JP2008015207A - Display device and method for controlling screen luminance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To finely control luminance corresponding to human visual characteristics without causing a large increase in the manufacture cost or much complication of a device. <P>SOLUTION: The display device is equipped with: an information extracting means 14 that extracts luminance information of a pixel having a luminance higher than a first threshold set in a higher luminance side than the median between the maximum luminance and the minimum luminance which can be displayed on a display unit, from video signals of the whole pixels in the display unit, and extracts luminance information of a pixel having a luminance lower than a second threshold set in a lower luminance side than the median between the maximum luminance and the minimum luminance which can be displayed on the display unit, from the video signals of the whole pixels in the display unit; and a light source control means 12 that controls the luminance output of a light source on the basis of the luminance information of the pixel having a higher luminance than the first threshold and on the luminance information of the pixel having a lower luminance than the second threshold. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a display device that displays a video signal and the like and a screen brightness control method thereof. More specifically, the present invention relates to a direct-view or projection-type display device and a screen brightness control method that have a light source and dynamically adjust the brightness of the light source according to a video signal to be displayed.

  Conventionally, with respect to display quality of a display device, there is a problem that screen brightness control that sufficiently reflects human visual characteristics is not performed.

  For example, when a high-luminance video is displayed, the problem is that the entire screen is too bright, or when the low-luminance image is displayed, the entire screen is not sufficiently reduced in brightness. It is a problem that a so-called black float occurs.

  In order to solve this problem, for example, an attempt has been made to dynamically control light source luminance by providing a correlation between a video signal and luminance adjustment of a light source (backlight).

  For example, in Patent Document 1, as shown in FIG. 7, 1) the screen is divided in the horizontal direction and the vertical direction, and 2) an average luminance level (APL: Average Picture Level) is obtained for each of the divided areas. 3) A configuration is described in which the output of a light source (fluorescent tube) provided for each region is controlled according to the level.

In Patent Document 2, as shown in FIGS. 8A to 8D, 1) First, the maximum luminance level (MAX) and the minimum luminance level (MIN) of the input video signal (FIG. 8A) are described. ) And the average luminance level (APL), the dynamic range of the video signal is expanded (FIG. 8B), and the video signal is level-shifted by the offset (FIG. 8C), and 2) A configuration is described in which the shift of the visual luminance level on the screen caused by the level shift is corrected by light source luminance adjustment (FIG. 8D).
JP 2000-321571 A (published on November 24, 2000) Japanese Patent Laid-Open No. 2001-27890 (released on January 30, 2001)

  However, in the configuration described in Patent Document 1, it is necessary to increase the number of regions to be divided and the number of light sources in order to perform fine luminance control within the screen. In addition, when the luminance of the light source is greatly different between the regions, an unnatural luminance change occurs at the boundary between the regions. Therefore, it is necessary to incorporate a device for suppressing the luminance. Therefore, there are problems such as an increase in manufacturing cost and a complicated apparatus.

  In the configuration described in Patent Document 2, the luminance adjustment of the light source is performed based only on the maximum luminance level, minimum luminance level, and average luminance level (APL) of the video signal. Therefore, there is a problem that fine luminance adjustment according to human visual characteristics cannot be performed. Furthermore, when the maximum luminance level and the minimum luminance level are respectively equal to the upper limit and the lower limit of the dynamic range, there is a problem that the backlight output adjustment itself is not performed.

  The present invention has been made in view of the above-mentioned problems, and its object is to fine-tune according to human visual characteristics without causing a significant increase in manufacturing cost and a significant complication of the apparatus. The object is to realize a display device and a screen brightness control method capable of adjusting brightness.

  In order to solve the above problems, the display device of the present invention is a display device including a display unit and a light source that irradiates the display unit. From the video signals of all the pixels of the display unit, the display unit In addition to extracting luminance information of pixels having a luminance higher than the first threshold set on the higher luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed in the video signal, the video signal of all the pixels of the display unit Information extracting means for extracting luminance information of a pixel having a luminance lower than a second threshold set on a lower luminance side than a median value of the maximum luminance and the minimum luminance that can be displayed on the display unit, Light source control means for adjusting a luminance output of the light source based on luminance information of a pixel having a luminance higher than the first threshold and luminance information of a pixel having a luminance lower than the second threshold; It is characterized by being provided There.

The screen brightness control method of the present invention is a screen brightness control method for controlling the brightness of the screen of the display device by adjusting the brightness output of the light source of the display device. From the signal, the luminance information of pixels having a luminance higher than the first threshold set on the higher luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit is extracted, and Among the video signals of all the pixels of the display unit of the display device, the luminance is lower than a second threshold value set on the lower luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit. Based on the first step of extracting the luminance information of the pixel, the luminance information of the pixel having a luminance higher than the first threshold, and the luminance information of the pixel having a luminance lower than the second threshold, The brightness output of the light source A psychological quantity (impression or intensity of stimulus) actually received when a human feels brightness or darkness is the brightness of the object (especially the brightness from a certain threshold value). Difference), the area of the object (specifically, the area occupied in the human visual field), the adaptation luminance (ambient illuminance), and the contrast effect. Therefore, in order to perform screen luminance control that matches human visual characteristics, it is necessary to reflect the parameters in the screen luminance control and light source control in the form that matches the human visual characteristics as accurately as possible.

  According to the above configuration, the luminance output of the light source is controlled not based on the entire luminance range of the video signal but on the luminance information of the high luminance part and the low luminance part defined based on the preset threshold value. Is called.

  Specifically, out of the video signals of all the pixels, for example, the luminance information of the pixels whose luminance is higher than the threshold value (first threshold value) that humans feel bright, and the threshold value (second threshold value) that humans feel dark, for example. The luminance information of the pixel having a lower luminance than) is selectively extracted, and the luminance output of the light source is adjusted based on the extracted luminance information.

  Therefore, unlike the conventional luminance adjustment based on the luminance average of the video signals of all the pixels, the luminance control is performed based on parameters that affect the psychological quantity actually received. For this reason, it is possible to perform fine luminance control that sufficiently reflects human visual characteristics.

  In addition, it is not necessary to newly increase the number of light sources, and this does not cause an increase in cost or complication of the apparatus.

  Therefore, it is possible to realize a display device and a screen luminance control method capable of performing fine luminance adjustment according to human visual characteristics without causing a significant increase in manufacturing cost and a great complexity of the device.

  In the display device according to the present invention, the first threshold value and the second threshold value are set based on the ambient illuminance detection unit that detects the illuminance around the display unit, and the ambient illuminance detected by the ambient illuminance detection unit. Preferably, a threshold setting unit is provided.

  According to the above configuration, a video signal with a high luminance and a low luminance according to the adaptation luminance (ambient illuminance), which is a parameter that affects human visual characteristics (a psychological amount when feeling brightness or darkness). Threshold values (first threshold value and second threshold value) for dividing the video signal can be determined. Therefore, it is possible to adjust the luminance according to the human visual characteristics.

  Specifically, since it is possible to perform luminance control by incorporating the effect of adaptation by ambient light, it is possible to reduce dazzling feeling and visual fatigue.

  In the display device of the present invention, in order to adjust the luminance output of the light source, the pixel area which is the luminance information of the pixel having luminance higher than the first threshold and the average luminance level (APL: Average Picture) of the pixel. The first index for determining the light source output from the level), and the area of the pixel as the luminance information of the pixel having the luminance lower than the second threshold and the average luminance level (APL) of the pixel, Exponential calculation means for obtaining a second exponent for determining the light source output from the light source is provided, and the light source control means adjusts the luminance of the light source output by a combination of the first exponent and the second exponent. It is preferable to do. Note that the pixel is a structural unit of the display unit, and the area of the pixel means a display area in the display unit.

  According to the above configuration, both the luminance and area of the image, which are parameters that affect human visual characteristics (psychological quantity), can be reflected in the control of the luminance output of the light source. Brightness control that matches the visual characteristics is possible.

  Note that the area occupied by the object in the human visual field is a parameter related to the viewing distance of the video, but it varies depending on the user and is difficult to reflect in the luminance control of the light source. Therefore, here, the area is a parameter that reflects the luminance control as viewed from a certain viewing distance.

  Further, since the first index from the luminance information of the video signal having a high luminance and the second index from the luminance information of the video signal having a low luminance are obtained, a comparison or combination of the plurality of indexes can be used. It becomes possible to control. That is, it is possible to control the light source in consideration of the contrast effect, which is a parameter that affects human visual characteristics (psychological quantity). Here, the contrast effect refers to, for example, a contrast between a portion with high luminance and a portion with low luminance.

  As a result, it is possible to display a high-contrast image with less glare, less visual fatigue, and less black float. Furthermore, the power consumption of the light source can be reduced.

  In the display device of the present invention, in order to adjust the luminance output of the light source, the pixel area which is the luminance information of the pixel having luminance higher than the first threshold, and the average luminance level (APL) of the pixel, A first index for determining a light source output from a difference from the first threshold, and an area of the pixel which is luminance information of a pixel having luminance lower than the second threshold; and a second threshold Exponential calculation means for obtaining a second index for determining the light source output from the difference from the average luminance level (APL) of the pixel is provided, and the light source control means includes the first index based on the type of image. It is preferable to adjust the luminance output of the light source by a combination of the first and second indices.

  According to the above configuration, a luminance difference from a specific threshold, which is a parameter affecting human visual characteristics (psychological quantity), can be reflected in luminance control of the light source. Therefore, it is possible to perform luminance control that better matches human visual characteristics.

  In the display device of the present invention, it is preferable that input means for setting and inputting the first threshold value and the second threshold value is provided.

  According to the above configuration, brightness control reflecting individual differences is possible, and brightness control according to personal preference is possible.

  As described above, the display device of the present invention can be displayed on the display unit from the video signals of all the pixels of the display unit in the display device including the display unit and the light source that irradiates the display unit. Luminance information of pixels having a luminance higher than the first threshold set on the higher luminance side than the median value of the maximum luminance and the minimum luminance is extracted, and from the video signals of all the pixels of the display unit Information extracting means for extracting luminance information of pixels having a luminance lower than a second threshold value set on a lower luminance side than a median value of the maximum luminance and the minimum luminance that can be displayed on the display unit; Light source control means for adjusting a luminance output of the light source based on luminance information of a pixel having a luminance higher than a threshold of 1 and luminance information of a pixel having a luminance lower than the second threshold; ing.

  Further, the screen brightness control method of the present invention is the screen brightness control method for controlling the brightness of the screen of the display device by adjusting the brightness output of the light source of the display device as described above. Brightness information of pixels having a brightness higher than the first threshold set on the higher brightness side than the median value of the maximum brightness and the minimum brightness that can be displayed on the display unit. The second threshold value set on the lower luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit is extracted from the video signals of all the pixels of the display unit of the display device. A first step of extracting luminance information of a pixel having a lower luminance, luminance information of a pixel having a luminance higher than the first threshold, and luminance information of a pixel having a luminance lower than the second threshold; Based on the light And a second step of adjusting the luminance output.

  Therefore, it is possible to realize a display device and a screen luminance control method capable of performing fine luminance adjustment according to human visual characteristics without causing a significant increase in manufacturing cost and a great complexity of the device. Play.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram illustrating a configuration of a display device 1 according to the present embodiment.

  As shown in FIG. 1, the display device 1 according to the present embodiment includes a display unit 2, a light source 3, and a control unit 10 that controls the display unit 2 and the light source 3. The control unit 10 includes a display control unit 11 for controlling the display unit 2, a light source control unit 12 as a light source control unit for controlling the light source 3, and the illuminance of ambient light of the display device 1. An illuminance detection unit 13 as ambient illuminance detection means for detection is provided.

  The control unit 10 is configured so that a video signal (input video signal) input to the display device 1 is transmitted not only to the display control unit 11 but also to the light source control unit 12. Yes. That is, a terminal (signal input terminal) through which the input video signal is input to the display device 1 is connected to the display control unit 11 and the light source control unit 12 via the information extraction unit 14 (information extraction means). Also connected to.

  The information extraction unit 14 includes a division circuit unit 15, an average luminance level (APL) detection unit 16 for each block, a luminance comparison unit 17, an area calculation unit 18, and an average luminance level (APL) detection unit 19 for each area. From the signal input terminal, the dividing circuit unit 15, the block average luminance level (APL) detection unit 16, the luminance comparison unit 17, the area calculation unit 18, and the area average luminance level (APL) detection unit 19 are arranged in this order. It is connected. Here, the block refers to each area that can be obtained by dividing the screen of the display unit 2 into the X direction and the Y direction.

  On the other hand, the illuminance detection unit 13 is connected to the luminance comparison unit 17 of the information extraction unit 14 via a threshold value calculation unit 20 as a threshold setting unit.

  The information extraction unit 14 to which an input video signal and the illuminance of ambient light are input is connected to the light source control unit 12. The light source control unit 12 includes an exponent calculation unit 21 as an exponent calculation unit, a lookup table unit 22 and a light source output control unit 23, and the exponent calculation unit 21 is an end of the information extraction unit 14. Is connected to an average luminance level (APL) detection unit 19 for each area located in the area.

  Here, the lookup table unit 22 is a comparison table of input and output, which will be described in detail later, and is used to determine the backlight output P based on the index calculated by the index calculation unit 21. Say.

  The area refers to an aggregate of blocks having a higher average luminance level (APL) and lower blocks than the threshold value calculated by the threshold value calculation unit 20 in the block.

  When the user sets the threshold (in the above configuration, the threshold calculator 20 calculates) according to preference (brightness control parameter user setting), the illuminance detector 13 and the threshold calculator 20 Is unnecessary, and an input device (input means, not shown) for allowing the user to input the threshold value to the luminance comparison unit 17 can be provided separately.

  Next, screen brightness control in the display device 1 of the present embodiment will be described.

  FIG. 2A, FIG. 3 and FIG. 4 show the screen brightness control flow (steps 1 to 9) of this embodiment in this order.

  Hereinafter, steps 1 to 3 will be described with reference to FIG.

(Step 1)
Step 1 is a step of measuring the ambient illuminance and determining the first threshold value and the second threshold value. Here, the threshold value is a value that becomes a boundary when a video signal having a high luminance and a video signal having a low luminance are distinguished from each other in the input video signal. Specifically, the first threshold value (L _W0 ) is a threshold value for classifying a video signal with high luminance in the video signal, and one second threshold value (L _B0 ) is the threshold value of the video signal. Among them, the threshold value is used when a low-brightness video signal is classified. The first threshold value is set on the higher luminance side than the median value of the maximum luminance and the minimum luminance in the input video signal. The second threshold value is set on the lower luminance side than the median value of the maximum luminance and the minimum luminance in the input video signal.

In step 1, the illuminance sensor provided in the illuminance detection unit 13 shown in FIG. 1 measures the illuminance of the ambient light, and based on the measurement result, the threshold value calculation unit 20 _sets the first threshold value (L _W0 ). A second threshold (L _B0 ) is determined. The illuminance to be measured is preferably screen illuminance.

The determination of the first threshold value (L _W0 ) and the second threshold value (L _B0 ) can be performed using, for example, the following arithmetic expression.

That is,
L _W0 = a ((5.62Ys ^0.31 + b ₁ −1.65) / 23) ^3.23
L _B0 = a ((5.62Ys ^0.31 + b ₂ −1.65) / 23) ^3.23
The first threshold value L _W0 and the second threshold value L _BO can be determined based on the above.

here,
a (coefficient representing the correlation between APL (Average Picture Level) and luminance): When the luminance when APL is y% is xcd / m ² , y = ax
b ₁ and b ₂ (variables for adjusting the threshold): 65 ≦ b ₁ ≦ 80, 20 ≦ b ₂ ≦ 35
Ys (Adaptive luminance): Ambient illuminance (cd / m ² )
It is.

These equations are so-called Haubner's equations,
L = 23Y ^0.31 -5.62Ys ^0.31 +1.65
It was derived with reference to. here,
L: Brightness sensation Y: Object brightness (cd / m ² )
Ys: Adaptive luminance (cd / m ² )
Indicates.

The first threshold value (L _W0 ) and the second threshold value (L _B0 ) are set in advance according to user's preference (user setting of brightness control parameter), and step 1 is configured. It is also possible. In this case, the first threshold value (L _W0 ) and the second threshold value (L _B0 ) may be selected so that the feeling of brightness is the same with respect to the ambient illuminance. The first threshold value (L _W0 ) and the second threshold value (L _B0 ) may be increased.

(Step 2)
Step 2 is a step of dividing the screen into blocks and calculating an average luminance level (APL: Average Picture Level) for each block. A block is an aggregate of pixels constituting the display unit, and indicates each area formed by dividing the screen of the display unit 2 into an X direction and a Y direction, as shown in FIG. .

  In step 2, the dividing circuit unit 15 shown in FIG. 1 divides the input video signal (image information) into signals for each block. The division of the input video signal is performed for each frame of the signal. The average luminance level (APL) detection unit 16 for each block calculates the average luminance level (APL) of the input video signal for each block.

  In the display device 1 according to the present embodiment, as shown in FIG. 2B, the screen is divided into 25 blocks by dividing the screen in 5 columns in both the X direction and the Y direction. The numerical values shown in FIG. 2B indicate the average luminance level (APL) for each block.

Note that the luminance of the input video signal is preferably standardized, and in this embodiment, the luminance is normalized with the maximum luminance value set to 100. Correspondingly, the maximum value of both the first threshold value (L _W0 ) and the second threshold value (L _B0 ) determined in step 1 is 100.

(Step 3)
Step 3 is a step of extracting blocks with high luminance and blocks with low luminance.

Specifically, the luminance comparison unit 17 shown in FIG. 1 compares the average luminance level (APL) of each block with the first threshold (L _W0 ) and the second threshold (L _B0 ), A block (brightness where the average luminance level (APL) is equal to or higher than the first threshold (L _W0 ) (high luminance block: white area) and a block whose average luminance level (APL) is equal to or lower than the second threshold (L _B0 ) Low block: black area).

Here, when the threshold value calculation unit 20 determines the first threshold value (L _W0 ) and the second threshold value (L _B0 ) (not when the user sets them), step 1 and step 2 Proceed in parallel. That is, the illuminance sensor of the illuminance detection unit 13 measures the illuminance of ambient light in real time, and determines the first threshold value (L _W0 ) and the second threshold value (L _B0 ) each time. Then, the first threshold value (L _W0 ) and the second threshold value (L _B0 ) are transmitted from the threshold value calculation unit 20 to the luminance comparison unit 17 in real time. Extracted.

On the other hand, when the user sets the first threshold (L _W0 ) and the second threshold (L _B0 ), the value input by the user from an input device (input means, not shown) provided separately. Is transmitted to the luminance comparison unit 17.

FIG. 2C shows that in the display device 1 according to the present embodiment, each block (25 blocks) belongs to a high luminance block (white region) or belongs to a low luminance block (black region). Is shown. Here, the first threshold value (L _W0 ) = 80 and the second threshold value (L _B0 ) = 20. A black background block indicates the black area block, and a white background block indicates the white area block. Gray blocks indicate blocks that do not belong to any of the above areas.

  Next, steps 4 to 6 will be described with reference to FIG.

(Step 4)
Step 4 is a step for obtaining the areas of the white region and the black region extracted in Step 3. This area means a display area in the display unit 2, and here, the area is represented by the number of the blocks. A _W represents the area (number of blocks) of the white region, and A _B represents the area (number of blocks) of the black region.

  Specifically, the area calculation unit 18 shown in FIG. 1 obtains the number of blocks in both areas.

In the display device 1 according to the present embodiment, as shown in FIG. 2C, the area (A _W ) of the white region is 5 blocks and the area (A _B ) of the black region is 7 blocks.

(Step 5)
Step 5 is a step of obtaining an average luminance level (APL) of blocks belonging to the white area and an average luminance level (APL) of blocks belonging to the black area. Here, the blocks belonging to each area are collectively referred to as an area. That is, all the blocks belonging to the white area are designated as white area areas, and all the blocks belonging to the black area are designated as black area areas.

  In step 5, the average luminance level (APL) detection unit 19 for each area shown in FIG. 1 calculates the average luminance level (APL) between the white area and the black area.

In the display device 1 according to the present embodiment, the average luminance level (APL) (L _Wa ) of the white region is 88, and the average luminance level (APL) (L _Ba ) of the black region is 10.

  This is the average value of the luminance of the five blocks belonging to the white area (80, 80, 90, 90, 100) and the luminance of the seven blocks belonging to the black area (10, 10, 10, 10, 10, 20, 20) Is the average value.

That is,
L _Wa = (80 × 2 + 90 × 2 + 100) / 5 = 88
L _Ba = (10 × 5 + 20) / 7 = 10
It becomes.

(Step 6)
Step 6 includes the difference between the average luminance level (APL) (L _Wa ) of the white area and the first threshold (L _W0 ) (difference from the white area threshold: ΔL _W ), and the average luminance of the black area This is a step of calculating a difference between the level (APL) (L _Ba ) and the second threshold value (L _B0 ) (difference from the black region threshold value: ΔL _B ). Here, the difference (ΔL _W and ΔL _B ) from the threshold is set to a positive number by obtaining the absolute value.

Specifically, the exponent calculation unit 21 shown in FIG. 1 calculates the difference (ΔL _W and ΔL _B ) from the threshold value based on the data transmitted from the average luminance level (APL) detection unit 19 for each area. .

In the display device 1 according to the present embodiment, since the average luminance level (APL) (L _Wa ) = 88 and the first threshold value (L _W0 ) = 80 in the white area, the difference (ΔL) from the threshold value in the white area _W ) is 8.

Further, since the average luminance level (APL) (L _Ba ) = 10 and the second threshold value (L _B0 ) = 20 in the black area, the difference (ΔL _B ) from the black area threshold is an absolute value of −10. The value is 10.

That is,
ΔLw = L _Wa −L _W0 , ΔL _B = − (L _Ba −L _B0 ),
ΔLw = 88−80 = 8, ΔL _B = − (10−20) = 10
It becomes.

  Next, steps 7 to 9 will be described with reference to FIG.

(Step 7)
Step 7 normalizes the area of the white region (A _W ), the area of the black region (A _B ), the difference from the white region threshold (ΔL _W ), and the difference from the black region threshold (ΔL _B ), This is a step of calculating A _WN , A _BN , ΔL _WN and ΔL _BN . This standardization is performed for the purpose of facilitating subsequent calculations.

Specifically, the exponent calculation unit 21 shown in FIG. _1, A W, _{A B,} the [Delta] L _W and [Delta] L _B, by normalizing the simplest number value of up to _10, A _{WN, A BN,} ΔL _WN and ΔL _BN are calculated.

In the display device 1 according to the present embodiment, the area of the white region (A _W ) = 5, the area of the black region (A _B ) = 7, the difference from the threshold value of the white region (ΔL _W ) = 8, and the threshold value of the black region Difference (ΔL _B ) = 10 is normalized, and A _WN = 2, A _BN = 3, ΔL _WN = 4, and ΔL _BN = 5.

(Step 8)
In step 8, based on A _WN , A _BN , ΔL _WN and ΔL _BN obtained in step 7, the exponent calculation unit 21 uses the white score (S _W ) as the first exponent and the second exponent as This is a step of calculating a black score (S _B ).

The white score (S _W ) represents the psychological amount received by the viewer (user) of the display device 1 with respect to a video signal with high luminance, that is, the subjective amount actually felt by the viewer (user). Value.

Similarly, the black score (S _B ) is a psychological quantity received by a viewer (user) of the display device 1 with respect to a video signal with low brightness, that is, a subjective amount actually felt by the viewer (user). This is a representative value.

The white score (S _W ) and the black score (S _B ) are indexes that determine the content of the brightness control of the light source 3 by the light source control unit 12.

As a formula for calculating the white score (S _W ), for example, the following formula can be used.

That is, the white score (S _W ) can be obtained by S _W = α × (ΔL _WN ) ⁿ × (A _WN ) ^m . The black score (S _B ) can be obtained in the same manner. That is, the black score (S _B ) is calculated from (ΔL _BN ) ⁿ and (A _BN ) ^m in the same manner as the white score (S _W ) is calculated from (ΔL _WN ) ⁿ and (A _WN ) ^m. be able to.

  Hereinafter, the meaning of the above formula will be described.

The white score (S _W ) is considered to be proportional to (ΔL _WN ) ⁿ and (A _WN ) ^m . The reason is that 1) the psychological quantity is considered to be proportional to the power function (n-th power and m-th power) of the strength of the stimulus (Stevens's law, etc.), and 2) the brightness at which the stimulus is displayed on the screen. In some cases, the factors of stimulation are considered to be brightness (ΔL _WN ) and area (A _WN ).

  Here, since the power functions n and m vary depending on the lighting environment, display device characteristics, user visual characteristics, and the like, it is preferable that the functions be designed so that the user can change the settings. Specific values of m and n are not particularly limited. For example, 0 <m <1, 0 <n <1 is preferable, and 0.1 ≦ m ≦ 0.5 and 0.1 ≦ n. ≦ 0.5 is more preferable.

  In the display device 1 of the present embodiment, n = 0.33 (according to Stevens's law) and m = 0.16 are typical values.

Moreover, it is preferable that the value of α is set so that the white score (S _W ) and the black score (S _B ) are normalized to values of 0 to 10.

In the display device 1 of the present embodiment, S _W = α × (ΔL _WN ) ⁿ × (A _WN ) ^m , and the maximum value of the white score (S _W ) when 0 <n <1, 0 <m <1. The value of α was determined so as to be 10. That is, when ΔL _WN = A _WN = 10, α = 3.236 so that S _W = 10. (Α = 10 / (10 ^0.33 × 10 ^0.16 ) = 3.236 (when n = 0.33, m = 0.16))
Therefore, in the display device 1 of the present embodiment,
S _W = 3.236 × (ΔL _WN ) ^0.33 × (A _WN ) ^0.16
S _B = 3.236 × (ΔL _BN ) ^0.33 × (A _BN ) ^0.16
It becomes.

Therefore, when ΔL _WN = 4 and A _WN = 2,
S _W = 3.236 × (4) ^0.33 × (2) ^0.16 ≈5.7
When ΔL _BN = 5 and A _BN = 3,
S _B = 3.236 × (5) ^0.33 × (3) ^0.16 ≈6.6.

That is, the white score (S _W ) = 5.7 and the black score (S _B ) = 6.6.

FIG. 5 shows the relationship between ΔL _WN and A _WN and the white score (S _W ) based on the above formula, S _W = 3.236 × (ΔL _WN ) ^0.33 × (A _WN ) ^0.16. It is a graph.

(Step 9)
Step 9 is a step of controlling (brightness adjustment) the backlight output (P) while referring to the lookup table based on the white score (S _W ) and the black score (S _B ) obtained in Step 8. is there. The look-up table (LUT) refers to an input / output comparison table used to determine the backlight output P based on the exponent calculated by the exponent computing unit 21.

Specifically, first, the white score (S _W ) and the black score (S _B ) calculated by the exponent calculation unit 21 shown in FIG. 1 are transmitted to the lookup table unit 22. Then, the look-up table unit 22 applies the transmitted white score (S _W ) and black score (S _B ) to the look-up table provided in the look-up table unit 22 in advance, and the backlight output P is obtained. decide.

  The backlight output P is transmitted from the lookup table unit 22 to the light source output control unit 23, and the light source output control unit 23 controls the light source 3 accordingly.

  FIG. 6 shows a lookup table of the display device 1 according to the present embodiment.

According to this lookup table, for example, the backlight output P is 80% when the white score (S _W ) = 4 and the black score (S _B ) = 6.

  Here, the difference from the conventional light source control method (method of controlling the light source based on the average luminance level (APL) of the entire screen) will be described.

In the conventional light source control method, for example, when the values of the white score (S _W ) and the black score (S _B ) are close, specifically, 1) the white score (S _W ) = 0 to 3 and the black score (S _B ) = 0-3, 2) white score (S _W ) = 4-7, black score (S _B ) = 4-7, 3) white score (S _W ) = 8-10 When the black score (S _B ) is 8 to 10, the average luminance level (APL) is recognized as about 50%, and the same backlight luminance control may be performed. It was difficult to perform brightness control.

This is because, in the cases 1), 2), and 3), the average luminance level (APL) of the entire screen becomes almost the same value. That is, when the values of the white score (S _W ) and the black score (S _B ) are close to each other, they are canceled out and the features are canceled out.

  On the other hand, in the display device 1 of the present embodiment, the backlight output P is 70% in the case of 1), 80% in the case of 2), and 100% in the case of 3). The backlight luminance can be controlled according to each case.

  Accordingly, in the case of 1), that is, when there are few features in both white (bright) display and black (dark) display, the backlight output is suppressed and the power consumption is reduced. On the other hand, in the case of 3), that is, when there are many black (dark) displays and white (bright) displays coexist to the same extent, it is possible to express the brightness of white (bright) displays.

Further, when the white score (S _W ) = 8 to 10 and the black score (S _B ) = 0 to 3 (when the black (dark) display is small and the white (bright) display occupies most), the backlight By setting the output P to 50%, it is possible to display white (bright) while reducing glare. On the other hand, when the white score (S _W ) = 0 to 3 and the black score (S _B ) = 8 to 10 (when white (bright) display is small and black (dark) display occupies most), the backlight is used. The black float can be reduced by setting the output P to 50%.

Further, when the white score (S _W ) = 4 to 7 and the black score (S _B ) = 8 to 10 (when the black (dark) display occupies the majority, the white (bright) display is partially present). The backlight output P is set to 75%, and the brightness of white (bright) display can be expressed while reducing the black floating.

As described above, by using the two parameters of the white score (S _W ) and the black score (S _B ) and performing luminance control by comparing and combining them, finer luminance control according to human visual characteristics is performed. Is possible. In addition, it reduces the visual burden caused by glare in high-brightness images and the black float in low-brightness images, which has been a problem with conventional display devices such as liquid crystal displays, while ensuring peak luminance characteristics and providing a sense of brightness. Can be maintained. Further, since the backlight luminance is appropriately controlled, the power consumption can be reduced.

  In the display device 1 of the present embodiment, the configuration of the display unit 2 is not particularly limited, and for example, a back-illuminated display device such as a liquid crystal panel can be used.

  In the display device 1 of the present embodiment, the configuration of the light source 3 is not particularly limited, and for example, a fluorescent tube backlight or an EL backlight provided on the back surface of the liquid crystal panel can be used.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The display brightness can be adjusted, and the present invention can be applied to a display device such as a liquid crystal display device provided with a fluorescent tube backlight or EL backlight.

1, showing an embodiment of the present invention, is a block diagram illustrating a configuration of a display device. FIG. (A) is a flowchart showing a flow of processing of an input video signal of the display device, (b) is a diagram showing an average luminance level (APL) distribution for each block of the display unit of the display device, c) is a diagram showing a white area and a black area of the display unit of the display device. FIG. 3 is a flow diagram illustrating a flow of processing of the input video signal, following FIG. FIG. 4 is a flowchart subsequent to FIG. 3, showing a flow of processing of the input video signal. It is a graph which shows the relationship between (DELTA) _LWN and _AWN, and a white score ( _Sw ). It is a figure which shows the example of the look-up table for determining the backlight output in the said display apparatus. It is a block diagram which shows a prior art and shows the principal part structure of an imaging device. It is a figure which shows a prior art and shows the control characteristic of the backlight control part of a liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 2 Display part 3 Light source 10 Control part 11 Display control part 12 Light source control part (light source control means)
13 Illuminance detection unit (ambient illumination detection means)
14 Information extraction unit (information extraction means)
DESCRIPTION OF SYMBOLS 15 Divided circuit part 16 Average luminance level (APL) detection part for every block 17 Brightness comparison part 18 Area calculation part 19 Average luminance level (APL) detection part for every area 20 Threshold value calculation part (threshold setting means)
21. Exponent calculation part (exponential calculation means)
22 Look-up table section 23 Light source output control section

Claims (6)

In a display device comprising a display unit and a light source that illuminates the display unit,
Among the video signals of all the pixels of the display unit, pixels having a luminance higher than the first threshold set on the higher luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit. In addition to extracting luminance information, the second threshold value set on the lower luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit is selected from the video signals of all the pixels of the display unit. Information extracting means for extracting luminance information of pixels having a low luminance;
Light source control means for adjusting a luminance output of the light source based on luminance information of a pixel having a luminance higher than the first threshold and luminance information of a pixel having a luminance lower than the second threshold. A display device characterized by being provided. Ambient illuminance detecting means for detecting the illuminance around the display unit;
2. The display according to claim 1, further comprising a threshold setting unit configured to set the first threshold and the second threshold based on the ambient illuminance detected by the ambient illuminance detection unit. apparatus. In order to adjust the luminance output of the light source, the light source output is obtained from the area of the pixel which is luminance information of the pixel having luminance higher than the first threshold and the average luminance level (APL: Average Picture Level) of the pixel. Determining a first index for determining and determining a light source output from an area of a pixel which is luminance information of a pixel having luminance lower than the second threshold and an average luminance level (APL) of the pixel Exponential calculation means for obtaining the second exponent is provided,
The display device according to claim 1, wherein the light source control unit adjusts the luminance of the light source output by a combination of the first index and the second index. In order to adjust the luminance output of the light source, the area of the pixel, which is the luminance information of the pixel having a luminance higher than the first threshold, and the difference between the average luminance level (APL) of the pixel and the first threshold A first index for determining a light source output from the pixel, and an area of the pixel which is luminance information of a pixel having luminance lower than the second threshold, and a second threshold and an average luminance level of the pixel ( An exponent calculation means for obtaining a second index for determining the light source output from the difference from (APL) is provided,
The display device according to claim 1, wherein the light source control unit adjusts a luminance output of the light source by a combination of the first index 1 and the second index.   The display device according to claim 1, further comprising an input unit configured to set and input the first threshold value and the second threshold value. In the screen brightness control method for controlling the brightness of the screen of the display device by adjusting the brightness output of the light source of the display device,
Among the video signals of all the pixels of the display unit of the display device, a luminance higher than a first threshold set on the higher luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit. In addition to extracting the luminance information of the pixel having, it is set on the lower luminance side than the median value of the maximum luminance and the minimum luminance that can be displayed on the display unit from the video signals of all the pixels of the display unit of the display device. A first step of extracting luminance information of pixels having a luminance lower than the second threshold;
A second step of adjusting a luminance output of the light source based on luminance information of a pixel having a luminance higher than the first threshold and luminance information of a pixel having a luminance lower than the second threshold; A screen brightness control method comprising:

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