JP2009186802A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of keeping the visual brightness of a video image (moving image) to be displayed on a liquid crystal panel successfully irrespective of a change of the state of the displayed image. <P>SOLUTION: An average luminance level of an input video signal is detected by a video processing circuit 2, the luminance of a backlight source 6 is automatically adjusted based on the latest value of the average luminance level and a change degree of the average luminance level within predetermined time by a dimming circuit 7 and a main control circuit 8. In this case, the adjustment width of the luminance of the backlight source 6 according to the latest value of the average luminance level is made larger when the change degree of the average luminance level is large than that when the change degree is small. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

In general, a liquid crystal display device includes a liquid crystal panel that displays an image (moving image) based on an input video signal, and a light source (backlight) that illuminates the liquid crystal panel from the back side.
In a liquid crystal display device, the visual brightness (brightness perceived by the viewer) of the displayed image depends on the balance between the luminance level of the entire displayed image (the gradation level of the image) and the luminance of the light source for the backlight. It depends. Specifically, if the video brightness level of the entire display video increases, the glare is alleviated by lowering the light source brightness, and if the video brightness level of the entire display video decreases, the light source brightness is increased. It is desirable to ensure sufficient brightness.
On the other hand, in Patent Document 1, in a liquid crystal display device, the feature amount (video luminance) is detected for each input video signal for one frame, and the luminance of the backlight light source is automatically set according to the feature amount. It has been proposed to adjust.
JP 2007-47733 A

By the way, the brightness (visual brightness) that the user of the liquid crystal display device feels when viewing the display image is the same as the level of the image brightness of the entire display image and the brightness of the light source for the backlight. However, due to the effects of afterimages, it may vary depending on the changes in the video seen in the past few seconds to about a few dozen seconds.
For example, if the brightness of the displayed video at a certain point in time is relatively high, the user may see a darker image before that point than when the same level of brightness has been continuously displayed up to that point. When the image is continuously displayed, the display image at the certain time is felt brighter. In addition, when the brightness of the displayed video at a certain time is relatively low, the user can display a brighter video before that time than when a video with the same brightness has been continuously displayed up to that time. When the image is continuously displayed, the display image at the certain point in time feels darker.
However, the technique disclosed in Patent Document 1 adjusts the luminance of the backlight light source in accordance with the latest feature amount (video luminance) detected for each input video signal for one frame. Depending on the situation of the video, there was a problem that the visual brightness of the displayed video (movie) could not be kept good.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to improve the visual brightness of the video (moving image) displayed on the liquid crystal panel regardless of the change in the status of the displayed video. An object of the present invention is to provide a liquid crystal display device that can be maintained at a high level.

In order to achieve the above object, a liquid crystal display device according to the present invention comprises a liquid crystal panel that displays an image based on an input video signal, and a light source that illuminates the liquid crystal panel, and further includes the following (1) and (2) Each component shown in FIG.
(1) Video signal feature amount detection means for detecting a feature amount of the input video signal.
(2) Light source luminance adjusting means for automatically adjusting the luminance of the light source based on the latest value of the feature amount of the input video signal and the degree of change of the feature amount within a predetermined time.
Here, a typical example of the feature amount of the input video signal is an index value of the video luminance of the input video signal, for example, an average luminance level (APL (Average Picture Level)) of the input video signal.
Further, the video signal feature quantity detecting means detects the feature quantity for each input video signal for one frame, for example.

The liquid crystal display device according to the present invention responds to the latest value (that is, the instantaneous value) of the feature amount of the input video signal in accordance with the degree of change in the characteristic amount of the input video signal (that is, the change in the status of the display video). The content of adjustment of the luminance of the light source for the backlight can be changed.
More specifically, when the feature quantity of the input video signal is an index value of the video luminance of the input video signal, the light source luminance adjusting means is a method when the change degree of the video luminance index value is large. However, it is conceivable that the adjustment range of the luminance of the light source corresponding to the latest value of the index value of the video luminance is made larger than when the degree of change is small.
Thereby, as will be described later, the visual brightness of the video (moving image) displayed on the liquid crystal panel can be kept good. Note that an average luminance level of the input video signal is considered as a typical example of the index value of the video luminance of the input video signal.
Further, the light source luminance adjusting means performs a process of setting the dimming information according to a change degree of the feature amount based on the dimming information and the latest value of the feature amount. It can be considered that the process is executed with a longer period than the process of automatically adjusting the brightness.
This is because the control corresponding to the visual afterimage with relatively low response is performed according to the change in the image luminance within a relatively long time, and the instantaneous value (latest value) of the feature amount that can change greatly in a short time is obtained. The corresponding control is performed in a short cycle. Thereby, the brightness of the light source for backlight is adjusted appropriately according to the purpose.

  According to the present invention, according to the change degree of the feature amount of the input video signal, the adjustment content of the luminance of the backlight light source according to the latest value of the feature amount can be changed. Regardless of the change, the visual brightness of the video (moving image) displayed on the liquid crystal panel can be kept good.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing the configuration of the main part of the liquid crystal display device X according to the embodiment of the present invention. FIG. 2 is a flowchart showing an example of the luminance adjustment procedure of the backlight source executed by the liquid crystal display device X. FIG. 3 is a graph of an example of dimming information candidates stored in the liquid crystal display device X.

First, the configuration of the main part of the liquid crystal display device X according to the embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 1, the liquid crystal display device X includes a video signal input unit 1, a video processing circuit 2, a liquid crystal drive circuit 3, a liquid crystal panel 4, an inverter circuit 5, a backlight light source 6, a light control circuit 7, and a main control circuit. 8 mag.
The video signal input unit 1 is an interface for inputting a video signal. Hereinafter, the video signal input through the video signal input unit 1 is referred to as an input video signal.
In addition, the video processing circuit 2 determines the video brightness (pixel gradation) of each of the three primary colors (R, G, B) of each pixel constituting one frame image in the moving image based on the input video signal for one frame. Are sequentially generated, and the frame signal is transmitted to the liquid crystal driving circuit 3. The video processing circuit 2 also performs a process of calculating a video brightness index value of the input video signal, the details of which will be described later.
Based on the frame signal sequentially transmitted from the video processing circuit 2 at a predetermined cycle, the liquid crystal driving circuit 3 displays one frame of video (one frame image) corresponding to the frame signal on the liquid crystal panel 4. This is a circuit that sequentially displays. As a result, the liquid crystal panel 4 (corresponding to the video display unit) displays a video (moving image) based on the input video signal.

The backlight source 6 includes a light source composed of a plurality of cold cathode tubes, and illuminates the liquid crystal panel 4 from the back side thereof. The backlight light source 6 may include a plurality of cold cathode tubes and LEDs, or may include a plurality of LEDs.
The inverter circuit 5 is a circuit that adjusts the power supplied to the backlight source 6 by PWM control in accordance with a control command (designation of duty ratio) from the dimming circuit 7.
The main control circuit 8 includes an MPU 81 that is a computing means, an EEPROM 82 that is a nonvolatile memory, and the like. The control process of the component is executed.

  The dimming circuit 7 is a circuit including an arithmetic circuit 71 and a register 72, and the arithmetic circuit 71 is based on information stored (stored) in the register 72 (set dimming information D1 described later). Then, the luminance of the backlight light source 6 is determined, and a duty ratio which is a control value for adjusting the power supplied to the backlight light source 6 is determined according to the determined luminance, and the duty ratio is supplied to the inverter circuit 5. Set (output). The inverter circuit 5 adjusts the power supplied to the backlight source 6 by performing PWM control according to the duty ratio set by the dimmer circuit 7. The dimming circuit 7 is embodied by, for example, an FPGA or an ASIC. It is also conceivable that the light control circuit 7 performs light control of the backlight light source 6 by adjusting the level of the DC voltage.

  Each time the input video signal for one frame is input, the video processing circuit 2 calculates an average luminance level (so-called APL (Average Picture Level)) as an index value of the video luminance of the video signal. The calculation result (latest value of APL) is stored (recorded) in a buffer (not shown) and transmitted to the dimming circuit 7. The average luminance level (APL) is a weighted average value of video luminances of the three primary colors (R, G, B) of all pixels in the input video signal for one frame. The average luminance level is an example of the feature amount of the input video signal, and the video processing circuit 2 is an example of means (video signal feature amount detection means) for detecting the feature amount. The buffer stores the APL values of the most recent predetermined number (hereinafter referred to as the change degree calculation frame number fa).

Further, the video processing circuit 2 receives the average luminance level stored in the buffer every time the input video signal corresponding to a predetermined number of frames (hereinafter referred to as the change monitoring frame number fb) is input. Based on this value, the change degree ΔAPL of the average luminance level within a predetermined time is calculated, and the calculation result (change degree of APL) is transmitted to the main control circuit 8.
Here, since the input video signal for one frame is input at a constant cycle, the average luminance level for each frame of the input video signal for a predetermined time is stored in the buffer. Will be. The change degree calculation frame number fa is, for example, one frame (fa = 1). It is also conceivable that a number of 2 or more is set in advance for the change degree calculation frame number fa.
Further, the average luminance level change ΔAPL is, for example, an average value Vn of the average luminance level in the most recent period of several hundred milliseconds to several seconds (for example, a period of about 1 second: hereinafter referred to as the most recent period). The index value indicates how much the average brightness level has changed with respect to the average value Vo in the period of several seconds to several tens of seconds before the most recent period (for example, about 10 seconds: hereinafter referred to as the past period). More specifically, the change degree ΔAPL of the average luminance level is the difference between the past average value Vo and the latest average value Vn (| Vn−Vo |), or the ratio between the difference and the past average value Vo. (| Vn−Vo | / Vo) or a value obtained by normalizing them can be considered.
In this way, the degree of change ΔAPL in the average luminance level calculated by the video processing circuit 2 is the degree of change in the average luminance level of the input video signal within a predetermined time (for example, about several seconds to several tens of seconds). Is an index value representing
The main control circuit 8 and the dimming circuit 7 update the average value (instantaneous value) of the average luminance level (an example of the feature amount of the input video signal) detected (calculated) by the video processing circuit 2 and The brightness of the backlight source 6 is automatically adjusted based on the average brightness level change ΔAPL. The luminance adjustment of the backlight light source 6 is performed by adjusting the power supplied to the backlight light source 6 (hereinafter referred to as light source power).

The EEPROM 82 included in the main control circuit 8 includes a dimming information candidate D1i representing a correspondence relationship between the average luminance level and a light source setting luminance representing a luminance adjustment value (setting value) of the backlight light source 6. (Multiple candidates) are stored in advance.
FIG. 3 is a graph showing an example of the dimming information candidate D1i stored in the EEPROM 82. As shown in FIG.
As shown in FIG. 3, each of the plurality of dimming information candidates D1i generally adjusts the light source setting luminance to be lower when the average luminance level is higher than when the average luminance level is lower. It is set information. However, the plurality of dimming information candidates D1i have different adjustment ranges of the light source setting luminance with respect to the average luminance level.
FIG. 3 shows a first dimming information candidate D11 having the smallest adjustment range of the light source setting luminance with respect to the average luminance level, and a third dimming information candidate D13 having the largest adjustment range of the light source setting luminance. And a second dimming information candidate D12 having an intermediate adjustment range.
The dimming information candidate D1i stored in the EEPROM 82 is look-up table information representing the correspondence relationship between the average luminance level and the light source setting luminance, information on an arithmetic expression, or the like.
In the liquid crystal display device X, the main control circuit 8 and the dimming circuit 7 have one candidate (from the plurality of dimming information candidates D1i based on the change degree ΔAPL of the average luminance level ( Dimming information) and automatically adjusting the luminance of the backlight source 6 based on the selected dimming information (hereinafter referred to as set dimming information D1) and the latest value of the average luminance level (light source luminance adjustment). Example of means).
The set dimming information D1 is used to maintain the brightness of the display image on the liquid crystal panel 4 in a good state that does not make the viewer feel dazzling or dark. This is information indicating how much the luminance (light emission amount) of the backlight source 6 should be adjusted according to (APL).

Next, an example of brightness adjustment processing of the backlight light source 6 by the main control circuit 8 and the dimming circuit 7 will be described in detail with reference to the flowchart shown in FIG. The luminance adjustment process shown in FIG. 2 is started from the start of energization of the liquid crystal display device X (at the time when the power is turned on). S1, S2,... Shown below represent identification codes of processing procedures (steps).
First, the MPU 81 in the main control circuit 8 selects one predetermined candidate (dimming information) from among a plurality of dimming information candidates D1i stored in advance in the EEPROM 82, and selects the selected information. The set dimming information D1 used for control is recorded in the register 72 of the dimming circuit 7 (S1). For example, the MPU 81 selects the first dimming information candidate D11 having the smallest adjustment range of the light source setting luminance as the default setting dimming information D1.
Next, each time the input video signal for one frame is input, the arithmetic circuit 71 in the dimming circuit 7 detects the input video signal for the one frame from the video processing circuit 2. The latest value of the average luminance level is acquired (S2).
Further, the arithmetic circuit 71 calculates the light source setting luminance according to the latest value of the average luminance level based on the set dimming information D1 stored in the register 72 and the latest value of the average luminance level. Calculate (S3).
Further, the arithmetic circuit 71 executes a dimming process according to the light source setting luminance calculated in step S3 (S4). Specifically, the arithmetic circuit 71 converts the light source setting luminance calculated in step S3 into a duty ratio that is a control value for adjusting the power supplied to the backlight light source 6 according to a predetermined conversion rule. The duty ratio is set (output) to the inverter circuit 5.
Thereby, the inverter circuit 5 adjusts the power supplied to the backlight light source 6 by performing PWM control according to the duty ratio set by the dimming circuit 7.
The processes in steps S2 to S4 described above are repeatedly executed every time the input video signal for one frame is input.

On the other hand, the MPU 81 in the main control circuit 8 receives the video every time the input video signal corresponding to the change rate monitoring frame number fb (for example, fb = 1) is input after the process of step S1 is completed. The degree of change ΔAPL of the average luminance level detected by the processing circuit 2 is acquired (S5).
Further, the MPU 81 determines the set dimming information D1 by selecting one candidate from the plurality of dimming information candidates D1i stored in advance in the EEPROM 82 in accordance with the degree of change ΔAPL. The set dimming information D1 is recorded in the register 72 of the dimming circuit 7 (S6). Thereafter, the dimming circuit 7 executes the dimming process (S4) based on the set dimming information D1 newly recorded in the register 72.
The process of step S6 is performed by selecting one candidate from among a plurality of dimming information candidates D1i stored in advance in the storage unit in accordance with the degree of change in the feature amount of the input video signal. It is an example of the process which sets the said setting light control information D1 used for the automatic adjustment of the brightness | luminance of the said backlight light source.
The processes in steps S5 and S6 described above are repeatedly executed every time the input video signal corresponding to the change degree monitoring frame number fb is input (that is, every time the change degree ΔAPL is detected).

In step S6, the MPU 81 has a larger adjustment range of the light source setting luminance in accordance with the average luminance level when the change degree ΔAPL is larger than when the change degree ΔAPL is smaller. Candidate D1i is selected.
For example, the MPU 81 determines whether the magnitude of the degree of change ΔAPL corresponds to any of a plurality of predetermined ranks (for example, “large change”, “during change”, “small change”), When the rank is “small change”, the first dimming information candidate D11 is displayed. When the rank is “changing”, the second dimming information candidate D12 is displayed. When the change is large, the third dimming information candidate D13 is selected as the set dimming information D1.
Thereby, the adjustment range of the luminance of the backlight source 6 according to the latest value of the average luminance level by the dimming circuit 7 is such that the variation ΔAPL is larger when the variation ΔAPL of the average luminance level is larger. It becomes larger than when it is small.
Therefore, for example, when the luminance of the display image at a certain point in time is relatively high, the luminance of the backlight light source 6 (the light source setting luminance) has been continuously displayed until the point of time. The lower luminance is set when the darker image is continuously displayed before that time.
In addition, when the brightness of the display image at a certain time is relatively low, the brightness of the backlight light source 6 (the light source setting brightness) has been continuously displayed until that time. Instead, the brightness is set higher when a brighter image is continuously displayed before that time.
As a result, the luminance adjustment of the backlight light source effect 6 is performed according to the intensity of the visual afterimage that changes according to the luminance of the past display image, and the liquid crystal panel 4 is adjusted regardless of the luminance change of the display image. The visual brightness of the displayed video (movie) is kept good.

In the liquid crystal display device X, the MPU 81 sets the set dimming information D1 in accordance with the degree of change ΔAPL in the average luminance level over a relatively long time (the input video signal for a plurality of frames). In parallel, the arithmetic circuit 71 performs the above-described operation based on the average luminance level (latest value) of the video signal and the set dimming information D1 for each input video signal for one frame (in a short time cycle). The brightness adjustment processing (S2 to S4) of the backlight light source 6 is executed.
That is, the liquid crystal display device X performs control corresponding to a visual afterimage that is relatively dull in response to a change in image luminance within a relatively long time, and increases for each frame image (in a short time). The control corresponding to the instantaneous value (latest value) of the average luminance level (APL) that can change is performed for each signal input for one frame. Thereby, the brightness adjustment of the backlight light source 6 is appropriately performed according to the purpose.

In the embodiment described above, the video processing circuit 2 calculates the average luminance level (APL) as the feature amount of the input video signal for one frame. Alternatively, other feature amounts such as an average value or a total value of video luminances in a video signal of any one of the three primary colors (for example, green) may be employed.
In addition to detecting (calculating) the latest value of the feature amount of the input video signal for each signal of one frame, for example, detecting the latest value of each signal of 2 to 3 frames may be considered. It is done.
In addition to the method shown in the embodiment, for example, the following method can be considered as the light source setting luminance calculation (determination) method.
For example, in the register 72, the first dimming information candidate D11 having the smallest adjustment range of the light source setting luminance with respect to the average luminance level, and the third dimming unit having the largest adjustment range of the light source setting luminance. Information candidates D13 are stored in advance.
Then, the arithmetic circuit 71 calculates a first light source setting luminance based on the latest value of the average luminance level and the first dimming information candidate D11, and further calculates the latest value of the average luminance level. A second light source setting luminance is calculated based on the third dimming information candidate D13.
Further, the arithmetic circuit 71 sets a weighting factor corresponding to the degree of change ΔAPL in the average luminance level, and uses the weighting factor to weight the first light source setting luminance and the second light source setting luminance. By calculating the average value, the light source setting luminance used for luminance adjustment is calculated. At this time, as the degree of change ΔAPL is larger, the weighting factor for the second light source setting luminance based on the third dimming information candidate D13 having a larger adjustment range of the light source setting luminance is increased.
Also by the light source setting luminance calculation method as described above, the same effects as those of the above-described embodiment can be obtained.

  The present invention can be applied to a liquid crystal display device.

1 is a block diagram illustrating a configuration of a main part of a liquid crystal display device X according to an embodiment of the present invention. 5 is a flowchart showing an example of a backlight light source luminance adjustment procedure executed by the liquid crystal display device X. The figure which graphed an example of the candidate of the light control information which the liquid crystal display device X memorize | stores.

Explanation of symbols

X: Liquid crystal display device 1: Video signal input unit 2: Video processing circuit 3: Liquid crystal drive circuit 4: Liquid crystal panel 5: Inverter circuit 6: Backlight light source 7: Dimming circuit 71: Arithmetic circuit 72: Register 8: Main control Circuit 81: MPU
82: EEPROM

Claims (9)

A liquid crystal display device comprising: a liquid crystal panel that displays an image based on an input video signal; and a light source that illuminates the liquid crystal panel,
Video signal feature quantity detecting means for detecting a feature quantity of the input video signal;
Light source luminance adjusting means for automatically adjusting the luminance of the light source based on the latest value of the feature amount of the input video signal and the degree of change of the feature amount within a predetermined time;
A liquid crystal display device comprising:   The liquid crystal display device according to claim 1, wherein the feature quantity of the input video signal is an index value of video brightness of the input video signal.   The light source brightness adjusting means is configured to adjust the brightness adjustment range of the light source according to the latest value of the image brightness index value when the change degree of the image brightness index value is larger than when the change degree is small. The liquid crystal display device according to claim 2, which is enlarged.   The liquid crystal display device according to claim 2, wherein the index value of the video luminance is an average luminance level of the input video signal.   The liquid crystal display device according to claim 1, wherein the video signal feature amount detection unit detects the feature amount for each input video signal for one frame. The light source luminance adjusting means is
Dimming information representing a correspondence relationship between the feature quantity and a control value for luminance adjustment of the light source is set according to the change degree of the feature quantity, and based on the dimming information and the latest value of the feature quantity The liquid crystal display device according to claim 1, wherein brightness of the light source is automatically adjusted. The light source luminance adjusting means is
The dimming information used for automatic adjustment of the luminance of the light source is selected by selecting one candidate from among a plurality of dimming information candidates stored in advance in the storage unit according to the degree of change in the feature amount. The liquid crystal display device according to claim 6, which is set.   8. The liquid crystal display device according to claim 6, wherein the light control information is look-up table information or arithmetic expression information representing a correspondence relationship between the feature amount and a control value for luminance adjustment of the light source. .   The light source brightness adjusting means executes a process of setting the dimming information according to the degree of change of the feature quantity, and sets the brightness of the light source based on the dimming information and the latest value of the feature quantity. The liquid crystal display device according to any one of claims 6 to 8, wherein the liquid crystal display device is executed at a cycle longer than the automatic adjustment processing.

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