JPH01194791A - Automatic white balancing correction circuit - Google Patents

Abstract

PURPOSE:To realize a further stabilized operation and to prevent the deterioration of color reproducibility by constituting the title circuit so that a white balancing correction action is started only when the mean value of color difference signals exceeds the output of an offset adding circuit or that of an inverter and that the operation is stopped when the difference between a white balancing correction reference value and the mean value of color difference signals goes to zero. CONSTITUTION:When color temperature changes from a state in white balancing, the mean value 108 is simultaneously varied, as well in case of changing a first color difference signal 102, and a white balancing correction value 125 is varied. When the value 108 exceeds the output 116 of the offset adding circuit 10a or that 117 of the inverter 11a and a switch circuit 6a is closed, a white balancing correction action is started. When the difference between the mean value 108 and a white balancing correction reference value 104 goes to zero, the circuit 6a is opened by a first switch control signal 125 to stop the white balancing correction action. As a result, the fluctuation in white balancing correction action can be reduced more stable action can be achieved, and the deterioration in color reproducibility can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a simple white balance correction circuit for a video camera.

2. Description of the Related Art In recent years, as the demand for video cameras has increased, there has been a demand for simple white balance correction circuits that are low in cost and have high performance. A conventional white balance correction circuit will be described below with reference to the drawings.

FIG. 2 shows a block diagram of a conventional white balance correction circuit. In Fig. 2, 1 is the image sensor output 1
o1 is a color reproduction process circuit that outputs a color difference signal 103, and 2 is an average value detection circuit that detects an average value 109 of the color difference signals. 6 compares the white balance correction reference value 106 and the average value 109, and calculates the difference as the white balance correction value 12.
This is a white balance comparison circuit that outputs the signal as 4.

The operation of the conventional white balance correction circuit configured as described above will be described below.

First, the white balance setting of the color difference signal 103 at the reference color temperature is performed using the white balance reference value 105. Next, when the color temperature changes, the color difference signal 103 changes and at the same time the average value 109 changes.

Unfortunately, the white balance correction value 124 fluctuates, and the color difference signal 103 due to color temperature changes in the color reproduction process circuit 1.
operates to suppress fluctuations in

As described above, white balance correction is performed by a series of circuit operations that suppress fluctuations in the color difference signal 103 due to changes in color temperature.

Problems to be Solved by the Invention However, with the above-described configuration, the white balance correction value 124 tends to fluctuate depending on the subject for which feedback is constantly working, resulting in unstable operation.

Further, when the color difference signal 103 includes color components, there is a problem in that the saturation decreases due to the suppression of the color components, and the color reproduction deteriorates accordingly.

In view of these problems, the present invention provides more stable operation,
In addition, the present invention provides a white balance correction circuit that improves deterioration in color reproduction.

Means for Solving the Problems In order to solve the above problems, an automatic white balance correction circuit of the present invention includes an average value detection circuit that detects the average value of a first color difference signal, and an output of the average value detection circuit and a white balance correction circuit of the present invention. A white balance correction unit that compares balance correction reference values, outputs a white balance correction value according to the difference, and outputs a first switch control signal when the output of the average value detection circuit and the white balance correction reference value match. a balance comparison circuit, an adder for adding the output of the average value detection circuit and the average value of the second color difference signal, an offset addition circuit for adding an offset to the output of the adder, and an output of the offset addition circuit. and an average value comparison that outputs a second switch control signal when the output value of the average value detection circuit exceeds a range between the output value of the offset adding circuit and the output value of the inverter. a switch circuit having a characteristic of being opened by the first switch control signal and closed by the second switch control signal; and a hold circuit that holds the white balance correction value applied via the switch circuit. , and a color reproduction process circuit that controls the white balance of the first color difference signal using the output of the hold circuit.

According to the above-described configuration, the present invention starts the white balance correction operation only when the average value of the color difference signal exceeds the output of the offset addition circuit or the output of the inverter, and the white balance correction reference value and the average value of the color difference signal are The operation will stop when the difference between
Since the average value component of the color difference signal is input to the average value comparison circuit, it is difficult to react to the color component and the deterioration of color reproduction is improved.

Embodiment Below, an automatic white balance correction circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an automatic white balance correction circuit in one embodiment of the present invention.

In FIG. 1, 1 is a color reproduction process circuit that receives an image sensor output 101 and outputs a first color difference signal 102 and a second color difference signal 103, and 2a and 2b represent the first and second color difference signals, respectively. These are first and second average value detection circuits that detect average values 108 and 105) of color difference signals 102 and 103.

8 and 12 are outputs 1 of the first average value detection circuit 2a.
08 are a first gain control circuit and a second gain control circuit that can arbitrarily select the gain, and 13 and 14 are a third gain control circuit that can arbitrarily select the gain of the output 1o9 of the second average value detection circuit 2b. circuit and a fourth gain control circuit.

9a is a first adder that adds the output 110 of the first gain control circuit 8 and the output 113 of the third gain control circuit 13; This is a second adder that adds the outputs 111 of the gain control circuits 14 of . 10a and 10b are first and second offset adding circuits that apply offsets to the outputs of the first and second adders 9a and 9b, respectively;
a and 11b are the first and second offset adding circuits 10a.

10b is an inverter that inverts outputs 116 and 114 of 10b. 3a is the output 108 of the second average value detection circuit 2a.
The output 116 of the first offset adding circuit 10a and the output 117 of the first inverter 11a are compared, and the output 108 indicating the average value of the first color difference signal is determined to be the output 116 and the output 11.
This is a first average value comparison circuit that outputs a second switch control signal 112 when the average value exceeds the range of 7. 3b compares the output 109 of the first average value detection circuit 2b, the output 114 of the second offset addition circuit 106, and the output 116 of the second inverter 116, and indicates the average value of the second dye signal. This is a second average value comparison circuit which outputs a second switch control signal 119 when the output 109 exceeds the range of the outputs 114 and 115.

5a compares the output 108 of the first average value detection circuit 2a with the white balance correction reference value 104, outputs a white balance correction value 126 according to the difference, and outputs the first switch control signal 121. 1, and 5b compares the output 109 of the second average value detection circuit 2b with the white balance correction reference value 105, outputs a white balance correction value 124 according to the difference, and outputs the white balance correction value 124 corresponding to the difference. 109 and the reference value 105, the first control signal 1
This is a second white balance comparison circuit that outputs 18. 6a
and 6b are respectively the second switch control signals 112,
119, the first switch control signal 12
White balance correction value 12 by opening by 1,118
This is a switch circuit for selecting whether the output of No. 6 is appropriate or not.

Also 7a.

7b is a hold circuit that holds white balance correction values 125 and 124, respectively, when switch circuits sa and 6b are open.

The operation of the automatic white balance correction circuit configured as described above will be explained.

Now, when the white balance is matched, the first and second switch circuits ea and eb are both in an open state, and the first and second hold circuits 7a and 7b are set to a hold value 106 that matches the white balance. 107 is output. Next, when the color temperature changes, the average value 108 also changes at the same time as the first color difference signal 102 changes, and the white balance correction value 12
However, the white balance correction is not necessarily performed depending on the state of the first switch circuit 6a. The white balance correction operation is started when the average value 108 is the output 116 of the offset adding circuit 10a or the output 11 of the inverter 11a.
7 and the switch circuit 7a closes, and when the difference between the average value 108 and the white balance correction reference value 104 becomes zero, the first switch control signal 125 opens the switch circuit 6a and stops the white balance correction operation. do. The hold circuit 7a holds the white balance correction value 126 at this time.

.

As described above, by preventing the white balance correction circuit from being a normally closed feedback circuit, fluctuations in the white balance correction operation can be reduced and more stable operation can be performed. Furthermore, the signals 116 and 117 that should be compared with the average value 108 in the average value comparison circuit 3 also contain components of the second color difference signal 103, making it difficult to react to color components other than color temperature components. Therefore, it is possible to improve the deterioration of color reproduction.

Effects of the Invention As described above, in the present invention, with the above-described configuration, the white balance correction operation is started only when the average value of the color difference signal exceeds the output of the offset addition circuit or the output of the inverter, and the white balance correction reference value is set. The operation stops when the difference between the average value of the second color difference signal and the average value of the color difference signal becomes zero, resulting in more stable operation.Also, since the average value component of the second color difference signal is input to the average value comparison circuit, the color component It is less sensitive to color reproduction, which improves the deterioration of color reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic white balance correction circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram of an automatic white balance correction circuit according to a conventional example. 1...Color reproduction process circuit, 2a, 2b...
...Average value detection circuit, 3a, 3b...Average value comparison circuit, 5a, 5b...White balance comparison circuit, sa, ab...Switch circuit, 7a ,
7b...Hold circuit, 8, 12, 13.14
...Gain control circuit, 9a. 9b...Addition circuit, 10a, 10b...
...Offset addition circuit, 11 &, 11b...
Inverting circuit.

Claims (1)

[Claims] an average value detection circuit that detects the average value of the first color difference signal;
The output of the average value detection circuit and the white balance correction reference value are compared, and a white balance correction value corresponding to the difference is output. a white balance comparison circuit that outputs a first switch control signal, an output of the average value detection circuit and a second switch control signal;
an adder for adding an average value of the color difference signals; an offset adding circuit for adding an offset to the output of the adder; and an inverter for inverting the output of the offset adding circuit;
an average value comparison circuit that outputs a second switch control signal when the output value of the average value detection circuit exceeds a range between the output value of the offset adding circuit and the output value of the inverter; a switch circuit that opens in response to a switch control signal and closes in response to the second switch control signal; a hold circuit that holds the white balance correction value applied via the switch circuit; 1. An automatic white balance correction circuit comprising: a color reproduction process circuit for controlling the white balance of the color difference signal of No. 1;