JP2005308792A - Liquid crystal television, backlight control apparatus and backlight control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it is difficult to set luminance of a liquid crystal panel to be optimum for a viewing image. <P>SOLUTION: A luminance average value detecting circuit 22 calculates a luminance average value Ave from an image signal obtained during a certain period and a microcomputer 50 compares the luminance average value with a predetermined threshold value Th. Based on the comparison result, a pulse signal P of a predetermined duty ratio is generated. The microcomputer 50 transmits the pulse signal P to an inverter 62 as a control signal and the inverter 62 changes the duty ratio of a driving pulse signal which is outputted from a switching circuit 62c based on the pulse signal P. A backlight 61 to which the driving pulse signal is applied changes the light emitting luminance and as a result, the liquid crystal panel 40 is light-emitted with the luminance optimum for a luminance level of the viewing image. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal television, a backlight control device, and a backlight control method.

  Conventionally, when adjusting the brightness of a liquid crystal panel, a user changes a setting value for output of a backlight via an operation panel or the like while checking the brightness of the screen.

Further, as a conventional technique, the black level is calculated based on the illuminance of the projected image calculated from the area of the image projected on the screen, the light beam emitted from the light source lamp and passing through the projection lens, and the illuminance on the screen near the projected image area. A projection-type image display device that calculates a correction value and controls electric power supplied to a light source means is known (for example, see Patent Document 1).
In the projection type image display device, the power supplied to the light source means is increased or decreased depending on the difference between the illuminance of the projected image and the illuminance on the screen near the projected image area.

As another conventional technique, a liquid crystal driving circuit that sets an analog video signal output from an analog unit to a black level during a predetermined blanking period when switching from a standby mode to a normal mode is also known (for example, a patent) Reference 2).
In the liquid crystal drive circuit, by providing a blanking period necessary for the analog video signal to stabilize, the LCD screen is prevented from being disturbed when switching from the standby mode to the normal mode.
Japanese Patent Laid-Open No. 2002-250906 JP 2003-216112 A

As described above, the dimming operation of the conventional liquid crystal panel is performed while the user confirms the brightness of the screen, and thus the operation is complicated. In addition, it is difficult to perform appropriate light control corresponding to a change in the received video signal.
Moreover, in the said patent document 1, adjustment of the output of a light source means is performed based on the illumination intensity of the said projection image | video, and the illumination intensity on the screen of a projection image area vicinity. Therefore, there is a problem that the output of the light source cannot be adjusted based on the characteristics of the video signal to be displayed by the video display device.
Since the above-mentioned patent document 2 only sets the image to the black level when switching from the standby mode to the normal mode, the light source is based on the characteristics of the video signal to be displayed by the video display device, as in the above-mentioned patent document 1. The output of could not be adjusted.

  The present invention has been made in view of the above problems, and a liquid crystal television, a backlight control device, and a liquid crystal television capable of easily controlling the brightness of a liquid crystal panel to an optimum brightness for a video signal to be displayed. An object of the present invention is to provide a backlight control method.

  In order to achieve the above object, a first aspect of the present invention is a liquid crystal panel having a display surface formed of a plurality of pixels, and a back disposed on the back side of the liquid crystal panel and irradiating the display surface of the liquid crystal panel from the back side A light, an inverter for lighting the backlight at a predetermined light emission luminance by applying a voltage to the backlight, and receiving a television broadcast signal via an antenna and receiving an intermediate frequency signal from the television broadcast signal An output tuner; a video signal processing circuit that extracts a video signal from the intermediate frequency signal input from the tuner and performs predetermined signal processing on the video signal; and an image on the liquid crystal panel based on the video signal In a liquid crystal television comprising a liquid crystal driver circuit for displaying the image and a microcomputer for controlling each component device, the backlight The video signal processing circuit includes a luminance average value detection circuit that detects an average luminance value of the video signal input during a certain period via the tuner, and the microcomputer detects the detection value. When the average value thus obtained is compared with a predetermined threshold value and it is determined that the average value exceeds the threshold value, the inverter is provided with a predetermined duty ratio for reducing the light emission luminance of the fluorescent tube. A pulse signal having a predetermined duty ratio for causing the inverter to increase the light emission luminance of the fluorescent tube when it is determined that the average value is lower than the threshold value. A signal is generated and transmitted to the inverter, and the inverter changes the output of the AC voltage supplied to the fluorescent tube based on the pulse signal transmitted from the microcomputer to change the luminance of the fluorescent tube. It is constituted to be of.

  In the first aspect of the invention, the liquid crystal television includes a liquid crystal panel having a display surface formed of a plurality of pixels, a liquid crystal panel disposed on the back side of the liquid crystal panel, and the liquid crystal panel display surface. A backlight that emits light from the back, an inverter that turns on the backlight with a predetermined light emission luminance by applying a voltage to the backlight, and a television broadcast signal received via an antenna and the television broadcast A tuner for outputting an intermediate frequency signal from the signal, a video signal processing circuit for extracting a video signal from the intermediate frequency signal input from the tuner and performing predetermined signal processing on the video signal, and based on the video signal A liquid crystal driver circuit for displaying an image on the liquid crystal panel, and a microcomputer for controlling the components.

  Here, the video signal processing circuit detects the average value of the luminance of the video signal input during a certain period via the tuner in the luminance average value detection circuit. The microcomputer compares the detected average value with a predetermined threshold value. When the microcomputer determines that the average value exceeds the threshold value, the microcomputer generates a pulse signal as a control signal for reducing the light emission luminance of the backlight in the inverter, and sends the pulse signal to the inverter. Send. On the other hand, if it is determined that the average value is below the threshold value, a pulse signal as a control signal for increasing the light emission luminance of the backlight is generated in the inverter and transmitted to the inverter. Each of the pulse signals has a predetermined duty ratio, and the output of the inverter is controlled based on each duty ratio.

The inverter receives the pulse signal transmitted from the microcomputer and changes the output of the AC voltage supplied to the backlight based on the pulse signal. As a result, when the average value of the luminance exceeds the threshold value, the light emission luminance of the backlight is reduced, and when the average value is lower than the threshold value, the light emission luminance of the backlight increases.
That is, according to the configuration of the present application, the light emission luminance of the backlight is controlled by comparing the average luminance of the video signal input during a certain period with a predetermined threshold value. As a result, the brightness of the screen of the liquid crystal television is automatically adjusted to an optimum brightness according to the luminance level of the video being viewed. In claim 1, the backlight is a fluorescent tube.

  According to a second aspect of the present invention, there is provided a backlight control device that controls a backlight that is disposed at a predetermined position near the liquid crystal panel and that irradiates the liquid crystal panel from the back, and includes a video signal included in the received television broadcast signal. Based on the determination result of the luminance value detecting means for detecting a predetermined luminance value from the above, a luminance level determining means for comparing the detected luminance value with a predetermined threshold value, and the determination result of the luminance level determining means. Backlight control means for changing the light emission luminance at a predetermined degree is provided.

In the invention of claim 2 configured as described above, the backlight control device controls the backlight which is disposed at a predetermined position near the liquid crystal panel and irradiates the liquid crystal panel from the back.
Here, the luminance value detecting means detects a predetermined luminance value from the video signal included in the received television broadcast signal. Next, the luminance level determining means compares the detected luminance value with a predetermined threshold value. Then, the backlight control means changes the light emission luminance of the backlight at a predetermined degree based on the determination result of the luminance level determination means. That is, according to the configuration of the present application, the light emission luminance of the backlight is controlled by comparing a predetermined luminance value of the input video signal with a predetermined threshold value. As a result, the brightness of the liquid crystal panel is automatically adjusted to an optimum brightness according to the luminance level of the video being viewed.

  According to a third aspect of the present invention, in the backlight control device according to the second aspect, the luminance value detecting means detects an average value of the luminance of the video signal inputted during a predetermined period, and the luminance level determining means. Is configured to compare the detected average value with the threshold value.

  In the invention of claim 3 configured as described above, the luminance value detecting means detects the average value of the luminance of the video signal input during a certain period. Then, the luminance level determining means compares the detected average value with the threshold value. It is desirable to change the brightness of the screen of the liquid crystal panel as appropriate so that the brightness is optimal for the video to be viewed. On the other hand, changing the brightness of the screen instantaneously one after another in accordance with the change of the video signal whose luminance value changes every moment gives the user unpleasant feeling. Therefore, in the configuration of the present application, the brightness of the liquid crystal panel that is optimal for video is adjusted by adjusting the backlight by comparing the average value of the luminance of the video signal input during a certain period and the threshold value, and the user Realized both viewing comfort and comfort.

  According to a fourth aspect of the present invention, in the backlight control device according to the second or third aspect, the backlight control means includes a microcomputer and an inverter, and the microcomputer has the brightness level determination means. When it is determined that the predetermined luminance value exceeds the threshold value, a control signal for reducing the light emission luminance of the backlight is generated and transmitted to the inverter, and the luminance level determination means is configured to output the predetermined luminance. When it is determined that the value is below the threshold value, a control signal for increasing the light emission luminance of the backlight is generated and transmitted to the inverter, and the inverter emits the backlight based on the control signal. The luminance is changed.

  In the invention of claim 4 configured as described above, the backlight control means comprises a microcomputer and an inverter. The microcomputer generates a control signal for reducing the light emission luminance of the backlight when the luminance level determining means determines that the predetermined luminance value exceeds the threshold value. On the other hand, when the brightness level determining means determines that the predetermined brightness value is below the threshold value, it generates a control signal for increasing the light emission brightness of the backlight. Then, the generated control signal is transmitted to the inverter. The inverter changes the light emission luminance of the backlight based on the control signal. That is, when the brightness level determining means determines that the predetermined brightness value exceeds the threshold value, the inverter reduces the light emission brightness of the backlight based on the control signal, and the brightness level determining means When it is determined that the luminance value is below the threshold value, the inverter increases the light emission luminance of the backlight based on the control signal.

  According to a fifth aspect of the present invention, in the backlight control device according to the fourth aspect, the microcomputer generates a pulse signal having a different duty ratio according to a determination result by the luminance level determining means, and the inverter converts the pulse signal into the pulse signal. Based on this, the output luminance of the backlight is changed by changing the output of the alternating voltage supplied to the backlight.

  In the invention of claim 5 configured as described above, the microcomputer generates pulse signals having different duty ratios according to the determination result by the luminance level determination means. The inverter receives a pulse signal having a predetermined duty ratio in each case where the determination results by the luminance level determination means are different, and changes the output of the AC voltage supplied to the backlight based on the pulse signal. As a result, the light emission luminance of the backlight changes to a luminance optimum for the received video signal.

According to a sixth aspect of the present invention, in the backlight control device according to the fifth aspect, the backlight control means includes a determination result obtained by the luminance level determination means and a duty ratio of a pulse signal generated based on the determination result. The correspondence relationship is stored in advance as data in a predetermined storage area.
That is, when the microcomputer recognizes the determination result by the luminance level determination means, the microcomputer can generate a pulse signal having a predetermined duty ratio with reference to the correspondence relationship. Note that the duty ratio of each pulse signal generated based on the determination result by the luminance level determination means may be set to a desired value by the user.

  A seventh aspect of the present invention is the backlight control device according to any one of the second to sixth aspects, wherein the backlight is a fluorescent tube. Since the fluorescent tube is lit by the AC voltage supplied from the inverter, the emission luminance can be easily changed by the output control of the inverter by the pulse signal generated by the microcomputer.

So far, the technical idea for changing the light emission luminance of the backlight of the liquid crystal panel has been described as the invention of the apparatus. However, this technical idea also holds true as an invention of a method for realizing this. Accordingly, the invention of claim 8 is a backlight control method for controlling a backlight which is disposed at a predetermined position of the liquid crystal panel and irradiates the liquid crystal panel from the back side, and includes an image included in the received television broadcast signal. A predetermined luminance value is detected from the signal, the detected luminance value is compared with a predetermined threshold value, and the luminance of the backlight is changed at a predetermined degree based on the comparison result.
Of course, it goes without saying that it is possible to grasp the invention of the method corresponding to the invention of claim 1 or the invention of claims 3 to 7 subordinate to claim 2.

As described above, according to the first aspect of the invention, the brightness of the screen of the liquid crystal television can be automatically adjusted to an optimum brightness according to the luminance level of the video to be viewed.
According to the second and eighth aspects of the present invention, the brightness of the liquid crystal panel can be automatically adjusted to an optimum brightness according to the luminance level of the video to be viewed.
Further, according to the invention of claim 3, it is possible to realize both the brightness of the liquid crystal panel optimal for video and the user's viewing comfort.
Further, according to the inventions according to claims 4 and 5, the light emission luminance of the backlight can be adjusted to an appropriate value with certainty.
Furthermore, according to the sixth aspect of the present invention, the microcomputer can easily generate a pulse signal having a predetermined duty ratio suitable for the determination result of the luminance level determination means.
According to the seventh aspect of the invention, the brightness of the liquid crystal panel is automatically adjusted to the optimum brightness according to the brightness level of the video to be viewed by adjusting the light emission brightness of the fluorescent tube. be able to.

Embodiments of the present invention will be described in the following order.
(1) Schematic configuration of liquid crystal television (2) Backlight control process (3) Summary

(1) Schematic Configuration of Liquid Crystal Television FIG. 1 shows a schematic configuration of a liquid crystal television according to an embodiment of the present invention.
As shown in the figure, the liquid crystal liquid crystal television 100 generally includes a tuner 10, an RGB signal generation circuit 20, a liquid crystal driver circuit 30, a liquid crystal panel 40, a microcomputer 50, and a backlight unit 60. In this configuration, the microcomputer 50 is connected to each part of the liquid crystal television 100 via the IIC bus 70, and the CPU 51 controls the entire liquid crystal television 100 in accordance with each program written in a memory such as the ROM 52 and the RAM 53. Control. An operation panel 54 and a remote control I / F 55 are connected to the microcomputer 50, and an input signal through the operation panel 54 or an input signal from the remote control through the remote control I / F 55 is used. Various processes in the liquid crystal television 100 can be controlled. In the present embodiment, the liquid crystal panel 40 is used as an image display element, but the present invention is not limited to this, and a display element such as a plasma panel may be used.

  The tuner 10 receives a television broadcast signal through the antenna 10a under the control of the microcomputer 50. The tuner 10 extracts a composite video signal as an intermediate frequency signal from the television broadcast signal while performing a predetermined signal amplification process and the like, and outputs it to the A / D conversion circuit 21 of the RGB signal generation circuit 20. The A / D conversion circuit 21 converts the input composite video signal into a digital signal according to the signal level. In the present embodiment, the RGB signal generation circuit 20 includes a luminance average value detection circuit 22. As will be described later, the luminance average value detection circuit 22 performs a process of calculating an average value of luminance of the video signal (luminance average value Ave).

  Hereinafter, general processing for the composite video signal converted into a digital signal will be described. That is, the Y / C separation circuit 23 performs separation into a luminance signal and a chroma signal based on the digitized composite video signal. The separated luminance signal is input to the image quality adjustment circuit 24, and after predetermined image quality adjustment such as contrast adjustment is performed, it is output to the matrix circuit 26. On the other hand, the separated chroma signal is demodulated into RY and BY color difference signals in the color demodulation circuit 25 and then output to the matrix circuit 26. In the matrix circuit 26, matrix conversion processing is performed based on the input luminance signal and color difference signal to generate an RGB signal as image data.

  The generated RGB signal is output to the liquid crystal driver circuit 30. The liquid crystal driver circuit 30 includes a pixel number conversion circuit 31, an image quality adjustment circuit 32, an output processing circuit 33, and a frame memory 34. The pixel number conversion circuit 31 receives the RGB signal and generates an RGB signal for one screen displayed on the liquid crystal panel 40 while performing a scaling process on the RGB signal. Then, the RGB signals for one screen are stored in the frame memory 34 as pixel information.

  The image quality adjustment circuit 32 performs the scaling process by the pixel number conversion circuit 31 and adjusts the brightness, contrast, black balance, and white balance for the RGB signals stored in the frame memory 34. The output processing circuit 33 performs gamma correction, dither processing, and the like on the RGB signal that has been subjected to image quality adjustment by the image quality adjustment circuit 32, and adds a background signal, an OSD signal, a blanking signal, and the like to the liquid crystal panel 40. To display the image.

  The backlight unit 60 includes a backlight 61 that serves as a light source for irradiating the liquid crystal panel 40 from the back side, and an inverter 62 that converts the DC voltage into an AC voltage and then supplies the AC voltage to the backlight 61 for lighting. It consists of. In the present embodiment, the backlight 61 is a fluorescent tube. Further, the inverter 62 is connected to the microcomputer 50. The inverter 62 receives the pulse signal P as a control signal from the microcomputer 50 and changes the duty ratio of the alternating voltage applied to the backlight 61 based on the pulse signal P. When an alternating voltage whose duty ratio is changed based on the pulse signal P is applied to the backlight 61, the light emission luminance of the backlight 61 changes as will be described later.

(2) Backlight Control Processing FIG. 2 shows an example of the composite video signal.
As shown in the figure, the synthesized video signal S has a horizontal blanking interval and a horizontal synchronization signal, and the video signal is synthesized between them. As described above, the luminance average value detection circuit 22 calculates the luminance average value Ave of the video signal that constitutes a part of the composite video signal S. In the present embodiment, the average luminance value Ave of the video signal in the range between the upper limit voltage Vmax indicating the white level and the lower limit voltage Vmin indicating the black level in the composite video signal S is calculated.

  The luminance average value detection circuit 22 calculates the luminance average value Ave after monitoring the input video signal for a certain period. As the fixed period, for example, a period of 1 minute can be considered. That is, instead of simply calculating the average luminance in one horizontal scanning period, the luminance values of the video signals input continuously for a certain period are totaled, and the average value of the total is calculated as the luminance average value Ave. In the figure, the composite video signal S is expressed in the form of an analog signal. However, in actual processing, the A / D conversion circuit 21 converts the composite video signal S into a digital signal having a gradation corresponding to each signal level. Convert to Then, based on the converted digital signal, the luminance average value detection circuit 22 performs a calculation process of the luminance average value Ave.

FIG. 3 is a flowchart showing the generation process of the pulse signal P by the microcomputer.
First, the microcomputer 50 inputs the average brightness value Ave in step S100. That is, the microcomputer 50 acquires the luminance average value Ave calculated by the luminance average value detection circuit 22.
Next, the microcomputer 50 acquires a predetermined threshold value Th previously stored in a storage device (not shown) such as a hard disk from the storage device (step S200). The threshold value Th may be set freely by the user via the operation panel 54 or the like.

When the luminance average value Ave and the threshold value Th are acquired, the microcomputer 50 compares the two values (steps S300 and S400). That is, it is determined whether the luminance level of the video signal received by the liquid crystal television 100 is high or low depending on whether the luminance average value Ave is higher or lower than the threshold value Th.
FIG. 4 shows, as an example, a correspondence relationship between the comparison result between the luminance average value Ave and the threshold value Th and the duty ratio of the pulse signal P generated by the microcomputer 50. The correspondence relationship table 80 shown in the figure is stored in advance in the storage device, similarly to the threshold value Th. Also, the duty ratio value in the correspondence relationship table 80 can be freely set by the user via the operation panel 54 or the like.

  The duty ratio is the ratio of the high (H) level to the period of the pulse signal. When the microcomputer 50 compares the luminance average value Ave and the threshold value Th, the microcomputer 50 refers to the correspondence table 80 and generates a pulse signal P having a duty ratio corresponding to the comparison result. That is, when it is determined that the luminance average value Ave is higher than the threshold value Th, the microcomputer 50 generates a pulse signal P1 having a low duty ratio (duty 70% according to the correspondence table 80) (step S500). On the other hand, when it is determined that the luminance average value Ave is lower than the threshold value Th, a pulse signal P2 having a high duty ratio (duty 90% according to the correspondence table 80) is generated (step S600), and the luminance average value Ave is generated. Is equal to the threshold value Th, a pulse signal P3 having a standard duty ratio (duty 80% according to the correspondence table 80) is generated (step S700).

  As described above, the microcomputer 50 transmits the pulse signal P generated with a different duty ratio depending on the comparison result between the luminance average value Ave and the threshold value Th to the inverter 62 as a control signal (step S800). Note that the evaluation with respect to the luminance average value Ave is not necessarily performed in comparison with the threshold value Th. For example, if a standard range is specified as the luminance level of the video signal, and a luminance average value Ave falls within the same range, a pulse signal with a standard duty ratio is generated. Thus, the duty ratio of the pulse signal P may be changed to a predetermined value.

FIG. 5 is a block diagram showing the backlight unit 60 and the microcomputer 50.
In the figure, an inverter 62 includes an oscillation circuit 62a, a waveform synthesis circuit 62b, and a switching circuit 62c. Further, the inverter 62 acquires a DC voltage through the connection line 62d. The DC voltage is supplied from a power supply circuit (not shown), and the power supply circuit converts commercial AC power into DC voltage in order to drive the entire liquid crystal television 100. The DC voltage is synthesized with an oscillation signal of a predetermined frequency generated by the oscillation circuit 62a and the waveform synthesis circuit 62b, and then outputted to the switching circuit 62c. The switching circuit 62 c converts the input DC voltage into a drive pulse signal and outputs it to the backlight 61.

  That is, the driving pulse signal is extracted on the output side by alternately switching the switching element 62c1 on and off with respect to the direct current input to the switching circuit 62c. The drive pulse signal output from the switching circuit 62c is applied to the electrode of the backlight 61, which is a fluorescent tube, and turns on the backlight 61. Here, the light emission luminance of the backlight 61 that is turned on in response to the supply of the drive pulse signal is determined by the duty ratio of the drive pulse signal. The backlight 61 is lit when the signal level of the drive pulse signal is H level, and is not lit when the signal level is L level. Accordingly, the luminance of the backlight 61 is determined by the ratio between the H level and the L level of the supplied driving pulse signal, and the higher the duty ratio of the driving pulse signal, the higher the luminance. Conversely, the lower the duty ratio of the drive pulse signal, the lower the luminance.

  In order to change the light emission luminance of the backlight 61, the duty ratio of the drive pulse signal may be changed. Specifically, the switching circuit 62c provides the inverter 62 with a control signal that changes the timing for switching the switching element 62c1. Therefore, the microcomputer 50 transmits a pulse signal P (any one of P1 to P3) as a control signal of the inverter 62 to the switching circuit 62c of the inverter 62.

  When the pulse signal P1 is supplied to the switching circuit 62c, the pulse signal P1 controls the switching timing of the switching element 62c1. As a result, the duty ratio of the drive pulse signal decreases. That is, when the luminance average value Ave is higher than the threshold value Th, the inverter 62 is controlled to reduce the duty ratio of the drive pulse signal to be output, and the light emission luminance of the backlight 61 is reduced. On the other hand, when the pulse signal P2 is given to the switching circuit 62c, the duty ratio of the drive pulse signal becomes high. That is, when the luminance average value Ave is lower than the threshold value Th, the inverter 62 is controlled to increase the duty ratio of the drive pulse signal to be output, and the light emission luminance of the backlight 61 is increased.

  When the pulse signal P3 is supplied to the switching circuit 62c, the pulse signal P3 controls the switching timing of the switching element 62c1. If the inverter 62 has been controlled by the pulse signal P1 until then, the duty ratio of the drive pulse signal increases. If the inverter 62 has been controlled by the pulse signal P2, the duty ratio of the drive pulse signal decreases. That is, when the average luminance value Ave is equal to the threshold value Th, the inverter 62 controls the standard duty ratio and turns on the backlight 61 with a predetermined light emission luminance set as standard brightness. .

  Thus, the light emission luminance of the backlight 61 changes as appropriate based on the comparison result between the luminance average value Ave and the threshold value Th. As a result, when a certain video is viewed on the liquid crystal television 100, the brightness of the screen of the liquid crystal panel 40 is automatically controlled to the optimal brightness for the luminance level of the video to be viewed.

  In the present embodiment, even when the backlight 61 is continuously controlled while receiving a television broadcast signal, the user's viewing comfort is not impaired. That is, if the luminance average value Ave is calculated in a short cycle such as one horizontal scanning period or several seconds and the emission luminance of the backlight 61 is changed based on the calculated value, the brightness of the screen is too high. It changes too often. Such frequent changes cause discomfort to the user who views the liquid crystal television 100. However, in the present embodiment, the calculation of the luminance average value Ave is performed over the predetermined period, for example, 1 minute. Therefore, the interval at which the light emission luminance of the backlight 61 changes is also at the certain period. As a result, it is possible to realize both the dimming of the backlight 61 to the light emission luminance in consideration of the characteristics of the viewed video and the user's viewing comfort.

  Further, according to the configuration of the present application, when adjusting the brightness of the screen of the liquid crystal panel 40, it is not necessary to perform signal processing on the video signal such as brightness adjustment. Therefore, the video based on the video signal extracted from the received television broadcast signal can be displayed on the liquid crystal panel 40 as it is.

(3) Summary As described above, the luminance average value detection circuit 22 calculates the luminance average value Ave from the video signal acquired during a certain period, and the microcomputer 50 calculates the luminance average value Ave and the predetermined threshold Th. Based on the result of the comparison, a pulse signal P having a predetermined duty ratio is generated. The microcomputer 50 transmits the pulse signal P as a control signal to the inverter 62, and the inverter 62 changes the duty ratio of the drive pulse signal output from the switching circuit 62c based on the pulse signal P. The backlight 61 to which such a drive pulse signal is applied changes its emission luminance, and as a result, the liquid crystal panel 40 emits light with an optimum luminance for the luminance level of the video signal to be viewed.

It is a schematic block diagram of the liquid crystal television concerning one Embodiment of this invention. It is explanatory drawing of a synthetic | combination video signal. It is the flowchart which showed the production | generation process of a pulse signal. It is the figure which showed the correspondence table. It is the block diagram which showed the backlight part and the microcomputer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Tuner 10a ... Antenna 20 ... RGB signal generation circuit 21 ... A / D conversion circuit 22 ... Luminance average value detection circuit 23 ... Y / C separation circuit 24 ... Image quality adjustment circuit 25 ... Color demodulation circuit 26 ... Matrix circuit 30 ... Liquid crystal Driver circuit 40 ... Liquid crystal panel 50 ... Microcomputer 51 ... CPU
52 ... ROM
53 ... RAM
54 ... Operation panel 55 ... Remote control I / F
60 ... Backlight 61 ... Backlight 62 ... Inverter 62a ... Oscillation circuit 62b ... Waveform synthesis circuit 62c ... Switching circuit 62c1 ... Switching element 80 ... Correspondence table 100 ... Liquid crystal television

Claims (8)

A liquid crystal panel having a display surface formed of a plurality of pixels, a backlight disposed on the back side of the liquid crystal panel and illuminating the display surface of the liquid crystal panel from the back surface, and applying a voltage to the backlight An inverter that turns on the backlight at a predetermined luminance, a tuner that receives a television broadcast signal via an antenna and outputs an intermediate frequency signal from the television broadcast signal, and an intermediate frequency that is input from the tuner A video signal processing circuit for extracting a video signal from the signal and performing predetermined signal processing on the video signal; a liquid crystal driver circuit for displaying an image on the liquid crystal panel based on the video signal; In a liquid crystal television equipped with a microcomputer to control,
The backlight is a fluorescent tube,
The video signal processing circuit includes a luminance average value detection circuit that detects an average luminance value of a video signal input during a certain period via the tuner,
The above microcomputer
Compare the detected average value with a predetermined threshold,
When it is determined that the average value exceeds the threshold value, the inverter generates a pulse signal having a predetermined duty ratio for reducing the light emission luminance of the fluorescent tube, and transmits the pulse signal to the inverter.
If it is determined that the average value is below the threshold value, the inverter generates a pulse signal having a predetermined duty ratio for increasing the light emission luminance of the fluorescent tube, and transmits the pulse signal to the inverter.
2. The liquid crystal television according to claim 1, wherein the inverter changes the light emission luminance of the fluorescent tube by changing the output of the alternating voltage supplied to the fluorescent tube based on the pulse signal transmitted from the microcomputer. A backlight control device that controls a backlight that is disposed at a predetermined position near the liquid crystal panel and that irradiates the liquid crystal panel from the back,
Luminance value detecting means for detecting a predetermined luminance value from the video signal included in the received television broadcast signal;
Brightness level discrimination means for comparing the detected brightness value with a predetermined threshold value;
Backlight control means for changing the light emission brightness of the backlight at a predetermined degree based on the determination result of the brightness level determination means;
A backlight control device comprising: The luminance value detecting means detects the average value of the luminance of the video signal input during a certain period, and the luminance level determining means compares the detected average value with the threshold value. The backlight control device according to claim 2, wherein The backlight control means comprises a microcomputer and an inverter,
When the brightness level determination means determines that the predetermined brightness value exceeds the threshold value, the microcomputer generates a control signal for reducing the light emission brightness of the backlight and transmits the control signal to the inverter. When the brightness level determining means determines that the predetermined brightness value is lower than the threshold value, it generates a control signal for increasing the light emission brightness of the backlight and transmits it to the inverter,
4. The backlight control apparatus according to claim 2, wherein the inverter changes the light emission luminance of the backlight based on the control signal. The microcomputer generates a pulse signal having a different duty ratio according to the determination result by the luminance level determination means, and the inverter changes the output of the AC voltage supplied to the backlight based on the pulse signal to change the backlight. The backlight control device according to claim 4, wherein the light emission luminance is changed. The backlight control unit stores in advance a correspondence relationship between a determination result by the luminance level determination unit and a duty ratio of a pulse signal generated based on the determination result as data in a predetermined storage area. The backlight control device according to claim 5. The backlight control apparatus according to claim 2, wherein the backlight is a fluorescent tube. A backlight control method for controlling a backlight disposed at a predetermined position of a liquid crystal panel and irradiating the liquid crystal panel from the back,
A predetermined luminance value is detected from the video signal included in the received television broadcast signal,
Compare the detected brightness value with a predetermined threshold,
A backlight control method, wherein the brightness of the backlight is changed by a predetermined degree based on the result of the comparison.

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