JPH07199848A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To suppress the reduction in color temperature, color reproducibility and color purity of a display picture and to obtain a good display by switching the white balance between the use of an external light and the use of an incorporated back light. CONSTITUTION:The liquid crystal display device uses an incorporated three wavelength fluorescent tube as an illuminating means of the liquid crystal panel under a normal condition. The device introduces an external light to the back of the liquid crystal panel and uses it as the illuminating means when the environmental brightness is high. When an external light is used, a gain switching signal is inputted to contrast adjusting circuits 12 and 13 from the external. When the fluorescent tube is used, for example, the ratio of gains among R, G and B are made to 1:1:1. When an external light is used, the ratio are made to 0.9:1:1.02 by switching the amplification factor of the circuits 12 and 13 so that the energy ratio of the external lights R, G and B which pass the liquid crystal panel is made closer to the energy ratio of R, G and B at the time of using the incorporated tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which a light source of a liquid crystal panel can also receive external light, and particularly when the external light is used as the light source of the liquid crystal display device, the color temperature of a display screen is increased. The display screen is designed to improve the color reproducibility, by correcting the spectral characteristics of the light source by switching the white balance between using external light and using the built-in backlight, or by adding an optical filter. It is intended to improve the color temperature and color reproducibility of.

[0002]

2. Description of the Related Art An example of a conventional liquid crystal display device of this type is
This will be described in detail with reference to FIGS. 13 and 14.

In the figure, 1 is a liquid crystal panel, 2 is a diffusion plate, and 4 is a light source, and usually a three-wavelength fluorescent tube is used. Reference numeral 5 is a reflector which reflects the light from the light source to the liquid crystal panel side.
Reference numeral 8 denotes a diffuse reflector which diffuses and transmits the light of the light source 4 and reflects the external light on the surface when the external light is used.

Since the liquid crystal panel does not emit light by itself, it is necessary to illuminate it from the back surface. Fluorescent tube or LE as the light source
Although D and EL are used, they consume a large amount of power. Therefore, some models such as portable liquid crystal televisions and video cameras use outdoor light as a light source of a liquid crystal panel to save power consumption.

In the structure shown in the figure, the liquid crystal panel 1 and the diffuser plate 2 (hereinafter referred to as the liquid crystal panel section) are normally closed and an image is displayed by using the built-in light source 4, and outdoor light such as outdoor light is displayed. In a bright place, the liquid crystal panel is opened, and the diffuse reflection plate 8 reflects external light to illuminate the liquid crystal panel 1.

[0006]

In the case of an AV liquid crystal panel, a full-color display is achieved by combining a three-wavelength fluorescent tube and red, green, and blue (hereinafter abbreviated as R, G, B) color filters. In order to effectively use the light from the lamp which is the light source, the peaks of R, G and B of the spectral transmittance of the color filter are the red (600
nm), green (550 nm), and blue (450 nm). The emission spectrum of the lamp is almost fixed due to the R, G, B colors themselves.

Normally, the color temperature of the liquid crystal display screen is adjusted to 6000 ° K to 7000 ° K when white is displayed so that the RGB transmittance of the color filter is balanced.
Design the RGB energy ratio of the fluorescent tube. On the other hand, external light due to sunlight or the like has a spectral characteristic different from that of a fluorescent tube and is as low as 4000 ° K to 6000 ° K. Therefore, if external light is used as it is as a light source of the liquid crystal display device in a liquid crystal panel designed on the assumption that a fluorescent tube is used, the color becomes reddish, and there is a problem that the function as a monitor cannot be achieved. .

The three-wavelength fluorescent tube is red (about 600n
m), green (about 550 nm), and blue (about 400 nm) strongly emit light, whereas external light such as sunlight has energy from infrared rays to ultraviolet rays. Therefore, for example, when trying to display green, only a light of 550 nm is displayed when a three-wavelength fluorescent tube is used, and thus a display color with high color purity is obtained, but when external light is used, it is from 500 nm to 600 nm.
Since light in a certain range is displayed as green, there is a problem that the color purity is low.

[0009]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal display device in which an illumination means required for a liquid crystal panel is usually a built-in backlight and external light is used as illumination means in a bright place such as outdoors. A video signal processing unit having a white balance circuit having a plurality of white balance adjustments in a video signal processing unit of a liquid crystal display device, white balance adjustment when a built-in light source is used as an illumination unit, and external light as an illumination unit. A white balance adjustment switching unit for switching between the white balance adjustment and the white balance adjustment is provided, and the color temperature of the display image is corrected by switching the white balance adjustment depending on the light source used.

Further, in the liquid crystal display device according to the present invention, when external light is used as a light source of the liquid crystal display device, an optical filter having a spectral transmittance characteristic close to the spectral characteristic of the built-in light emitting means is used. It corrects the temperature.

Furthermore, the liquid crystal display device according to the present invention is such that, when external light is used as the light source of the liquid crystal display device, the color temperature is increased by using an optical filter having a transmission peak near red, green and blue. is there.

[0012]

According to the present invention, in the video signal processing unit for processing the video signal input to the liquid crystal display device, the gains of the R, G and B signals are respectively obtained when the built-in backlight is used and when external light is used. By changing the value, good color temperature and color reproducibility can be obtained even when the built-in backlight and external light having a different balance of R, G, and B are used.

Further, according to the present invention, when external light having a spectral characteristic different from that of the backlight device built in the liquid crystal display device is used as a light source of the liquid crystal panel, the spectral characteristic of the external light is provided between the liquid crystal panel and the external light. Insert an optical filter that approximates the spectral characteristics of the built-in backlight device. As a result, good color temperature and color reproducibility can be obtained even when the built-in backlight and external light having a different balance of R, G, and B are used.

Further, according to the present invention, the liquid crystal display device is provided with an optical filter having a high transmittance at three wavelengths of red, green and blue, and a characteristic of reflecting or absorbing light in other wavelength regions. A display device having high color purity can be obtained even when external light is used as a light source.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described in detail below with reference to FIGS. 1 to 6. The same parts as those of the above-mentioned conventional example are designated by the same reference numerals, and the description thereof will be omitted. .

2 and 3 show the basic structure of the liquid crystal display device according to the present invention. In FIGS. 2 and 3, 1 is a liquid crystal panel, 2 is a diffusion plate, 3 is a light guide plate, 4 is a light source, and usually a three-wavelength fluorescent tube is used.
Etc. are used. Reference numeral 5 is a reflector which reflects the light from the light source to the liquid crystal panel side. Since the liquid crystal panel does not emit light by itself, it is necessary to illuminate it from the back. In the example shown in the figure, the liquid crystal panel 1 and the diffusion plate 2 (hereinafter, referred to as a liquid crystal panel section) are normally closed to display an image using the built-in light source 4. By opening and reflecting the external light by the reflection plate 5 to illuminate the liquid crystal panel 1, power consumption can be saved.

In the case of an AV liquid crystal panel, full color is displayed by a combination of a three-wavelength fluorescent tube and red, green, and blue (hereinafter abbreviated as R, G, B) color filters. In order to effectively use the light from the lamp, the R, G, and B peaks of the spectral transmittance of the color filter are near the red (600 nm), green (550 nm), and blue (450 nm) emission spectra of the three-wavelength fluorescent tube. According to. The emission spectrum of the lamp is almost fixed due to the R, G, B colors themselves.

Normally, the color temperature of the liquid crystal display screen is adjusted to about 6000 ° K to 7000 ° K when white is displayed, the balance of the R, G, B transmittances of the color filters, and the R of the fluorescent tube. , G, B energy ratio is designed.

FIG. 4 shows the spectral characteristics of the fluorescent tube, and FIG. 5 shows the spectral transmittance characteristics of the liquid crystal panel. In this example, the color temperature of the fluorescent tube is about 12000 ° K. On the other hand, as shown in FIG. 6, external light such as sunlight has a red and RGB energy ratio different from that of a fluorescent tube and has a strong red color temperature of 4000 ° K to 6 ° C.
As low as 000 ° K. Therefore, if external light is used as it is as a light source of the liquid crystal display device in a liquid crystal panel designed assuming the use of a fluorescent tube, the color becomes reddish.

Therefore, when the liquid crystal panel portion is opened and external light is used as a light source, the light having a yellow or red region is suppressed in order to correct the R, G, B energy ratio of the external light. R, G, B of video signals input to the liquid crystal panel
Change the gain of.

FIG. 1 shows an example of a signal processing circuit. In the figure, reference numerals 9, 10, 11 denote R, G, B input video signals, respectively. 12 is a circuit for adjusting the contrast of the R signal,
Reference numeral 13 is a circuit for adjusting the contrast of the B signal, 14 is a circuit for making various corrections such as image brightness and gamma, and 15 is an R
A circuit for adjusting the brightness of the signal, 16 is a circuit for adjusting the brightness of the B signal, and an output signal from this circuit is sent to a liquid crystal panel (not shown).

In the above-mentioned conventional liquid crystal display device, these adjustment items were almost fixed after adjusting once, except for adjusting the brightness. On the other hand, for example, when a fluorescent tube is used, the ratio of R, G, B gains is 1: 1:
1. When using outside light, set the contrast adjustment circuit to 1 so that the ratio changes to 0.9: 1: 1.02.
By switching the amplification factor of 3, the energy ratio of R, G, B of the external light passing through the liquid crystal panel is made close to the R, G, B energy ratio when the built-in light source is used, and the external light It is possible to improve color reproducibility and color temperature when used. Actually, when the outside light is used, the gain switching signal is input to the contrast adjusting circuits 12 and 13 from the outside.
As a result, the contrast adjusting circuits 12 and 13 are
The gain of is adjusted to a predetermined gain.

The gain switching signal may be manually generated or may be automatically generated in response to opening / closing of the liquid crystal panel 1. By adjusting the bright adjusting circuits 15 and 16, almost the same effect can be obtained.

Further, in this example, the outside light is treated as a light source having a lower color temperature than the built-in light source, but the outside light may have a higher color temperature depending on the type of the built-in light source. In that case, R, G, B should be controlled so that the light in the blue to green region is suppressed.
By designing the gain ratio of, the color temperature of the external light can be suppressed and the color temperature and color reproducibility of the result display screen can be improved.

The present invention is intended to improve color reproducibility and color temperature by changing the white balance of the video signal, and the structure of the display device itself is not limited to the above embodiment.

Next, another embodiment of the liquid crystal display device of the present invention will be described in detail with reference to FIGS. 7 to 9. The same parts as those in the above-mentioned one embodiment are designated by the same reference numerals and the description thereof will be omitted. Omit it.

FIG. 7 is a block diagram of the liquid crystal display device according to this embodiment.

In the figure, 1 is a liquid crystal panel, 2 is a diffusion plate, 3 is a light guide plate, and 4 is a light source. Usually, a three-wavelength fluorescent tube is used, as well as a light emitting diode, EL and the like. 5
Is a reflector that reflects the light from the light source to the liquid crystal panel side. 6 is an optical filter. Since the liquid crystal panel does not emit light by itself, it is necessary to illuminate it from the back. In the example shown in the figure, the liquid crystal panel 1 and the diffusion plate 2 (hereinafter, referred to as a liquid crystal panel section) are normally closed to display an image using the built-in light source 4. By opening and reflecting the external light by the reflector sheet 5 to illuminate the liquid crystal panel 1, power consumption can be saved.

In the case of a liquid crystal panel for AV, full color is displayed by a combination of a three-wavelength fluorescent tube and red, green and blue (hereinafter abbreviated as R, G and B) color filters. In order to effectively utilize the light from the lamp, the R, G, and B peaks of the spectral transmittance of the color filter are the emission spectrum of a three-wavelength fluorescent tube: red (600 nm), green (550 nm),
It is adjusted to near blue (450 nm). The emission spectrum of the lamp is almost fixed due to the R, G, B colors themselves.

Usually, the color temperature of the liquid crystal display screen is set to about 6000 ° K to 7000 ° K when white is displayed, the balance of the R, G, B transmittances of the color filters and the R of the fluorescent tube are adjusted. , G, B energy ratio is designed. The spectral characteristics of the fluorescent tube and the spectral transmittance characteristics of the liquid crystal panel are
This is as shown in FIGS. 4 and 5. On the other hand, external light such as sunlight is R, G,
The energy ratio of B is different, the red is strong, and the color temperature is 4000.
It is as low as ° K to 6000 ° K. Therefore, if external light is used as it is as a light source of the liquid crystal display device in a liquid crystal panel designed assuming the use of a fluorescent tube, the color becomes reddish.

Therefore, when the liquid crystal panel is opened and external light is used as the light source, in order to correct the energy ratio of R, G, and B of the external light, as shown in FIG. An optical filter 6 having a characteristic of suppressing spectral transmittance is provided. By passing light through this optical filter 6, R,
By making the energy ratio of G and B close to the energy ratio of R, G and B of the built-in light source, color reproducibility and color temperature when using external light can be improved. The position of the display device optical filter is not limited to the position shown in the figure.
The effect can be obtained if it is in the light path such as the front and back of the light guide plate.

Further, in this example, the outside light is treated as a light source having a lower color temperature than the built-in light source, but the outside light may have a higher color temperature depending on the type of the built-in light source. In that case, if you use a filter that suppresses light in the blue to green region,
It is possible to suppress the color temperature of external light and improve the color temperature of the result display screen.

The present invention is intended to improve color reproducibility and color temperature by allowing light to pass through the optical filter, and the structure of the display device itself is not limited to this embodiment. In this embodiment, the edge light type backlight using the light guide plate has been described, but the same effect can be obtained with the direct type backlight.

Further, the color temperature of the built-in light source is set to a color temperature similar to that of outside light, and R, G, and
By designing the balance of B transmittance, the gains of R, G, and B signals, the spectral reflectance of the reflector, and the LB filter on the assumption that outside light is used, the color temperature and color reproducibility can be improved depending on the light source. It won't get worse.

Further, another embodiment of the liquid crystal display device of the present invention will be described in detail with reference to FIGS. 10 to 12. The same parts as those in the above-mentioned one embodiment are designated by the same reference numerals.
The description is omitted.

FIG. 10 is a block diagram of the liquid crystal display device according to this embodiment.

In the figure, 1 is a liquid crystal panel, 2 is a diffusing plate, 3 is a light guide plate, 4 is a light source, and usually a three-wavelength fluorescent tube is used as well as a light emitting diode, EL or the like. Reference numeral 5 is a reflector which reflects the light from the light source to the liquid crystal panel side.
7 is an optical filter. Since the liquid crystal panel does not emit light by itself, it is necessary to illuminate it from the back. In the example shown in the figure, the liquid crystal panel 1 and the diffusion plate 2 (hereinafter, referred to as a liquid crystal panel section) are normally closed to display an image using the built-in light source 4. By opening and reflecting the external light by the reflector sheet 5 to illuminate the liquid crystal panel 1, power consumption can be saved.

In the case of an AV liquid crystal panel, full color is displayed by a combination of a three-wavelength fluorescent tube and red, green and blue (hereinafter abbreviated as R, G and B) color filters. Three-wavelength fluorescent tubes are red (600 nm), green (550 nm), blue (45 nm)
It emits strong light near 0 nm). The spectral characteristics of the fluorescent tube and the spectral transmittance characteristics of the liquid crystal panel are as shown in FIGS. 4 and 5. On the other hand, the outside light from sunlight etc.
As shown in FIG. 6, the energy ratio of R, G, and B is different from that of the fluorescent tube, and there is energy in all wavelengths from infrared rays to ultraviolet rays. Therefore, for example, when green is displayed, when a three-wavelength fluorescent tube is used as a light source, green is displayed near 550 nm.
As shown in 1, the light in the range of about 500 nm to 600 nm is displayed as green, and the display color is a color mixture with a low color purity.

Therefore, as shown in FIG. 12, an optical filter 7 having a characteristic of having a high transmittance at three wavelengths of red, green and blue and reflecting or absorbing light in other wavelength regions is used in a liquid crystal display device. Set up. The optical filter 7 having such characteristics is obtained by a thin film that reflects a specific wavelength or a material that absorbs light of a specific wavelength such as neodymium. In addition,
The condition of the spectral transmittance varies depending on each material, the light source, etc., and is not limited to that shown in FIG. 12 itself.

By passing external light through the optical filter 7 and making it the same as a light source having peaks in R, G and B like a three-wavelength fluorescent tube, high color purity is obtained even when external light is used as a light source. A display device can be obtained.

The position of the optical filter 7 in the display device is not limited to the position shown in FIG. 10, and the effect can be obtained if it is in the light path such as the front and back of the liquid crystal panel, the front and back of the light guide plate. At this time, since light of R, G, and B3 wavelengths of the fluorescent tube, which is a built-in light source, is almost transmitted through this filter, there is no optical problem even if it is always attached to the liquid crystal panel for use.

[0042]

As described above, according to the present invention, the spectral characteristic of the light source is corrected by switching the white balance between the use of external light and the use of the built-in backlight, or by attaching an optical filter. . As a result, it is possible to prevent deterioration of the color temperature, color reproducibility, and color purity of the display screen when external light is used as the light source of the liquid crystal display device, which has been a problem in the related art. Is.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a video signal processing unit that corrects a color temperature according to an exemplary embodiment of the present invention.

FIG. 2 is a perspective view illustrating a liquid crystal display device when using external light according to an embodiment of the present invention.

FIG. 3 is a side view illustrating a liquid crystal display device when using external light according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a spectral distribution of a three-wavelength fluorescent tube according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing spectral transmittance characteristics of a color filter of a liquid crystal panel according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a typical spectral distribution of sunlight.

FIG. 7 is a side view illustrating a liquid crystal display device when using an optical filter according to another embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a spectral transmittance of an optical filter according to another embodiment of the present invention.

FIG. 9 is an explanatory diagram showing an example of a spectral distribution of sunlight.

FIG. 10 is a side view showing a liquid crystal display device when using an optical filter according to another embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a spectral transmittance of an optical filter according to another embodiment of the present invention.

FIG. 12 is an explanatory diagram showing an example of a spectral distribution when the liquid crystal display device displays green.

FIG. 13 is a perspective view illustrating a conventional liquid crystal display device when using external light.

FIG. 14 is a side view illustrating a conventional liquid crystal display device when using external light.

[Explanation of symbols]

 1 Liquid crystal panel 2 Diffuser 3 Light guide 4 Light source 5 Reflector 6 Optical filter 7 Optical filter 8 Diffuse reflector 9 Image red signal 10 Image green signal 11 Image blue signal 12 Red signal contrast adjustment circuit 13 Blue signal contrast adjustment circuit 14 Image correction circuit 15 Red signal bright adjustment circuit 16 Blue signal bright adjustment circuit

Claims (3)

[Claims] 1. A light source required as an illuminating means for a liquid crystal panel, which is usually a light emitting means for emitting a built-in light,
In a liquid crystal display device that guides external light to the back surface of the liquid crystal panel as a lighting means in bright surroundings, when the video signal processing unit having a white balance circuit with multiple white balance adjustments and the built-in light source are used as the lighting means. Is equipped with a white balance adjustment switching unit that switches between the white balance adjustment and the white balance adjustment when external light is used as the illumination means, and the color temperature of the displayed image can be corrected by switching the white balance adjustment depending on the light source used. Characteristic liquid crystal display device. 2. A light source required as a lighting means for a liquid crystal panel, which is usually a light emitting means for emitting a built-in light is used,
In a liquid crystal display device that guides external light to the back surface of the liquid crystal panel to serve as a lighting means in a bright environment, when using external light as the lighting means for the liquid crystal panel, a spectral transmittance close to that of the built-in light emitting means is used. A liquid crystal display device characterized by correcting a color temperature using an optical filter having characteristics. 3. A light source required as a lighting means for a liquid crystal panel, which is usually a light emitting means for emitting a built-in light is used.
In a liquid crystal display device that guides external light to the back surface of the liquid crystal panel as a lighting means in bright surroundings, when using external light as lighting means for the liquid crystal panel, red,
A liquid crystal display device characterized by increasing the color purity by using an optical filter having a transmission peak near green and blue.