JPH0817497B2 - Automatic white balance correction device - Google Patents

Description

The present invention relates to an automatic white balance correction device in an image pickup device such as a video camera or an electronic still camera.

[Prior Art] Various proposals have been made at present for an automatic white balance correction device such as a video camera, some of which use a color temperature sensor and some of which use a video signal. Among them, a conventional example of an automatic white balance correction apparatus using a video signal will be described with reference to the drawings.

FIG. 2 is a block diagram showing an outline of an automatic white balance correction apparatus using a video signal, which was reported at the National Conference of the Television Society of 1986. 1 is an image sensor, 2 is a luminance signal / color signal generation circuit, 3 , 4 is a gain control circuit, 5 is a color difference signal generation circuit, 6 is an encoder, 7 and 8 are gate circuits, and 9 and 10.
Is a clipping circuit, 11 is an RB signal detection circuit, 12 is an averaging circuit, 13 is a comparison amplifier, 14 is a tracking correction circuit, and the gate circuits 7 and 8 to the tracking correction circuit 14 are automatic white balance correction devices. Are configured. Second
In the device shown in the figure, the optical signal incident on the image sensor 1 is photoelectrically converted here, extracted as an electric signal, and output to the luminance signal color signal generation circuit 2. The luminance signal / color signal generation circuit 2 generates a luminance signal Y _H having a luminance signal band, a luminance signal Y _{L in the} color signal band, a color signal R, and a color signal B. The color signals R and B are input to the gain control circuits 3 and 4, respectively, and amplified by the control signals from the tracking correction circuit 14 and output as color signals R'and color signals B ', respectively. The color difference signals (R−Y _L ), (B− are input to the color difference signal generation circuit 5 together with Y _L.
Y _L) is generated, the color difference signals _{(R-Y L), (} B-Y L)
Is input to the encoder 6 together with the luminance signal Y _H , where a standard television signal is generated from the input signal and output. Here, the color difference signals (R−Y _L ) and (B−
Y _L ) is also input to the automatic white balance correction circuit 15.

The color difference signals (R−Y _L ) and (B−Y _L ) are input to gate circuits 7 and 8, respectively, where unnecessary signals within the blanking period, abnormal color difference signals due to signal collapse during high-luminance shooting, etc. Has been removed. The signals output from the gate circuits 7 and 8 are input to the clipping circuits 9 and 10, respectively, where the signals exceeding the level of the color difference signal within the practical color temperature range are clipped, and the RB signal detection circuit 11 receives the signals. Is output. Here, the outputs (R−Y _L ) ′ from the clipping circuits 9 and 10 are
By taking the difference (B-Y _L) 'detects the (R-B) signals. The averaging circuit 12 averages the (RB) signal from the RB detecting circuit 11 and converts it to a DC signal. The comparison amplifier 13 compares the signal from the averaging circuit 12 with the reference voltage V _ref and outputs a signal corresponding to it to the tracking correction circuit 14. Tracking correction circuit
In 14, based on the signal from the comparison amplifier 13, to generate a signal for controlling the gain of the gain control circuit 3, 4 so that the white balance is corrected, the gain control circuit 3,
Output to 4. Since the negative feedback loop is configured as described above, the white balance-corrected color difference signal can be supplied to the encoder 6.

[Problems to be Solved by the Invention] In the conventional device as described above, in a light source similar to the Planck's radiation formula such as sunlight and halogen lamp light, when the subject is white, the above (R-Y _L ) Signal, (B-
Y _L ) signals are both zero and are in a white balanced state. However, in the case of a light source such as a fluorescent lamp, the emission spectrum distribution is different from the above Planck's radiation formula, so (R -B) Even if the signal becomes zero, the above ((R
Since the −Y _L ) signal and the (B−Y _L ) signal do not become zero, there is a problem that white balance cannot be achieved.

The present invention has been made to solve such a problem, and provides an automatic white balance correction device capable of performing good white balance adjustment regardless of whether the illumination light source is close to Planck's radiation formula or not. The purpose is to do.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the automatic white balance correction apparatus of the present invention uses the difference between the signal components of the two color difference signals obtained from the color signals. A means for detecting the first signal, a means for comparing the first signal from the detecting means with a first reference voltage adjusted to be equal to a DC voltage when the first signal becomes zero. Switching means for selecting one of a second reference voltage and a third reference voltage preset by the positive / negative of the first signal based on the output from the comparing means, and the output from the switching means. Means for averaging, a first tracking correction circuit using the output of the averaging means as an input signal, and means for detecting a second signal of the sum of signal components of the two color difference signals,
On the basis of the output from this comparing means, means for comparing the second signal from this detecting means with a fourth reference voltage adjusted to be equal to the DC voltage when this second signal becomes zero. , Switching means for selecting one of a fifth reference voltage and a sixth reference voltage set in advance depending on whether the second signal is positive or negative, means for averaging the output from this switching means, and this averaging A second tracking correction circuit that receives the output of the means as an input signal, and a first adder that adds the outputs of the R signal system among the outputs from the two tracking correction circuits, and the B signal system. A second adder for adding the outputs is provided, and the output of these two adders controls the gain of each color signal.

[Operation] With the above configuration, regardless of whether the illumination light approximates Planck's radiation formula or not,
Good automatic white balance adjustment is possible.

[Embodiment] FIG. 1 is a block diagram showing a schematic configuration of an automatic white balance correction apparatus which is an embodiment of the present invention in FIG. First
The terminals K, L, M, N in the figure correspond to those shown in FIG. 2 shown in the conventional device, and the automatic white balance correction circuit 26 in FIG. It corresponds to the balance correction circuit 15.

The apparatus of Figure 1, the outputted the color difference signals from the color difference signal generation circuit _{5 (R-Y L),} (B-Y L) terminals M, N
Through the RB detection circuit 16 and the Mg-G detection circuit 21.

In the RB detection circuit 16, the color difference signal (R-
The difference between ( _YL ) and ( _BYL ) is taken to produce the (RB) signal. The comparison amplifier 17 is a device for comparing the RB signal output from the RB detection circuit 16 with the first reference voltage V _ref1. The first reference voltage V _ref1 is zero for the RB signal. It is adjusted to be the same as the DC voltage when.
Here, in the present embodiment, the output of the comparison amplifier 17 is set to "H" level when R> B and "L" level when R <B. Reference _numeral 18 denotes a switching circuit, which switches and outputs the second and third reference voltages V _ref2 and V _ref3 which are predetermined when the output of the comparison amplifier 17 is “H” level and “L” level, respectively. It is a device. That is, the output of the RB detection circuit 16 is R
> B, that is, when the color temperature of the illumination light is low, the second reference voltage V _ref2 is output, and when R <B, the third reference voltage V _ref3 is output. The averaging circuit 19 is a device for averaging the output from the switching circuit 18, takes a certain value between the second and third reference voltages V _ref2 and V _ref3 , and has a low color temperature of illumination light. It sometimes takes a value close to the second reference voltage V _ref2 , and takes a value close to the third reference voltage V _ref3 as the color temperature increases. In the first tracking correction circuit 20, when the output of the averaging circuit 19 is close to the second reference voltage V _ref2 , that is, when the color temperature is low, a control signal for reducing the gain of the gain control circuit 3 and the gain A control signal for increasing the gain of the control circuit 4 is produced. Conversely, when it is close to the third reference voltage V _ref3 , that is, when the color temperature is high, a control signal for increasing the gain of the gain control circuit 3 and a control signal for decreasing the gain of the gain control circuit 4 are generated.

At this time, the two control signals have a relationship in which the white balance is correctly corrected in a practical color temperature range of the light source (for example, 2800 ° K to 8000 ° K) which is close to the Planck's radiation formula. .

In the Mg-G detection circuit 21, the color difference signals ( _RYL ), (B
Taking the sum of the -Y _L) are producing (R + B-2Y _L) signal. In the comparison amplifier 22, the (R + B-2Y _L ) signal output from the Mg-G detection circuit 21 and the fourth reference voltage V _ref4.
This fourth reference voltage V _ref4
Is adjusted to be the same as the DC voltage when the (R + B-2Y _L ) signal becomes zero. Here, in this embodiment, R
When + B> 2Y _L , the output of the comparison amplifier 22 is at "H" level,
When R + B <2Y _L , it shall be at "L" level. Reference _numeral 23 is a switching circuit, which switches and outputs the fifth and sixth reference voltages V _ref5 and V _ref6 which are predetermined when the output of the comparison amplifier 22 is “H” level and “L” level, respectively. It is a device. That is, at this time, the output of the Mg-G detection circuit 21 is R +
When B> 2Y _L is indicated, the output of the switching circuit 23 is the fifth reference voltage V _ref5 , and when R + B <2Y _L is indicated, the sixth reference voltage V _ref6 is output. Also, in the case of approximating the Planck's radiation formula, since R + _{B≈2Y L} , (V _ref7 + V
_A value close to _ref8 ) / 2 is output. The averaging circuit 23 is a device for averaging the output from the switching circuit 23,
It takes a value between the fifth and sixth reference voltages V _ref5 and V _ref6 , and the value changes depending on the spectral radiant emittance of the illumination light. In the second tracking correction circuit 25, the output of the averaging circuit 24 is the fifth
When it is close to the reference voltage V _{ref5 of} , the control signal for reducing the gain of the gain control circuit 3 and the control signal for reducing the gain of the gain control circuit 4 are generated. On the contrary, when it is close to the sixth reference voltage V _ref6 , a control signal for increasing the gain of the gain control circuit 3 is generated, and a control signal for increasing the gain of the signal from the gain control circuit 4 is generated.
The first and second adders 26 and 27 add the control signals from the first and second tracking correction circuits 20 and 25 to the respective signals of the R signal system and the B signal system, and gain control circuits 3 and 4 are added. Is output to. At this time, as described above, when the illumination light approximates the Planck's radiation formula, the second tracking correction circuit 25 outputs a substantially constant control signal, while the first tracking correction circuit 25 outputs the first control signal. The tracking correction circuit 20 outputs a control signal according to the color temperature of the illumination light, and the first and second adders 26 and 27 add the control signal so that the white balance correction can be performed correctly. I am adding in. The gain control circuits 3 and 4 control the gains of the color signals by the control signals from the adders 26 and 27, and output them to the color difference signal generation circuit 5. In the above-described configuration, since the present embodiment forms a negative feedback loop as a whole, the color difference signal white balance has been corrected properly (R-Y _L), a (B-Y _L), the above-mentioned It can be supplied to the encoder 6.

In the present embodiment, the width of the output signal from the second tracking correction circuit 25 is narrowed, and, for example, when the white fluorescent lamp is the illumination light, the extent to which the white balance is corrected correctly is set to its limit. It is possible to configure an automatic white balance correction device that is not significantly affected by the green color of the leaves on the screen.

In the present embodiment, the gain of the color signals R and B is controlled to correct the white balance,
Other methods, such as a configuration in which the low-frequency luminance signal is added or subtracted to / from the color difference signal at a certain ratio, can be easily implemented. Furthermore, it is easy to add the clip circuits 9 and 10 to the gate circuits 7 and 8 of the conventional example in the present invention.

EFFECTS OF THE INVENTION As described above, according to the present invention, there is provided the means for detecting the first signal of the difference between the signal components of the two color difference signals obtained from the color signals, and the first signal from the detection means. , This first
Means for comparing the first reference voltage adjusted to be equal to the DC voltage when the signal of 0 becomes zero, and a second preset by the sign of the first signal based on the output from the comparing means. Switching means for selecting one of the reference voltage and the third reference voltage, means for averaging the output from the switching means, and a first tracking correction circuit using the output of the switching means as an input signal. Further, the means for detecting the second signal of the sum of the signal components of the two color difference signals, the second signal from the detecting means, and the direct current voltage when the second signal becomes zero are adjusted to be equal. Based on the output from the comparing means and the compared fourth reference voltage,
Switching means for selecting one of a fifth reference voltage and a sixth reference voltage set in advance depending on whether the second signal is positive or negative, a means for averaging the output from the switching means, and an averaging means. And a second tracking correction circuit that uses the output of the above as an input signal, and adds the outputs of the R signal system among the outputs from the two tracking correction circuits.
And a second adder for adding the output of the B signal system, and the gain of each color signal is controlled by the outputs of these two adders. The white balance can be corrected well whether it is close to the formula or not.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an automatic white balance correction apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an outline of an automatic white balance correction apparatus using a conventional video signal. is there. In the figure. 1: Image sensor 2: Luminance signal / color signal generation circuit 3, 4: Gain control circuit 5: Color difference signal generation circuit 6: Encoder 16: RB detection circuit 17, 22: Comparison amplifier 18, 23: Switching circuit 19, 24: Averaging circuit 20, 25: Tracking correction circuit 21: Mg-G detection circuit 26, 27: Adder

Claims (1)

[Claims] 1. An automatic white balance correction apparatus for performing white balance correction by feedback-controlling the gain of a color signal obtained from an image pickup device, the signal components of two color difference signals obtained from the color signal. A means for detecting the first signal of the difference, and a first means from the detecting means.
And a means for comparing the first reference voltage adjusted to be equal to the DC voltage when the first signal becomes zero,
Switching means for selecting one of a second reference voltage and a third reference voltage preset by the positive or negative of the first signal based on the output from the comparing means, and the output from the switching means is averaged. Means, a first tracking correction circuit using the output of the averaging means as an input signal, a means for detecting a second signal of the sum of the signal components of the two color difference signals, and this detecting means. Means for comparing the second signal from the second reference signal with a fourth reference voltage adjusted to be equal to the DC voltage when the second signal becomes zero, and based on the output from the comparing means, Switching means for selecting one of a fifth reference voltage and a sixth reference voltage preset by the positive or negative of the signal of No. 2, a means for averaging the output from this switching means, and an output of this averaging means. Track with the input signal And a second adder that adds the outputs of the R signal system and the outputs of the B signal system among the outputs from the two tracking correction circuits. However, the automatic white balance correction apparatus is characterized in that the gain of each color signal is controlled by the outputs of these two adders.