JP2005249891A - Liquid crystal display device, backlight control method, and recording medium recording backlight control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device, a backlight control method, and a recording medium on which a backlight control program is recorded, in which contrast is correctly expressed and power consumption can be further reduced without deterioration of image quality.
A liquid crystal display device 1 is inversely proportional to the luminance level of an input video signal, a luminance level detecting unit 11 for detecting the luminance level of the input video signal, a video level adjusting unit 12 for adjusting the level of the input video signal. A video level gain limiting unit 13 that limits the gain of the video level adjusting unit 12 so as to obtain a video signal level, and a backlight gamma that converts the output signal of the luminance level detecting unit 11 so that a predetermined backlight luminance can be obtained. A correction unit 18, a backlight light amount limiting unit 19 that controls the light amount of the backlight based on the output of the backlight gamma correction unit 18, and a backlight drive circuit 20 are provided.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device including a backlight, and more particularly to a liquid crystal display device with reduced power consumption, a backlight control method, and a recording medium on which a backlight control program is recorded.

  In a portable device, by reducing the power consumption of the device, the usage time of the battery can be extended, or the battery can be reduced in size, which contributes to the reduction in size and weight of the device. In a device equipped with a liquid crystal display device, the proportion of the power consumption of the liquid crystal backlight is large in the total power consumption, and this reduction in power consumption is strongly demanded.

  A portable display device typified by a portable television receiver is battery-powered when used portable. In this type of portable display device, the power consumed by the backlight unit is the largest, and the battery driving time varies greatly depending on whether the backlight is turned on or off and its brightness. Generally, the display screen is easy to see when the luminance of the backlight is high, and difficult to see when the luminance is low. Also, the optimum brightness varies depending on the ambient brightness. Since the use of the backlight greatly affects the battery driving time, the backlight luminance is controlled to extend the battery driving time.

  As a technique for reducing the power consumption of the backlight, Patent Document 1 is disclosed. The liquid crystal display device described in Patent Document 1 controls the level of the video signal supplied to the liquid crystal according to the maximum value of the input video signal level, and at the same time controls the brightness of the backlight. It is intended to reduce power consumption.

FIG. 5 is a block diagram showing a configuration of the liquid crystal display device described in Patent Document 1. In FIG.
In FIG. 5, the liquid crystal display device is an amplifier 102 that amplifies the video signal input from the input unit 101, a signal processing circuit 103 that processes the amplified video signal, and the signal processed video signal that is optimal for A / D conversion. A conversion level adjustment amplifier 104 that amplifies the signal to a certain level, an A / D converter 105 that performs analog-to-digital conversion on the video signal input through the conversion level adjustment amplifier 104, and a liquid crystal display based on the digitized video signal A control signal for detecting the maximum level of the luminance signal from the driving circuit 106, the transmissive liquid crystal display 110, and the signal processing circuit 103 and amplifying the gain of the conversion level adjustment amplifier 104 in inverse proportion to the maximum level of the luminance signal; Luminance level detection circuit 107 that sends out a control signal that changes the amount of light in proportion to the maximum level of the luminance signal. A light amount control circuit 108 for controlling the light intensity of the backlight 109 in response to a control signal from the luminance level detecting circuit 107, and a backlight 109 for illuminating the liquid crystal display 110 from behind.

JP-A-11-109317

  However, in such a conventional liquid crystal display device, the gamma characteristic of the system is not taken into consideration, and there is a disadvantage that an accurate contrast reproduction cannot be expected as it is and the image quality is deteriorated. This drawback will be described below.

  In a television system, the gamma value of a display device is generally assumed to be 2.2. This is because the cathode ray tube gamma was adopted because the cathode ray tube was the main display device before. In order to obtain correct contrast reproduction when displayed on a display device with gamma 2.2, the imaging device side is prescribed to perform reverse correction of gamma 2.2, that is, correction of gamma 0.45.

FIG. 6 is a diagram illustrating gamma correction of the television system.
In FIG. 6, reference numeral 41 represents the input voltage (x) vs. luminance (y) characteristics of the cathode ray tube, and shows the relationship of the following equation (1).
y = k * x ^ γ (1)
Where k is a proportional constant, and γ = 2.2

Reference numeral 42 in FIG. 6 is a characteristic of the imaging apparatus, which represents the subject luminance (x) versus output voltage (y) characteristic, and shows the relationship of the following equation (2).
y = m * x ^ γ (2)
Where m is a proportionality constant and γ = 0.45.
As shown in the above equation (2), the cathode ray tube characteristic is reversely corrected.

As the overall characteristics of the imaging device and the cathode ray tube, a straight line is obtained as indicated by numeral 43 in FIG.
The video signal that is generally handled is a video signal output from the apparatus that has been γ-corrected in this way.

  In recent liquid crystal display devices, the input / output characteristics of the liquid crystal itself are different from those of a cathode ray tube, and an example is shown in FIG.

FIG. 7 is a diagram illustrating the gamma characteristic of the liquid crystal display device.
In this example, the voltage (V) versus transmittance (T) characteristics are inverted S-shaped. However, as described above, the video signal is created on the assumption that γ = 2.2 of the cathode ray tube, so that correct contrast reproduction cannot be obtained as it is. Therefore, a gamma correction circuit for matching with the liquid crystal display device is required. There are various ways of performing this correction. For example, FIG. 8 shows an example in which a gamma correction circuit is provided in the drive circuit 106 in the conventional example of FIG.

FIG. 8 is a block diagram showing a configuration of a driving circuit having a gamma correction circuit of a conventional liquid crystal display device.
In FIG. 8, the drive circuit 106 includes an input terminal 30, a gamma correction circuit 31 for adjusting to γ of the liquid crystal display, a signal processing circuit 32 for driving liquid crystal, and a timing pulse generating circuit 33 for driving. . By the operation of the gamma correction circuit 31, the characteristics viewed from the input terminal 30 are corrected so as to match the characteristics of the cathode ray tube. That is, γ = 2.2. In this way, in the conventional example of FIG. 5, the gamma characteristic after the drive circuit 106 is assumed to be 2.2.

  FIG. 9 is a diagram showing a result of simulating how a conventional display device (FIG. 5) reproduces a liquid crystal display when the subject brightness changes. 9A shows simulation results when the backlight control and signal level control are not performed, and FIG. 9B shows simulation results when the backlight control and signal level control are performed. As indicated by reference numeral 70 in FIG. 9, the liquid crystal display luminance L is a product of the liquid crystal display transmittance T and the backlight luminance b (L = T * b).

  As shown in FIG. 9B, the gain of the conversion level adjustment amplifier 104 is proportional to the peak luminance, and the backlight luminance b is inversely proportional to the peak luminance. In FIG. 9A, the maximum brightness of the liquid crystal display is 100% when the subject brightness is 0 to 100%, and the maximum brightness of the liquid crystal display is 20% when the subject brightness is 0 to 20%. Has been obtained. However, in FIG. 9B, the maximum brightness of the liquid crystal display is 100% when the subject brightness is 0 to 100%, but the peak brightness when the subject brightness is 0 to 20% is 48% for the liquid crystal and bright. It has been reproduced. Similarly, when the subject brightness is 0 to 5%, it is reproduced brightly. As described above, the conventional method shown in FIG. 5 cannot accurately display the luminance in consideration of the γ characteristic of the television system.

  In terms of power consumption, in the case of FIG. 9A, the backlight brightness is always 100%, which is the maximum. In FIG. 9B, when the subject brightness is 0 to 20%, the backlight brightness is 48% and subject brightness 0 to 5%, the backlight brightness is 21%, and the power consumption of the backlight is almost proportional to the backlight brightness. Therefore, it can be said that the effect of reducing the power consumption appears. However, the brightness reproduced as described above is too bright, suggesting the possibility of making the backlight darker and further reducing power consumption.

  Another disadvantage of the conventional apparatus is that the gain of the amplifier is increased in proportion to the luminance signal, so that there is a problem that the S / N deteriorates due to excessive gain depending on the image content. For example, in FIG. 9B, when the subject brightness is 0 to 5%, the gain of the conversion level adjustment amplifier 6 is 4.8 times, and image quality deterioration occurs due to the gain increase. Furthermore, there is a concern that when the gain is increased, the gamma correction value is shifted and the image quality is deteriorated.

  The present invention has been made in view of such a problem, and a liquid crystal display device, a backlight control method, and a liquid crystal display device that can correctly reduce the power consumption without degrading the image quality because the contrast is correctly expressed. It is an object to provide a recording medium on which a backlight control program is recorded.

  The liquid crystal display device of the present invention is a liquid crystal display device having a backlight, and is characterized by comprising means for performing gamma correction on the luminance level of the backlight.

  A liquid crystal display device according to the present invention is a liquid crystal display device having a backlight, wherein a luminance level detecting means for detecting a luminance level of an input video signal and an output signal of the luminance level detecting means are transmitted with a predetermined backlight luminance. Backlight gamma correction means for conversion so as to be obtained, and backlight control means for controlling the luminance of the backlight based on the output of the backlight gamma correction means. As a result, the gain is not increased excessively and good image quality is maintained.

  More preferably, the backlight gamma correction means corrects the luminance level of the backlight to be linear so that the luminance signal level of the input image is correctly expressed.

  Further, as a more preferable specific form, the gain of the video level adjusting means for adjusting the level of the input video signal and the video level adjusting means to limit the video signal level inversely proportional to the luminance level of the input video signal are limited. Video level gain limiting means.

  As a more preferred specific form, the backlight control means includes a backlight light quantity limiting means for limiting the light quantity of the backlight.

  The brightness level detection means may detect the maximum value of the video signal, and the brightness level detection means may detect an average value of the video signal. Further, the luminance level detecting means may calculate a luminance level from a maximum value and an average value of the video signal. As a result, it is possible to further reduce the power consumption, the contrast is correctly expressed, and the image quality does not deteriorate.

  A backlight control method according to the present invention is a backlight control method for a liquid crystal display device including a backlight, the step of detecting a luminance level of an input video signal, and a detected luminance level output signal as a predetermined backlight. The method includes a step of performing gamma correction so as to obtain luminance, and a step of controlling the luminance of the backlight based on the output of the gamma correction.

  Furthermore, it is more preferable to have a step of adjusting the level of the input video signal and a step of limiting the gain so that the video signal level is inversely proportional to the luminance level of the input video signal.

  From another viewpoint, the present invention provides a backlight control method for a liquid crystal display device including a backlight, the step of detecting the luminance level of an input video signal, and the detected luminance level output signal as a predetermined backlight. A computer-readable recording characterized by recording a program for causing a computer to execute a gamma correction step so as to obtain luminance and a step of controlling the luminance of the backlight based on the output of the gamma correction. It is a medium.

  As described above in detail, according to the present invention, the contrast is correctly expressed, and the power consumption can be further reduced without degrading the image quality.

  Hereinafter, preferred embodiments of a liquid crystal display device and a backlight control method of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device according to this embodiment can be applied to a display device of a digital television receiver.

  In FIG. 1, a liquid crystal display device 1 includes an input unit 10 for inputting a video signal, a luminance level detecting unit 11 for detecting a luminance signal level of the input video signal, and a video level adjusting unit 12 for adjusting the level of the video signal. The video level gain limiting means 13 for limiting the gain of the video signal, the video signal gamma correction means 14 for performing a predetermined gamma correction according to the gain set in the video level adjusting means 12, and the output of the video luminance level detecting means 11 Based on the gamma control means 15 for controlling the video signal gamma correction means 14 based on this, the liquid crystal drive circuit 16 for generating signal processing and drive pulses for driving the liquid crystal display, the liquid crystal display 17, and the output of the luminance level detection means 11. Backlight gamma correction means 18 for converting the signal so that a predetermined backlight luminance can be obtained, and the backlight A backlight quantity limiting means 19 to limit the amount to a predetermined range, the backlight driving circuit 20 for driving and lighting the backlight 21 according to the input signal, and a backlight 21.

  The backlight light quantity limiting means 19 and the backlight driving circuit 20 constitute a backlight control means for controlling the luminance of the backlight based on the output of the backlight gamma correction means 18.

  The luminance level detection means 11 detects the luminance signal level of the input video signal. For example, the detection of the luminance signal level detects the maximum value of the luminance signal.

  The video level adjusting unit 12 is controlled by the video level gain limiting unit 13 to adjust the level of the video signal.

  The video level gain limiting unit 13 controls the video level adjusting unit 12 by converting the output of the luminance level detecting unit 11 into a signal for controlling the video level adjusting unit 12. Here, the video level gain limiting unit 13 limits the gain of the video level adjusting unit 12 so that the video signal level is inversely proportional to the luminance level of the input video signal. This will be described with reference to FIG.

  FIG. 2 is a diagram showing the input / output characteristics of the video level gain limiting means 13. The input in FIG. 7 is the maximum value of the input signal, and the output is the gain of the video level adjusting means 12. Reference numeral 71 represents a characteristic. As shown in FIG. 2, the intermediate region is inversely proportional to the input, and is limited to a predetermined output Gmax when the input is small, and is limited to a predetermined output Gmin when the input is large. The reason for limiting the gain to Gmax is that if the gain is increased too much, the S / N of the video deteriorates and the image quality deteriorates, and even if the gain is increased to some extent, the effect of reducing the power consumption is reduced. Restrict. Further, the limitation to Gmin is that the luminance of the backlight does not increase to 100% or more, so the gain is limited accordingly. In this example, Gmax = 4.0 and Gmin = 1.0.

  Returning to the description of FIG. 1, the video signal gamma correction unit 14 is controlled by the gamma control unit 15, and predetermined gamma correction is performed according to the gain set in the video level adjustment unit 12.

  The gamma control unit 15 controls the video signal gamma correction unit 14 by converting the output of the video luminance level detection unit 11 into a signal for controlling the video signal gamma correction unit 14.

Here, the reason why the video signal gamma correction means 14 is necessary will be described.
In general, the gamma correction circuit is a circuit that obtains a characteristic such as numeral 42 in FIG. 6, for example. However, it is difficult to accurately realize this characteristic, and a normal approximate characteristic is used. In particular, when the input is in the vicinity of 0, the gain is in a very high state, which is difficult to realize, and even if it can be realized, there will be a lot of noise and it will be unusable. For this reason, a linear approximation or the like is performed to limit the gain. Considering the case where the level of the signal approximately corrected in this way is adjusted by the video level adjusting means 12, an error from the theoretical gamma characteristic increases due to the gain to be adjusted. In particular, this effect increases when the gain is increased. Therefore, the video signal gamma correction means 14 is necessary to reduce this error.

  Further, as an active usage, there is a case where the gain of the video level adjusting means 12 is increased. An example of increasing the gain is when the maximum value of the video is small, in other words, when the screen is dark. In this case, it is possible to actively increase the gamma correction to make the image easy to see.

  The liquid crystal driving circuit 16 generates signal processing and driving pulses for driving the liquid crystal display. Here, it is assumed that the liquid crystal drive circuit 16 includes a gamma correction circuit for adjusting the gamma of the liquid crystal to the gamma of the cathode ray tube as described in the drive circuit 106 in the conventional example of FIG.

  The backlight gamma correction unit 18 converts the luminance value detected by the luminance level detection unit 11 into a predetermined control voltage.

  FIG. 3 is a diagram showing input / output characteristics of the backlight gamma correction means 18. As indicated by reference numeral 81 in FIG. 3, the input / output characteristic of the backlight gamma correction means 18 is set to gamma 2.2. Here, if the gamma of the system is other than 2.2, the setting should be made accordingly.

  The backlight light quantity limiting means 19 provides limit values Cmax and Cmin as shown by numeral 82 in FIG. 3 in order to limit the light quantity of the backlight to a predetermined range. This is set according to the video level gain limiting means. In this example, Cmax = 100% and Cmin = 4.6% in accordance with Gmax = 4.0 and Gmin = 1.0.

  FIG. 4 is a diagram showing a result of simulating how the liquid crystal display device 1 reproduces the liquid crystal display when the subject brightness changes. FIG. 4 is confirmed under the same conditions as in FIG. As shown by reference numeral 101 in FIG. 4, the liquid crystal display luminance L is expressed by multiplying the liquid crystal display transmittance T and the backlight luminance b (L = T * b). The backlight luminance b in FIG. 4 is that the backlight luminance is limited (b∝C) by the backlight light amount limiting means 19 output C (= x ^ γ2) by gamma correction.

  In the case of B in FIG. 4, as is clear from comparison with B in FIG. 9, when the subject brightness is 0 to 20%, the backlight brightness can be lowered to 20% and the body brightness is 0 to 0%. When it is 3%, the backlight luminance can be lowered to 4.6%, and it can be seen that the effect of lower power consumption is more effective than the conventional one. The contrast of the subject is displayed correctly. Further, as can be seen from the case where the body brightness is 0 to 3%, the gain is limited to 4.0, and the gain does not increase excessively even when the subject brightness is dark. Therefore, S / N does not deteriorate.

  In the above description, the luminance level detecting means 11 has been described as detecting the maximum value of the luminance signal, but this allows the maximum value of the input signal to be correctly expressed. However, considering the dynamic range of display, it is not always necessary to express the maximum luminance, but it may be better to display the average value where the luminance signals are concentrated. In this case, better image quality can be obtained by using an average value for luminance level detection or using a value calculated from the average value and the maximum value.

  As described above, the liquid crystal display device 1 according to the present embodiment includes the luminance level detection unit 11 that detects the luminance level of the input video signal, the video level adjustment unit 12 that adjusts the level of the input video signal, and the input video signal. The video level gain limiting means 13 for limiting the gain of the video level adjusting means 12 so that the video signal level is inversely proportional to the luminance level of the video signal, and the output signal of the luminance level detecting means 11 so that a predetermined backlight luminance can be obtained. A backlight gamma correction means 18 for converting to a backlight, a backlight light quantity limiting means 19 for controlling the light quantity of the backlight based on the output of the backlight gamma correction means 18, and a backlight drive circuit 20. The control method detects the luminance level of the input video signal, and outputs the detected luminance level output signal to a predetermined backlight luminance. The brightness of the backlight is controlled based on the output of the previous normal correction, so that the backlight brightness can be reduced appropriately, and the power consumption can be reduced. Contrast can be expressed correctly. Furthermore, since the subject brightness is appropriate, it is possible to prevent image quality deterioration.

  Note that the liquid crystal display device and the backlight control method of the present invention are not limited to the above-described embodiments, and it goes without saying that various changes can be made without departing from the scope of the present invention. For example, the present invention can be applied to a television receiver as described above, but is not limited thereto, and can be applied to all liquid crystal display devices and backlight control methods. Furthermore, it may be an apparatus integrated with information equipment functions represented by a personal computer.

  In the above embodiments, the names of the liquid crystal display device and the backlight control method are used. However, this is for convenience of explanation, and may be a backlight control device, a portable viewing device, a display control method, or the like. Of course.

  In the above-described embodiment, an example in which a multi-lamp type backlight including a plurality of fluorescent lamps is used on the back of the display is common, but the same applies to a front light when a reflective liquid crystal display is used. Needless to say, it can be applied. Furthermore, it is suitable for application to self-luminous displays such as organic EL (electroluminescence) from the viewpoint of brightness adjustment and energy saving that are easy for the user to see.

  The liquid crystal display device and the backlight control method described above are also realized by a program for causing the liquid crystal display device and the backlight control method to function. This program is stored in a computer-readable recording medium. In the present invention, as the recording medium, the main memory itself may be a program medium, or a program reading device is provided as an external storage device and can be read by inserting the recording medium therein. May be. In either case, the stored program may be configured to be accessed and executed by the CPU, or in any case, the program is read and the read program is not shown in a program storage area. The program may be downloaded and executed by the program. It is assumed that this download program is stored in the main device in advance.

  Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a floppy disk or a hard disk, a CD-ROM / MO / MD / DVD, or the like. It may be a medium carrying a fixed program including a semiconductor memory such as a disk system of the above optical disk, a card system such as an IC card / optical card, or a mask ROM, EPROM, EEPROM, flash ROM or the like.

  Furthermore, although not shown in the figure, when a means capable of connection to an external communication network is provided, the program is fluidly supported so that the program is downloaded from the communication network via the communication connection means. It may be a medium. When the program is downloaded from the communication network in this way, the download program may be stored in the main device in advance, or may be installed from another recording medium. The content stored in the recording medium is not limited to a program, and may be data.

It is a block diagram which shows the structure of the liquid crystal display device of embodiment of this invention. It is a figure which shows the input-output characteristic of the image level gain limiting means of the liquid crystal display device of this Embodiment. It is a figure which shows the input-output characteristic of the backlight gamma correction means of the liquid crystal display device of this Embodiment. It is a figure which shows the result of having simulated how it reproduces to a liquid crystal display when the photographic subject brightness of the liquid crystal display device of this embodiment changes. It is a block diagram which shows the structure of the conventional liquid crystal display device. It is a figure which shows the gamma correction of a television system. It is a figure which shows the gamma characteristic of a liquid crystal display device. It is a block diagram which shows the structure of the drive circuit with the gamma correction circuit of the conventional liquid crystal display device. It is a figure which shows the result of having simulated how it reproduces on a liquid crystal display when the photographic subject brightness | luminance of the conventional display apparatus changes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 10 Input part 11 Brightness level detection means 12 Image | video level adjustment means 13 Image | video level gain limitation means 14 Image | video signal gamma correction means 15 Gamma control means 16 Liquid crystal drive circuit 17 Liquid crystal display 18 Backlight gamma correction means 19 Backlight light quantity Limiting means (backlight control means)
20 Backlight drive circuit (backlight control means)
21 Backlight

Claims (11)

A liquid crystal display device having a backlight,
A liquid crystal display device comprising: means for performing gamma correction on the luminance level of the backlight. A liquid crystal display device having a backlight,
Luminance level detection means for detecting the luminance level of the input video signal;
Backlight gamma correction means for converting the output signal of the brightness level detection means so as to obtain a predetermined backlight brightness;
And a backlight control means for controlling the luminance of the backlight based on the output of the backlight gamma correction means.   3. The liquid crystal display device according to claim 2, wherein the backlight gamma correction unit corrects the luminance level so as to be linear with respect to the backlight. Furthermore, video level adjusting means for adjusting the level of the input video signal,
3. The liquid crystal display device according to claim 2, further comprising video level gain limiting means for limiting the gain of the video level adjusting means so that the video signal level is inversely proportional to the luminance level of the input video signal.   The liquid crystal display device according to claim 2, wherein the backlight control unit includes a backlight light amount limiting unit that limits a light amount of the backlight.   3. The liquid crystal display device according to claim 2, wherein the brightness level detecting means detects a maximum value of the video signal.   3. The liquid crystal display device according to claim 2, wherein the luminance level detecting means detects an average value of the video signal.   8. The liquid crystal display device according to claim 2, wherein the luminance level detection unit calculates a luminance level from a maximum value and an average value of the video signal. A backlight control method for a liquid crystal display device including a backlight,
Detecting the luminance level of the input video signal;
Gamma correcting the detected luminance level output signal so as to obtain a predetermined backlight luminance;
And a step of controlling the luminance of the backlight based on the output of the gamma correction. A step of adjusting the level of the input video signal;
10. The backlight control method according to claim 9, further comprising a step of limiting the gain so that the video signal level is inversely proportional to the luminance level of the input video signal.   A backlight control method for a liquid crystal display device having a backlight, comprising: detecting a luminance level of an input video signal; and performing gamma correction on the detected luminance level output signal so as to obtain a predetermined backlight luminance. A computer-readable recording medium having recorded thereon a program for causing a computer to execute the step and the step of controlling the luminance of the backlight based on the output of the gamma correction.

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