JPS61105991A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To avoid a trouble such as the appearance of the influences of up and down change of a count value for 1 bit at the time of automatic follow-up white balance adjusting becoming a change in color by integrating the D/A conversion output of counted value through a time constant circuit and supplying to a gain controlling circuit. CONSTITUTION:In a vertical blanking section, the light receiving outputs of red, green and blue from external photo-electric elements 1R, 1G, 1B are supplied to gain controlling circuits 9R, 9B in stead of the output of an image pickup element 3. Light receiving output levels of red, green and blue through circuits 9R, 9B are compared with each other, and the comparison outputs are supplied to the up down controlling terminal of up down counters 32R, 32B, and the counted value is controlled to make light receiving output levels of red, green and blue with a specified ratio. The A/D conversion output of the counted values are supplied directly to circuits 9R, 9B in the vertical blanking section. However, the outside of the vertical blanking section, the outputs are supplied to circuits 9R, 9B through time constant circuits 40R, 50B.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a white balance adjustment device for a video camera, and more particularly to an automatic tracking type adjustment device.

[Conventional technology]

In a video camera, if the white balance is not adjusted, the hue of the reproduced image will shift due to the difference in color temperature of the subject. Therefore, various methods for adjusting the white balance have been proposed, but one method that automatically adjusts the white balance is to use an external light-receiving element installed separately from the main image sensor that captures the image of the subject, and this external light-receiving element. There is an automatic tracking type that uses a diffuser plate provided in front of the element.

For example, as one of them, the present applicant
No. 86504" was proposed.

This is achieved by providing an external light receiving element that has the same spectral characteristics as the main image sensor, and placing a semi-transparent white diffuser in front of this external light receiving element to transmit white light from the external light receiving element. When a white subject is imaged using these three primary color signals, the level ratio of the three primary color signals from the main image sensor is i:i:t. The level is controlled so that the

FIG. 2 is a system diagram of one embodiment of this white balance adjustment device.

In Figure 2, (IR), (IG) and (IB)
are red, green and blue external light receiving elements that have the same spectral characteristics as the main sensor of the camera, and these include, for example, red, green and blue filters FR, FC, FB and photodiodes DR, DC,
It is composed of a combination of DBs.

These light receiving elements (II?), (IG) and (IB
) is provided with a white semi-transparent diffuser &(2) on the front side.

These external light receiving elements (IR), (IG) and (IR
) Furthermore, the diffuser plate (2) is provided at a fixed position separately from the image sensor (3).

These external light receiving elements (IR), (IG) and (IB
) output is passed through the switch circuit (4) to the AGC amplifier (
5) in a time-sharing manner. This AGC amplifier (5)
is intended to perform gain control according to the movement of the camera's iris (aperture).

The output of this AGC amplifier (5) is time-divisionally switched by a switch circuit (6), and the red, green, and blue outputs are sent to a sampling hold circuit (7R).

(7G) and (7B).

The switch circuits (4) and (6) are respectively switched in conjunction with the three terminals by a horizontal synchronizing pulse Sll from the terminal (21). Therefore, the red external light receiving element (I
The output of R) is output by °ζAGC amplifier (
5) to the sampling and holding circuit (7R), and the output of the light receiving element (IG) is supplied to the sampling and holding circuit (7B) through the amplifier (5) in the next horizontal section. The above steps are repeated in three horizontal periods. Therefore, the sampling and holding circuits (7R), (7) and (7B) output hold outputs obtained by applying AGC to the outputs obtained from the external light receiving elements (IR), (IG) and (IB). is obtained and supplied to the switch circuit (8). The switch circuit (8) is also supplied with primary color signals of red, green, and blue from the imaging signal processing circuit (2o) of the camera.

This switch circuit (8) receives a signal VBL from the terminal (22) that is at a high level only in the vertical blanking section.
K takes out the output from the sampling and holding circuits (7R) (7G) (7B) in the vertical blanking section, and takes out the red, green and blue primary color signal outputs R, G, B from the circuit (2o) in other sections. is made to take out.

In the vertical blanking period, the red output from the sampling and holding circuit (7R) is supplied to one input terminal of the comparison circuit (IOR) through the gain control circuit (9R) and from the sampling and holding circuit (7G). The green output of this comparison circuit (IOR)
A comparison output corresponding to the level difference between the two is obtained from this. Similarly, the blue output from the sampling hold circuit (7B) is sent to the comparison circuit (IOB) through the gain control circuit (9B).
The green output is supplied to one input terminal of the comparison circuit Cl0B), and a comparison output corresponding to the level difference between the two is obtained.

The outputs of these comparison circuits (IOR) and (IOB) are supplied to gain control circuits (9R) and (9B) through switch circuits (IIR) and (IIB), respectively. In this case, the switch circuit (ill?) and the CII
B) is turned on during the vertical blanking period in synchronization with the switching of the switch circuit (8) by the signal VBLK. Therefore, in this vertical blanking interval, the gains of the gain control circuits (9R) and (9B) are determined by the outputs of the comparison circuits (IOR) and (IOB).
The levels of the red, green and blue outputs from the switch circuit (8) are controlled to be 1:1:1. Then, the outputs of the comparison circuits (IOR) and (IOB) when the output levels of red, green, and blue become 1:l:1 are stored in the memory capacitors (12R and (12B)). .

In the video section other than the vertical blanking section, the switch circuit (8) obtains the red, green, and blue primary color signals from the imaging signal processing circuit 1B (20), but at this time, the gain control circuit (9R) and (9B) is a capacitor (
Since the gain is controlled by the storage level of (12R) and (12B), these three primary color signals are output to the output terminal (
13R) (13G) and (13B).

As described above, the diffuser plate (2) and the external light receiving element (IR
) (IG) (IB) and three external light receiving elements (IR) using the vertical blanking section.
Since the gain control millivoltage of the circuit (9R) and (9B) is stored in the capacitors (12R) and (12B) so that the output of (IG) (IB) is 1:1:1, you can change the shooting location. 4) Automatic tracking of this allows you to always obtain an image output with a well-balanced white balance.

[Problem that the invention seeks to solve]

Since the automatic white balance adjustment device 11II shown in FIG. 1 is constructed entirely of analog circuits, it is difficult to provide a memory function for the white balance adjustment voltage over a long period of time. Therefore, it is difficult to add a white balance hold function, that is, a function to stop automatic tracking and maintain the white balance adjustment voltage at the time when automatic tracking is stopped.

Therefore, it is conceivable to configure the circuit with a digital circuit.

By the way, instead of an automatic tracking type that uses an external light receiving element, the following circuit can be considered as a device that automatically adjusts white balance by capturing an image of a white subject with an image sensor and turning on a white balance adjustment switch.

That is, Fig. 3 is an example of this, and the circuit (3
0) is a white balance adjustment pressure generation circuit, which is integrated into an IC.

In this example, the switch circuit (8) of the example in FIG. 2 is not used, and the red and blue primary color signals R and B from the imaging signal processing circuit (20) are directly transmitted to the gain control circuit (9R
) and (9B), and its output is supplied to the output terminal (13
R) and (138''), and the green primary color signal is directly taken out to the output terminal (13G).

The generation circuit (30) includes a comparison circuit (31R) and (31B>
and up/down counter (32R) and (32B >
It consists of a D/A converter (33R) and (33B). The red and blue primary color signals R and B passed through the gain control circuits (9R) and (9B) are respectively input to the input terminals (30R) and (30B) of the circuit (30).
The green primary color signal G is supplied to one input terminal of the comparator circuits (31R) and (31B) through the input terminal
30G) through the comparison circuit (31R) and (31B
> is supplied to the other input terminal. The outputs of the comparison circuits (31R) and (3113) are supplied to the up/down control terminals of the up/down counters (32R) and (32B). Controlled to count down when. Also, this counter (32R) and (32B
) is supplied with the vertical synchronizing pulse VD through the input terminal (34) only during the period when the non-locking switch (36) is on. Furthermore, the count value output of this counter (32R) and (32B) is
3B) are converted into analog voltages ER and EB, and the respective voltages ER and EB are output terminals (35R) and (35B) of the circuit (30) as white balance g1Mffi voltages.
Gain control circuit (9R) and (9B) through
is supplied to.

When performing white balance adjustment with this device, place a diffuser plate (2') in front of the image sensor (3) and turn on the switch (36).As the diffuser plate (2'),
In other words, you can use a white plastic translucent plate as a lens cap and attach it to the front of the lens.

In this way, three primary color signals R, C, and B are obtained from the image signal processing circuit (20) when a white subject is imaged. In the generation circuit (30), a counter (32R
), the vertical synchronizing pulse VD is counted up or down and the count value changes, and the counter (32B
), the vertical synchronizing pulse VD is counted up or down, and its cant value changes. Then, the terminal (3
0R) When the levels of the three primary color signals from (30G) and (30B) become equal, while the switch (36) is on, up-counting and down-counting are performed alternately for each pulse of the vertical synchronization pulse. The value increases or decreases by 1 bit, but when the switch (36) is turned off, the count value of the counter (32R) (32B) stops either by increasing or decreasing by 1 bit. Therefore, after that, this count value is held and is used for the D/A converter (33R) and (33B).
> converted.

analog adjustment voltages ER and EB. The adjusted voltages ER and EB at this time are output terminals (13R)
The three primary color signal levels obtained in (13G) and (13B) are 1:1:1. In other words, the white balance is correct. Therefore, if you then remove the lens cap and start shooting, you will be able to take photos with the white balance maintained at that shooting position.

White balance like this! If the IM adjustment voltage is obtained digitally using a counter instead of analogously as in the example shown in FIG. 2, it is easy to maintain the white balance adjustment voltage for a long period of time.

Therefore, it is conceivable to apply the circuit (3o) shown in FIG. 3 to the device shown in FIG. However, in the case of automatic tracking,
In order to operate the circuit (3o) during the vertical blanking period, the count values of the counters (32R) and (32B) are changed up and down by l bits for each field even when the white balance is maintained, as mentioned above. do. Therefore, the adjustment voltages ER and EB also increase or decrease by 1 bit, causing a color change for each field. It is sufficient if this 1-bit color change is below the detection limit, but this poses a problem in the accuracy of the D/A converter and also causes the disadvantage that it takes time to converge to a state where the white balance can be maintained.

The present invention aims to provide an automatic tracking type white balance adjustment circuit that uses a digital circuit as described above and does not have the above-mentioned drawbacks.

[Means for solving problems]

In this invention, an external light receiving element (IR) is provided separately from the image sensor (3) and has the same spectral characteristics as the image sensor (3).
(IG) (1B) and this external light receiving element (IR)
(IG) A diffuser plate (2) placed in front of (IB), a gain control circuit (9R) (9B) provided for the output from the image sensor (3), and a clock with a period less than the vertical period. Up/down counters (32R) (32B) that count
Convert the count value from R) (32B) to an analog voltage, and use the analog voltage to control the gain control circuit (
9R) D/ to control the gain of (9B)
A converter (33R) (33B') and a time constant circuit (40R) (50B) with a time constant longer than the vertical period.
).

[Operation] External light receiving element (IR) in the vertical blanking section
(IG) The red, green, and blue light reception outputs from (IB) are supplied to the gain control circuit (9R) (9B) instead of the output of the image sensor (3), and this gain control circuit (91?) ( Red through 9B).

The green and blue light receiving output levels are compared, and the comparison output is supplied to the up/down control terminal of the up/down counter (32R) (32B) so that the red, green, and blue light receiving output levels are in a predetermined ratio. The count value is controlled, and the A/D conversion output of this count value is directly sent to the gain control circuit (9R) in the vertical blanking section.
(9B) is supplied to the gain control circuit (9R) (9B) via the time constant circuit ('40R) (50B) except in the vertical blanking section.

〔Example〕

FIG. 1 shows an example of the device of the present invention, in which the control voltages to the gain control circuits (9R) and (9B) are the voltages ER and ER generated in the white balance adjustment voltage generation circuit (30) shown in the example in FIG. EB is used. and,
In this case, a resistor (41) and a capacitor ( 42), a time constant circuit (40R) consisting of a switch circuit (43) and a resistor (5
1), capacitor (52).

A time constant circuit (50B) consisting of a switch circuit (53) is connected. And switch circuits (43) and (53
) is the vertical blanking signal VBLK from terminal (22)
Accordingly, the vertical blanking section is turned off and the other sections are turned on. In other words, in the vertical blanking section, the voltage ER
and EB are gain control circuits (9R) and (9B
) through resistors (41) and (51), but the voltages ER and E are supplied directly to
B is supplied to gain control circuits (9R) and (9B) through time constant circuits (40R) and (50B), respectively. In this case, the time constant circuit (40R) and (50R)
The time constant of B) is longer than the vertical period, and is such that a change of one bit per 1 field period is not noticeable. For example, this is about 1 second.

Further, in this example, the vertical synchronizing pulse VD supplied to the circuit (30) as a black signal is supplied to the input terminal (34) via the switch (60). This switch (6
0) is [Auto J, rOFF J, rONE
PUS has three switching positions, rO
When in the FFJ position, the movable contact is at the free end as shown in the figure, and the vertical synchronizing pulse VD is not supplied to the circuit (30). Next time you are in the "Auto" position,
The movable contact is locked to the terminal AUTO side, and the vertical synchronization pulse VD is always supplied to the circuit (30). rONEPu
s The old position is a non-locking position, and r
When the rONE POS is turned from the OFFJ position to the old position side, the movable contact is connected to the terminal ONE side only while it is turned down, and the vertical synchronizing pulse VD is supplied to the circuit (30) only during that period.

The other parts are constructed similarly to the example shown in FIG.

With the above configuration, when the switch (60) is in the "auto" switching position, the external light receiving elements (IR) to (IB) obtained from the switch circuit (8) in the vertical blanking section are Adjustment voltages ER and EB are generated in the generation circuit (30) based on the outputs, which are then applied to the gain control circuits (9R) and (9R).
B). In this case, the voltages ER and EB are 1
Although the switch circuit (43) and (
53) is turned on, and therefore the voltages ER and EB are integrated and supplied by the time constant circuits (40R) and (50B), so the influence of this 1-bit change is eliminated. Moreover, the switch circuits (43) and (53) are turned off during the vertical blanking period, and the voltages ER and EB are directly applied to the gain control circuit (9R) and (
9B), the convergence time of Hovit balance will not be delayed.

Next, the switch (60) is set to the position El 7 r'ONE
When set to PIISHJ, the adjustment voltages ER and EB are changed only while connected to the terminal ONE side, and when the hand is released, the adjustment voltages ER, E, and B are held at that time.

After that, even if the switch circuit (8) is switched to the state shown in the figure in the vertical blanking section, the counter (32R) and (32
Since the clock pulse of B) is not input, the voltages ER and EB at that time remain as they are, and a hold tag can be realized.

In this example, circuits 1 to 3 (30) can be used as IC circuits, which is a great advantage in terms of circuit configuration and cost.

The clock for the counters (32R) and (32B) is a vertical synchronizing pulse VD, which may be used as a vertical blanking pulse VBL, or may be a pulse with a period shorter than the vertical period.

〔Effect of the invention〕

According to this invention, since the white balance m-contact voltage can be generated using an up-down counter, a hold function can be easily realized, and the gain control is performed by integrating the D/A conversion output of the count value via a time constant circuit. Since the signal is supplied to the circuit, it is possible to avoid the inconvenience that the influence of the vertical change in the count value for one bit appears as a color change when adjusting the white balance of automatic tracking.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the inventive device, Fig. 2 is a block diagram of an example of the previously proposed automatic tracking type white balance adjustment device, and Fig. 3 shows digital white balance adjustment voltage. FIG. 2 is a block diagram of an example of a white balance adjustment device using a generating circuit. (IR) (IG) (1B) is an external light receiving element, (
2) is the diffuser plate, (3) is the main image sensor, (9R)
(9B) is a gain control circuit, (30) is a white balance adjustment voltage generation circuit, (31R) (31
B) is a comparison circuit, (32R) (32B) is an up/down counter, (33R') (33B) is a D/A
It is a converter.

Claims (1)

[Claims] an external light-receiving element that is provided separately from the image sensor and has the same spectral characteristics as the image sensor; a diffuser plate that is disposed in front of the external light-receiver; and a gain control circuit that is provided for the output from the image sensor; an up/down counter that counts clocks with a period equal to or less than the vertical period; a D/A converter that converts the count value from this counter into an analog voltage and controls the gain of the gain control circuit with the analog voltage; and a time constant circuit with a time constant longer than the vertical period, and red, green, and blue light reception outputs from the external light receiving element are supplied to the gain control circuit in place of the output of the image pickup element during the vertical blanking interval. At the same time, the red, green, and blue light receiving output levels through this gain control circuit are compared, and the comparison output is supplied to the up/down control terminal of the up/down counter to adjust the red, green, and blue light receiving output levels. The count value is controlled so as to have a predetermined ratio, and the A/D conversion output of this count value is directly supplied to the gain control circuit during the vertical blanking period, and to the time constant circuit outside the vertical blanking period. A white balance adjustment device configured to be supplied to the gain control circuit through the white balance adjustment device.