JP3101352B2 - 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. Further, 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 pickup device, 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, white balance control at the time of recording a still image is performed by using a signal read from the image sensor before recording the still image.

[0005] Further, as an improved invention of the above-mentioned invention, the applicant of the present invention, prior to exposure for recording a still image (hereinafter referred to as main exposure), calculates the integrated value of the color signal read from the image pickup circuit at the time of light shielding, An application for an electronic still camera that subtracts from an integral value of a color signal read from an imaging circuit at the time of exposure prior to image recording (hereinafter, simply referred to as pre-exposure) has been filed (Japanese Patent Application No. 2-208245). The electronic still camera according to the present invention focuses on the fact that an error component obtained due to a factor other than a color signal of a subject is caused by an offset of an operational amplifier provided in an integration circuit of each color signal, and reduces the error component. It is.

[0006]

However, in the above-mentioned electronic still camera, as described above, the image pickup device in the light-shielded state is read out for each still image photographing, and an integrated value of a color signal at that time is formed. Therefore, a time lag between the time when the release scan is performed at each shooting and the time when the actual shooting screen is captured is increased.

Under such a background, the present invention minimizes the time from the release operation to the taking of the photographing screen in each photographing, and achieves a good white balance by using only the signal from the photographing means. It is an object to provide an electronic still camera capable of performing control.

[0008]

For such a purpose,
According to the present invention, there is provided an electronic device which includes an imaging unit for converting subject light into an electric signal, and an integration circuit for integrating a video signal of the imaging unit, and performs white balance control based on the video signal of the integration circuit. In the still camera, a video signal of the imaging unit obtained when the imaging unit is shielded from light is integrated by the integration circuit, and a value obtained by the integration circuit is used as a first operation value during main exposure. Storage means for storing a plurality of times for use in white balance control of the video signal obtained in step (a), and integrating the video signal from the imaging means obtained when pre-exposure is performed in accordance with the first operation. The white balance control value is obtained by subtracting the first operand value stored by the storage means from the second operand value obtained by the integration circuit and the second operand value obtained by the integration circuit. And control means for controlling the white balance of the video signal of the imaging means obtained when the main exposure is performed based on the obtained white balance control value in response to the second operation. And

[0009]

With the above construction, the operation of the image pickup means for obtaining the first operation value becomes only the minimum necessary number of times, and when the first operation value does not need to be updated, the photographing is performed. It is possible to minimize the time from the instruction to the capture of the desired screen.

[0010]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a block diagram showing a schematic configuration of an electronic still camera as one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an image sensor for converting an optical image into an electric signal, 2 a luminance signal processing circuit for processing an output signal from the image sensor 1 to generate a high-frequency luminance signal YH, and 3a a color signal processor. In the circuit, R (red), B (blue), G (green)
Make a signal. Reference numerals 4 and 5 denote variable gain amplifiers for adjusting the white balance of the R and B signals. 3b is a color signal processing circuit for forming R, B, YL (low-band luminance) signals from R, B, G signals, and 6a, 6b are subtraction circuits, and a color difference signal R
-YL and B-YL are made. Reference numerals 8a, 8b and 8c denote clamping circuits for clamping the obtained R-YL, B-YL and YL signals to a predetermined voltage determined by the reference voltage source 11. Reference numerals 9a and 9b denote clip circuits for suppressing a signal in a high-saturation portion because a white balance is shifted due to the influence of a high-saturation object in the subject. 10b and 10c are 9a and 9
This is an integration circuit for integrating the output signals b and 8c.
Reference numeral 12 denotes a photometric circuit for measuring the brightness (luminance) of the subject.

Reference numeral 7 denotes an arithmetic control unit for forming a white balance control signal for controlling the variable gain amplifiers 4 and 5 from the outputs of the integrating circuits 10a, 10b and 10c.

Reference numeral 13 denotes a decoding signal C. A sync generating circuit for generating Sync, a decoding sync signal and a high-frequency luminance signal Y
H, a mixer for mixing H, 15 a shutter, 16 a shutter drive circuit for driving the shutter 15, 17 an image sensor 1
Is an image sensor driving circuit that drives the image sensor. RR is a release member that turns on the switch SW1 in the first stroke and turns on the switch SW2 in the second stroke. PS
W is a power switch of the electronic still camera.

Reference numeral 20 denotes each of the switches SW1, SW2, PSW
A system controller 21 for detecting the on / off state of the device and controlling each part of the apparatus;
It receives L, B-YL and converts them into a signal form suitable for magnetic recording. This is a recording signal processing circuit.

The recording signal processing circuit 21 performs, for example, a process of FM-modulating the luminance signal Y and the color difference signals R-YL and B-YL, respectively, and frequency-multiplexing them, as is well known. The gate circuit 22 is controlled by the system controller 20, gates a desired one screen of the video signal output from the recording signal processing circuit 21, and supplies it to an electromagnetic conversion system 23 including a magnetic head or the like. As a result, a still image signal of a desired screen is recorded on a magnetic recording medium such as a magnetic disk.

Next, the operation of the electronic still camera of FIG. 1 will be described. FIG. 2 is a flowchart for explaining the operation of the system controller 20 in FIG.
FIG. 3 is a timing chart for explaining the photographing operation of the electronic still camera of FIG.

Hereinafter, description will be given according to the flowchart of FIG.

In FIG. 2, when the power switch PSW is turned on at step S1 and the switch SW1 is turned on by the operation of the first stroke of the release member RR at step S2, the system controller 2 is turned on.
If it is 0, it is determined in step S3 whether or not the clock value of the internal clock circuit is equal to or greater than a predetermined value Tth.

Here, this time value is read out from the image pickup device in a light-shielded state, the color difference signals B-YL and R-YL are integrated, and a series of operations of storing the integrated values are performed every time a series of operations are performed in step S5. Reset by. Therefore, if the time after the reset has passed for a predetermined time or more, step S
The process proceeds from step 3 to step S4, and if not, the process proceeds to step S6.

Here, the operation in step S4 will be described with reference to the timing chart of FIG.

First, the brightness of the object is measured by the photometric circuit 12, and a control value fixed to the variable gain amplifier is output from the arithmetic and control unit 7. Next, during the period from t1 to t2, unnecessary charges accumulated in one image sensor are cleared, the / RESET pulse of f is set high at t3, and the integration operation is started, and the integration value is started during the period from t4 to t5. Is read into the arithmetic control unit 7. In addition, shutter 1 between t6 and t7
In a state in which 5 is closed, reading from the image sensor 1 is performed by the circuit 17 during the period from t8 to t9. The difference is the offset of each integrator, and this value is stored in a memory provided in the arithmetic and control unit 7.

When the processing in step S4 as described above is completed, in step S5 the timer value of the timer circuit in the system controller 20 is reset, and the flow advances to step S7. Here, the switch S is moved by the second stroke of the release member RR.
When W2 is turned on, the process proceeds to step S9, and when the hand is released from the release member RR and the switch SW1 is turned off, the process returns to step S2 via steps S8 and S10.

Therefore, when the switch SW2 is turned on, a photographing process is performed in step S9.

The operation at the time of photographing will be described below with reference to the timing chart of FIG.

First, during the period from t11 to t12, 1
Unnecessary charges stored in the image sensor are cleared, the shutter 15 is opened by the circuit 16 at t13, and the PRE exposure is performed for a predetermined period determined by the previous photometry result. t1
When the PRE exposure ends at 4, the reset pulse sent from the arithmetic and control unit 7 to the integration circuits 10a, 10b, and 10c is set high at t15 to start the integration operation. From t16 to t1
The integration output is read during the period 7, and at t18, the reading of the electric charge accumulated in the image sensor at the time of the pre-exposure is started.

The read signal is supplied to the color signal processing circuit 3
The signals are converted into R, G, and B signals at a, and the R and B signals are amplified by the white balance adjustment amplifiers 4 and 5 with a gain determined by the fixed control voltage previously set, and are amplified by the color signal processing circuit 3b. The signals are converted into R, B, and YL signals,
The three signals R-YL, BY, and YL are obtained from a and 6b.

These signals are supplied to the clamp circuits 8a, 8b,
At 8c, the signal is clamped at a predetermined potential determined by the reference voltage source 11, and the color difference signals R-YL and B-YL are clipped in the high chroma portion. The outputs of 9a, 9b and 8c are integrated by integrating circuits 10a, 10b and 10c, respectively, to obtain integrated values R-YL, B-YL and YL. When this reading is completed at t19, the integrated output is read into the arithmetic and control unit 7 during a period from t20 to t21. The difference between this value and the value read at t16 is the integrated value of each color signal. By subtracting the previously stored offset value from this value, the correct integrated value of the color signal can be obtained. The arithmetic control unit 7 uses this value to calculate a white balance control value and outputs it.

Next, during the period from t23 to t24, unnecessary charges accumulated in the image sensor 1 are cleared again, the shutter is opened during the period from t25 to t26, the charges are accumulated in the image sensor 1, and not shown at t27. When a PG signal synchronized with the rotation of the magnetic disk comes, the signal charge stored in the image sensor 1 is read out in synchronization with the PG, and REC /
The gate circuit 22 is opened by GATE and the electromagnetic conversion system 23 is opened.
To record a video signal on a magnetic disk.

With the above operation, one photographing operation is completed. Thereafter, the value of the offset of the integrator stored before the predetermined period Tth is held, and during the next photographing, the offset is corrected using this value.

That is, at step S3, the time value is set to the predetermined value Tt.
h, the process proceeds to step S16, and the photometric circuit 1
2 only. Then, when the switch SW2 is turned on, the process directly proceeds to step S9 to perform the above-described photographing operation. The operation in step S9 is the same as the operation from t11 to t28 in the timing chart of FIG.

In step S10, the power switch PSW
Is detected, the processing according to the flowchart of FIG. 3 is terminated.

With this configuration, it is not necessary to read out the image sensor in the light-shielded state in order to measure the offset value of the integration circuit every time photographing is performed. Time (time lag) can be shortened.

Next, another embodiment of the present invention will be described.

The configuration of the electronic still camera of this embodiment is the same as the configuration of FIG. 1, and a detailed description is omitted. In this embodiment, when the switch SW1 is first turned on after the power switch PSW is turned on, the image sensor 1 is read out in the light-shielded state as described above, and the offset of the integrator is measured. Until is turned off, this offset value is stored in the memory in the arithmetic and control unit 7.

During photographing during this time, the integral value measured at the time of pre-exposure is always corrected using the offset value stored in the memory.

FIG. 4 is a flow chart for explaining the operation of the system controller 20 in this embodiment. In FIG. 4, the same reference numerals are given to the same processing steps as those in FIG.

That is, in FIG. 4, when the power switch PSW is turned on at step S1, the variable P is set to 0 at step 11, and when the switch SW1 is turned on, the variable P is set to 0. If there is, the processing of the above-mentioned step S4 is performed, and 1 is set to this variable P in step S12.

The meaning of the variable P is that if P is 0, the process according to step S4 has not yet been performed after power-on, and if P is 1, it indicates that the process according to step S4 has already been performed. That is, if it is determined in step S13 that P is 1, only the photometric process is performed in step S6, and the camera enters a photographing standby state.

Other operations are exactly the same as those of the above-described embodiment, and the same effects can be expected.

In the above-described embodiment, whether the operation of measuring the offset value of the integrating circuit is performed only when the first switch SW1 is turned on after the time period of the time circuit exceeds the predetermined period Tth. Although the configuration is performed only when the first switch SW1 is turned on after the power is turned on, for example, the above two conditions can be combined. That is, the above-described measurement operation is performed only when the time has exceeded the predetermined period Tth for the first time after the power is turned on, or the first time after the power is turned on or the first time after the time has exceeded the predetermined period Tth. It is also possible to adopt a configuration in which the measurement operation is performed when the switch SW1 is turned on.

In the electronic still camera according to the present embodiment, an initial value is read into the integrated value at the timings t4 and t16 in FIG. 3, and then the integration result is read at the timings t8 and t20. Calculate the difference value,
Further, the difference value calculated in the light-shielded state is subtracted from the difference value calculated in the pre-exposure. However, the integrated value read at the timing of t8 is simply referred to as t20.
A similar result can be obtained by subtracting from the integrated value read at the timing of (1).

In this case, the operation control section 7 can read the integral value only at two times t8 and t20.

[0044]

As described above, according to the electronic still camera of the present invention, the first operation value according to the video signal read from the image pickup means prior to the pre-exposure and the read value from the image pickup means during the pre-exposure. The second according to the output video signal
In controlling the white balance using the calculated values of the above, the means for storing the first calculated values is provided, so that the operation of the imaging means for obtaining the first calculated values is minimized. When only the number of times is required and the first operand value does not need to be updated, the time from the photographing instruction to the capture of a desired screen can be minimized.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating an operation of a system controller of the electronic still camera in FIG. 1;

FIG. 3 is a timing chart for explaining the operation of the electronic still camera in FIG. 1;

FIG. 4 is a flowchart for explaining the operation of the system controller of the electronic still camera according to one 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 unit 10a, 10b, 10c Integration circuit 15 Shutter 20 System controller 21 Recording signal processing circuit 22 Gate circuit 23 Electromagnetic conversion system RR release member SW1, SW2 Switch PSW Power switch

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 9/04 H04N 9/73

Claims (4)

(57) [Claims] 1. An electronic still comprising: an image pickup means for converting subject light into an electric signal; and an integration circuit for integrating a video signal of the image pickup means, and performing white balance control based on the video signal of the integration circuit. In the camera, a video signal of the imaging unit obtained when the imaging unit is shielded from light is integrated by the integration circuit, and a value obtained by the integration circuit is used as a first operand value during the main exposure. Storage means for storing in advance a plurality of times for use in white balance control of the obtained video signal, and a video signal from the imaging means obtained when pre-exposure is performed in accordance with a first operation; To obtain a white balance control value by subtracting the first operand value stored by the storage means from the second operand value obtained by the integration circuit. And control means for controlling the white balance of the video signal of the imaging means obtained when the main exposure is performed based on the obtained white balance control value in response to the second operation. An electronic still camera characterized by the following. 2. The electronic still according to claim 1, wherein said storage means cancels the storage of said first operand value when a predetermined period has elapsed from its capture. camera. 3. The electronic still according to claim 1, wherein said storage means cancels the storage of said first operand value when the power supply of the camera body is turned off. camera. 4. The image processing device according to claim 1, wherein when the first operation value is not stored in the storage device, the imaging device is shielded from light by the shutter device. An electronic still camera, comprising: control means for executing reading of a video signal by the imaging means in order to obtain the first operation value.