JP3491032B2 - Automatic white balance control circuit for electronic still video camera - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance control circuit for an electronic still video camera.

[0002]

2. Description of the Related Art As a general white balance control method for strobe emission in a conventional automatic white balance control circuit of an electronic still video camera, a set value for a color temperature detected from a light source other than strobe is used during strobe emission. Instead, a method of shooting with a fixed white balance setting value according to the color temperature of the strobe is used.

Further, when the measured distance is equal to or greater than a predetermined value, a method of determining a white balance correction value is used without using a strobe (see Japanese Patent Laid-Open No. 141786/1993), and distance information between a subject and an image sensor is used. There is known a method of making an error less likely to occur when the strobe light does not sufficiently reach the subject, such as a method of correcting color temperature information at the time of strobe light emission (see Japanese Patent Laid-Open No. 2-288575).

[0004]

A conventional white balance control method for an electronic still video camera in an automatic white balance control circuit at the time of strobe emission is to adjust the white balance based only on the color temperature of the strobe light. When the color temperature of the light source is greatly different from that of the strobe light source and the subject and the background are far apart, the color tone of the subject and the color tone of the background are significantly different, which may cause unnatural appearance.

As an example, when a gray scale chart is photographed against a white wall as a background under a fluorescent lamp, if the white balance is photographed in accordance with the color temperature of strobe light, the gray scale chart White balance correction is applied so that the color difference becomes zero, and it becomes completely achromatic.
White walls appear yellow. At this time, if the gray scale chart occupies only a small area on the screen, it tends to give an impression that the white balance is totally displaced.

Further, the method of determining the white balance correction value for strobe light according to the distance between the background and the subject adds the color temperature information of the surrounding light source to the control reference when the strobe light does not reach the subject sufficiently. However, when the strobe light reaches the subject sufficiently, the above-mentioned problem occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to reduce the frequency of capturing an unnatural image when the color tone of the subject and the color tone of the background are greatly different when the strobe is made to emit light. It is a thing.

[0008]

In order to achieve the above object, the present invention has a zoom mechanism having means for outputting a zoom position according to a zoom magnification of an optical system, and uses a charge-coupled device as an imaging device. In the automatic white balance control circuit of the electronic still video camera used, a color temperature detection circuit that detects the white balance control value corresponding to the color temperature of external light based on the image signal when pre-exposure is performed without flashing the strobe. When the flash is emitted during shooting, the average value of both the white balance control value output from the color temperature detection circuit and the initial setting value corresponding to the color temperature of the flash light set in the memory is detected. , A white balance correction circuit for performing white balance control by converting to a white balance correction amount. In this white balance correction circuit, the white balance control value of the color temperature detection circuit and The weighted average value of both of the initial setting value corresponding to the color temperature of the strobe light set in the memory is provided by means of weighting at a fixed ratio, and the white balance correction amount is converted to the white balance correction amount. An automatic white balance control circuit for an electronic still video camera configured to perform balance control, comprising means for adjusting a weighting ratio when detecting a weighted average of control values in the white balance correction circuit. Thus, based on the output of the zoom mechanism, the weight of the control value output by the color temperature detection circuit is increased as the zoom magnification is lower, and the color temperature of the strobe light set in the memory is increased as the zoom magnification is increased. The weight of the corresponding initial setting value is increased, the weighted average value is detected, the white balance correction amount is converted, and the white balance control is performed. To.

Further, a focus mechanism having means for outputting the focus position of the optical system is provided, and when adjusting the weighting ratio when detecting the weighted average value of the control values in the white balance correction circuit, Based on the output of the focus mechanism, the weight of the white balance control value output from the color temperature detection circuit is increased as the distance to the subject increases, and the color of the strobe light set in the memory increases as the distance to the subject decreases. The weight of the initial setting value corresponding to the temperature is increased, and based on the output of the zoom mechanism, the weight of the control value output from the color temperature detection circuit is increased as the zoom magnification is lower, and the memory is increased as the zoom magnification is increased. The weight of the initial setting value corresponding to the color temperature of the strobe light set to is increased, the weighted average value is detected, and the white balance correction amount is converted to the white balance control. Characterized by being configured to perform.

[0010]

In the automatic white balance control circuit of the electronic still video camera according to the present invention having the above-described structure, when the strobe is made to emit light, preliminary exposure is performed without emitting the strobe light in advance.
Based on the image signal at that time, the average value of both the white balance correction value corresponding to the color temperature of the light source detected by the color temperature detection circuit and the white balance correction value for the color temperature of the strobe light set in the memory. Is detected and converted into a white balance correction amount, and white balance control is performed during main exposure for recording an image.

By providing a means for weighting the white balance correction value detected by the color temperature detection circuit and the white balance correction value for the color temperature of the strobe light set in the memory at a constant ratio, a weighted average of both is obtained. Find the value,
By converting to a white balance correction amount, both weighted average values are detected, and by converting to a white balance correction amount, it is possible to perform more comfortable white balance control during main exposure.

A zoom mechanism for detecting the zoom position of the optical system when determining the weighting ratio of both the white balance correction value detected by the color temperature detection circuit and the white balance correction value for the color temperature of the strobe light. Based on the output of, the weight of the white balance correction value detected by the color temperature detection circuit is increased as the zoom magnification of the optical system is lower, and the weight of the initial setting value with respect to the color temperature of the strobe light is increased as the zoom magnification is increased. By providing the means and detecting the weighted average value of both of them, and converting the weighted average value into the white balance correction amount, it is possible to perform good white balance control in which the zoom magnification is taken into consideration during the main exposure.

When determining the weighting ratio of both the white balance correction value detected by the color temperature detection circuit and the white balance correction value for the color temperature of the strobe light, a focus mechanism for detecting the focus position of the optical system is used. Based on the focus position output, the weight of the white balance correction value detected by the color temperature detection circuit increases as the distance to the subject increases, and the white balance correction value for the color temperature of the strobe light increases as the distance to the subject decreases. The weight of the white balance correction value output from the color temperature detection circuit is increased as the zoom magnification of the optical system is decreased and the weight of the white balance correction value is increased by the zoom position output of the zoom mechanism. Is provided with a means for increasing the weight of the initial setting value, and the weighted average value of the both is detected and converted into a white balance correction amount. The Rukoto, not during the exposure zoom magnification only allows optimum white balance control that distance is considered to the subject.

[0014]

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

FIG. 1 is a block diagram showing a configuration of a reference example of an automatic white balance control circuit in an electronic still video camera for explaining an embodiment of the present invention, in which 1 is a lens of an optical system and 2 is an image sensor. A CCD (charge-coupled device) sensor, input light passing through the lens 1 is imaged on the surface of the CCD sensor 2 and converted into an electrical RGB image signal for output. Here, R, G, and B are Red, Green, and B, respectively.
It is a signal of lue. 3a and 3b are an R gain amplifier and a B gain amplifier.
The R and B signals output from the D sensor 2 are amplified and attenuated and output. A matrix circuit 4 converts the G output signal of the CCD sensor 2 and the R and B output signals of the R and B gain amplifiers 3a and 3b into Y, Cr and Cb signals and outputs them. here,
Y is a luminance signal, and Cr and Cb are color difference signals for Red and Blue, respectively.

Reference numeral 5 denotes a color temperature detection circuit, which detects the control amounts of the R and B gains corresponding to the color temperature of the illumination on the basis of the Y, Cr and Cb output signals of the matrix circuit 4 and outputs the R and B gain signals. Output. A brightness detection circuit 6 detects the brightness of the subject based on the Y output signal of the matrix circuit 4 and determines whether or not strobe light emission by the strobe 7 is necessary. If light emission is necessary, strobe light emission is performed. Output an instruction signal.
A strobe control circuit 8 controls the strobe 7. The strobe control circuit 8 controls the light emission of the strobe 7 when the strobe light emission instruction signal is output from the brightness detection circuit 6. A strobe setting value memory 9 holds R and B gain setting values corresponding to the color temperature of the strobe 7,
Outputs R and B strobe signals.

Reference numeral 10 denotes a white balance correction circuit, which corresponds to the white balance correction amount according to the R and B gain output signals of the color temperature detection circuit 5 when the strobe control circuit 8 does not output the strobe emission instruction signal. When the R and B gain amplifier control signals are output and the strobe light emission instruction signal is output, the average value of both the R and B gain output values of the color temperature detection circuit 5 and the output of the strobe set value memory 9 is detected. Then, the white balance control is performed by converting and outputting the control signals of the R and B gain amplifiers 3a and 3b corresponding to the white balance correction amount.

Further, a weighted average value is detected by weighting both the output of the color temperature detection circuit 5 and the set value for strobe light by a predetermined constant weight, and R corresponding to the white balance correction amount is detected. , B gain amplifiers 3a and 3b are converted into control signals and output to perform white balance control.

An image recording device 11 records the image taken in after the white balance adjustment. Reference numeral 15 denotes a system control circuit, which prohibits stroboscopic light emission and image recording during pre-exposure, and after the R and B gain signals of the color temperature detection circuit 5 are input to the white balance correction circuit 10, the stroboscopic light 7 is emitted to cause the above-mentioned. The main exposure is performed according to the white balance control operation, and a series of system operations for recording an image in the image recording device 11 are controlled.

FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. Members corresponding to those described in the reference example of FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted.

In FIG. 2, reference numeral 12 denotes a zoom mechanism in an optical system mainly composed of the lens 1, which adjusts an image pickup magnification of the optical system and outputs a zoom position signal corresponding to the zoom magnification at that time. A focus mechanism 13 adjusts the imaging focus of the optical system and outputs a focus position signal corresponding to the focus position at that time.

Reference numeral 14 denotes a white balance correction circuit, which is different in function from the white balance correction circuit 10 described in the reference example in the following points. That is, the white balance correction circuit 14 corresponds to the white balance correction amounts corresponding to the white balance correction amounts according to the R and B gain output signals of the color temperature detection circuit 5 when the strobe control circuit 8 does not output the strobe emission instruction signal. When the gain amplifier control signal is output and the strobe light emission instruction signal is output, both the R and B gain output values of the color temperature detection circuit 5 and the output value of the strobe setting value memory 9 are set.
After performing weighting according to the zoom position output signal of the zoom mechanism 12 and the focus mechanism 13 and the focus position output signal, the weighted average value of R, which corresponds to the white balance correction amount,
B gain amplifiers 3a and 3b are converted into control signals and output,
Performs white balance control.

Here, when weighting is performed, the weight of the white balance correction value detected by the color temperature detection circuit 5 is increased as the zoom magnification becomes lower based on the zoom position output, and as the zoom magnification becomes higher, the strobe light becomes stronger. Increasing the weight of the initial setting value for the color temperature of the light, or based on the focus position output in addition to the weighting, the R and B gain output values of the color temperature detection circuit 5 as the distance to the subject increases. It is conceivable that the weight of the output value of the strobe setting value memory 9 is increased as the distance to the subject becomes shorter.

FIG. 3 shows the relationship between the distance to the object and the weighting coefficient in the white balance correction circuit 14. In FIG. 3, the horizontal axis represents the focus position and the zoom position, and the vertical axis represents the R and B gains and the coefficient when weighting the strobe light setting value. According to this characteristic, when the focus position is the farthest point or the zoom position is the lowest magnification, the weights of the R and B output values are “1” and the weights of the strobe light setting values are “0”. When the focus position is at the closest point, or when the zoom position is at the maximum magnification, the weight of the set value for strobe light is “1”, R,
The weight of the B gain output value becomes “0”. The final weighting coefficient for both the focus position and the zoom position is the average value of the coefficient detected by the focus position and the output detected by the zoom position.

In the above-described embodiment, the pre-exposure is performed without emitting the strobe light, and the white balance control value corresponding to the color temperature of the light source detected from the image signal at that time and the white balance control value corresponding to the color temperature of the strobe light. Since the white balance control is performed by using both the average value of the balance control values and the weighted average value as the white balance correction value, there is no significant difference in the color tone between the subject to which the strobe light reaches and the background to which the strobe light does not reach. As compared with the method of performing white balance control corresponding to only the color temperature of strobe light, an image with less discomfort in color tone is obtained more frequently.

[0026]

As described above, the automatic white balance control circuit of the electronic still video camera according to the present invention is characterized by:
According to the described automatic white balance control circuit, by using the zoom position information, the area occupied by the subject where the strobe light sufficiently reaches is automatically detected in the shooting screen, and the light source increases as the background area increases. The weight of the white balance control value corresponding to the color temperature of is increased, the weight of the control value corresponding to the strobe light is increased as the area of the subject becomes wider, and then the weighted average value is detected to obtain the white balance correction amount. Since the white balance control is performed, optimal automatic white balance control can be performed without considering the zoom magnification.

According to the automatic white balance control circuit of the second aspect, in addition to the zoom position information according to the first aspect, the focus position information is utilized to increase the distance to the subject and the background area to increase. By increasing the weight of the white balance control value corresponding to the color temperature of the light source, and conversely, the closer the distance to the subject is and the wider the subject's screen is, the more weight is added to the control value corresponding to the strobe light. ,
Optimal automatic white balance control is possible without considering not only the zoom magnification but also the distance to the subject.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a reference example of an automatic white balance control circuit in an electronic still video camera for explaining an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration in an exemplary embodiment of the present invention.

FIG. 3 is a relationship diagram of a zoom position, a focus position and a weighting coefficient in the present embodiment.

[Explanation of symbols]

1 ... Lens, 2 ... CCD sensor, 3a, 3b ... Gain amplifier, 4 ... Matrix circuit, 5 ... Color temperature detection circuit, 6 ... Luminance detection circuit, 7 ... Strobe, 8 ... Strobe control circuit, 9
... Strobe set value memory, 10, 14 ... White balance correction circuit, 11 ... Image recording device, 12 ... Zoom mechanism, 13 ... Focus mechanism, 15 ... System control circuit.

Claims (2)

(57) [Claims] 1. A zoom position according to a zoom magnification of an optical system.
In an automatic white balance control circuit for an electronic still video camera that has a zoom mechanism equipped with a means for outputting a charge-coupled device as an image sensor, the image signal obtained by performing pre-exposure without firing the strobe is used as a basis. The color temperature detection circuit that detects the white balance control value corresponding to the color temperature of the external light, and the white balance control value output from the color temperature detection circuit when the strobe is emitted at the time of shooting and preset in the memory detecting an average value of both the initial setting value corresponding to the color temperature of the flash light, and a white balance correction circuit for performing white balance control is converted to a white balance correction amount, the white
In the balance correction circuit, the white balance of the color temperature detection circuit
Lance control value and color of strobe light preset in memory
Both the default value corresponding to the temperature and the
By providing a means for finding the weighted average value of both
Detected and converted to white balance correction amount to control white balance
Electronic still video camera configured to perform
A white balance control circuit, wherein in the white balance correction circuit, a weighted average value of control values
Providing means for adjusting the weighting ratio when detecting
Therefore, based on the output of the zoom mechanism, the lower the zoom magnification is, the more the output of the color temperature detection circuit is controlled.
The higher the value weight and the higher the zoom ratio, the more strobes are set in the memory.
Increase the weight of the initial setting value corresponding to the color temperature of light,
Detect the weighted average value and convert it to the white balance correction amount
An automatic white balance control circuit for electronic still video cameras, characterized by being configured to perform white balance control. 2. A means for outputting a focus position of an optical system
It has a focus mechanism equipped with
Weighting when detecting the weighted average of control values on the road
Adjust the output of the focus mechanism when adjusting the
Based on the above, as the distance to the subject increases, the color temperature detection circuit
Increase the weight of the white balance control value output by
The closer the distance is to the
Increase the weight of the default value corresponding to the color temperature,
Based on the output of the zoom mechanism, the lower the zoom magnification,
Increase the weight of the control value output from the color temperature detection circuit
However, the higher the zoom factor, the more flash
Increase the weight of the initial setting value corresponding to the color temperature of light,
2. An automatic white balance control circuit for an electronic still video camera according to claim 1, wherein the weighted average value is detected and converted into a white balance correction amount for white balance control.