JPS63290482A - Automatic white balancing device - Google Patents

Abstract

PURPOSE:To always obtain a suitable white balance value with simple circuit constitution by using a reference level signal generation means for open loop control in common with a preset means for gain control suitable for strobo characteristic in addition to its original use. CONSTITUTION:A color output signal from an image pickup means is controlled by a gain control means 4. Outputs from the means 4 are integrated by field integration holding means 16-18 by using a first timing signal outputted from a timing control circuit 49. Based on the output of this integration, arithmetic means 24, 21 calculate a signal level value corresponding to a gain control signal. The preset output circuit 42 generates a reference level signal in such a level as equal to a gain control signal level that is suitable for a light source. This reference level signal or an output from the arithmetic means 24, 21 is selected by an output selection circuit 46, and supplied to the gain control means 4 as a gain control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an auto white balance device, and more particularly to an auto white balance device used in a color imaging device such as an electronic camera.

[Prior Art] In recent years, electronic still cameras that can take still images in the same way as silver halide film cameras have been proposed. The basic configuration of an electronic still camera is almost the same as that of a video camera. An auto white balance device in a color video camera, etc. uses a color signal gain control amplifier (hereinafter abbreviated as OCA) in the video signal system to control the color light of the three primary colors of R (red), G (green), and B (blue). The ratio of color signals R, G, and H is adjusted to 11:1. Therefore, in conventional auto white balance devices, the output of the GCA is fed back by a white balance detection circuit and compared with a reference voltage, and the error is guided to the gain control terminal of the OCA, and the gain of the OCA is adjusted in a direction that reduces the error. I was in control. In a device that performs white balance adjustment in a closed loop like this, even if the input signal level changes or the characteristics of the GCA change slightly due to temperature changes, etc., it is stable and is not affected by these changes. It has the advantage of being able to extract signals at a certain level.

[Problems to be solved by the invention] However, in a closed-loop auto white balance device, due to the delay element in the feedback loop,
The OC is applied to the controlled signal supplied to the input terminal of the OCA.
The control signal supplied to the gain control terminal of A is significantly delayed, and the responsiveness of gain control is poor. In general, closed-loop auto white balance devices are very effective for video cameras that capture continuous movie images because they do not require such high-speed response for gain control. Since the purpose is to obtain one image in a short period of time, particularly high-speed response is required.

Additionally, auto white balance devices generally cannot perform correct white balance adjustment for light that only exists during exposure, such as strobe light, so a strobe preset circuit is installed separately from the auto white balance device's electrical circuit. When using a strobe, it is necessary to use the preset circuit to control the gain of the color signal in accordance with the characteristics of the strobe. However, providing a strobe preset circuit separately from a circuit for daylight auto white balance will make the device more complicated.

In view of these problems, the present invention provides an auto white balance device that can be applied to an electronic camera capable of still photography with daylight and strobe light, and does not require a preset circuit especially for strobe lights. With the goal.

[Means for Solving the Problems] The auto white balance device of the present invention includes a gain control means for controlling the gain of a color output signal of an imaging means according to the level of a given gain control signal, and a gain control means for controlling the gain of the color output signal of the imaging means according to the level of the control signal; and an integration means for integrating the output signal of the imaging means or the amplified signal of the output signal during a period defined by the first timing signal. 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. and supplying the reference level signal as a gain control signal to the gain control means at least during a period defined by the first timing signal, and when the second timing signal is issued after this period. a switching means for supplying the output of the arithmetic means to the gain control means at a timing defined by the first timing signal; timing control means for emitting both of the timing signals in advance of the point in time defined by the second timing signal, and for not emitting the second timing signal when the device is in a preset mode; It will be equipped.

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

[Embodiment] FIG. 1 is a block diagram of an auto white balance device showing an embodiment of the present invention.

The auto white balance device shown in FIG. 1 is applied to an electronic camera capable of still photography and movie photography. An image sensor (not shown) of this electronic camera is also used as a photometric sensor for white balance control of this automatic white balance device. The R signal and B signal of the color video signal are alternately transmitted from this image pickup device to the video processing circuit 3 through line 1 line-sequentially, and the G signal is transmitted through line 2. In the video processing circuit 3, a GCA 4 is inserted in line 1 of the above line sequence for automatic white balance adjustment. This O
CA has two Gs each controlled independently by two systems of control signals sent from the control line 48, which will be described later.
The GCA includes a CA, by which the gains of the R signal and B signal are respectively set.
4 output line 5 R, B color signals and line 2 G
The color signal is sent to the next stage circuit as a video signal and at the same time is used as control information for gain control of the GCA 4. In other words, with this auto white balance device,
By performing gain control of CA4, R, B, G
The color signal level is 1:1:1.

A buffer circuit 8 is connected to the G signal line 2,
A buffer circuit 9 is connected to the R/B signal line 5 on the output side of the GCA 4. The output terminal of the buffer circuit 8 is connected to the switch 11 of the high level cut circuit 10,
The output terminal of the buffer circuit 9 is a high level cut circuit 10
It is connected to the switch 12 of. The high level cut circuit 10 is a circuit that cuts the transmission of the color video signals when the levels of the G and R/B signals reach approximately the saturation level, and is connected to the switches 11, 12 . It consists of a variable resistor 13 and a comparator 14. In other words, the dynamic range of the image sensor has a limit, so when the image sensor receives a high-brightness image, the high-brightness component of the color video signal becomes saturated. A high level cut circuit 10 is used to prevent the signal from being integrated. In this high level cut circuit 10, the output of the buffer circuit 8, that is, G
The level of the 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 turns the switches 11.12 from the on state to the off state, and the buffer circuits 8, 9 The output is cut off from being sent to the subsequent stage. Switches 11 and 12 are controlled by detecting the level of the G signal.When imaging a high-brightness subject with a normal light distribution, the R, B, and G color video signals output from the image sensor are controlled by detecting the level of the G signal. This is because the G signal component does not reach the saturation level uniformly, but in many cases the G signal component reaches the saturation level first. The output terminal of the switch 11 is connected to a field integral holding circuit 16, and the output terminal of the switch 12 is connected to field integral holding circuits 17 and 18 via an R/B signal separation circuit 15. The field integral holding circuit 16 holds the G signal at 1
The field integration holding circuits 17 and 18 integrate the R signal and B signal separated by the R/B signal separation circuit 15 and hold the integrated signals over the effective scanning period of the field. Integrate and hold over a period of time. Field integral hold circuit 16, 17 and 18
is the subsequent division/digital sample and hold circuit 2
Connected to 0. The division/digital sample and hold circuit 20 takes in each output of the field integral holding circuits 17 and 18 regarding the R and B color signals during the vertical blanking period, and calculates the outputs from the field integral holding circuit 16 regarding the G color signal. This is a circuit that divides, obtains and holds the respective ratios R/G and B/G. This division/digital sample and hold circuit 20 is provided with a dual type current addition type D/A converter 21. Two D/A in this D/A converter 21
Conversion units 22 and 23 convert the count values of the self-propelled counter 24 connected to this D/A converter 21 into analog values. The D/A converter 22 is related to the R signal, and the D/A converter 23 is related to the B signal. A changeover switch 25 is connected to the reference input terminal ref of the D/A converter 21 for switching between the output of the field integration holding circuit 16 and the reference voltage V ref of the reference voltage generation circuit 26 in response to a changeover signal SL.

An output terminal of a comparator 27 is connected to a latch input terminal 1atch of the division/digital sample and hold circuit 20. Both input terminals of the comparator 27 are connected to a changeover switch 28. which is switched by a changeover signal S2.
29 are connected.

The changeover switch 28 connects the field integral holding circuits 17 and 18.
The changeover switch 29 switches the output of the D/A converters 22 and 23 and inputs it to the other input terminal of the comparator 27. be. In addition, the input selection terminal sel of the D/A converter 21 to which the switching signal S2 is applied is connected to the digital input from the self-propelled counter 24 and the latch signal which is the output of the comparator 27 which is manually input from the latch input terminal 1atch. This is to distribute the signals to the D/A converters 22 and 23 corresponding to the R signal system and the B signal system, respectively, in synchronization with S2. Note that the output of the unselected D/A converter is held at the last state when it was selected.

As the output stage of the division/digital sample and 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 during still photography, and includes inverting amplifiers 31 and 32 that amplify the outputs of the D/A converters 22 and 23, respectively, and an output selection circuit 46 that outputs the outputs of the inverting amplifiers 31 and 32. It consists of an output line 33 that sends to.

The feedback control output circuit 34 is a circuit used during movie shooting, and converts the outputs of the D/A converters 22 and 23 into reference voltages V re of variable resistors 35 and 36, respectively.
Differential amplifier 37.3 comparing f'l, V ref2
8, a low-pass filter (hereinafter abbreviated as LPF) 39.40 connected to the output side of the differential amplifier 37.38 for system stability, and the output of this LPF 39.40 to the output selection circuit 46. It consists of an output line 41 for sending.

Further, a preset output circuit 42 is provided for presetting the gain of the GCA 4 to a known value, and the preset output circuit 42 is connected to the reference voltage Vrer3. Vre(
'4 (In the preset suitable for strobe light, the reference voltage V
ref3', Vrar4') to adjust the RlB color signal gain 43.44
and the reference voltage Vrel'3. set by the variable resistors 43 and 44. Vrel'4 (Vrer3'.

It consists of an output line 45 that sends the level of Vre['4') to an output selection circuit 46.

The output selection circuit 46 is provided with a selection switch 47, and a contact terminal 47a of the switch 47.

47b and 47c are respectively connected to the output lines 45°33.
41 is connected, and a contact terminal 47d, which is switched by the switching signal S3 and connected to any one of the contact terminals 47a, 47b, and 47c, is connected to a gain control terminal of the GCA 4 by a control line 48. Switching signals SL, S2. S
3 is generated by the timing control circuit 49.

Note that the output lines 33, 41, 45 . Output selection circuit 46 and selection switch 47 (47a
, 47 b, 47 c, 47 d), the control line 48 is a two-system parallel (independent) system, and the first
The figure shows it in a simplified state.

Here, the general configuration of the entire system of an electronic camera to which the above auto white balance device is applied will be explained with reference to FIG.
The exposure control device 51 is controlled by transmitting and receiving signals to and from a system controller 52 including a microcomputer. The system controller 52 has a function of a timing control circuit 49 that generates the switching signals S1, S2.33, etc., a photometric information processing function, and the like. The exposure control device 51 includes control circuits for a strobe, an aperture, a shutter, and the like.

The input terminal of the system controller 52 includes a strobe selection switch 53. A still/movie selection switch 54 and a photometric sensor 55 are connected. For example, when a strobe is used, the strobe selection switch 53 is turned on, and the input terminal, which is set to "H" by the pull-up resistor 56 when the strobe is not used, becomes "L" at this time. Further, the still/movie selection switch 54 is, for example, turned off during still shooting to set the input terminal of the system controller 52 to "H" by means of a pull-up resistor 57, and turned on to set the input terminal to "L" during movie shooting. Furthermore, in this embodiment, the 7TPl light sensor 55 for exposure control is
Although a well-known sensor is used which is disposed at an appropriate position of the camera independently of the image sensor, it goes without saying that the image sensor may also be used as the photometric sensor 55 for controlling exposure.

Next, the operation of the auto white balance device will be explained. Lines 1 and 2 are supplied with image signals whose gain is to be controlled based on the output of the imaging probe. As shown in FIG. 3, this image signal has field periods fL, f2 . There is a vertical blanking period Bl, B2 . B3...
・It has.

First, the case of still photography will be explained. 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 47.
connected to a. Therefore, the output line 45 of the preset output circuit 42 is connected to the control line 48, and the voltage V rar3 is preset by the variable resistor 43°44.
．． V rer4 is input to the gain control terminal of GCA4. Thereby, the GCA 4 is controlled to a reference gain for white balance in still photography.

Thereafter, when the shutter button is pressed, the shutter opens within the first field period fl and exposure for white balance is performed. When the exposure is completed, a video signal corresponding to the exposure amount is read out from the imaging probe 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. During this read field period f2, a reference value preset by the preset output circuit 42 is given as a gain control signal of the GCA 4. Then, the field period f of this readout is
2 video signal is sent to line 2 for actual white balance control to be performed in the subsequent field period f3.
, 5 to the buffer circuit 8.9. The G signal that has passed through the buffer circuit 8 is input to the field integral holding circuit 16 via the switch 11 of the high level cut circuit 10, and the R and B signals that have passed through the buffer circuit 9 are input to the field integration holding circuit 16.
R/B after passing through switch 12 of level cut circuit 10
The signals are separated by the signal separation circuit 15 and input to field integration and holding circuits 17 and 18, respectively.

The field integration holding circuits 16, 17, and 18 integrate the G, R, and B signals, respectively, over one field period f2 of charge readout from the image sensor, but the subject light is very strong and the dynamic of the image sensor When the G signal level rises to a saturation level corresponding to the upper limit of the range, this high brightness range is cut off 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 in level at the end of the field period f2 and are inputted to the division/digital sample and hold circuit 20.

Then, the division/digital sample and hold circuit 2 is divided by the vertical blanking period B2 following the field period f2.
0 is activated. Changeover switch 2 is activated by the start changeover signal Sl.
5 is switched to the output side of the field integration holding circuit 16 as shown, and the G signal integrated over one field period is sent to the reference input terminal r of the D/A converter 21.
It is input to ef. Further, the changeover switches 28 and 29 are alternately switched to either the R or B signal side in synchronization with the changeover signal S2. That is, in the illustrated state, the switching signal S
2, the R signal side is selected, and the output of the field integral holding circuit 17 and the output of the D/A converter 22 are compared by the comparator 27. When the D/A converter 22 starts D/A converting the output of the self-running counter 24 in response to the switching signal S2 input to the input selection terminal sel, the D/A converter 22
/A converter 22. The output of is led to the comparator 27 through the changeover switch 29, and the field integral holding 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 1atch, and the analog value of the D/A converter 22 is latched. Ru. 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.

After the D/A conversion by the D/A converter 22 is completed, the B signal side is selected by the switching signal S2 in the second half of the same vertical blanking period B2, and the output of the field integral holding circuit 18 and the D/A conversion are The output of the D/A converter 23 is compared with the output of the D/A converter 23 by a comparator 27, and when both inputs of the comparator 27 match, the analog value of the D/A converter 23 is latched. The analog value of the D/A converter 23 at this time is equal to the output signal B of the field integral holding circuit 18. When the D/A conversion by the dual/A converters 22 and 23 is completed, the changeover switch 25 is switched to the reference voltage generation circuit 2 by the changeover signal S1 at the end of this vertical blanking period B2.
6, the reference voltage Vref is switched to the output side of the D/A
It is input to the converter 210 reference input terminal ref. Then, the analog values R and B of the D/A converter 22.23 become
The ratio of the respective switched reference input voltages Vref'/
Since G is multiplied as a coefficient, the output of the D/A converter 22 is held at Vref'xR/G, and the output of the D/A converter 23
The output of is held at VrerXB/G.

Then, when the vertical blanking period B2 ends and the next field period f3 starts, the output contact terminal 47d of the selection switch 47 of the output selection circuit 46 changes to the oven control contact terminal at the start of the next field period f3. Since the connection is switched to 47b, the D/A converter 2
The outputs of 2.23 are amplified by inverting amplifiers 31.32 of the open control output circuit 30, respectively, and the outputs of the output lines 3
3 through a control line 48 to the gain control terminal of the GCA 4. Therefore, after the field period f3, the gain control that provides the optimal white balance for the still image photographed within the first field period fl is GCA.
This will be done in 4.

Note that when a strobe light is used in still photography, the oven control as described above is unnecessary because strobe light has fixed spectral characteristics unlike daylight. Therefore, in this case, the output contact terminal 47d of the changeover switch 47 is connected to the preset contact terminal 47a by the switching signal S3. In this case, the output contact terminal 47d is connected to the oven control contact terminal 47b midway.
Preset contact terminal 4 without switching the connection to
7a, exposure by strobe light is performed, and when data extracted from the image sensor is input to the GCA 4, the variable resistor 43.4 of the precent output circuit 42
Reference voltage Vr suitable for strobe light set in 4
ef3' and V ref'4' are applied to the gain control terminal of the GCA 4 to perform white balance control suitable for a strobe. Therefore, in this auto white balance device, the preset output circuit 42 has a simple configuration, serving both as a preset circuit for providing a reference value for open loop control and as a strobe preset circuit. Note that the "preset mode" during strobe lighting also includes so-called auto preset.

Also, instead of providing the preset output circuit 42,
It is also possible to use the preset function of the self-propelled counter 24 and cause the D/A converter 21 to generate a preset signal.

Next, the case of movie shooting will be explained. In the case of movie shooting, the contact terminal 4 of the selection switch 47 of the output selection circuit 46
7d 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 4.
Connected to 8.

In this case, the G signal data taken out from line 2 for white balance control and the R and B signal data taken out from line 5 on the output side of GCA 4 are each buffered as in the case of still photography. After passing through circuits 8 and 9, the high brightness level is removed by a high level cut circuit 10, and the R and B signals are separated by an R/B signal separation circuit 15. The G, R, and B signals are integrated for one field period and guided to the division/digital sample/hold circuit 20, where the above-mentioned division operation is performed during the vertical blanking period. Then, from the D/A converter 22.23 (VrerXR/G)
, (Vrer xB/G) are output. The output of this D/A converter 22.23 (Vref xR/G), (
VrerxB/G) is the feedback control output circuit 3
Reference voltages V refl and V rer of variable resistors 35 and 36 are inputted to differential amplifiers 37 and 38 of 4, respectively.
2 and the comparison output of the differential amplifier 37.38 is LP
F39.40, and is manually inputted to the gain control terminal of the GCA 4 through an output line 41 and a control line 48. In the case of movie shooting, since video signals are continuously output from the image processing circuit 3, R and B signals are not preset in the GCA 4. /G), (V
ref'
VrerXR/G).

(VrerXB/G) and the reference voltage V re['l
.

By comparing with Vref2 and performing feedback control, Vre('1-Vrer2
- If adjusted so that it becomes V rer, R/G-1,
It becomes B/G-1.

In FIG. 1, the output selection circuit 46 has been described assuming that two parallel selection switches 47 are switched in accordance with the command of the switching signal s3, but specifically, an analog multiplexer IC is used as the output selection circuit 46, For example, "standard logic IC4053" can be applied. In this case, to explain one of the two parallel systems, its circuit diagram has the configuration shown in FIG. The applied switching signals S3a and S3b are both “H”
At this time, the analog switches 58 and 59 are both connected to one contact terminal as shown in the figure, and the signal from the feedback control contact terminal 47c is guided to the output contact terminal 47d.

Also, 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 side opposite to that shown in the figure, so the signal from the oven control contact terminal 47b is guided to the output contact terminal 47d. The signal S3a may be "L" or "H", but if the switching signal S3b is "L"
”, the analog switch 59 is connected to the other contact terminal on the opposite side from the one shown in the figure, so that the signal from the preset contact terminal 47a is connected to the output contact terminal 47.
be guided by d.

By the way, in the above auto white balance device,
As the D/A converter 21, a current addition type that is easy to achieve accuracy in principle is used, but the current addition type D/A converter 21
When the A converter 21 is used, there is a problem in 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 addressed by providing an inverting amplifier. However, to avoid complicating the circuit due to space considerations for electronic cameras, here:
Field integral holding circuit 16 provided in the preceding stage
, 17. This problem is solved by considering the configuration of 17.18. That is, the field integral holding circuit 16 is of an inverting type, and the field integral holding circuits 17 and 18 are of a non-inverting type. Alternatively, if an inverting type is used for the field integration and holding circuit 16, a non-inverting type may be used for the field integration and holding circuits 17 and 18.

Therefore, next, the above-mentioned field integral holding circuit 16°17.
18 specific circuit configurations, for example, G
The field integral holding circuit 16 for signals has an inverting type configuration as shown in FIG. 5, and the field integral holding circuits 17 and 18 for R and B signals have a non-inverting type configuration as shown in FIG. Ru.

In FIG. 5, the field integral holding circuit 16 includes a hold switch 61 . Resistance 62.63. Operational amplifier 64.
It is composed of an integrating capacitor 65 and a reset switch 66. When the hold switch 61 connected between the input terminal and ground is open, the input terminal signal Vi
n is input to the inverting input terminal of the operational amplifier 64 through the resistor 62. 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 the operational amplifier 64.
When the inverting input terminal of the operational amplifier 64 is open, the signal charge input to the inverting input terminal of the operational amplifier 64 is accumulated in the integrating capacitor 65, and an integrated voltage V out is output to the output terminal of the operational amplifier 64. Such a circuit configuration is generally well known as an integrating circuit, and the integrated voltage V out is expressed as in the following equation (1).

In addition, in this formula (1), R is the resistance value of the resistor 62,
C is the capacitance of the integrating capacitor 65. Integration start point 1
1 is equal to the timing tR when the reset switch 66 is opened for a short time and reset by the reset signal Rs, and the integration end time t2 is equal to the timing t11 when the hold switch 61 is closed and held by the hold signal Hd.

In contrast to such a field integral holding circuit 16, the field integral holding circuits 17, 18 are connected to hold switches 71.18, as shown in FIG. Resistor 72°73, operational amplifier 74. Integrating capacitor 75 and reset switch 76
However, the other end of a resistor 72 with a resistance value R is connected to the inverting input terminal of the operational amplifier 74, and the other end of the resistor 73 is connected to the non-inverting input terminal of the operational amplifier 74. The difference is that the end is connected to an input terminal to which a signal Vln is applied and is grounded via a hold switch 71.

A non-inverting type integrating circuit configured such that the input signal Vin is input to the non-inverting input terminal of the operational amplifier 74 is generally not used as an integrating circuit. That is, the integrated voltage V obtained by the integrating circuit shown in FIG.
out' is expressed as in the following equation (2).

In other words, as is clear from equation (2), the input signal Vin is always applied as a bias during the integration operation, and the integration voltage Vout' becomes the integration voltage Vout'. , unless the input signal Vin added as a bias is removed, it is not possible to correctly obtain the integrated voltage that changes over time.

However, in this auto white balance device, the field integral holding circuits 17 and 18 are used, and the integral voltage Vout' during the integral operation shown in equation (2) above is
There is no problem with that. When the hold switch 71 is closed at the timing t2-tll by the hold signal Hd at the end of the integration, the input terminal is grounded at this point.
Since the input signal Vin is at the ground level, at this held timing tl+, the integral type of equation (2) is obtained.

In this way, the integrated voltage at the time when the integration for one field period is completed and held is the fifth value expressed by the above equation (1).
The inversion type circuit shown in the figure is the field integral holding circuit 1.
6, and the non-inverting circuit shown in FIG. The configuration in combination with the addition type D/A converter 21 becomes simple.

FIG. 7 shows a modification of the high level cut circuit 10. The circuit of the embodiment device shown in Fig. 1 above employs a line sequential system, but in Fig. 7, the G, R, and B signals from the image sensor are read out on independent lines. ing. In this high level cut circuit 80, each of the read G, R, and B signals is compared with a reference level of a variable resistor 81 by comparators 82G, 82R, and 82B, respectively. Since the reference level of the variable resistor 81 is set below the saturation level of the image sensor, the combination
All outputs of 82G, 82R, and 82B are "L". For this reason, G, R.

A switch 85G inserted into an independent line of the B signal,
The output of the three-man-powered OR gate 84 that controls each gate of 85R and 85B is "L", and the output of the OR gate 84 that controls each gate of 85R and 85B is "L".
, 85B are all closed.

When an extremely bright subject image is captured by the image sensor, if any color signal among the G, R, and B signals exceeds the reference level of the variable resistor 81, one of the comparators 82G, 82R, and 82B The output of the comparator corresponding to the above color signal becomes "H", and the OR gate 8
The output of 4 also becomes “H” and all switches 85G and 8
5R.

85B opens to cut off the G, R, and B color signals from being transmitted to the subsequent field integration holding circuit.

As mentioned above, as long as an image sensor captures a subject with a normal color distribution, among the G, R, and B color signals,
Since the G signal reaches the saturation level at the earliest point, if the circuit configuration shown in FIG. 1 is applied to the configuration of independent readout lines for the G, R, and B signals shown in FIG. 7 above, A high level cut circuit 9o shown in FIG. 8 is constructed. Therefore, this high level cut circuit 9o is
Comparator 8 in the above high level cut circuit 80
2G, 82R, 82B and the OR gate 84 are simply replaced with one comparator 82.

To summarize the main components of the auto white balance device described above, the main components are: a gain control means (GCA4) that controls the gain of the color output signal of the imaging means according to the level of the applied gain control signal; and an output signal of the imaging means. Alternatively, an integrating means (field integral holding means 16, 17, 18) for integrating the amplified signal of the output power signal during the period specified by the first timing signal, and a gain control signal corresponding to the output of the integrating means are provided. arithmetic means (self-running counter 24, D/A converter 21) for calculating a signal level value to be calculated; and a reference level signal for generating a reference level signal having a level equal to a gain control signal level suitable for a certain light source light. generating means (preset output circuit) and supplying the reference level signal to the gain control means as a gain control signal during at least a period defined by the first timing signal, and after this period, the second timing signal is supplied to the gain control means. a switching means (output selection circuit) for supplying the output of the arithmetic means to the gain control means at the timing specified by the signal when the signal is issued; The timing signals are emitted for a period defined by the timing signal or prior to the time defined by the second timing signal, and when the device is in the preset mode, the second timing signal is emitted. Timing control means (timing control circuit 49, system controller 52, etc.) that prevents the emission of
It is composed of.

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

[Brief explanation 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 diagram of the entire system of an electronic camera to which the above auto white balance device is applied, and FIG. is a waveform diagram of the color signal supplied to the auto white balance device, FIG. 4 is an electrical circuit diagram showing a specific example of the output selection circuit shown in FIG. 1, and FIGS. 5 and 6 are the above diagrams. Electrical circuit diagrams showing specific configurations of the two different types of feedback integral holding circuits in FIG. 1, and FIGS. FIG. 4...GCA (gain control means)16.
17.18... Field integral holding circuit (integrating means) 21... D/A converter (calculating means) 24.
... Self-propelled counter (calculating 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)

[Claims] Gain control means for controlling the gain of the color output signal of the imaging means according to the level of a given gain control signal; an integrating means for integrating over a period defined by the signal; an arithmetic means for calculating a signal level value corresponding to the gain control signal based on the output of the integrating means; and a level equal to the gain control signal level suitable for a certain light source light. a reference level signal generating means for generating a reference level signal of; supplying the reference level signal as a gain control signal to the gain control means at least during a period defined by the first timing signal; a switching means for supplying the output of the arithmetic means to the gain control means at the timing specified by the timing signal No. 2 when the timing signal No. 2 is issued; The period defined by the timing signal is the second period defined by the timing signal.
timing control means configured to emit both of the timing signals in advance of the timing specified by the second timing signal, and not to emit the second timing signal when the device is in a preset mode; An auto white balance device that is characterized by: