JP2009237510A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply luminance corresponding to an image characteristic of a picture area at which a user is apt to practically look and to suppress power consumption as much as possible. <P>SOLUTION: An APL measurement part 14 in a liquid crystal display device extracts prescribed partial areas from respective frame areas of a video signal received by a tuner 12 or the like and measures the partial APLs of the extracted partial areas of respective frames, a total APL of all areas of respective frames and an APL ratio based on the ratio of the partial APLs to the total APL. A microcomputer 21 which is a control part controls light emission luminance distribution of a backlight unit 17 in accordance with the measured APL ratio. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that modulates the luminance of a backlight in accordance with the characteristics of an image.

  The video signal is divided into m in the horizontal direction and n in the vertical direction according to the arrangement of the backlight light source, and each of the divided video signals according to the level of average luminance (APL (Average Picture Level)). An invention about area active luminance control in which brightness is adjusted by controlling a duty ratio of an inverter of a backlight source is disclosed.

For example, Patent Document 1 discloses a technique for adjusting the luminance so that even if there is a bright range or a dark range on the screen, the range is easy to see. Here, the video signal included in the broadcast wave received by the antenna is divided into m in the horizontal direction and n in the vertical direction according to the arrangement of the light source of the backlight, and the average luminance of each of the divided video signals ( The brightness is adjusted by controlling the duty ratio of the inverter of each light source according to the level of APL).
Further, Patent Document 2 discloses a method of increasing the luminance in order to improve the contrast on a screen with a low APL and decreasing the luminance to suppress glare on a screen with a high APL.
JP 2000-321571 A Japanese Patent No. 3863904

  With the configuration of Patent Document 1, it is considered that a dark screen region or a bright screen range can be easily seen partially or locally. In particular, in the so-called two-screen display in which video information having different contents is displayed on the left and right of the screen, the brightness levels of the left and right images are clearly different (for example, two-screen display of cinema video and news video, etc.) It is also considered an effective control technique.

  However, the above method is not necessarily an effective method. That is, although the brightness of the backlight light source can be partially controlled, the configuration is limited to dividing the light emitting area in the vertical direction and the horizontal direction as described in Patent Document 1, and the light source is The number of parts necessary for the drive circuit (such as a switching circuit) is required for the amount of light that is divided and turned on, which may cause a complicated configuration.

In addition, if the image displayed in the above configuration is a single-screen image in which a locally bright area is formed in a curved shape near the periphery of the screen (in the sense that it is not the center) When the curved area is displayed by two divided areas, if the brightness level around the curved area is different for each divided area, the brightness of the two light sources that irradiate the curved area from the back of the liquid crystal panel may be different. It is done. Accordingly, it may be considered that the division to the brightness of the light source does not necessarily provide the optimum viewing state.
In addition, a drive circuit or the like is required for each divided backlight, the configuration becomes complicated, and the cost can be significantly increased.

On the other hand, in recent years, there has been a demand for further lower power consumption with respect to the power consumption of the backlight, which increases as the liquid crystal display device has a larger screen (for example, about 50 inches or more). A low power consumption countermeasure that does not increase the number of points and a method for reducing the power consumption under the minimum necessary conditions for the product are desired.
In particular, a large-screen liquid crystal display device often displays an image with a relatively low APL, such as a cinema image, and is therefore often placed in a dark place. Under such usage conditions, when displaying a video signal with a high APL, a display process that expresses the dynamic range more is performed than a method of simply controlling the backlight brightly, and the contrast of the image is sufficiently enhanced. It is considered that the expression can meet the needs of the user, and in the use environment as described above, it cannot be said that the optimum brightness is determined only by the brightness of the image.

  Therefore, in view of the above problems, the present invention provides a liquid crystal display device that can suppress power consumption as much as possible by an appropriate luminance distribution corresponding to the image characteristics of a screen region that a user tends to pay attention to. It is intended.

  In order to solve the above problems, a first technical means of the present invention includes a receiving unit that receives a video signal composed of a plurality of frames, a plurality of pixels, and each pixel included in the video signal. A liquid crystal panel that drives the pixels with a predetermined voltage based on the number of gradations, a backlight unit that provides a predetermined range of brightness from the back of the liquid crystal panel, and a predetermined area from each frame area of the video signal received by the receiver A partial area extracting unit for extracting a partial area; a partial APL measuring unit for measuring a partial APL that is an APL of the extracted partial area of each frame; and an overall APL measurement for measuring an entire APL that is an APL of the entire area of each frame And a control unit for controlling the light emission distribution of the backlight unit according to the measured partial APL and the entire APL.

  The second technical means of the present invention is characterized in that, in the first technical means, the control unit controls the light emission distribution of the backlight unit by the ratio of the partial APL to the entire APL.

  According to a third technical means of the present invention, in the first or second technical means, the partial region extracted by the partial APL detection unit is a partial region including at least the center of each frame. It is.

  According to a fourth technical means of the present invention, in any one of the first to third technical means, the partial area extracted by the partial APL detection unit is an area that dynamically changes in accordance with a predetermined video feature. It is characterized by being.

  According to a fifth technical means of the present invention, in the fourth technical means, weighting is performed when measuring the partial APL from the partial area, and the weighting is changed according to the genre of the video signal. It is.

  A sixth technical means of the present invention is the technical means according to any one of the first to fifth technical means, wherein the backlight portion is constituted by a plurality of fluorescent tubes arranged in parallel, and is a portion extracted by the partial APL detection portion The region is a region corresponding to at least two consecutive ones of the plurality of fluorescent tubes.

According to the present invention, it is possible to suppress power consumption as much as possible by an appropriate luminance distribution corresponding to the image characteristics of a screen region that is often apt to be watched by a user.
In particular, according to the present invention, the power distribution is suppressed as much as possible by appropriately setting the luminance distribution of the backlight corresponding to the image characteristics of the screen area, which the user tends to pay attention to, in accordance with the APL of the video signal. It becomes possible.

  FIG. 1 is a block diagram for explaining a configuration of an embodiment of a liquid crystal display device according to the present invention. In the liquid crystal display device 1, a tuner 12 as a receiving unit selects a broadcast signal received by the antenna 11. The decoder 13 decodes and demultiplexes the broadcast signal selected by the tuner 12 and outputs a video signal for driving the liquid crystal panel 20 and genre data included in the electronic program information of the broadcast signal. .

  The video signal separated by the decoder 13 is input to an LCD controller 19 that drives and controls the liquid crystal panel 20 after various video processes are performed by the video processing unit 18. The LCD controller 19 outputs a liquid crystal drive signal to a gate driver and a source driver (not shown) of the liquid crystal panel 20 based on the input video signal, whereby an image according to the video signal is displayed on the liquid crystal panel 20. The liquid crystal panel 20 has a plurality of pixels, and each pixel is driven with a predetermined voltage based on the gradation of each pixel included in the video signal.

  The video signal separated by the decoder 13 is also output to the APL measurement unit 14. In the APL measurement unit 14, the APL for each frame of the video signal output from the decoder 13 (entire APL) and the APL (partial region including the center of the frame) of the partial region that is easy for the user to watch in the frame APL) and the APL ratio represented by the ratio of the partial APL and the total APL are measured. That is, the APL measurement unit 14 corresponds to the entire APL measurement unit, partial region extraction unit, and partial APL measurement unit of the present invention. The video signal for measuring APL may be input from an external device or a recording medium connected to the liquid crystal display device 1.

  The measured total APL and the APL ratio are sent to the filter 15 to adjust the followability to each APL change. The APL ratio is sent to the microcomputer 21 as information necessary for the microcomputer 21 to determine whether or not to rewrite the brightness control table. Further, the entire APL is sent to the backlight control unit 16, and the emission luminance control of the backlight light source according to the entire APL is performed based on the luminance control characteristics of the luminance control table described later.

  In the example shown in FIG. 1, the APL is measured by the video signal decoded by the decoder 13, but the APL may be measured after the video processing by the video processing unit 18. However, the video processing unit 18 may perform, for example, OSD (on-screen display) display processing, scaling processing, or letterbox display (screen area restriction by a black mask or the like) processing. In this case, when APL is measured from a video signal output from the decoder 13 (that is, video processing by the video processing unit 18 is not performed), the backlight corresponding to the true video signal is not affected by the video processing. The brightness can be controlled. Therefore, it is more preferable to measure APL from the video signal before video processing as shown in FIG.

  The filter 15 regulates the followability to the APL change between frames when controlling the light emission luminance of the backlight light source according to the measurement value of the entire APL, and is constituted by, for example, a multistage digital filter. The calculated APL ratio can also be set as appropriate by following the output APL ratio according to the actual time change of the APL ratio by passing through the filter 15.

  This filter 15 inputs APL (overall APL, APL ratio) for each frame measured by the APL measurement unit 14, and for each frame, the APL for one or more frames in the past, respectively. The output APL is calculated by performing a weighted average operation according to Here, it is possible to variably set the number of past frame steps to be reflected to the frame of interest, and set a weighting factor for each of the frame of interest and the past frame (for the set number of steps).

  Then, when the APL of the frame of interest is input, the input APL and the APLs of the frames corresponding to the number of used stages in the past are subjected to a weighted average calculation according to the respective weighting coefficients, and the obtained APL is output. Thereby, the followability of the output APL according to the actual APL change can be set as appropriate. Here, the number of filter stages and the weighting value can be set in accordance with the genre data input to the microcomputer 21. The number of stages and the weighting value of the filter 15 can be appropriately set as described above, and the ON / OFF setting of the filter function is also possible.

  The entire APL output from the filter 15 is input to the backlight control unit 16. Based on the selected luminance control table 23, the backlight control unit 16 outputs a backlight luminance adjustment signal for adjusting the light emission luminance of the backlight light source according to the input entire APL, and the light source of the backlight unit 17 Controls the luminance.

For example, as shown in FIG. 2, the backlight unit 17 is configured by arranging a plurality of thin fluorescent tubes 31 at equal intervals in a housing 30 attached to the back surface of the liquid crystal panel 20. Further, the diffusing plate 32 uniformly diffuses the illumination light emitted from the fluorescent tube 31.
In this case, for example, the backlight unit 17 changes the signal period ratio (duty ratio) of the high potential level and the low potential level of the rectangular wave in accordance with the backlight luminance adjustment signal input from the backlight control unit 16. A dimming control circuit that outputs the dimming signal as a dimming signal, receives the dimming signal from the dimming control circuit, generates an alternating voltage with a period and voltage according to the dimming signal, and applies this to the fluorescent tube 31 And an inverter (not shown) that is driven to light. The inverter operates when the output of the dimming control circuit is at a high potential level, stops operating when the output is at a low potential level, and performs an intermittent operation according to the output duty of the dimming control circuit. The brightness of the backlight portion is adjusted.

  Further, as shown in FIG. 3, the backlight unit 17 has a plurality of LED light sources composed of three primary colors of red, green, and blue, that is, a red light source 41 and a green, in a housing 30 attached to the back surface of the liquid crystal panel 20. A light source 42 and a blue light source 43 may be provided. The light emission luminance of the LED light source can be controlled by the LED current for each LED light source. Although not shown, a backlight unit 17 that uses a combination of the above fluorescent tube and LED can also be applied. At this time, the liquid crystal panel 20 may be illuminated by a so-called side edge type configuration in which light from a fluorescent tube or an LED light source is made uniform by using a light guide plate.

  In addition, the liquid crystal display device 1 includes a brightness sensor 24 as brightness detection means for detecting the brightness around the liquid crystal display device 1 (ambient illuminance). As the brightness sensor 24, for example, a photodiode can be applied. In the brightness sensor 24, a DC voltage signal corresponding to the detected ambient light is generated and output to the microcomputer 21. The microcomputer 21 outputs a control signal for selecting a luminance control table to be used for the light emission luminance control of the backlight light source according to the DC voltage signal corresponding to the ambient light, and adjusts the luminance control value of the luminance control table. Output the brightness adjustment coefficient.

The liquid crystal display device 1 also includes a remote control light receiving unit 25 for receiving a remote control signal transmitted from the remote control device 27. The remote control light receiving unit 25 is constituted by a light receiving LED for receiving a remote control operation signal using infrared rays, for example.
The remote control operation signal received by the remote control light receiving unit 25 is input to the microcomputer 21 which is a control unit. The microcomputer 21 performs predetermined control according to the input remote control operation signal. For example, in the present embodiment, the user can select a desired image adjustment mode from a plurality of image adjustment modes prepared in advance using the remote control device 27 and can perform setting control on the liquid crystal display device 1.

As described above, the luminance control table 23 of this example defines the relationship of the emission luminance of the backlight light source according to the entire APL of the input video signal. Alternatively, it may be one that defines the relationship of the backlight emission luminance according to the ambient illuminance, or a plurality of ones that determine the relationship of the backlight emission luminance according to the overall APL are prepared according to the ambient illuminance. There may be.
A plurality of brightness control tables (look-up tables) that can be selected in advance are stored in a table storage memory 22 such as a ROM, and measured according to the APL ratio measured by the APL measurement unit 14 and input to the microcomputer 21 via the filter 15. A brightness control table is selected. Here, the microcomputer 21 can select the brightness control table used for the control by designating the table No. to be used according to the APL ratio. Alternatively, when the luminance control table is selected and changed, the changed luminance control table may be obtained by calculation.
In this case, even with the same APL ratio, different brightness control tables can be selected according to the image adjustment mode, the brightness around the liquid crystal display device, the genre data, and the like.

  In FIG. 1, the luminance adjustment coefficient is used for setting the brightness of the entire screen in accordance with a user operation. For example, on the menu screen held by the liquid crystal display device 1, screen brightness adjustment items are set. The user can set an arbitrary screen brightness by operating the setting item. The microcomputer 21 in FIG. 1 recognizes the brightness setting and outputs a brightness adjustment coefficient to the multiplier 26 according to the set brightness. The multiplier 26 turns on the backlight light source with the brightness according to the brightness setting by multiplying the brightness conversion value by the brightness control table currently used by the brightness adjustment coefficient.

  The brightness adjustment coefficient changes the slope of the brightness control characteristic of the brightness control table. That is, when using a brightness adjustment coefficient that darkens the screen at a constant rate, the slope of the brightness control characteristic changes in a decreasing direction. In addition, when using a brightness adjustment coefficient that brightens the screen, the slope of the brightness change characteristic increases, but the limiter works at 100% brightness of the backlight source, and it is limited so that the brightness does not increase beyond that. The

  The above brightness adjustment coefficient is different from the change of the brightness control characteristic according to the APL ratio of the liquid crystal display device according to the present invention. The light emission luminance of the backlight light source is controlled based on the luminance control table 23 selected from the luminance control table stored in the table storage memory 22, and is set to the user setting with respect to the luminance control characteristic value of the luminance control table. The luminance adjustment coefficient based thereon is multiplied and output to the backlight control unit 16.

  In one embodiment of the liquid crystal display device according to the present invention, the luminance distribution of the backlight is selected according to the APL ratio measured by the APL measuring unit 14, and the video signal measured by the APL measuring unit 14 is maintained while maintaining the luminance distribution. By changing the luminance level of the backlight in accordance with the overall APL, the display quality (luminance, contrast, sharpness, etc.) of the display image and the power consumption of the backlight light source can be optimized.

  In another embodiment of the liquid crystal display device according to the present invention, a brightness distribution of the backlight is selected according to the APL ratio measured by the APL measurement unit 14, and the brightness sensor 24 is used while maintaining the brightness distribution. By changing the brightness level of the backlight according to the measured brightness (ambient illuminance) around the liquid crystal display device, the display quality of the display image (luminance, contrast, sharpness, etc.) The power consumption of the backlight light source can be optimized. Also, these controls may be performed for each image mode that can be presented by the liquid crystal display device.

FIG. 4 is a diagram showing a configuration example of a direct type backlight system that is an example of the backlight unit of the present invention, and a plurality of fluorescent tubes are arranged in the column direction and are driven simultaneously in synchronism with every two fluorescent tubes. Three sets of configurations are shown.
As shown in the figure, the fluorescent tubes 31a to 31f are arranged in parallel, and the respective fluorescent tubes 31a to 31f are connected to the first inverter substrate 50 and the second inverter substrate 60 provided at the left and right ends thereof. The Each of the fluorescent tubes 31a to 31f is connected to a pair of inverter circuits 51, 61, or 52, 62, or 53, 63 every two. Each of these inverter circuits 51 to 53, 61 to 63 is mounted on the first inverter board 50 or the second inverter board 60 side by side in the same direction as the fluorescent tube arrangement direction.

The inverter circuits 51 and 61 to which the fluorescent tubes 31a and 31b are connected and the inverter circuits 53 and 63 to which the fluorescent tubes 31e and 31f are connected receive the dimming signal D1 output from the backlight control unit 16. Then, the brightness corresponding to the duty ratio of the dimming signal D1 is controlled so that each connected fluorescent tube emits light.
The inverter circuits 52 and 62 to which the other fluorescent tubes 31c and 31d are connected also receive the dimming signal D2 output from the backlight control unit 16, and the luminance according to the duty ratio of the dimming signal D2 Are controlled so that each connected fluorescent tube emits light.

At this time, the backlight control unit 16 outputs dimming signals D1 and D2 each having a predetermined duty ratio according to the following configuration.
The backlight control unit 16 includes a triangular wave forming circuit 161 that outputs a triangular wave for on / off control of each inverter circuit at a frequency (approximately several hundred to 60 Hz) sufficiently lower than the driving frequency (several tens of kHz) of the fluorescent tube; A first dimming signal generation circuit (first operational amplifier) 162 that generates a PWM dimming signal D1 and D2 by comparing the triangular wave signal output from the triangular wave forming circuit 161 with predetermined voltage values Vd1 and Vd2, respectively. And a second dimming signal generation circuit (second operational amplifier) 163.

At this time, the predetermined voltage values D1 voltage (Vd1) and D2 voltage (Vd2) are set values (Vd1-1, Vd2-1) for modulating the luminance distribution of the backlight stored in the ROM 70, respectively. , (Vd1-2, Vd2-2), (Vd1-3, Vd2-3).
The luminance distribution of the backlight is set by the difference or ratio of the values of (Vd1, Vd2), and the microcomputer 21 performs control so that the optimal luminance distribution is obtained by the APL value or APL ratio which is one of the feature amounts of the video signal. Is done.

In the case of an inverter circuit that drives a fluorescent tube having a long length (1 m or more) and a small diameter (about 3 to 7 mm) as in a large and thin LCD, two inverters that drive a pair of fluorescent tubes as shown in FIG. A voltage is applied to the fluorescent tube by an AC high voltage signal having a predetermined frequency (several tens of kHz) output from the inverter circuits (51, 61), (52, 62), (53, 63) in opposite phases to each other. Due to the phenomenon, the phosphor inside the fluorescent tube emits light.
For this purpose, each of the inverter circuits has at least a secondary winding for boosting the input voltage and outputting it to the electrodes of the fluorescent tube, and for boosting the voltage signal output from these secondary windings. Are provided with a primary winding provided integrally with the secondary winding. Still further, a bridge circuit (including both a full bridge and a half bridge) composed of two or four transistors in order to switch the direction of the current flowing through the primary winding at a constant period, A control signal generation circuit or the like for alternately controlling the on / off state is mainly provided.

With the above configuration, an optimal luminance distribution can be formed in a backlight having a configuration in which fluorescent tubes arranged in parallel are driven simultaneously. In particular, the light quantity of each fluorescent tube is controlled by the duty ratio of the dimming signal D.
In addition, in the case of a separately-excited inverter circuit, the same function as described above can be realized by modulating the timing of the oscillation signals (P, N) in the central portion and the peripheral portion with the dimming signal D alone. . In this case, the luminance distribution according to the video signal can be provided without increasing the dimming line.

  As shown in FIG. 4, the connections between the inverter circuits 51 to 53 and 61 to 63 are synchronized or phase-reversed so that AC power whose phase is inverted is applied to both ends of the fluorescent tubes 31 a to 31 f. Configured. In addition, as an example similar to the above-described configuration example, the present invention is not limited to the above-described driving of the six fluorescent tubes, but a plurality of fluorescent tubes are connected and driven in parallel. Also good.

  Then, the microcomputer 21 of the liquid crystal display device uses the luminance distribution selected according to the APL ratio measured by the APL measuring unit 14 and uses the luminance distribution selected by the APL measuring unit 14 to determine the luminance of the backlight according to the APL (overall APL) measured by the APL measuring unit 14. Control of the backlight is performed according to the ambient illuminance detected by the brightness sensor 24 in accordance with the selected dimming curve.

Example 1
FIG. 5 is a flowchart for explaining a control example of the first embodiment by the liquid crystal display device of the present invention. In the control flow of the microcomputer 21 in this embodiment, control is performed so as to output an optimal backlight luminance based on two pieces of information, that is, the entire APL and the APL ratio. The following will be described with reference to the configuration of FIG.
First, the APL measurement unit 14 calculates a video characteristic value of the input video signal (step S1). The video characteristic value is an APL ratio represented by total APL, partial APL, partial APL / total APL for each frame of the input video signal. The area for calculating the partial APL is a specific area within a predetermined frame, for example, a partial area including the center of the frame.

When the value of the APL ratio (partial APL / total APL) of the video signal measured by the APL measurement unit 14 is input to the microcomputer 21, the microcomputer 21 selects a luminance distribution by dividing into cases according to the following conditions ( Steps S2 to S6).
[Condition 1-1] When APL ratio is 0.5 or less → Select luminance distribution C3 [Condition 1-2] When APL ratio is 0.5 to 1.0 → Select luminance distribution C2 [Condition 1-3 If the APL ratio is greater than 1.0 → select the luminance distribution C1 and use the selected luminance distribution to determine the backlight duty ratio according to the total average luminance level (overall APL) (step S7). That is, the luminance of the backlight is modulated according to the entire APL while maintaining the shape of the selected luminance distribution.

  FIG. 6 is a diagram illustrating a setting example of the luminance distribution of the backlight in the screen. The luminance distributions C1 to C3 define the luminance distribution in the screen due to the backlight. In this example, the backlight arrangement direction (in this case, the vertical direction) and the backlight luminance (representing the backlight luminance adjustment signal). Value). Here, an optimum luminance distribution is selected from the viewpoint of power consumption and ease of viewing due to high contrast, according to the range of values taken by the APL ratio of the measured video signal. As an example, in the case of a video signal having a high APL ratio (= the brightness of the central portion of the image tends to be relatively bright compared to the surroundings), the luminance is higher than that of the peripheral portion in order to emphasize the contrast of the central portion. And the dimming signals D1 and D2 are set to the ROM values so that the luminance distribution C1 is output at a relatively lower luminance in consideration of the low power consumption and the dynamic range of the entire screen. Control by (Vd1, Vd2).

On the other hand, in the case of a video signal with a low APL ratio (= the brightness at the center of the image is relatively unchanged compared to the surroundings), on the contrary, the microcomputer indicates that the specific range is a locally bright video signal. Therefore, the dimming signals D1 and D2 are formed so that a relatively uniform luminance distribution is formed on the whole and the luminance distribution C3 of the backlight reflecting the gradation characteristics of each pixel of the video signal is formed. Is controlled by the ROM values (Vd1, Vd2).
At that time, the luminance value is controlled so that the total power consumption of the backlight in the luminance distribution C1 does not become extremely high as compared with the case of the luminance distribution C3. It can be said that this is a preferable control for the purpose.

For selection of the luminance distribution in the relationship between the APL ratio and the overall APL, refer to FIG. 7 in which several video signals are illustrated. FIG. 7 is a diagram conceptually showing examples I1 to I6 of video signals in which the overall APL and the APL ratio have a specific relationship. The horizontal axis represents APL, which is higher from right to left.
Here, it is assumed that the partial area for measuring the partial APL of the video signal is the central two areas of the frame divided into four in the vertical direction. That is, in this example, as shown in FIG. 8, it is assumed that the partial area 101 indicated by hatching is set as an area having a half area of the entire screen at the center in the vertical direction of the entire screen 100. For example, the partial area 101 can be set as an area corresponding to two consecutive fluorescent tubes arranged in parallel.

In this case, when the three images (I1), (I3), and (I5) having a relatively low APL are compared, the relative characterization can be performed as follows.
Video (I1): White is distributed around the screen, the center is a black image, the overall APL is low, and the APL ratio << 1.0.
Video (I3): White of the same degree is distributed around the screen and in the center, the overall APL is low, and the APL ratio is about 1.0.
Video (I5): White is distributed in the center of the screen, the periphery is a black image, the overall APL is low, and the APL ratio >> 1.0.

  In these three images of the same APL (I1, I3, I5), the image (I1) having brightness only in the peripheral part is displayed with a relatively uniform luminance distribution C3, and moderate brightness in each of the periphery and the center. A certain image (I3) is displayed with a relatively bright luminance distribution (C2) at the center, and an image (I5) that is bright only at the center is bright because the image area that the user tends to watch is bright. In order to achieve this, the distribution characteristics are classified so as to display the luminance distribution C1 having a relatively bright center.

On the other hand, video (I2), (I4), and (I6) are also given the same correlation as video (I1), (I3), and (I5). It becomes possible to select a light curve.
Video (I2): White is distributed around the screen, the center is a black image, the overall APL is high, and the APL ratio << 1.0. In this case, the dimming curve C3 is selected.
Video (I4): An image in which white of the same degree is distributed around the screen and in the center, the overall APL is high, and the APL ratio is approximately 1.0. In this case, the dimming curve C2 is selected.
Video (I6): White is distributed in the center of the screen, the periphery is a black image, the overall APL is high, and the APL ratio is 1.0. In this case, the dimming curve C1 is selected.

  Based on the technical idea as described above, in the present embodiment, the microcomputer 21 optimizes from the luminance distributions C1 to C3 previously stored in the table storage memory 22 in accordance with the input APL ratio value. A data group indicating the luminance distribution is selected, and a process of writing the series of data groups in the luminance control table 23 is performed. As a result, an optimum luminance distribution that balances the viewpoint of contrast and low power consumption is selected according to the APL ratio that is a characteristic of the input video signal.

  Finally, the backlight control unit 16 relates to the duty ratio of the backlight luminance adjustment signal corresponding to the value of APL previously written in the luminance control table in accordance with the entire APL of the video signal input via the filter 15. By extracting the information, an optimal backlight luminance adjustment signal for the input APL value and APL ratio is output.

For example, it is assumed that the dimming characteristics that define the relationship between the APL and the light emission luminance of the backlight (BL) are as shown in FIG. In this case, a luminance control table is created to control the backlight by multiplying any data group of the luminance distributions C1 to C3 selected according to the APL ratio with the data of the dimming characteristics shown in FIG.
In the case of this dimming characteristic, the backlight value tends to increase as APL decreases. In this case, as the backlight value increases, the difference between the central luminance and the peripheral luminance is maintained when multiplied by the selected luminance distribution, and the tendency of the mountain distribution with high central BL luminance becomes stronger. As the backlight value decreases, the tendency of uniform distribution of low center BL luminance increases. That is, the tendency shown by the arrow M shown in FIG. 7 is obtained.

FIG. 9 is a diagram for explaining the configuration of the APL measurement unit and details of its processing. The APL measurement unit 14 includes a first APL measurement unit 141, a second APL measurement unit (including a standardized arithmetic circuit) 142, a division circuit 143, and counter circuits (1) to (3) as main constituent circuits.
The first APL measurement unit 141 calculates an APL (overall APL) in the entire screen area of each frame image sent at 60 frames / second or 120 frames / second. Here, the total APL is calculated by integrating the number of gradations for each pixel in a memory circuit or the like in synchronization with the horizontal synchronizing signal (Hsync) or vertical synchronizing signal (Vsync) in the video signal.

  On the other hand, the second APL measurement unit 142 similarly calculates an APL (partial APL) in a part of the screen area of each frame image sent at 60 frames / second or 120 frames / second. Here, the number of gradations for each pixel in the video area (for example, the partial area 101 in FIG. 8) specified in advance is synchronized with the horizontal synchronizing signal (Hsync) or vertical synchronizing signal (Vsync) in the video signal. The partial APL is calculated by integrating in a memory circuit or the like.

  The following means is used as an example of a partial area specifying method for calculating the partial APL. In other words, the microcomputer 21 relates to the APL measurement unit 14 with respect to the first horizontal line number (Hstart) for specifying the horizontal line for starting the APL measurement and the second horizontal line (Hend) for specifying the horizontal line for ending the APL measurement. Each of the information (V (Hstart), V (Hend)) is specified in advance in the counter circuits (1) and (2).

  The counter circuits (1) and (2) sequentially read the horizontal synchronization signal (Hsync) sent from the video signal, and thereby the determination circuit 144 (mainly an AND circuit) for starting or ending the measurement in each circuit. The second APL measurement unit 142 integrates the APL values in the determined period, and performs APL measurement in the partial region.

  If the values integrated in the first APL measurement unit 141 and the second APL measurement unit 142 are divided as they are, the APL values may not be divided due to the difference in the areas of the screen areas. , Calculating the coefficient of the total pixel number ratio between the first screen area and the second screen area from the information (V (Hstart), V (Hend)) related to the second horizontal line (Hend), and the first APL measuring unit 141 and the second horizontal line (Hend) You may provide the normalization arithmetic circuit 145 which normalized the numerical scale with 2APL measurement part 142. FIG. However, in consideration of a sufficient calculation time for the subsequent division circuit 143, the value of the APL ratio calculated by the division circuit 143 is output as a numerical value that is not subjected to the normalization calculation, rather than providing the normalization calculation circuit 145, and the backlight. The value may be sent directly to the control unit 16 so as to be determined in the subsequent processing.

As an example of an arithmetic circuit for calculating a value serving as an index for comparing the characteristics of each image with respect to the APL of the entire screen (first screen region) and the partial screen (second screen region) thus calculated. In this embodiment, the division circuit 143 is illustrated. The arithmetic circuit is controlled to start arithmetic processing at the time when the integration of all APLs is completed in order to calculate the sum of the APLs.
For example, information V (Hfb) corresponding to the number of horizontal lines (Hfb) corresponding to the blanking period designated in advance by the microcomputer 21 in the counter circuit (3) is stored, and the stored number and each frame are stored. As a result of comparison with the number of horizontal synchronization signals counted in the above, the arithmetic processing is started by transmitting a signal for starting the arithmetic processing to the division circuit 145 as the arithmetic circuit when the blanking period is reached. The numerical value obtained by the calculation performed during the vertical blanking period is transmitted as an APL ratio to the subsequent filter 15. With the above configuration and processing, the APL measurement unit 14 calculates and calculates the APL ratio.

  In the above configuration example, as the best example, a division circuit is introduced for each APL of the entire screen area and partial area of the video signal. For example, it may be a subtraction circuit for each APL value, or may be a function circuit that forms a function composed of any combination of addition, subtraction, multiplication, and division.

  In the above embodiment, the combination of the full screen area and the partial area to be measured by APL is specified as two screen areas, that is, the full screen area and the partial screen divided in the horizontal direction. The relationship between each area of the full screen area and the partial area is not limited to this, and one area may include at least a part of the other area. Among these, a more preferable combination is a combination in which one region includes the entire other region. In this case, the first APL measurement unit 141 may be configured with the same configuration as the counter circuits (1) and (2) configured with the second APL measurement unit 142, for example.

(Example 2)
FIG. 11 is a flowchart for explaining a control example of the second embodiment by the liquid crystal display device of the present invention. In the control flow of the microcomputer 21 in this embodiment, control is performed so as to output an optimal backlight luminance based on two pieces of information, that is, the ambient illuminance of the liquid crystal display device and the APL ratio.
First, the APL measurement unit 14 calculates a video characteristic value of the input video signal (step S11). Here, the video characteristic value is an overall APL for each frame of the input video signal, a partial APL for each frame, and an APL ratio represented by partial APL / total APL. The partial APL is a partial area within a predetermined frame, for example, a partial area including the center of the frame.

When the value of the APL ratio (partial APL / overall APL) of the video signal measured by the APL measurement unit 14 is input to the microcomputer 21, the microcomputer 21 selects the luminance distribution by dividing the value according to the following conditions. (Steps S12 to S16). The luminance distribution to be selected is any one of the luminance distributions C1 to C3 shown in FIG.
[Condition 2-1] When APL ratio is 0.5 or less → Select luminance distribution C3 [Condition 2-2] When APL ratio is 0.5 to 1.0 → Select luminance distribution C2 [Condition 2-3 If the APL ratio is greater than 1.5: Select the luminance distribution C1 and use the selected luminance distribution to determine the backlight duty ratio according to the ambient illuminance (step S17). The ambient illuminance is illuminance information around the video display device detected by the brightness sensor 24.

For example, it is assumed that the dimming characteristics defining the relationship between the ambient illuminance and the backlight are as shown in FIG. In this case, a luminance control table for controlling the backlight is created by multiplying any data group of the luminance distributions C1 to C3 selected according to the APL ratio and the data of the dimming characteristics shown in FIG. .
In the case of this dimming characteristic, the backlight value tends to increase as the ambient illuminance increases. In this case, as the backlight value increases, the difference between the central luminance and the peripheral luminance is maintained when multiplied by the selected luminance distribution, and the tendency of the mountain distribution with high central BL luminance becomes stronger. As the backlight value decreases, the tendency of uniform distribution of low center BL luminance increases.

  In the present embodiment, an optimum luminance distribution is selected from the viewpoint of power consumption and ease of viewing due to high contrast according to the range of values taken by the APL ratio of the measured video signal. In other words, when the APL ratio of the video signal is high, the microcomputer 21 has a higher brightness at the center of the screen than the surroundings or the whole, and therefore the center of the screen is compared with the surroundings to emphasize the contrast at the center of the screen. When the setting voltage (Vd1, Vd2) of the dimming signal corresponding to the bright brightness distribution C1 is selected and the APL ratio is low, the brightness at the center of the screen is relatively low and lower than the contrast. In order to drive with power consumption, for example, a set value (Vd1, Vd2) of a dimming signal corresponding to the luminance distribution C3 is selected to cause each fluorescent tube to emit light as an optimal luminance distribution.

  FIG. 13 is a diagram showing a relationship between the APL ratio of each video signal and a preferable luminance distribution. Here, the APL ratio measured by the APL measurement unit 14 is high, that is, the backlight according to the high degree of concentration of brightness (or the number of gradations) in a predetermined partial region in the frame of the video signal. Controls the luminance distribution. That is, the luminance distribution is selected such that the higher the APL ratio, which is the ratio between the partial area APL and the entire APL, the brighter the center of the screen is relative to the peripheral area.

  Then, while maintaining the selected luminance distribution, control is performed so as to modulate the luminance of the backlight as a whole in accordance with the ambient illuminance. Thereby, the brightness of the backlight is controlled so that the contrast between the bright part and the dark part of the screen is optimized. In particular, it is preferable to control the backlight brightness so that the backlight brightness is brighter when the ambient illuminance is bright, and the backlight brightness is darker when the ambient illuminance is dark. At this time, as described above, the higher the backlight value, the more the difference between the central luminance and the peripheral luminance is maintained when multiplied by the selected luminance distribution, and the high central BL luminance has a mountain-shaped distribution. The tendency becomes stronger. That is, the tendency shown by the arrow M shown in FIG. 13 is obtained.

In the first embodiment, the light emission luminance of the backlight is controlled by applying a dimming characteristic that defines the APL and the backlight luminance to the selected luminance distribution. In the second embodiment, the selected luminance distribution is used. In contrast, the light emission luminance of the backlight is controlled by applying a dimming characteristic that defines the ambient illuminance and the backlight luminance.
In contrast, a plurality of dimming characteristics that prescribe APL and backlight luminance are prepared in advance according to the ambient illuminance, and the above dimming characteristics are selected according to the measured ambient illuminance and applied to the luminance distribution. It may be. In this case, a dimming characteristic that preliminarily stores the entire APL and backlight luminance stored in the table storage memory 22 is selected in accordance with the value of the ambient illuminance input to the microcomputer 21, and dimming is performed based on the dimming characteristic. A data group indicating the set voltage of the signal is selected, and a process of writing the series of data groups in the luminance control table is performed. As a result, the optimum luminance distribution and luminance characteristics that balance the viewpoint of contrast and low power consumption are respectively selected from the APL ratio that is a characteristic of the input video signal.

(Example 3)
14 and 15 are flowcharts for explaining a control example of the third embodiment by the liquid crystal display device of the present invention. In the control flow of the microcomputer 21 in the present embodiment, as in the first embodiment, the backlight luminance distribution is selected according to the APL ratio, and the backlight according to the entire APL while maintaining the selected luminance distribution. However, in this embodiment, the partial area of each frame for calculating the partial APL is dynamically changed in accordance with the characteristics of the video signal, and the position of the characteristic area is further changed. Control to change the luminance distribution of the backlight is performed according to the above.

  In each of the above embodiments, the partial APL used for calculating the APL ratio is measured in a predetermined area within the frame. However, in this embodiment, the measurement area of the partial APL is set according to the characteristics included in the video. Change dynamically. As features included in the video, for example, a video of a human face or a telop can be applied. In the embodiment according to the present invention, the backlight luminance modulation corresponding to the image characteristics of the screen area that the user tends to watch is performed. From such a point, the face of the person that the user tends to watch An image area including a telop is set as a partial area used for measurement of the partial APL. Then, the luminance distribution setting is performed so that the image area that the user tends to pay attention to becomes the brightest in the screen.

As shown in FIG. 12, first, a feature region of the input video signal is extracted (step S21). The feature area is a screen area that the user tends to pay attention to. The feature area is an area of a face image part or a telop area included in the video signal.
As a technique for extracting a face from a video, various techniques such as a feature extraction method have already been released and put into practical use. The same applies to telop detection, and various techniques are known, such as detecting a telop from a change in luminance exceeding a threshold on the time axis. The face detection and telop detection according to the present embodiment do not particularly limit the detection method itself, and conventionally known techniques can be appropriately applied. Then, the detected image area of the face portion and the image area including the telop are extracted as feature areas. In the case of a face, the image portion of the face itself may be defined as a feature region, or a rectangular region inscribed by the face image may be defined as a feature region, and the definition method can be determined as appropriate. Similarly, in the telop, a region including the telop can be determined as appropriate.

The feature region extraction unit for extracting the feature region can be executed by the APL measurement unit 14 in the configuration of FIG. Alternatively, a feature region extraction unit block may be provided between the decoder 13 and the APL measurement unit 14.
Further, the feature region is not limited to the above-described face or telop, and a feature that can be easily watched by the user and can be extracted from the video signal can be appropriately selected.

  When the above-described feature area is extracted in step S21, the V position (position in the vertical direction of the screen) of the feature area included in the video signal is detected (step S22). Here, since the arrangement direction of the fluorescent tubes is the vertical direction and the vertical distribution is defined as the luminance distribution, the vertical position of the feature region is also detected. For example, it is assumed that the face detection position is 1 / 4V and the telop detection position is 3 / 4V. 1 / 4V indicates the uppermost area when the screen is divided into four in the vertical direction, and 3 / 4V indicates the third area from the top of the four divisions.

  Then, the weighting of the feature area is determined (step S23). Weighting gives weighting to the luminance value of the backlight. For example, the weight is set to 100% when a face is detected, and the overlap finding is set to 80% when a telop is detected.

  At this time, the genre data included in the video signal and the genre data of the video signal input to the microcomputer 21 are input to the feature region extraction unit, and weighting is determined according to the genre data. The weighting according to the genre data is determined in advance, and the feature area extraction unit determines the weighting to be used according to the input genre data.

  Then, the APL measurement unit 14 calculates a video characteristic value (step S24). The video characteristic value is an overall APL for each frame of the input video signal, a partial APL for each frame (APL of a characteristic region), and an APL ratio represented by partial APL / total APL. The partial APL is an APL of the extracted feature region.

Then, the APL measurement unit 14 inputs the value of the APL ratio (partial APL / total APL) of the video signal to the microcomputer 21. The microcomputer 21 selects the luminance distribution by dividing the value according to the following conditions (steps S25 to S29). The subsequent luminance distribution selection processing is the same as that in the first embodiment, and any one of the luminance distributions C1 to C3 shown in FIG. 6 is selected according to the obtained APL ratio. That means
[Condition 3-1] When APL ratio is 0.5 or less → Select luminance distribution C3 [Condition 3-2] When APL ratio is 0.5 to 1.0 → Select luminance distribution C2 [Condition 3-3 ] When APL ratio is greater than 1.0 → Select luminance distribution C1

  Then, using the selected luminance distribution, the luminance distribution is set in accordance with the V position of the detected feature region (face or telop). In this case, by setting the relative luminance of the luminance distribution × weighting, a luminance distribution according to the weighting is generated, and the luminance distribution is set so that the luminance peak position is matched with the V position of the feature region. A luminance distribution is determined (step S30). Finally, while maintaining the luminance distribution, the duty ratio is determined according to the entire APL, and the luminance of the backlight is controlled (step S31).

  FIG. 16 is a diagram for explaining an example of generating a luminance distribution according to a feature region. Here, as described above, a face and a telop are detected as feature regions, and weighting at this time is 100% for the face, 80% for the telop, the position of the face is 1/4 V, and the position of the telop is 3 / It shall be 4V. Further, it is assumed that the luminance distribution C1 is selected according to the APL ratio in the partial face area, and the luminance distribution C3 is selected according to the APL ratio in the partial area of the telop.

In this case, as shown in FIG. 14, using the luminance distribution C1 selected according to the APL ratio, in the case of a face, a luminance distribution C1 ′ having a peak position at ¼ V is set. In this case, since the weight of the face is 100%, a luminance distribution having the same shape as the selected luminance distribution C1 and a peak of ¼ V is set.
Similarly, in the case of a telop, a luminance distribution C3 selected according to the APL ratio is used, and a luminance distribution C3 ′ obtained by multiplying the relative luminance value of the luminance distribution C3 by a weight of 80% of the telop is set at a position of 3 / 4V. Set the luminance distribution with a peak.

  When the luminance distribution of the entire screen is determined by the above processing, the duty ratio is determined according to the entire APL of the screen while maintaining the luminance distribution (step S31). Thereby, the screen luminance is modulated according to the entire APL.

  On the other hand, as shown in FIG. 13, when a feature region such as a face or a telop cannot be extracted in step S21, a video characteristic value is calculated with a predetermined screen center region as a partial region (step S32). . The video characteristic value is an overall APL for each frame of the input video signal, a partial APL for each frame, and an APL ratio represented by partial APL / total APL.

Then, the APL measurement unit 14 inputs the value of the APL ratio (partial APL / overall APL) of the video signal to the microcomputer 21, and the microcomputer 21 selects the luminance distribution by performing case classification using the value (step S 33). To S37). The luminance distribution selection process is the same as in steps S26 to S29, and any one of the luminance distributions C1 to C3 shown in FIG. 6 is selected according to the obtained APL ratio. That means
[Condition 3-4] When APL ratio is 0.5 or less → Select luminance distribution C3 [Condition 3-5] When APL ratio is 0.5 to 1.0 → Select luminance distribution C2 [Condition 3-6 ] When APL ratio is greater than 1.0 → Select luminance distribution C1

  When the luminance distribution is determined, the duty ratio is determined according to the entire APL of the screen while maintaining the luminance distribution (step S38). Thereby, the screen luminance is modulated according to the entire APL.

  As described above, the microcomputer 21 selects an optimal luminance distribution from the viewpoint of power consumption and high visibility due to the range of values taken by the APL ratio of the input video signal measured by the APL measurement unit 14. Let In particular, in this embodiment, an image area that is likely to be watched by the user is dynamically extracted and the backlight luminance modulation is performed. Therefore, the brightness corresponding to the image characteristics of the image area that is likely to be watched by the user as described above. It is possible to reduce power consumption while supplying power.

It is a block diagram showing the liquid crystal display device which concerns on this invention. It is a figure which shows the example of mounting the backlight part and liquid crystal panel in the liquid crystal display device of this invention. It is a figure which shows the other mounting example of the backlight part in the liquid crystal display device of this invention, and a liquid crystal panel. It is a figure which shows the example of a partial structure of the backlight part in the liquid crystal display device of this invention. It is a flowchart for demonstrating the example of control of the 1st Example by the liquid crystal display device of this invention. It is a figure which shows the example of a setting of the luminance distribution of the backlight in the screen in the liquid crystal display device of this invention. It is a figure for demonstrating the example of the video signal in which the whole APL and APL ratio have specific relationship. It is a figure for demonstrating the example of a setting of a partial area | region. It is a figure which shows an example of the light control characteristic applied to the selected luminance distribution. It is a figure for demonstrating the structure of an APL measurement part, and the detail of the process. It is a flowchart for demonstrating the example of control of the 2nd Example by the liquid crystal display device of this invention. It is a figure which shows the other example of the light control characteristic applied to the selected luminance distribution. It is a figure for demonstrating the example of the video signal with which ambient illumination and an APL ratio have a specific relationship. It is a flowchart for demonstrating the example of control of the 3rd Example by the liquid crystal display device of this invention. It is a flowchart for demonstrating the example of control of the 3rd Example by the liquid crystal display device of this invention, and is a figure which shows the flow following FIG. It is a figure for demonstrating the production | generation example of the luminance distribution according to a feature area.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 11 ... Antenna, 12 ... Tuner, 13 ... Decoder, 14 ... APL measurement part, 15 ... Filter, 16 ... Backlight control part, 17 ... Backlight unit, 18 ... Image processing part, 19 ... LCD Controller, 20 ... Liquid crystal panel, 21 ... Microcomputer, 22 ... Table storage memory, 23 ... Brightness control table, 24 ... Brightness sensor, 25 ... Remote control light receiving unit, 26 ... Multiplier, 27 ... Remote control device, 30 ... Housing, 31 ... Fluorescent tube, 31a, 31b, 31c, 31d, 31e, 31f ... Fluorescent tube, 32 ... Diffuser, 41 ... Red light source, 42 ... Green light source, 43 ... Blue light source, 50 ... Inverter board, 51, 61 ... Inverter circuit, 52, 62 ... Inverter circuit, 53,63 ... Inverter circuit, 60 ... Inverter board, 70 ... ROM, 100 ... Full screen, 01 ... partial area, 141 ... measuring section, 142 ... measuring section, 143 ... division circuit, 144 ... judgment circuit, 145 ... normalized calculation circuit, 145 ... division circuit, 161 ... triangular wave forming circuit.

Claims (6)

A receiver for receiving a video signal composed of a plurality of frames;
A liquid crystal panel having a plurality of pixels and driving the pixels at a predetermined voltage based on the number of gradations of each pixel included in the video signal;
A backlight unit that provides a predetermined range of brightness from the back of the liquid crystal panel;
A partial region extraction unit that extracts a predetermined partial region from each frame region of the video signal received by the reception unit;
A partial APL measurement unit that measures a partial APL that is an APL of a partial region of each extracted frame;
An overall APL measurement unit that measures an overall APL that is an APL of an entire area of each frame;
A liquid crystal display device comprising: a control unit that controls a light emission distribution of the backlight unit according to the measured partial APL and the entire APL.   2. The liquid crystal display device according to claim 1, wherein the control unit controls a light emission distribution of the backlight unit based on a ratio of the partial APL to the entire APL. 3.   3. The liquid crystal display device according to claim 1, wherein the partial area extracted by the partial APL detection unit is a partial area including at least the center of each frame.   4. The liquid crystal display device according to claim 1, wherein the partial region extracted by the partial APL detection unit is a region that dynamically changes in accordance with a predetermined video feature. A characteristic liquid crystal display device.   5. The liquid crystal display device according to claim 4, wherein weighting is performed on the light emission luminance of the partial area, and the weighting is changed according to a genre of the video signal.   The liquid crystal display device according to any one of claims 1 to 5, wherein the backlight unit is configured by a plurality of fluorescent tubes arranged in parallel, and the partial region extracted by the partial APL detection unit is at least the A liquid crystal display device characterized in that the region corresponds to two consecutive fluorescent tubes.

Images