JP3347352B2 - Electronic still camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera, and more particularly to an electronic still camera which controls white balance using a signal read from an image pickup means.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed and implemented for controlling white balance in an electronic still camera. For example, detecting the color temperature of the light source light using a colorimetric sensor and a colorimetric circuit provided separately from the imaging circuit,
A configuration is known in which the levels of a plurality of color signals are controlled according to the detected color temperature.

As described above, when a colorimetric circuit for detecting the color temperature of light from a light source is used, the colorimetric circuit is generally expensive, and a colorimetric sensor must be provided separately from the image sensor. This hinders miniaturization and cost reduction of the device. In addition, in this method, it is necessary to perform adjustment for matching the spectral characteristics of the photometric circuit and the color filter of the image sensor, and this adjustment is necessary, which is troublesome.

[0004] Against this background, the present applicant has previously filed a patent application for the invention of an electronic still camera capable of optimal white balance control using only signals output from an image pickup circuit (Japanese Patent Application No. Hei 10-26139). 1-255507). In the electronic still camera according to the present invention, the white balance control at the time of photographing a still image (at the time of main exposure) is performed by using a signal read from the image sensor at the time of exposure (at the time of pre-exposure) prior to photographing of a still image. Is what you do.

[0005]

Generally, when white balance control is performed using a video signal captured, color components of a predetermined level or more are clipped in order to suppress the influence of subject color. , For white balance control. This clip level is
In a color temperature range in which white balance is controlled, the color temperature is set to a level range in which the color temperature changes with a change in the light source color.

However, when exposure correction is performed during pre-exposure, the level of the color signal changes accordingly, so that the controllable range of the white balance changes. That is, when the exposure is corrected to the release side, the level of the color signal increases, so that clipping is applied in a range narrower than a required color temperature range, and white balance control can be performed only in a narrow range.

If the exposure at the time of the pre-exposure is corrected to the closed side, the level of the color signal also becomes small, and it becomes difficult to apply a clip. Therefore, the white balance control is affected by the subject. It will be easier.

Under such a background, the present invention has an effect on the exposure control at the time of pre-exposure prior to photographing (main exposure) in an electronic still camera which controls white balance using a signal read from an imaging means. An object of the present invention is to provide an electronic still camera capable of performing stable and white balance control that is not affected by a subject without changing a control range.

[0009]

For such a purpose,
According to the present invention, a main exposure operation, exposure means for executing first and second pre-exposure operations prior to the main exposure operation, and an exposure control value obtained by the first pre-exposure operation And a suppression unit for suppressing a signal level of a color signal read from the imaging unit in the second pre-exposure operation, and a suppression control unit based on an exposure control value obtained by the first pre-exposure operation. The second
A suppression level control means for controlling a suppression level for suppressing a signal level of a color signal read from the imaging means in the pre-exposure operation; and a suppression level read from the imaging means in the second pre-exposure operation suppressed by the suppression means. An electronic still camera having white balance control means for controlling a white balance of a color signal read from the imaging means at the time of the main exposure operation based on the color signal component to be read.

[0010]

With the above arrangement, even when the exposure is corrected during the pre-exposure, the suppression level of the level suppression means does not relatively change with respect to the video signal level, and the required color temperature is always maintained. White balance control is possible in the range.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail.

(First Embodiment) FIG. 1 is a block diagram showing a schematic configuration of an electronic still camera as a first embodiment of the present invention.

[0013] In FIG. 1, the imaging device 1 for converting an optical image into an electrical signal, 2 is a luminance signal processing circuit for forming a high frequency luminance signal Y _H by processing the output signal from the imaging device 1, 3
a also processes the output signal from the image sensor 1 to obtain R
This is a color signal processing circuit that forms (red), B (blue), and G (green) signals.

Reference numerals 4 and 5 denote variable gain amplifiers for controlling white balance, and 3b denotes R, B, and R signals using the R and B signals via the variable gain amplifiers 4 and 5 and the G signal from the color signal processing circuit 3a. This is a color signal processing circuit that forms a Y _L (low-band luminance) signal.

Numerals 6a and 6b denote subtraction circuits, and the color difference signals R
-Y _L, to form a B-Y _L. 8a, 8b, 8c are respectively a clamp circuit that clamps to the _{R-Y L, B-Y} L, a predetermined reference voltage which is determined by the reference voltage source 11 and Y _L.

Further, as described above, when the subject contains a highly saturated object as described above, the white balance is deviated due to the influence of the object.
This is a peak clipping circuit (suppression means) for suppressing a signal of a high chroma portion in the outputs of a and 8b. here,
The clip levels of the clip circuits 9a and 9b are determined by a clip level control signal output from the arithmetic control unit 7 described later.
It will be controlled by CONT.

Reference numerals 10a, 10b and 10c denote clip circuits 9.
a, 9b, an integrating circuit for integrating the output signals of the clamp circuit 8c; and 12, a photometric circuit for measuring the brightness (luminance) of the subject.

Reference numeral 7 denotes an arithmetic control unit, which is an integration circuit 10a,
A white balance control signal for controlling the variable gain amplifiers 4 and 5 is formed by using output signals of 10b and 10c.

[0019] 13 synchronizing signal generating circuit for generating a composite synchronizing signal, 14 is a mixer for mixing the composite synchronizing signal from the synchronizing signal generating circuit 13 to the high band luminance signal Y _H, 15 shutter, 16 a shutter 15 A shutter drive circuit for driving,
Reference numeral 17 denotes an image sensor driving circuit that drives the image sensor 1.

Reference numeral RR denotes a release member, which turns on the switch SW1 by the operation of the first stroke and turns on the switch SW2 by the second stroke. PSW is a power switch of the electronic still camera of this embodiment.

Reference numeral 20 denotes each switch SW1, SW2, PSW
A system controller for controlling the respective units by detecting the on-off of 21 output signal Y _H + S and color difference signals R-Y _L of the mixer 14 receives the B-Y _L, the signal form suitable for these magnetic recording This is a recording signal processing circuit for conversion.

The recording signal processing circuit 21 performs, for example, a process of FM-modulating the luminance signal Y, the color difference signals R-Y _L , and B-Y _L , respectively, and frequency-multiplexing them, as is well known. The gate circuit 22 is controlled by the system controller 20 and outputs a desired one of the video signals output from the recording signal processing circuit 21.
The screen is gated and supplied to an electromagnetic conversion system such as a magnetic head at a desired timing. As a result, a still image signal of a desired screen is recorded on a magnetic recording medium such as a magnetic disk.

FIG. 2 is a timing chart for explaining the operation of the electronic still camera of this embodiment, and FIG. 3 is a flowchart for explaining the operation of this embodiment.
The operation will be described below with reference to these drawings.

When the power switch PSW is turned on, the processing according to the flowchart of FIG. 3 is started. In this state, when the switch SW1 is turned on by operating the release member RR (step S1), a magnetic field (not shown) is generated in the electromagnetic conversion system 23. A servo operation for rotating a disk or the like is started (step S2).

Then, the operation of detecting the brightness of the object (photometry) by the photometry circuit 12 is started (step S3), and when the photometry operation is completed, the switch SW2 is turned on by operating the release member RR (steps S3, S4). ), And proceed to step S31.

Here, it is determined in step S31 whether or not exposure correction is to be performed in accordance with the result of the photometry. If exposure correction is to be performed, in step S32, the arithmetic and control unit 7 causes the clipping circuit to control the clipping circuit by the control signal CONT. 9a, 9b
Is changed, and the process proceeds to step S6.

That is, in step S32, if the exposure correction is applied to the release (over) side, the color signal increases, so that the clip level is normally set as shown in FIG. )). In addition, when exposure correction is applied to the closed (under) side, the color signal becomes small. Therefore, as shown in FIG. 6C, the clip level is made smaller than usual. If the exposure correction is not performed, the process proceeds to step S6 without changing the clip level.

In step S6, a fixed value is set as the white balance control voltage at the time of pre-exposure by the arithmetic and control unit 7.
Output to the variable gain amplifiers 4 and 5, and then t
At timings 0 to t1, unnecessary charges accumulated in the image sensor 1 are cleared (step S7), and t
The shutter 15 is opened at 2 and a period t according to the previous photometric result
Pre-exposure is performed for 2 to t3 (step S8). When the pre-exposure is completed, at t4, the integration reset pulse RESET shown in FIG.
R-Y _L , B-Y _L , Y _L according to 0a, 10b, 10c
Start the integration operation of each signal.

From t5 to t6, the arithmetic control unit 7 samples and reads the initial values of the outputs of the integration circuits 10a, 10b, 10c (step S9).

Next, from t7, the signal charges accumulated during the pre-exposure of the image sensor 1 are read out (step S1).
0). The signal read out here is a color signal processing circuit 3
The signals are converted into R, G, B signals at a, and the R, B signals are amplified by the variable gain amplifiers 4, 5 for white balance adjustment with gains according to the control voltage previously set at step S6. And supplied to the color signal processing circuit 3b.

[0031] In the color signal processing circuit 3b, R by using these signals, B, Y _L signal respectively derived, further subtraction circuit 6a, 6b by _{R-Y L, B-Y} L signal Y
Obtained with the _L signal.

These signals are supplied to clamp circuits 8a, 8b,
At 8c, each is clamped to the reference potential from the reference voltage source,
Further, the high chroma portions of the color difference signals R-Y _L and B-Y _L are clipped within the clip levels by clip circuits 9a and 9b whose clip levels are controlled.

The outputs of the clipping circuits 9a, 9b and the clamp circuit 8c are integrated by integrating circuits 10a, 10b, 10c, respectively, and these integrating circuits 10a, 10b, 10c are integrated.
The integral outputs ∫R−Y _L , ∫B−Y _L , and ∫Y _L are obtained from c. These integrated outputs are the first at t8.
After the end of the first pre-exposure, it is read by the arithmetic and control unit 7 from t9 to t10 (step S11).

Here, the difference between the integration initial value read in step S9 and the integration output read in step S11 becomes the integration value of each signal. The arithmetic control unit 7 calculates a white balance control value based on the integral value of each signal (step S12), and outputs this value to the variable gain amplifiers 4, 5 as a white balance control value (step S13). The operation of the integration circuit ends at t11 in FIG.

The white balance control at the time of the main exposure is performed based on the white balance control value obtained by the pre-exposure.

That is, when the white balance control value by the pre-exposure is output in step S13, t12 to t12
At 13, unnecessary charges accumulated in the image sensor are cleared again (step S 21), and the shutter 15 is opened during the period from t 14 to t 15 to perform main exposure (step S 2).
2), charges are stored in the image sensor 1;

When a PG signal synchronized with the rotation of the magnetic disk (not shown) arrives at step S23, the signal charges stored in the image pickup device 1 are read out in synchronization with the PG signal, and the gate circuit 22 is synchronized with the signal charge. Then, a recording signal is supplied to the electromagnetic conversion system 23, and a still image signal for one screen is recorded on the magnetic disk (step S24).

According to the electronic still camera of the embodiment as described above, even if exposure correction is performed at the time of pre-exposure, the clip level changes following the change of the color signal level. No problem such as change occurs. Therefore, there is no problem that the white balance control is not effective or the subject is strongly influenced by the subject.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS.

The configuration itself of the device of the second embodiment is the same as that of the first embodiment described above, and is as shown in FIG. FIG. 4 is a timing chart for explaining the operation of the second embodiment, and FIG.
6 is a flowchart for explaining the operation of the embodiment.

The electronic still camera according to the present embodiment has a configuration in which the pre-exposure can be performed a plurality of times, and when the exposure is corrected based on the result of the first pre-exposure, the second pre-exposure is performed.

In FIG. 4, the same reference numerals are given to the timings at which the same operation as in FIG. 2 is performed.
In FIG. 6, the same steps as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As in the case of the first embodiment described above, when the photometry step is completed in step S5, the process unconditionally proceeds to step S6 in the present embodiment, and the fixed value of the first pre-exposure , And the operation relating to the first pre-exposure is performed in steps S7 to S11 during a period indicated by t0 to t11 in FIG.
The operations in steps S7 to S11 are the same as those described in the first embodiment.
This is the same as the operation at the time of pre-exposure in the embodiment.

Here, in step S11, the integral output ∫
_{R-Y L, ∫B-Y} L, reads the ∫Y _L, but calculates the integral value of each signal in the arithmetic control unit 7 described above, in step S33, the integral value for this time Y _L is an appropriate level It is determined whether or not it is. If the integrated value of Y _L is not at the appropriate level, the next exposure, that is, the second pre-exposure is performed, and the exposure is corrected together.

If it is determined in step S33 that the exposure correction is to be performed, the second pre-exposure is performed. Before that, the clip levels are corrected by the clip circuits 9a and 9b in step S34. Do. This correction is the same as in the first embodiment described above, and is performed to compensate for the level change of the color signal due to the exposure correction.

Then, in step S35, a fixed white balance control value is output again, and the process proceeds to the second pre-exposure step from step S14.

That is, in the electronic still camera of the second embodiment, steps S14 to S18 (t0 'to t1) are performed.
1 ′), the operations of steps S7 to S11 (t
0 to t11) are repeated. That is, performs pre-exposure of the second round, the integral initial value during the second round of pre-exposure and the integrated output ∫R-Y _L, ∫B-
Y _L and ΔY _L are read in steps S16 and S18.

Then, in steps S19 and S20, a white balance control value is calculated in accordance with the integrated value of each signal obtained from the read data and output to the variable gain amplifiers 4 and 5. Move to the photographing process.

The white balance control at the time of the main exposure is performed based on the white balance control value obtained by the second pre-exposure.

On the other hand, if it is determined in step S33 that the exposure correction is not to be performed, the process proceeds to step S1.
Then, the process proceeds to step S9, and the control value of the white balance is calculated and output based on the integral value of each signal obtained by the first pre-exposure, and the main exposure (photographing) operation of step S21 and subsequent steps is performed as it is.

This is because when exposure compensation is not applied,
This means that the exposure at the time of pre-exposure was appropriate as described above, and there is no possibility that the clip will be applied in a narrow range or the clip will not be applied as described above. In such a case, the time lag from the operation of the release member RR to the actual shooting can be made shorter than in the case where the exposure correction is applied.

With the configuration of the second embodiment as described above, the same effects as those of the first embodiment can be obtained, and when exposure correction is applied, the clip levels of the clip circuits 9a and 9b are controlled and Since the calculation of the control value of the white balance itself is performed again, the calculation of the control value of the white balance itself is also performed with the proper exposure, and the possibility that the control range of the white balance changes is further reduced.

In the second embodiment described above, the first
Although exposure correction by the integral value of Y _L at times th pre-exposure are configured to perform second round of pre-exposure all if such, only when the above certain value exposure correction amount second
It is also possible to configure so as to perform the second pre-exposure. In this case, although the accuracy of the white balance control is slightly inferior, the time lag can be shortened as a whole.

[0054]

As described above, according to the electronic still camera of the present invention, the suppression level of the video signal at the time of the pre-exposure is controlled in accordance with the exposure control value. Instead, white balance control is always possible in a required color temperature range.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an electronic still camera according to a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the electronic still camera according to the first embodiment of the present invention.

FIG. 3 is a flowchart for explaining the operation of the system controller of the electronic still camera according to the first embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the electronic still camera according to the second embodiment of the present invention.

FIG. 5 is a flowchart for explaining the operation of the system controller of the electronic still camera according to the second embodiment of the present invention.

FIG. 6 is a waveform chart for explaining a clip level control operation according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 3a, 3b Color signal processing circuit 4, 5 Variable gain amplifier 7 Operation control part 8a, 8b Clamp circuit 9a, 9b Clip circuit 10a, 10b, 10c Integration circuit 15 Shutter 16 Shutter drive circuit 20 System controller 21 Recording signal processing Circuit 22 Gate circuit 23 Electromagnetic conversion system RR Release member SW1, SW2 Switch PSW Power switch

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 9/73 H04N 9/04 H04N 5/235-5/243

Claims (2)

(57) [Claims] An exposure unit configured to execute first and second pre-exposure operations prior to the main exposure operation; and an exposure control value obtained by the first pre-exposure operation. A suppression unit for suppressing a signal level of a color signal read from an imaging unit in the second pre-exposure operation; and the suppression unit based on an exposure control value obtained by the first pre-exposure operation. A suppression level control unit for controlling a suppression level for suppressing a signal level of a color signal read from the imaging unit in the second pre-exposure operation; and the imaging unit in the second pre-exposure operation suppressed by the suppression unit. A white signal for controlling a white balance of a color signal read from the image pickup means at the time of the main exposure operation, based on a color signal component read from An electronic still camera having a light balance control means. 2. The method according to claim 1, wherein the exposure unit performs the second pre-exposure operation based on a difference between an exposure control value for performing the first pre-exposure operation and an exposure control value obtained by the first pre-exposure.
An electronic still camera for determining whether or not to perform a pre-exposure.