JP2001054121A - Color temperature correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color temperature correction device that can automatically control the color temperature of a photographed object continuously at high speed over a wide range. SOLUTION: The color temperature correction device consists of a liquid crystal filter 2 comprising one or a plurality of liquid crystal cells where a guest-host liquid crystal containing a dichromatic pigment is clamped by transparent bases with a transparent electrode and the absorption spectroscopy characteristic of the guest-host liquid crystal is controlled by a voltage applied to the transparent electrode, a color sensor 4 that detects a color temperature of a lighting light 3 and a voltage control section 7 that generates an AC voltage to be applied to the transparent electrode of the liquid crystal filter 2 on the basis of spectroscopy information from the color sensor 4. Since the voltage of the liquid crystal filter 2 whose absorption spectroscopy characteristic is controlled by an applied voltage is controlled on the basis of the spectroscopy information from the color sensor 4 detecting the color temperature of the lighting light 3 of the object, the color temperature of a video image obtained by photographing the object can continuously be controlled at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus capable of controlling a color temperature of an image of a subject, and more particularly to a color temperature correction apparatus suitable for photographing an image in a situation where an illumination light source changes variously.

[0002]

2. Description of the Related Art In photographing a subject, for example, in a television shooting involving movement inside and outside the room, when the subject moves from outdoors to indoors, the illumination light source changes from sunlight to indoor incandescent lamps. Color temperature greatly changes, the white balance of the captured image is lost, and accurate color tone cannot be reproduced.

Conventionally, in order to correct the color temperature in such a case, a color glass having a specific spectral characteristic has been inserted as a filter for correcting the color temperature into a photographing optical system of an imaging device such as a television camera. .

Alternatively, the signal intensity of the three primary colors (red, green, and blue) of a captured image is electronically amplified and attenuated, and the signal balance of each color is changed to correct the color temperature of the image. Was also adopted.

[0005]

However, the color temperature compensating filter using the color glass as described above has the following disadvantages.

1) Color glass must be mechanically inserted into the image pickup optical system, and it takes time to switch color temperature correction.

2) Since color glass has a fixed color temperature correction range, it can be applied only to a specific light source. To cope with various light sources, a plurality of different color glass filters are prepared, and Had to be replaced accordingly.

On the other hand, the method of electronically correcting the color temperature of an image by changing the signal balance of each color as described above also involves the followings. 1) A strong peak input of a specific color exceeding the dynamic range of an imaging device such as a CCD. Cannot cope, and cannot reproduce colors.

2) A weak color signal to be amplified causes a problem such as a reduction in a signal-to-noise (S / N) ratio, so that the color temperature range that can be corrected is limited.

The present invention has been made to solve such a problem, and an object of the present invention is to determine the color temperature of an object to be photographed (that is, the color temperature of a light image incident on an image sensor). It is an object of the present invention to provide a color temperature correction device capable of high-speed, continuous and automatic control over a wide range.

[0011]

In order to achieve the above-mentioned object, the invention of a color temperature correcting apparatus according to claim 1 is characterized in that a guest-host liquid crystal containing a dichroic dye is sandwiched between transparent substrates with transparent electrodes, A liquid crystal filter composed of one or more liquid crystal cells in which the absorption spectral characteristic of the guest host liquid crystal is controlled by a voltage applied to the transparent electrode, a color sensor for detecting a color temperature of illumination light of a subject, and the color sensor. And a voltage controller for generating an AC voltage to be applied to the transparent electrode of the liquid crystal filter based on the spectral information.

Here, the color sensor includes at least two or more photodetectors for detecting light in different visible wavelength ranges, and acquires spectral information of incident light.

Further, the voltage control section determines an AC voltage intensity to be applied to the transparent electrode of the liquid crystal filter according to a ratio or a difference between electric output signals from the two or more photodetectors of the color sensor. Can be characterized.

Further, the liquid crystal filter may be characterized in that the liquid crystal cells in which the molecular orientation is orthogonal are stacked to eliminate the polarization dependence of the liquid crystal filter. Alternatively, the molecular orientation of the guest-host liquid crystal containing the dichroic dye is twisted.

The absorption characteristics of the dichroic dye of the liquid crystal filter are designed in consideration of the spectral ratio between incandescent lamp and sunlight, and are obtained by mixing at least two types of dichroic dyes having different absorption peak wavelengths. Thus, it is possible to obtain characteristics that are substantially the same as those of an existing color glass filter.

Further, the color sensor may be integrated with the voltage control unit.

Further, the color sensor and the voltage control section may be integrated with an image pickup device.

Further, the liquid crystal filter may be provided in front of an imaging lens of an imaging device or between the imaging lens and an imaging device.

(Function) The color temperature compensator according to the present invention
The voltage control of the liquid crystal filter that can control the spectral characteristics of the transmitted light is performed based on the spectral information from the color sensor that receives the illumination light. By changing the applied voltage, the molecular orientation of the dichroic dye in the liquid crystal filter is controlled at a high speed of several tens of milliseconds, and the color temperature of the captured subject image can be instantaneously corrected.

Further, the voltage intensity applied to the liquid crystal filter is automatically changed in accordance with the color temperature of the light source of the illumination, so that the color temperature of the subject image is continuously controlled.

In addition, since the liquid crystal filter always keeps the color temperature of the light image incident on the image pickup device at an appropriate value, it is possible to perform a wide range of color temperature correction of a captured image.

Therefore, the use of the color temperature correcting apparatus of the present invention enables the photographing with excellent image quality even in a photographing environment where the light source changes.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of a color temperature correction device according to the present invention. The color temperature correction device according to the present embodiment includes a liquid crystal filter 2 in which the absorptance (absorption spectral characteristic) of a specific wavelength component changes with respect to incident light 1 from a subject according to the intensity of an applied voltage, and illumination light 3 from the subject. A color sensor 4 for detecting color temperature information (spectral information), and an electric signal (spectral information) sent from the color sensor 4 via a lead wire 6 and an appropriate AC signal to the liquid crystal filter 2 according to the electric signal. And a voltage controller 7 for supplying a voltage via a lead wire 6.

Since the liquid crystal filter 2 is driven by the voltage control unit 7 based on the spectral information of the color sensor 4, the transmitted light of which the color temperature of the incident light 1 has been corrected is transmitted to an image pickup device (not shown) in the video camera 8. No), and the color temperature of the captured image is automatically corrected.

The liquid crystal filter 2 is inserted into an imaging optical system of a video camera 8 and is mounted in front of an imaging lens (for example, a zoom lens) 9 in the embodiment of FIG. Power for the voltage control unit 7 and the color sensor 4 is supplied from the video camera 8 via the lead wire 10.

FIG. 2 shows an embodiment of the liquid crystal filter 2. The liquid crystal filter 2 for converting the color temperature is composed of two guest-host liquid crystal cells 15 in which a liquid crystal 12 containing molecules of a dichroic dye 11 having different light absorption rates depending on the molecular arrangement is sandwiched between a pair of glass substrates 14 with transparent electrodes 13. Consists of The added dichroic dye 11 does not absorb the long-wavelength light 16 (red light) and has a spectral characteristic that the shorter-wavelength light 17 (blue light) absorbs more strongly. 18 has the function of lowering the color temperature.

The AC voltage 1 is applied to the transparent electrode 13 of the liquid crystal cell 15.
When 9 is not applied, as shown in FIG. 2A, the molecules of the liquid crystal 12 and the molecules of the dichroic dye 11 are oriented parallel to the glass substrate 14 (homogeneous orientation). Strongly absorb the blue light 17 vibrating in the direction of the dye molecules.

On the other hand, when a voltage is applied to the transparent electrode 13 of the liquid crystal cell 15, the molecules of the dichroic dye 11 together with the molecules of the liquid crystal 12 are oriented in the direction of the electric field, as shown in FIG.
That is, both molecules rise perpendicular to the substrate, and the absorption of blue light 17 decreases, so that the color temperature of transmitted light 18 increases. By changing the voltage intensity to the transparent electrode 13, the arrangement direction of the molecules of the liquid crystal 12 and the molecules of the dichroic dye 11 change in an analog manner.
Is continuously controlled.

In order to lower the color temperature of the light source in this way, it is possible to use one type of dichroic dye 11 having an absorption peak on the short wavelength side in the liquid crystal filter 2, but a plurality of dichroic dyes 11 having different absorption peak wavelengths can be used. The dichroic dye 11 is desirably combined to have spectral characteristics such that the shorter wavelength light 17 gradually absorbs more. Conversely, a single dye or multiple
If the long-wavelength light 16 is made to have a higher light absorption characteristic by using the chromatic pigment 11, it is possible to raise the color temperature more than the light of the original light source.

Since the dichroic dye 11 strongly absorbs the vibration component (polarization component) of light in the direction of the major axis of the molecule, the liquid crystal cell 15 whose molecular orientation is orthogonal in the configuration example of FIG.
By stacking the sheets, the polarization dependence of light absorption is eliminated.

On the other hand, the liquid crystal filter 2 can be constituted by using one liquid crystal cell 15,
In that case, a polarizing film (not shown) is
If it is arranged before or after the above, only one of the polarized light components can be used, and the light loss of the transmitted light 18 increases. On the other hand, liquid crystal 1
It is also possible to configure a liquid crystal cell (white tailor type guest-host liquid crystal) in which the orientation of the two molecules is twisted and their torsion axes are set in the horizontal or vertical direction with respect to the glass substrate 14. In that case, a polarizing film is used. The liquid crystal filter 2 can be realized with only one liquid crystal cell without using the liquid crystal cell, and the utilization efficiency of the incident light 1 can be increased.

In the configuration example of the liquid crystal filter 2 shown in FIG. 2, when the AC voltage 19 is not applied to the transparent electrode 13, the liquid crystal cell 15 is homogeneously aligned.
2 has a positive dielectric anisotropy, but homeotropic alignment in which liquid crystal molecules stand with respect to the glass substrate 14 in the absence of an applied voltage is also applicable to the present invention. 12 has a negative dielectric anisotropy.

As a material of the liquid crystal 12, a smectic liquid crystal, a nematic liquid crystal, and a cholesteric liquid crystal can be used, but a nematic liquid crystal is advantageous for obtaining a high-speed response.

[0035]

Next, an example of actual production of a color temperature compensator according to the present invention and measurement results will be described in detail.

A liquid crystal filter shown in FIG.
First, In was placed on a soda glass substrate 14 having a thickness of 1.1 mm.
_A 0.07 μm thick transparent electrode 13 made of ₂ O ₃ : Sn was deposited. Next, a thickness of 0.05 μm is formed on the transparent electrode 13.
After applying a polyimide film (AL-1254, manufactured by Nippon Synthetic Rubber Co., Ltd.), a rubbing alignment film was formed by rubbing with a rayon roll. In FIG. 2, the rubbing alignment film is not shown. Next, two substrates 14 with the alignment film were bonded to each other with a spherical spacer (Nippon Shokubai Co., Ltd., GP-H60, 6 μm diameter) facing the alignment film. The gap between the two substrates 14 was 6 μm.

In this gap, the dichroic dye 11 having an absorption peak wavelength of 390 to 398 nm (Japan Photographic Dye Laboratories, G-207) and an absorption peak wavelength of 543 to 543 nm are used.
556 nm dichroic dye 11 (Japan Photographic Dye Institute, G
-471) were added at 2 wt% and 0.
Nematic liquid crystal 12 (Merck Japan Ltd., BL-008, dielectric anisotropy Δε = 17.3,
Refractive index anisotropy (n = 0.28) was filled. The addition ratio of the dye 11 is based on the total amount of the liquid crystal 12 and the dye.

Light 1 of various wavelengths is applied to the liquid crystal filter 2 in which the two liquid crystal cells 15 thus prepared are laminated.
FIG. 3 shows the result of measuring the transmittance.
When no voltage is applied to the liquid crystal filter 2, the wavelength 7
The spectral characteristics show that the transmittance decreases as the wavelength decreases from 00 nm to 400 nm. This characteristic is based on the existing colored glass filter (HOYA, LA-1) shown for reference.
This is a characteristic similar to (40).

On the other hand, 5 V is applied to the color temperature correction filter 2.
Is applied, the transmittance increases at a wavelength of about 650 nm or less. As described above, it was confirmed that the absorption spectral characteristics of the liquid crystal filter 2 can be controlled by the applied voltage. FIG. 3 shows that the color temperature lowered by application of the voltage of 5 V approaches the color temperature of the light source.

The light of the xenon lamp of 100 W is passed through the liquid crystal filter 2 described above, and the color temperature of the transmitted light 18 is measured while changing the voltage applied to the liquid crystal filter 2 by a color thermometer (COLOR-Minolta, Inc.). METER
The result (measured value) measured in 2) is shown by a solid line in FIG. From FIG. 4, it was confirmed that in the liquid crystal filter 2, by continuously changing the applied voltage up to 10 V, the color temperature can be continuously reduced within a specific range (3500 K to 5000 K). . The response speed of the liquid crystal filter 2 to a change in the applied voltage was as fast as 100 ms or less.

In order to drive the liquid crystal filter 2 accurately with voltage, the color temperature of the illuminating light 3 from the direction of the subject must be grasped. In normal shooting, the illumination light 3 also reaches the position of the video camera 8. Therefore, in this embodiment, separately from the video imaging system of the video camera 8,
Is attached to the video camera 8 with a small color sensor 4 that detects the direction from the subject.

The color sensor 4 includes at least two light detecting elements for detecting light in different visible wavelength ranges,
The spectral information of the incident light 1 is obtained. It is possible to use an existing color thermometer for the color sensor 4, but in that case, since the absolute value of the color temperature is obtained, the electronic circuit becomes complicated and the device becomes large.

Here, as one embodiment, the color sensor 4 and the voltage control unit 7 shown in the configuration example of FIG. 5 were prototyped to reduce the size and cost of the drive system. That is,
The intensities Pb and Pr of the blue light 17 and the red light 16 constituting the illumination light 3 from the subject direction are detected by the blue light detection element 21 and the red light detection element 22 of the color sensor 4 at a wide angle (120 °), and the color is detected. As an indication of the temperature, the arithmetic circuit 23 of the voltage control unit 7 uses the intensity ratio of blue light to red light (Pb / P
r) was determined. The difference signal between the blue light and the red light (Pb−
It is possible to use Pr) as a guide for voltage control. In this case, however, the control voltage of the liquid crystal filter 2 depends on the absolute value of the amount of light, in addition to the intensity balance at each wavelength, so that the signal ratio Signal strength (Pb / Pr) is more advantageous.

Blue and red light detecting elements 21 and 22
Have sensitivity wavelengths of 400 nm to 500 nm and 5
Hamamatsu Photonics' silicon photodiodes S6428 and S6430 of 60 nm to 660 nm were used.
FIG. 6 shows their spectral sensitivity characteristics.

Further, in order to simplify the voltage control unit 7 of FIG. 1, the color temperature characteristic of the liquid crystal filter 2 is linearly changed with respect to the measured value of the solid line as shown by the model value of the broken line in FIG. , And the upper limit of the AC voltage applied to the liquid crystal filter 2 is 4 V with an incandescent lamp (3200 K), and the lower limit is 0.5 V with sunlight (color temperature of 5000 K or more).
The signal intensity ratio was reduced in proportion to the value of Pb / Pr.

The above-described color sensor 4 and voltage control section 7 are preferably integrated with each other or integrated with an image pickup device 8 such as a television camera. By using the power supply from the above, the entire drive system can be made compact. The prototype voltage control unit 7 has a small size of 100 × 65 × 35 mm, so that it can be easily mounted on the video camera 8 main unit. Further, the DC power supply 12 V for driving the zoom lens of the video camera main unit is connected to the power supply of the voltage control unit 7. Can be shared as Furthermore, the liquid crystal filter 2 (effective diameter 80 mm)
It was stored in a holder in front of the zoom lens 9 facing the subject. Since the liquid crystal filter 2 is compact, it can be inserted between the imaging lens 9 and the imaging device (not shown) of the video camera 8.

FIG. 7 shows the operating characteristics of the liquid crystal filter 2 on the chromaticity diagram. Since the chromaticity of the liquid crystal filter 2 changes along a black body radiation curve (shown by a broken line) according to the voltage applied to the liquid crystal filter 2, no color shift occurs. Actually, it was confirmed that white and skin color were naturally reproduced both indoors (incandescent light) and outdoors (sunlight), and that the color balance was smoothly converted and corrected without a sense of incongruity. Also, the operation was good under a fluorescent lamp (4500K).

(Other Embodiments) The present invention can be applied not only to a moving image camera but also to a still image camera.

[0049]

As described above, according to the present invention,
The liquid crystal filter containing dichroic dyes is configured to control the voltage appropriately based on the spectral information of the illumination light acquired by the color sensor, so that the color temperature of the captured image of the subject can be continuously and rapidly increased. Can be controlled automatically.

Therefore, the color temperature correction apparatus of the present invention has the advantages that it can seamlessly take pictures indoors and outdoors, can respond to instantaneous scene changes by high-speed operation, and can be attached to and detached from a conventional camera because it is compact. However, due to these advantages, this device is expected to be effective in broadcast programs where the illumination light changes in various ways, and can be applied to a wide range of optical photography applications, such as television and movie shooting. It is.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of one embodiment of a color temperature correction device of the present invention.

FIGS. 2A and 2B are diagrams illustrating an operation example of the liquid crystal filter of the present invention, wherein FIG. 2A is a conceptual diagram illustrating a state in which no voltage is applied, and FIG.

FIG. 3 is a characteristic diagram showing an example of the relationship between the wavelength of incident light and the transmittance of the liquid crystal filter according to the present invention.

FIG. 4 is a characteristic diagram showing an example of a relationship between an applied voltage and a color temperature of a liquid crystal filter according to the present invention.

FIG. 5 is a block diagram illustrating a configuration example of a color sensor and a voltage control unit according to the present invention.

FIG. 6 is a characteristic diagram showing an example of the relationship between light sensitivity (output current) and wavelength of a photodetector of a color sensor according to the present invention.

FIG. 7 is a characteristic diagram showing an example of chromaticity characteristics of the liquid crystal filter according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incident light 2 Liquid crystal filter 3 Illumination light 4 Color sensor 5 Lead wire 6 Lead wire 7 Voltage control unit 8 Imaging device (video camera) 9 Zoom lens 10 Lead wire 11 Dichroic dye 12 Liquid crystal 13 Transparent electrode 14 Glass substrate 15 Liquid crystal Cell 16 Red light 17 Blue light 18 Transmitted light 19 AC voltage 20 Switch 21 Blue light detection element 22 Red light detection element 23 Arithmetic circuit 24 Limiting circuit 25 Bias circuit 26 Multiplier 27 AC oscillator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tahito Aida 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan Broadcasting Corporation Research Institute (72) Inventor Kenichi Iwashita 1-11-1 Higashisakura, Higashi-ku, Nagoya-shi No. Japan Broadcasting Corporation Nagoya Broadcasting Station (72) Inventor Shinya Umeda 1-11-1 Higashisakura, Higashi-ku, Nagoya-shi F-term in Nagoya Broadcasting Station F-term (reference) 2H088 EA22 EA49 JA06 MA05 5C065 AA01 BB01 DD02 EE15 EE20

Claims (9)

[Claims] 2. A liquid crystal display comprising: a guest-host liquid crystal containing a dichroic dye sandwiched between transparent substrates having a transparent electrode; and one or more liquid crystals in which absorption spectral characteristics of the guest-host liquid crystal are controlled by a voltage applied to the transparent electrode. A liquid crystal filter composed of cells; a color sensor for detecting a color temperature of illumination light of a subject; and a voltage controller for generating an alternating voltage to be applied to the transparent electrode of the liquid crystal filter based on spectral information from the color sensor. And a color temperature correction device. 2. The color according to claim 1, wherein the color sensor includes at least two or more photodetectors for detecting light in different visible wavelength ranges, and acquires spectral information of incident light. Temperature correction device. 3. The voltage control unit determines an AC voltage intensity applied to the transparent electrode of the liquid crystal filter according to a ratio or a difference between electric output signals from the two or more photodetectors of the color sensor. 3. The color temperature correction device according to claim 1, wherein 4. The color temperature according to claim 1, wherein the liquid crystal filter is formed by laminating liquid crystal cells in which molecular orientations are orthogonal to each other to eliminate polarization dependence of the liquid crystal filter. Correction device. 5. The color temperature correction device according to claim 1, wherein the molecular orientation of the guest-host liquid crystal containing the dichroic dye is twisted. 6. The absorption characteristic of the dichroic dye of the liquid crystal filter is designed in consideration of the spectral ratio between incandescent lamp and sunlight, and a mixture of at least two types of dichroic dyes having different absorption peak wavelengths. 6. A color temperature compensator according to claim 1, wherein said color temperature filter has characteristics substantially equivalent to those of an existing color glass filter. 7. The color temperature correction device according to claim 1, wherein the color sensor is integrated with the voltage control unit. 8. The color temperature correction device according to claim 1, wherein the color sensor and the voltage control unit are integrated with an imaging device. 9. The liquid crystal filter according to claim 1, wherein the liquid crystal filter is mounted in front of an imaging lens of an imaging device or between the imaging lens and an imaging element. 3. The color temperature correction device according to 1.