JP2012155194A - Image display device and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a change in display color in an image display device that uses a light emitting element, such as an LED, as a light source for a back light.SOLUTION: The ambient temperature of the light emitting element at the time of setting a target luminance value for display luminance is detected. If the detected temperature at the time of setting is lower than a predetermined threshold, a light source luminance value, which is a luminance value for a back light, is set to a value higher than the target luminance value. A correction is made such that the luminance value is decreased relative to an image signal by an amount that the light source luminance value is higher than the target luminance value. Thereby the display luminance is made equal to the target luminance value. The ambient temperature of the light emitting element is feedback controlled such that the light source luminance value and an amount of luminance value correction, determined when these target luminance values are set, are used as initial values and, after that, the amount of light emitted by the light emitting element is adjusted using as a control target value the temperature at the setting time. According to the light source luminance value that changes by adjusting the amount of light emitted by the light emitting element, the luminance value of an image signal is adjusted by an image processing, thereby the display luminance value is made equal to the target luminance value.

Description

  The present invention relates to an image display device and a control method thereof.

Liquid crystal displays using LEDs (Light Emitting Diodes) as light sources have been put into practical use. The LED has a characteristic that the light emission characteristic changes according to the ambient temperature. When the display is turned on, the light source and internal components of the display start to generate heat, so the ambient temperature of the LED gradually increases after the power is turned on. Further, when the temperature of the environment where the display is installed changes, the ambient temperature of the LED changes in conjunction with the change of the environmental temperature. When the ambient temperature of the LED changes, the light emission characteristics of the LED of the light source change, so the display color of the display changes.

  Conventionally, in a lighting device using an LED as a light source, a technique for suppressing a change in the light emission intensity of the LED when the ambient temperature of the LED changes has been proposed (see, for example, Patent Document 1). In the invention described in Patent Document 1, the temperature difference between the ambient temperature of the LED during actual use and the ambient temperature of the LED when the manufacturer adjusts the white balance before shipment (initial setting) is a predetermined value. In the case described above, the value of the current applied to the LED is adjusted so that the light emission intensity is the same as the light emission intensity at the initial setting.

  The light emission intensity of the LED changes according to the ambient temperature, but with this correction, the light emission intensity of the LED in actual use approaches the light emission intensity of the LED at the initial setting. Therefore, even when the ambient temperature of the LED changes in actual use as compared with the temperature at the initial setting, it is possible to realize a white balance close to the white balance adjusted at the initial setting.

JP 2007-87816 A

  However, the LED has a characteristic that the emission spectrum changes as the emission intensity changes according to the ambient temperature. In the technique described in Patent Document 1, even if the light emission intensity is adjusted by controlling the applied current value to the LED according to the ambient temperature of the LED in actual use, the ambient temperature of the LED in actual use is the initial setting. It does not always coincide with the ambient temperature of the LED. When the ambient temperature of the LED during actual use is different from the ambient temperature of the LED during initial setting, the emission spectrum of the LED during actual use changes from the emission spectrum of the LED during initial setting.

  A liquid crystal panel having a color filter and a liquid crystal display having a backlight that uses an LED as a light source have a problem that the display color changes when the emission spectrum of the LED changes.

Although Patent Document 1 describes that the ambient temperature of the LED is lowered to the initial setting temperature by using a cooling fan, a large-sized component such as a cooling fan is required for a liquid crystal display that is required to be thin. It is not realistic to install it.
Therefore, an object of the present invention is to provide a technique for reducing fluctuations in display color in an image display apparatus using a light emitting element such as an LED as a light source of a backlight.

The present invention includes a backlight having one or more light emitting elements,
A display panel for displaying an image by changing the transmittance of light incident from the backlight for each pixel according to an input image signal;
Backlight control means for controlling a light source luminance value, which is a luminance value of a backlight, by adjusting a light emission amount of the light emitting element;
Image processing means for correcting a luminance value for an image signal input to the display panel;
Temperature detecting means for detecting the temperature around the light emitting element of the backlight; and
Setting means for setting a target luminance value which is a target value of the display luminance of the display panel;
When the set temperature, which is the ambient temperature of the light emitting element detected by the temperature detecting means when the target brightness value is set by the setting means, is lower than a predetermined threshold, it is controlled by the backlight control means. The image processing is performed such that the initial value of the light source luminance value is set to a value higher than the target luminance value, and the display luminance is equal to the target luminance value according to a difference between the initial value of the light source luminance value and the target luminance value. Initial value setting means for setting an initial value of a correction amount for reducing the luminance value of the image signal by the means;
Have
After the target brightness value is set by the setting means,
The backlight control unit adjusts the light emission amount of the light emitting element within a range where the light source luminance value does not fall below the target luminance value, thereby setting the temperature around the light emitting element detected by the temperature detecting unit. Control the light source brightness value so that it approaches the hourly temperature,
The image processing means is a correction amount for reducing the brightness value of the image signal so that the display brightness becomes equal to the target brightness value in accordance with a difference between the light source brightness value controlled by the backlight control means and the target brightness value. Adjust the
An image display device characterized by the above.

The present invention includes a backlight having one or more light emitting elements,
A display panel for displaying an image by changing the transmittance of light incident from the backlight for each pixel according to an input image signal;
A method for controlling an image display device comprising:
A backlight control step of controlling a light source luminance value, which is a luminance value of a backlight, by adjusting a light emission amount of the light emitting element;
An image processing step of correcting a luminance value for an image signal input to the display panel;
A temperature detection step of detecting a temperature around the light emitting element of the backlight; and
A setting step of setting a target luminance value that is a target value of the display luminance of the display panel;
When the set temperature, which is the ambient temperature of the light emitting element detected by the temperature detecting step when the target luminance value is set by the setting step, is lower than a predetermined threshold value, it is controlled by the backlight control step. The image processing is performed such that the initial value of the light source luminance value is set to a value higher than the target luminance value, and the display luminance is equal to the target luminance value according to a difference between the initial value of the light source luminance value and the target luminance value. An initial value setting step for setting an initial value of a correction amount for reducing the luminance value of the image signal in the process;
Have
After the target brightness value is set by the setting step,
The backlight control step adjusts the light emission amount of the light emitting element within a range where the light source luminance value does not fall below the target luminance value, thereby setting the temperature around the light emitting element detected by the temperature detecting step. Control the light source brightness value so that it approaches the hourly temperature,
The image processing step includes a correction amount for reducing the luminance value of the image signal so that the display luminance becomes equal to the target luminance value according to a difference between the light source luminance value controlled by the backlight control step and the target luminance value. Adjust the
This is a method for controlling an image display device.

  ADVANTAGE OF THE INVENTION According to this invention, the fluctuation | variation of a display color can be reduced in the image display apparatus using light emitting elements, such as LED, as a light source of a backlight.

The block diagram which shows the structure of the image display apparatus of an Example A flowchart showing the operation of the image display apparatus when setting the target luminance value Example of relationship between detected temperature and light source luminance value when setting target luminance value Flow chart showing operation of steady process of image display device Time change of ambient temperature of LED at power-on in conventional image display device Example of time change of ambient temperature of LED at power-on of image display device

Example 1
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration of a liquid crystal display including an example of an image display device to which the present invention can be applied. In FIG. 1, this embodiment includes an image input unit 110, an image signal correction unit 120, a display unit 130, a storage unit 140, a light source control unit 150, a light source unit 160, a temperature detection unit 170, and a target luminance value setting unit 180. Composed.

The image input unit 110 receives image signals from image input terminals such as HDMI (High-Definition Multimedia Interface), DVI (Digital Visual Interface), and DisplayPort. The image input unit 110 is connected to an image output device such as a personal computer, a video player, or an image storage unit (not shown). The image input unit 110 receives an image signal output from the image output device, and outputs the received image signal to the image signal correction unit 120.

  The image signal correction unit 120 corrects the luminance value for the image signal input from the image input unit 110 according to a target luminance value output from the storage unit 140 described later and a light source luminance value output from the light source control unit 150. Image processing is performed (image processing means). The image signal correction unit 120 corrects the luminance value of the image signal by multiplying the pixel value of each pixel by a gain value. The gain value is a value in the range of 0 to 1. When the gain value is 1, each pixel value of the image signal is multiplied by 1 (multiplied by 1), so the luminance value of the image signal does not change before and after correction. .

  As the gain value decreases, each pixel value of the image signal decreases, so that under the same light emission amount of the light source unit 160, the corrected image signal is darker than the uncorrected image signal. That is, when the gain value is other than 1, the image signal correction unit 120 performs correction for reducing the luminance value on the input image signal.

  The smaller the gain value, the larger the correction amount by which the luminance value of the image signal by the image signal correction unit 120 is reduced. For example, the image signal correction unit 120 may be configured as a part of an image processing unit (not shown) that corrects the luminance value, color, gamma, and the like of the image signal in accordance with display characteristics of the display unit 130 described later. good. The image signal correction unit 120 outputs the corrected image signal to the display unit 130.

  The display unit 130 is configured by, for example, a liquid crystal panel, and changes the transmittance of light incident from the light source unit 160 for each pixel in accordance with the image signal input from the image signal correction unit 120 (display panel). The light source unit 160 emits light from the back surface of the display unit 130, and the liquid crystal panel of the display unit 130 is controlled according to the image signal input from the image signal correction unit 120, whereby an image is displayed on the display unit 130. The

The storage unit 140 is a rewritable storage medium such as a nonvolatile memory, and stores a target luminance value and a set temperature (storage means). The target luminance value is a target value for the luminance (display luminance) of the image displayed on the display unit 130. The larger the display luminance value, the brighter the image is displayed on the display unit 130, and the smaller the display luminance value, the darker the image is displayed on the display unit 130. The image display apparatus according to the present embodiment operates so that the display luminance value becomes equal to the target luminance value.

  Therefore, the user can adjust the display brightness by setting the target brightness value to an arbitrary value. That is, when the user increases the target luminance value, the image display apparatus operates so that the image display on the display unit 130 becomes brighter and when the user decreases the target luminance value, the image display on the display unit 130 becomes darker. .

  The setting temperature is the ambient temperature of the LEDs (light emitting elements) constituting the light source unit 160 detected by the temperature detection unit 170 described later when the user changes the target luminance value and adjusts the display luminance (setting temperature). ). The storage unit 140 outputs the target luminance value to the image signal correction unit 120 and the light source control unit 150, and outputs the set temperature to the light source control unit 150.

  The light source control unit 150 receives the target luminance value and setting temperature from the storage unit 140 and the detected temperature from the temperature detection unit 170, and controls the light source luminance value by adjusting the light emission amount of the light source unit 160 (backlight control). means). The light source luminance value is the luminance value of the light source unit 160, and the display unit 130 displays when the image signal correction unit 120 sets the gain value to 1, that is, when correction for changing the luminance value is not performed on the image signal. It corresponds to the luminance value.

  The display brightness of the display unit 130 in this case is the display brightness when a white image is displayed. The light source control unit 150 outputs the light source luminance value to the image signal correction unit 120. When the image signal correction unit 120 sets the gain value to a value smaller than 1, that is, the display luminance value of the display unit 130 when correcting the image signal to reduce the luminance value is lower than the light source luminance value.

The light source controller 150 outputs a PWM (Pulse Wide Modulation) signal, which is a pulse signal, to the light source unit 160 and controls the light emission amount of the light source unit 160 by changing the duty ratio of the PWM signal. Details of control of the light source unit 160 by the light source control unit 150 will be described later. The light source control unit 150 may be configured as a part of a microcomputer, for example.

  The light source unit 160 is a planar light-emitting body composed of a plurality of LEDs, and emits white light from the back surface of the display unit 130 (backlight). The amount of light emitted from the light source unit 160 can be controlled by a PWM signal output from the light source control unit 150.

  Each LED constituting the light source unit 160 is turned on when the PWM signal output from the light source control unit 150 is High, and is turned off during the Low period. Therefore, when the duty ratio of the PWM signal output from the light source control unit 150 increases, the High period of the PWM signal becomes longer and the lighting period of the LED also becomes longer, so that the light emission amount of the light source unit 160 increases.

  When the duty ratio of the PWM signal is decreased, the High period of the PWM signal is shortened and the lighting period of the LED is also shortened, so that the light emission amount of the light source unit 160 is decreased. The LED constituting the light source unit 160 may be a white LED or a combination of a plurality of other color LEDs such as a red LED, a green LED, and a blue LED, and each color is mixed to emit white light. good.

The temperature detection unit 170 includes a temperature sensor and an A / D converter. The temperature sensor detects the ambient temperature of the LEDs constituting the light source unit 160 and outputs an analog signal as a detection result to the A / D converter. The A / D converter converts the detection signal of the temperature sensor into a digital value. The temperature detection unit 170 converts the digital value converted by the A / D converter into a Celsius temperature, and outputs the converted temperature as a detection temperature to the storage unit 140 and the light source control unit 150 (temperature detection unit).

  The target luminance value setting unit 180 receives an input of the target luminance value from the user and passes it to the storage unit 140 (setting unit). The target luminance value setting unit 180 may be, for example, an operation button or a remote controller provided on the main body of the image display device, or a PC connected to the image display device.

(Explanation of operation example)
Next, an operation example of the image display apparatus when the user sets the target luminance value will be described. The display brightness can be adjusted by changing the target brightness value held by the storage unit 140. The target luminance value is changed by the target luminance value setting unit 180. For example, the user can input an instruction to change the target luminance value to the image display device by pressing a button or the like provided on the image display device while viewing the screen.

  The user can also input an instruction to change the target luminance value by operating a computer connected to the image display device. In that case, the display brightness of the image display device is adjusted by inputting, to the image display device, an instruction to change the target brightness value held in the storage unit 140 via the communication line based on the input instruction. The

  FIG. 2 is a flowchart showing the operation of the image display apparatus in the present embodiment when the user sets the target luminance value.

  When the user changes the target luminance value in step S11 of FIG. 2, the target luminance value setting unit 180 transmits the changed target luminance value to the storage unit 140, and the storage unit 140 stores the changed target luminance value. .

  In step S <b> 12, the temperature detection unit 170 detects the ambient temperature of the LEDs constituting the light source unit 160.

  In step S13, the light source control unit 150 emits light from the light source unit 160 according to the target luminance value stored in the storage unit 140 and the ambient temperature (detected temperature) of the LED detected by the temperature detection unit 170 in step S12. Adjust the amount and control the light source brightness value.

  FIG. 3 shows the relationship between the detected temperature and the light source luminance value. In FIG. 3, the horizontal axis represents the detected temperature of the temperature detection unit 170, and the vertical axis represents the light source luminance value. The temperature threshold TH (predetermined threshold) is a fixed value determined in advance at the time of design. For example, the LED of the LED detected by the temperature detection unit 170 when the image display device is used at the upper limit temperature of the recommended environmental temperature of the image display device. It can be ambient temperature.

  When the detected temperature is equal to or higher than the temperature threshold TH, the light source control unit 150 adjusts the light emission amount of the light source unit 160 so that the light source luminance value matches the target luminance value output from the storage unit 140. When the detected temperature is lower than the temperature threshold TH, the light source control unit 150 adjusts the light emission amount of the light source unit 160 so that the light source luminance value is higher than the target luminance value by the luminance increase amount ΔBL.

  That is, the light source control unit 150 sets the initial value in the control of the light source luminance value to a value equal to the target luminance value when the detected temperature is equal to or higher than the temperature threshold TH, and when the detected temperature is lower than the temperature threshold TH, A value higher than the target luminance value is set (initial value setting means).

  Here, the luminance increase amount ΔBL will be described. When the environmental temperature at which the image display device is installed increases, the ambient temperature of the LED increases, and when the environmental temperature decreases, the ambient temperature of the LED decreases. On the other hand, the ambient temperature of the LED is also related to the light emission amount of the light source unit 160.

  When the light emission amount of the light source unit 160 increases, the ambient temperature of the LED increases as compared with before the light emission amount of the light source unit 160 increases due to an increase in the heat generation amount of the light source. When the light emission amount of the light source unit 160 decreases, the ambient temperature of the LED decreases due to a decrease in the heat generation amount of the light source unit 160 compared to before the light emission amount of the light source unit 160 decreases.

  Therefore, even if the environmental temperature rises, if the light emission amount of the light source unit 160 is reduced to reduce the heat generation amount of the light source, it is possible to suppress an increase in the ambient temperature of the LED. However, if the light emission amount of the light source unit 160 is lowered to suppress an increase in the ambient temperature of the LED, the light source luminance value is lowered, so that the display luminance is lowered and falls below the target luminance value.

  In order to avoid this, the initial value of the light source luminance value is set higher than the target luminance value in advance when the user sets the target luminance value. That is, there is enough margin to prevent the light source luminance value from falling below the target luminance value even if the light emission amount of the light source unit 160 is decreased to suppress the increase in the ambient temperature of the LED when the environmental temperature increases. Let me. This margin is the luminance increase amount ΔBL (the difference between the initial value of the light source luminance value and the target luminance value).

  The lower the temperature detected by the temperature detection unit 170 when setting the target luminance value, the higher the possibility that the ambient temperature of the LED will rise above the setting temperature due to an increase in the environmental temperature after setting the target luminance value. In that case, the emission spectrum of the LED will deviate from the setting of the target luminance value, and the display color may change.

  When an increase in ambient temperature of the LED is detected after setting the target luminance value, the luminance increases when the set temperature is low so that the light emission amount of the light source unit 160 can be reduced while suppressing the decrease in display luminance. The amount ΔBL is set to a large value.

  On the other hand, if the temperature detected by the temperature detection unit 170 at the time of setting the target luminance value is sufficiently high, the ambient temperature of the LED hardly increases further after the setting of the target luminance value, so the luminance increase amount ΔBL is a small value. And

  That is, the luminance increase amount ΔBL suppresses a decrease in display luminance when the light source luminance value is decreased by reducing the light emission amount of the light source unit 160 in order to suppress an increase in the ambient temperature of the LED after setting the target luminance value. It is the margin of the light source luminance value provided in advance so that it can be done. When the light source luminance value is higher than the target luminance value, the image signal correction unit 120 decreases the gain value (increases the correction amount for correcting the luminance value to decrease).

  Thereby, the excess (difference) of the light source luminance value with respect to the target luminance value is canceled, and the display luminance value can be made to match the target luminance value. However, if the light source luminance value becomes lower than the target luminance value, the display luminance value will be lower than the target luminance value even if the gain value is maximized (1). In order to prevent the light source luminance value from becoming lower than the target luminance value when control is performed to reduce the light source luminance value so as to suppress an increase in the ambient temperature of the LED, the light source luminance value is set in advance to the target luminance value. The luminance is increased by the amount of increase ΔBL.

  The light source control unit 150 controls the light emission amount of the light source unit 160 by changing the duty ratio of the PWM signal output to the light source unit 160, and sets the light source luminance value corresponding to the light emission amount of the light source unit 160 to the image signal correction unit 120. Output.

When the set temperature is lower than the temperature threshold TH, the light source luminance value is set to a value higher than the target luminance value, and therefore the display luminance value is higher than the target luminance value at this stage. When the set temperature is equal to or higher than the temperature threshold TH, the light source luminance value is set to a value equal to the target luminance value, and at this stage, the display luminance value matches the target luminance value.

  In step S14, the image signal correction unit 120 corrects the luminance value of the image signal so that the display luminance matches the target luminance value. In step S13, when the detected temperature is equal to or higher than TH, the image signal correction unit 120 sets the gain value to 1 because the light source luminance value output from the light source control unit 150 matches the target luminance value. That is, the image signal correction unit 120 does not perform correction that reduces the luminance value of the image signal.

  In step S13, when the detected temperature is lower than TH, the light source luminance value output from the light source control unit 150 is higher than the target luminance value by the luminance increase amount ΔBL, so the image signal correction unit 120 sets the luminance value of the image signal. Make corrections to lower. In this case, for example, when the target luminance value is L and the light source luminance value is BL, the image signal correction unit 120 sets the gain value G to L / BL. The image signal correction unit 120 multiplies each pixel of the image signal by the calculated gain value G to correct the luminance value of the image signal.

  Through the processing in step S14 described above, the display luminance matches the target luminance value. In this manner, an image for setting an initial value of a correction amount for reducing the luminance value of the image signal so that the display luminance value becomes equal to the target luminance value according to the light source luminance value determined according to the set temperature. The signal correction unit 120 functions as an initial value setting unit of the present invention.

  In step S <b> 15, the temperature detection unit 170 detects the ambient temperature of the LEDs constituting the light source unit 160.

  In step S16, the storage unit 140 stores the detected temperature detected by the temperature detection unit 170 in step S15 as the set time temperature.

  Subsequently, an operation example of the image display device after the user sets the target luminance value will be described. FIG. 4 is a flowchart showing the operation content of the steady process of the image display apparatus. After the user sets the target luminance value, the image display device periodically executes the process shown in FIG.

  In step S <b> 21, the temperature detection unit 170 detects the ambient temperature of the LEDs constituting the light source unit 160.

  In step S22, the light source control unit 150 compares the temperature detected by the temperature detection unit 170 in step S21 with the setting temperature stored in the storage unit 140 when setting the target luminance value. As a result of the comparison, if the detected temperature is higher than the set temperature, the light source controller 150 proceeds to step S23. If the detected temperature is lower than the set temperature, the light source controller 150 proceeds to step S25. When the detected temperature is equal to the set temperature, the light source control unit 150 ends the process of the flowchart shown in FIG.

  If the detected temperature is higher than the set temperature, the light source control unit 150 performs control to lower the light source luminance value in step S23 in order to lower the ambient temperature of the LED. Specifically, the light source control unit 150 reduces the light emission amount of the light source unit 160 by changing the duty ratio of the PWM signal output to the light source unit 160. At this time, the light source control unit 150 reduces the light emission amount of the light source unit 160 within a range where the light source luminance value does not fall below the target luminance value. Further, the light source control unit 150 outputs the changed light source luminance value to the image signal correction unit 120.

In step S24, the image signal correction unit 120 calculates a gain value based on the light source luminance value changed by the light source control unit 150 in step S23. For example, when the target luminance value is L1 and the light source luminance value after the light source control unit 150 has changed in step S23 is BL1, the image signal correction unit 120 sets the gain value G1 to L1 / BL1. The image signal correction unit 120 multiplies each pixel of the image signal by the calculated gain value G1, and corrects the luminance value of the image signal. As a result, the display brightness matches the target brightness value.

  On the other hand, when the detected temperature is lower than the preset temperature, the light source control unit 150 performs control to increase the light source luminance value in order to increase the ambient temperature of the LED in step S25. Specifically, the light source control unit 150 increases the light emission amount of the light source unit 160 by changing the duty ratio of the PWM signal output to the light source unit 160. Further, the light source control unit 150 outputs the changed light source luminance value to the image signal correction unit 120.

  In step S26, the image signal correction unit 120 calculates a gain value based on the light source luminance value changed by the light source control unit 150 in step S25. For example, when the target luminance value is L2 and the light source luminance value after the light source control unit 150 has changed in step S25 is BL2, the image signal correction unit 120 sets the gain value G2 to L2 / BL2. The image signal correction unit 120 multiplies each pixel of the image signal by the calculated gain value G2, and corrects the luminance value of the image signal. As a result, the display brightness matches the target brightness value.

  By executing the control of the flowchart shown in FIG. 4 as described above, when the detected temperature is higher than the set temperature, the light emission amount of the light source unit 160 is lowered, so that the heat generation amount of the light source is reduced, and the LED Ambient temperature decreases. Further, when the detected temperature is lower than the set temperature, the light emission amount of the light source unit 160 is increased, so that the heat generation amount of the light source is increased and the ambient temperature of the LED is increased.

  By periodically executing the process of the flowchart shown in FIG. 4, the light source luminance value is controlled so that the detected temperature approaches the set temperature. Therefore, even if there is a disturbance with respect to the ambient temperature of the LED such as a change in the environmental temperature after the user sets the target brightness value, the ambient temperature of the LED is prevented from greatly changing from the set temperature due to the disturbance. The Therefore, after the user sets the target luminance value, the change in the emission spectrum of the LED is suppressed, and the change in display color is suppressed.

  In the above control, when the detected temperature rises above the set temperature, the light emission amount of the light source unit 160 is lowered, but the image signal correction unit 120 raises the gain value in a direction approaching 1 to lower the luminance value of the image signal. Since the correction amount is reduced, it is possible to suppress a decrease in display luminance as a result.

  If the set temperature is lower than the temperature threshold TH when the user sets the target luminance value, the initial value of the light source luminance value is set to be brighter than the target luminance value according to the flowchart shown in FIG. Therefore, even if the light emission amount of the light source unit 160 is decreased according to the flowchart of FIG.

  Further, when the detected temperature becomes lower than the set temperature, the light emission amount of the light source unit 160 is increased, but the image signal correction unit 120 cancels the increase in the light source luminance value due to the increase in the light emission amount of the light source unit 160. Decrease the gain value. Therefore, since the correction amount for reducing the luminance value of the image signal is increased, the display luminance does not increase as a result.

  Subsequently, after the user sets the target luminance value, the operation of the image display apparatus when the power of the image display apparatus is once turned off and then turned on will be described.

When the power of the image display device is turned on, the power supply portion inside the image display device starts to generate heat. Moreover, since the LED of the light source unit 160 is lit, the light source unit 160 starts to generate heat. FIG. 5 shows an example of a change in ambient temperature of the LED after the power is turned on in the conventional image display device.

  In FIG. 5, the horizontal axis represents the elapsed time since the power was turned on, and the vertical axis represents the ambient temperature of the LED. Since the heat generation inside the display starts after the power is turned on, the ambient temperature of the LED gradually increases as time elapses. Until the ambient temperature of the LED converges, the display color changes due to the temperature characteristics of the LED. In addition, when the convergence value of the ambient temperature of the LED is not equal to the ambient temperature of the LED when the user sets the target brightness value (setting temperature), the display color is different from when the target brightness value is set. It will shift.

  In the image display apparatus according to the present embodiment, the process of the flowchart shown in FIG. 4 is executed periodically (at regular intervals) immediately after the power is turned on.

  In step S <b> 21 of FIG. 4, the temperature detection unit 170 detects the ambient temperature of the LEDs constituting the light source unit 160.

  In step S22, the light source control unit 150 compares the temperature detected by the temperature detection unit 170 in step S21 with the setting temperature stored in the storage unit 140 when setting the target luminance value. As a result of the comparison, if the current detected temperature is higher than the set temperature, the light source controller 150 proceeds to step S23. If the detected temperature is lower than the set temperature, the light source controller 150 proceeds to step S25. When the detected temperature is equal to the set temperature, the light source control unit 150 ends the process of the flowchart shown in FIG.

  Immediately after the power is turned on, the inside of the display is in the middle of gradually starting to generate heat, so the ambient temperature of the LED is still low. Accordingly, since the detected temperature is lower than the set temperature, the light source control unit 150 proceeds to step S25.

  In step S <b> 25, the light source control unit 150 performs control to increase the light source luminance value in order to increase the ambient temperature of the LED to approach the set temperature. Specifically, the light source control unit 150 changes the duty ratio of the PWM signal output to the light source unit 160 and increases the light emission amount of the light source unit 160. In addition, the light source control unit 150 outputs the light source luminance value after increasing the light emission amount of the light source unit 160 to the image signal correction unit 120.

  In step S26, the image signal correction unit 120 calculates a gain value based on the light source luminance value changed by the light source control unit 150 in step S25. For example, when the target luminance value is L3 and the light source luminance value after the light source control unit 150 has changed in step S25 is BL3, the image signal correction unit 120 sets the gain value G3 to L3 / BL3. The image signal correction unit 120 multiplies each pixel of the image signal by the calculated gain value G3 to correct the luminance value of the image signal. Here, since the light source luminance value is increased, the gain value is decreased. As a result, the increase in the light source luminance value is offset by the decrease in the gain value, and the display luminance matches the target luminance value.

  FIG. 6 shows a change in ambient temperature of the LEDs constituting the light source unit 160 when the above-described control is performed after the power is turned on in the image display apparatus according to the present embodiment. In FIG. 6, the horizontal axis represents the elapsed time since the power was turned on, and the vertical axis represents the ambient temperature of the LED detected by the temperature detection unit 170.

Immediately after the power is turned on, since the detected temperature is lower than the set temperature, the processing of the flowchart shown in FIG. 4 is executed, so that the image display device operates to increase the light emission amount of the light source. Therefore, the amount of heat generated by the light source is increased, and the ambient temperature of the LED rapidly increases compared to the change in ambient temperature of the LED after power-on in the conventional image display device shown in FIG. Time to approach is shortened.
Therefore, the period during which the display color shift occurs due to the difference between the ambient temperature of the LED and the set temperature is shorter than that of the conventional image display device.

  In the image display apparatus according to the present embodiment, the light source luminance value is controlled by the process shown in FIG. 4, so that the ambient temperature of the LED converges to the set temperature as shown in FIG. 6. Therefore, the LED emission spectrum is prevented from deviating from the LED emission spectrum when the user sets the target luminance value, and the display color is stabilized.

  When there are a plurality of temperature detection units 170, when the brightness value of the screen is adjusted so as not to be uneven, the individual temperature detection units 170 perform the processing of the flow from step S12 onward in FIG. The detected temperature when there is no unevenness in the brightness value of the screen is stored in the storage unit 140 as the setting temperature in the flow of FIG. Even when the environmental temperature changes, the variation in display color can be reduced while suppressing unevenness.

  As described above, according to this embodiment, even when the environmental temperature in which the image display device is installed changes, the variation in display color can be reduced. Further, since the ambient temperature of the LED is controlled by adjusting the light emission amount of the LED, a cooling device such as a fan is not required, which is advantageous for making the image display device main body thin.

In the image display apparatus of this embodiment, the display color approaches the display color at the time of target luminance value adjustment immediately after the power is turned on, and stable display is performed with the display color. Suitable for applications that require display.
Further, since the ambient temperature of the LED operates so as to approach the set temperature which is the temperature when the user sets the target brightness value, the display color when the user sets the target brightness value can be maintained.

120 image signal correction unit, 130 display unit, 150 light source control unit, 160 light source unit, 170 temperature detection unit, 180 target luminance value setting unit

Claims (7)

A backlight having one or more light emitting elements;
A display panel for displaying an image by changing the transmittance of light incident from the backlight for each pixel according to an input image signal;
Backlight control means for controlling a light source luminance value, which is a luminance value of a backlight, by adjusting a light emission amount of the light emitting element;
Image processing means for correcting a luminance value for an image signal input to the display panel;
Temperature detecting means for detecting the temperature around the light emitting element of the backlight; and
Setting means for setting a target luminance value which is a target value of the display luminance of the display panel;
When the set temperature, which is the ambient temperature of the light emitting element detected by the temperature detecting means when the target brightness value is set by the setting means, is lower than a predetermined threshold, it is controlled by the backlight control means. The image processing is performed such that the initial value of the light source luminance value is set to a value higher than the target luminance value, and the display luminance is equal to the target luminance value according to a difference between the initial value of the light source luminance value and the target luminance value. Initial value setting means for setting an initial value of a correction amount for reducing the luminance value of the image signal by the means;
Have
After the target brightness value is set by the setting means,
The backlight control unit adjusts the light emission amount of the light emitting element within a range where the light source luminance value does not fall below the target luminance value, thereby setting the temperature around the light emitting element detected by the temperature detecting unit. Control the light source brightness value so that it approaches the hourly temperature,
The image processing means is a correction amount for reducing the brightness value of the image signal so that the display brightness becomes equal to the target brightness value in accordance with a difference between the light source brightness value controlled by the backlight control means and the target brightness value. Adjust the
An image display device characterized by that. The backlight control means includes
When the ambient temperature of the light emitting element detected by the temperature detecting means becomes higher than the set temperature, the light source luminance value is reduced by reducing the light emission amount of the light emitting element,
When the ambient temperature of the light emitting element detected by the temperature detecting means is lower than the set temperature, the light source luminance value is increased by increasing the light emission amount of the light emitting element,
The image processing means includes
When the backlight control means decreases the light source luminance value, the correction amount for decreasing the luminance value of the image signal is reduced,
The image display apparatus according to claim 1, wherein when the backlight control unit increases the light source luminance value, the correction amount for decreasing the luminance value of the image signal is increased.   The initial value setting means, when the setting temperature is lower than a predetermined threshold, the initial value of the light source luminance value is set such that the difference between the initial value of the light source luminance value and the target luminance value increases as the setting temperature decreases. The image display device according to claim 1, wherein: is set. Storage means for storing a target luminance value, a set temperature, an initial value of the light source luminance value, and an initial value of a correction amount for reducing the luminance value of the image signal;
Immediately after the image display device is turned on,
The backlight control means uses the initial value of the light source luminance value read from the storage means as the initial value of the light source luminance value, and reads the ambient temperature of the light emitting element detected by the temperature detection means from the storage means. Control the light source brightness value to approach the set temperature
The image processing means uses the initial value of the correction amount for reducing the luminance value of the image signal read from the storage means as the initial value of the correction amount for reducing the luminance value of the image signal, and is controlled by the backlight control means. Adjusting the correction amount for reducing the luminance value of the image signal so that the display luminance is equal to the target luminance value according to the difference of the light source luminance value with respect to the target luminance value read from the storage unit.
The image display device according to claim 1, wherein the image display device is an image display device.   5. The image display device according to claim 1, wherein the light emitting element includes a white LED having a characteristic that an emission spectrum changes according to an ambient temperature.   5. The light emitting device according to claim 1, wherein the light emitting element includes at least one of a red LED, a green LED, and a blue LED having a characteristic that an emission spectrum changes according to an ambient temperature. The image display device described. A backlight having one or more light emitting elements;
A display panel for displaying an image by changing the transmittance of light incident from the backlight for each pixel according to an input image signal;
A method for controlling an image display device comprising:
A backlight control step of controlling a light source luminance value, which is a luminance value of a backlight, by adjusting a light emission amount of the light emitting element;
An image processing step of correcting a luminance value for an image signal input to the display panel;
A temperature detection step of detecting a temperature around the light emitting element of the backlight; and
A setting step of setting a target luminance value that is a target value of the display luminance of the display panel;
When the set temperature, which is the ambient temperature of the light emitting element detected by the temperature detecting step when the target luminance value is set by the setting step, is lower than a predetermined threshold value, it is controlled by the backlight control step. The image processing is performed such that the initial value of the light source luminance value is set to a value higher than the target luminance value, and the display luminance is equal to the target luminance value according to a difference between the initial value of the light source luminance value and the target luminance value. An initial value setting step for setting an initial value of a correction amount for reducing the luminance value of the image signal in the process;
Have
After the target brightness value is set by the setting step,
The backlight control step adjusts the light emission amount of the light emitting element within a range where the light source luminance value does not fall below the target luminance value, thereby setting the temperature around the light emitting element detected by the temperature detecting step. Control the light source brightness value so that it approaches the hourly temperature,
The image processing step includes a correction amount for reducing the luminance value of the image signal so that the display luminance becomes equal to the target luminance value according to a difference between the light source luminance value controlled by the backlight control step and the target luminance value. Adjust the
And a control method for the image display device.

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