JPS63169196A - Automatic white balance correcting device - Google Patents

Abstract

PURPOSE:To perform the adequate correction of a white balance by means of detecting automatically that a special light source such as a fluorescent lamp, etc., is the light source, when it is used by outputting a prescribed color balance control signal when a prescribed color temperature is detected. CONSTITUTION:By setting a reference voltage Vrefi lower than the output voltage of an amplification circuit 9 in the case of, for instance, the fluorescent lamp (white color), a comparison circuit 12 outputs the output of 'H' level. Besides, because an intensity of illumination is low under a general fluorescent lamp illumination, by setting the reference voltage at the value at the time of the prescribed intensity of illumination, which a photosensor 5 detects, the comparison circuit 12 outputs the 'H' level when it is darker than the general fluorescent lamp illumination. When the color temperature of an external light is high and the intensity of illumination is low, the fluorescent lamp is detected by getting the logical product of the outputs of the respective comparison circuits 12 by means of an AND circuit, and the correction at the time of the fluorescent lamp is performed by a switching circuit. Thus, when the light source of a camera is the special light source, not conforming to Plank's law of radiation, such as the fluorescent lamp, etc., it is automatically detected and the white balance can be adequately corrected.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides automatic whitening in video cameras, etc.
The present invention relates to a balance correction device.

(Prior Art) FIG. 5 shows a configuration block diagram of an example of this type of automatic white balance correction circuit in a conventional video camera or electronic camera. 21 is an infrared cut filter, 22 is a red filter, 23 is a blue filter, 24.25 is a pair of 7-point sensors, 26.27 is a pair of logarithmic compression circuits, 28 is a subtraction circuit, 29 is an amplifier, and 30 is a control signal generator. In the circuit
31 represents an own balance correction signal.

To summarize the operation, external light that has entered through the infrared cut filter 21 passes through the red filter 22 and the blue filter 23 and is inputted to each of the photosensors 24 and 25, respectively. Each of the logarithmic compression circuits 26 and 27 is a circuit for logarithmically compressing each signal output from the photosensors 24 and 25.
6, the output of the other logarithmic compression circuit 27 (X
This is a circuit for subtracting Gin. The output signal from the subtraction circuit 28 uniquely corresponds to each output signal ratio of the photosensors 24 and 25.

Furthermore, the amplifier circuit 29 converts the output from the subtracter 28 into
The control signal generation circuit 30 performs correction control for controlling a gain control amplifier (not shown) that performs self-balance correction based on the output signal from the amplifier circuit 29. This is a circuit for creating a signal 31.

As described above, since the output from the subtracter 28 corresponds to the ratio of the red component to the blue component of the incident light, if the amplifier circuit 29 and the control signal generation circuit 30 are appropriately set, An appropriate self-balance correction control signal 31 for color temperature,
It can be output from the control signal generation circuit 30.

(Problem to be Solved by the Invention) However, in the conventional configuration as described above, three rays under illumination having a spectral radiant emittance close to the value given by the "blank radiant (formula)" are used. However, under the illumination of a light source that does not approximate the blank radiation agent, such as a light source with a special spectral distribution such as a fluorescent lamp, it is difficult to correct the white balance correctly. There were many things I couldn't do.

The present invention has been made in view of one or more of the problems of the conventional example, and aims to provide a means for eliminating the above-mentioned drawbacks and enabling good automatic white balance correction even under illumination such as fluorescent lighting. The purpose is

(Means for Solving the Problem) Therefore, in the present invention, a plurality of photosensors having different spectral transmission characteristics, a first detection means for detecting color temperature from the output ratio of the photosensors, and an outside light a second detection means for detecting the brightness of the light beam, and configured to output a predetermined color balance control signal when a predetermined color temperature is detected by the first detection means;
This aims to achieve the above objective.

(Function) With the above configuration, when the light source in a video camera or the like is a special light source such as a fluorescent lamp, this can be automatically detected and appropriate white balance correction can be performed.

(Example) The present invention will be explained below based on examples.

FIG. 1 shows a block diagram of an embodiment of an automatic white balance correction circuit for a television camera according to the present invention.

(composition) In FIG. 1, l is an infrared cut filter.

2 is a red filter, 3 is a green filter, 4.5 is a pair of photosensors each having a red/green filter 2/3 on the front, 6.7 is a photosensor 4.5, respectively.
8 is a subtracter for subtracting the output Iba code of the other logarithmic compression circuit 6 from one logarithmic J, E compression circuit 7; ,
An amplifier circuit 10 converts the output No. 16 from the subtracter 8 to a level that is easy to process No. 15, and 10 is a control circuit No. 8 for self-balance correction from the output signal from the amplifier circuit 9, together with a switching circuit 15. This is a control signal generation circuit for creating two systems of 16.

Next, 11 is an amplification circuit for amplifying the output signal from the logarithmic compressor 7, and 12 is an amplification circuit for amplifying the output signal from the amplification circuit 9.
If it is larger than the predetermined reference voltage V ref+, “
A comparison circuit 13 for outputting an "H" level and otherwise outputting an "L" level outputs an "H" level when the output from the amplifier circuit 11 is small compared to another predetermined reference voltage v112. "H" level, otherwise "L"
This is a comparison circuit for outputting the level. 14 is an AND circuit that takes the AND of both comparison circuits 12 and 13; 15 is
This is a switching circuit for switching to the switch terminal a side when the output from the AND circuit 14 is at the "L" level, and switching to the switch terminal A side when the output from the AND circuit 14 is at the "H" level.

VFLI, V□, 2 are preset voltages applied to each of the switch terminals, and these voltages correspond to the R:G:
The control voltage value is such that B is 1:1:1.

(Operation) Next, the operation of the above configuration will be explained with reference to FIGS. 2 to 4. FIG. 2 is a characteristic diagram of wavelength of incident light versus relative radiant emittance, FIG. 3 is a characteristic diagram of incident light wavelength versus spectral transmittance of each of the optical filters, and FIG. 4 is a characteristic diagram of incident light wavelength versus spectral transmittance. 2 is an operation sequence flowchart of the present embodiment.

In Fig. 2, characteristic curve A is a fluorescent lamp (white) as an example of a specific light source, curve B is a color temperature of 3200K, and curve C is an outline of the relative spectral radiant emittance of each light source with a color temperature of 8500 as a reference light source. The horizontal axis shows the wavelength (
(unit: nm), and the relative radiant emittance is plotted on the vertical axis.

Moreover, FIG. 3 is a diagram showing M and L in the spectral transmittance characteristics of the infrared cut filter 1, red filter 2, and green filter 3 in FIG. 1, respectively, and the horizontal axis is the wavelength (unit: nm). , the transmittance (%) is plotted on the vertical axis.

Each characteristic curve M.

In the illustrated example, L has a predetermined half-width centered around a specific wavelength of about 635 nm.

In FIG. 1, external light incident through the infrared cut filter 1 reaches each of the seven sensors 415 through the red/green filters 2/3. Bowl logarithmic compressor 6.7
The output characteristics of the filters increase monotonically with respect to the amount of incident light, and the optical characteristics of the infrared cut/red/green filters 1/2/3 are shown in /M/L in Figure 3. and the spectral sensitivity characteristics of each photosensor 415 are similar to the visual characteristics of the human eye (for example, a
-3i (amorphous silicon) photodiode, etc.), subtraction P! The output potential of I8 is It o
gB/R, the color temperature is increased in proportion to the color temperature of external light incident on the infrared cut filter 1.

As mentioned above, if the red/green outside filter 2/3 is selected to have the characteristics shown in Figure 3 M/L, the external light incident on the infrared cut filter 1 will be changed to the fluorescent lamp (white) shown in Figure 2. When the fluorescent lamp has A characteristics, there is almost no R component of the fluorescent lamp, so the output voltage of the subtracter 8 in FIG.
(e.g. 8500).

This effect is greater than that using R and B sensors for fluorescent lamps.
This is because it is easy to detect a decrease in the spectrum at a wavelength of 00 nm or more.

The potential of the reference voltage V rpfl in FIG.
By setting the output potential slightly lower than the output potential of the comparator circuit 12, the output of the comparator circuit 12 is at the "H" level in the case of the -F A characteristic. In addition, in general fluorescent lighting F,
Since the illuminance is low to some extent (for example, less than 1000j2ux, there are few cases of
ffiux), the comparator circuit 13 outputs the "H" level when it is darker than general fluorescent lighting.

When the color temperature of outside light is high to some extent and the illuminance is low (in this example, the color temperature is 8500K, 1000ffiu
(below x) is extremely small, so the AND circuit 14 takes the logical product of the outputs of each comparison circuit 12 and 13 to detect the fluorescent lamp (white), and the switching circuit 15 detects the L distribution light. Correct the case of a light (gain 311 to weaken G). )It is carried out.

The flowchart in FIG. 4 shows for reference the outline of the sequence when controlled by microcomputer software.

As described above, when the light source of the camera is a special light source that does not follow the blank radiation law, such as a fluorescent lamp, this can be automatically detected and appropriate white balance correction can be performed.

(Other Embodiments) In the Embodiment, an example was shown in which the illuminance of the light source was detected based on the output level of the photosensor 5.
For example, the output of the waste photo sensor 4.5 may be calculated and applied.
Alternatively, each of the photosensors 4. It is also possible to apply outputs of photosensors other than '5.

In addition, as the illuminance detection means mentioned above, the camera's bidet 4'A
``Although the f-level can be used, it is also possible to detect and apply the opening of the aperture blades for exposure control.

Furthermore, in the embodiment, fluorescent lamps are detected by detecting the output ratio of the R and 6 sensors 415, but the outputs of the R and Cy (cyan) sensors may also be used.

In short, it is sufficient to detect the sharp fall on the right side of the 600 nm peak of the fluorescent lamp spectrum (FIG. 2A) by the output ratio of the R filter 2 and the G filter 3.

It goes without saying that other color sensors (for example, B sensor) may also be included.

(Effects of the Invention) As explained above, according to the present invention, even when a video camera or the like encounters a special light source such as a fluorescent lamp, it can automatically detect this and achieve a good self-adjustment. Balance correction can now be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the self-balance correction circuit according to the present invention, FIG. 2 is a graph showing the incident light wavelength versus relative radiant emittance characteristic, and FIG. 3 is a diagram showing the incident light of each optical filter. FIG. 4v4 of the wavelength vs. spectral transmittance characteristic diagram is an operation flowchart in the case of a fluorescent lamp light source in this embodiment, and FIG. 5 is a block diagram of an example of a conventional white balance correction circuit. 2/3-----One red/green filter (optical filter)
4.5--7 Auto sensor 8--1 Subtractor 9.11-1 Amplifier 10--1 Control signal generator 12.13-1 Comparison vessel

Claims (5)

[Claims] (1) A plurality of photosensors each having different spectral transmission characteristics, a first detection means for detecting color temperature from the output ratio of the photosensors, and a second detection means for detecting the brightness of external light rays. 1. An automatic white balance correction apparatus comprising: a detection means, and configured to output a predetermined color balance control signal when a predetermined color temperature is detected by the first detection means. (2) The automatic white balance correction apparatus according to claim 1, wherein the second detection means is configured to apply the output of at least one of the plurality of photosensors. (3) The automatic white balance correction device according to claim 1, wherein the second detection means is configured to calculate and apply each output of the plurality of photosensors. (4) The automatic white balance correction apparatus according to claim 1, wherein the second detection means is configured to apply the output of a light receiving means other than the plurality of photosensors. (5) The automatic white balance correction device according to claim 4, wherein the light receiving means converts an optical image into a video signal.