JP2004166310A - White balance adjustment device for still video cameras - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow an optimum white balance adjustment under a strobing photography condition for a still video camera. <P>SOLUTION: Gain control signals GR0 and GB0 for red color and blue color under a non-strobing photography condition are set based on an imaging data with half-pressed release switch (S1-S3). When in the strobing photography, a weighted averaging process with a weighting of a product K1. K2 for weightings K1 and K2 for imaging distance and luminance is applied to the gain control signals GR0 and GB0 to set gain control signals GR and GB (S4-S6, S7). <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a white balance adjusting device for a still video camera that adjusts a white balance based on subject image data captured by an image sensor before actual photographing.

In recent years, an optical image of a subject is formed on a solid-state imaging device such as a CCD via an optical imaging system such as an imaging lens and an aperture, and an electric image signal that is photoelectrically converted and output by the imaging device is recorded on a recording medium. Still video cameras configured to record are in practical use.
In this type of still video camera, the amounts of the three primary color components R (red), B (blue), and G (green) are equal to each other in order to correct the difference in the wavelength distribution of light due to the illumination light of the subject. In addition, white balance adjustment is performed by controlling the gain of the color component. As the white balance adjustment, for example, the gains of R and B are changed while the gain of G is kept constant, and the integrated value of the color difference signals RY and BY (Y; luminance signal) becomes zero. As described above, a method is known in which the gains of R and B are determined by feedback control (see Patent Document 1).

In this method, since the respective color components (R, B, G) are evenly mixed in a photographed image of a general subject, the value obtained by averaging the color difference signals of the entire image is the same as that of the image of the achromatic subject. It is equivalent, and utilizes an empirical rule that when the color temperature of the subject illumination changes, the color component amount of the entire image changes within the range of the color temperature change.
On the other hand, in the feedback method as described above, since it takes time to calculate the gain, a gain for white balance adjustment corresponding to each color temperature corresponding to a plurality of typical subject illumination lights is obtained in advance. In some cases, the gain of the image with the best white balance among the images obtained by performing the tone control with each gain is determined as the gain for the main photographing.
JP-A-63-133351

  By the way, as described above, even if the gain for white balance adjustment is determined based on the imaging data, if the flash photography (shooting with the flash firing) is performed, the imaging without the flash emission is performed. Since the white balance adjustment is performed with the gain based on the data, there is a problem that good white balance adjustment is not performed. For this reason, when performing flash photography, there is a type in which white balance is adjusted with a gain determined according to the relationship between the color temperature and chromaticity of the flash light. Therefore, good white balance adjustment is not always performed.

  The present invention has been made in view of such a conventional problem, and has as its object to enable optimal white balance adjustment even under flash photography conditions.

Therefore, the invention according to claim 1 is, as shown in FIG.
In a white balance adjustment device of a still video camera that determines an adjustment amount of a white balance based on subject imaging data captured by an imaging device before main shooting,
Strobe shooting determining means for determining whether to perform shooting by emitting strobe light based on the subject imaging data,
When it is determined by the flash shooting determining means that shooting with flash light is to be performed, the relationship between the color temperature and chromaticity of the flash light and the color temperature and chromaticity of the subject illumination light in the subject image data And a gain control signal forming means for forming a gain control signal for white balance adjustment used at the time of actual shooting, based on
Is characterized by comprising.

With this configuration, at the time of flash shooting, the gain control formed based on the relationship between the color temperature and the chromaticity of both the flash light and the subject illumination light other than the flash light obtained based on the imaging data. Optimal white balance adjustment can be performed using the signal.
In the invention according to claim 2, the gain control signal forming means weights the gain control signal and a gain control signal corresponding to the subject illumination light in the subject imaging data in accordance with a distance between the subject and the camera. Is changed to form a gain control signal for white balance adjustment.

With this configuration, the smaller the distance between the subject and the camera, the greater the amount of strobe light received by the subject. Therefore, by increasing the weight of the gain control signal based on the strobe light, A gain control signal that appropriately reflects the degree of influence with the subject illumination light is formed.
The gain control signal forming means may include a gain control signal corresponding to strobe light and a gain control signal corresponding to subject illumination light in the subject image data in accordance with a brightness level of the subject image data. It is characterized in that a gain control signal for white balance adjustment is formed by changing the weight of the signal.

  In this way, the light receiving ratio of the strobe light becomes relatively higher as the brightness of the image data becomes smaller and the subject illumination becomes darker when the strobe light is not emitted. Therefore, the weight of the gain control signal by the strobe light should be increased. Thus, a gain control signal that appropriately reflects the degree of influence between the strobe light and the other object illumination light is formed.

Hereinafter, embodiments of the present invention will be described.
FIG. 2 shows a hardware configuration of a still video camera to which the automatic focusing device according to the present invention is applied.
In the figure, an optical image of a subject obtained through an optical imaging system including an imaging lens 101, a focus lens 102, an iris diaphragm 103, and the like is formed on a solid-state imaging device, for example, a CCD 104. The focus lens 102 and the iris diaphragm 103 are driven by a lens driving circuit 121 and an iris driving circuit 120, respectively.

  The CCD 4 photoelectrically converts the formed light image into a charge amount, and outputs it as an analog electric image signal by a transfer pulse from the CCD drive circuit 7. The analog electric image signal output from the CCD 4 is reduced in noise by a CDS (correlated double sampling) circuit, and the gain is adjusted by AGC. Then, after being converted into a digital image signal by the A / D converter 106, it is subjected to luminance processing and color processing by the process circuit 109, and is converted into a digital video signal (for example, a luminance signal and a color difference signal).

  The main CPU 110 controls the operation of each unit, and the strobe 116 driven by the light emitting circuit 115 is controlled so as to emit light at the time of photographing. Further, AE (automatic exposure control), AWB (white balance adjustment), and AF (automatic focus control) processes are all performed under the control of the main CPU 110 using data of the imaging surface. These processes are performed by the process circuit 107 supplying data, the main CPU 110 performing arithmetic processing, and controlling the aperture drive circuit 120, the lens drive circuit 121, the CCD drive circuit 125, and the color processing circuit in the process circuit 107. Do. Further, the main CPU 110 controls each unit according to the operation state of various switches (power switch, release switch, reproduction switch, etc.) of the operation panel 130, and displays necessary information on the liquid crystal display unit 131.

Here, the case where the main CPU 110 controls the whole still video camera has been described, but the configuration may be such that the sub CPU and the main CPU share the operation.
When recording this digital video signal, data compression is performed in the compression / expansion circuit 108. Then, the data is recorded by the recording / reproducing circuit 109 on the memory card 111 composed of an SRAM, a flash memory, or the like.

  At the time of reproduction, compressed data of the digital video signal stored in the memory card 111 is read by the recording / reproduction circuit 109. Then, the compressed data is expanded in the compression / expansion circuit 108 to return the digital video signal to the original size. Then, the signal is converted into an analog video signal by the D / A converter 112, and is output to the external device as a video signal of a predetermined level by the output circuit 113.

In the case of through reproduction, a digital video signal is directly sent from the process circuit 107 to the D / A converter 112, and the image captured by the CCD 104 is continuously output to the outside as a video signal in real time.
Next, an embodiment corresponding to flash photography of the present invention will be described. The strobe light has a different color temperature and chromaticity relationship from the standard illumination light such as the daylight or incandescent light and the special illumination light CWF of the fluorescent lamp. In consideration of this point, a gain control signal corresponding to the relationship between the color temperature and the chromaticity of the strobe light is set, and the strobe light is photographed using the gain control signal dedicated to the strobe light. Has been proposed.

  However, in actuality, even when shooting with a flash, the subject receives light around the subject in addition to the flash light. Therefore, if the gain control signal according to only the characteristics of the flash light is used as described above, it is not always necessary to obtain a good white balance. No adjustment is made. Therefore, in the present embodiment, at the time of flash shooting, white balance adjustment is performed based on the relationship between the color temperature and chromaticity of both the flash light and the subject illumination light other than the flash light obtained based on the imaging data. Of the gain control signal for the control.

Specific control of the present embodiment will be described with reference to the flowchart of FIG.
In step 1, it is determined whether or not the release switch has been half-pressed. If the release switch has been half-pressed, the process proceeds to step 2, where the subject is imaged on the CCD 104.
In step 3, the values GR0 and GB0 of the R and B gain control signals are set as follows based on the image data corresponding to the subject illumination light in a state where the strobe light from the CCD 104 is not emitted.

  In the first example, D75 (daylight), D50, INC (incandescent light) are used as a plurality of standard illumination lights having a relationship close to the relationship between the color temperature and the chromaticity of the perfect radiator, and a deviation from the relationship. For CWF (fluorescent lamp) as a special illumination light which emits a greenish light, the value of a gain control signal for white balance adjustment according to the color temperature of the illumination light is stored in a memory and prepared in advance. deep. Each value of the gain control signal is obtained from the relationship between the color temperature and the R and B gain control signal values as shown in FIG. 4 (D75: □, D50: 〇, INC: △, CWF: ×).

FIG. 5 shows the details of setting the values GR0 and GB0 of the gain control signals of R and B according to the first example under the non-flash shooting condition.
In step 11, the gain of the R and B components is controlled with respect to the obtained imaging data by the gain control signal of each illumination light. Here, the gain control only for the R and B components is performed only by changing the R and B components while keeping the G component constant because the ratio of R, B and G to the color temperature of each illumination light is determined. , R, B, G can be adjusted so as to make the ratio of 1: 1: 1.

  In step 12, the standard illumination light D75, D50, INC having the best white balance is selected. Here, the illumination light having the best white balance is closest to the current subject illumination light among these standard illumination lights. Here, whether the white balance is good or bad is determined assuming that the image data on which the gain control has been performed, in which the R component and the B component are the most uniform, has the best white balance. That is, as described above, since the gain control signal of each illumination light is set so that the ratio of R, B, and G is 1: 1: 1, the gain control signal of the illumination light close to the actual illumination light is used. If controlled by a signal, the ratio of R and B can be made closer to 1: 1. As a specific discrimination method, as shown in FIG. 6, pixels satisfying R> B and pixels satisfying R <B are counted with respect to the RB axis. And the one closest to 1: l is selected. Since RB = (RY)-(BY) and the color difference signals (RY) and (BY) are obtained, the color difference signal (RY) is obtained for each pixel. , (B−Y), it is possible to discriminate between a pixel having a large R component and a pixel having a large B component, and it is sufficient to count the number of both pixels and obtain the ratio.

However, only by this determination, there is a possibility that the illumination light is the special illumination light CWF.
In step 13, the white light having the best white balance among the standard illumination light is compared with the image data obtained when the gain is controlled by the special illumination light CWF. Select the illumination light. Specifically, the fact that the special illumination light CWF (fluorescent lamp) has a larger G component than the standard illumination light is used. That is, as shown by the crosses in FIG. 4, the gain control signal corresponding to the special illumination light CWF is used to correct the increase of the G component so as to correct the greenish image under the special illumination light CWF to white. In order to cancel each other, both the R gain control signal and the B gain control signal are set to larger values than the gain control signals of the same color temperature of the standard illumination light.

  Therefore, if the actual subject illumination light is the special illumination light CWF, the image whose gain is controlled by the gain control signal corresponding to the special illumination light CWF has a uniform G component and its complementary color of Mg (magenta) component. However, in the image whose gain is controlled by the gain control signal of the standard illumination light, even in the image having the best white balance, the G component is relatively increased and the Mg component is decreased. Conversely, when the actual subject illumination light is the standard illumination light, in the image whose gain is controlled by the gain control signal corresponding to the standard illumination light, the G component and the Mg component are equal, but the special illumination light When gain control is performed using the gain control signal of the CWF, the gains of R and B are strengthened so as to cancel the G component. As a result, the G component is reduced and the Mg component is increased.

  Therefore, the ratio of the Mg and G components is compared between the image whose gain is controlled by the gain control signal of the selected standard illumination light and the image whose gain is controlled by the special illumination light CWF. Specifically, in FIG. 7, since Mg-G = (RY) + (BY), it is determined whether the sum of the color difference signals (RY) and (BY) is positive or negative. This makes it possible to discriminate between a pixel having a large amount of Mg component and a pixel having a large amount of G component for each pixel, and it is possible to determine the ratio of the number of pixels of both.

  If the ratio between the Mg component and the G component when the gain is controlled by the selected standard illumination light is close to 1: 1 and the ratio of the Mg component is relatively high when the gain is controlled by the special illumination light, the subject It is determined that the illumination light is illumination light close to the selected standard illumination light, and the gain control signal of the standard illumination light is selected as gain control signals GR0 and GB0 for white balance adjustment at the time of actual photographing (step S1). 15).

On the other hand, when the ratio between the Mg component and the G component when the gain is controlled by the special illumination light is close to 1: 1, and when the ratio of the G component is relatively high when the gain is controlled by the standard illumination light, the subject illumination light is high. Although there is a possibility that the illumination light is special illumination light, there is still a possibility that the illumination light is standard illumination light in a shooting situation described later.
That is, when an image is taken outdoors, particularly in a place with a lot of greenery such as plants, the color obtained by mixing the respective color components of the image does not become an achromatic color, but becomes an image having a large amount of G components. Therefore, when the ratio between the Mg component and the G component is obtained for an image when gain control is performed using a gain control signal such as the standard illumination light D75 corresponding to the illumination light at the time of shooting, the G component has a large ratio. When gain control is performed on this image using the gain control signal of the special illumination light CWF, the ratio of Mg to G becomes a value close to 1: l due to the function of canceling G. I can't.

  Therefore, attention is paid to the fact that such daylight illumination outdoors has sufficiently high luminance as compared with the special illumination light CWF such as a fluorescent light, and the luminance of the image data is compared to make a determination. That is, when it is determined that the brightness of the image data is equal to or higher than the predetermined level, it is determined that the image is taken in a place where there is much green under the daylight illumination, and the process proceeds to step 15 where the standard value selected in step 12 is selected. The gain control signal of the illumination light is determined as gain control signals GR0 and GB0 for white balance adjustment at the time of actual photographing.

  If it is determined in step 16 that the brightness of the image data is lower than the predetermined level, it is determined that the image is being shot with special illumination light CWF such as a fluorescent lamp having low brightness, and the process proceeds to step 17 where the special illumination light is determined. The gain control signal of the CWF is determined as gain control signals R0 and B0 for white balance adjustment at the time of actual photographing. As described above, the determination between the standard illumination light and the special illumination light CWF is made based on the ratio between the R component and the B component in the image data after gain control, similarly to the determination in the standard illumination light. However, in the special illumination light CWF, the gain control signals for R and B are set so as to be evenly increased so as to cancel out the increase in the G component, so that the special illumination light CWF and the standard illumination having a color temperature close to each other are set. The ratio of R and B in the image data does not change with light, and cannot be distinguished.

  Therefore, the possibility of the special illumination light CWF is determined by determining the ratio of Mg and G as described above, and furthermore, the distinction with a special photographing state having a lot of green can be performed satisfactorily by the luminance. It is possible to accurately determine the illumination light with a small amount of arithmetic processing and perform a good white balance adjustment. In addition, since the special illumination light CWF can be determined by detecting flicker, it can be configured to use the flicker.

  When the color temperature of the gain control signal selected from the plurality of standard illumination lights is significantly different from the color temperature of the special illumination light CWF, the color temperature is not compared with the special illumination light CWF. The gain control signal of the selected standard illumination light may be determined as a gain control signal for white balance adjustment at the time of actual photographing. For example, in INC, the magnitude relationship between R and B is opposite to the magnitude relationship between R and B of the special illumination light CWF. Therefore, when the INC is selected, the gain control signal for the actual photographing is directly used. It can be determined as

In addition, when it is determined that the photographing situation has a lot of green outdoors, with respect to the feedback-corrected gain control signals GRG and GBG of the R and B at that time, GRG-GR = GBG-GB. The gain control signals GR and GB of R and B in the illumination light may be used as the gain control signals GR0 and GB0 for the actual photographing.
Next, a second example of setting the values GR0 and GB0 of the gain control signals of R and B under the non-flash shooting condition will be described.

  The second example is applied to a method of performing white balance adjustment while performing feedback correction on a gain control signal. As described above, in the feedback control method, for example, a feedback control method is known in which the gains of R and B are feedback-controlled so that the integrated values of the color difference signals (RY) and (BY) become zero. ing. In such a feedback control method, if the control width is not limited, white balance adjustment is performed on an arbitrary image so that the entire average value is achromatic, so that the G component is large as in the special illumination light CWF. Good white balance adjustment can be performed even for images shot with illumination light.

  However, as described in the first example, when the white balance adjustment is automatically performed as described above when, for example, a place with a lot of green is photographed under daylight, the G component is averaged. Since the image is adjusted so as to correct an image having a lot of white, the green portion is faded white, and the originally white portion is an image which is purple (magenta) which is a complementary color of green. If the gains of R and B are limited to prevent this, the captured image will be greenish under the special illumination light CWF.

  Therefore, in the second example, while the gain control signals of R and B are feedback-controlled to enable white balance adjustment with the special illumination light CWF, shooting under the special illumination light CWF and green under the daylight are performed. In the latter case, a gain control signal corresponding to daylight illumination is used instead of a feedback control-corrected gain control signal for white balance adjustment in actual shooting. To

FIG. 8 shows the details of setting the values GR0 and GB0 of the gain control signals of R and B according to the second example under the non-flash shooting condition.
That is, in step 21, the magnitude of R and B and the magnitude of Mg and G are determined in the same manner as in the first example, and the gain control signals of R and B are initialized according to the combination of these magnitude relationships. Feedback-corrects the value. Specifically, as in the above-described embodiment, the magnitude of R and B is determined based on the sign of the difference between the color difference signals (RY) and (BY), and the color difference signals (RY) and (BY) are determined. The magnitude of Mg and G is determined based on the sign of the sum of Y).

  When R> B and Mg> G, the gain control signal of R is decreased, when R> B and Mg <G, the gain control signal of B is increased, and when R <B and Mg> G, When the gain control signal of B is decreased, and when R <B and Mg <G, the gain control signal of R is increased, and when the magnitude relation is inverted by the correction, a finer correction is made according to the magnitude relation. The above correction is repeated until the absolute values of (RB) and (Mg-G) fall within a predetermined range.

When the absolute value falls within the predetermined range, the feedback correction is completed and the process proceeds to step 22 and thereafter, based on the feedback-corrected R and B gain control signals, whether the subject illumination light is the special illumination light CWF, or It is determined whether the location is a daylight-rich green place.
Specifically, under both conditions described above, image data having a large amount of G component is obtained. Therefore, compared with the gain control signal under the normal photographing condition with the standard illumination light, the R gain is adjusted to correct the increase of the G component. Both the control signal and the B gain control signal have increased values. Therefore, first, in step 22, it is determined whether or not the R gain control signal is equal to or greater than a predetermined value R1 and the B gain control signal is equal to or greater than a predetermined value B1. It is determined that the shooting condition is satisfied.

If it is determined in step 22 that none of the photographing conditions is satisfied, it is determined that the photographing condition is a normal photographing condition under standard illumination light, and the process proceeds to step 23, in which gain control of the feedback corrected R and B is performed. The signal is determined as it is as gain control signals GR0 and GB0 for white balance adjustment at the time of actual photographing.
On the other hand, when it is determined that any one of the photographing conditions is satisfied, the process proceeds to step 24, where it is determined whether the brightness of the image data is equal to or higher than a predetermined level, as in the first example. It is determined that the shooting condition is under the special illumination light CWF. In this case, the greenish image may be corrected. It is determined as gain control signals GR0 and GB0 for white balance adjustment at the time of actual photographing.

  If it is determined in step 24 that the brightness of the image data is equal to or higher than the predetermined level, it is determined that the image capturing condition is a green-rich place under daylight, and in this case, the gain control signal is feedback-corrected. When the gain control is performed, the green portion fades white, and the white portion becomes a purple image. For this reason, in this condition, the process proceeds to step 25, and the R gain control signal RD75 and the B gain control signal BD75 shown in FIG. Switching is performed so as to be used as the gain control signals GR0 and GB0. In this embodiment, D75 is used as daylight, but D65 and D50 may be used.

In this way, the white balance can be adjusted with high accuracy not only under normal shooting conditions under standard illumination light, but also under shooting conditions under greenish illumination light such as fluorescent light, and especially in daylight. Even under special shooting conditions such as shooting a place where there is a lot of green below, excessive white balance adjustment is prevented and appropriate white balance adjustment according to the original color is performed.
As described above, according to the first example or the second example, after the values GR0 and GB0 of the gain control signals of R and B under the non-flash shooting condition are set, the process proceeds to step 4 in FIG.

In step 4, it is determined whether or not the flash photography condition is satisfied from the luminance information based on the image data. If it is determined that the flash shooting condition is not satisfied, the process proceeds to step 5 and the gain control signals GR0 and GB0 determined in step 12 are determined as gain control signals for actual shooting.
On the other hand, if it is determined in step 4 that the shooting condition is the strobe lighting shooting condition, the process proceeds to step 6 where the weighting coefficient K1 corresponding to the distance between the subject and the camera from the imaging data and the luminance obtained from the imaging data are used. The weight coefficient K2 is obtained by calculation or retrieval from a data table. Here, the weighting coefficients K1 and K2 are used for calculating a weight when a gain control signal corresponding to subject illumination light other than the strobe light and a gain control signal corresponding to the strobe light are weighted and averaged. K1 is set so as to increase the weight of the gain control signals GR1 and GB1 by the strobe light because the amount of strobe light received by the subject increases as the distance between the subject and the camera decreases. Is set such that the weight of the gain control signals GR1 and GB1 based on the strobe light is increased because the ratio of light reception of the strobe light becomes relatively larger as the luminance becomes smaller and darker.

In step 7, gain control signals GR1 and GB1 obtained from the relationship between the color temperature and chromaticity of the strobe illumination light using the weighting factors K1 and K2, and a value GR0 of the gain control signal GR0 under the non-strobe illumination condition. , GB0 are weighted and averaged as in the following equation to determine gain control signals GR and GB for white balance adjustment at the time of actual photographing.
GR = K1, K2, GR1 + (1-K1, K2) GR0
GB = K1, K2, GB1 + (1-K1, K2) GB0
In this way, the optimal white balance can be adjusted even during flash photography by using the gain control signal formed by reflecting the degree of influence between the flash light and the illumination light other than the flash light.

FIG. 2 is a block diagram showing the configuration and functions of the invention of claim 1. FIG. 1 is a block diagram showing a hardware configuration of a still video camera according to an embodiment. 5 is a flowchart for determining a gain control signal according to the embodiment. FIG. 3 is a diagram illustrating a relationship between a color temperature of each illumination light and a gain control signal value. 9 is a flowchart illustrating a first example of setting a gain control signal under non-flash shooting conditions. FIG. 9 is a diagram illustrating a magnitude relationship between R and B component amounts in the first example. FIG. 4 is a diagram illustrating a magnitude relationship between Mg and G component amounts in a first example. 9 is a flowchart illustrating a second example of setting a gain control signal under non-flash shooting conditions.

Explanation of reference numerals

1 shooting lens 2 focus lens 3 aperture 4 CCD
5 Lens drive circuit 6 Iris drive circuit 7 CCD drive circuit 8 A / D converter 9 Process circuit
10 Compression circuit
11 Recording circuit
12 IC card
13 Digital AF evaluator
14 Main CPU

Claims (3)

In a white balance adjustment device of a still video camera that determines an adjustment amount of a white balance based on subject imaging data captured by an imaging device before main shooting,
Strobe shooting determining means for determining whether to perform shooting by emitting strobe light based on the subject imaging data,
When it is determined by the flash shooting determining means that shooting with flash light is to be performed, the relationship between the color temperature and chromaticity of the flash light and the color temperature and chromaticity of the subject illumination light in the subject image data And a gain control signal forming means for forming a gain control signal for white balance adjustment used at the time of actual shooting, based on
And a white balance adjusting device for a still video camera.   The gain control signal forming means changes the weight of the gain control signal corresponding to the strobe light and the gain control signal corresponding to the subject illumination light in the subject imaging data according to the distance between the subject and the camera to change the white balance. The white balance adjusting device for a still video camera according to claim 1, wherein a gain control signal for adjustment is formed.   The gain control signal forming means changes the weight of the gain control signal corresponding to the strobe light and the gain control signal corresponding to the object illumination light in the object image data according to the brightness level of the object image data to change the white balance. 3. The white balance adjusting device for a still video camera according to claim 1, wherein a gain control signal for adjustment is formed.

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