performed when the local dimming control of the dimming unit 4 is effective can be reduced.

If the difference between the color measurement result and the target value is equal to or smaller than the third threshold value in step S19 (step S19: No), the process proceeds to step S9 and subsequent steps in FIG.
When the difference is larger than the third threshold (step S19: Yes), the first calibration is performed (step S20), the calibration execution flag is set to 2 (step S21), and the processing is performed after step S9. Move on.

As described above, the frequency of the first calibration is performed by changing the threshold for comparing the difference between the color measurement result and the target value depending on whether the local dimming control of the dimming unit 4 is valid or invalid. Can be changed.
At this time, by increasing the value of the third threshold value, it is possible to reduce the frequency of performing the first calibration with relatively low accuracy when the local dimming control of the dimming unit 4 is effective.

It is possible to omit step S20 and not to perform the first calibration with relatively low accuracy when the local dimming control of the dimming unit 4 is effective.
Even when calibration is not performed in step S20, the calibration execution flag is set to 2 when the difference between the colorimetric result and the target value is greater than the third threshold value.
Therefore, the second calibration in step S13 is performed, and the display accuracy can be maintained.

(Example 3)
In the first and second embodiments, when there is a request for shifting to the power saving mode, if the value of the calibration execution flag is 2, the second calibration is performed.
In the third embodiment, when the calibration execution flag is 2, the color measurement is performed again by the optical sensor, and the second calibration is performed only when the difference between the color measurement result and the target value is large. Furthermore, power consumption is suppressed.

In the third embodiment, the operations in steps S1 to S11 in the first embodiment are the same as those in the first embodiment, and thus the description thereof is omitted.
FIG. 6 is a flowchart illustrating the operation of the liquid crystal display device according to the third embodiment in a portion corresponding to FIG. 4 (step S9 to step S14) of the first embodiment.
In FIG. 6, when it is determined in step S11 that the calibration execution flag is 2, a colorimetric pattern is displayed, and the current display characteristic is measured by the optical sensor 11 (step S22). ).

Next, the difference between the colorimetric result and the theoretical value is calculated (step S23), and the difference is compared with a preset threshold value (step S24).
If the difference is equal to or smaller than the threshold value as a result of the comparison (step S24: No), the process proceeds to step S14, and the transition to the power saving mode is performed.
When the difference is larger than the threshold value (step S24: Yes), the local dimming control of the dimming unit 4 is invalidated in step S12, and the second calibration is performed (step S13).

  According to the present embodiment, even when there is a request for shifting to the power saving mode and the calibration execution flag is 2, the second calibration is not always executed, and the color measurement result and the target value The second calibration is performed only when the difference is large. Thereby, it is possible to suppress power consumption related to the execution of calibration.

1: liquid crystal display device, 2: backlight, 3: liquid crystal panel, 4: dimming unit, 5: calibration unit, 9: storage unit, 10: control unit

Claims (9)

LCD panel,
A backlight that irradiates the liquid crystal panel from the back, is divided into a plurality of light emitting blocks, and the amount of light emission can be independently controlled for each light emitting block;
A liquid crystal display device comprising:
Backlight control means capable of performing local dimming control for controlling the amount of light emission for each light emission block according to an input image signal;
As the operation mode of the liquid crystal display device, a power supply control means capable of switching between a normal mode for displaying an image based on an input image signal and a power saving mode for stopping a predetermined function to reduce power consumption,
Calibration of a liquid crystal display device based on a comparison result between a colorimetric value acquired from a colorimetric means for measuring the transmitted light from the liquid crystal panel and a predetermined target value, wherein the liquid crystal display device is in a normal mode Calibration means capable of performing a first calibration that is sometimes performed and a second calibration that is performed when the liquid crystal display device shifts from the normal mode to the power saving mode;
Storage means for storing a calibration execution history including information on whether or not the local dimming control was performed on the backlight when the calibration means performed the first calibration;
Have
When there is no execution history of the first calibration when the local dimming control is not performed, when the calibration means has a request to shift from the normal mode to the power saving mode of the liquid crystal display device A liquid crystal display device that performs the second calibration by stopping the local dimming control.   The liquid crystal display device according to claim 1, wherein the calibration unit performs the first calibration at regular time intervals when the liquid crystal display device is in a normal mode.   3. The first calibration according to claim 1, wherein the calibration unit performs the first calibration when a difference between the colorimetric value and the target value is larger than a threshold value when the liquid crystal display device is in a normal mode. Liquid crystal display device.   4. The liquid crystal display device according to claim 3, wherein the threshold value is different depending on whether the local dimming control is performed on the backlight or not. 5.   The threshold value used when the local dimming control is performed on the backlight is larger than the threshold value used when the local dimming control is not performed on the backlight. Item 5. A liquid crystal display device according to item 4.   The said calibration means does not perform said 1st calibration, when the said local dimming control is performed with respect to the said backlight, when the said liquid crystal display device is a normal mode. 2. A liquid crystal display device according to item 1.   The liquid crystal display device according to claim 1, wherein the calibration unit always performs the second calibration when the liquid crystal display device shifts from a normal mode to a power saving mode.   The calibration means performs the second calibration when the difference between the colorimetric value and the target value is larger than a threshold value when the liquid crystal display device shifts from a normal mode to a power saving mode. Item 7. The liquid crystal display device according to any one of items 1 to 6. LCD panel,
A backlight that irradiates the liquid crystal panel from the back, is divided into a plurality of light emitting blocks, and the amount of light emission can be independently controlled for each light emitting block;
A liquid crystal display device calibration method comprising:
A backlight control step for performing local dimming control for controlling the amount of light emission for each light emission block according to the input image signal;
As an operation mode of the liquid crystal display device, a power supply control step of switching between a normal mode for displaying an image based on an input image signal and a power saving mode for stopping a predetermined function to reduce power consumption,
Calibration of a liquid crystal display device based on a comparison result between a colorimetric value acquired from a colorimetric means for measuring the transmitted light from the liquid crystal panel and a predetermined target value, wherein the liquid crystal display device is in a normal mode A calibration process for performing a first calibration sometimes performed and a second calibration performed when the liquid crystal display device shifts from the normal mode to the power saving mode;
A step of reading from the storage means a calibration execution history including information on whether or not the local dimming control has been performed on the backlight when the first calibration is performed in the calibration step;
Have
When there is no execution history of the first calibration when the local dimming control is not performed, in the calibration step, when there is a request to shift from the normal mode to the power saving mode of the liquid crystal display device A liquid crystal display calibration method for performing the second calibration by stopping the local dimming control.

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