JPH084344B2 - Auto white balance circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an auto white balance circuit,
The present invention relates to an auto white balance circuit which is applied to a color video camera, an electronic camera, etc. and automatically adjusts white balance according to the color temperature of light from a light source.

[Prior Art] As is well known, as an auto white balance circuit applied to an image pickup apparatus such as a television camera or an electronic camera, a so-called one-touch auto white balance system circuit has been popular. The auto white balance circuit of this system obtains a "white standard" by pointing the TV camera at a white subject each time you shoot, or by covering the front of the shooting lens with a white cap attached to the camera. These color difference signals are synchronized with the timing of the setting operation (push button operation) so that the video signal becomes a state corresponding to “white”, that is, the two color difference signals RY and BY are zero. The gain is automatically adjusted, and thereafter the adjusted state is held by the storage means until the next push button operation is performed. Therefore, in this method, it is necessary to repeat the white balance setting operation for each shot, which is troublesome to handle. In addition, the photographer may forget to perform the setting operation and may take a picture without maintaining the correct white balance. For this reason, recently, a television camera having a so-called full-auto white balance system circuit that completely automates the white balance operation has been developed. An example of this type of white balance circuit is shown in FIG.

In FIG. 4, the portion surrounded by the chain double-dashed line is the white balance circuit 10 in the television camera. An R signal R _IN from an image pickup means (not shown) such as an image pickup tube or a solid-state image pickup device is amplified by a variable gain amplifier 11 with a gain set in the same circuit, and then an R-Y matrix circuit 12 at the next stage. , The signal is processed by being combined with the low-frequency luminance signal Y _L which is one component of the output of the image pickup means, and the color difference signal R−
It is output as Y. This color difference signal RY output is a resistance
It is averaged by the integrating circuit 13 composed of R ₁ and the capacitor C ₁ , and is input to the inverting input terminal of the operational amplifier 14. Operational amplifier 14
The reference voltage V _REF1 is applied to the non-inverting input terminal of the, and the output of the operational amplifier 14 is applied to the variable gain amplifier 11 as its gain setting signal. On the other hand, B from the image pickup means
Similarly, the signal B _IN is amplified by the gain of the variable gain amplifier 15 in the same gain, and then the BY of the next stage is used.
The matrix circuit 16 performs signal processing on the low-frequency luminance signal Y _L , and outputs the color-difference signal BY. The color difference signals BY are averaged by the integrating circuit 17 including the resistor R ₂ and the capacitor C ₂ and input to the inverting input terminal of the operational amplifier 18. The reference voltage V _REF2 is applied to the non-inverting input terminal of the operational amplifier 18, and the output of the operational amplifier 18 is applied to the variable gain amplifier 15 as its gain setting signal.

The color difference signals R-Y and B-Y output from the white balance circuit 10 are input to the encoder 20, where signal processing such as double balance modulation is performed and converted into a chroma signal (so-called C signal). Is output. The C signal is the color multiplexer 30 is combined with the sync burst signal from the high-frequency luminance signal Y _H and a separate oscillation circuit from the image pickup means, NTSC composite video signal (color signal) is formed.

Here, the white balance adjustment in the white balance circuit 10 is performed as follows. That is, in this full auto white balance method, even if the subject is not completely white, the color difference signal obtained corresponding to the subject including each color on average is the level of the color difference signal obtained corresponding to the white subject. Since it is obtained with a signal that is positively and negatively averaged centered around, the average value of such color difference signals is approximately equal to the color difference signal level obtained when a white subject is imaged with the light source light at that time. It is based on the assumption that it will be. Generally, two color difference signals RY and B-corresponding to an all-white subject under the light source light
Y is zero if the white balance is adjusted properly (that is, the signal level is equal to each reference value V
_{(Equal to REF1} and V _REF2 ), and if the adjustment is not proper, there will be a positive or negative bias. The white balance circuit 10 shown in FIG. 4 operates so as to eliminate the bias of the color difference signal levels. For example, if the color temperature of the light from the light source changes at a certain point in time, the B signal from the image pickup means is changed.
The level of B _IN rises and the level of R signal R _IN falls.
Then, the level of the color difference signal BY rises, and the color difference signal R
Although the level of −Y changes in a decreasing direction, the signals input to the respective operational amplifiers 18 and 14 as the average value of the changing levels via the integrating circuits 17 and 13 corresponding to this change, respectively. Rises and falls. as a result,
The operational amplifiers 18 and 14 operate to decrease and increase the gains of the corresponding variable gain amplifiers 11 and 15, respectively, and as a result, the levels of the color difference signals BY and RY are kept at their reference values. It is adjusted so as to sag (that is, to keep BY = 0 and RY = 0).

As described above, in the white balance circuit 10 of the above method, it is assumed that the average value of the color difference signals obtained for the subject including each color should be zero even when the subject is not completely white. Therefore, the adjustment operation is performed in the same manner as in the case of always capturing an image of a white object. Therefore, the closed loop control is performed for the two color difference signals without particularly detecting the color temperature of the light source light. A circuit in which a digital method is applied to the above-described automatic white balance circuit to perform more accurate white balance adjustment has already been proposed (see Japanese Patent Laid-Open No. 56-169986).

On the other hand, an auto white balance circuit has also been proposed in which the color temperature of the light source light is actually detected and the white balance adjustment is fully automatically performed based on the color temperature (for example, Japanese Patent Laid-Open No. 56-4993). See the bulletin). Such an automatic white balance circuit is configured as shown in FIG. 5, for example. In FIG. 5, the opto-white filter 41 is provided on the front surface, and the light receiver 4 includes a light receiving element 42 that reacts to the R component and a light receiving element 43 that reacts to the B component, and the outputs of the respective light receiving elements 42, 43 are logarithmically expressed. Preamplifier for compression 4
Imaging the color temperature detection circuit 40 having 5,46 and an arithmetic circuit 47 for obtaining an output corresponding to the color temperature of the light incident on the light receiver 44 based on the outputs of the preamplifiers 45, 46. It is provided independently of the means (not shown). And this circuit 40
The color balance adjusting circuit 50 obtains the adjusting signals corresponding to the respective gains of the variable gain amplifier 61 of the R signal system and the variable gain amplifier 62 of the B signal system based on the color temperature information detected by the adjustment signal. The white balance adjustment is performed by controlling each of the above gains.

[Problems to be Solved by the Invention] In the conventional circuit described with reference to FIG. 4, closed loop control is performed for the two color difference signals R-Y and B-Y, so that the circuit is strong against disturbance, but on the other hand However, a problem occurs because the white balance adjustment operation is performed without actually detecting the color temperature of the light source light. That is, as described above, even if the subject is not entirely white,
Usually, it is based on the assumption that the subject exhibits each color, and if they are averaged, they will be almost equivalent to white. Therefore, when an image of a single primary color subject (for example, a plate whose entire surface is red) is picked up, the color also moves toward white and fading occurs. This is because the circuit shown in FIG. 4 is essentially incapable of discriminating between changes in the R and B signals due to color temperature and changes in the R and B signals due to changes in the color of the subject. is there.

Further, in the conventional circuit described with reference to FIG.
Since the color temperature of the light source light is actually detected and the white balance adjustment operation is performed based on this detected value, the above-mentioned inconvenience in the circuit of FIG. 4 does not occur. However, in this type of auto white balance circuit, it is necessary to provide color temperature detection means separately from the image pickup means,
As the configuration becomes complicated, the exterior design of the camera becomes difficult depending on, for example, the position of the video camera where the color temperature detecting means is arranged. Further, with respect to the color signals R and B or the color difference signals R-Y and B-Y (collectively referred to as video signals), the gain control of each video signal system is performed without detecting their levels. That is, there is a problem that it is vulnerable to disturbance because only open loop control is performed on the video signal.

The present invention has been made in view of the above points, and does not cause fading even when photographing an object of a single primary color, is resistant to disturbance, and is a fully automatic auto white balance circuit having a simple configuration. The purpose is to provide.

[Means and Actions for Solving Problems] The auto white balance circuit of the present invention includes a first variable gain amplifying means for controlling the gain of the first color information signal from the image pickup means, and the above-mentioned image pickup means. Second variable gain amplifying means for controlling the gain of the second color information signal, a signal based on the first color information signal relating to the output of the first variable gain amplifying means, and the second variable gain amplifying means. Color temperature detection means for obtaining a color temperature detection signal corresponding to a color temperature by a ratio of signals based on the second color information signal related to the output of the means,
In order to control the gains of the first variable gain amplifying means and the second variable gain amplifying means based on the color temperature detecting means, both variable gain amplifying means are provided with the color temperature detecting signal or a signal corresponding to the color temperature detecting signal. Color temperature detection signal supply means for supplying,
It is characterized in that each closed loop is formed for the automatic gain control of the first variable gain amplifying means and the second variable gain amplifying means to perform the white balance adjusting operation.

Practical Example FIG. 1 is a block diagram of an auto white balance circuit showing an embodiment of the present invention. Imaging means (not shown)
The R signal R _IN as a signal relating to the first color information is amplified by the first variable gain amplifier 71 with a gain set by the output of the amplifier 77 as described later, and then R-Y of the next stage. In the matrix circuit 72, signal processing is performed by combining with the low-frequency luminance signal Y _L which is one component of the output of the image pickup means,
The color difference signal R-Y as the first color system signal is output. The color difference signal R-Y is integrated and averaged by an integrating circuit 73 composed of a resistor R ₃ and a capacitor C ₃ , and a color temperature detecting circuit 79
Is input to Further, the B signal B _IN as a signal relating to the second color information from the image pickup means is also exactly the same as the gain set by the output of the inverting amplifier 78 in the second variable gain amplifier 75 as described later. After being amplified, the next stage B-
In the Y matrix circuit 76, signal processing is performed together with the low band luminance signal Y _L , and the signal is output as a color difference signal BY as a second color system signal. The color signals B-Y are integrated and averaged by the integrating circuit 74 composed of the resistor R ₄ and the capacitor C _4, it is input to the color temperature detection circuit 79 as a color temperature detection means. The other ends of the capacitors C ₃ and C ₄ are grounded. The values of the resistors R ₃ and R ₄ and the capacitors C ₃ and C ₄ of the integrating circuits 73 and 74 are R ₃ =
R ₄ , C ₃ = C ₄ is set.

The color temperature detection circuit 79 calculates the ratio {(BY) / (RY)} from the color difference signals RY and BY, and uses this as a DC color temperature detection signal in the amplifier 77, Lead to 78. The value of the color temperature detection signal {(BY) / (RY)}, which is the ratio of the color difference signals RY and BY, changes as shown in FIG. 2 with respect to the change in color temperature. It will be done. Then, this color temperature detection signal {(BY) / (RY)}
Is appropriately amplified with the same polarity by the amplifier 77 forming a part of the color temperature detection signal supply means, and the amplified color temperature detection signal is corrected by the first variable gain amplifier 71 to control the gain of the R signal. It is input as a signal. The color temperature detection signal {(R−Y) / (R−Y)} is inverted and amplified by an inverting amplifier 78 forming a part of the color temperature detection signal supply means, and the inverted and amplified signal is obtained. Is input to the second variable gain amplifier 75 as a correction signal for controlling the gain of the B signal. As described above, the correction signal generating circuit including the color temperature detecting circuit 79 and the amplifier 77 forms a closed loop of the R signal system, and the correction signal generating circuit including the color temperature detecting circuit 79 and the amplifier 78 forms a closed loop of the B signal system. Are formed. Then, in each of the amplifiers 77 and 78, the offset value of each of the closed loops can be adjusted by the offset variable resistors 77a and 78a. Auto white balance circuit configured in this way
The color difference signals R-Y and B-Y, which are the outputs of 70, are input to the encoder 20 (see FIG. 4) and the like for signal processing.

On the other hand, the control target value of the white balance on the camera side with respect to the change of the color temperature (the control value for reproducing the white of the subject to the white on the television receiver with respect to the change of the color temperature) is as shown in FIG. , The R signal is represented by the characteristic of the control value V _R , and the B signal is represented by the characteristic of the control value V _B.
Therefore, when the color temperature detection circuit 79 outputs a color temperature detection signal that changes with respect to the color temperature as shown in FIG.
In the amplifier 77, its amplification factor and the variable resistor 77
By adjusting the offset value by a, the amplifier 77
As correction signal characteristics that match the variable gain to the amplifier 71 of the control value V _R characteristic of R signal system is input from, again, the amplification factor and the variable resistor 78a of the inverting amplifier 78
By adjusting the offset value by, the correction signal having the characteristic matching the characteristic of the control value V _B is input from the amplifier 78 to the variable gain amplifier 75 of the B signal system. By doing so, the white balance adjustment can be performed so as to approach the target value in a closed loop that is clear from FIG. 1 with the signal that has detected the color temperature of the actual incident light. However, there is no fading, and proper color balance control can be performed.

Further, as a basic characteristic of the feedback loop, it is clear that even if disturbance is applied to each closed loop of the R and B systems, the disturbance is suppressed to 1 / loop gain. That is, the information about the color temperature is detected by the DC signal of {(BY) / (RY)}, and the closed loops as described above are formed so as to control the gains of the R signal and the B signal. What is happening is that {(BY) / (R-
Y)} is applied to each closed loop as a disturbance, the characteristics of the correction signals from the amplifiers 77, 78 are matched with the white balance control target value by the closed loops of R and B. Stable full auto white balance adjustment will be realized without the influence of such disturbance.

In the above embodiment, the color temperature detection circuit 79 detects the color temperature of the illumination light by taking the ratio of the color difference signals R-Y and B-Y.
The color temperature may be detected by the ratio (B / R).

As described above, according to the present invention, the white balance is adjusted according to the color temperature of the light incident on the image pickup means, so that there is no fading even when a single primary color subject is picked up, and the variable gain is variable. Since the gain control of the amplifier is performed in a closed loop, it is resistant to disturbances and has a simple structure, which enables white balance adjustment with completely automated operation.

[Brief description of drawings]

FIG. 1 is a block diagram of an auto white balance circuit showing an embodiment of the present invention, FIG. 2 is an output characteristic diagram of a color temperature detection circuit of the auto white balance circuit shown in FIG. 1, and FIG. FIG. 4 is a diagram showing a white balance control target value on the camera side with respect to color temperature, FIG. 4 is a block diagram showing an example of a conventional auto white balance circuit, and FIG. 5 is another conventional auto white balance circuit. It is a block diagram showing an example of. 70: Auto white balance circuit 71: First variable gain amplifier 75: Second variable gain amplifier 77: Amplifier (correction signal generation circuit) 78: Inverting amplifier (correction signal generation circuit) 79: Color Temperature detection circuit (correction signal generation circuit)

Claims (1)

[Claims] 1. A first variable gain amplifying means for controlling a gain of a first color information signal from an image pickup means, and a second variable gain for controlling a gain of a second color information signal from the image pickup means. An amplifying means, a signal based on the first color information signal relating to the output of the first variable gain amplifying means, and a signal based on the second color information signal relating to the output of the second variable gain amplifying means. A color temperature detecting means for obtaining a color temperature detecting signal corresponding to a color temperature according to a ratio, and for controlling the gains of the first variable gain amplifying means and the second variable gain amplifying means based on the color temperature detecting signal. A color temperature detection signal supply means for supplying the color temperature detection signal or a signal corresponding to the color temperature detection signal to the both variable gain amplification means, the first variable gain amplification means and the second variable gain amplification means being provided. Each closed loop for automatic gain control The automatic white balance circuit is characterized by forming a loop to perform a white balance adjustment operation.