JPH074012B2 - Electronic camera auto white balance device using strobe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic white balance device for an electronic camera using a strobe, and more particularly, a strobe having a curtain running type focal plane shutter and cooperating with the shutter. The present invention relates to an automatic white balance device for automatically performing color temperature correction in an electronic still camera using a camera.

[Prior Art] In an electronic still camera (hereinafter, referred to as an electronic camera) developed in recent years, in order to obtain a high-quality color image, it is necessary to adjust a white balance according to a light source, like a color video camera. is necessary. Up to now, as a method of adjusting the white balance, a method of detecting the color temperature of the subject by an external sensor and adjusting the white balance based on the detection output, or
A method of performing adjustment by processing color information obtained from a video signal is generally used.

By the way, when photographing with a strobe, the strobe light has color temperature information different from that of outside light and changes instantaneously. Therefore, the above white balance adjustment method cannot be applied when the strobe is used. However, since the color temperature information of the strobe light can be known in advance, it can be understood that the white balance should be fixed to a set value suitable for the color temperature information of the strobe light when using the strobe. For example, in a simple manner, the white balance may be fixed to a so-called daylight set value, or for a highly accurate set value, a dedicated set value corresponding to the spectral characteristic of the strobe used. An apparatus for fixing the white balance is already known (see Japanese Patent Laid-Open No. 58-225792).
However, in such a device, for example, there is a possibility that the user may forget to release the lock state corresponding to the strobe when the strobe is not used.

Therefore, as an attempt to automate the setting of white balance when using a flash, it has been considered to turn on the switch of the flash or fix the white balance to a setting value compatible with the flash when the charge-up of the flash is detected. Although it can be expected to have some effects, it detects and switches the flash-enabled state.

[Problems to be Solved by the Invention] On the other hand, there is known a so-called TTL direct photometric camera that uses a curtain-running focal plane shutter to perform reflection photometry on the front curtain surface and the film surface. When a strobe is attached to this TTL direct metering camera, direct light metering measures natural light, and if the amount of natural light is insufficient when the shutter is fully opened, the flash firing start is controlled to compensate for the insufficient amount of light. ing. Due to recent advances in photometry and precision technology, it is expected that such direct photometry will soon be applied to electronic cameras. However, when applying TTL direct metering to an electronic camera and shooting with a strobe,
Even if the strobe is in the “light-emission enabled state” and the white balance is fixed to a setting value that can accommodate the strobe, the strobe will not actually fire if the amount of natural light is sufficient at this time. That is, in this case, the white balance is set to correspond to the strobe, even though the shooting is performed with natural light, and there is a possibility that an appropriate white balance value may not be obtained.

The present invention has been made focusing on such problems,
If a strobe is generated, the white balance is fixed to the setting value corresponding to the strobe, and if the strobe does not fire, the normal auto white balance adjustment according to the color temperature information of the external light should be performed. It is an object of the present invention to provide an automatic white balance device for an electronic camera using a strobe, which is adapted to automatically perform a switching operation.

[Means and Actions for Solving Problems] In order to achieve the above object, an automatic white balance device for an electronic camera using a strobe according to the present invention is configured to detect the completion time of traveling of a front curtain of a curtain running type focal plane shutter. Means for generating a first signal representing the second signal, means for generating a second signal representing the time when the rear curtain of the focal plane shutter starts traveling, and means for receiving the first signal and the second signal. Strobe emission for causing the strobe to emit light based on the arrival of the first signal, with only a specific state in which the first signal precedes the second signal in time as a strobe use-appropriate state. A control circuit that generates a start signal, and a white balance that adjusts the white balance control value to a set value that matches the strobe light based on the strobe light emission start signal. And a balance setting circuit.

[Examples] Hereinafter, the present invention will be described with reference to illustrated examples.

FIG. 1 is a block diagram of an electric circuit of an automatic white balance device for an electronic camera using a strobe, showing an embodiment of the present invention. In an electronic camera having this automatic white balance device, first, the outline of the control operation of the curtain running type focal plane shutter will be described with reference to the time chart of FIG. 3. The shutter control circuit 11 in the camera issues a shutter curtain operation command a. It is designed to be used. The shutter curtain operation command a rises to the "H" level by pressing down the release button for starting exposure, and the light receiving element 13, the light quantity integrating circuit 14,
"L" by the output emitted when the proper amount of light is obtained from the photometric circuit consisting of the comparator 15 and the differentiating circuit 17
It is a signal that falls to the level. This shutter curtain operation command a
The focal plane shutter device 12 is controlled by the above, and when the rising edge of the shutter curtain operation command a is guided to the shutter device 12, the front curtain starts running. When the front curtain has completed traveling, the front curtain traveling completion signal b is sent from the shutter device 12 to the shutter control circuit 11.
Is emitted. Further, when the trailing edge of the shutter curtain operation command a is guided to the shutter device 12 by the photometric output from the differentiating circuit 17, the trailing curtain starts running, and when the trailing curtain completes running, The curtain running completion signal c is issued. Although a slight time lag t occurs between the rising and falling of the shutter curtain operation command a and the start of traveling of the shutter curtain, this time lag t is negligible.

By the way, only when the shutter curtain operation command a falls after the front curtain running completion signal b is issued, that is, at the shutter time when the photographing screen 1 shown in FIG. The attached strobe 24 is made to emit light, and the strobe 24 does not emit light at a high shutter speed such that the trailing edge of the shutter curtain operation command a precedes the trailing curtain travel completion signal b. ing. That is, as shown in FIG. 4, the rear shutter 3 starts traveling before the front curtain 2 has finished traveling in the direction of the arrow x on the photographing screen 1, that is, a high shutter speed such as so-called slit exposure is performed. If the strobe is fired at the time, the shutter curtain will be shaded on the photographing screen 1 and the exposure unevenness will occur because the stroboscopic light emission time is very short. After the traveling is completed at the tip of No. 1, the traveling of the rear curtain 3 is started, and the strobe light is emitted only at the low shutter speed at which the entire area of the photographing screen 1 is completely exposed.

Next, the auto white balance device shown in FIG. 1 will be further described in detail.

The AND gate 18 is used to generate the strobe light emission start signal A from the shutter curtain operation command a issued from the shutter control circuit 11 and the front curtain traveling completion signal b issued from the focal plane shutter device 12 in response to this command a. Has been. That is, one input terminal of the AND gate 18 is connected to the signal line of the shutter curtain operation command a, and the other input terminal of the AND gate 18 is connected to the signal line of the front curtain traveling completion signal b, and the AND gate 18 The output terminal of is a terminal Ta for transmitting the light emission start signal A to the strobe 24.
It is connected to the. The terminal Tb for sending the light emission stop signal B to the strobe 24 is connected to the output terminal of the differentiating circuit 17 of the photometry circuit.

The output terminal of the AND gate 18 is connected to the input terminal IN of the white balance setting circuit 19, and the strobe emission start signal A from the AND gate 18 is input to the input terminal IN.
From the white balance setting circuit 19, the gain control signals V _R and V _B for changing the gain of the color signals R _IN and B _IN are sent to the variable gain amplifiers 20 and 21. I am trying to fix it to the set value corresponding to the strobe light. When the strobe emission start signal A is not supplied to the white balance setting circuit 19, the white balance setting circuit 19
Is a gain control signal V _R , V that changes according to the color temperature information of the external light
_B is sent to the variable gain amplifiers 20 and 21, respectively, and the normal auto white balance control operation is performed.

A specific electric circuit of the white balance setting circuit 19 is configured, for example, as shown in FIG. That is, in FIG. 2, the white balance setting circuit 19 is an AND gate.
A monostable multivibrator 22 that outputs an “H” level signal e of time T when a strobe light emission start signal A is input from the input terminal IN from 18 and this monostable multivibrator
An inverter 23 that inverts the output signal of 22 and a switch 24 that passes the auto white balance gain control signals V _RA and V _BA, which are in the ON state and are in accordance with the color temperature information of the outside light, respectively. 25 and a set voltage signal V _RO , which gives an appropriate white balance to the strobe light.
The variable resistors 26 and 27 for setting V _BO , respectively, and the normal are in the off state, and the output signal of the monostable multivibrator 22 turns them on to pass the set voltage signals V _RO and V _BO , respectively. The switches 28 and 29 are included.

The operation of the automatic white balance device configured as described above when the strobe 24 emits light will be described with reference to the time chart shown in FIG. 5. When the release button is pressed to start exposure, a trigger pulse is emitted. After a certain time lag, the shutter control circuit 11 issues an "H" level shutter curtain operation command a. The shutter curtain operation command a indicates the focal plane shutter device 12
The leading curtain starts running after a slight time lag t from its rising edge (see FIG. 3). Also,
When the shutter control circuit 11 generates the shutter curtain operation command a, it sends an integration start signal to the light amount integration circuit 14 of the photometric circuit to release the reset, and the light amount integration circuit 14 starts integration of the light amount. Before the integration start signal is input, the light amount integration circuit 14 is in a state where the integration is reset. In this case, since the subject light is dark, the integrated voltage which is the output of the light quantity integrating circuit 14 rises with a gentle slope.

Further, since the shutter curtain operation command a is guided to one input end of the AND gate 18, thereafter, the front curtain travel completion signal b is issued from the focal plane shutter device 12 to the other input terminal of the AND gate 18. When guided, this is sent to the terminal Ta as a strobe light emission start signal A.
Then, the strobe 24 mounted on this camera starts the light emission by the strobe light emission start signal A.

The output of the light quantity integrating circuit 14 after the strobe 24 emits light rises at a steep slope, and when the proper exposure is obtained, it matches the predetermined reference voltage V _ref set by the variable resistor 16 of the comparator 15 and the comparator 15 output goes to “H” level. Then, a differentiation pulse is issued from the differentiation circuit 17 at the rise of the output of the comparator 15, and the differentiation pulse is guided to the shutter control circuit 11 to set the shutter curtain operation command a to "L" level. The trailing curtain starts running as described above. The output differential pulse of the differentiating circuit 17 is the terminal
Since the strobe light emission stop signal B is sent to Tb, the strobe light 24 stops emitting light by this strobe light emission stop signal B. In this way, when the time of the front curtain travel completion signal b precedes the trailing time of the shutter curtain operation command a,
Since the front curtain running completion signal b passes through the AND gate 18, the strobe light emission start signal A is issued at the time when the signal b is generated.

Strobe light emission start signal A emitted from AND gate 18
Is also supplied to the white balance setting circuit 19, and when input from its input terminal IN to the monostable multivibrator 22,
The monostable multivibrator 22 is triggered by the trailing edge of the strobe light emission start signal A and sends out the signal e of "H" level for the time T. The "H" level time T of the signal e corresponds to the time until the shooting by the strobe light is completed by the emission stop signal B being issued. When the signal e is sent from the monostable multivibrator 22, the switch 2
Since the signal inverted by the inverter 23 is applied to the control ends of the switches 4 and 25, the switches 24 and 25 are switched from the ON state to the OFF state, and the signal e remains unchanged at the control ends of the switches 28 and 29. As a result of being applied, the switches 28 and 29 are switched from the off state to the on state. Therefore, the gain control signals V _RA and V _BA for auto white balance that change according to the external light
Are cut off at the switches 24 and 25, and instead, set voltage signals V _RO and V _BO that give proper white balance to the strobe light are output to the output terminals OUT ₁ and OUT ₂ through the switches 28 and 29, respectively. The gain control signals V _R and V _B of the variable gain amplifiers 20 and 21 (see FIG. 1) are transmitted. Therefore, during the time T, the variable gain amplifiers 20 and 21 receive the color signals R _IN and B _IN.
Are amplified by a predetermined gain to obtain color signals R _OUT and B _OUT that obtain an appropriate white balance for strobe light.

After the strobe 24 stops emitting light by the strobe emission stop signal B, the output signal e of the monostable multivibrator 22
Becomes the "L" level, the switches 24 and 25 are returned to the on state and the switches 28 and 29 are returned to the off state, respectively, and the normal auto white balance gain control signal V _RA ,
V _BA returns to the state where it is given as the gain control signals V _R and V _B of the variable gain amplifiers 20 and 21.

Next, the case where the strobe does not emit light because the shutter speed is fast will be described with reference to FIG. 6. As in the case described above, when the shutter curtain operation command a is issued after the exposure start trigger pulse is generated, When the shutter curtain operation command a rises, the front curtain starts to run, and the light amount integration circuit 14 is reset to start integration of the photocurrent of the light receiving element 13. By the way, in this case, since the subject light is bright, the integrated voltage rises at a steep slope, and the integrated voltage is increased before the front curtain completes traveling, that is, before the front curtain traveling completion signal b is issued. Reference voltage V _{ref of} comparator 15
Since the differential pulse is emitted from the differential circuit 17 of the photometry circuit, the shutter curtain operation command a becomes "L" level at this point, and the rear curtain starts running. Then, after the running of the trailing curtain, the running of the leading curtain is completed, the leading curtain running completion signal b is issued, and the exposure is finished. Therefore, if the trailing edge of the shutter curtain operation command a precedes the trailing curtain travel completion signal b, the strobe light emission start signal A is not issued. Therefore, the flash 24 does not emit light. Therefore, even if a differentiating pulse is emitted from the differentiating circuit 17 and guided to the terminal Tb at the time of the proper exposure, it is natural that this pulse is not used as the strobe light emission stop signal B.

Since the strobe light emission start signal A is not issued, the monostable multivibrator 22 does not operate even in the white balance setting circuit 19, and accordingly the switches 24 and 25
Remains on and switches 28 and 29 remain off, so the gain control signal changes according to the color temperature information of the external light.
V _RA and V _BA are obtained as the gain control signals V _R and V _B of the variable gain amplifiers 20 and 21 as they are, and normal automatic white balance adjustment is performed.

[Effects of the Invention] As described above, according to the present invention, the signal emitted when the front curtain of the focal plane shutter completes traveling, the strobe light emission precedes in time the signal emitted when the trailing curtain starts traveling. When the white balance is controlled, the white balance control value is fixed to the setting value corresponding to the flash light, and if the flash does not fire even if the flash is used,
Since the switching operation is automatically performed so that the normal auto white balance adjustment is performed according to the color temperature information of the outside light, a good color image is always taken even if the photographer does not recognize whether or not the flash fires. can do.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of an automatic white balance device showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the white balance setting circuit in FIG. 1, and FIG. FIG. 4 is a time chart for explaining a basic operation of shutter control in the apparatus shown in FIG. 1, FIG. 4 is a front view in the vicinity of a photographing screen for explaining a running operation of a curtain running type focal plane shutter, and FIG. FIG. 6 is a time chart of signals of respective parts during operation of the device shown in FIG. 1 when the strobe emits light. FIG. 6 shows during operation of the device shown in FIG. 1 when the strobe does not emit light. It is a time chart of each part signal. 2 ... Front curtain 3 ... Rear curtain 11 ... Shutter control circuit (means for issuing a first signal) 12 ... Focal plane shutter device (means for issuing a second signal) 18 ... AND gate (control circuit) 19 …… White balance setting circuit 24 …… Strobe

Claims (1)

[Claims] 1. A means for generating a first signal indicating the time when a front curtain of a curtain running type focal plane shutter has completed traveling, and a second signal which indicates a time when the rear curtain of the focal plane shutter starts traveling. Means for receiving the first signal and the second signal, and only the specific state in which the first signal precedes the second signal in time is set as the strobe use compatible state. A control circuit that generates a strobe light emission start signal for causing the strobe light to emit light based on the arrival of the signal No. 1, and a set value that adjusts the white balance control value to the strobe light based on the strobe light emission start signal. An automatic white balance device for an electronic camera using a strobe, characterized in that it has a white balance setting circuit adapted to.