JP2014035524A - Image display device and control method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology capable of measuring ambient light with a simple configuration without decreasing visibility of an image displayed on a screen.SOLUTION: An image display device is provided, including a display panel, a backlight disposed on the backside of the display panel, and measuring means disposed between the backlight and the display panel or on a substrate of the backlight. The measuring means is operated in a plurality of operation modes which include a first mode of measuring light emitting from the backlight while the backlight is lighting, and a second mode of measuring ambient light transmitting through the screen while the backlight is turned off.

Description

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

  When the user views the image displayed on the image display device, the brightness and color on the screen may deviate from desired values due to the influence of ambient light (illuminance and saturation of the ambient light) irradiated on the screen. is there.

  A conventional technique for solving such a problem is disclosed in Patent Document 1, for example. Specifically, in the technique disclosed in Patent Document 1, ambient light is measured by an ambient light sensor provided in front of an image display device (display). Then, based on the measurement value of the ambient light, the backlight is controlled or the image processing for the input image signal is performed so that the change in the brightness and the color on the screen due to the ambient light is suppressed.

  Here, when the ambient light is uniformly irradiated on the entire screen, the ambient light can be accurately measured by one ambient light sensor. However, the ambient light is not always irradiated uniformly on the screen. For example, ambient light such as light from a desk lamp installed near the image display device, light leaking from a curtain, natural light, and the like may be locally irradiated on a partial area of the screen. Further, even if ambient light is irradiated on the entire screen, the amount of ambient light irradiation may vary within the screen.

  If a plurality of ambient light sensors are used, the measurement accuracy of ambient light that is unevenly irradiated on the screen can be increased, but the cost increases. In addition, if a plurality of ambient light sensors are provided on the screen, the measurement accuracy of the ambient light irradiated unevenly on the screen is improved as compared with the case where a plurality of ambient light sensors are provided around the screen (for example, the bezel). However, the visibility of the image displayed on the screen is reduced.

Japanese Patent Laid-Open No. 07-255063

  An object of the present invention is to provide a technique capable of measuring ambient light with a simple configuration without reducing the visibility of an image displayed on a screen.

The image display device of the present invention is
A display panel;
A backlight provided on the back side of the display panel;
Measuring means provided between the backlight and the display panel or on the substrate of the backlight;
Have
The measurement means includes a first mode for measuring light emitted from the backlight with the backlight turned on, and a second mode for measuring ambient light transmitted through the screen with the backlight turned off. It is characterized by operating in a plurality of operation modes including

The control method of the image display device of the present invention includes:
A display panel;
A backlight provided on the back side of the display panel;
A measurement unit provided between the backlight and the display panel or on the substrate of the backlight;
A method for controlling an image display device comprising:
A first measurement step of measuring light emitted from the backlight in a state where the backlight is lit by the measurement unit;
A second measurement step of measuring ambient light transmitted through the screen with the backlight turned off by the measurement unit;
It is characterized by having.

  According to the present invention, ambient light can be measured with a simple configuration without reducing the visibility of an image displayed on the screen.

FIG. 1 is a block diagram illustrating an example of a functional configuration of an image display device according to a first embodiment. 7 is a flowchart illustrating an example of a processing flow of the image display apparatus according to the first embodiment. 1 is a diagram illustrating an example of a rough hardware configuration of an image display apparatus according to Embodiment 1. FIG. The figure which shows an example of the state of the image display apparatus at the time of backlight light monitoring mode The figure which shows an example of the state of the image display apparatus at the time of environmental light measurement mode A graph showing an example of a function representing a change in relative luminance value with respect to a change in wavelength FIG. 7 is a block diagram illustrating an example of a functional configuration of an image display apparatus according to a second embodiment. 10 is a flowchart illustrating an example of a processing flow of the image display apparatus according to the second embodiment.

<Example 1>
An image display apparatus and a control method thereof according to Embodiment 1 of the present invention will be described.
FIG. 3 is a diagram illustrating an example of a rough hardware configuration of the image display apparatus according to the present embodiment. FIG. 3 shows part of a cross section obtained by a plane perpendicular to the screen. The image display apparatus according to the present embodiment includes a display panel (a liquid crystal panel in the present embodiment), a backlight, a measurement unit (sensor 211), a diffusion plate 207, and the like.

The liquid crystal panel includes a plurality of liquid crystal elements having corresponding colors different from each other. The liquid crystal element has a color filter and a liquid crystal shutter. In the example of FIG. 3, the liquid crystal panel includes red, green, and blue liquid crystal elements. The red liquid crystal element includes a liquid crystal shutter 201 and an R color filter 204. The green liquid crystal element has a liquid crystal shutter 202 and a G color filter 205. The blue liquid crystal element has a liquid crystal shutter 203 and a B color filter 206. The R color filter 204 is a color filter that selectively transmits red light. The G color filter 205 is a color filter that selectively transmits green light. The B color filter 206 is a color filter that selectively transmits blue light.
The liquid crystal shutters 201 to 203 may have the same configuration or different configurations.
The liquid crystal elements are not limited to red, green, and blue liquid crystal elements. A yellow liquid crystal element may be used.

The backlight is provided on the back side of the display panel. The backlight includes a substrate 212 facing the back surface of the display panel, and a light source provided on the substrate 212 (liquid crystal panel side). In the example of FIG. 3, the backlight includes, as light sources, an R light source 208 that emits red light, a G light source 209 that emits green light, and a B light source 210 that emits blue light. The light source is, for example, an LED (Light Emitting Diode), a cold cathode tube, an organic EL (Electro Luminescence) element, or the like.
The light source is not limited to the R light source 208, the G light source 209, and the B light source 210. For example, a white light source that emits white light, a yellow light source that emits yellow light, or the like may be used.
Note that the number of light sources may be one or plural. For example, only one white light source may be used.

  The diffusion plate 207 diffuses incident light.

  The measurement unit (sensor 211) is provided between the backlight and the display panel or on the substrate of the backlight. In order to efficiently use the light from the backlight, the sensor 211 is preferably provided at a position that does not block the light from the backlight. In the example of FIG. 3, the sensor 211 is provided on the substrate 212 (on the liquid crystal panel side) so as not to block light from the backlight (for example, light from each light source).

In this embodiment, the sensor 211 measures both light from the backlight (backlight light) and ambient light. Specifically, the backlight light is measured with the backlight turned on. In a state where the backlight is turned off (in this embodiment, the backlight is turned off and the liquid crystal shutter is opened), the ambient light is transmitted to the sensor 211 through the screen. Therefore, the ambient light transmitted through the screen with the backlight turned off is measured. Even when the backlight is turned on, ambient light may be transmitted to the sensor 211 through the screen. However, since the brightness of the ambient light input to the sensor 211 is sufficiently lower than the brightness of the backlight light input to the sensor 211, the influence of the ambient light on the measured value of the backlight light can be ignored.
Note that the position of the sensor 211 is not limited to the position on the substrate 212. For example, the sensor 211 may be provided at a position away from the substrate 212.
In addition, when the light emission luminance of each light source and the transmittance of each liquid crystal shutter are controlled in consideration that a part of the light from the backlight is blocked by the sensor 211, a part of the light from the backlight is It may be blocked by the sensor 211.
Note that it is preferable that a plurality of sensors 211 be provided over the entire screen in order to measure variations in the backlight light and ambient light within the screen.

  Hereinafter, the processing flow of the image display apparatus according to the present embodiment will be described with reference to FIGS. FIG. 1 is a block diagram illustrating an example of a functional configuration of the image display apparatus according to the present embodiment. FIG. 2 is a flowchart illustrating an example of a processing flow of the image display apparatus according to the present embodiment.

  First, in S <b> 101, the sensor unit 101 (sensor 211) measures the luminance of incident light and outputs the measurement value to the measurement value determination unit 103. Thereafter, the process proceeds to S102.

In this embodiment, the sensor unit 101 operates in a plurality of operation modes including a backlight light monitoring mode (first mode) and an ambient light measurement mode (second mode). The backlight light monitoring mode is an operation mode in which light emitted from the backlight is measured (first measurement) in a state where the backlight is turned on. The ambient light measurement mode is an operation mode in which ambient light transmitted through the screen with the backlight turned off is measured (second measurement).
The operation mode is set and switched, for example, at a timing corresponding to a user operation or at a predetermined timing. For example, the backlight light monitoring mode is automatically set at the start of use of the image display device, and after the backlight light is measured, the operation mode is automatically switched to the ambient light measurement mode.
The mode information generation unit 102 generates mode information indicating the current operation mode, and outputs the mode information to the measurement value determination unit 103, the backlight control unit 105, and the shutter control unit 108. The backlight control unit 105 controls the backlight with a backlight control value corresponding to the operation mode. The shutter control unit 108 controls the liquid crystal shutter (the transmittance of the liquid crystal shutter) with a shutter control value (image signal) corresponding to the operation mode. A method for controlling the backlight and the liquid crystal shutter according to the operation mode will be described later.

In S102, the measurement value determination unit 103 determines the current operation mode from the mode information.
When the current operation mode is the backlight light monitoring mode, the measurement value determination unit 103 determines that the measurement value obtained in S101 is the measurement value of the backlight light. Then, the measurement value determination unit 103 adds the information indicating that the measurement value obtained in S101 is the measurement value of the backlight light, and outputs it to the backlight control value determination unit 104 (S103).
When the current operation mode is the ambient light measurement mode, the measurement value determination unit 103 determines that the measurement value obtained in S101 is the measurement value of ambient light. Then, the measurement value determination unit 103 adds the information indicating that the measurement value obtained in S101 is the measurement value of the ambient light, and outputs it to the backlight control value determination unit 104 (S104).

  In the present embodiment, the processes of S101 to S104 are repeatedly performed for each of the backlight light monitoring mode and the ambient light measurement mode. Thereafter, the process proceeds to S105.

In S105 and S106, the backlight control value determination unit 104 and the backlight control unit 105 control the backlight based on the measured value of the backlight light and the measured value of the ambient light.
Specifically, in S105, the backlight control value determination unit 104 controls the backlight (specifically, each light source) based on the measurement value of the backlight light and the measurement value of the ambient light. Determine the control value. The backlight control value determination unit 104 outputs the determined backlight control value to the backlight control unit 105. Thereafter, the process proceeds to S106.
In S106, the backlight control unit 105 controls the backlight (specifically, each light source) according to the backlight control value determined in S105. Specifically, each light source is controlled to emit light with light emission luminance corresponding to the backlight control value.

  A specific example of measurement of backlight light and ambient light will be described.

An example in which the operation mode is the backlight light monitoring mode will be described.
When the operation mode is the backlight light monitoring mode, the backlight control unit 105 turns on the R light source 208, the G light source 209, and the B light source 210 in order. For example, the backlight control unit 105 turns on the R light source 208, the G light source 209, and the B light source 210 in order at a reference value (for example, a predetermined backlight control value). FIG. 4 shows a state where only the G light source 209 is turned on. For each color, the sensor unit 101 measures the luminance of the backlight light in a state where the light source of that color is turned on. Specifically, as shown in FIG. 4, the backlight light is diffused by the diffusion plate 207. Then, the diffused backlight light enters the sensor unit 101 (sensor 211) and is measured.

As shown in FIG. 4, the backlight light may be measured with the liquid crystal shutter corresponding to the color to be measured open, or may be measured with all the liquid crystal shutters open. Measurement may be performed with all the liquid crystal shutters closed. In order to reduce the influence of ambient light on the measurement value of the backlight light, the backlight light is preferably measured with all the liquid crystal shutters closed.
A relative luminance value or a color (for example, color temperature or chromaticity) may be calculated as the measured value of the backlight light.

The backlight obtained by lighting the R light source 208, Lr, the luminance value of the backlight light obtained by lighting the G light source 209, Lg, and the B light source 210. Let the luminance value of light be Lb. The relative luminance values of Lr, Lg, and Lb (relative values with respect to the luminance values of the backlight lights of other colors) Ir, Ig, and Ib can be calculated using Equations 1-1 to 1-3. In Expressions 1-1 to 1-3, MAX (Lr, Lg, Lb) represents the maximum value among Lr, Lg, and Lb.

Ir = Lr / MAX (Lr, Lg, Lb) (Formula 1-1)
Ig = Lg / MAX (Lr, Lg, Lb) (Formula 1-2)
Ib = Lb / MAX (Lr, Lg, Lb) (Formula 1-3)

The color temperature T of the backlight light can be calculated by the following method, for example.
First, the wavelength (synthetic wavelength) λt of the combined light of the light emitted from each light source is calculated using Equation 2. λr is the wavelength of light emitted from the R light source 208. λg is the wavelength of light emitted from the G light source 209. λb is the wavelength of the light emitted from the B light source 210. The wavelengths λr, λg, and λb are predetermined values.

λt = λr × Ir + λg × Ig + λb × Ib (Formula 2)

Then, a function representing the relationship between the wavelength and the relative luminance value is calculated from the wavelengths λr, λg, and λb and the relative luminance values Ir, Ig, and Ib. Specifically, as shown in FIG. 6, a function representing a change in relative luminance value with respect to a change in wavelength is calculated. The function in FIG. 6 can be calculated using, for example, a minimum approximation method.
Next, a relative luminance value I (λt) corresponding to λt is calculated from the function of FIG.
Then, the color temperature T is calculated using Equation 3. π is the circumference, h is the Planck constant, c is the speed of light, and k is the Boltzmann constant.

I (λt) = 8πhc / {λt ⁵ × (exp (hc / (kTλt))) − 1}
... (Formula 3)

An example when the operation mode is the ambient light measurement mode will be described.
When the operation mode is the ambient light measurement mode, the backlight control unit 105 turns off all of the R light source 208, the G light source 209, and the B light source 210. The shutter control unit 108 opens the liquid crystal shutters 201 to 203 in order. For example, when the liquid crystal shutter 201 is opened, the shutter control unit 108 sets the transmittance of the liquid crystal shutter 201 to the maximum value and sets the transmittance of the liquid crystal shutters 202 and 203 to the minimum value. FIG. 5 shows a state in which only the liquid crystal shutter 203 corresponding to blue is opened. For each color, the sensor unit 101 measures the luminance of the ambient light in a state where the transmittance of the liquid crystal element corresponding to the color other than the color is set to the minimum value. Specifically, as shown in FIG. 5, the ambient light passes through the screen and is diffused by the diffusion plate 207. Then, the diffused ambient light is incident on the sensor unit 101 (sensor 211) and measured. At this time, ambient light passes through a liquid crystal element of a specific color (specifically, a color filter of a specific color). Therefore, the sensor 211 measures a specific color component of ambient light (in the example of FIG. 5, the blue component of ambient light).

The ambient light irradiated on the screen is ambient light before being diffused by the diffusion plate 207. For this reason, it is preferable that the ambient light before being diffused by the diffusion plate 207 is measured. In order to measure the ambient light before being diffused by the diffusion plate 207, the sensor 211 is preferably provided on the display panel side of the diffusion plate 207.
Similar to the backlight light, a relative luminance value or a color (for example, color temperature, chromaticity) may be calculated as a measurement value of the ambient light. The relative luminance value and color of ambient light can be calculated in the same manner as the relative luminance value and color of backlight light. However, when calculating the combined wavelength, the wavelength of light transmitted through each color filter is used instead of the wavelength of light emitted from each light source.

The ambient light passes through various members (for example, a liquid crystal shutter, a color filter, a diffusion plate) and enters the sensor. Since the transmittance of each member is not 100%, the luminance of the ambient light decreases from reaching the screen to reaching the sensor. It is preferable to obtain a brightness value in which the above-described decrease is compensated for as the brightness value of the ambient light. For example, by adjusting the gain value of the sensor (switching the gain value of the sensor in accordance with the operation mode), a luminance value in which the above-described decrease is compensated can be obtained as the luminance value of the ambient light.
Specifically, the luminance value of the ambient light when reaching the screen is set to 100 cd / m ² . Here, assuming that the transmittance (maximum value) of the liquid crystal shutter is 90%, the transmittance of the color filter is 30%, and the transmittance of the diffusion plate is 40%, the luminance value of the ambient light when reaching the sensor is 11 cd / the m ^2. That is, the brightness of the ambient light decreases to about 1/10 after reaching the screen and reaching the sensor. In this case, the brightness value of the ambient light when it reaches the screen can be measured by setting the gain value of the sensor 10 times that in the backlight light monitoring mode in the ambient light measurement mode.
Note that the sensor gain value may be a constant value, and a correction process may be performed to compensate for the decrease in the luminance value measured in the ambient light measurement mode.

A specific example of determining the backlight control value will be described.
By determining the backlight control value based on the measurement value of the backlight light, it is possible to correct the change (time-dependent change) of the backlight light. As a result, it is possible to reduce changes in luminance, color, or both on the screen due to changes in backlight light.
Further, by determining the backlight control value based on the measured value of the ambient light, it is possible to reduce changes in the brightness, color, or both on the screen due to the ambient light.
In the present embodiment, the backlight control value is determined using the measured value of the backlight light and the measured value of the ambient light, so that the change in the backlight light and the brightness on the screen due to the ambient light, the color, or Both changes are reduced.

The backlight control value can be determined using, for example, expressions 4-1 to 4-3. BLr is a backlight control value of the R light source 208. BLg is a backlight control value of the G light source 209. BLb is a backlight control value of the B light source 209. SBLr is a reference value (for example, a predetermined backlight control value) of the R light source 208. SBLg is a reference value of the G light source 209. SBLb is a reference value of the B light source 209. ALr is the measured luminance value of the red component of the ambient light. ALg is the measured luminance value of the green component of the ambient light. ALb is the measured luminance value of the blue component of the ambient light. SALr is a luminance value of a red component of predetermined ambient light. SALg is a luminance value of a green component of predetermined ambient light. SALb is a luminance value of a blue component of predetermined ambient light. Lr is the luminance value of the backlight light measured with the R light source 208 turned on. Lg is the luminance value of the backlight light measured with the G light source 209 turned on. Lb is the luminance value of the backlight light measured with the B light source 210 turned on. SLr is an expected value of Lr corresponding to SBLr. SLg is an expected value of Lg corresponding to SBLg. SLb is an expected value of Lb corresponding to SBLb.

BLr = SBLr × (SALr / ALr) × (SLr / Lr) (Formula 4-1)
BLg = SBLg × (SALg / ALg) × (SLg / Lg) (Formula 4-2)
BLb = SBLb × (SALb / ALb) × (SLb / Lb) (Formula 4-3)

  The method for determining the backlight control value is not limited to the above method, and various methods can be employed. For example, the backlight control value may be determined using a table in which a combination of a backlight light value and an ambient light value is associated with a backlight control value. When a plurality of sensors are provided, representative values (average value, mode value, intermediate value, maximum value, minimum value) of measured values of the plurality of sensors are indicated as ALr, ALg, ALb, Lr, Lg, Lb. Etc.) may be used.

When the backlight is composed of a plurality of divided areas that can be individually controlled and a plurality of sensors are provided (for example, a sensor is provided for each divided area), for each divided area, expressions 5-1 to 5-1 The backlight control value may be determined using 5-3. MAX (ALr) is the maximum value of ALr for each divided region, MAX (ALg) is the maximum value of ALg for each divided region, and MAX (ALb) is the maximum value of ALb for each divided region. MAX (Lr) is the maximum value of Lr for each divided region, MAX (Lg) is the maximum value of Lg for each divided region, and MAX (Lb) is the maximum value of Lb for each divided region. The other values are values corresponding to the divided areas to be processed. For example, BLr is the backlight control value of the R light source 208 (R light source 208 provided in the processing target divided region) corresponding to the processing target divided region. ALr that divides MAX (ALr) is the luminance value of the red component of the ambient light measured by the sensor 211 corresponding to the divided area to be processed. Lr that divides MAX (Lr) is the luminance value of the backlight light measured by the sensor 211 corresponding to the division area to be processed, and is measured with all the R light sources 208 turned on at the reference value. This is the brightness value of the light.

BLr = SBLr × (MAX (ALr) / ALr) × (MAX (Lr) / Lr)
... (Formula 5-1)
BLg = SBLg × (MAX (ALg) / ALg) × (MAX (Lg) / Lg)
... (Formula 5-2)
BLb = SBLb × (MAX (ALb) / ALb) × (MAX (Lb) / Lb)
... (Formula 5-3)

  As described above, according to the present embodiment, not only backlight light but also ambient light is measured by the backlight light measurement (monitoring) sensor provided in the image display apparatus. As a result, the ambient light can be measured with a simple configuration without reducing the visibility of the image displayed on the screen. Specifically, an increase in cost due to a separate sensor for measuring ambient light can be prevented by a simple configuration in which the sensor for measuring backlight light has a function of measuring ambient light. In addition, since the sensor is provided in the image display device (a position not perceived by the user when the user views the screen), the ambient light is measured without reducing the visibility of the image displayed on the screen. be able to.

Further, according to the present embodiment, the backlight is controlled based on the measured value of the backlight light and the measured value of the ambient light. Thereby, the change of the brightness | luminance on a screen, a color, or both by the change of backlight light and environmental light can be reduced.
When the backlight is composed of a plurality of divided areas and a plurality of sensors are provided, the backlight control value of each divided area is determined based on the measurement values obtained by the plurality of sensors, thereby obtaining the backlight. It is possible to reduce luminance unevenness, color unevenness, or both on the screen due to a change in light and ambient light.

In this embodiment, an example in which the image display device is a liquid crystal display device has been described. However, the image display device is not limited to a liquid crystal display device. For example, the image display device may be an organic EL display device having a backlight using an organic EL element as a light source and a display panel having a color filter.
In addition, although backlight light and environmental light shall be measured for every color, it is not restricted to this. For example, the measured value of the backlight light may be a value obtained in a state where all the light sources are turned on. The measured value of ambient light may be a value obtained with all liquid crystal shutters open.
In this embodiment, the backlight is controlled based on the measured value of the backlight light and the measured value of the ambient light. However, the present invention is not limited to this. For example, the image display device includes an image processing unit that performs image processing on an input image signal (an image signal input to the image display device) based on a measured value of backlight light and a measured value of ambient light. It may be. It is possible to reduce the change in the brightness, color, or both on the screen due to the change in the backlight and the ambient light, not by the backlight control but also by the image processing. Both backlight control and image processing may reduce changes in backlight brightness and on-screen brightness, color, or both due to ambient light.

<Example 2>
An image display apparatus and a control method thereof according to Embodiment 2 of the present invention will be described.
Conventionally, there is a technique for determining a backlight control value based on a pixel value of an input image signal. For example, the brightness of the backlight is reduced when displaying a dark image signal as a whole. Thereby, power consumption can be reduced and contrast can be improved. Further, a technique for determining a backlight control value of a divided area based on a pixel value of an image signal corresponding to the divided area for each divided area using a backlight composed of a plurality of divided areas that can be individually controlled. There is. Such a technique is called local dimming. Contrast can be further improved by local dimming.
However, even if the above prior art is used, the brightness, color, or both on the screen changes due to the influence of ambient light, and thus a desired display cannot be performed. In addition, when the backlight characteristics change due to repeated use (when the backlight light changes with time), the luminance, color, or both on the screen also changes. Cannot display.
In this embodiment, a configuration that can solve such a problem will be described.

The rough hardware configuration of the image display apparatus according to the present embodiment is the same as that of the first embodiment (FIG. 3). However, in this embodiment, it is assumed that the backlight is composed of a plurality of divided regions that can be individually controlled. For example, the backlight includes an R light source 208, a G light source 209, and a B light source 210 for each divided region.
In this embodiment, it is assumed that the sensor 211 is provided for each divided area, but the present invention is not limited to this. The number of sensors 211 may be larger or smaller than the number of divided regions (the number of sensors 211 may be one).

  Hereinafter, the processing flow of the image display apparatus according to the present embodiment will be described with reference to FIGS. FIG. 7 is a block diagram illustrating an example of a functional configuration of the image display apparatus according to the present embodiment. FIG. 8 is a flowchart illustrating an example of a processing flow of the image display apparatus according to the present embodiment.

The processing of S201 to S204 is the same as the processing of S101 to S104 in FIG.
In S <b> 205, the input image signal is input to the backlight control value temporary determination unit 106. The backlight control value provisional determination unit 106 provisionally determines the backlight control value based on the pixel value of the input image signal. Specifically, for each divided area, the backlight control value of the divided area is determined based on the pixel value of the image signal corresponding to the divided area. The temporarily determined backlight control value is output to the backlight control value determination unit 104.
In addition, the process of S201-S204 and the process of S205 may be performed in parallel, and may be performed in order. Either the process of S201 to S204 or the process of S205 may be performed first.

  Following the processing of S201 to S205, the backlight control value determination unit 104 determines the backlight control value determined in S205 based on the measurement value of the backlight light and the measurement value of the environmental light for each divided region. Is corrected (S206). The backlight control value determination unit 104 outputs the corrected backlight control value to the backlight control unit 105.

Specifically, the backlight control value is corrected for each divided region using Equations 6-1 to 6-3. MAX (ALr) is the maximum value of ALr for each divided region, MAX (ALg) is the maximum value of ALg for each divided region, and MAX (ALb) is the maximum value of ALb for each divided region. MAX (Lr) is the maximum value of Lr for each divided region, MAX (Lg) is the maximum value of Lg for each divided region, and MAX (Lb) is the maximum value of Lb for each divided region. The other values are values corresponding to the divided areas to be processed. For example, BLr is a backlight control value after correction of the R light source 208 corresponding to the divided area to be processed. BLg is a backlight control value after correction of the G light source 209 corresponding to the divided area to be processed. BLb is a backlight control value after correction of the B light source 210 corresponding to the divided area to be processed. LDr is a backlight control value before correction of the R light source 208 corresponding to the divided area to be processed. LDg is a backlight control value before correction of the G light source 209 corresponding to the division area to be processed. LDb is a backlight control value before correction of the B light source 210 corresponding to the divided area to be processed. ALr that divides MAX (ALr) is the luminance value of the red component of the ambient light measured by the sensor 211 corresponding to the divided area to be processed. Lr that divides MAX (Lr) is the luminance value of the backlight light measured by the sensor 211 corresponding to the division area to be processed, and is measured with all the R light sources 208 turned on at the reference value. This is the brightness value of the light.

BLr = LDr × (MAX (ALr) / ALr) × (MAX (Lr) / Lr)
... (Formula 6-1)
BLg = LDg × (MAX (ALg) / ALg) × (MAX (Lg) / Lg)
... (Formula 6-2)
BLb = LDb × (MAX (ALb) / ALb) × (MAX (Lb) / Lb)
... (Formula 6-3)

Note that the method for correcting the backlight control value is not limited to the above method, and various methods can be employed. For example, a correction coefficient is selected from a table in which a combination of a backlight light value and an ambient light value is associated with a correction coefficient of the backlight control value, and the backlight control value is determined using the selected correction coefficient. It may be corrected. Further, instead of MAX (ALr), MAX (ALg), MAX (ALb), MAX (Lr), MAX (Lg), MAX (Lb), other representative values (mode value, average value, intermediate value, A minimum value) may be used. SALr, SALg, SALb is used instead of MAX (ALr), MAX (ALg), MAX (ALb), and SLr, SLg, SLb is used instead of MAX (Lr), MAX (Lg), MAX (Lb). Also good.

  Following S206, the backlight control unit 105 controls the backlight according to the backlight control value corrected in S205 (S207).

Note that the image processing unit 107 may perform image processing on the input image signal. Specifically, the image processing unit 107 may perform image processing on the input image signal based on the corrected backlight control value and the measured value of ambient light.
In that case, the processing of S208 and S209 is performed after S206. Note that the processing of S208 and S209 may be performed in parallel with the processing of S207, or may be performed before or after S207.
In S <b> 208, the backlight control value determination unit 104 outputs the corrected backlight control value for each divided region and the ambient light measurement value for each divided region to the image processing unit 107. Then, the image processing unit 107, based on the corrected backlight control value and the measured value of the ambient light, changes in the light emitted from the backlight, the brightness on the screen due to the ambient light, the color, Alternatively, the input image signal is corrected so that both changes are reduced. In this embodiment, the backlight luminance distribution and the ambient light luminance distribution are determined from the corrected backlight control value for each divided region and the measured value of the ambient light for each divided region. Based on the luminance distribution, the input image signal is corrected so that the luminance unevenness is reduced. The image processing unit 107 outputs the corrected image signal (or the shutter control value of each pixel corresponding to the corrected image signal) to the shutter control unit 108. Note that image processing may be performed in units of pixels or may be performed in units of divided areas.
In step S209, the shutter control unit 108 controls the liquid crystal shutter according to the corrected image signal.

  As described above, according to the present embodiment, the backlight control value based on the image signal is corrected based on the measured value of the backlight light and the measured value of the ambient light. Further, the input image signal is corrected based on the corrected backlight control value and the measured value of the ambient light. Thereby, in the image display apparatus that controls the backlight based on the image signal, it is possible to reduce changes in the brightness, color, or both on the screen due to the change in the backlight light and the ambient light.

Note that the image processing may or may not be performed. If the image processing is performed, it is possible to further reduce changes in luminance, color, or both on the screen due to changes in backlight light and ambient light. Further, if the gradation is expanded or compressed so that the brightness on the screen of the brightest part does not change by the above image processing, the contrast can be further increased. Image processing may be performed based on the backlight light measurement value and the ambient light measurement value instead of the corrected backlight control value and the ambient light measurement value.
In the present embodiment, an example of an image display apparatus having a local dimming function has been described. However, the present invention is not limited to this. For example, a backlight control value common to the entire screen may be determined based on the pixel value of the input image signal. The determined backlight control value may be corrected based on the measured value of the backlight light and the measured value of the ambient light.

201-203 Liquid crystal shutter 204-206 Color filter 208-210 Light source 211 Sensor 212 Substrate

Claims (16)

A display panel;
A backlight provided on the back side of the display panel;
Measuring means provided between the backlight and the display panel or on the substrate of the backlight;
Have
The measurement means includes a first mode for measuring light emitted from the backlight with the backlight turned on, and a second mode for measuring ambient light transmitted through the screen with the backlight turned off. An image display device that operates in a plurality of operation modes including: The display panel is a liquid crystal panel having a plurality of liquid crystal elements corresponding to different colors,
The second mode is an operation mode for measuring the brightness of ambient light in a state where the transmittance of a liquid crystal element corresponding to a color other than that color is set to a minimum value for each color. The image display device described in 1. The image display apparatus according to claim 2, wherein in the second mode, the chromaticity of the ambient light is further calculated from the measured luminance value for each color. Based on the measured value of the light emitted from the backlight and the measured value of the ambient light, the change in the light emitted from the backlight and the brightness, color, or both on the screen due to the ambient light The image display apparatus according to claim 1, further comprising a control unit that controls the backlight so that a change in the light intensity is reduced. The control means includes
Determine a control value for controlling the backlight based on the pixel value of the input image signal,
The image display apparatus according to claim 4, wherein the determined control value is corrected based on a measured value of light emitted from the backlight and a measured value of ambient light. The backlight is composed of a plurality of divided regions that can be individually controlled,
The control means includes
For each of the divided areas, a control value for the divided area is determined based on the pixel value of the image signal corresponding to the divided area.
6. The image display according to claim 5, wherein the determined control value is corrected based on a measured value of light emitted from the backlight and a measured value of ambient light for each of the divided regions. apparatus. Based on the control value after correction and the measured value of ambient light, the change in the light emitted from the backlight and the change in brightness, color, or both on the screen due to the ambient light are reduced. The image display device according to claim 5, further comprising image processing means for performing image processing on the input image signal. Based on the measured value of the light emitted from the backlight and the measured value of the ambient light, the change in the light emitted from the backlight and the brightness, color, or both on the screen due to the ambient light The image display device according to claim 1, further comprising image processing means for performing image processing on the input image signal so that a change in the image signal is reduced. A display panel;
A backlight provided on the back side of the display panel;
A measurement unit provided between the backlight and the display panel or on the substrate of the backlight;
A method for controlling an image display device comprising:
A first measurement step of measuring light emitted from the backlight in a state where the backlight is lit by the measurement unit;
A second measurement step of measuring ambient light transmitted through the screen with the backlight turned off by the measurement unit;
A control method for an image display device, comprising: The display panel is a liquid crystal panel having a plurality of liquid crystal elements corresponding to different colors,
In the second measurement step, the brightness of the ambient light is measured for each color in a state where the transmittance of the liquid crystal element corresponding to the color other than the color is set to the minimum value by the measurement unit. The method for controlling an image display device according to claim 9, wherein the method is a step of calculating chromaticity of ambient light from a measured value. The method of controlling an image display device according to claim 10, wherein in the second measurement step, the measurement unit further calculates chromaticity of ambient light from a measurement value of luminance for each color. Based on the measured value of the light emitted from the backlight and the measured value of the ambient light, the change in the light emitted from the backlight and the brightness, color, or both on the screen due to the ambient light The method for controlling an image display device according to claim 9, further comprising a control step of controlling the backlight so that a change in the brightness is reduced. In the control step,
A control value for controlling the backlight is determined based on the pixel value of the input image signal,
13. The control method for an image display device according to claim 12, wherein the determined control value is corrected based on a measured value of light emitted from the backlight and a measured value of ambient light. The backlight is composed of a plurality of divided regions that can be individually controlled,
In the control step,
For each of the divided areas, based on the pixel value of the image signal corresponding to the divided area, the control value of the divided area is determined,
The image according to claim 13, wherein the determined control value is corrected based on a measured value of light emitted from the backlight and a measured value of ambient light for each of the divided regions. Display device control method. Based on the control value after correction and the measured value of ambient light, the change in the light emitted from the backlight and the change in brightness, color, or both on the screen due to the ambient light are reduced. The image display apparatus control method according to claim 13, further comprising an image processing step of performing image processing on the input image signal. Based on the measured value of the light emitted from the backlight and the measured value of the ambient light, the change in the light emitted from the backlight and the brightness, color, or both on the screen due to the ambient light The method for controlling an image display device according to claim 9, further comprising an image processing step of performing image processing on the input image signal so that a change in the image signal is reduced.

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