JP2008152008A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively correct tincture of blue in a black level region, when the luminance level of an input signal is low. <P>SOLUTION: The liquid crystal display comprises a liquid crystal panel which displays an inputted video signal; a backlight which has a structure permitting the adjustment of a color temperature and irradiates the liquid crystal panel; a signal luminance level detection section which detects the information on the luminance of the inputted video signal and generates a luminance level signal; and a backlight signal generating section which controls the color temperature of the backlight so as to lower the same, when the luminance level signal obtained in the signal luminance level detecting section is lower than a prescribed set value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for adjusting the color temperature of a display device, and more particularly to a liquid crystal display device.

  As a conventional liquid crystal display device, a transmissive liquid crystal is widely used. The liquid crystal display device is not a self-luminous display device such as a cathode ray tube, but has a structure that displays using a backlight on the back of the liquid crystal display panel. This backlight includes a fluorescent tube and a light emitting diode. Is used.

  Currently, liquid crystal display devices are used in various applications, such as digital cameras, notebook PCs, and portable information terminals, taking advantage of their light weight and thin features. Since display characteristics such as luminance, color reproducibility, and viewing angle characteristics are further improved, liquid crystal display devices are often used in liquid crystal televisions in addition to the above-described applications. Thus, the liquid crystal display device can be expected to further develop as a display device in the future.

  However, as described in Japanese Patent Application Laid-Open No. 2000-75838, in a liquid crystal display device, the relationship between the liquid crystal driving voltage and the transmittance has wavelength dependency of light. That is, as shown in FIG. 9, the characteristics are different for each of the three primary colors red, green, and blue. For this reason, when the signal level of the input video is lowered, there is a problem that the black level region is bluish in the display image. It has been very difficult to improve this problem with a liquid crystal panel alone.

On the other hand, as the luminance signal level is lowered, the gain control circuit is controlled to attenuate the gain of the blue signal, thereby correcting the phenomenon in which the blue level region is bluish due to the decrease in the level of the input signal.
JP 2000-75838 A

  In the above-mentioned Japanese Patent Application Laid-Open No. 2000-75838, there is a problem that an increase in the circuit is unavoidable because it is necessary to provide a gain control circuit. Furthermore, when the gain control circuit is used when the input signal is dark, there is a problem that the gradation of the signal is lost.

  The present invention has been made in order to improve the above-described problems, and realizes a liquid crystal image display device that effectively corrects blueness in a black level region when the signal level of an input video signal is lowered. Objective.

  In order to solve the above-described problem, a liquid crystal display device of the present invention detects a luminance level information of a liquid crystal panel that displays an input video signal, a backlight that illuminates the liquid crystal panel, and a video signal. Luminance level detection means for generating a signal, and backlight control signal generation means for generating a backlight control signal for controlling the color temperature of the backlight based on the luminance level signal, the backlight comprising: The color temperature is adjusted based on the backlight control signal.

  According to the liquid crystal image display device of the present invention, when the luminance level of the input video signal is low, the color temperature is lowered by the backlight, and the phenomenon that the bluishness of the black level region in the liquid crystal display is corrected is corrected. As a result, it is possible to suppress a change in color tone caused by the luminance level of the input video signal without causing an increase in the number of circuits. As a result, the color temperature can be improved on the liquid crystal panel side, a good display performance can be obtained, and the display power of the display can be greatly enhanced.

Hereinafter, some examples relating to embodiments of the present invention will be described with reference to the drawings. In the drawings, elements that represent substantially the same configuration, operation, and effect are denoted by the same reference numerals. In addition, the numbers described below are all illustrated for specifically explaining the present invention, and the present invention is not limited to the illustrated numbers. Furthermore, the connection relationship between the constituent elements is illustrated for specifically explaining the present invention, and the connection relationship for realizing the function of the present invention is not limited to this.
(Embodiment 1)

  FIG. 1 is a block diagram showing a liquid crystal display device according to the first embodiment. In FIG. 1, a liquid crystal panel 1 displays an input video signal S0 by irradiating a backlight 2 disposed on the back surface as a light source. The backlight 2 has a configuration capable of adjusting its color temperature. The signal luminance level detection unit 3 detects the luminance level of the input video signal S0, and generates a luminance level signal S3 representing luminance level information of the video signal S0 such as an average luminance level, a maximum luminance level, and a minimum luminance level. Output to the control parameter calculation unit 4. The average luminance level represents an average value of luminance levels of the video signal S0. The maximum luminance level represents the maximum luminance level of the video signal S0. The minimum luminance level represents the minimum value of the luminance level of the video signal S0. The signal luminance level detector 3 is also called a luminance level detector.

  The control parameter calculation unit 4 generates a control parameter signal S4 representing the color temperature information of the backlight 2 using the luminance level signal S3. The control parameter calculation unit 4 is also called a control parameter signal generation unit. The backlight control unit 5 generates a backlight control signal S5 for controlling the color temperature of the backlight 2 based on the control parameter signal S4, and outputs the backlight control signal S5 to the backlight 2. The backlight 2 is adjusted in color temperature based on the backlight control signal S5. The control parameter calculation unit 4 and the backlight control unit 5 constitute a backlight control signal generation unit.

  As shown in the first embodiment configured as described above, the control parameter calculation unit 4 calculates the control data of the backlight 2 using the luminance level signal S3. At this time, if the luminance level signal S3 is smaller than a predetermined value, the backlight control signal S5 is generated so that the color temperature of the backlight 2 is lowered. As a result, the color temperature of the light emitted from the backlight 2 is lowered to reduce the blueness, and the blueness that occurs in the area indicating the vicinity of the black level in the liquid crystal screen (hereinafter referred to as the black level area) is corrected. This is realized by controlling the light 2.

  Hereinafter, the operation of the first embodiment will be described. The basic configuration of control is as follows. Based on the luminance level signal S3, when the luminance level is low, that is, in the low luminance level state, the color temperature of the backlight 2 is controlled to be low in order to correct the bluishness of the black level region generated in the liquid crystal display. The parameter signal S4 is set. When the luminance level is not low, that is, in the non-low luminance level state, the control parameter signal S4 of the backlight 2 sets a standard value that does not lower the color temperature, and uses this standard value as a normal control value.

  Here, the luminance levels of the video signal S0 and the screen of the liquid crystal panel 1 are divided into a low luminance level having a low luminance level and a non-low luminance level having a luminance level higher than the low luminance level. The black level represents the lowest level among the low luminance levels. The high luminance level represents a higher level than the non-low luminance level including a level near the middle of the white level and the black level. The low luminance level state is called a low luminance level state, and the non-low luminance level state is called a non-low luminance level state. A state near the black level including the black level is called a black level state. A state near the high luminance level including the high luminance level is referred to as a high luminance level state. In addition, an area indicating a low luminance level state in the screen is a low luminance level area, an area indicating a non-low luminance level state is a non-low luminance level area, an area indicating a black level state is a black level area, and a high luminance level state is indicated. The areas are called high luminance level areas.

  As described above, by correcting the color temperature of the backlight 2 by adaptive processing in accordance with the luminance level signal S3, the black level can be obtained without causing contrast deterioration in a low luminance level state that is unavoidable in video signal processing. The blueness of the area can be improved. When the color temperature is always corrected including the case where the non-low luminance level region is included in the screen, the screen becomes reddish in the non-low luminance level region, and the hue of the entire screen changes. By changing the color temperature only when the entire screen is in the low luminance level state, it is possible to effectively correct only the blueness of the black level region.

  The state of change in color temperature by the backlight 2 described above is shown in the chromaticity diagram of FIG. By changing the control parameter signal S4 of the backlight 2 by the luminance level signal S3, the color temperature moves from point A to point B in FIG. At point B, the blue component is weaker than at point A, and it can be seen that the blueness generated in the black level region in the liquid crystal screen can be corrected.

  In the control parameter calculation unit 4 of FIG. 1, a simple configuration that determines that the screen is dark based on the luminance level signal S3 is a configuration that determines the magnitude of the average luminance level of the luminance level signal S3. When the luminance level signal S3 representing the average luminance level is equal to or lower than a predetermined average luminance level threshold, it is determined that the screen is dark, and the control parameter signal S4 may be set so as to lower the color temperature of the backlight 2.

  When only the average luminance level is used, if the average luminance level is near the black level, it can be determined that the entire screen is also in the black level state. However, when the average luminance level is a low luminance level, a non-low luminance level region may be included in the screen. If the color temperature is lowered in this state, the color tone is changed even though the blue level area is not bluish on the liquid crystal screen, which causes a bad effect.

  Thus, it is necessary for adjusting the color temperature to more accurately determine that the black level region exists in the screen. In order to grasp the black level region more accurately, the minimum luminance level is used for determining the brightness in addition to the average luminance level.

  When the average luminance level is close to the minimum luminance level and both are low luminance levels, the black level region does not exist in the screen except for a special case where the entire screen is a black level. In this case, even if the color temperature of the backlight 2 is lowered, the effect of correcting the blueness of the black level region cannot be obtained. On the other hand, when the average luminance level is the low luminance level and the minimum luminance level is close to the black level, it can be determined that the black level region partially exists in the screen. In this case, the effect of correcting the blueness of the black level region can be sufficiently obtained.

  When the minimum luminance level is used in addition to the average luminance level, it can be determined that there is a black level region even when a region near the black level exists in a small area in the screen as compared with the case where only the average luminance level is used. Thereby, the brightness of the screen can be accurately determined as compared with the case where only the average luminance level is used. If the color temperature of the backlight 2 is lowered using this result, the blueness correction of the black level region of the screen can be effectively performed.

  As described above, when the average luminance level of the luminance level signal S3 is equal to or lower than the predetermined average luminance level threshold and the minimum luminance level is equal to or lower than the predetermined minimum luminance level threshold smaller than the average luminance level threshold, the luminance value is low. Therefore, it is clear that lowering the color temperature of the backlight 2 at this time is effective for improving the image quality of the screen.

Further, the minimum luminance level threshold is particularly effective around 1 candela / square meter. When the luminance level is smaller than the vicinity of this value, it is an area where bluishness is particularly likely to occur in the black level area. Therefore, when the value of the minimum luminance level is about 1 candela / square meter or less, it is possible to effectively correct the blue level of the black level region by increasing the ratio of decreasing the color temperature of the backlight 2. Is possible.
(Embodiment 2)

  In the second embodiment, a description will be given focusing on differences from the first embodiment. Since other configurations, operations, and effects are the same as those of the first embodiment, description thereof is omitted.

  When controlling the color temperature of the backlight 2, in the case of a screen as shown in FIG. FIG. 3 shows an image in which there is a white area with a small area, that is, a high-luminance level area having a high maximum luminance level, in addition to the fact that the entire screen is dark and the black level area is bluish. Yes.

  As the luminance information, both the average luminance level and the minimum luminance level are low values. In this case, the maximum luminance level is a high value. In this case, when a determination is made using the average luminance level and the minimum luminance level using the configuration shown in Embodiment 1, the color of the backlight 2 is low because the average luminance level and the minimum luminance level are low. Control is performed to correct the blueness of the black level region by lowering the temperature. However, when there is a high luminance level region in a part of the screen as shown in FIG. 3, if the color temperature of the backlight 2 is lowered to correct the blueness of the black level region, the color temperature of the high luminance level region is reduced. Will also go down. The influence of the decrease in the color temperature in the high luminance level region on the screen is large, and the change in the color tone of the two white regions in FIG. 3 becomes conspicuous.

  Therefore, the following configuration may be used for such a screen. In order to determine that the image includes a high luminance level area on the screen, in addition to the average luminance level and the minimum luminance level as luminance information, the maximum luminance level representing the maximum luminance level of the video signal S0 is also detected. Like that. In the first embodiment, the average luminance level and the minimum luminance level are used as the luminance information. If both of these values are low, it is determined that the luminance level of the screen is low, and the bluishness of the black level region on the liquid crystal screen is determined. In order to compensate, the color temperature of the backlight 2 was lowered. On the other hand, in Embodiment 2, in addition to the average luminance level and the minimum luminance level, the maximum luminance level is also detected as the luminance information.

  In addition to the case where the average luminance level is equal to or smaller than the average luminance level threshold and the minimum luminance level is equal to or smaller than the minimum luminance level threshold, the case where the maximum luminance level is equal to or larger than the predetermined maximum luminance level threshold larger than the average luminance level threshold. As described above, there is a low luminance level region, but it is determined that a high luminance level region also exists. In the control for correcting the blue level of the black level region on the liquid crystal screen at this time, the color temperature of the backlight 2 is lowered in the first embodiment. In the second embodiment, instead of lowering the color temperature of the backlight 2, the signal processing unit 7 controls the color temperature of the video signal S0 by the luminance level signal S3, and lowers the color temperature other than near the high luminance level region. To correct blueness in the black level area.

  By such video signal processing, the color temperature is lowered except in the high luminance level region, thereby increasing the luminance level. However, since the difference from the high luminance level region is large, that is, the high luminance level region is originally bright, even if the luminance level other than the high luminance level region increases, the influence on the screen is small. As a result, the blue level of the black level region can be corrected without causing a decrease in the color temperature of the high luminance level region. In this way, the black level area is bluish, but it is possible to realize the desired operation by detecting the maximum brightness level in addition to the average brightness level and the minimum brightness level for images including the high brightness level area. I understand.

  Next, the case where the maximum luminance level of one area of the screen is not as high as described above, that is, the case where the maximum luminance level is smaller than the maximum luminance level threshold, for example, a level near the middle between the white level and the black level will be described. In this case, even if the color temperature of the backlight 2 is lowered and the color temperature of the entire screen is lowered, the change of the color tone in the area where the maximum luminance level is smaller than the maximum luminance level threshold value is the maximum luminance level threshold value. There are few compared with the above case. Therefore, the blue level of the black level region is corrected by lowering the color temperature of the backlight 2, and the decrease of the color temperature of the high luminance level region is increased by increasing the color temperature of the high luminance level region by video signal processing. You can respond by raising

  As described above, when the color temperature is changed by the control of the backlight 2, the color temperature is lowered in a region other than the low luminance level region to be originally corrected by changing the color temperature. In particular, if there is a high luminance level area in the screen, the influence of that area becomes large. In order to avoid this, the high brightness level region is corrected to increase the color temperature by video signal processing. As a result, only the blue level correction of the black level area by lowering the color temperature of the backlight 2 appears as an effect, and the area of the screen that does not require the correction of the color temperature is not affected. That is, it is possible to perform only the blueness correction of the black level region in the low luminance level region without increasing the adverse effect that affects other than the low luminance level region, and to enhance the effect.

A configuration in which the color temperature is changed by the signal processing described above is shown in FIG. The signal processing unit 7 uses the luminance level signal S3 to generate the video processing signal S7 by lowering the overall color temperature of the video signal S0 or raising the color temperature of only the high luminance level region. The signal processing unit 7 is also called a video signal processing unit. The signal processing unit 7 in FIG. 4 performs processing to increase or decrease the blue component of the video signal by increasing the gain of the blue signal or adjusting the γ characteristic of the blue signal based on the luminance information. To change the color temperature of the video signal. In this way, when a signal including a high luminance level region is input, in addition to the color temperature control by the backlight control signal S5, the video signal processing is performed in the signal processing unit 7, thereby occurring in the liquid crystal screen. Correction is possible for blueness in the black level region.
(Embodiment 3)

  In the third embodiment, a description will be given focusing on differences from the first and second embodiments. Other configurations, operations, and effects are the same as those of the first and second embodiments, and thus description thereof is omitted.

  In Embodiment 3, the configuration of the backlight 2 capable of adjusting the color temperature will be described. As the configuration, first, in FIG. 5, the backlight 50 includes an R light source 52, a G light source 53, and a B light source 54. The color temperature is adjusted by changing the light emission ratio of R, G, and B according to the backlight control signal S51 from the backlight control unit 51. In order to lower the color temperature of the backlight 50, the B light emission ratio may be lowered or the R light emission ratio may be increased. The R light source 52, the G light source 53, and the B light source 54 are all configured by light emitting diodes.

  In FIG. 6, the backlight 60 includes a cold cathode tube 62 and a blue LED 63. In this configuration, the cold-cathode tube 62 and the blue LED 63 are normally used while being lit. On the other hand, when it is determined that the screen is dark by the luminance level signal S3 as described above and the color temperature of the backlight 60 is lowered to correct the blueness of the black level area of the screen, the luminance level of the blue LED 63 is lowered. Let In the cold cathode fluorescent lamp 62 and the blue LED 63 constituting the backlight 60, the luminance of the cold cathode fluorescent lamp 62 is the same as that in the normal state. Therefore, by reducing the luminance of the blue LED 63, the backlight 60 as a whole has a blue component. Weaken. Along with this, the blue component of the screen is also weakened to correct the blue level region blueness.

  FIG. 7 shows a configuration example of a backlight 70 including a cold cathode tube 72 and a red LED 73. In this configuration, normally, only the cold cathode tube 72 is lit. On the other hand, as described above, when the brightness level signal S3 determines that the screen is dark and the color temperature of the backlight 70 is lowered to correct blueness in the black level area of the screen, the red LED 73 is turned on. . In the cold cathode tube 72 and the red LED 73 constituting the backlight 70, the cold cathode tube 72 is lit in the same manner as in the normal state, so that the luminance is in the same state as in the normal state. Accordingly, since the red LED 73 is turned on to increase the red component in the backlight 70 as a whole, that is, the blue component is weakened, the blue component of the screen is weakened and the blue level of the black level region can be corrected.

  Moreover, you may comprise the backlight 2 from a cold cathode tube, blue LED, and red LED. In this configuration, normally, both the cold cathode fluorescent lamp and the blue LED are turned on, and the red LED is turned off. When the color temperature of the backlight 2 is lowered in order to correct the blueness of the black level area of the screen, the red LED may be turned on at the same time as the luminance of the blue LED is lowered.

As a simple configuration example, the backlight 2 is composed of two cold cathode tubes having a high color temperature and cold cathode tubes having a low color temperature, and emits light. The color temperature can be controlled by switching between these two cold cathode fluorescent lamps. When the luminance level signal S3 of the video signal S0 is not low, the cold cathode tube having a high color temperature is turned on. When it is determined from the luminance level information of the input signal that the luminance level is low, that is, the screen is dark, the cold cathode tube having a low color temperature is turned on to lower the color temperature of the backlight 2. In this manner, the blue color of the black level area displayed on the liquid crystal is corrected as the color temperature of the backlight 2 decreases.
(Embodiment 4)

  In the fourth embodiment, points different from the first to third embodiments will be mainly described. Other configurations, operations, and effects are the same as those of the first to third embodiments, and thus description thereof is omitted.

  When the cinema mode is set by a user setting or the like on a television or the like, the color tone is changed by the video signal processing, but this operation can also be realized by the control of the color temperature by the backlight 2 described so far. Therefore, the user information may be used in addition to the screen luminance information to determine the color temperature setting of the backlight 2. The user setting information is used to determine that an overall dark image is input to the video signal S0, and the color temperature of the backlight 2 is lowered. In contrast to the color tone adjustment by the video signal processing, the color tone adjustment can be realized only by controlling the color temperature of the backlight 2, which is an effective technique.

  FIG. 8 is a configuration example in which user information is used for color temperature control of the backlight 2. The user setting unit 6 generates a user setting signal S6 representing television mode information such as a cinema mode set by the user. The control parameter calculation unit 4 sets the color temperature of the backlight 2 using both the luminance level signal S3 and the user setting signal S6.

  As described above, in the first to fourth embodiments, when the luminance level of the input video signal is low, the color temperature is lowered by the backlight to correct the phenomenon that the blue level region is bluish in the liquid crystal display. As a result, it is possible to suppress a change in color tone caused by the luminance level of the input video signal without causing an increase in the number of circuits. As a result, the color temperature can be improved on the liquid crystal panel side, a good display performance can be obtained, and the display power of the display can be greatly enhanced.

  The above description of the embodiments is merely an example embodying the present invention. The present invention is not limited to these examples, and can be easily configured by those skilled in the art using the technology of the present invention. It can be expanded to various examples.

  The present invention can be used for an image display device.

1 is a block diagram showing a liquid crystal display device according to Embodiment 1 of the present invention. Explanatory drawing of the color temperature control by Embodiment 1 of this invention. Explanatory drawing of the video screen by Embodiment 2 of this invention. The block diagram which shows the liquid crystal display device by Embodiment 2 of this invention. Explanatory drawing which shows the structure of the backlight by Embodiment 3 of this invention. Explanatory drawing which shows the structure of the backlight by Embodiment 3 of this invention. Explanatory drawing which shows the structure of the backlight by Embodiment 3 of this invention. The block diagram which shows the liquid crystal display device by Embodiment 4 of this invention. The block diagram which shows the drive voltage and transmittance | permeability of the liquid crystal by a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal panel 2 Backlight 3 Signal luminance level detection part 4 Control parameter calculating part 5 Backlight control part 6 User setting part 7 Signal processing part 50 Backlight 51 Backlight control part 52 R light source 53 G light source 54 B light source 60 Backlight 61 Backlight control unit 62 Cold cathode tube 63 Blue LED
70 Backlight 71 Backlight Control Unit 72 Cold Cathode Tube 73 Red LED

Claims (9)

A liquid crystal panel that displays the input video signal;
A backlight for illuminating the liquid crystal panel;
Luminance level detection means for detecting luminance level information of the video signal and generating a luminance level signal;
A backlight control signal generating means for generating a backlight control signal for controlling the color temperature of the backlight based on a luminance level signal;
The liquid crystal display device according to claim 1, wherein a color temperature of the backlight is adjusted based on a backlight control signal. The backlight control signal generating means is
Control parameter signal generating means for generating a control parameter signal representing color temperature information of the backlight based on a luminance level signal;
The liquid crystal display device according to claim 1, further comprising a backlight control unit that generates a backlight control signal for controlling a color temperature of the backlight based on a control parameter signal.   2. The liquid crystal according to claim 1, wherein the luminance level detecting means detects an average luminance level representing an average value of luminance levels of the video signal and a minimum luminance level representing a minimum value of the luminance level of the video signal. Display device.   The backlight control signal generation means is configured to detect the color temperature of the backlight when the average luminance level of the luminance level signal is equal to or lower than a first predetermined value and the minimum luminance level is equal to or lower than a second predetermined value smaller than the first predetermined value. The liquid crystal display device according to claim 3, wherein the liquid crystal display device is controlled to be low.   5. The liquid crystal display device according to claim 4, wherein the second predetermined value is approximately 1 candela / square meter. Furthermore, based on the luminance level signal, it has video signal processing means for controlling the color temperature of the video signal and generating a video processing signal,
The liquid crystal panel displays a video processing signal,
The luminance level detecting means detects an average luminance level, a minimum luminance level, and a maximum luminance level representing a maximum value of the luminance level of the video signal,
The video signal processing means has an average luminance level of the luminance level signal equal to or lower than a first predetermined value, a minimum luminance level equal to or lower than a second predetermined value, and a maximum luminance level equal to or higher than a third predetermined value greater than the first predetermined value. Control the color temperature of the video signal,
The backlight control signal generating means is configured to output the backlight when the average luminance level of the luminance level signal is less than or equal to a first predetermined value, the minimum luminance level is less than or equal to a second predetermined value, and the maximum luminance level is less than a third predetermined value. 2. The liquid crystal display device according to claim 1, wherein the color temperature of the light is controlled. The backlight is
In general, a light emitting diode that emits red light,
In general, a light-emitting diode that emits green light,
The liquid crystal display device according to claim 1, further comprising: a light emitting diode that emits blue light. The backlight is
In general, at least one of a light emitting diode that emits red or a light emitting diode that emits blue substantially,
The liquid crystal display device according to claim 1, further comprising a cold cathode tube.   The liquid crystal display device according to claim 1, wherein the backlight includes two cold cathode tubes having different color temperatures.

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