JP3101392B2 - 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 photometric 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 colorimetric circuit and the color filter of the image sensor, and this adjustment work is troublesome in that it is necessary.

[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 photographing a still image (at the time of actual exposure) is performed 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. Things.

[0005]

However, in the above-mentioned electronic still camera, if the white balance control value at the time of the pre-exposure greatly deviates from the color temperature of the light source at the time of the pre-exposure, it is output. The level of each color signal corresponding to white deviates from the clamp level.

In general, when white balance control is performed by using a captured video signal, color components of a predetermined level or more are clipped and used for white balance control in order to suppress shooting of a subject color. However, as described above, if the white balance control value at the time of the pre-exposure greatly deviates from the color temperature of the light source at the time of the pre-exposure, the control of the white balance tends to be influenced by the subject.

If the white balance control value at the time of pre-exposure greatly deviates from the color temperature of the light source at the time of pre-exposure, the correction amount of the level of a plurality of color signals becomes large. Analog errors increase. For example, in order to form a white balance control signal, an integrated value of a color signal for one screen is used, but there is a problem such as a variation in integration characteristics between colors.

In the above-described white balance control, since the white balance is controlled from a single screen, it is easily affected by the object color. That is, when a high-saturation subject exists on the screen and the occupied area is large, good white balance control may not be performed.

Under such a background, the present invention relates to an electronic still camera for controlling white balance by using a signal read from an image pickup means. It is an object to provide an electronic still camera capable of performing control.

[0010]

For such a purpose,
According to the present invention, an imaging unit that converts subject light into an electric signal, a main exposure for photographing a desired screen, and an exposure unit that operates at a pre-exposure preceding the same, and an output signal of the imaging unit are used. Control information forming means for forming control information relating to color temperature, and when the color temperature at the time of pre-exposure obtained from the output signal of the imaging means is within a predetermined range, the imaging means at the time of the pre-exposure The white balance of the output signal of the imaging unit at the time of the main exposure is controlled according to the control information formed by the output signal, and the color temperature at the time of the pre-exposure obtained from the output signal of the imaging unit is out of a predetermined range. A white rose for controlling a white balance of an output signal of the imaging unit at the time of the main exposure according to control information formed by an output signal of the imaging unit at the time of photographing in the past; It has a configuration comprising a scan control unit.

[0011]

[0012]

As described above, by controlling the white balance at the time of pre-exposure in accordance with the information formed at the time of photographing in the past, the white balance at the time of pre-exposure can be made to correspond to the color temperature of the light source. It is possible to perform stable white balance control without being affected by the color temperature.

In addition, since the information formed at the time of the past photographing and the information formed at the time of the pre-exposure are used for controlling the white balance at the time of the main exposure, the influence of the object color at the time of the photographing can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment 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 a first embodiment of the present invention.

[0016] 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 signal 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, if the subject contains a high chroma as described above, the white balance is deviated due to the influence of the subject, so that the clamp circuits 8a, 8b and 8c are provided. Is a peak clipping circuit for suppressing a signal in a high-level portion in the output of FIG. 10a,
10b and 10c are clip circuits 9a and 9
integration circuits for integrating the output signals b, 9c;
b, 12c is output ∫R-Y _L of the integrating circuit, ∫B
A / D converters for analog-digital (A / D) conversion of −Y _L and ΔY _L , and 18 are A / D converters 12a, 12b, 1
Digital values [Delta] R-Y _L to output 2c, ΔB-Y _L, ΔY
Let _{L be} a digital value ΔR, Δ corresponding to the R, G, B signals.
This is a matrix circuit that converts the values into G and ΔB.

Reference numeral 7 denotes an arithmetic control unit, which is a matrix circuit 1
The white balance control signal for controlling the variable gain amplifiers 4 and 5 is formed by using the digital values ΔR, ΔG and ΔB output from 8. A memory 19 exchanges data with the arithmetic control unit 7.

[0021] 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 for driving the image sensor 1, and reference numeral 24 denotes a photometric circuit for measuring the brightness (luminance) of the subject.

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

Reference numeral 20 denotes a system controller for detecting the output of the photometric circuit 24 and on / off of the switches SW1, SW2, and PSW to control each unit of the apparatus.
Receiving the output signal Y _H + S and color difference signals R-Y _L, the B-Y _L, which is a recording signal processing circuit for converting a signal form suitable them to magnetic recording.

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. Gate circuit 2
Reference numeral 2 denotes an electromagnetic conversion system which 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 comprises a magnetic head or the like.
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 flow chart for explaining the operation of the present embodiment, FIG. 3 is a timing chart for explaining the operation of the electronic still camera of the present embodiment, FIG. 4 is the color temperature of the light source, and the above-mentioned white color. FIG. 9 is a characteristic diagram illustrating a relationship between a balance control signal and gains of R and B variable gain amplifiers 4 and 5; The operation will be described below with reference to these drawings.

When the power switch PSW is turned on (step S1), the arithmetic and control unit 7 sets a fixed white balance control value in the memory 19 (step S2). This control value is a control value corresponding to a standard color temperature, and is a control value corresponding to a point indicated by a in FIG.

In this state, when the switch SW1 is turned on by operating the release member RR (step S3), a servo operation for rotating a magnetic disk (not shown) in the electromagnetic conversion system 23 is started (step S5).

Then, the operation (photometry) of detecting the brightness of the object by the photometric circuit 24 is started (step S6), and when the switch SW2 is turned on by operating the release member RR in the state where the photometric operation is completed (step S7, S
8) The arithmetic control unit 7 reads the white balance control value stored in the memory 19 (step S9).

Here, the white balance control value is:
In the first shooting after the power is turned on, the standard white balance control value set in step S2 is used. However, in the second and subsequent shootings, as described later, the white balance control value in the past shooting is used. .

The white balance control value read in the white balance S9 is output from the arithmetic control unit 7 to the variable gain amplifiers 4 and 5 as a white balance control value at the time of pre-exposure. The relationship between the control value (control voltage) and the gain of each of the amplifiers 4 and 5 is as shown in FIG.

Thereafter, at timings t0 to t1 in FIG. 3, unnecessary charges accumulated in the image pickup device 1 are cleared (step S10), and at t2, the shutter 15 is opened, and the image is determined according to the previous photometry result. Period t2 to t3
The pre-exposure is performed in (step S11). When controlling the aperture (not shown) during the pre-exposure, the aperture value is determined according to the photometric signal.

When the pre-exposure is completed, at t4,
The integration reset pulse RESET shown in FIG.
Y _L, B-Y _L, starts integration operation of signals Y _L.

At t5 to t6, the arithmetic control unit 7 samples and reads the initial values of the outputs ΔR, ΔG, and ΔB of the matrix circuit 18 (step S12).

Next, from t7, the signal charges accumulated during the pre-exposure of the image sensor 1 are read out (step S1).
3). 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 S9. And supplied to the color signal processing circuit 3b.

[0035] 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 _L
Obtained with the signal.

These signals are supplied to the clamp circuits 8a, 8b,
At 8c, they are clamped to the reference potential from the reference voltage source 11, respectively, and the high chroma portions of the color difference signals R-Y _L and B-Y _L are clipped by the clip circuits 9a and 9b.

The outputs of the clip 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 output is further A / D converter circuit 12a as a digital value _{ΔR-Y L, ΔB-Y} L, ΔY L
Is converted to a digital value Δ by the matrix circuit 18.
It is converted to R, ΔG, ΔB. This digital value ΔR, Δ
G and ΔB are read into the arithmetic and control unit 7 from t9 to t10 after the first pre-exposure is completed at t8 in FIG. 3 (step S14).

Here, the difference between the initial value read in step S12 and the value read in step S13 is data used for white balance control. The arithmetic control unit 7 calculates a white balance control value based on the data (step S15), and outputs this value to the variable gain amplifiers 4 and 5 as a white balance control value (step S16). The operation of the integration circuit is represented by t1 in FIG.
It ends with 1.

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 obtained by the pre-exposure is output in step S16, the white balance control value is stored in the memory 19 for later photographing, and is stored in the image pickup device from t12 to t13. The unnecessary unnecessary charges are cleared again (step S1).
8) During the period from t14 to t15, the shutter 15 is opened, main exposure is performed (step S19), and electric charges are accumulated in the image sensor 1.

In step S20, when a PG signal synchronized with the rotation of the magnetic disk (not shown) arrives, 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 this. Then, the recording signal is supplied to the electromagnetic conversion system 23 by recording and closing, and a still image signal for one screen is recorded on the magnetic disk (step S21).

When the recording of the still image signal for one screen is completed, the process returns to step S3 and waits for the operation of the next release switch RR. If the switch SW1 is turned on next, the white balance control value read out in step S9 Are obtained at the time of the previous photographing, and at the time of pre-exposure, the gains of the variable gain amplifiers 4 and 5 are determined by the white balance control value.

On the other hand, if the power switch PSW is turned off in the standby state of the operation of the release switch RR (step S4), the contents stored in the memory 19 are cleared (step S22), and the process ends. Thereafter, when the power switch PSW is turned on again to perform photographing, it goes without saying that the variable gain amplifiers 4 and 5 at the time of pre-exposure have the standard white balance control values read in step S2.

According to the electronic still camera of the embodiment as described above, the white balance at the time of the pre-exposure is controlled by the white balance control value at the time of the past photographing. Therefore,
The control value of the white balance at the time of the main exposure is formed by using a video signal formed under the white balance control which does not have a large deviation from the color temperature.

That is, the gain of the variable gain amplifiers 4 and 5 at the time of the first pre-exposure after the power is turned on is determined by the white balance control value corresponding to the color temperature at the point a in FIG. It is assumed that the white balance control value at the time of main exposure determined by the obtained color temperature information is a value corresponding to the color temperature at point b in FIG. In general, in an electronic still camera, it is general that the power is turned on under conditions in which shooting is desired, and the power is turned off when a plurality of images have been shot, and the same as the first shooting after the second shooting. It is likely to be performed under a simple light source.

Therefore, the white balance control value at the time of the first exposure is close to the white balance control value corresponding to the color temperature in the second photographing. For example, the second
Assuming that the ideal white balance control value in the second photographing corresponds to the color temperature at point b 'in FIG. 4, the white balance offset at the time of pre-exposure and at the time of main exposure is x'. It is smaller than the white balance offset x when pre-exposure is performed with the balance control value.

That is, in the present embodiment, the amount of correction of the gain of the variable gain amplifiers 4 and 5 at the time of the main exposure can be made sufficiently small, and the white balance caused by the variation in the characteristics of the integration circuits 10a, 10b and 10c and the like. Deviation is minimized.

The clamp levels of the clamp circuits 8a, 8b and 8c correspond to almost white irrespective of the state at the time of photographing, and the clipping circuits 9a, 9b and c9 ensure that a high chroma portion is only a required amount. Since clipping can be performed, white balance control that makes it difficult to capture a subject can be performed.

FIG. 5 is a block diagram showing a schematic configuration of an electronic still camera as a second embodiment of the present invention.
The same reference numerals are given to the same components as in the first embodiment.

In the figure, reference numeral 26 denotes A / D converters 12a and 12
b, the digital value [Delta] R-Y _L to output 12c, ΔB-
A color temperature calculation circuit that derives color temperature information from Y _L and ΔY _L. For example, ΔR and ΔB are determined from these and ΔR / ΔB
Is derived to form color temperature information. Also, 25
Is a memory capable of storing a plurality of pieces of color temperature information, and can supply a plurality of pieces of color temperature information stored in the arithmetic and control unit 7.

FIG. 6 is a flowchart for explaining the operation of the present embodiment. Steps similar to those in FIG. 2 are denoted by the same reference numerals. FIG. 7 is a diagram for explaining the color temperature ranges I, II, III, IV, and V defined in the present embodiment. The operation will be described below with reference to these drawings.

In FIG. 7, each of the areas II, III, and IV is a color temperature range in which white balance control can be followed. Among them, the area III is a light source that is sensed as "white" by human eyes, and the area II is " The region IV is a color temperature range corresponding to a light source that feels “slightly blue”. Regions I and V are outside the white balance control tracking range, ie,
This is a color temperature range corresponding to color temperature information obtained when a subject with a strong object color, for example, a person is photographed against a red wall.

When the power switch PSW is turned on (step S1), the arithmetic and control unit 7a clears all the color temperature information at the time of the past photographing stored in the memory 25 (step S31).

In this state, the switch SW1 is turned on by operating the release member RR, and when the switch SW2 is turned on after the photometry is completed (step S8), the operation for pre-exposure is started.

That is, in step S32, the memory 25
Is read, and the color temperature of the light source is estimated from the color temperature data (step S33). Here, the operation of step S33 will be described in detail.

The arithmetic control unit 7a reads out the color temperature information stored in the memory 25 at the time of all past photographing after the power is turned on in step S32. Step S33
In these data, except for the data outside the white balance tracking range, that is, the color temperature data corresponding to the region I and the region V in FIG. The estimated color temperature data is estimated to be the color temperature of the light source under the current shooting conditions. Then, the color temperature data is stored in the areas II and II in FIG.
It is determined which of I and IV it belongs to, and light source data indicating this is generated.

Here, in the first photographing after the power is turned on, since the memory 25 has been cleared in step S31, color temperature data cannot be obtained. Also,
Even when all the color temperature data obtained by past photographing belong to the regions I and V, effective color temperature data cannot be obtained. Therefore, in these cases, a standard light source is assumed, and the light source data is data indicating the area II.

Next, a control value of the white balance corresponding to the color temperature of the light source data is derived, and this control value is set as a white balance control value at the time of pre-exposure, and the arithmetic control unit 7 executes the calculation.
a to the variable gain amplifiers 4 and 5 (step S3).
4). Here, there are actually three types of white balance control values at the time of the pre-exposure corresponding to the areas II, III and IV.

Thereafter, steps S10, S11, S13
, The pre-exposure operation is performed in the same manner as in the first embodiment. Then, in step S35, the color temperature information derived by the color temperature calculation circuit 26 is read from the image signal obtained at the time of the pre-exposure.

Here, if the color temperature information is information corresponding to the regions I and V (step S35), the color temperature information is strongly influenced by the object color and is meaningless. The white balance control value derived in step S34 is output as it is in step 37.

On the other hand, if the color temperature information read in step S35 is the information corresponding to the areas II, III, IV, the process proceeds to step S37, where the white balance control is performed using the color temperature information obtained at the time of the pre-exposure. Calculate the value.
Since the white balance correction characteristic differs depending on the white balance control state at the time of the pre-exposure as shown in FIG. 7, the white balance control state at the time of the pre-exposure corresponds to any of the regions II, III, and IV. The derivation calculation of the white balance control value is switched depending on whether the operation is performed. Specifically, the color temperature region at the time of the pre-exposure is the region II.
In the case of, the photographing is performed under a light source which is originally reddish, so that the calculated white balance control value is offset so that the image pickup signal is also slightly reddish.

Next, when the white balance control value is output in step S37, the color temperature information read in step S35 is stored in the memory 19 for later photographing, and the first color temperature information is stored in step S18 to step S20. The same main exposure and photographing operation as in the embodiment are performed.

After this operation, the flow returns to step S3 to wait for the operation of the next release switch RR.
Is turned off (step S4), the process ends.

In the second embodiment as described above, the gain amplifiers 4 and 5 at the time of pre-exposure are controlled by the light source data, so that the gain amplifiers 4 and 5 can be brought into a state corresponding to the light source. Similarly, the correction amount of the white balance can be reduced, and similarly, the deviation of the white balance due to the variation of each part of the circuit is reduced.

In the present embodiment, the white balance control at the time of the main exposure is also determined based on the past information of a plurality of screens, so that it is not affected by a single subject.
Stable white balance control can be performed. Furthermore, since correction according to the color temperature of the light source is possible, a natural captured image corresponding to the color temperature of the light source can be recorded.

In the second embodiment, both the gains of the gain control amplifiers 4 and 5 at the time of pre-exposure and the gains of the gain control amplifiers 4 and 5 at the time of main exposure are based on the color temperature information obtained during the past photographing. However, it is also possible to adopt a configuration in which only the gain at the time of the main exposure is determined according to the color temperature information obtained at the time of the past photographing. In this case, the gains of the gain control amplifiers 4 and 5 at the time of the pre-exposure are fixed values, but the points that are not affected by a single subject and that a natural captured image can be recorded are the same as in the second embodiment. An effect can be obtained.

[0067]

As described above, according to the electronic still camera of the present invention, the white balance at the time of the pre-exposure is controlled by using the information on the color temperature formed at the time of the past photographing. The situation that the white balance at the time of pre-exposure does not greatly deviate from the color temperature of the light source does not occur.
In addition, it was possible to take a picture under a good white balance at the time of the main exposure, without being affected by the state of the subject at the time of the pre-exposure.

Further, in the electronic still camera of the present invention, the white balance at the time of the main exposure is controlled in accordance with the information on the color temperature formed at the time of the past photographing and at the time of the pre-exposure, so that it is hardly affected by a single subject. , And stable white balance control can be performed.

[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 flowchart for explaining an operation of a system controller of the electronic still camera shown in FIG.

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

FIG. 4 is a characteristic diagram showing a relationship between a color temperature of a light source, a white balance control signal, and a gain of a variable gain amplifier in the electronic still camera shown in FIG.

FIG. 5 is a block diagram illustrating a configuration of an electronic still camera according to a second embodiment of the present invention.

FIG. 6 is a flowchart for explaining the operation of the system controller of the electronic still camera shown in FIG. 2;

FIG. 7 is a diagram for explaining a color temperature range defined by the electronic still camera shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 3a, 3b Color signal processing circuit 4, 5 Variable gain amplifier 7, 7a Operation control unit 8a, 8b Clamp circuit 9a, 9b Clip circuit 10a, 10b, 10c Integrator circuit 12a, 12b, 12c A / D converter 15 Shutter 16 Shutter drive circuit 18 Matrix circuit 19, 25 Memory 20 System controller 21 Recording signal processing circuit 22 Gate circuit 23 Electromagnetic conversion system 24 Photometry circuit 26 Color temperature calculation circuit RR Release member SW1, SW2 switch PSW Power switch

Continuation of the front page (56) References JP-A-3-117295 (JP, A) JP-A-58-215890 (JP, A) JP-A-63-203085 (JP, A) JP-A-3-17991 (JP) JP-A-2-27884 (JP, A) JP-A 1-293087 (JP, A) JP-A-57-155888 (JP, A) JP-A-58-215891 (JP, A) 2-234588 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/73 H04N 9/04

Claims (4)

(57) [Claims] An imaging unit that converts subject light into an electric signal; an exposure unit that operates during a main exposure for photographing a desired screen and a pre-exposure preceding the imaging unit; and an output signal of the imaging unit. Control information forming means for forming control information relating to the color temperature; and when the color temperature at the time of pre-exposure obtained from the output signal of the imaging means is within a predetermined range, the output of the imaging means at the time of the pre-exposure. Controlling the white balance of the output signal of the imaging means at the time of the main exposure according to the control information formed by the signal, and when the color temperature at the time of the pre-exposure obtained from the output signal of the imaging means is out of a predetermined range. A white balun for controlling a white balance of an output signal of the imaging unit at the time of the main exposure according to control information formed by an output signal of the imaging unit at the time of photographing in the past An electronic still camera, comprising: 2. The image processing apparatus according to claim 1, wherein the white balance control unit controls a gain of a plurality of color signals formed from output signals of the imaging unit, and detects a color temperature using the output signal of the imaging unit. Means for outputting color temperature information by
A calculating means for calculating gain control information for controlling a gain of the gain control means using the color temperature information; and a storage means for storing the color temperature information as the control information. The gain control unit is controlled during the main exposure by the gain control information calculated by the calculation unit using the color temperature information obtained or the color temperature information detected during the pre-exposure. Item 1. The electronic still camera according to item 1. 3. The calculation means estimates a color temperature of a light source using the color temperature information detected during a plurality of past shootings, and is formed using color temperature information detected during the pre-exposure. 3. The electronic still camera according to claim 2, wherein the gain control information is corrected according to the color temperature of the light source. 4. The apparatus according to claim 2, wherein the storage unit clears the stored color temperature information in response to an operation of a power switch for supplying power to each unit of the camera.
Electronic still camera.