JP6288972B2 - Image display apparatus and control method thereof - Google Patents

Description

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

  In recent years, a liquid crystal display device having a backlight using a light emitting diode (LED) as a light source has become widespread. In particular, a liquid crystal display device having a direct type backlight in which a plurality of LEDs are arranged in an array is rapidly spreading. In the direct type backlight, local dimming control for partially adjusting the light emission amount can be performed relatively easily. By performing local dimming (local dimming) control, it is possible to improve the contrast ratio (ratio between maximum luminance and minimum luminance) and reduce power consumption.

  Here, as a method of adjusting the light emission amount of the backlight, there are a method of adjusting the current value supplied to the LED and a method of adjusting the lighting time of the LED. In the method of adjusting the current value supplied to the LED, the light emission luminance (instantaneous value) of the LED can be reduced by reducing the current value, and the light emission amount of the LED can be reduced. That is, the brightness of the backlight can be reduced by reducing the current value. Then, by increasing the current value, the light emission luminance of the LED can be increased, and as a result, the light emission amount of the LED can be increased. That is, the brightness of the backlight can be increased by increasing the current value. In the method of adjusting the lighting time of the LED, the light emission amount of the LED can be increased by extending the lighting time, and the light emission amount of the LED can be reduced by shortening the lighting time.

  Generally, a method of adjusting the lighting time is used because of high power efficiency. The adjustment of the lighting time is called PWM (Pulse Width Modulation) control. In the PWM control, the ratio (duty ratio) between the lighting time and the light-off time in a certain period (light emission control period) is changed.

  Here, the LED has characteristics such as individual differences, aging deterioration, temperature deterioration, and the like. Therefore, in the direct type backlight described above, it has been difficult to keep the light emission amount of the backlight (for example, the light emission amount in the light emission control period) constant and uniform over a long period of time. Therefore, as a method of keeping the light emission amount of the backlight constant and uniform, the light emission luminance of each light source unit is detected using an optical sensor provided in the vicinity of the backlight, and each light source is adjusted so that the detected value approaches the target value. A method for correcting the current value supplied to the unit (so-called feedback control) has been proposed (see, for example, Patent Document 1). The light source unit is, for example, the minimum unit of the backlight that can control the light emission amount. In other words, the backlight has a configuration capable of controlling the light emission amount for each light source unit.

JP 2006-40764 A

  However, in general, noise is mixed in the detection result of the light emission luminance (for example, a voltage value corresponding to the light emission luminance). Therefore, in order to increase the accuracy of the detection result, it is necessary to acquire the detected value of the light emission luminance a plurality of times, or to provide high-frequency noise by providing an LPF (low-pass filter) in the sensor circuit. When such processing is performed, the time required for the light sensor to detect the light emission luminance increases. Therefore, when the lighting time for one time is short (for example, the display mode of the image display device is a low luminance mode in which the brightness on the screen is darkened, and the lighting time is shortened in order to reduce the light emission amount of the backlight. In some cases, the detection of the emission luminance could not be completed within the lighting time. If the detection of the light emission brightness cannot be completed within the lighting time, the detection result cannot be obtained or an incorrect detection result may be obtained. Therefore, the amount of light emitted from the backlight (light emitting unit) is controlled with high accuracy. Can not do it.

  An object of this invention is to provide the technique which can control the light emission amount of a light emission part with high precision.

The image display device of the present invention is
A light emitting means comprising an LED light source;
A display panel that displays an image on a screen by transmitting light emitted from the light emitting means;
Determining means for determining the light emission luminance of the light emitting means based on image data;
Control means for controlling the light emission amount of the LED light source by controlling the LED light source by PWM (Pulse Width Modulation) ;
First detection means for detecting the amount of light from the LED light source;
Second detection means for detecting the temperature of the LED light source;
Have
When the temperature of the LED light source detected by the second detection unit is equal to or lower than a predetermined temperature and the light emission luminance determined by the determination unit is lower than the first predetermined luminance, the control unit, When the first detection means detects light, an extension process for extending the lighting time of the LED light source is executed.

The control method of the image display device of the present invention includes:
A control method for an image display device, comprising: a light emitting unit including an LED light source; and a display panel that displays an image on a screen by transmitting light emitted from the light emitting unit.
A determining step of determining the light emission brightness of the light emitting means based on image data;
A control step of controlling a light emission amount of the LED light source by controlling the LED light source by PWM (Pulse Width Modulation) ;
A first detection step of detecting light from the LED light source;
A second detection step of detecting the temperature of the LED light source;
Have
In the control step, when the temperature of the LED light source detected in the second detection step is equal to or lower than a predetermined temperature, and the light emission luminance determined in the determination step is lower than the first predetermined luminance, When detecting light in the first detection step, an extension process for extending a lighting time of the LED light source is performed.

  ADVANTAGE OF THE INVENTION According to this invention, the light quantity detection accuracy from a light source can be raised, suppressing the tint fluctuation | variation of the light source of a light emission part, and the light emission amount of a light emission part can be controlled with high precision.

1 is a block diagram illustrating an example of a configuration of a light source device according to a first embodiment. FIG. 3 is a schematic diagram illustrating an example of a configuration of a backlight unit according to the first embodiment. 7 is a flowchart illustrating an example of a method for recording a target light sensor value and an initial lighting time according to the first embodiment. The figure which shows an example of the nonuniformity measurement condition which concerns on Example 1, a nonuniformity measurement result, and an initial lighting time The figure which shows an example of the lighting control of the light source unit at the time of normal operation based on Example 1. FIG. The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 1. FIG. The figure which shows an example of the target optical sensor value which concerns on Example 1. FIG. 10 is a flowchart illustrating an example of a light emission amount control process according to the first embodiment. The figure which shows an example of the lighting control of the light source unit at the time of normal operation based on Example 1. FIG. The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 1. FIG. The figure which shows an example of the lighting control of the light source unit at the time of normal operation based on Example 1. FIG. The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 1. FIG. FIG. 6 is a block diagram illustrating an example of a configuration of a light source device according to a second embodiment. 10 is a flowchart illustrating an example of a light emission amount control process according to the second embodiment. The figure which shows an example of the relationship between the electric current value which concerns on Example 2, and luminous efficiency. An example of the table showing the relationship between the current value and the correction value according to the second embodiment The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 2. FIG. FIG. 6 is a block diagram illustrating an example of a configuration of a light source device according to a third embodiment. 10 is a flowchart illustrating an example of a light emission amount control process according to the third embodiment. An example of the table showing the lighting time after the extension concerning Example 3 An example of the table showing the electric current value after reduction concerning Example 3 The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 3. FIG. FIG. 6 is a block diagram illustrating an example of a configuration of a light source device according to a fourth embodiment. Schematic diagram showing an example of the configuration of the backlight unit according to the fourth embodiment. 9 is a flowchart illustrating an example of a method for recording a target light sensor value and an initial lighting time according to the fourth embodiment. The figure which shows an example of the target optical sensor value which concerns on Example 4. FIG. 10 is a flowchart illustrating an example of a light emission amount control process according to the fourth embodiment. An example of the table showing the lighting time extension magnification and the current value reduction magnification according to the fourth embodiment The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 4. FIG. The figure which shows an example of the temperature transition when the lighting time concerning Example 4 changes The figure which shows an example of the lighting control of the light source unit at the time of the optical sensor value detection which concerns on Example 4. FIG.

<Example 1>
Hereinafter, a light source device and a control method thereof according to Embodiment 1 of the present invention will be described.

  In this embodiment, when the state of the light source device is a low-brightness state (a state where one lighting time of the light source included in the light source device is shorter than the sensor detection time), the one lighting time of the light source is extended. The value of current supplied to is reduced. The sensor detection time is a time required for detecting light from the light source by the optical sensor. Then, the light emission amount of the light source is controlled based on the detection result (detection result of the optical sensor) in a state where the lighting time is extended and the current value is reduced. Thereby, even if the state of the light source device is a low luminance state, a highly accurate detection result can be obtained, and the light emission amount of the light source can be controlled with high accuracy. The light source device controls the turning on and off of the light source every certain period (light emission control period). The light emission amount is, for example, the light emission amount in one lighting or the light emission amount in the light emission control period.

  In this embodiment, the light emission amount is constant if the value obtained by multiplying the lighting time by the current value is constant.

  First, the configuration of the light source device according to the present embodiment will be described with reference to FIGS. 1 and 2. The light source device according to the present embodiment can be used as a backlight of an image display device such as a liquid crystal display device, or a lighting device such as a street lamp or a room lamp. In this embodiment, an example in which the light source device is a backlight of an image display device will be described. In the image display apparatus according to the present embodiment, the display panel displays an image on the screen by transmitting light emitted from the backlight. The image display device is not limited to a transmissive liquid crystal display device. The image display device may be a display device having an independent light source. For example, the image display device may be a reflective liquid crystal display device. In addition, the image display device may be a MEMS shutter type display using a MEMS (Micro Electro Mechanical System) shutter instead of the liquid crystal element.

  FIG. 1 is a block diagram illustrating an example of the configuration of the light source device according to the present embodiment.

  A light source device 100 (hereinafter referred to as a backlight) shown in FIG. 1 includes a backlight unit 110 and a control unit 120.

  The backlight unit 110 includes a plurality of light source units (shown by broken lines in the drawing) and a plurality of optical sensors 112. The light source unit is, for example, the minimum unit of the backlight 100 (backlight unit 110) that can control the light emission amount. In other words, the backlight 100 has a configuration capable of controlling the light emission amount for each light source unit. One light source unit has a plurality of LEDs 111 connected in series as a light source.

  The control unit 120 includes a light sensor value acquisition unit 121, a backlight control unit 122, a target light sensor value storage unit 123, an initial lighting time storage unit 124, and a backlight drive unit 125. The backlight control unit 122 includes a lighting time adjustment unit 130 and a current value adjustment unit 131.

  FIG. 2 is a schematic diagram illustrating an example of the arrangement of the LEDs 111 and the optical sensors 112 of the backlight unit 110 according to the present embodiment. In the example of FIG. 2, the backlight unit 110 is divided into six light source units 0 to 5 in 2 rows and 3 columns. In one light source unit, 16 LEDs are arranged in an array as a light source. The 16 LEDs of one light source unit are lit (emitted) with the same current value and lighting time. The light sources 0 to 5 are provided with optical sensors A to F, respectively.

  The number of light source units may be more or less than six. The number of light source units may be one. A plurality of photosensors may be provided for one light source unit, or a plurality of photosensors may be provided for a plurality of light source units.

  Here, an outline of a process for keeping the light emission amount of the backlight 100 constant and uniform will be described.

  In the target light sensor value storage unit 123, a target light sensor value (target light sensor value for each light source unit) set in the adjustment process at the time of production is recorded in advance. The target light sensor value is a target value of light (light from the light source unit) detected by the light sensor.

  The initial lighting time storage unit 124 stores lighting times (one lighting time after unevenness correction for each light source unit) set in the adjustment process at the time of production.

  In the initial state, the backlight 100 is repeatedly turned on and off according to the lighting time stored in the initial lighting time storage unit 124. At this time, a predetermined current value is supplied to each light source unit.

  When the backlight 100 is turned on, the backlight control unit 122 periodically performs a light emission amount control process. The light emission amount control processing is control processing for controlling (correcting) the light emission amount of each light source unit based on the detection result (light sensor value) of the light sensor. The optical sensor value is, for example, light emission luminance (instantaneous value) or light amount (cumulative value).

  Specifically, in the light emission amount control process, the optical sensor value acquisition unit 121 acquires an optical sensor value from the optical sensor for each light source unit in response to an instruction from the backlight control unit 122. The backlight control unit 122 compares the optical sensor value acquired by the optical sensor value acquisition unit 121 with the target optical sensor value stored in the target optical sensor value storage unit 123 for each light source unit. For each light source unit, the backlight control unit 122 determines (adjusts) the current value supplied to the light source unit and the lighting time of the light source unit according to the comparison result. Then, the backlight control unit 122 outputs a current value (adjusted current value) and lighting time (adjusted lighting time) for each light source unit to the backlight driving unit 125.

  The backlight drive unit 125 drives (lights) the light source unit for each light source unit with the current value and lighting time output from the backlight control unit 122.

  One lighting time of each light source unit can be changed. For example, the user can adjust the brightness of the backlight (lighting time of each light source unit). When the lighting time of one light source unit is shorter than a predetermined time, the light emission amount of the light source unit cannot be controlled with high accuracy. Specifically, in the light emission amount control process, the light sensor value cannot be acquired, or an inaccurate light sensor value is acquired, and thus the light emission amount of the light source unit cannot be accurately controlled. In this embodiment, in such a case, an accurate photosensor value is obtained by adjusting the lighting time and the current value using the lighting time adjusting unit 130 and the current value adjusting unit 131, and thus the light source unit of the light source unit. It becomes possible to control the light emission amount with high accuracy.

  In this embodiment, it is assumed that the predetermined time is a time required for detecting light by the optical sensor (a time required for acquiring the optical sensor value in the light emission amount control process).

  Note that the brightness of the backlight may be automatically changed based on the surrounding environment, image data, and the like.

  Next, a method for recording the target light sensor value and the initial lighting time will be described with reference to FIG. FIG. 3 is a flowchart illustrating an example of a method for recording the target light sensor value and the initial lighting time. The process flow of FIG. 3 is implemented in the adjustment process at the time of production, for example.

  First, in S150, the backlight control unit 122 instructs the backlight driving unit 125 to light all the LEDs 111 with a predetermined current value and lighting time. The backlight drive unit 125 turns on all the LEDs 111 with a predetermined current value and lighting time according to an instruction from the backlight control unit 122. An example of the current value and lighting time for each light source unit at this time is shown in FIG. In the example of FIG. 4, 500 is set as the current value of each light source unit. In addition, 500 is set as the lighting time of each light source unit.

  The current value (current control value) is an integer from 0 to 1000, and the current value (value of the actually supplied current) increases linearly as the current control value increases. For example, when the current control value is 1000, double the current when the current control value is 500 is supplied to the light source unit. When the current control value is 0, no current is supplied to the light source unit, and the light source unit is turned off.

  The lighting time (lighting time control value) is an integer from 0 to 1000, and the lighting time (actual time) increases linearly as the lighting time control value increases. For example, when the lighting time control value is 1000, the actual lighting time is twice as long as the lighting time control value is 500. When the lighting time control value is 0, the actual lighting time is 0, and the light source unit is turned off.

  The range of the current value (current control value) and lighting time (lighting time control value) is not limited to the above values (0 to 1000). Further, the actual current value may increase nonlinearly with respect to the increase in the current control value, or the actual current value may decrease with respect to the increase in the current control value. The same applies to the lighting time control value.

  Next, in S151, luminance unevenness in the display area (luminance unevenness on the screen of the image display device) is measured by an external measuring instrument (not shown). And the backlight control part 122 correct | amends the lighting time of each light source unit so that the brightness | luminance of a display area may become fixed and uniform based on the measurement result of a brightness nonuniformity. For example, when the unevenness measurement result (the ratio of the luminance on the screen to the expected luminance) of the light source unit 0 is 95%, the lighting time is extended to increase the light emission amount of the light source unit 0. Specifically, since the lighting time before adjustment is 500, the lighting time is adjusted to 526 (= 500 × 100/95). Thereby, the luminance of the deficiency (5%) is complemented. An example of the unevenness measurement result for each light source unit and the adjusted lighting time (initial lighting time) are shown in FIG.

  In S <b> 152, the backlight control unit 122 records the initial lighting time for each light source unit in the initial lighting time storage unit 124.

  In S151, both the lighting time and the current value may be adjusted, and the adjusted lighting time and current value may be recorded. In that case, in the initial state, the backlight 100 is lit with the adjusted lighting time and current value. Alternatively, only the current value may be adjusted and the adjusted current value may be recorded. In that case, in the initial state, the backlight 100 is lit with the adjusted current value and a predetermined lighting time.

  Next, in S153, the backlight control unit 122 instructs the backlight driving unit 125 to create a period in which only a specific light source unit is lit. For example, it is assumed that each light source unit is turned on / off within the light emission control period as shown in FIG. When the backlight control unit 122 instructs to create a period in which only the light source unit 0 is lit, the backlight driving unit 125 temporarily adjusts the lighting period of the backlight as shown in FIG. Create a period when only unit 0 is lit. At this time, the backlight drive unit 125 notifies the backlight control unit 122 that a period during which only a specific light source unit is lit is created.

  Then, when the backlight driving unit 125 notifies the backlight control unit 122 that a period during which only a specific light source unit is lit is generated, the process proceeds to S154. In S154, the backlight control unit 122 instructs the optical sensor value acquisition unit 121 to acquire the optical sensor value of a specific light source unit. The optical sensor value acquisition unit 121 acquires an optical sensor value from an optical sensor provided in a specific light source unit. The optical sensor value is acquired a plurality of times for noise removal. Then, representative values (average value, mode value, intermediate value, etc.) of the plurality of acquired optical sensor values are acquired as final optical sensor values. Further, a time difference occurs until light from the specific unit is detected in a state where only the specific light source unit is turned on. Therefore, in order to determine the final optical sensor value, it is necessary to maintain a state where only a specific light source unit is lit.

  In addition, the process which acquires an optical sensor value from an optical sensor is performed only once, the process (filter process) which removes noise is performed to the acquired optical sensor value, and the optical sensor value after a filter process is made into final optical sensor value You may get as Further, the final photosensor value may be obtained by performing filtering on the representative value (representative value of a plurality of photosensor values).

  Next, in S155, the backlight control unit 122 records the optical sensor value acquired in S154 in the target optical sensor value storage unit 123 as the target optical sensor value.

  In step S156, the backlight control unit 122 determines whether the target light sensor values of all the light source units have been recorded. When the target light sensor values of all the light source units are recorded, this processing flow is ended. When there is a light source unit in which the target light sensor value is not recorded, the backlight control unit 122 sets a light source unit in which the target light sensor value is not recorded as the specific light source unit. Then, the process returns to S153.

  An example of the target light sensor value for each light source unit determined in this way is shown in FIG.

  Next, a method for controlling the light emission amount of the backlight 100 according to the present embodiment (light emission amount control process) will be described with reference to FIG. FIG. 8 is a flowchart showing an example of a method for controlling the light emission amount of the backlight 100, specifically, a method for keeping the light emission amount (brightness) of the entire backlight 100 constant. The processing flow in FIG. 8 is performed at regular intervals, for example, during a period in which the user uses the image display device. The certain time is a time during which the light emission amount does not change significantly due to a temperature change or the like, such as 10 seconds.

  The execution timing of the processing flow in FIG. 8 is not limited to the above timing. For example, the processing flow of FIG. 8 may be performed with a user's instruction to correct the light emission amount as a trigger.

  First, in S170, the backlight control unit 122 determines whether or not the lighting time is sufficient when only the specific light source unit is turned on to acquire the optical sensor value. Specifically, whether or not the lighting time of one specific light source unit is longer than the time required to detect light with the optical sensor (the time required to acquire the optical sensor value in the light emission amount control process). Determine whether.

The lighting time varies when, for example, the user makes a setting for adjusting the brightness of the image display device (screen). Specifically, it is assumed that the backlight luminance when the target sensor value and the initial lighting time are recorded is 200 cd / m ² . When the user adjusts the brightness of the image display device and reduces the backlight luminance to 100 cd / m ² , the lighting time of all the light source units is reduced to half. The backlight luminance may be adjusted by adjusting only the current value or both the lighting time and the current value.

  As described above, when acquiring the optical sensor value, it is necessary to maintain a state where only a specific light source unit is lit for a certain period of time. Therefore, when the user greatly reduces the backlight luminance, there may be a case where a sufficient period for acquiring the optical sensor value cannot be secured. For example, when the actual lighting time when the lighting time (lighting time control value) is 1000 is 12 ms and the time required to detect light by the optical sensor is 1 ms, the lighting time of a specific light source unit Must be greater than or equal to 84 (= 1000/12).

  In S170, it is determined whether or not the lighting time X of the specific light source unit is equal to or longer than the time 84 required to detect light with the optical sensor. Note that information on the time required to detect light by the optical sensor is recorded in the backlight 100 in advance.

  If the lighting time X is less than 84 (S170: No), the process proceeds to S171. When the lighting time X is 84 or more (S170: Yes), the process proceeds to S173.

  In S171, the backlight control unit 122 extends the lighting time of the specific light source unit during the light emission amount control process so that the accurate light sensor value can be acquired in a state where only the specific light source unit is turned on. Execute the process. The lighting time is extended using the lighting time adjusting unit 130. Specifically, the lighting time is extended beyond the time necessary for detecting light with the optical sensor. For example, when the lighting time before the extension of a specific light source unit (set lighting time) is 50, as shown in FIG. 9, the lighting time is shorter than the time required to detect light by the optical sensor. The optical sensor value cannot be acquired or the inaccurate optical sensor value is acquired. The lighting time 50 is multiplied by 1.68 by the processing of S171. Thereby, the lighting time 50 is extended to the same time 84 as the time required for detecting light with the optical sensor.

  In addition, the lighting time after extension does not need to correspond with the time required in order to detect light with an optical sensor. The lighting time after the extension may be shorter or longer than the time necessary for detecting light with the optical sensor. However, from the viewpoint of light detection accuracy, it is preferable that the lighting time is extended beyond the time necessary for detecting light with the optical sensor.

  Next to S171, in S172, the backlight control unit 122 reduces the current value supplied to the specific light source unit so that the increase in the amount of light emission due to the extension of the lighting time in S171 is suppressed. The current value is reduced using the current value adjusting unit 131. In this embodiment, the current value is reduced so that the value obtained by multiplying the lighting time after extension by the current value after reduction matches the value obtained by multiplying the lighting time before extension by the current value before reduction. For example, when the lighting time of a specific light source unit is extended by 1.68 times in S171, the current value supplied to the specific light source unit is multiplied by 0.596 (= 1 / 1.68). As a result, if the current value (set current value) before reduction of a specific light source unit is 500, the current value after reduction is 298.

  Following the processing in S172, the processing proceeds to S173.

  The method for reducing the current value is not limited to the above method. For example, the value obtained by multiplying the lighting time after extension by the current value after reduction may be larger or smaller than the value obtained by multiplying the lighting time before extension by the current value before reduction. What is necessary is just to suppress the increase in the light emission amount by extending the lighting time in S171, and the magnitude of the suppression amount does not matter.

  In S173, the backlight control unit 122 instructs the backlight driving unit 125 to create a period in which only a specific light source unit is lit. Specifically, in the case of Yes determination in S170, an instruction is made to create a period in which only a specific light source unit is lit with the set lighting time and the set current value. In the case of No determination in S170, an instruction is given to create a period in which only a specific light source unit is lit with the extended lighting time and the reduced current value (the lighting time determined in S171 and the current value determined in S172). The The backlight drive unit 125 creates a period during which only a specific light source unit emits light in response to an instruction from the backlight control unit 122, and creates a period during which only the specific light source unit emits light to the backlight control unit 122. Notify that. An example of the lighting time and current value at this time is shown in FIG. FIG. 10 is an example in the case of No determination in S170, and is an example in which the lighting time before extension and the current value before reduction are the values shown in FIG.

  When the backlight drive unit 125 notifies the backlight control unit 122 that a period during which only a specific light source unit is lit is created, the process proceeds to S174. In S174, the backlight control unit 122 instructs the optical sensor value acquisition unit 121 to acquire the optical sensor value of a specific light source unit. The optical sensor value acquisition unit 121 acquires an optical sensor value from an optical sensor provided in a specific light source unit. As described above, the optical sensor value is acquired a plurality of times, and a representative value of the acquired optical sensor values is acquired as the final optical sensor value.

  As described above, in this embodiment, when the lighting time for one specific light source unit is shorter than the time required for detecting light by the optical sensor, the lighting time is extended and the current value is reduced. . Therefore, when the lighting time of one time of a specific light source unit is shorter than the time required for detecting light with a photosensor, in S174, the lighting time is extended and the current value is reduced. Detection result (optical sensor value) is acquired.

  When the lighting time of a specific light source unit is longer than the time required to detect light by the light sensor, the detection result when the light source unit is turned on with the set lighting time and the set current value ( Light sensor value) is acquired.

  In step S175, the backlight control unit 122 acquires the target light sensor value of the specific light source unit from the target light sensor value storage unit 123.

  By the processing after S176, the light emission amount of each light source unit is controlled based on the optical sensor value acquired in S174. Specifically, in the case of Yes determination in S170, the light emission amount of the light source unit is controlled based on the detection result (light sensor value) in a state where the light source unit is lit with the set lighting time and the set current value. In the case of No determination in S170, the light emission amount of the light source unit is controlled based on the detection result (light sensor value) in a state where the lighting time is extended and the current value is reduced.

  Specifically, when the current value is reduced in S172, in S176, the backlight control unit 122 adjusts the target light sensor value according to the reduced current value. When the current value changes, the light emission luminance (instantaneous value) also changes. This processing is processing for calculating a target light sensor value that matches the light emission luminance after the change in consideration of such a change in light emission luminance. For example, it is assumed that the specific light source unit is the light source unit 0. The target optical sensor value of the light source unit 0 when the current value of the light source unit 0 is 500 is 500 as shown in FIG. In this embodiment, the target optical sensor value is also reduced to 298 (= (298/500) × 500) in accordance with the current value 298 after the light source unit 0 is reduced.

  In S176, the backlight control unit 122 calculates a correction value for the set lighting time (hereinafter, lighting time correction value) from the light sensor value acquired in S174 and the target light sensor value. Here, when the current value is reduced in S172, the adjusted target light sensor value is used. The lighting time correction value is a correction coefficient by which the set lighting time is multiplied in order to correct the change in the light emission amount. For example, it is assumed that the specific light source unit is the light source unit 0. When the optical sensor value obtained by lighting only the light source unit 0 is 250, the target optical sensor value of the light source unit 0 is 298, and thus the lighting time correction value is 1.192 (= 298/250). .

  Next, in S177, the backlight control unit 122 determines whether the lighting time correction values of all the light source units have been calculated. If the lighting time correction values for all the light source units have been calculated, the process proceeds to S178. When there is a light source unit for which the lighting time correction value is not calculated, the light source unit for which the lighting time correction value is not calculated is set as the specific light source unit. Then, the process returns to S170.

  In S178, the backlight control unit 122 calculates a corrected set lighting time (hereinafter, corrected lighting time) for each light source unit. The corrected lighting time is calculated by multiplying the set lighting time before correction by the lighting time correction value. Specifically, when the set lighting time before correction of the light source unit 0 is 50 and the lighting time correction value is 1.192, the lighting time after correction is 60 (= 50 × 1.192).

  The light emission amount may be corrected by correcting the set current value instead of the set lighting time, or the light emission amount may be corrected by correcting both the set lighting time and the set current value.

  As described above, according to this embodiment, even when the set lighting time is short as shown in FIG. 11 and the light sensor value cannot be normally acquired, the lighting time is changed as shown in FIG. A simple optical sensor value can be acquired. Therefore, the light emission amount of each light source unit can be controlled (corrected; feedback control) with high accuracy, and the light emission amount of the entire backlight can be kept constant.

  Further, in the present embodiment, not only the lighting time but also the current value is changed, so that the change in the light amount due to the changing of the lighting time can be reduced, and a desired optical sensor value can be obtained. In addition, a change in display luminance (brightness on the screen) due to changing the lighting time can be suppressed.

  The light source may be one LED or a plurality of LEDs. The light source may be configured using a cold cathode tube or the like instead of the LED.

  In this embodiment, the example in which the light emission luminance of the light source is changed by changing the current value supplied to the light source has been described. However, the light emission luminance of the light source is changed by changing the voltage value applied to the light source. Also good.

<Example 2>
Hereinafter, a light source device and a control method thereof according to Embodiment 2 of the present invention will be described.

  Some light sources have a characteristic that the light emission efficiency changes depending on the change in the current value to be supplied. For example, LEDs have such characteristics. In the present embodiment, an example will be described in which when the light source has such characteristics, the reduced current value obtained in the first embodiment is corrected in consideration of the characteristics. By performing such correction, when the light source has the above characteristics, it is possible to obtain a photosensor value with higher accuracy than in the first embodiment, and to control the light emission amount of the light source device with higher accuracy than in the first embodiment. Can do.

  First, the configuration of the light source device according to the present embodiment will be described with reference to FIG.

  FIG. 13 is a block diagram illustrating an example of the configuration of the light source device according to the present embodiment.

  In FIG. 13, the same reference numerals are given to the same functional units as those in the first embodiment (FIG. 1), and the description thereof is omitted.

  The backlight control unit 122 according to the present embodiment further includes a current value correction unit 230. The current value correction unit 230 reduces the current value (reduced by the current value adjustment unit 131) so that the light emission amount does not change when the lighting time is extended and the current value is reduced in order to acquire the optical sensor value. Corrected current value). As the current value adjusting unit 131 reduces the current value, the light emission efficiency of the light source unit changes. As the luminous efficiency changes, the amount of emitted light also changes. Based on the relationship between the current value and the light emission efficiency, the current value correction unit 230 corrects the reduced current value so that the change in the light emission amount due to the change in the light emission efficiency is suppressed.

  Since the method for recording the target light sensor value and the initial light emission period is the same as that in the first embodiment, the description thereof is omitted.

  Next, a method for controlling the light emission amount of the backlight 100 according to the present embodiment (light emission amount control process) will be described with reference to FIG. FIG. 14 is a flowchart illustrating an example of a method for controlling the light emission amount of the backlight 100 according to the present embodiment, specifically, a method for keeping the light emission amount (brightness) of the entire backlight 100 constant. The processing flow of FIG. 14 is performed at regular intervals, for example, during a period in which the user uses the image display device.

  In FIG. 14, the same reference numerals are assigned to the same processes as those in the first embodiment (FIG. 8), and the description thereof is omitted.

  In the present embodiment, the process of S270 is performed after the process of S172, and the process proceeds to S173 after the process of S270.

  In S <b> 270, the backlight control unit 122 corrects the current value after reduction (the current value reduced in S <b> 172) using the current value correction unit 230.

  As described above, some light source units (specifically, light-emitting elements such as LEDs) have a characteristic in which the light emission efficiency changes according to the change in the current value to be supplied. For example, some light source units have characteristics as shown in FIG. In the characteristics of FIG. 15, the luminous efficiency is 1 when the current value is 500, and the luminous efficiency is 0.6 when the current value is 250. In order to control (correct) the light emission amount of the backlight 100 with higher accuracy, it is necessary to consider such characteristics.

  The current value correction unit 230 has, for example, a correction table as shown in FIG. The correction table of FIG. 16 is a table that represents the relationship between the current value and the correction value. Specifically, the correction table of FIG. 16 represents a correction value (current correction value) for the current value for each reduced current value. The current correction value is a correction coefficient that is multiplied by the reduced current value in order to suppress the change in the light emission amount due to the change in the light emission efficiency. In this embodiment, a current correction value for a current value that does not exist in the correction table is calculated by interpolation. Note that a current correction value corresponding to a current value closest to the current value in the correction table may be used as a current correction value for a current value that does not exist in the correction table. When the current value after reduction is 298, the current value 298 after reduction is the current value 277 (= ((298-290) × (0.93-0.92) / ( 300-290) +0.92) × 298).

  The current correction value is not determined using a correction table, but is a function that represents the relationship between the current value and the light emission efficiency (a function that represents the relationship between the current value after reduction and the current correction value). It may be calculated. Further, the current value after reduction may be corrected using a table or a function that represents the relationship between the current value before correction and the current value after correction.

  As described above, according to the present embodiment, even when the set lighting time is short and the light sensor value cannot be normally obtained as shown in FIG. 11, the lighting time and the current value are changed as shown in FIG. A highly accurate optical sensor value can be acquired. Even when the light emission efficiency changes due to a change in current value, a highly accurate photosensor value can be acquired by correcting the reduced current value. Therefore, the light emission amount of each light source unit can be controlled (corrected) with high accuracy, and the light emission amount of the entire backlight can be kept constant. Specifically, when the light emission efficiency changes due to a change in current value, it is possible to acquire a photosensor value with higher accuracy than in the first embodiment, and to control the light emission amount of the light source device with higher accuracy than in the first embodiment. it can.

  In the present embodiment, the reduced current value is corrected based on the relationship between the current value and the light emission efficiency, but the present invention is not limited to this. For example, the acquired optical sensor value may be corrected based on the relationship between the current value and the luminous efficiency so that a change in the optical sensor value due to a change in the luminous efficiency is suppressed. Further, the corrected light emission amount (corrected lighting time for correction) determined by the method of the first embodiment may be corrected based on the relationship between the current value and the light emission efficiency. However, if the current value after the reduction is corrected, it is possible to suppress a large change in the light emission amount during the light emission amount control process.

<Example 3>
Hereinafter, a light source device and a control method thereof according to Embodiment 3 of the present invention will be described. In the present embodiment, an example in which the lighting time after extension and the current value after reduction are determined in advance will be described.

  First, the configuration of the light source device according to the present embodiment will be described with reference to FIG.

  FIG. 18 is a block diagram illustrating an example of the configuration of the light source device according to the present embodiment.

  In FIG. 18, the same reference numerals are given to the same functional units as those in the first embodiment (FIG. 1), and the description thereof is omitted.

  The backlight control unit 122 according to the present embodiment includes a lighting time magnification selection unit 330 and a current value magnification selection unit 331.

  In the lighting time magnification selection unit 330, a table representing the lighting time after extension for each set lighting time is recorded in advance. Then, the lighting time magnification selection unit 330 extends the set lighting time to the lighting time after extension corresponding to the current setting lighting time in the table. In this embodiment, as shown in FIG. 20, a table indicating the magnification of the set lighting time is recorded for each set lighting time, and the set lighting time is extended by multiplying the corresponding magnification.

  In the current value magnification selection unit 331, a table representing the current value after reduction for each set lighting time is recorded in advance. Then, the current value magnification selection unit 331 reduces the set current value to a reduced current value associated with the current set lighting time in the table. In the present embodiment, as shown in FIG. 21, a table representing the magnification of the set current value is recorded for each set lighting time, and the set current value is reduced by multiplying the corresponding magnification.

  For each set lighting time, not the magnification but the lighting time after extension or the current value after reduction may be associated. Further, one table representing the extended lighting time and the reduced current value for each set lighting time may be recorded in advance. A function may be recorded instead of a table.

  Since the recording method of the target light sensor value and the initial light emission period is the same as that of the first embodiment, the description thereof is omitted.

  Next, a method for controlling the light emission amount of the backlight 100 according to the present embodiment (light emission amount control process) will be described with reference to FIG. FIG. 19 is a flowchart illustrating an example of a method for controlling the light emission amount of the backlight 100 according to the present embodiment, specifically, a method for keeping the light emission amount (brightness) of the entire backlight 100 constant. For example, the processing flow of FIG. 19 is performed at regular intervals during a period in which the user uses the image display device.

  In FIG. 19, the same processes as those in the first embodiment (FIG. 8) are denoted by the same reference numerals, and the description thereof is omitted.

  In the present embodiment, the processes of S370 and S371 are performed instead of the processes of S171 and S172 of FIG.

  In S370, the backlight control unit 122 uses the lighting time magnification selection unit 330 to select a magnification for extending the set lighting time and extend the set lighting time. Specifically, the magnification corresponding to the currently set lighting time is selected from the table of FIG. Then, the set lighting time is extended by multiplying the currently set lighting time by the selected magnification. When the current set light emission period is 50, the magnification is 5, and the lighting time after extension is 250 (= 50 × 5).

  In step S <b> 371, the backlight control unit 122 uses the current value magnification selection unit 331 to select a magnification for reducing the set current value and reduce the set current value. Specifically, the magnification corresponding to the currently set lighting time is selected from the table of FIG. Then, the set current value is reduced by multiplying the currently set current value by the selected magnification. When the current set light emission period is 50 and the current set current value is 500, the magnification is 1/5, and the current value after reduction is 100 (= 500 × 1/5).

  As described above, according to this embodiment, even when the set lighting time is short as shown in FIG. 11 and the light sensor value cannot be normally obtained, the lighting time and the current value are changed as shown in FIG. A highly accurate optical sensor value can be acquired. Therefore, the light emission amount of each light source unit can be controlled (corrected) with high accuracy, and the light emission amount of the entire backlight can be kept constant.

<Example 4>
Hereinafter, a light source device and a control method thereof according to Embodiment 4 of the present invention will be described.

  Some light sources have a characteristic that the light emission efficiency changes due to a change in temperature inside the light source element (temperature of the light source itself; light source temperature). For example, the LED has a characteristic that the luminous efficiency decreases as the temperature inside the element increases, and the luminous efficiency increases as the temperature inside the element decreases. In this embodiment, when the light source has such characteristics, an example in which the lighting period is extended and the current value is controlled in consideration of the characteristics will be described.

  First, the configuration of the light source device according to the present embodiment will be described with reference to FIGS.

  FIG. 23 is a block diagram illustrating an example of the configuration of the light source device according to the present embodiment. FIG. 24 is a schematic diagram illustrating an example of the configuration of the backlight unit according to the present embodiment.

  In FIG. 23, the same reference numerals are given to the same functional units as those in the first embodiment (FIG. 1), and the description thereof is omitted.

  The light emitting device 100 according to the present embodiment further includes a temperature sensor value acquisition unit 430 in addition to the optical sensor value acquisition unit 121. In response to an instruction from the backlight control unit 122, the temperature sensor value acquisition unit 430 generates a temperature for each light source unit from a temperature sensor 432 (temperature sensors a to f) provided for each light source unit as shown in FIG. Get the sensor value. In the present embodiment, extension of the lighting period and reduction of the current value are controlled based on the temperature sensor value acquired by the temperature sensor value acquisition unit 430. Note that the temperature sensor value is, for example, a Celsius temperature when acquiring the optical sensor value. Strictly speaking, the temperature sensor value is the temperature in the vicinity of the light source to be measured, not the light source temperature, but the temperature sensor value changes based on the change in the light source temperature. For ease of explanation, the temperature sensor value is interpreted as the light source temperature for convenience.

  The light emitting device 100 according to the present embodiment further includes a reference temperature sensor value storage unit 431 in addition to the target light sensor value storage unit 123. The reference temperature sensor value storage unit 431 is a reference temperature sensor value when acquiring a target light sensor value in an adjustment process during production.

  Next, a method for recording the target light sensor value, the reference temperature sensor value, and the initial lighting time according to the present embodiment will be described with reference to FIG. FIG. 25 is a flowchart illustrating an example of a method for recording the target light sensor value, the reference temperature sensor value, and the initial lighting time. The processing flow in FIG. 25 is performed, for example, in an adjustment process during production. Furthermore, the adjustment process at the time of production in the present embodiment is performed in a constant temperature environment.

  In FIG. 25, the same processes as those in the first embodiment (FIG. 8) are denoted by the same reference numerals, and the description thereof is omitted.

  Since the processing from S150 to S153 in the present embodiment is the same as that in Embodiment 1, the description thereof is omitted.

  In S153, when the backlight driving unit 125 notifies the backlight control unit 122 that a period during which only a specific light source unit is lit is generated, the process proceeds to S450. In S450, the backlight control unit 122 instructs the optical sensor value acquisition unit 121 to acquire the optical sensor value of the specific light source unit, and acquires the temperature sensor value from the temperature sensor value acquisition unit 430. Instruct to do. The optical sensor value acquisition unit 121 acquires an optical sensor value from the optical sensor 112 (first detection unit) provided in the specific light source unit, and the temperature sensor value acquisition unit 430 is provided in the specific light source unit. A temperature sensor value is acquired from the temperature sensor 432 (second detection unit). Also in the present embodiment, as in the first embodiment, the optical sensor value is acquired a plurality of times for noise removal. Then, representative values (average value, mode value, intermediate value, etc.) of the plurality of acquired optical sensor values are acquired as final optical sensor values. Also in the present embodiment, as in the first embodiment, there is a time difference until light from the specific unit is detected in a state where only the specific light source unit is turned on. Therefore, in order to determine the final optical sensor value, it is necessary to maintain a state where only a specific light source unit is lit.

  Next, in S451, the backlight control unit 122 records the optical sensor value acquired in S450 in the target optical sensor value storage unit 123 as the target optical sensor value. Moreover, the temperature sensor value at the time of acquiring the optical sensor value is recorded in the temperature sensor storage unit 431 as the reference temperature sensor value.

  In step S452, the backlight control unit 122 determines whether the target light sensor values and the reference temperature sensor values of all the light source units have been recorded. When the target light sensor value and the reference temperature sensor value of all the light source units are recorded, this processing flow is ended. When there is a light source unit in which the target light sensor value and the reference temperature sensor value are not recorded, the backlight control unit 122 sets the light source unit in which the target light sensor value is not recorded as the specific light source unit. . Then, the process returns to S153.

  An example of the target light sensor value and the reference temperature sensor value for each light source unit determined in this manner is shown in FIG.

  In the present embodiment, the upper limit (maximum luminance) of the luminance of the backlight 100 is set by the user in a plurality of stages (for example, five stages of 50 cd / m2, 100 cd / m2, 200 cd / m2, 300 cd / m2, and 400 cd / m2). A case where it can be set will be described. Furthermore, a case where the backlight 100 is used with the maximum brightness set to 200 cd / m 2 by the user will be described. In order to obtain a luminance of 200 cd / m 2, 500 is set as the current value of each light source unit, and 500 is set as the lighting time of each light source unit.

  In the present embodiment, the target light sensor value and the reference temperature sensor value for each light source unit are set such that, for example, the backlight 100 emits light with a maximum luminance of 50 cd / m2, or the backlight 100 emits light with a maximum luminance of 100 cd / m2. It is assumed that each maximum luminance that can be set in the image display device to be used is calculated and recorded, for example, when emitting light with a maximum luminance of 300 cd / m 2 or when emitting light with a maximum luminance of 400 cd / m 2. Note that the target light sensor value and the reference temperature sensor value for each light source unit do not necessarily have to be calculated for a plurality of maximum luminances. For example, the target light sensor value and the reference temperature sensor value are calculated for only one maximum luminance, such as when the backlight 100 is caused to emit light at a maximum value of a plurality of maximum luminances that can be set (in the present embodiment, 400 cd / m 2). May be. In this case, the target light sensor value and the reference temperature sensor value for other maximum brightnesses are obtained by multiplying the target light sensor value and the reference temperature sensor value calculated for the maximum value of the maximum brightness by a predetermined correction coefficient. What is necessary is just to calculate.

  Note that the maximum luminance described above can be said to be the upper limit value of the display luminance.

  Next, a method for controlling the light emission amount of the backlight 100 according to the present embodiment (light emission amount control process) will be described with reference to FIG. FIG. 27 is a flowchart illustrating an example of a method for controlling the light emission amount of the backlight 100 according to the present embodiment, specifically, a method for keeping the light emission amount (brightness) of the entire backlight 100 constant. The processing flow in FIG. 27 is performed at regular intervals, for example, during a period in which the user uses the image display device. As described above, in the present embodiment, a case where the user uses the image display device by setting the maximum luminance of the image display device to 200 cd / m 2 will be described.

  In this embodiment, first, in S469, whether the light emission luminance of a specific light source unit that is a target for which the light emission amount is corrected (feedback control is performed) is lower than a first predetermined luminance (for example, 60 cd / m 2). Determine whether or not. When the light emission luminance of the specific light source unit to be subjected to feedback control is lower than the first predetermined luminance (S469: Yes), the process proceeds to S470. When the light emission luminance of the specific light source unit to be subjected to feedback control is equal to or higher than the first predetermined luminance (S469: No), the process proceeds to S473. The reason why the process proceeds to S470 when the light emission luminance of the specific light source unit is lower than the first predetermined luminance (S469: Yes) will be described later.

  Next, in S <b> 470, when the backlight control unit 122 acquires the optical sensor value by lighting only the specific light source unit, the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is the reference temperature sensor value. It is determined whether the value is lower than the predetermined value. In other words, in S470, when the backlight control unit 122 acquires a light sensor value by turning on only a specific light source unit, the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is equal to or lower than a predetermined temperature. It is determined whether or not. Here, the predetermined temperature is a temperature that is lower than the reference temperature sensor value by a predetermined value. The reference temperature sensor value is a reference temperature sensor value corresponding to the maximum luminance set by the user. Specifically, in this embodiment, since the maximum brightness is set to 200 cd / m 2 by the user, the value shown in FIG. 26 is applied as the reference temperature sensor value.

  The lighting time of the light source varies depending on, for example, input image data. Specifically, it is assumed that the backlight luminance when the target sensor value and the initial lighting time in the case of all white image data are recorded is 200 cd / m 2. When the backlight luminance is reduced to 100 cd / m 2 according to the image data, the lighting time of all the light source units is reduced to half. However, if the lighting time is shortened so that the backlight luminance is lowered, the temperature of the light source itself is lowered and the light emission efficiency is increased. Therefore, in this embodiment, control for adjusting the backlight luminance to 100 cd / m 2 is performed by further reducing the lighting time of the light source in consideration of the change in light emission efficiency due to the temperature change of the light source itself.

  In this embodiment, as in the first embodiment, it is assumed that the lighting time required for detecting light by the optical sensor is 84 or more. Furthermore, in this embodiment, information (table or function) representing the relationship between the light source temperature, the lighting time extension magnification and the current value reduction magnification is recorded in advance in a memory (not shown). The lighting time extension magnification is a lighting time extension magnification for setting the lighting time to 84 or more. The current value reduction magnification is a current value reduction magnification (current value reduction magnification) when the light source is turned on for a lighting time based on the corresponding lighting time extension magnification. Specifically, the backlight 100 holds a table as shown in FIG. FIG. 28 is an example of a table showing the lighting time extension magnification and the current value reduction magnification according to the present embodiment. In the example of FIG. 28, when the light source temperature is 41 to 44 ° C., the lighting time extension magnification is 20, and the current value reduction magnification is 1/20, and when the light source temperature is 44 to 48 ° C., the lighting time extension magnification. 5, the current value reduction magnification is 1/5, and when the light source temperature is 48 to 52 ° C., the lighting time extension magnification is 2, the current value reduction magnification is 1/2 and the light source temperature is 52 to 56 ° C. In this case, the lighting time extension magnification is 1.5 and the current value reduction magnification is 1 / 1.5.

  Normally, the light emission brightness of the backlight is adjusted according to the lighting time, and the current value is corrected by applying the current value reduction magnification described above only when the light source temperature changes by a predetermined value or more from the reference temperature sensor value. Thus, the light emission luminance of the backlight is adjusted.

  In S470, when it is determined that the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is a value lower than the reference temperature sensor value by a predetermined value or more (S470: Yes), the process proceeds to S471. In S470, when it is determined that the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is not a value lower than the reference temperature sensor value by a predetermined value or more (S470: No), the process proceeds to S473.

  In S471 and S472, according to the table shown in FIG. 28, the backlight control unit 122 multiplies the current set current value and lighting time by the current value reduction magnification and the lighting time extension magnification corresponding to the light source temperature during lighting. Then, the current value and the lighting time are corrected. The lighting time is extended using the lighting time adjusting unit 130.

  For example, assume that the lighting time of a specific light source unit is 80. Since the light source temperature at the lighting time of 80 is lower than the light source temperature when the lighting time is 500, the light emission efficiency is high. Therefore, if correction for shortening the lighting time is performed based on the light source temperature, the lighting time after correction is naturally shorter than 84, which is a lighting time necessary for detecting light by the optical sensor 112. Then, the problem that an optical sensor value cannot be acquired or an inaccurate optical sensor value is acquired due to a decrease in the number of times the optical sensor value is acquired becomes even greater.

  Therefore, in this embodiment, the lighting time and the current value are changed according to the table of FIG. In the following description, it is assumed that the specific light source unit is the light source unit 0 and the reference temperature (reference temperature sensor value) is 60 ° C. as shown in FIG. In this embodiment, the light source temperature (temperature sensor value) when the lighting time is 500 is 60 ° C., the light source temperature (temperature sensor value) when the lighting time is 80 is 50 ° C., and the predetermined value is 4 ° C. Will be described. In the present embodiment, it is assumed that the light emission luminance of a specific light source unit is changed from 200 cd / m 2 to 32 cd / m 2 according to the input image data, and the lighting time is changed from 500 to 80. Since the changed emission luminance 32 cd / m 2 is lower than the first predetermined luminance of 60 cd / m 2, the process proceeds from S469 to S470. The light source temperature gradually decreases from the light source temperature of 60 ° C. when the lighting time is 500 toward the light source temperature of 50 ° C. when the lighting time is 80. When a certain amount of time has elapsed, the temperature becomes 56 ° C. (= 60 ° C. (reference temperature) −4 ° C. (predetermined value)), which is a predetermined temperature. Thus, in this embodiment, when the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is 56 or less, which is lower than the reference temperature sensor value 60 by the predetermined value 4, the acquired temperature sensor value is the reference temperature sensor. The condition that the value is lower than the value by a predetermined value or more is satisfied. In other words, in this embodiment, when the lighting time is reduced to 80 and the light emission luminance is reduced to 32 cd / m 2, the condition that the light source temperature is equal to or lower than the predetermined temperature (56 ° C.) is satisfied in S470. Become. As described above, when the light source temperature becomes equal to or lower than the predetermined temperature, the process proceeds from S470 to S471. In this embodiment, the case where the light source temperature is 50 ° C. will be described. At this time, in S470, the condition that the temperature sensor value 50 acquired by the temperature sensor value acquisition unit 430 is a value that is a predetermined value 4 or more lower than the reference temperature sensor value 60 (a value that is lower than the predetermined temperature 56). In order to satisfy, the flow proceeds from S470 to S471.

  In S471, the lighting time is extended according to the table of FIG. In the present embodiment, an extension process is performed in which the lighting time is extended by a factor of 2 in the table of FIG. 28, which is 2 as the lighting time extension magnification when the light source temperature is 50 ° C. More specifically, in the table of FIG. 28, 160 (= 80 × 80 ×) which is equal to or longer than the time required to detect light by the optical sensor using 2 which is the lighting time extension magnification when the light source temperature is 50 ° C. The lighting time is extended until 2).

  Following the processing in S471, the processing proceeds to S472.

  In S472, the backlight control unit 122 reduces the current value supplied to the specific light source unit so that the increase in the light emission amount due to the extension of the lighting time in S471 is suppressed. The current value is reduced using the current value adjusting unit 131. In this embodiment, the current value is reduced so that the value obtained by multiplying the lighting time after extension by the current value after reduction matches the value obtained by multiplying the lighting time before extension by the current value before reduction. For example, when the lighting time of a specific light source unit is extended twice in S471, the current value supplied to the specific light source unit is multiplied by 0.5 (= 1/2). As a result, if the current value (set current value) before reduction of a specific light source unit is 500, the current value after reduction is 250 (= 500 × 1/2).

  Here, when the light emission luminance of the specific light source unit is lower than the first predetermined luminance and the temperature sensor value acquired by the temperature sensor value acquisition unit 430 is lower than the reference temperature sensor value by a predetermined value or more, The reason why the lighting time and the current value are corrected will be described with reference to FIG. FIG. 30 is a diagram showing a temperature transition when the lighting time is changed from 500 to 80, and shows a case where the lighting time is 500 at time 0, the lighting time is 80 at time T1, and the lighting time is 500 at time T3. . At this time, the temperature is near the reference temperature at time 0 to T1, and the temperature gradually decreases from time T1. At time T2, the temperature is 4 ° C. lower than the reference temperature, and reaches the minimum temperature at time T3.

  In this embodiment, when the light emission luminance of a specific light source unit is lower than the first predetermined luminance, the lighting time of the specific light source unit is shorter than the time required for the light sensor to detect light. turn into. As a result, an inaccurate optical sensor value may be acquired because the optical sensor value cannot be acquired or the number of acquisitions of the optical sensor value decreases. For this reason, control for reducing the current value and extending the lighting time (control for correcting the current value and the lighting time) is required. Specifically, when the lighting time of a specific light source unit is changed from 500 to 80, and the light source temperature gradually decreases as in the period of time T1 to T2, the light emission efficiency of the light source gradually increases. Therefore, in this embodiment, control is performed to further shorten the lighting time from 80 in accordance with the increase in the light emission efficiency of the light source. However, as the lighting time is gradually shortened, the accuracy of the acquired optical sensor value also decreases with time. Therefore, when the lighting time is changed from 500 to 80, in order to increase the accuracy of the optical sensor value to be acquired, if the current value is reduced and the lighting time is extended, the current value is reduced. The emission color of the light source changes from the timing when the current value is reduced. As a result, the color of the display image also changes. Therefore, in this embodiment, in order to suppress the change in the color of the display image (deterioration in image quality) as much as possible, priority is given to the suppression of the change in the color of the display image at times T1 to T2, and the acquisition accuracy of the optical sensor value is somewhat I think it ’s okay. Based on such an idea, the light sensor value is acquired with a gradually shortened lighting time without performing control for correcting the current value and the lighting time. Therefore, even if the determination is Yes in S469, if the determination is No in S470, the process proceeds to S473 without performing the processes in S471 and S472. However, the accuracy of the acquired optical sensor value gradually decreases, and the accuracy of feedback control also decreases. Therefore, in this embodiment, in order to ensure the accuracy of the feedback control to some extent, when the temperature of the light source is lowered to a temperature that reaches a predetermined light emission efficiency, control is performed to correct the current value and the lighting time, and the optical sensor. The value is acquired and the accuracy of the acquired optical sensor value is increased. In other words, in this embodiment, when the light source temperature falls to a temperature that is lower than the reference temperature by a predetermined value (4 ° C.), the current value and the lighting time are controlled to obtain a photosensor value, Increase the accuracy of the acquired optical sensor values.

  Following the processing in S472, the processing proceeds to S473.

  In S473, the backlight control unit 122 instructs the backlight driving unit 125 to create a period in which only a specific light source unit is lit. Specifically, in the case of Yes determination in S470, a period in which only a specific light source unit is lit with the extended lighting time and the reduced current value (the lighting time determined in S471 and the current value determined in S472). The instruction to make is made. The backlight drive unit 125 creates a period during which only a specific light source unit emits light in response to an instruction from the backlight control unit 122, and creates a period during which only the specific light source unit emits light to the backlight control unit 122. Notify that. An example of the lighting time and current value at this time is shown in FIG. FIG. 29 is an example in the case of Yes determination in S470, and is an example in which the lighting time before extension and the current value before reduction are the same as those in Example 1 and the values shown in FIG.

  On the other hand, if the determination in S470 is No, in S473, as described above, an instruction to create a period during which only a specific light source unit is lit with the set lighting time and the set current value is issued. Then, the backlight driving unit 125 creates a period in which only a specific light source unit emits light in response to an instruction from the backlight control unit 122, and a period in which only the specific light source unit emits light to the backlight control unit 122. Notify that you have created.

  In S473, when the backlight drive unit 125 notifies the backlight control unit 122 that a period during which only a specific light source unit is turned on is generated, the process proceeds to S474. In S474, the backlight control unit 122 instructs the optical sensor value acquisition unit 121 to acquire the optical sensor value of the specific light source unit, and also instructs the temperature sensor value acquisition unit 430 to detect the temperature sensor of the specific light source unit. Instructs to get the value. And the optical sensor value acquisition part 121 acquires an optical sensor value from the optical sensor 112 provided in the specific light source unit, and the temperature sensor value acquisition part 430 is temperature from the temperature sensor 432 provided in the specific light source unit. Get the sensor value. As described above, the optical sensor value is acquired a plurality of times, and a representative value of the acquired optical sensor values is acquired as the final optical sensor value.

  Further, as described above, in this embodiment, a predetermined value between the reference temperature set in the adjustment process at the time of production and the temperature sensor value (light source temperature) during lighting corresponding to the set maximum brightness. When the above temperature difference occurs, the current value is reduced while extending the lighting time. Therefore, even if the light emission efficiency of the light source increases due to the change in the light source temperature and it is necessary to shorten the lighting time of the light source, one lighting time of a specific light source unit is It is adjusted to be longer than the time required to detect.

  In S474, as described above, when the light source temperature during lighting is lower than the reference temperature set in the adjustment process at the time of production corresponding to the set maximum brightness, the lighting time is extended and A detection result (light sensor value) in a state where the current value is reduced is acquired. On the other hand, if the temperature sensor value (light source temperature) during lighting is not lower than the reference temperature set in the adjustment process during production corresponding to the set maximum brightness, the set lighting time and setting A detection result (light sensor value) in a state where the light source unit is turned on with the current value is acquired.

  In step S475, the backlight control unit 122 acquires the target light sensor value of the specific light source unit from the target light sensor value storage unit 123.

  Through the processing after S476, the light emission amount of each light source unit is controlled based on the optical sensor value acquired in S474. Specifically, in the case of Yes determination in S470, the light emission amount of the light source unit is controlled based on the detection result (light sensor value) in the state where the lighting time is extended and the current value is reduced. In the case of No determination in S470, the light emission amount of the light source unit is controlled based on the detection result (light sensor value) in a state where the light source unit is lit with the set lighting time and the set current value.

  Specifically, when the current value is reduced in S472, in S476, the backlight control unit 122 adjusts the target light sensor value according to the reduced current value. When the current value changes, the light emission luminance (instantaneous value) also changes. This processing is processing for calculating a target light sensor value that matches the light emission luminance after the change in consideration of such a change in light emission luminance. For example, the target light sensor value of the light source unit 0 when the current value of the light source unit 0 which is a specific light source unit is 500 is 500 as shown in FIG. In this embodiment, the target optical sensor value is also reduced to 250 (= (250/500) × 500) in accordance with the current value 250 after the light source unit 0 is reduced.

  Further, in S476, the backlight control unit 122 calculates a correction value for the set lighting time (hereinafter, lighting time correction value) from the light sensor value acquired in S474 and the target light sensor value. If the current value is reduced in S472, the adjusted target light sensor value is used.

  The lighting time correction value is a correction coefficient by which the set lighting time is multiplied in order to correct the change in the light emission amount. For example, when the light sensor value obtained by lighting only the light source unit 0 that is a specific light source unit is 300, the target light sensor value of the light source unit 0 is 250, and thus the lighting time correction value is 0.83. (= 250/300).

  Next, in S477, the backlight control unit 122 determines whether lighting time correction values for all the light source units have been calculated. If lighting time correction values for all light source units have been calculated, the process proceeds to S478. When there is a light source unit for which the lighting time correction value is not calculated, the light source unit for which the lighting time correction value is not calculated is set as the specific light source unit. Then, the process returns to S469.

  In S478, the backlight control unit 122 calculates a corrected lighting time for each light source unit. The corrected lighting time is calculated by multiplying the set lighting time before correction by the lighting time correction value. Specifically, when the set lighting time before correction of the light source unit 0 is 160 and the lighting time correction value is 0.83, the lighting time after correction is 133 (= 160 × 0.83).

  Here, the execution timing of the optical sensor value acquisition control in the present invention when the lighting time is changed from 500 to 80 will be described with reference to FIG. As described above, the lighting time 500 is changed at time 0, the lighting time 80 is changed at time T1, and the lighting time 500 is changed at time T3. At this time, the temperature is near the reference temperature at time 0 to T1, and the temperature gradually decreases from time T1. At time T2, the temperature is 4 ° C. lower than the reference temperature, and reaches the lowest temperature at lighting time 80 at time T3. Then, the temperature gradually increases from time T3, and after time T4, the difference from the reference temperature becomes 4 ° C. or less. At this time, the time T2 to T3 is a period having a difference of 4 ° C. or more from the reference temperature. In this period, the lighting time is extended and the current value is reduced. Note that the times T3 to T4 are periods with a difference of 4 ° C. or more from the reference temperature, but since the lighting time is 500, it is not necessary to extend the lighting time and reduce the current value, and set lighting What is necessary is just to detect an optical sensor value in the state which turned on the light source unit with time and the setting electric current value.

  When the backlight 100 is used with the maximum luminance set low, it is experimentally derived that the luminance change (luminance unevenness) due to the temperature change of the light source is so small that it does not affect the user and can be ignored. . Therefore, when the maximum brightness of the backlight 100 set at the time of use is low, it is not always necessary to acquire the sensor value. That is, when the maximum luminance of the backlight 100 set at the time of use is equal to or lower than a second predetermined luminance (for example, 50 cd / m2 or lower), the above processing may not be applied and sensor value acquisition may be stopped. . In other words, only when the maximum brightness of the backlight 100 set at the time of use is higher than the second predetermined brightness, the control of the present embodiment (lighting time extension process considering the light source temperature) is performed. It may be. In addition, when the maximum luminance of the backlight 100 is equal to or lower than the second predetermined luminance and the lighting time of the specific light source unit is shorter than the predetermined time, the acquisition of the sensor value is continued. The sensor value of a specific light source unit may not be used for feedback control for the specific light source unit.

  The light emission amount may be corrected by correcting the set current value instead of the set lighting time, or the light emission amount may be corrected by correcting both the set lighting time and the set current value.

  As described above, according to the present embodiment, even when the set lighting time is short and the optical sensor value cannot be normally acquired, the high-precision light can be obtained by changing the lighting time and the current value as shown in FIG. Sensor value can be acquired. Therefore, the light emission amount of each light source unit can be controlled (corrected) with high accuracy, and the light emission amount of the entire backlight can be kept constant.

  In addition, since the current value is changed only when the temperature changes more than a predetermined value, it is possible to suppress the occurrence of luminance unevenness and color unevenness due to the current value change.

  In the present embodiment, the maximum brightness of the backlight 100 at the time of use is set by the user setting, but the present invention is not limited to this. For example, a control unit (not shown) included in the image display device may automatically set the maximum luminance of the backlight 100 based on the genre of the image displayed on the image display device. Further, the image display device further includes an external light sensor, and a control unit included in the image display device automatically sets the maximum luminance of the backlight 100 according to the brightness of external light (environmental light) during use. May be.

  As mentioned above, although preferred embodiment of this invention was described referring drawings, this invention is not limited to the example which concerns. In Examples 1 to 4, the example in which the current value is reduced with the extension of the lighting time of the light source has been described. However, the display luminance is reduced by reducing the transmittance of the display panel with the extension of the lighting time of the light source. You may adjust.

0-5 Light source unit 100 Light source device (backlight)
112 Optical sensor 432 Temperature sensor 122 Backlight control unit

Claims (16)

A light emitting means comprising an LED light source;
A display panel that displays an image on a screen by transmitting light emitted from the light emitting means;
Determining means for determining the light emission luminance of the light emitting means based on image data;
Control means for controlling the light emission amount of the LED light source by controlling the LED light source by PWM (Pulse Width Modulation) ;
First detection means for detecting the amount of light from the LED light source;
Second detection means for detecting the temperature of the LED light source;
Have
When the temperature of the LED light source detected by the second detection unit is equal to or lower than a predetermined temperature and the light emission luminance determined by the determination unit is lower than the first predetermined luminance, the control unit, An image display device, wherein an extension process for extending a lighting time of the LED light source is executed when the first detection means detects light. When the temperature of the LED light source detected by the second detection unit is equal to or lower than a predetermined temperature and the light emission luminance determined by the determination unit is lower than the first predetermined luminance, the control unit, When the first detection means detects light, the extension process is executed, and the current value supplied to the LED light source is reduced according to the extension process, thereby controlling the light emission amount of the LED light source. The image display device according to claim 1. When the temperature of the LED light source detected by the second detection unit is equal to or lower than a predetermined temperature and the light emission luminance determined by the determination unit is lower than the first predetermined luminance, the control unit, 2. The control device according to claim 1, wherein when the first detection unit detects light, the extension process is executed and a control for reducing the transmittance of the display panel according to the extension process is executed. The image display device described.   The control means reduces the current value so that a value obtained by multiplying the lighting time after extension by the current value after reduction matches a value obtained by multiplying the lighting time before extension by the current value before reduction. The image display device according to claim 2. The LED light source has a characteristic that the light emission efficiency changes according to the reduction of the current value,
The image display device further includes a correction unit that corrects the reduced current value so that a change in light emission amount due to a change in light emission efficiency of the LED light source is suppressed.
The control means is configured such that the value obtained by multiplying the lighting time after extension by the current value after correction by the correction means matches the value obtained by multiplying the lighting time before extension by the current value before reduction. The image display device according to claim 2, wherein the image display device is reduced.   When the preset maximum brightness of the light emitting means is higher than a second predetermined brightness, the control means executes the extension process, and the preset maximum brightness of the light emitting means is the second brightness. 6. The image display device according to claim 1, wherein the control unit does not execute the extension processing when the brightness is equal to or less than a predetermined luminance. 7. The extension process according to claim 1, wherein the extension process is a process of extending a lighting time of the LED light source to a time required for detecting light by the first detection means. The image display device described in 1. Even if the lighting time of the LED light source is shorter than the time required for detecting the light by the first detection means, the control means can control the temperature of the LED light source detected by the second detection means. The image display device according to claim 1, wherein the extension process is not performed when the predetermined temperature is exceeded. A control method for an image display device, comprising: a light emitting unit including an LED light source; and a display panel that displays an image on a screen by transmitting light emitted from the light emitting unit.
A determining step of determining the light emission brightness of the light emitting means based on image data;
A control step of controlling a light emission amount of the LED light source by controlling the LED light source by PWM (Pulse Width Modulation) ;
A first detection step of detecting light from the LED light source;
A second detection step of detecting the temperature of the LED light source;
Have
In the control step, when the temperature of the LED light source detected in the second detection step is equal to or lower than a predetermined temperature, and the light emission luminance determined in the determination step is lower than the first predetermined luminance, A method for controlling an image display device, comprising: performing an extension process for extending a lighting time of the LED light source when detecting light in the first detection step. In the control step, when the temperature of the LED light source detected in the second detection step is equal to or lower than a predetermined temperature, and the light emission luminance determined in the determination step is lower than the first predetermined luminance, When detecting light in the first detection step, an extension process is performed to extend the lighting time of the LED light source beyond the time required to detect light in the first detection step, and the LED The method for controlling an image display device according to claim 9, wherein a light emission amount of the LED light source is controlled by reducing a current value supplied to the light source according to the extension process. In the control step, when the temperature of the LED light source detected in the second detection step is equal to or lower than a predetermined temperature, and the light emission luminance determined in the determination step is lower than the first predetermined luminance, When detecting light in the first detection step, an extension process for extending the lighting time of the LED light source beyond the time required for detecting light in the first detection step is performed, and the display The control method for an image display device according to claim 9, wherein control for reducing the transmittance of the panel according to the extension processing is executed.   In the control step, the current value is reduced so that a value obtained by multiplying the lighting time after extension by the current value after reduction matches a value obtained by multiplying the lighting time before extension by the current value before reduction. The method for controlling an image display device according to claim 10. The LED light source has a characteristic that the light emission efficiency changes according to the reduction of the current value,
The control method of the image display device further includes a correction step of correcting the current value after reduction so that a change in light emission amount due to a change in light emission efficiency of the LED light source is suppressed.
In the control step, the current value is set such that a value obtained by multiplying the lighting time after extension by the current value after correction in the correction step matches a value obtained by multiplying the lighting time before extension by the current value before reduction. The method of controlling an image display device according to claim 10, wherein:   If the preset maximum brightness of the light emitting means is higher than a second predetermined brightness, the control step executes the extension process, and the preset maximum brightness of the light emitting means is the second brightness. 14. The method of controlling an image display device according to claim 9, wherein the extension process is not executed in the control step when the brightness is equal to or less than a predetermined luminance. The extension process is a process of extending a lighting time of the LED light source to a time required to detect light in the first detection step or more. A control method for an image display device according to the item. In the control step, even if the lighting time of the LED light source is shorter than the time required to detect light in the first detection step, the temperature of the LED light source detected by the second detection step is 16. The method for controlling an image display device according to claim 9, wherein the extension process is not executed when the predetermined temperature is exceeded.

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