JP2547213B2 - Auto white balance device - Google Patents

Description

The present invention relates to an auto white balance device, and more particularly to an auto white balance device used in a color image pickup device such as an electronic camera.

[Prior Art] In recent years, an electronic still camera capable of taking a still image like a silver salt film camera has been proposed. The basic configuration of the electronic still camera is almost the same as that of the video camera. Auto white balance devices for color video cameras, etc. are R (red), G (green), B (blue)
Regarding the primary color light, a color signal gain control amplifier (hereinafter abbreviated as GCA) in a video signal system adjusts the ratio of the color signals R, G, B to be 1: 1: 1. Therefore, in the conventional auto white balance device, the output of GCA is fed back by the white balance detection circuit and compared with the reference voltage, and the error is guided to the gain control terminal of GCA, and the gain of GCA is reduced in the direction of reducing the error. Had control. In such a device in which the white balance is adjusted in a closed loop, even if the input signal level changes, the GCA
There is an advantage that even if the characteristics of (1) change slightly, a signal of a stable level that is not affected by these changes can be taken out.

[Problems to be Solved by the Invention] However, in the closed-loop auto white balance device, due to the delay element in the feedback loop, the GCA for the controlled signal supplied to the input terminal of the GCA is reduced.
The control signal supplied to the gain control terminal of
The response of gain control is poor. Generally, a video camera that obtains continuous movie images does not require a high-speed response for gain control, so a closed-loop auto white balance device is very effective, but it is an electronic still camera. In
Since the purpose is to obtain one image in a short time, particularly high speed response is required.

Also, in general, an automatic white balance device cannot perform correct white balance adjustment for light such as strobe light that exists only during exposure.
It was necessary to provide a strobe preset circuit separately from the electric circuit of the auto white balance device so that when the strobe is used, the gain control of the color signal that matches the strobe characteristics is performed by the preset circuit. However, if the strobe preset circuit is provided separately from the circuit for daylight auto white balance, the device becomes so complicated.

In view of such a problem, the present invention provides an automatic white balance device that can be applied to an electronic camera capable of still photography related to daylight and strobe light and that does not require a strobe-specific preset circuit. With the goal.

[Means for Solving Problems] An auto white balance device of the present invention includes a gain control means for controlling a gain of a color output signal of an image pickup means according to a level of a given gain control signal, and a given gain. Gain control means for controlling the gain of the color output signal of the image pickup means according to the level of the control signal, and integration for integrating the output signal of the image pickup means or the amplified signal of the output signal during the period defined by the first timing signal. Means, computing means for calculating a signal level value corresponding to the gain control signal based on the output of the integrating means, and a reference level signal for generating a reference level signal having a level equal to the gain control signal level suitable for a certain light source light. The gain control means uses the reference level signal as a gain control signal during at least a period defined by the generation means and the first timing signal. And a switching means for supplying the output of the arithmetic means to the gain control means at a timing defined by the second timing signal when the second timing signal is issued after this period, and the present device is open loop control. When in the mode, when both the timing signals are issued so that the period defined by the first timing signal precedes the time point defined by the second timing signal, the device is in the preset mode. Includes timing control means that does not emit the second timing signal.

[Operation] When the operation mode is set to the open loop control mode, the signal based on the output of the photographing means is integrated during the period defined by the first timing signal, and the calculation is performed based on this integrated output. During the integration period, the reference level signal is given to the gain control means as the gain control signal, and the calculation output is the second
Is supplied to the gain control means as a gain control signal. When the operation mode is the strobe preset mode, the second timing signal is not issued and only the reference level signal is given as the gain control signal.

[Examples] FIG. 1 is a block diagram of an automatic white balance device showing an example of the present invention.

The auto white balance device shown in FIG.
It is applied to electronic cameras capable of still photography and movie photography. An image pickup device (not shown) of this electronic camera is also used as a photometric sensor for controlling the white balance of the automatic white balance device. An R signal and a B signal of a color video signal are alternately transmitted from the image sensor to a video processing circuit 3 through a line 1 in a line-sequential manner, and a G signal is transmitted through a line 2. In the video processing circuit 3, GCA4 is inserted in the line-sequential line 1 for automatic white balance adjustment. This GCA
Comprises two GCAs independently controlled by two control signals sent from the control line 48 described below, whereby the gains of the R signal and the B signal are set, respectively. The R and B color signals on the output line 5 of the GCA4 and the G color signal on the line 2 are sent to the circuit at the next stage as video signals and are used as control information for controlling the gain of the GCA4. In other words, the gain control of GCA4 is performed by this automatic white balance device, so that the R, B, and G color signal levels become 1: 1: 1.

A buffer circuit 8 is connected to the line 2 of the G signal, and a buffer circuit 9 is connected to the line 5 of the R / B signal on the output side of the GCA4. The output terminal of the buffer circuit 8 is connected to the switch 11 of the high-level cut circuit 10, and the output terminal of the buffer circuit 9 is connected to the switch 12 of the high-level cut circuit 10. The high level cut circuit 10 is G,
It is a circuit that cuts off the transmission of these color video signals when the level of the R / B signal reaches a substantially saturated level, and comprises the switches 11 and 12, the variable resistor 13 and the comparator 14. That is, since the dynamic range of the image sensor has a limit, when the image sensor receives a high-brightness image, the high-brightness component of the color video signal is saturated. The high-level cut circuit 10 is used to prevent the integration by the following. In this high level cut circuit 10, the output of the buffer circuit 8, that is, the level of the G signal is compared with the reference level set by the variable resistor 13, and when the level of the G signal exceeds the reference level, the output of the comparator 14 causes the switch 11 , 1
2 is switched from the on state to the off state so that the output of the buffer circuits 8 and 9 is stopped from being sent to the subsequent stage. The switches 11 and 12 are controlled by detecting the level of the G signal because the R, B, and G color video signals output from the image sensor when a high-brightness subject having a normal light distribution is imaged. This is because the saturation level does not reach the saturation level uniformly, but in many cases, the components of the G signal first reach the saturation level. The output terminal of the switch 11 is connected to the field integration holding circuit 16, and the output terminal of the switch 12 is connected to the field integration holding circuits 17, 18 via the R / B signal separation circuit 15.
The field integration holding circuit 16 integrates the G signal over the effective scanning period of one field and holds it, and the field integration holding circuits 17 and 18 are R / B signal separation circuits.
The R signal and the B signal separated at 15 are each integrated and held over the period of one field. The field integration holding circuits 16, 17 and 18 are connected to a subsequent division / digital sample / hold circuit 20. The division / digital sample and hold circuit 20 takes in the outputs of the field integration holding circuits 17 and 18 for the R and B color signals in the vertical blanking period, and outputs the outputs of the field integration holding circuit 16 for the G color signal. It is a circuit that divides and obtains and holds the respective ratios R / G and B / G. The division and digital sample-and-hold circuit 20 is provided with a dual type current addition type D / A converter 21. Two D / A converters 22 and 23 in this D / A converter 21
Is the self-propelled counter 2 connected to this D / A converter 21
The count value of 4 is converted into an analog value. The D / A converter 22 is for the R signal, and the D / A converter 23 is for the B signal. Reference input terminal r of D / A converter 21
A switch 25 for switching between the output of the field integration holding circuit 16 and the reference voltage Vref of the reference voltage generation circuit 26 by the switching signal S1 is connected to ef. Latch input terminal of the division and digital sample-and-hold circuit 20
The output terminal of the comparator 27 is connected to h.
The changeover switches 28 and 29 that are switched by the changeover signal S2 are connected to both input terminals of the comparator 27. The changeover switch 28 switches the outputs of the field integration holding circuits 17 and 18 and inputs them to one input terminal of the comparator 27, and the changeover switch 29 switches the outputs of the D / A converters 22 and 23 to change the comparator. It is input to the other input terminal of 27. In addition, the D / A to which the switching signal S2 is applied
The input selection terminal sel of the converter 21 is a self-propelled counter 24
The latch signal output from the comparator 27 input from the digital input and the latch input terminal latch is transferred to the D / A converters 22 and 23 corresponding to the R signal system and the B signal system, respectively, in synchronization with the switching signal S2. It is to separate. The output of the D / A converter that is not selected is held in the last state when it was selected.

As an output stage of the division / digital sample / hold circuit 20, an open control output circuit 30 and a feedback control output circuit 34 are provided.

The open control output circuit 30 is a circuit used at the time of still photography, and includes inverting amplifiers 31 and 32 for amplifying the outputs of the D / A converters 22 and 23, respectively, and outputs the outputs of the inverting amplifiers 31 and 32 to an output selection circuit 46. Output line 33 to be sent to

The feedback control output circuit 34 is a circuit used during movie shooting, and includes differential amplifiers 37, 38 for comparing the outputs of the D / A converters 22, 23 with the reference voltages Vref1, Vref2 of the variable resistors 35, 36, respectively. , Differential amplifier 37 for system stability,
Low-pass filter (hereinafter LPF) connected to the output side of 38
39, 40) and an output line 41 for sending the outputs of the LPFs 39, 40 to an output selection circuit 46.

Further, a preset output circuit 42 for presetting the gain of GCA4 to a known value is provided, and the preset output circuit 42 has reference voltages Vref3, Vref4 (reference voltages Vref3 ′, Vref4 ′ for presets suitable for strobe light). ) To adjust the R and B color signal gains.
3,44 and the reference voltage V set by the variable resistors 43,44
The output line 45 sends the levels of ref3 and Vref4 (Vref3 ', Vref4') to the output selection circuit 46.

The output selection circuit 46 is provided with a selection switch 47, and the output lines 45, 33, 41 are respectively connected to the contact terminals 47a, 47b, 47c of the switch 47, and are switched by the switching signal S3 to be switched to the contact terminals 47a. , 47b, and 47c are connected to a gain control terminal of the GCA4 by a control line. The switching signals S1, S2, S3 are generated by the timing control circuit 49.

The output lines 33, 41, 45, the output selection circuit 46, and the selection switch 47 (47a, 47b, 47c, 47
d), the control line 48 is a two-system parallel (independent) system, which is shown in a simplified state in FIG.

Here, a schematic configuration of the entire electronic camera system to which the above-mentioned auto white balance device is applied will be described with reference to FIG.
The exposure controller 51 is controlled by transmitting and receiving signals to and from a system controller 52 including a microcomputer. The system controller 52 uses the switching signal
It has a function of a timing control circuit 49 for generating S1, S2, S3 and the like, a photometric information processing function and the like. The exposure control device 51 includes control circuits such as a strobe, an aperture, and a shutter.

A strobe selection switch 53, a still / movie selection switch 54, and a photometric sensor 55 are connected to input terminals of the system controller 52. For example, when the strobe is used, the strobe selection switch 53 is turned on, and when the strobe is not used, the input terminal which has been set to “H” by the pull-up resistor 56 at this time becomes “L”. The still / movie selection switch 54 is, for example, turned off during still photography, and the input terminal of the system controller 52 is set to “H” by a pull-up resistor 57, and turned on during movie photography to set the input terminal to “L”. Further, in this embodiment, as the photometric sensor 55 for exposure control, a well-known sensor arranged at an appropriate position of the camera independently of the image sensor is used, but of course, the image sensor for exposure control is used. It may be also used as the photometric sensor 55.

Next, the operation of the automatic white balance device will be described. An image signal to be gain-controlled based on the output of the image sensor is supplied to the lines 1 and 2. As shown in FIG. 3, this image signal has vertical blanking periods B1, B2, B3,... Between the signals in the field periods f1, f2, f3,.

First, the case of still photography will be described. In the case of still photography, the output contact terminal 47d of the selection switch 47 of the output selection circuit 46 is initially connected to the preset side contact terminal 47a. Therefore, the output line 45 of the preset output circuit 42 is connected to the control line 48, and the voltages Vref3, Vref4 preset by the variable resistors 43, 44 are input to the gain control terminal of the GCA4. As a result, GCA4 is controlled to a reference gain for white balance in still photography. Thereafter, when the shutter button is pressed, the shutter is opened within the period f1 of the first one field, and exposure for white balance is performed. When the exposure is completed, a video signal corresponding to the exposure amount is read from the image sensor in the next field period f2, so that the R and B signals are input to line 1 and the G signal is input to line 2. In the field period f2 of this read, the reference value preset by the preset output circuit 42 is given as the gain control signal of GCA4. Then, the video signal in the readout field period f2 is input to the buffer circuits 8 and 9 from lines 2 and 5 for the actual white balance control performed in the subsequent field period f3. The G signal passed through the buffer circuit 8 is input to the field integration holding circuit 16 via the switch 11 of the high level cut circuit 10, and the R and B signals passed through the buffer circuit 9 are passed through the switch 12 of the high level cut circuit 10. After that, they are separated by the R / B signal separation circuit 15 and input to the field integration holding circuits 17 and 18, respectively. The field integration holding circuits 16, 17, and 18 respectively integrate the G, R, and B signals over one field period f2 of charge reading from the image sensor, but the subject light is very strong, and the dynamic range of the image sensor is G up to the saturation level corresponding to the upper limit
When the signal level rises, the range of the high brightness portion is cut by the high level cut circuit 10 and only the effective component is integrated. The G, R, and B signals integrated over one field period are held at the end of the field period f2 and input to the division / digital sample / hold circuit 20. Then, in the vertical blanking period B2 following the field period f2, the division and digital sample hold circuit 20 operates. The changeover switch 25 is changed over to the output side of the field integration holding circuit 16 by the start changeover signal S1 as shown in the figure, and the G signal integrated over one field period is supplied to the reference input terminal ref of the D / A converter 21. Is entered. Further, the changeover switches 28 and 29 are alternately switched to either side of the R and B signals in synchronization with the changeover signal S2. That is, in the state shown in the figure, the R signal side is selected by the switching signal S2 and the output of the field integration holding circuit 17
The output of the D / A converter 22 is compared by the comparator 27. When the D / A conversion unit 22 starts D / A conversion of the output of the self-propelled counter 24 by the switching signal S2 input to the input selection terminal sel, the output of the D / A conversion unit 22 is output to the comparator through the changeover switch 29. Guided by 27 Field integration hold circuit 17
Is compared with the output of. Then, when the output level of the D / A converter 22 matches the output level of the field integral holding circuit 17, the output of the comparator 27 is sent to the latch input terminal latch, and the analog value of the D / A converter 22 is latched. It The analog value of the D / A converter 22 at this time is equal to the output signal R of the field integral holding circuit 17.

When the D / A conversion by the D / A conversion unit 22 is completed, the switching signal S2 is subsequently supplied in the latter half of the same vertical blanking period B2.
The B signal side is selected by the field integration holding circuit 18
Is compared with the output of the D / A converter 23 by the comparator 27, and when both inputs of the comparator 27 match, D / A
The analog value of the A converter 23 is latched. D / A at this time
The analog value of the conversion unit 23 is equal to the output signal B of the field integration holding circuit 18. When the D / A conversion by both D / A converters 22 and 23 is completed, at the end of this vertical blanking period B2, the switch 25 is switched by the switch signal S1 to the reference voltage generating circuit.
The reference voltage Vref is input to the reference input terminal ref of the D / A converter 21. Then, the analog values R and B of the D / A converters 22 and 23 are multiplied by the ratio Vref / G of the switched reference input voltage as a coefficient.
The output of the D / A converter 22 is held at Vref × R / G, and the D / A converter 2
The output of 3 is held at Vref × B / G.

When the vertical blanking period B2 ends and the next field period f3 rises, this field period
At the rising edge of f3, the selection switch 47 of the output selection circuit 46
Since the output contact terminal 47d switches the connection to the open control contact terminal 47b, the outputs of the D / A converters 22 and 23 are respectively amplified by the inverting amplifiers 31 and 32 of the open control output circuit 30, and the output line From 33 through control line 48
Input to A4 gain control pin. Therefore, after the field period f3, the gain control for obtaining the optimum white balance for the still image captured within the first field period f1 is performed in GCA4.

Note that when a strobe is used in still photography, the strobe light has a spectral characteristic that is different from that of daylight, and thus the above-described open control is unnecessary. Therefore, in this case, the output contact terminal 47d of the changeover switch 47 is changed to the preset contact terminal 47a by the changeover signal S3.
Connected to. And in this case, the output contact terminal
When 47d does not switch the connection to the open control contact terminal 47b on the way and is still connected to the preset contact terminal 47a, exposure by strobe light is performed, and the data extracted from the image sensor is input to GCA4. The white balance control suitable for the strobe is performed by applying the reference voltages Vref3 ', Vref4' passed through the strobe light set by the variable resistors 43, 44 of the preset output circuit 42 to the gain control terminal of GCA4. Therefore, in this auto white balance device, the preset output circuit 42 has a simple structure because it serves as both a preset circuit for giving a reference value for open loop control and a strobe preset circuit. Note that the "preset mode" at the time of strobe also includes so-called auto preset.

Also, instead of providing the preset output circuit 42,
Using the preset function of the self-propelled counter 24, a preset signal can be generated by the D / A converter 21.

Next, the case of movie shooting will be described. In the case of movie shooting, the contact terminal 47d of the selection switch 47 of the output selection circuit 46
Is connected to the contact terminal 47c, so that the output line 41 of the feedback control output circuit 34 is connected to the control line 48. In this case, line 2 is used for white balance control.
The data of the G signal taken out from and the data of the R and B signals taken out from the line 5 on the output side of the GCA4 pass through the buffer circuits 8 and 9, respectively, as in the case of the above still photography, and pass through the high level cut circuit. High brightness level is removed at 10, R, B
The signals are separated by the R / B signal separation circuit 15, and then the G, R, and B signals are integrated by the field integration holding circuits 16, 17, and 18 for one field period, and the divided and digital sample hold circuit 20 is obtained. The division / digital sample and hold circuit 20 performs the above-described division operation during the vertical blanking period, and the D / A conversion units 22 and 23 generate (Vref ×
R / G), (Vref x B / G) are output. This D / A converter 22,
The outputs (Vref × R / G) and (Vref × B / G) of 23 are input to the differential amplifiers 37 and 38 of the feedback control output circuit 34,
The reference voltages Vref1 and Vref2 of the variable resistors 35 and 36 are compared with each other, and the comparison outputs of the differential amplifiers 37 and 38 pass through LPFs 39 and 40,
The signal is input from the output line 41 to the gain control terminal of the GCA4 through the control line 48. In the case of movie shooting, since the video signal is continuously output from the image processing circuit 3, the GCA4 does not preset the R and B signals. Therefore, the output of the D / A converters 22 and 23 (Vref × R / G), (Vref × B
/ G) is not an appropriate value in the first read field period, but the D / A conversion outputs (Vref × R / G) and (Vref
× B / G) and the reference voltages Vref1 and Vref2 are compared and feedback control is performed, so that Vref1
R / G = 1, B / G = if adjusted so that = Vref2 = Vref
Becomes 1.

In FIG. 1, the output selection circuit 46 has been described as the two-system parallel selection switch 47 performing the switching operation according to the command of the switching signal S3. Specifically, an analog multiplexer IC is used as the output selection circuit 46, For example, “standard logic IC4053” can be applied. in this case,
Explaining one of the two parallel systems, the circuit diagram is as shown in FIG. 4, which is issued from the system controller 52 and is applied to the respective gate terminals of the analog switches 58 and 59. Switching signal S3a, S3b
When both are "H", the analog switches 58 and 59 are both connected to one contact terminal as shown in the figure, and the signal of the feedback control contact terminal 47c is conducted to the output contact terminal 47d. I will Further, when the switching signal S3a is "L" and the switching signal S3b is "H", only the analog switch 58 is connected to the other contact terminal on the opposite side to that shown in the figure. The signal of 47b is guided to the output contact terminal 47d. Further, the switching signal S3a may be "L" or "H", but the switching signal S3b
Is "L", the analog switch 59 is in a state of being connected to the other contact terminal on the opposite side of the drawing, so that the signal of the preset contact terminal 47a is guided to the output contact terminal 47d.

By the way, in the above auto white balance device, the current addition type D / A converter 21 is used in principle because it is easy to obtain accuracy in principle.
When the converter 21 is used, there is a problem that the output voltage is inverted with respect to the reference input voltage due to the characteristics of the current-voltage converter included in the output stage. Therefore,
This is usually dealt with by providing an inverting amplifier. However, in order to avoid complicating the circuit for space reasons of the electronic camera, here, the field integration holding circuit 16, 17, 18 provided in the preceding stage is used.
This problem is solved by considering the configuration of. That is, an inversion type is used for the field integration holding circuit 16,
Non-inverting type field integration holding circuits 17 and 18 are used. Alternatively, when an inversion type field integration holding circuit 16 is used, the field integration holding circuits 17, 1
A non-inverting type may be used for 8.

Therefore, the specific circuit configuration of the field integration and holding circuits 16, 17, and 18 will be described next. For example, the field integration and holding circuit 16 for the G signal has an inversion type configuration as shown in FIG. The field integration holding circuits 17 and 18 for the B signal are of a non-inverting type as shown in FIG.

In FIG. 5, the field integration holding circuit 16 includes a hold switch 61, resistors 62 and 63, an operational amplifier 64, an integration capacitor 65, and a reset switch 66. When the hold switch 61 connected between the input terminal and the ground is open, the signal Vin at the input terminal is input to the inverting input terminal of the operational amplifier 64 through the resistor 62. Operational amplifier 64
Since a parallel circuit of an integrating capacitor 65 and a reset switch 66 is connected between the inverting input terminal and the output terminal of
When the reset switch 66 is open, the signal charge input to the inverting input terminal of the operational amplifier 64 is accumulated in the integrating capacitor 65, and the integrated voltage Vout is output to the output terminal of the operational amplifier 64. Such a circuit configuration is generally known as an integration circuit, and the integration voltage Vout is expressed by the following equation (1).

In the equation (1), R is the resistance value of the resistor 62, C
Is the capacity of the integrating capacitor 65. The integration start time t1 is equal to the timing tR when the reset switch 65 is closed and reset by the reset signal Rs for a short time, and the integration end time t2
Is equal to the timing tH when the hold switch 61 is closed and held by the hold signal Hd.

In contrast to such a field integration holding circuit 16, the field integration holding circuits 17 and 18 are substantially constituted by a hold switch 71, resistors 72 and 73, an operational amplifier 74, an integration capacitor 75 and a reset switch 76, as shown in FIG. The other end of the resistor 72 having a resistance value R having one end connected to the inverting input terminal of the operational amplifier 74 is grounded.
The difference is that the other end of the resistor 73, one end of which is connected to the non-inverting input terminal 74, is connected to the input terminal to which the signal Vin is applied, and is grounded via the hold switch 71. As described above, the non-inverting type integrator having the configuration in which the input signal Vin is input to the non-inverting input terminal of the operational amplifier 74 includes:
Generally, it is not used as an integrating circuit. That is,
An integrated voltage obtained by the integrating circuit shown in FIG.
Vout 'is expressed by the following equation (2).

That is, as is apparent from the equation (2), since the integrated voltage Vout ′ is always added with the input signal Vin as the bias during the integration operation, it is necessary to use it as a non-inverting type integration circuit. , If the input signal Vin added as the bias is not removed, the integrated voltage that changes with time cannot be correctly obtained.

However, in this auto white balance device, it is used as the field integration holding circuits 17 and 18, and the integrated voltage Vout 'during the integrating operation shown in the above equation (2) does not matter. Hold switch 71 at the end of integration
Is closed by the hold signal Hd at the timing of t2 = tH, the input terminal is grounded at this point and the input signal Vin
Becomes the ground level, the integrated voltage Vout ′ of the above equation (2) at the held timing tH is Becomes

In this way, the inversion type circuit shown in FIG. 5 in which the integrated voltage at the time when the integration for one field period is completed and held is represented by the above formula (1) is the field integration holding circuit.
By using the non-inverting circuit shown in FIG. 6 in which the integral voltage is expressed by the above equation (2) as the field integration holding circuits 17 and 18, the current in the division and digital sample and hold circuit 20 is used. Additive D / A converter 21
The configuration of the combination with the above is simplified.

FIG. 7 shows a modification of the high-level cut circuit 10. The circuit of the apparatus of the embodiment shown in FIG. 1 employs a line-sequential system. In FIG. 7, the G, R, and B signals from the image sensor are read out to independent lines. ing. In this high level cut circuit 80, the read G,
Each signal of R and B is compared with the reference level of the variable resistor 81 by comparators 82G, 82R and 82B, respectively. Since the reference level of the variable resistor 81 is set to be equal to or lower than the saturation level of the image sensor, all outputs of the comparators 82G, 82R, and 82B are "L". Therefore, the output of the 3-input OR gate 84 that controls the gates of the switches 85G, 85R, and 85B inserted in the independent lines of G, R, and B signals is "L".
Then, the switches 85G, 85R, 85B are all closed.

When a very high-luminance subject image is captured by the image sensor, any one of the G, R, and B color signals is
When the reference level of variable resistor 81 is exceeded, comparator 82G,
Of the 82R and 82B, the output of the comparator corresponding to the above color signal becomes "H", the output of the OR gate 84 also becomes "H", and all the switches 85G, 85R and 85B are opened, and the colors of G, R and B are changed. The signal is cut off from being transmitted to the field integration holding circuit in the subsequent stage.

As described above, as long as an image sensor captures a subject having a normal color distribution, the G, R, and B color signals
Since the signal reaches the saturation level at the earliest point, if the circuit configuration shown in FIG. 1 is applied to the configuration of the independent read lines of the G, R, and B signals shown in FIG. The high level cut circuit 90 shown in FIG. 8 is configured. Therefore, the high-level cut circuit 90 has a simple configuration in which the comparators 82G, 82R, 82B and the OR gate 84 in the high-level cut circuit 80 are replaced with one comparator 82.

The main components of the above-described auto white balance device are summarized as follows: gain control means (GCA4) for controlling the gain of the color output signal of the image pickup means according to the level of the given gain control signal, and the output signal of the image pickup means. Alternatively, an integration means (field integration holding means) for integrating the amplified signal of the output signal during the period defined by the first timing signal.
16,17,18), calculation means (self-propelled counter 24, D / A converter 21) for calculating the signal level value corresponding to the gain control signal based on the output of this integration means, and adapted to a certain light source light A reference level signal generating means (preset output circuit) for generating a reference level signal having a level equal to the gain control signal level, and the reference level signal as a gain control signal at least during a period defined by the first timing signal. The gain control means is supplied with the second gain after this period.
When the timing signal is issued, the switching means (output selection circuit) for supplying the output of the arithmetic means to the gain control means at the timing defined by the signal, and when the present device is in the open loop control mode, , The two timing signals are emitted so that the period defined by the first timing signal precedes the time defined by the second timing signal, and when the device is in the preset mode, the second timing signal is output. Timing control means (timing control circuit 49,
System controller 52, etc.).

[Effect of the Invention] As described above, according to the present invention, the reference level signal generating means for the open loop control can be used also as the preset means for the gain control suitable for the strobe characteristics. The configuration is simple and an appropriate white balance value can be obtained for both daylight and strobe light.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of an auto white balance device showing an embodiment of the present invention, FIG. 2 is a block configuration diagram of an entire system of an electronic camera to which the auto white balance device is applied, and FIG. Is a waveform diagram of a color signal supplied to the automatic white balance device, FIG. 4 is an electric circuit diagram showing a concrete example of the output selection circuit in FIG. 1, and FIGS. FIG. 1 is an electric circuit diagram showing a concrete configuration of two different feedback integral holding circuits, and FIGS. 7 and 8 are electric circuits showing respective modifications of the high level cut circuit shown in FIG. It is a circuit diagram. 4 …… GCA (gain control means) 16,17,18 …… Field integration holding circuit (integration means) 21 …… D / A converter (calculation means) 24 …… Self-propelled counter (calculation means) 42 …… Preset Output circuit (reference level signal generation means) 46 …… Output selection circuit (switching means) 49 …… Timing control circuit (timing control means) 52 …… System controller (timing control means)

Claims (1)

(57) [Claims] 1. A gain control means for controlling the gain of a color output signal of an image pickup means according to a level of a given gain control signal, and an output signal of the image pickup means or an amplified signal of the output signal as a first timing signal. Integrating means for integrating during the period defined by, the calculating means for calculating the signal level value corresponding to the gain control signal based on the output of the integrating means, and the gain control signal level suitable for a certain light source light. A reference level signal generating means for generating a reference level signal, and the reference level signal is supplied to the gain control means as a gain control signal during at least a period defined by the first timing signal, and a second level after this period. When the timing signal is output, the switching means for supplying the output of the arithmetic means to the gain control means at the timing specified by the signal. And the device is in the open loop control mode, the period defined by the first timing signal is the second
Timing control means for issuing both of the timing signals so as to precede the time point defined by the timing signal, and not for issuing the second timing signal when the device is in the preset mode. Auto white balance device characterized by