JP2011075765A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which displays an image improved in image quality performance for a viewer who views a dark image in dark environment. <P>SOLUTION: The liquid crystal display device includes a liquid crystal panel which performs color display by controlling transmittance of a plurality of arrayed pixels, and a light source unit which emits light toward the liquid crystal panel. The liquid crystal display device includes: a brightness detection means for detecting environmental illuminance in environment where the liquid crystal panel is arranged; a luminance level obtaining means for obtaining the luminance level of an image of a display object from the input image signal; a determination means for determining whether the environmental illuminance is equal to or under a predetermined illuminance reference value and a luminance level is equal to or under a predetermined luminance reference value; and an image signal conversion means for converting the image signal to a control signal for the liquid crystal panel. When the environmental illuminance is equal to or under the illuminance reference value and the luminance level is equal to or under the luminance reference value, the image signal conversion means converts the image signal into the control signal by compensating saturation of the image of the display object. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

  Liquid crystal display devices have the advantage of being thinner and lighter than CRT (Cathode Ray Tube, commonly referred to as a cathode ray tube), which was the mainstream of display devices in the 20th century, as well as the development of viewing angle expansion technology and video technology. With the advancement of image quality improvement technology, the applications and markets have been expanded to monitors for desktop personal computers, monitors for printing and design, and home televisions.

  In these applications, there is a strong demand for good color reproducibility and a high contrast ratio. The contrast ratio in the liquid crystal display device is such that the luminance in black display is not zero but has a finite value (hereinafter referred to as black luminance), and therefore the luminance in white display determined by the effective transmittance of the liquid crystal panel (hereinafter referred to as white luminance). Defined by the black luminance.

  Patent Document 1 discloses a display device capable of realizing appropriate screen display luminance in accordance with the feature amount of video and ambient brightness, and sufficiently reducing power consumption.

JP 2007-241236 A

  Here, unlike the office environment, a liquid crystal display device for color display such as a home TV often has a chance to view a dark image such as a movie in a relatively dark room. Improvement is required.

  However, human visual perception characteristics are different in bright and dark environments. Under the so-called mesopic condition, Purkinje shift occurs and the maximum wavelength of visibility is 555 nm (maximum visibility in photopic vision). Wavelength) to 507 nm (the maximum wavelength of visibility in dark vision). For this reason, since the color tone that is felt in photopic vision is different in mesopic vision, the way the image is felt differs greatly in the case of faint vision and in photopic vision.

  The Purkinje shift occurs, for example, when a dark image including many pixels that emit light with black luminance or many pixels that emit light with the same luminance as black luminance is viewed in a dark room. In this case, the viewer feels that the image quality performance has deteriorated. Specifically, a viewer who views a dark image in a dark environment will feel that the image is bluish.

  An object of the present invention is to provide a liquid crystal display device that displays an image with improved image quality performance for a viewer who views a dark image in a dark environment. In addition, other problems other than the above-described problems will be clarified from the entire description of the present specification or the drawings.

  In view of the above problems, the present invention is a liquid crystal display device having a liquid crystal panel that performs color display by controlling the transmittance of a plurality of arranged pixels, and a light source unit that emits light toward the liquid crystal panel. Brightness detecting means for detecting environmental illuminance in an environment in which the liquid crystal panel is disposed, luminance level acquiring means for acquiring the luminance level of an image to be displayed from the input image signal, and Determining means for determining whether or not the luminance level is equal to or lower than a predetermined luminance reference value and the luminance level is equal to or lower than a predetermined luminance reference value; and an image for converting the image signal into a control signal for the liquid crystal panel Signal converting means, wherein the image signal converting means has the display pair when the environmental illuminance is less than or equal to the illuminance reference value and the luminance level is less than or equal to the luminance reference value. To compensate the saturation of the image converted into the control signal, characterized in that.

  In the liquid crystal display device according to the aspect of the invention, the liquid crystal panel may perform color display by emitting red, green, and blue light, and the image signal conversion unit may be configured such that the environmental illuminance is less than or equal to the illuminance reference value. When the luminance level is equal to or lower than the luminance reference value, the transmittance of a pixel emitting blue light is reduced, or the transmittance of a pixel emitting red light or a pixel emitting green light is improved. Thus, the saturation of the image to be displayed may be compensated. Note that the transmissive liquid crystal panel is responsible for adjusting the transmitted light intensity of the light from the backlight disposed on the back surface, and strictly speaking, the pixels of the liquid crystal panel are not emitting light, Since the display image for the observer is light emitted from the liquid crystal panel, no particular distinction is made in terms of expression.

  In one aspect of the liquid crystal display device according to the present invention, when at least the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value, the light source unit is The brightness of the light emitted toward the liquid crystal panel may be reduced as at least one of the illuminance and the brightness level decreases.

  In one aspect of the liquid crystal display device according to the present invention, when at least the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value, the light source unit is As at least one of illuminance and the luminance level decreases, the luminance of light emitted toward the liquid crystal panel is reduced, and the image signal conversion means is configured to reduce the luminance of light emitted from the light source unit toward the liquid crystal panel. It is possible to compensate while improving the upper limit of the transmittance of the plurality of pixels controlled to display the image to be displayed as the image is reduced.

In one aspect of the liquid crystal display device according to the present invention, the illuminance reference value is a value detected by the brightness detection means in an environment where the vertical illumination with which the liquid crystal display device is illuminated is 50 lux. When the luminance level is the maximum luminance value in the display target image, the luminance reference value is 50 nits, and when the luminance level is the average luminance value in the display target image. The luminance reference value may be 20 nits. The definition of knit (nt) is the luminance in the direction when the luminous intensity of a flat light source of 1 square meter is 1 cd in the direction perpendicular to the plane, and 1 nt = 1 cd / m ² .

  In one aspect of the liquid crystal display device according to the present invention, when the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value, black displayed by the liquid crystal panel is displayed. The chromaticity of the display is characterized in that, in the LAB color system using the spectral luminous efficiency of scotopic vision, the saturation Δab does not exceed 3.4 and the coordinate axes a and b are values of 0 or less. Also good.

  In the liquid crystal display device according to one embodiment of the present invention, the liquid crystal panel may include a layer including a dye that absorbs light having a wavelength of 480 nm to 520 nm.

  In one mode of the liquid crystal display device according to the present invention, the light source unit emits light to the liquid crystal panel when the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value. Spectral characteristics are 480 nm to 520 nm than spectral characteristics in light emission to the liquid crystal panel of the light source unit when the ambient illuminance is larger than the illuminance reference value or the luminance level is larger than the luminance reference value. The ratio of the light of the wavelength may be low.

  In one aspect of the liquid crystal display device according to the present invention, the image signal conversion means includes compensation control information for converting the image signal into the control signal, and the ambient illuminance is less than or equal to the illuminance reference value. And when the said brightness | luminance level becomes below the said brightness | luminance reference value, it is good also as converting the said image signal according to the said compensation control information.

  In one aspect of the liquid crystal display device according to the present invention, the compensation control information is a table and a relational expression generated based on a spectral luminous efficiency lower than a spectral luminous efficiency of photopic vision, The image signal may be converted into the control signal according to the table and the relational expression.

  An object of the present invention is to provide a liquid crystal display device that displays an image with improved image quality performance for a viewer who views a dark image in a dark environment.

It is a block diagram showing the functional structure and hardware constitutions of the liquid crystal display device which concern on one Embodiment of this invention. It is a figure explaining the color matching function for expressing the psychophysical quantity of a color. It is a figure which shows the chromaticity coordinate of the LAB color system based on the spectral luminous efficiency of dark place vision. 1 is a schematic cross-sectional view illustrating a liquid crystal display device according to an embodiment of the present invention. It is a schematic cross section of the vicinity of one pixel (dot) of the liquid crystal display device according to an embodiment of the present invention. It is a schematic cross section near an active element of a liquid crystal display device according to an embodiment of the present invention. It is a schematic diagram of the vicinity of one picture element of the color filter substrate of the liquid crystal display device according to the embodiment of the present invention. 1 is an enlarged plan view of one pixel of a liquid crystal display device according to an embodiment of the present invention. It is a schematic cross section of the vicinity of one picture element of the liquid crystal display device according to the embodiment of the present invention. It is CIE1976u'v 'chromaticity coordinate diagram, and is a diagram showing a first black example. It is a figure which shows the quality determination of the 1st black coloring described in FIG. 10 by the test subject under the mesopic condition. It is a figure which shows the quality determination of the color of the black display compensated with the look-up table for dark places by the test subject under twilight condition. It is a figure which shows a mode that each black display of FIG. 12 was plotted on the other chromaticity coordinate using the spectral luminous efficiency of photopic vision.

  Next, an embodiment of a liquid crystal display device according to the present invention will be described with reference to FIGS. However, the present invention can be realized in various forms, and is not limited to the embodiments described herein, and various changes and modifications can be made by those skilled in the art within the scope of the technical idea.

  FIG. 1 is a block diagram showing a functional configuration and a hardware configuration of a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device according to the present embodiment includes a liquid crystal panel 120 and a light source unit 110 (backlight), and further, a brightness sensor 101 (brightness detection means) that detects the brightness of the surrounding environment (hereinafter, environmental illuminance). And a determination unit 102 that receives the ambient illuminance and the image signal and determines whether or not these satisfy a predetermined condition, and converts the image signal based on the determination result of the determination unit 102 to the liquid crystal panel 120. Image signal converting means 103 for outputting a control signal.

  The determination unit 102 includes a luminance level acquisition unit 105. First, the luminance level acquisition unit 105 acquires the luminance level of an image to be displayed on the liquid crystal panel 120 from the input image signal. Then, the determination unit 102 determines whether or not these are below the respective reference values according to the acquired luminance level and the environmental illuminance detected by the brightness sensor 101. When the luminance level is equal to or lower than a predetermined reference value (hereinafter referred to as luminance reference value) and the environmental illuminance is equal to or lower than a predetermined reference value (hereinafter referred to as illuminance reference value), the image signal conversion means 103 is used by the viewer. The input image signal is converted into a control signal so as to compensate for the effect of Purkinje shift occurring in step S2. The determination unit 102 and the image signal conversion unit 103 are mounted, for example, in a peripheral circuit of the liquid crystal display device.

  The image signal conversion means 103 in the present embodiment includes a scotopic LUT 106 (a scotopic vision lookup table) applied when the luminance level is equal to or lower than the luminance reference value and the environmental illuminance is equal to or lower than the illuminance reference value. A photopic LUT 107 (photopic look-up table) to be applied to cases other than the above is held. In particular, the scotopic LUT 106 is held as compensation control information in a storage unit such as a RAM or a ROM included in the image signal conversion unit 103. The compensation control information is information for compensating the input image signal and converting it into a control signal for the liquid crystal panel, and the image signal becomes a control signal for controlling the transmittance of the liquid crystal panel 120 according to the compensation control information. The saturation of the displayed image is compensated by the conversion. The compensation control information is generated based on the spectral luminous efficiency in dark place vision, as will be described later. In the following description, the case where the luminance level is equal to or lower than the luminance reference value and the environmental illuminance is equal to or lower than the illuminance reference value will be described as a condition that causes the viewer to have low vision. However, since whether or not it becomes dimmed depends on the individual differences of the viewers and the retinal illuminance, the dimmed vision does not necessarily occur in the viewer in the above case. It is also assumed that dizziness occurs.

  Here, the luminance level indicates a feature amount related to the magnitude of luminance in an image to be displayed, and may be the maximum gradation value of one frame image, or in one frame image. It may be an average value of gradation. In this embodiment, the maximum luminance value obtained by converting the maximum gradation value of one frame image into luminance is adopted as the luminance level, but the average gradation value in the one frame image is converted into luminance. The average luminance value may be adopted, both the maximum luminance value and the average luminance value may be adopted, or a feature amount combining these may be adopted. In these cases, when the maximum luminance value and the average luminance value are derived from the image signal, the default luminance that the light source unit 110 emits is assumed.

  In the light source unit 110 according to the present embodiment, the luminance of light emitted toward the liquid crystal panel 120 is controlled in accordance with the luminance level under the condition of low vision. Specifically, when at least the environmental illuminance and the luminance level are equal to or less than the reference value, the light source unit 110 receives information on the luminance level via the determination unit 102, and the light source unit decreases as the luminance level decreases. The luminance emitted by 110 is reduced. By reducing the brightness of the light source unit 110 as it approaches dark place vision, the black brightness in black display or the display brightness close to black display is reduced, and a dark image is expressed well. It should be noted that a dark image is satisfactorily expressed even when the luminance of the light source unit 110 is reduced as the ambient illuminance decreases under the condition of dimming.

  In particular, in the case of dimmed vision, blue is more easily recognized as the dark vision is approached. A dark image whose luminance level is equal to or lower than the luminance reference value includes many pixels that display black or display close to black. In order to compensate for the saturation when faint vision occurs, it is conceivable to reduce the transmittance of pixels emitting blue light and to improve the transmittance of pixels emitting red and green light. However, in the dark image in which the transmittance of the image to be displayed is generally low, the latter is often used to compensate for the saturation, and the brightness is easily improved. Therefore, when the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value, the luminance of the light source unit 110 is reduced as the luminance level (or environmental illuminance) further decreases. In order to compensate for the degree, it is possible to prevent the brightness from being improved, and a dark image is expressed well. Note that the luminance of the light source unit 110 may be reduced linearly, nonlinearly, or stepwise as the luminance level (or environmental illuminance) decreases, or both the environmental illuminance and the luminance level are functions. As an alternative, the luminance of the light source unit may be reduced.

  Further, when the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value, the image signal conversion unit 103 displays the image to be displayed as the luminance of the light source unit 110 is decreased. The upper limit of the transmittance of the pixels of the liquid crystal panel 120 is improved. That is, the image signal conversion means 103 compensates while improving the upper limit of the transmittance of the pixels of the liquid crystal panel controlled to display the display target image as the luminance level (or environmental illuminance) decreases. . As a result, a clear image is displayed by effectively utilizing the liquid crystal driving range under thin vision conditions.

  In the present embodiment, when the viewer is in the condition of thin vision, the image signal is converted into a control signal according to the scotopic LUT 106 and output to the liquid crystal panel 120. The scotopic vision LUT 106 is a look-up table for conversion to image display based on the spectral luminous efficiency of scotopic vision. In addition, when the photopic vision condition is satisfied for the viewer (a condition that does not result in faint vision, that is, when the luminance level is greater than the luminance reference value or the environmental illuminance is greater than the illuminance reference value), The image signal is converted in accordance with the observation LUT 107 and output to the liquid crystal panel 120. The photopic vision LUT 107 is a look-up table for conversion to image display based on the spectral luminous efficiency of photopic vision. When the image signal corresponds to a signal for controlling the transmittance of the liquid crystal panel 120 under the photopic condition, the photopic LUT 107 is not particularly required.

、

、

（図２に示す）を用いて求められる三刺激値Ｘ、Ｙ、Ｚで、下記数式（１）〜（５）のように定義される。

In general, chromaticity coordinates (CIE 1931xy, CIE 1976 u′v ′, and LAB color system are all defined by XYZ values) are obtained using spectral photosensitivity efficiency of photopic vision. In contrast, the scotopic vision LUT 106 uses chromaticity coordinates converted using the spectral luminous efficiency of scotopic vision. First, specifically, the chromaticity coordinates (x, y) of the CIE color system are the color matching functions.

,

,

The tristimulus values X, Y, and Z obtained using (shown in FIG. 2) are defined as the following mathematical formulas (1) to (5).

は一絵素（画像としての最小単位で、三原色であれば赤、緑、青の３ドットで構成される）の分光放射輝度である。図２に示す等色関数

は、明所視の分光視感効率と等しく、Ｙは一絵素の輝度に相当する。 Here, k is a coefficient used for convenience,

Is the spectral radiance of one picture element (which is the smallest unit of an image and is composed of three dots of red, green, and blue for the three primary colors). Color matching function shown in FIG.

Is equal to the spectral luminous efficiency of photopic vision, and Y corresponds to the luminance of one picture element.

（図２に示す）を用いて、数式(２)、(４)、(５)は数式(６)〜(８)に置き換えられる。数式（６）〜（８）では、それぞれ、暗所視（Scotopic vision）の分光視感効率を用いて値が導出されることから、添え字Sをつける。

Here, in the case of scotopic vision, the spectral luminous efficiency of scotopic vision

(Shown in FIG. 2), equations (2), (4), (5) are replaced by equations (6)-(8). In Equations (6) to (8), since a value is derived using the spectral luminous efficiency of scotopic vision, the subscript S is added.

  It is known that human visual perception changes from photopic vision, twilight vision, and scotopic vision as the surroundings become darker. These are defined under various conditions such as photometric conditions, ambient illuminance, or retinal illuminance, and do not switch at a certain threshold. For example, when the light entering the retina is 100 nits or more, for example, Is completely photopic. For example, under a starry sky with no moon (environmental illuminance of 0.01 lux or less), when only light and dark are perceived and colors are hardly recognized, it can be said that the vision is almost completely dark. Therefore, the condition during this period can be considered to be dimmed. Under dimmed conditions, the visibility (spectral luminous efficiency) gradually increases from a state close to photopic vision to a state close to scotopic vision. It is thought to shift from photopic to scotopic (purkinje shift). In the present embodiment, the scotopic LUT 106 derived using the spectral luminous efficiency of scotopic vision under the condition of dimming is used. Here, using multiple tables and relational expressions derived using spectral luminous efficiency that gradually approaches the spectral luminous efficiency of scotopic vision as it approaches scotopic vision from mesopic vision, The saturation of the image may be compensated. In any case, the saturation may be compensated by a table or a relational expression generated based on the spectral luminous efficiency lower than the photopic spectral luminous efficiency. Then, saturation is compensated by using a table and a relational expression generated based on the spectral luminous efficiency of scotopic vision in which the peak is lower than the spectral luminous efficiency of photopic vision, Compensation accuracy can be improved while reducing the circuit scale.

  In black display, the gradation of 3 dots of RGB is usually zero (strictly speaking, 16 gradations may be substantially black in the input signal of the television, so the minimum luminance under normal viewing conditions is black. Display). In the case of a transmissive liquid crystal display device, as described above, the luminance does not become zero but has black luminance even when all the dots become zero gradation. The black luminance in the black display in which all the gradations of the dots are zero, or the substantial black display as described above has a finite luminance (Y), and therefore, chromaticity coordinates are given. In the present specification, the condition for photopic vision (in this embodiment, the condition for non-trivial vision, i.e., when the luminance level is greater than the luminance reference value or the ambient illuminance is greater than the illuminance reference value). The black display will be described below as the first black.

Further, in the present embodiment, under the condition of faint vision (in this embodiment, the luminance level is equal to or lower than the luminance reference value and the environmental illuminance is equal to or lower than the illuminance reference value), the luminance level decreases in two stages. The luminance emitted from the light source unit 110 is reduced. Therefore, under the condition of low visibility, the black display when the luminance level is high in the two stages may be the second black, and the black display when the luminance level is low may be the third black. In this case, the luminance of the light source unit 110 decreases and the black luminance decreases in the order of first black, second black, and third black. Note that when multi-color LEDs are used for the light source unit 110, not only the luminance but also the saturation can be adjusted. Therefore, the compensation of the saturation by the image signal conversion unit 103 and the control of the chromaticity of the light source unit 110 are combined. Second black and third black may be set. In the present embodiment, in the case of displaying the second or third black, a condition for faint viewing (for example, a pixel that emits green light of an image of one frame with an environmental illuminance of 50 lux or less) Therefore, unlike the case of displaying the first black, a look-up table based on the chromaticity coordinates for dark place vision is applied. The blackness at this time is such that Δa _s b _s defined by the equation (11) is 3.4 or less in the value indicated by the LAB color system defined by the following equations (9) and (10). And both a and b are set to 0 or a negative value.

  The inventors conducted a subjective evaluation on 24 people (age composition was 20 to 60 years old, 18 men, 6 women). As a result, the surroundings are dark (for example, the ambient illuminance is 50 lux or less), the maximum luminance value of one frame image signal (one same screen) is 50 nits or less, or the average luminance value of one frame image signal is 20 nits or less. Under such conditions, even when looking at the same screen in photopic vision, the results clearly showed that the colors looked different, or that the colors were somehow different. In addition, if the maximum luminance value of an image signal (one same screen) of one frame is less than 10 nits under the condition that it is almost a dark room (equivalent to a movie theater), all of them will “look clearly different in color”. I answered.

  According to the subjective evaluations conducted by the inventors, Purkinje shift occurs under vertical illumination of about 50 lux or lighting conditions that allow some reading, and the spectral efficiency of scotopic vision is more visible than photopic vision. Become dominant. In other words, the result that it can be judged that the color looks different is obtained. Therefore, in the present embodiment, the brightness sensor 101 that detects brightness is provided, and when the environmental illumination received from the brightness sensor 101 is determined by the determination unit 102 to be 50 lux or less, the determination unit 102 Determination of the luminance level in the image signal is started. The brightness sensor 101 according to the present embodiment is a sensor arranged on the upper frame of the liquid crystal display device for detecting vertical illumination in order to ensure the accuracy of determination. When the sensor is arranged at the lower part of the display screen, the illuminance reference value needs to be 10 lux or less, and this value is 50 lux when the brightness sensor 101 is arranged in the upper frame. It corresponds to the value detected in the environment.

  The luminance level acquisition unit 105 performs the histogram analysis on the maximum luminance value and the average luminance value in one frame in the image signal. Whether it is photopic or scotopic depends on human visual perception depending on the total amount of light received by the retina and the total luminance in the field of view. Therefore, for example, when the average luminance value is 30 nits or less and the maximum luminance value is 50 nits or less, the luminance reference value may be provided so as to compensate the saturation with reference to the scotopic LUT 106. Note that the luminance level acquisition unit 105 according to the present embodiment acquires the maximum luminance value in one frame in the image signal, but may acquire an average value of the maximum luminance values in a plurality of frames. Further, the image signal conversion unit 103 may compensate for the saturation of the image of the frame to be displayed next after the image of the frame to be displayed for which the luminance level has been acquired.

  The determination by the determination means 102 may be a parallel condition of the respective upper limit values as described above. For example, for determination of the illuminance reference value, I: 50 lux or less, 20 lux or more, II: less than 20 lux, 10 lux or more, III: Multiple ranges may be provided such as less than 10 lux. For the I determination, the average luminance value is 15 nits or less, the maximum luminance value is 35 nits or less, for the II determination, the average luminance value is 20 nits or less, the maximum luminance value is 50 nits or less, for the III determination, the average luminance value is 30 nits or less, and the maximum luminance value is 70 nits or less. A luminance reference value obtained by combining feature quantities of two luminance values may be provided as different conditions for each range. This is a determination based on the total amount of light in the field of view, assuming that both the ambient illuminance and the image to be displayed enter the field of view. When the ambient illuminance is low, it is easy to become dimmed, so the luminance reference value based on the average luminance value and the maximum luminance value is increased.

Next, when 16 subjects were shown various black displays and judged to be good black (less colored and felt good black) in a dark room, Δa _s b _s <3.4, In addition, when both a and b have a chromaticity satisfying 0 or a negative value, 80% answered that the black was good. FIG. 3 is a diagram showing the chromaticity coordinates of the LAB color system based on the spectral luminous efficiency in dark place vision. A shaded area in FIG. 3 shows a range where Δa _s b _s <3.4 and both a and b satisfy 0 or a negative value. Whether the black display in the dark room is within the shaded area in FIG. 3 is determined by arranging the liquid crystal display device according to the present embodiment in, for example, a complete dark room to display all pixels in black. Judgment is made according to equations (1), (3), (6), (9), and (10) using measured values and spectral radiance values measured with a spectral radiance meter arranged toward the display device. Is done.

In the LAB color system, the color is expressed using four psychological primary colors, and the a-axis indicates red (positive), green (negative), the b-axis indicates yellow (positive), and blue (negative). Zero origin indicates an achromatic color. Δa _s b _s is an index indicating the saturation of the color, and it can be said that the greater the value, the more vivid the color. The third quadrant in which Δa _s b _s <3.4 and both a and b are negative values indicates a range from blue to cyan to green in terms of color names.

  The ambient environment when watching TV at home can be broadly divided into two types when the ambient illuminance is bright, such as a brightly lit room during the day or at night, and when the ambient illuminance is dark in a darkly lit room at night. In addition, as content to be viewed, news, information programs, variety, etc., when the average gradation value of the input image signal is bright (around 40% when the maximum luminance is 255), There are various cases where a dark screen such as a horror movie, a fantasy movie, an SF movie, or the like with an average gradation value of 15% or less continues.

  In the liquid crystal display device according to the present embodiment, at least two types of black display, which are the most important, are provided as the first black in order to always provide good image quality under viewing conditions with different environments and contents. The black under the photopic environment, and the black under the environment that becomes faintly visible as the second black.

  Note that, as in the above-described embodiment, in a dimmed environment, the luminance of the light source unit 110 is decreased in two stages as the luminance level decreases so that the second black and the third black are obtained. Assuming that the program is viewed in a TV station program production room or a nearly complete dark room (environmental illuminance of 1 lux or less), the light source unit 110 can be used as the ambient illuminance decreases in a dimmed environment. The brightness may be reduced, and the second black and darker-looking black than the second black may be prepared as the third black.

The scotopic LUT 106 for controlling the display for mesopic vision in this embodiment is determined according to the LAB color system, not the commonly used CIE1931xy chromaticity coordinates and CIE1976 u′v ′ chromaticity coordinates. This is because neither the xy chromaticity nor the u′v ′ chromaticity coordinate has a measure for the brightness of the image. When considering human visual perception, a scale of brightness (luminance) is required. For example, if there is a liquid crystal display device in which one is 0.3 nits and the other is 0.6 nits, even if black display is the same u′v ′ chromaticity coordinate, almost all viewers will see the former black display. Like. Also, if one is 0.3 nits and a very reddish black, and the other is 0.6 nits and a black that is almost achromatic, a considerable audience prefers the latter black display. On the other hand, the black display controlled by Δa _s b _s in the LAB color system is greatly related to the value of Y representing brightness as shown in equations (9) and (10). For this reason, even if u′v ′ chromaticity coordinates are equal, Δa _s b _s is different if the brightness is different, which is effective as a scale for setting the second black.

  Brightness sensor 101 and determination means 102 for determining the dimming condition described above, luminance level acquisition means 105 for acquiring the luminance level of the image to be displayed, dark vision for displaying the second black The liquid crystal display device 1 and the liquid crystal display device 2 having the look-up table (dark vision LUT 106) and the image signal conversion means 103 will be specifically described below.

[Liquid crystal display device 1]
FIG. 4 is a schematic cross-sectional view illustrating the liquid crystal display device 1 according to this embodiment. The liquid crystal display device 1 according to the present embodiment includes a liquid crystal cell 15, an upper polarizing plate (analyzer) 11 and a lower polarizing plate (polarizer) 12 formed on the outside of the liquid crystal cell 15, an optical sheet 17, and a light source. The unit 110 is configured to be included. The light source unit 110 supplies light to the liquid crystal panel 120 including the analyzer 11 and the polarizer 12 outside the liquid crystal cell 15 via the optical sheet 17. FIG. 5 is a schematic cross-sectional view of the vicinity of one pixel (dot) of the liquid crystal display device 1 according to the present embodiment. FIG. 6 is a schematic diagram showing a configuration near one pixel of the active matrix substrate of the liquid crystal display device 1 according to the present embodiment, and FIG. 7 is a picture of the color filter substrate of the liquid crystal display device 1 according to the present embodiment. FIG. 4 is a schematic view of the vicinity of a prime element (in this embodiment, one pixel composed of three dots of R, G, and B pixels).

  The liquid crystal display device 1 according to the present embodiment includes a liquid crystal panel 120 (with a polarizer and an analyzer attached to a liquid crystal cell), a light source unit 110, and a peripheral circuit of the liquid crystal panel, as shown in FIG. A determination unit 102 and an image signal conversion unit 103 are mounted.

[Active matrix substrate]
On the active matrix substrate 31, an optically substantially transparent common electrode (common electrode) 33 made of ITO (indium-tin oxide), a scanning electrode (gate electrode) 34 made of Mo / Al (molybdenum / aluminum), The common electrode wiring 46 (common wiring) 46 is formed so as to overlap the ITO common electrode 33. A gate insulating film 37 made of silicon nitride is formed so as to cover the common electrode 33, the gate electrode 34, and the common electrode wiring 46. A semiconductor film 41 made of amorphous silicon or polysilicon is disposed on the scan electrode 34 via a gate insulating film 37, and functions as an active layer of a thin film transistor (TFT) as an active element. Further, a signal electrode (drain electrode) 36 and a pixel electrode (source electrode) wiring 48 made of Cr / Mo (chromium / molybdenum) are disposed so as to overlap a part of the pattern of the semiconductor film 41, and all of these are covered. Thus, the protective insulating film 38 made of silicon nitride is formed. The electrode material is not limited to this embodiment. For example, ITO may be IZO which is a transparent electrode material, or may be an electrode material using copper for wiring.

  Further, as shown in FIG. 6, ITO pixel electrode (source electrode) 35 connected to metal (Cr / Mo) pixel electrode (source electrode) wiring 48 through through hole 45 formed in protective insulating film 38. Is disposed on the protective insulating film 38. FIG. 8 is an enlarged plan view of one pixel of the liquid crystal display device according to this embodiment. As shown in FIG. 8, the ITO common electrode (common electrode) 33 is formed in a flat plate shape in the area of one pixel in plan view, and the ITO pixel electrode (source electrode) 35 is inclined by about 8 degrees. It is formed in a comb-teeth shape. The liquid crystal display device according to the present embodiment has a diagonal number of 37 inches and a number of pixels corresponding to full high vision of 1920 × RGB × 1080 pixels.

[Color filter substrate]
As shown in FIG. 7, a black matrix 44 is formed on the color filter substrate 32 through coating, pre-baking, exposure, development, rinsing, and post-baking processes by a photolithography method that is a regular method using a black resist. The The thickness of the black matrix 44 is set so that the optical density is 3 or more.

  Next, using three colors of color resists, a color filter layer was formed through the steps of coating, pre-baking, exposure, development, rinsing, and post-baking according to a photolithography method which is a usual method. In this embodiment, blue is set to 3.0 μm, green is set to 2.8 μm, and red is set to 2.7 μm. However, the film thickness may be appropriately adjusted to a desired color purity or the thickness of the liquid crystal layer. In this embodiment, the black matrix 44 is formed so as to surround one pixel, but is formed in a region overlapping the scanning electrode 34 of the active matrix substrate 31. Moreover, you may use the color filter board | substrate 32 produced with the method generally called an inkjet system.

  As the spectral characteristics of the color filter, the spectral transmission light intensity of 480 nm or more in the blue filter is sufficiently low, for example, 10% or less with respect to the maximum spectral transmission light intensity of the blue filter, and the spectral characteristic of 510 nm or less in the green filter. When a sufficiently low material is used so that the transmitted light intensity is, for example, 10% or less with respect to the maximum spectral transmitted light intensity of the green filter, it is possible to suppress a change in color tone in dimmed vision and look up in the dark place. There is an effect that the conversion control of the table can be easily performed. In the present embodiment, since the spectral luminous efficiency of dark place vision applied under thin vision conditions has a peak at a wavelength of 507 nm, the human visual perception characteristic changes dramatically in a dark environment. If there is no light emission characteristic, it is possible to reduce the difference in appearance in a photopic environment and a light-vision environment. Specifically, for example, a dye that absorbs light having a wavelength of 480 to 520 nm is added to the color filter layer 42, added to the overcoat layer 43, or a dye layer that absorbs light having a wavelength of 480 to 520 nm. There is a means such as laminating separately.

  Next, an overcoat layer 43 is formed for the purpose of planarization and protection of the color filter layer 42. After the application, if it is a photosensitive resin, it is cured by ultraviolet irradiation and heating, or if it is a thermosetting resin, it is cured at a predetermined temperature and time. The overcoat layer 43 may be omitted if the color filter layer 42 is relatively flat in the pixel and if liquid crystal contamination due to impurities from the color filter layer 42 can be prevented.

  Next, the columnar spacer 47 is formed with a height of approximately 3.9 μm on the black matrix sandwiched between the red pixels by a photolithographic method and an etching process, which are regular methods, using a photosensitive resin. In addition, the position of the columnar spacer 47 can be formed at an arbitrary position as necessary, and is not limited to this embodiment. Alternatively, a method of selectively arranging at a predetermined position using a ball spacer may be used.

[LCD panel]
Each of the active matrix substrate 31 and the color filter substrate 32 is formed by printing a polyamic acid varnish. For example, alignment films 22 and 23 made of a dense polyimide film of about 100 nm are formed by a heat treatment at 230 ° C. for 30 minutes. The films 22 and 23 are aligned by rubbing or the like. The alignment film material is not particularly limited. For example, polyimide or amine component using 2,2-bis [4- (p-aminophenoxy) phenylpropane] as diamine and pyromellitic dianhydride as acid anhydride. Paraphenylenediamine, diaminodiphenylmethane, or the like may be used, and an aliphatic tetracarboxylic dianhydride or pyromellitic acid anhydride may be used as the acid anhydride component. Alternatively, for example, an alignment film formed of soluble polyimide that can be fired at a low temperature of about 200 ° C. may be used. In the present embodiment, the rubbing method is used. However, the present invention is not limited to this. For example, a photo-sensitive alignment film material may be used to form an alignment film by irradiation with polarized ultraviolet rays, or diamond. An ion beam method using like carbon may be used. In the present embodiment, the liquid crystal alignment direction is the direction of the scanning electrode 34 shown in FIG. 8, that is, the horizontal direction of the drawing.

  Next, a sealing agent is applied to the periphery of one substrate, a nematic liquid crystal composition is applied by an inkjet method, and the active matrix substrate 31 and the color filter substrate 32 are opposed to each other to assemble the liquid crystal cell 15.

  The polarizer 12 and the analyzer 11 are attached to the active matrix substrate 31 and the color filter substrate 32, respectively. In the present embodiment, the polarization axis of the polarizer 12 is the same direction as the liquid crystal alignment direction, and the analyzer 11 is a direction orthogonal to the polarizer. The direction in which the polarization axes are reversed may be used. The polarizer is provided with an optical retardation film as a viewing angle compensation layer.

  The viewing angle compensation layer may be a retardation film or a method of forming a polarizing layer having negative uniaxiality as the viewing angle compensation layer.

[Light source unit]
The configuration of the light source unit 110 can be arbitrarily selected from a direct type using a three-wavelength fluorescent tube as a light source, a direct type using a light emitting diode or a side light type, and a planar light source using an organic EL. The optical sheet 17 is disposed between the light source unit 110 and the liquid crystal panel 120. If the optical sheet 17 is a direct type or a planar light source, a diffusion plate, a diffusion sheet, a prism sheet, a polarization conversion sheet, or the like is used. In the case of a side light type, a light guide plate is required for this. The fluorescent tube may be either a hot cathode tube or a cold cathode tube.

  Further, in the light emission characteristics (spectral) of the light source, when a light source that does not emit light in the wavelength range of 480 nm to 530 nm is used, a change in color tone in dimming can be suppressed, and a look-up table for dark place vision (darkness) There is an effect that the compensation control of the image signal by the observation LUT 106) can be facilitated. Since the spectral luminous efficiency of scotopic vision applied under twilight vision has a peak at a wavelength of 507 nm, the human visual perception characteristic changes dramatically in a dark environment. If this is not done, the difference in appearance between the photopic vision environment and the light vision vision environment can be reduced.

  In addition, you may use the light source unit 110 which can change the spectral characteristic of the light source unit 110 by the case where it becomes a photopic vision, and the case where it becomes a faint vision. Specifically, the spectral radiance when the ambient illuminance is less than or equal to the illuminance reference value and the brightness level is less than or equal to the brightness reference value, the ambient illuminance is greater than the illuminance reference value, or the brightness level is greater than the brightness reference value. The ratio of radiance at a wavelength of 480 nm or more and 520 nm or less is lower than the spectral radiance of

[Liquid crystal display device 2]
In the liquid crystal display device 2 according to the present embodiment, as shown in FIG. 9, a liquid crystal cell in a vertical alignment mode is used. The production of the liquid crystal panel 120 in the vertical alignment mode is briefly described below, but is in accordance with a regular method and is not limited to the description in this specification.

[Color filter substrate]
The color filter substrate is formed by forming a chromium film with a thickness of 160 nm and a chromium oxide film with a thickness of 40 nm on a non-alkali glass substrate 32 having a thickness of 0.7 mm by continuous sputtering, applying a positive resist, pre-baking, exposing, The black matrix 44 was formed through the steps of development, etching, peeling, and washing. Next, using each color resist, a color filter was formed through the steps of coating, pre-baking, exposure, development, rinsing, and post-baking according to a photolithography method which is a usual method. In the second embodiment, the main pixel red is 2.5 μm, green is 2.7 μm, blue is 2.9 μm, the subpixel red is 2.2 μm, and green is 2.4 μm. What is necessary is just to match | combine suitably with respect to purity or a liquid-crystal layer thickness.

  Next, ITO was vacuum-deposited with a thickness of 140 nm by sputtering, and a common electrode pattern was formed by crystallization by heating at 240 ° C. for 90 minutes, a photo process, and an etching process. The opening of the common electrode 33 sandwiches the opening of the pixel electrode 35 in the middle. Next, columnar spacers were formed at a height of approximately 3.5 μm on a black matrix sandwiched between blue pixels by a photolithographic method and etching, which are regular methods, using a photosensitive resin.

[Active matrix substrate]
A scanning electrode (gate electrode) 34 (not shown) made of Mo / Al (molybdenum / aluminum) was formed on a non-alkali glass substrate 31 having a thickness of 0.7 mm as an active matrix substrate. A storage capacitor electrode may be formed of chromium or aluminum in the same layer (not shown). A gate insulating film 37 was formed so as to cover them, and a signal electrode (drain electrode) 36 and a thin film transistor were formed (not shown). A protective insulating film 38 was formed so as to cover them, and a pixel electrode 35 having an opening pattern was formed thereon with ITO. A transparent conductor such as IZO may be used. An active matrix substrate composed of 1920 × 3 (corresponding to R, G, B) signal electrodes 36 and 1080 scanning electrodes 34 was obtained.

[Liquid crystal cell]
Alignment films 22 and 23 were formed on the active matrix substrate and the color filter substrate, respectively. The alignment films 22 and 23 according to the second embodiment are vertically aligned. A sealing agent was applied to the periphery of the substrate, and a liquid crystal material having negative dielectric anisotropy was dropped and sealed by the ODF method to assemble the liquid crystal panel 120. The polarizing plates 11 and 12 were orthogonally crossed with the transmission axis of the incident side polarizing plate 12 as the long side direction of the substrate and the transmission axis of the output side polarizing plate 11 as the short side direction of the substrate. As the polarizing plate, a viewing angle compensating polarizing plate having a birefringent film that compensates viewing angle characteristics was used. Thereafter, peripheral circuits, the light source unit 110 and the like were connected to the liquid crystal panel 120 to form a liquid crystal module, and the liquid crystal display device 2 was obtained. An LED is used for the light source unit 110.

  In this example, a PVA mode liquid crystal display device using an ITO notch pattern was used. However, in the case of the MVA method in which protrusions are provided on the color filter substrate, after the ITO formation, the protrusion process is performed. Proceed to the column spacer process.

  Hereinafter, an example of a liquid crystal display device that realizes a good black display under thin vision conditions using the liquid crystal display device 1 and the liquid crystal display device 2 according to the above-described embodiment will be described. Since this is black display control for the viewer, either of the liquid crystal display modes of the liquid crystal display devices 1 and 2 may be applied. The difference between the liquid crystal display devices is that there is a difference in the first black display in photopic vision. For example, when the liquid crystal display devices 1 and 2 according to the above-described embodiment are combined with light sources having different color temperatures and the black display shown in FIG. 10 is displayed, all the subjects determined to be good black. FIG. 10 is a CIE 1976 u′v ′ chromaticity coordinate diagram, and a position indicated by Δ in the drawing is an achromatic color gamut. The distance from this point increases the color (in this case, the bluish color increases), but the surrounding environment is bright (in this case 250 lux). In this case, all are 0.6 nits or less), and all are determined to be good black.

  Here, as a comparison, first, using the liquid crystal display device 1 and the liquid crystal display device 2 that do not have the brightness sensor 101, the image signal conversion means 103, and the like, the subject is tested under dimming conditions (ambient environment 10 lux). Black display was shown. FIG. 11 shows a liquid crystal display device in which the majority of the subjects answered that the black was good as ◯, and a liquid crystal display device in which the majority of the subjects replied that the color was not good because they were concerned about coloring. It is clear that the distance of the chromaticity coordinates of the achromatic color does not match the good black determination.

Next, by using the liquid crystal display device 1 and the liquid crystal display device 2 according to the present embodiment, the second black whose saturation was compensated by applying the scotopic LUT 106 in the image signal conversion unit 103 was displayed. In this embodiment, the luminance of the light source unit 110 when displaying the second black is halved as compared with the case of displaying the first black, and the color of the black display is increased by the pixels emitting blue, red, and green. The degree is changing. FIG. 12 is a diagram showing the determination of the quality of the black display color compensated by the dark-sighted look-up table by the test subject under the mesopic condition. For comparison, a display in which the gradation of black display is intentionally controlled is also shown. A liquid crystal display device in which the subjects who answered good black are the majority is indicated by ◇, and a liquid crystal display device in which the majority is concerned about coloring and is not good is indicated by x. As shown in FIG. 12, it is determined that Δa _s b _s is equal to or less than 3.4, and a range where both a and b are negative values is good black display, and otherwise, it is determined that coloring is a concern. The

  Note that when compensation control using a look-up table based on the spectral luminous efficiency of scotopic vision is not performed, the blackness of FIG. 12 displayed in this embodiment is plotted to the value shown in FIG. In the chromaticity coordinates shown in FIG. 13, the distance from the origin and the pass / fail judgment do not match, so the scotopic LUT 106 for good black display cannot be derived.

  In addition, the second black black display according to the above-described embodiment is effective in a liquid crystal display device with high light utilization efficiency such as an IPS liquid crystal display device. This is because liquid crystal display devices with high light utilization efficiency often have high transmitted light intensity in the vicinity of a wavelength of 550 nm with high luminous efficiency in the spectral transmission characteristics of white display. This is a spectral characteristic mainly utilizing the birefringence of the liquid crystal. At this time, the transmitted light as the liquid crystal panel 120 has a low chromaticity and a slightly yellowish chromaticity. In the liquid crystal display device, since the color temperature of white display is set to approximately 12000K, such a liquid crystal panel requires a high light source such as 20000K for the color temperature of the light source. On the other hand, in black display, light leakage of short-wavelength light occurs due to the light scattering of the liquid crystal and color filters, the wavelength dependence of the polarization degree of the orthogonal polarizer, etc., not the spectroscopy caused by the birefringence of the liquid crystal. It becomes easy to do and becomes bluish. On the other hand, since light from a light source having a high color temperature is transmitted, the black display tends to be strongly bluish. And in mesopic vision, since the sensitivity with respect to blue becomes high, blueness is emphasized more.

  11 upper polarizing plate (analyzer), 12 lower polarizing plate (polarizer), 15 liquid crystal cell, 17 optical sheet, 21 liquid crystal layer, 22, 23 alignment film, 31 active matrix substrate, 32 color filter substrate, 33 common electrode ( Common electrode), 34 Scan electrode (gate electrode), 35 Pixel electrode (source electrode), 36 Signal electrode (drain electrode), 37 Insulating film, 38 Protective insulating film, 41 Semiconductor film, 42 Color filter (colored) layer, 43 Overcoat layer, 44 Black matrix, 45 Through hole, 46 Common electrode wiring, 47 Columnar spacer, 48 Pixel electrode wiring, 101 Brightness detection means, 102 Determination means, 103 Image signal conversion means, 105 Brightness level acquisition means, 106 Dark Observation LUT, 107 Photopic LUT, 110 Light source unit, 120 LCD panel .

Claims (10)

A liquid crystal display device having a liquid crystal panel that performs color display by controlling the transmittance of a plurality of arranged pixels, and a light source unit that emits light toward the liquid crystal panel,
Brightness detection means for detecting environmental illuminance in an environment in which the liquid crystal panel is disposed;
Luminance level acquisition means for acquiring the luminance level of the image to be displayed from the input image signal;
Determining means for determining whether the environmental illuminance is equal to or less than a predetermined illuminance reference value and the luminance level is equal to or less than a predetermined luminance reference value;
Image signal conversion means for converting the image signal into a control signal for the liquid crystal panel;
The image signal conversion means includes
When the ambient illuminance is less than or equal to the illuminance reference value and the luminance level is less than or equal to the luminance reference value, the saturation of the display target image is compensated and converted to the control signal.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
The liquid crystal panel displays colors by emitting light in red, green and blue,
The image signal conversion means includes
When the ambient illuminance is less than or equal to the illuminance reference value and the luminance level is less than or equal to the luminance reference value, the transmittance of a pixel that emits blue light is reduced, or a pixel that emits red light or green Compensating the saturation of the image to be displayed by improving the transmittance of the pixels that emit light,
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1 or 2,
In the case where at least the environmental illuminance is not more than the illuminance reference value and the luminance level is not more than the luminance reference value,
The light source unit is
As at least one of the ambient illuminance or the luminance level decreases, the luminance of light emitted toward the liquid crystal panel is reduced.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1 or 2,
In the case where at least the environmental illuminance is not more than the illuminance reference value and the luminance level is not more than the luminance reference value,
The light source unit is
As at least one of the ambient illuminance or the luminance level decreases, the luminance of light emitted toward the liquid crystal panel is reduced,
The image signal conversion means includes
Compensating while improving the upper limit of the transmittance of the plurality of pixels controlled to display the image to be displayed as the luminance of light emitted from the light source unit toward the liquid crystal panel is reduced.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
The illuminance reference value is a value detected from the brightness detection means in an environment where the vertical illumination with which the liquid crystal display device is illuminated is 50 lux,
When the luminance level is a maximum luminance value in the display target image, the luminance reference value is 50 nits, and when the luminance level is an average luminance value in the display target image, The luminance reference value is 20 nits.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
When the ambient illuminance is less than or equal to the illuminance reference value and the luminance level is less than or equal to the luminance reference value, the chromaticity of black display displayed by the liquid crystal panel is the spectral luminous efficiency of dark place vision In the LAB color system using, the saturation Δab does not exceed 3.4, and the coordinate axes a and b are values of 0 or less.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
The liquid crystal panel has a layer containing a dye that absorbs light having a wavelength of 480 nm to 520 nm.
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
Spectral characteristics in light emission to the liquid crystal panel of the light source unit when the environmental illuminance is equal to or lower than the illuminance reference value and the luminance level is equal to or lower than the luminance reference value.
Light having a wavelength of 480 nm to 520 nm than the spectral characteristics of light emission to the liquid crystal panel of the light source unit when the environmental illuminance is larger than the illuminance reference value or the luminance level is larger than the luminance reference value. The proportion of
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 1,
The image signal conversion means includes
Compensation control information for converting the image signal into the control signal,
When the ambient illuminance is less than or equal to the illuminance reference value and the luminance level is less than or equal to the luminance reference value, the image signal is converted according to the compensation control information;
A liquid crystal display device characterized by the above. The liquid crystal display device according to claim 9,
The compensation control information is a table and a relational expression generated based on a spectral luminous efficiency lower than the spectral luminous efficiency of photopic vision,
The image signal is converted into the control signal according to the table and the relational expression.
A liquid crystal display device characterized by the above.

Images