JP2019113652A - Liquid crystal display - Google Patents

Abstract

To provide a liquid crystal display that includes a backlight using quantum dots, has a wide color gamut, and can perform HDR display, can obtain high luminance necessary for the HDR display, and can obtain a predetermined color balance while ensuring improvement in power efficiency and luminance gradation on a low-luminance side by controlling an LED application current.SOLUTION: A liquid crystal display comprises: a blue LED unit 512; a quantum dot sheet 506 that includes quantum dots emitting red light and green light with the emission of blue light as excitation light; a display control unit 504; and a backlight control value determination unit 508 that determines the LED application current value of the blue LED unit. The quantum dot sheet has a quantum dot content that is adjusted so that predetermined luminance and color balance can be obtained while the LED application current is the maximum value within an assumed range; the backlight control value determination unit 508 sets the LED application current to a low-current value when display luminance is low; the display control unit 504 performs control of obtaining the predetermined color balance by performing control of correcting pixel luminance.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a liquid crystal display device having a backlight using quantum dot light emission.

  A quantum dot is a particle of a semiconductor having a particle diameter of several nm to about 20 nm, and, like a phosphor, is excited by light to emit light. Emission energy is limited by the effect of electron confinement, and has a narrow spectrum emission characteristic with high quantum efficiency. By adjusting the particle size and the material, it is possible to create predetermined spectral characteristics. The smaller the particle size, the shorter wavelength light is output, and the larger the particle size, the longer wavelength light is output. An application to a wide color gamut display has been devised using the characteristic that the color purity of light emission is high and the light emission characteristics can be controlled (Patent Document 1).

  An outline of the light emission principle of quantum dots will be described. The excitation light excites the electrons in the quantum dot, and then emits light of a wavelength corresponding to the band gap energy of the electrons to stabilize the electrons. Band gap energy is an inherent amount of quantum dots. Therefore, light emission of a predetermined color can be obtained by making the band gap energy correspond to the color required.

  For example, when the excitation light is blue light and is irradiated to a member including two types of quantum dots emitting red and green, red and green quantum dot emission can be obtained. A part of the blue light is transmitted as it is without contributing to the quantum dot excitation, and as a result, white light composed of red, green and blue light is obtained.

  The white light thus obtained is applicable to a backlight for liquid crystal. Each color component constituting the white light of the backlight has narrow spectral characteristics, which enables color expression in a wide color gamut. As described above, it is possible to obtain good backlight light for a wide color gamut display by using monochromatic excitation light.

  On the other hand, video equipment using technology called HDR (High Dynamic Range) for expanding the luminance dynamic range of video is becoming widespread. In the HDR compatible device, it is possible to reproduce the luminance in the natural world which can not be expressed in the luminance range of the conventional standard as it is. Although a large number of signal gradations are required to express the expanded luminance range, the current HDR standard uses a technology that achieves the same number of gradations as the conventional one (see Non-Patent Document 1). This is a technology in which more gradations are allocated to the low luminance side according to human visual characteristics, and a small number of gradations are allocated to the high luminance side so that the gradation difference can not be determined.

  The backlight of a liquid crystal display capable of HDR display is often configured using an LED. In order to realize the HDR display, it is necessary to cause the LED to emit light at high luminance and to secure luminance gradation at low luminance. The light emission luminance of the LED can be controlled using both control of the LED application current and PWM (Pulse Width Modulation) control of the LED light emission time.

  In general, when the LED application current is high, the light emission efficiency of the LED is lowered, which causes heat generation and power consumption also increases. In addition, in order to secure the luminance gradation on the low luminance side only by PWM control in a state where the LED applied current is high, PWM control with extremely high accuracy and high gradation is required, and the technical difficulty becomes high. From the above, when the required luminance is low, the LED application current may be set low, and control may be performed to set the LED application current high only when high luminance is required.

  It is expected that a wide color gamut and an HDR-displayable display can be realized by applying the above-described quantum dot light emission technology to an HDR-displayable display.

Unexamined-Japanese-Patent No. 2006-310303

SMPTE ST. 2084 standard

  The characteristics of light obtained by quantum dots that generate red and green converted light by blue excitation light are white depending on the content and ratio of blue excitation light intensity, red light emission quantum dots, and green light emission quantum dots. The color balance of the light and the brightness are determined. In general, a quantum dot member used for backlighting can not change the characteristics of the quantum dot once made.

  When the LED application current value of the blue excitation light source is increased to correspond to the HDR display, the light amount exceeds the conversion efficiency that can be converted to red and green, and the predetermined luminance is not obtained at high luminance. In addition, when the LED applied current value of the blue excitation light source is changed, the amount of blue light to be transmitted and the amount of converted light are changed to red and green, so that the color balance of the obtained white light is changed. there were.

  Therefore, the present invention is a liquid crystal display device capable of performing HDR display with a wide color gamut using quantum dots, and a liquid crystal display device capable of achieving both the adjustment of the LED application current of the light source LED and a predetermined color balance Intended to provide.

  In order to solve the problems described above, a liquid crystal display device according to the present invention is a liquid crystal panel. A backlight serving as illumination light for the liquid crystal panel in which a blue LED emitting blue light is disposed, a backlight control means for controlling the backlight, and red and green lights using the light of the blue LED as excitation light A liquid crystal display device comprising quantum dot light emitting means including quantum dots, and display control means for controlling display pixels of the liquid crystal panel, wherein the quantum dot light emitting means has an LED applied current value of the blue LED The quantum dot content is adjusted so that the required luminance and color balance can be obtained at the maximum value of the assumed use range, and the backlight control unit is configured to control the LED application current required from the blue display luminance. Backlight control value determining means for determining a value, wherein the backlight control value determining means determines that the LED application current value is lower than an estimated maximum value. Calculating a luminance compression correction coefficient of red and green pixel luminance of the liquid crystal panel and sending it to the display control means, wherein the display control means performs luminance compression on red and green pixels according to the luminance compression correction coefficient It is characterized in that control is performed to obtain a predetermined color balance by performing correction.

  Another liquid crystal display device according to the present invention includes a liquid crystal panel, a backlight serving as illumination light of the liquid crystal panel in which a blue LED emitting blue light is disposed, and a backlight control unit for controlling the backlight. A liquid crystal display device comprising: a quantum dot light emitting means including quantum dots emitting red and green lights with the light emission of the blue LED as excitation light; and a display control means for controlling display pixels of the liquid crystal panel. The quantum dot content is adjusted so that the required luminance and color balance can be obtained when the LED application current value of the blue LED is the maximum value of the expected use range, in the quantum dot light emitting means. The control means includes backlight control value determination means for determining the LED applied current value required from the blue display luminance, and the backlight control value determination means The LED applied current value is determined so that the LED applied current value can be subjected to the luminance expansion correction of the blue pixel luminance, and the luminance expansion correction coefficient of the blue pixel luminance of the liquid crystal panel is calculated. The display control means is controlled to obtain a predetermined color balance by performing correction to expand the luminance of the blue pixel by the luminance expansion correction coefficient.

  According to the present invention, in a liquid crystal display device capable of providing a wide color gamut and HDR display with a backlight using quantum dots, high luminance necessary for HDR display can be obtained, and control of LED applied current is performed. It becomes possible to obtain a predetermined color balance. As a result, control of the LED application current becomes possible, which makes it possible to improve the power efficiency on the low luminance side and secure the luminance gradation.

FIG. 1 is a schematic configuration diagram of a liquid crystal display device using quantum dots according to the first and second embodiments of the present invention. It is a conceptual diagram of the luminescence characteristic at the time of LED maximum current of the back light which used the quantum dot concerning the 1st and 2nd embodiment. It is a graph which shows the relationship of the LED current value of a backlight using the quantum dot which concerns on 1st and 2nd embodiment, and a normalized luminescence intensity. It is a conceptual diagram of the luminescence characteristic at the time of LED low current of the back light which used the quantum dot concerning a 1st embodiment. It is a block diagram which shows the structure of the liquid crystal display using the quantum dot which concerns on 1st and 2nd embodiment. It is a flowchart which shows the operation | movement flow of the liquid crystal display device using the quantum dot which concerns on 1st Embodiment. It is a graph which shows the panel pixel gradation of the backlight using the quantum dot which concerns on 2nd Embodiment, and the relationship of pixel brightness. It is a conceptual diagram of the luminescence characteristic at the time of LED low current of the back light which used the quantum dot concerning a 2nd embodiment. It is a flowchart which shows the operation | movement flow of the liquid crystal display device using the quantum dot which concerns on 2nd Embodiment.

First Embodiment
FIG. 1 shows a schematic diagram of a backlight and a liquid crystal panel of a liquid crystal display device, which is one of the embodiments of the present invention. A back light 101 is installed on the rear surface of the device, and a liquid crystal panel 104 is installed on the front surface. A quantum dot 103 is inserted between the two.

  The backlight 101 is a light source on the surface that illuminates the liquid crystal panel 104, and has a direct backlight structure. The backlight 101 has a structure in which blue LEDs 102 are arranged in an array, and a plurality of luminance sensors 105 are arranged inside. The blue LED 102 emits blue light and serves as excitation light of the quantum dot 103 and blue light source of the liquid crystal panel 104. The luminance sensor 105 is a sensor that detects light emission luminance in the backlight 101. The luminance of each of red, blue and green can be detected.

  The quantum dot sheet 103 is a sheet-like wavelength conversion member including red and green quantum dots. The blue excitation light from the backlight 101 excites the internal quantum dots to emit red and green light when transitioning to a stable state. The blue light to be irradiated includes light to be transmitted in combination with light used as excitation light. When the red and green luminescence and blue transmitted light from the quantum dot sheet 103 are combined, it becomes white light, which becomes the light source of the liquid crystal panel 104.

  The liquid crystal panel 104 has a configuration in which a liquid crystal layer in which pixels are arranged, a polarizing filter, a transparent electrode, and a color filter are stacked. The transmittance of light of red, green and blue is controlled for each pixel of the liquid crystal. The light from the quantum dot sheet 103 is controlled in transmittance for each pixel by the liquid crystal panel 104 to form an image.

  The color balance generated by the quantum dot sheet 103 will be described. Here, the color balance means the degree of deviation of white determined by the ratio of each of red and green light emission and blue transmitted light when displaying white. In order to express the white color defined by the image and the image standard, it is necessary to set the ratio of red, green and blue defined by the standard. In a state in which the color balance is shifted, that is, in a state in which the ratio of red, green, and blue is different from the ratio defined in the standard, correct color development can not be performed, and the user recognizes the display image as different colors. In order to avoid this, it is necessary to emit light in a predetermined state of color balance.

  The color balance is determined by the red and green luminous efficiency and blue transmittance of the quantum dot sheet 103. The luminous efficiency and the transmittance can be adjusted by the content of quantum dots contained in the quantum dot sheet 103. Specifically, the content of quantum dots depends on the density of quantum dots in the sheet and the thickness of the sheet. Generally, it is difficult to change and adjust the quantum dot content once it has been built.

  Subsequently, the principle of operation of the present invention will be described using graphs of the conceptual diagrams of brightness in FIGS. 2 to 4 and graphs. FIG. 2 illustrates the luminance characteristics when the LED application current value is the maximum value of the use expected range. FIG. 2A shows a conceptual diagram of light source luminance. The ordinate represents the amount of current applied to the blue LED 102, and the abscissa represents the light emission time. The light emission time of the blue LED 102 is PWM controlled. The on period of the PWM width and the off period are repeated in the PWM cycle. The ratio of the on period of PWM is the PWM duty, and FIG. 2A shows the state where the PWM duty is 100%.

  The applied current value of the LED can control the light emission luminance per unit time of the LED. Therefore, the luminance of the LED is determined by the LED current value and the PWM duty which is the ratio of the light emission period. Conceptually, it can be considered that the area indicated by the rectangle of the LED current value and the PWM width corresponds to the luminance.

  FIG. 2 (B) shows the light emission intensity distribution of each color of red, green and blue when the LED applied current value reaches the maximum value of the expected use range. The horizontal axis is the light emission wavelength, and the vertical axis is the light emission intensity after passing through the quantum dot sheet 103. The light emission intensity on the vertical axis is normalized by the light emission intensity to achieve a predetermined color balance.

  The emission wavelength becomes longer in the order of blue, green and red, resulting in a profile having a peak at the wavelength corresponding to each color. The higher the peak, the stronger the emission intensity, and the lower the peak, the weaker the emission intensity. The blue emission intensity after emitting light from the blue LED 102 and passing through the quantum dot sheet 103 is shown as blue 201. The green emission intensity converted from the excitation light of the blue LED 102 to green by the quantum dot sheet 103 is shown as green 202. Similarly, the red emission intensity converted to red is shown in red 203.

  The quantum dot content of the quantum dot sheet 103 is set so that the color balance when the LED applied current value reaches the maximum value of the use expected range is in a predetermined state as shown by blue 201, green 202, and red 203. . In this way, the maximum luminance and color balance in the maximum state of the LED application current required for the HDR display are secured.

  The color balance shown in FIG. 2B becomes a different color balance when the LED applied current is decreased. The adjustment method will be described with reference to FIGS. 3 and 4.

  FIG. 3 is a graph showing the relationship between the LED current value and the normalized emission intensity. The relationship between the LED current value of each of red, green, and blue and the normalized emission intensity is shown. The relationship between the normalized emission intensity of blue light after transmission through the quantum dot sheet 103 and the LED current of the blue LED 103 is indicated by blue 301. Similarly, the relationship between the normalized emission intensity of red converted light and green converted light by the quantum dot sheet 103 and the LED current is shown in red and green 302. Here, red and green have the same tendency, so they are shown in the same straight line.

  As the amount of LED current decreases, the emission intensity of the blue transmitted light indicates that the color balance decreases more than a predetermined state. Conversely, the emission intensity of the red / green conversion light indicates that the color balance is increased above a predetermined state. When the LED current decreases and the excitation light per unit time decreases, the conversion efficiency determined by the quantum dot content of the quantum dot sheet 103 has a margin, so the ratio of converted light of red and green increases. The proportion of blue transmitted light decreases accordingly.

  As described with reference to FIG. 2, the quantum dot sheet 103 is set such that the LED application current value has a predetermined color balance at the maximum value of the use assumed range. Therefore, the normalized emission intensities shown by blue 301 and red / green 302 are 1 at the maximum current value.

  FIG. 4 illustrates the luminance characteristics when the LED applied current value is decreased, on the assumption that the low luminance side display is performed in the HDR display. In this embodiment, in order to simplify the description, it is assumed that the LED application current value has two ways of setting the maximum current value and setting the low current value. When the luminance required for display is low enough, the current can be set to a low current value.

  Note that, even if the low current value setting can take a plurality of values, the present invention can be applied by performing the same determination for each of the plurality of low current values.

  FIG. 4A shows a conceptual diagram of light source luminance. The LED current value is low, and the light emission luminance is also low. FIG. 4B shows emission intensity distributions of red, green and blue when the LED current value is decreased. As in FIG. 2B, the horizontal axis is the light emission wavelength, the vertical axis is the light emission intensity after passing through the quantum dot sheet 103, and the light emission intensity on the vertical axis is normalized with a predetermined light emission intensity. The blue light emission intensity of the blue transmitted light of the quantum dot sheet 103 is shown as blue 401. The green emission intensity converted from the excitation light of the blue LED 102 to green by the quantum dot sheet 103 is shown as green 402 (before adjustment). Similarly, the red emission intensity converted to red is shown in red 403 (before adjustment). The proportion of blue is relatively low.

  As shown in FIG. 4B, the proportion of red and green is larger than that of blue emission intensity, and the color balance is broken.

  The display brightness can be controlled by the PWM duty that drives the blue LED 102. However, at this time, the proportion of red and green in white light does not change, and the color balance does not change. Therefore, the red and green luminances are adjusted by compressing the pixel luminance on the liquid crystal panel 104 side. The green emission intensity after color balance adjustment on the liquid crystal panel 104 side is shown as green 404 (after adjustment). The red light emission intensity after color balance adjustment on the liquid crystal panel 104 side is shown in red 405 (after adjustment).

  The basic concept of the method of setting the characteristics of the quantum dot sheet 103 corresponding to the HDR display of the present invention and the method of adjusting the color balance has been described above. Next, a specific adjustment procedure and means for realizing this operation will be described. A block diagram of a liquid crystal display device using a backlight of quantum dot emission which is one embodiment of the present invention is shown in FIG.

  A backlight control unit 501, a control system unit 502, a backlight unit 503, a display control unit 504, a video data bus 511, a liquid crystal panel unit 505, and a quantum dot sheet 506. For each part, the internal configuration, the functions it is responsible for, and the input / output relationship between each other will be described.

  The backlight control unit 501 is responsible for adjustment of the color balance of the backlight and brightness control. Details of the internal configuration will be described later. It receives display control information from the control system unit 502 and the display control unit 504, determines backlight control information, and sends it to the backlight unit 503. Also, from the backlight unit 503, feedback control of luminance and color balance is performed in response to the detection result of the RGB luminance sensor unit 513.

  The backlight unit 503 is an illumination of the liquid crystal display device, and corresponds to the backlight 101 of FIG. 1. A blue LED unit 512 and an RGB luminance sensor unit 513 are provided. They correspond to the blue LED 102 and the luminance sensor 103 in FIG. 1, respectively. The blue LED unit 512 is a light emitting diode that emits blue light with a predetermined luminance in accordance with the drive signal. The drive signal is a PWM drive waveform and an LED applied current value, and is sent from the LED PWM control unit 509 and the LED current control unit 510, respectively. The light of the blue LED unit 512 is used as a light source for both the excitation light of the quantum dot sheet 506 and the blue light source of the liquid crystal panel unit 505.

  The RGB luminance sensor 513 is a sensor that detects the luminance of each of red, green, and blue. This corresponds to the luminance sensor 105 of FIG. A luminance sensor is a device that converts light into an electrical signal, and obtains an electrical signal level according to the light intensity. A color filter corresponding to the color to be detected is provided on the luminance sensor, and the luminance of each color can be detected. The luminance detection result is sent to the backlight control unit 501 as an electrical signal.

  The quantum dot sheet 506 is a sheet-like wavelength conversion member including quantum dots, and corresponds to the quantum dot sheet 103 in FIG. 1. In response to the excitation light from the blue LED unit 512, it generates red and green converted light and irradiates the liquid crystal panel unit 505. As described with reference to FIG. 2, the quantum dot content, that is, the content density and the thickness can be maintained so that the luminance required for the LED application current value at the maximum value of the intended use range can be secured and the predetermined color balance is achieved. Is set.

  The liquid crystal panel unit 505 corresponds to the liquid crystal panel 104 in FIG. The liquid crystal pixels are controlled by receiving the driving electric signal from the display control unit 504, and the transmittance of the white light from the quantum dot sheet 506 is adjusted for each pixel to form an image.

  The video data bus 511 is a bus that passes video data input from the outside. The display control unit 504 is a bus dedicated to video data connected to the liquid crystal panel unit 505.

  A display control unit 504 controls input / output of video data and video processing. The video data input via the video data bus 511 is sent to the liquid crystal panel unit 505. Control of the backlight brightness may be performed according to the video data, and in this case, the backlight control unit 501 mutually transmits and receives information for backlight brightness control. As the color balance adjustment of the backlight control unit 501 is insufficient, the pixel value of the liquid crystal panel unit 505 is compressed or expanded to adjust the color balance of the final display. Information for color balance adjustment for this is received from the backlight control unit 501.

  A control system unit 502 is responsible for overall system operation control of the liquid crystal display device. It is the part that mainly realizes control by software. Control information necessary for backlight control is sent to the backlight control unit 501.

  The control system unit 502 includes a RAM 514, a CPU 515, a light emission characteristic holding unit 516, and a system bus 517. The RAM 514 stores various data such as programs and control data. CPU 515 reads data from RAM 514 and, in response, sends control commands to system bus 517. The process in which the CPU 515 operates in accordance with the software information in the RAM 514 in this manner is hereinafter simply referred to as software process.

  The light emission characteristic holding unit 516 holds the characteristics of the quantum dot sheet 506 and the blue LED unit 512. Specifically, the relationship between the light emission intensity and the LED current value shown in FIG. 3 is maintained.

  A system bus 517 is a bus that connects the components that make up the control system unit 502. Transmission and reception of data and commands are performed via the system bus 517 to control each part.

  Subsequently, details of the inside of the backlight control unit 501 will be described. A display luminance determination unit 507, a backlight control value determination unit 508, an LED PWM control unit 509, and an LED current control unit 510 are configured.

  The display luminance determination unit 507 receives the luminance information mainly determined by the user operation from the control system unit 502 and the luminance information determined by the video data from the display control unit 504, and finally outputs it in the liquid crystal display device. To determine the display brightness. The determined luminance information is sent to the backlight control value determination unit 508.

  The backlight control value determination unit 508 uses the display luminance determined by the display luminance determination unit 507 to determine a control value for driving the blue LED unit 512. The control value is a PWM value and a current value. The details of the determination method will be described later with reference to the flowchart of FIG. The determined PWM value is sent to the LED PWM control unit 509. The determined current value is sent to the LED current control unit 510.

  The LED PWM control unit 509 generates a PWM driving waveform based on the received PWM value and sends it to the blue LED unit 512.

  The LED current control unit 510 is a current source of the applied current of the LED, generates a current based on the received current value, and sends it to the blue LED 512.

  The process flow of setting the LED application current value and adjusting the color balance of the liquid crystal display device shown in the present embodiment will be described using the flowchart of FIG. 6 and the block diagram of FIG. FIG. 6 shows a color balance adjustment flow of the backlight.

  This flow is performed at timing when the high luminance display and the low luminance display of the HDR display change after the video data is input. For example, it is the change timing of the display mode setting of the user. When the display mode is automatically set according to the video data, each frame is performed. Alternatively, only the display mode determination may be performed every frame, and this flow may be performed at the timing when the display mode changes.

  When video data is input and processing is started, in step S601, the luminance to be displayed by the liquid crystal display device is determined. This processing is performed by the display luminance determination unit 507. As described above, the display luminance is determined based on the luminance information from the control system unit 502 and the display control unit 504. Subsequently, the process proceeds to step S602.

  In step S602, the LED applied current value is set. Thereafter, the backlight control value determination unit 508 performs the processing from step S602 to step S605. If the blue light emission luminance of the display luminance determined in step S601 is equal to or less than the luminance at the low current value setting, it is determined as the low current value. If the maximum current value is required, such as when high-intensity display of HDR is required, the maximum current value is determined. Subsequently, the process proceeds to step S603.

  In step S603, the PWM duty of the LED is determined. The PWM duty is determined from the LED current value determined in step S602 so that the display luminance determined in step S601 is obtained. The PWM duty is calculated from the LED current value so that the blue light emission luminance becomes a predetermined light emission luminance. Subsequently, the process proceeds to step S604.

  In step S604, the LED application current value determined in step S601 is determined. If it is the maximum current value, the process proceeds to step S606. If the current value is low, the process proceeds to step S605.

  In step S605, a liquid crystal panel pixel luminance correction coefficient is calculated so as to achieve predetermined color balance. When the LED application current is a low current value, the emission intensities of red and green become high, as described with reference to FIG. The color balance is adjusted by compressing the luminance by multiplying the red and green pixel values by the correction coefficient. The luminous intensity of red, blue and green at low current is held by the luminous characteristic holding unit 516. Alternatively, the detection result from the RGB luminance sensor unit 513 may be used. The backlight control value determination unit 508 obtains the light emission intensity information via the system bus 517, and calculates red and green correction coefficients to achieve a predetermined color balance. The calculated correction coefficient is sent to the display control unit 504, and the display control unit 504 performs correction by multiplying the red and green correction coefficients by the pixels of the video data. Subsequently, the process proceeds to step S606.

  In step S606, image display from the liquid crystal panel unit 505 is obtained. First, the backlight control value determination unit 508 sends the PWM duty determined in step S604 and the LED current value determined in step S603 to the LED PWM control unit 509 and the LED current control unit 510, respectively. The LED PWM control unit 509 and the LED current control unit 510 respectively generate a PWM drive waveform and an LED applied current value, and drive the blue LED unit 512. When the light emitted from the blue LED unit 512 is irradiated to the quantum dot sheet 506, backlight light having a predetermined color balance can be obtained.

  At this time, the display control unit 504 performs pixel control of the liquid crystal panel unit 505 in accordance with the video data. Finally, when the liquid crystal panel unit 503 is irradiated with the backlight light from the quantum dot sheet 506, the user can obtain an image display with a predetermined color balance.

  By the above configuration, processing, and operation, in the liquid crystal display device using the quantum dots, control such that the color balance of the backlight light is predetermined can be performed, and the user can view the image with correct color development.

Second Embodiment
In the correction of pixel luminance described in the first embodiment, color balance is corrected by compressing pixel luminance of red and green. However, when the pixel luminance is compressed, the accuracy of the pixel gradation is reduced. In the present embodiment, a method of correcting the color balance without reducing the gradation accuracy will be described.

  The schematic configuration of the liquid crystal display device described in the present embodiment is the same as that of FIG. In the quantum dot sheet 103, as in the contents described with reference to FIG. 2 and FIG. 3, the quantum dot content is set so that the maximum luminance and color balance can be secured in the LED applied current maximum state required for HDR display. There is. Here, when the LED applied current value is set to a low current value, the proportion of red and green increases compared to the emission intensity of blue, and the color balance is broken.

  FIG. 7 shows a graph of the relationship between blue panel pixel tone and pixel luminance. The horizontal axis represents panel pixel gradation, and the vertical axis represents display pixel luminance. Because of the HDR display, the pixel brightness on the vertical axis has a wide range. There are two LED application current values: low current value setting and maximum current value setting, and a high current region is selected for high brightness display, and a low current region is selected for low brightness display.

  The relationship between panel pixel gradation and display pixel luminance in a high current region is shown at high current 701. While covering to a high luminance area, the pixel gradation becomes rough.

  The relationship between the panel pixel gradation and the display pixel luminance in the low current region is shown at low current (before pixel correction) 702. The accuracy of the pixel tone can be secured.

  The luminance that can be displayed at low current (before pixel correction) 702 is the determination reference of the low luminance area and the high luminance area before pixel correction, and this is indicated by the line of Yth. Here, to adjust the color balance, consider expanding the blue panel pixel luminance. In the low current setting, since the luminance of blue is relatively low, in order to correct this, the luminance of blue pixel may be expanded. In the direction in which the pixel luminance is expanded, it is possible to prevent the decrease in gradation accuracy.

  The relationship between the panel pixel tone and the display pixel luminance after correction with extended pixel luminance with α as the correction coefficient is shown at low current (after pixel correction) 703. The maximum pixel luminance that can be achieved after correction is indicated by the line Yth '. By determining the high current region and the low current region using this determination threshold, it is possible to expand the blue pixel luminance.

  FIG. 8 shows the luminance characteristics when the LED application current is set to a low current value so as to enable blue pixel luminance expansion in HDR display. The blue light emission intensity distribution before color balance adjustment is shown in blue (before adjustment) 801. The emission intensity distributions of green and red are shown in green 802 and red 803, respectively. A light emission intensity distribution after correction by expanding pixel luminance is shown in blue (after adjustment) 804. By setting the region where blue pixel expansion is possible to a low current value, it is possible to adjust to a predetermined color balance without reducing the accuracy of the pixel tone.

  The block diagram of the liquid crystal display device described in the present embodiment is the same as FIG. 5, and the description will be omitted. A process flow of LED applied current value setting and color balance adjustment is shown in the flowchart of FIG. Only the differences from the process flow described with reference to FIG. 6 in the first embodiment will be described.

  After the display luminance is determined in step S601, the process proceeds to step S901. In step S901, the LED applied current value is set. This process is performed by the backlight control value determination unit 508. If the blue light emission luminance of the display luminance determined in step S601 is equal to or less than the determination threshold Yth ′ described with reference to FIG. 7, it is determined that the current value is low. If the maximum current value is required, such as when high-intensity display of HDR is required, the maximum current value is determined. Subsequently, the process proceeds to step S603.

  Description of steps S603, S604, and S606 is omitted. If it is determined in step S604 that the LED application current value is a low current value setting, the process proceeds to step S902.

  In step S902, a liquid crystal panel pixel luminance correction coefficient is calculated so as to achieve predetermined color balance. When the LED applied current is a low current value, the blue light emission intensity decreases as described with reference to FIG. The color balance is adjusted by multiplying the blue pixel value by the correction coefficient to extend the pixel luminance. The backlight control value determination unit 508 acquires emission intensity information of red, blue, and green at low current from the emission characteristic storage unit 516 via the system bus 517, and corrects blue so as to achieve a predetermined color balance. Calculate the coefficient. The calculated correction coefficient is sent to the display control unit 504, and the display control unit 504 performs correction by multiplying the pixels of the video data by the blue correction coefficient. Subsequently, the process proceeds to step S606.

  With the above configuration, processing, and operation, in the liquid crystal display device using quantum dots, control such that the color balance of the backlight light becomes predetermined can be performed without compressing the pixel luminance, and the user can correct color development You can watch the video on

101 Backlight 102 Blue LED
103 quantum dot sheet 104 liquid crystal panel 105 luminance sensor 501 back light control section 502 control system section 503 back light section 504 display control section 505 liquid crystal panel section 506 quantum dot sheet 507 display brightness decision section 508 back light control value decision section 509 LED PWM Control unit 510 LED current control unit 511 Image data bus 512 Blue LED unit 513 RGB luminance sensor unit 514 RAM
515 CPU 516 luminescence brightness holding unit 517 system bus

Claims (2)

With liquid crystal panel. A backlight serving as illumination light for the liquid crystal panel in which a blue LED emitting blue light is disposed, a backlight control means for controlling the backlight, and red and green lights using the light of the blue LED as excitation light A liquid crystal display device comprising quantum dot light emitting means including quantum dots, and display control means for controlling display pixels of the liquid crystal panel,
The quantum dot content is adjusted so that the required luminance and color balance can be obtained when the LED application current value of the blue LED is at the maximum value of the expected use range, in the quantum dot light emitting means.
The backlight control means has backlight control value determination means for determining the LED applied current value required from the blue display luminance,
The backlight control value determining means calculates a luminance compression correction coefficient of red and green pixel luminances of the liquid crystal panel and sends it to the display control means when the LED applied current value is lower than an estimated maximum value. ,
The liquid crystal display device, wherein the display control means performs control to obtain a predetermined color balance by performing correction for performing luminance compression on red and green pixels with the luminance compression correction coefficient. A liquid crystal panel, a backlight serving as illumination light of the liquid crystal panel in which a blue LED emitting blue light is disposed, backlight control means for controlling the backlight, red and green using light emitted from the blue LED as excitation light A liquid crystal display device comprising: quantum dot light emitting means including quantum dots emitting light; and display control means for controlling display pixels of the liquid crystal panel,
In the quantum dot light emitting means, the quantum dot content is adjusted such that the required luminance and color balance can be obtained when the LED application current value of the blue LED is the maximum value in the assumed use range,
The backlight control means has backlight control value determination means for determining the LED applied current value required from the blue display luminance,
The backlight control value determination means determines the LED application current value so that the LED application current value can be subjected to luminance expansion correction of blue pixel luminance, and the luminance of the blue pixel luminance of the liquid crystal panel is determined. Calculating an extended correction coefficient and sending it to the display control means;
The liquid crystal display device, wherein the display control means performs control to obtain a predetermined color balance by performing correction to expand the luminance of the blue pixel by the luminance expansion correction coefficient.