JP3086753B2 - Video camera and focusing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera (still / still) for performing photometry and focusing control using a video signal obtained by preliminary photographing a subject image by a solid-state electronic image pickup device.
Movie video camera and still video camera) and a focusing method thereof.

[0002]

2. Description of the Related Art Many video cameras have an automatic exposure adjustment (so-called AE) function for automatically setting an exposure amount and an automatic focus adjustment (so-called AF) function for automatically performing focusing control. I have. These functions are performed in a time-series manner, such as first performing automatic exposure adjustment and then performing automatic focus adjustment, so that it takes a relatively long time.
In particular, when a subject is preliminarily photographed using a solid-state electronic image pickup device and automatic exposure adjustment and automatic focusing adjustment are performed using the video signal, it takes 1/60 second to output a video signal of one field. However, it may take a considerable amount of time to perform the preliminary photographing many times for both adjustments.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a video camera which achieves automatic exposure adjustment and automatic focus adjustment using a video signal obtained by a preliminary photographing from a solid-state electronic image pickup device. It can be done in a short time.

According to the present invention, photometry is performed by integrating a luminance signal component extracted from a video signal of one field of a video signal of one field and two fields output from a solid-state electronic image sensor at a frame period over a photometry area. The integral value for focusing control is obtained by integrating the high frequency component for distance measurement extracted from the video signal of the other field over the distance measurement area, and the exposure amount based on the photometric value is adjusted. In a video camera that adjusts the focus position based on the above integral value, a distance measuring sensor for predictive distance measurement, and an imaging lens based on distance measurement data obtained from the distance measuring sensor are provided. An initial positioning means for positioning the imaging lens at an initial position deviated in one direction from the in-focus position, and a frame cycle for moving the imaging lens in a direction opposite to the one direction Focusing control means is provided for performing integration of the high-frequency component for each of a plurality of fields while moving the imaging lens by a predetermined distance, and positioning the imaging lens at a position corresponding to the maximum value of the integration value for the plurality of fields. It is characterized by the following.

[0005] In the focusing method of a video camera according to the present invention, a preliminary distance measurement is performed by using a distance measurement sensor, and an image pickup lens is moved from an in-focus position to one position based on the distance measurement data obtained by the preliminary distance measurement. Initially positioned at a position deviated in the direction, integration of high-frequency components for distance measurement is performed for each field for a plurality of fields while moving the imaging lens by a predetermined distance in a direction opposite to the one direction. The imaging lens is positioned at a position corresponding to the maximum value of the obtained integrated values.

In the video camera of the present invention, since the integration of the high-frequency component of the video signal for focus control is performed after the exposure amount is appropriately adjusted, accurate focus control is possible. Becomes

In particular, according to the present invention, based on distance measurement data obtained from a distance measurement sensor for preliminary distance measurement, the initial position of the imaging lens near the focusing position, more precisely, in one direction from the focusing position, is determined. While moving the imaging lens by a predetermined distance in the direction opposite to the one direction,
Since the integrated value of the high-frequency component for distance measurement extracted from the video signal is obtained, and the imaging lens is finally positioned at a position corresponding to the maximum value, high-accuracy focusing can be achieved quickly.

In the present invention, integration for automatic exposure control and automatic focus control are performed on two-field video signals constituting one frame read from a solid-state electronic image pickup device by preliminarily photographing a subject. Integration is performed alternately for each field. That is, since the photometric processing is performed in parallel during the distance measuring processing, if the exposure condition changes during that time, it is immediately detected.

According to a preferred embodiment of the present invention, when the exposure amount is changed during the integration operation for focusing control, integration for focusing control is performed again after the exposure amount is changed. If the exposure condition is changed during the focus control, accurate focus control cannot be guaranteed. The change of the exposure condition occurs due to a change in environment, movement of a subject, and the like. According to this embodiment, when the exposure condition is changed during the focus control, the integration of the high-frequency component is performed again.
Accurate focus control is always possible, and focus control following a moving subject is also possible.

[0010]

An embodiment in which the present invention is applied to a digital still camera will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a digital communication system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an electric configuration of the still camera.

The imaging optical system includes an imaging lens 24, an aperture (not shown), and a CCD 4 as a solid-state electronic imaging device (image sensor). Although a mechanical shutter is provided if necessary, the shutter function is generally achieved by an electronic shutter realized by controlling the CCD 4. The imaging lens 24 forms an object image on the CCD 4, and is an imaging lens driving device controlled by the CPU 3.
It is moved by 25 and positioned at the in-focus position.

In this embodiment, a photometric sensor 26 is provided for preliminary photometry, and a distance measurement sensor 27 is provided for preliminary distance measurement. Photometric data and distance measurement data from these sensors 26 and 27 are sent to the CPU 3. Given. CPU3
Controls at least one of the aperture value and the shutter speed based on the photometric data obtained from the photometric sensor 26 so that the exposure amount to the CCD 4 falls within a substantially appropriate range. The CPU 3 also positions the imaging lens 24 near the in-focus position via the imaging lens driving device 25 based on the distance measurement data from the distance measurement sensor 27.

[0014] Preliminary photographing is performed after such approximate exposure amount adjustment based on the preliminary photometry and approximate focusing control based on the preliminary distance measurement. By this preliminary shooting, CCD
The calculation of the photometric value, the precise exposure control, and the high-precision focusing control are performed using the video signal obtained from Step 4. The high-precision exposure control and focusing control will be described later in detail.

A clock signal generating circuit (hereinafter referred to as CG) 1 includes a clock signal CLK, a horizontal transfer pulse H for driving a horizontal transfer path of the CCD 4, a substrate removal pulse SUB for discharging unnecessary charges, and an A field vertical transfer. A pulse VA and a B field vertical transfer pulse VB are generated. Further, CG1 generates a field index signal FI and an X timing signal XTM for strobe light emission.

The clock signal CLK is supplied to a synchronizing signal generation circuit (hereinafter, referred to as SSG) 2. The SSG 2 generates a horizontal synchronizing signal HD and a vertical synchronizing signal VD based on the clock signal CLK and supplies them to CG1.

The horizontal transfer pulse H is applied to a CCD (solid-state electronic image sensor) 4. Substrate removal pulse SUB and A
The field vertical transfer pulse VA is applied to the CCD 4 via the V driver 5, and the B field vertical transfer pulse VB is applied to the CCD 4 via the V driver 6.

The field index signal FI, the X timing signal XTM and the horizontal synchronizing signal HD
3 given. The shutter enable signal TS indicating that the exposure condition has been set from the CPU 3 to the CG 1.
EN and an electronic shutter control signal TS1 for starting exposure in the CCD 4 are provided.

In the CCD 4, the substrate removal pulses SUB, A
Interlaced shooting is performed by the field vertical transfer pulse VA, the B field vertical transfer pulse VB, and the horizontal transfer pulse H, and the A-field and B-field video signals (G, G, B, G color sequential signals) are generated alternately every one field period. And read sequentially. The driving of the CCD 4 (imaging and reading of a video signal) is performed at least at the time of photographing and for precise photometric processing and distance measuring processing prior thereto.

A-field and B-field video signals representing the subject image output from the CCD 4 are passed through a correlated double sampling circuit (CDS) 7 to a color separation circuit 8.
And three primary colors, G (green), R (red) and B
(Blue) color signal.

The color signals G, R, B are supplied to a variable gain amplifier (hereinafter, referred to as GCA) 9. A specific circuit example of the GCA 9 is shown in FIG. 2, and the GCA 9 includes variable gain amplifiers 91r, 92r, 91g, 92g and 91b, 92b provided for R, G and B signals, respectively. In the GCA 9, the correction of the variation between the colors of the light transmittance of the color filters provided in the CCD 4 (hereinafter referred to as color filter sensitivity ratio correction) is performed by an amplifier.
After the white balance adjustment is performed by the amplifiers 92r, 92g and 92b, the output color signals R, G and B are supplied to the gamma correction circuit 10. This is for performing focusing control described later with high accuracy, and details thereof will be described later. For the purpose of focusing control, at least the color filter sensitivity ratio correction may be performed, but in addition to this, it is more preferable to perform white balance adjustment.

The output color signals R, G, B of the GCA 9 are subjected to gradation correction by a gamma correction circuit 10 and input to a clamp and resampling circuit 11.

The clamping and resampling circuit 11
The three color signals R, G, and B are clamped, and re-sampled to re-convert them into color sequential signals of RGB,... Which match the color filter arrangement in the CCD 4. This color sequential signal is input to a gain control and blanking circuit 12. A gain control and blanking circuit 12 amplifies the color sequential signal to an appropriate level for recording and adds a blanking signal thereto. The output signal of the gain control and blanking circuit 12 is provided to a first input terminal S1 of a changeover switch 13.

Prior to the actual photographing, precise photometric processing (exposure control) and focusing control are performed as described above. The photometric processing is performed using a low frequency component of the video signal obtained from the CCD 4 by the preliminary photographing, and the focus control is performed using a high frequency component of the video signal.

[0025] For light measurement process, in order to extract the low-frequency component of the video signal representing the image in the metering area provided in the photographing region of the CCD 4 (described below), Y _L synthesizing circuit 15,
A gate circuit 16, an integration circuit 17, and an amplification circuit 18 are provided. The output signal of the amplifier circuit 18 is the second signal of the changeover switch 13.
To the input terminal S2.

On the other hand, for focusing control, a gate circuit is provided to extract a high-frequency component of a video signal representing an image in a distance measuring area (described later) provided in a photographing area of the CCD 4.
19. Band-pass filter (BPF) 2
0, a detection circuit 21, an integration circuit 22, and an amplification circuit 23 are provided. The output signal of the amplifier circuit 23 is provided to a third input terminal S3 of the changeover switch 13.

The changeover switch 13 is controlled by the CPU 3, and controls the gain control and blanking circuit 12,
One of the output signals of the amplifier circuits 18 and 23 is selected and output. The output signal of the changeover switch 13 is A /
The data is supplied to a D converter 14 and converted into digital data.

In the photometric processing and the focusing control prior to the actual photographing, the changeover switch 13 selects and outputs one of the input signals of the input terminals S2 and S3. As will be described later, the changeover switch 13 is basically switched between the input terminals S2 and S3 for each field. The photometric processing is performed by selecting the input terminal S2 during the period of the A field (first field) constituting one frame, and the input terminal S3 is selected during the period of the B field (second field). Performs focus control. Since it is considered that the A-field image and the B-field image constituting one frame represent a field image at substantially the same point, the video signal of the B-field is converted to the video signal of the B-field for photometric processing. Each of them can be used for focusing processing. In such photometric processing and focusing control, the output data of the A / D converter 14 is taken into the CPU 3.

After the photometric processing, the exposure control (control of the aperture and the shutter) based thereon, and the focusing control (positioning of the imaging lens 24), the actual photographing is performed. At this time, the changeover switch 13 is switched so as to select the input terminal S1. A video signal obtained from the CCD 4 by the actual photographing is input to an A / D converter 14 via the circuits 7, 8, 9, 10, 11, 12 and the changeover switch 13, and the A / D converter 14 outputs a digital image. After being converted into data and subjected to processing such as Y / C separation and data compression by an image data processing circuit (not shown), it is recorded on a recording medium such as a memory card.

First, of the photometric processing (and exposure control based thereon) and focusing control prior to the actual photographing, the photometric processing will be described.

The photometric processing is as described above Y _L synthesizing circuit 15,
This is performed using a gate circuit 16, an integration circuit 17, and an amplification circuit 18. Y _L output color signal R of the synthesis circuit 15 GCA9,
G and B are given.

FIG. 3 shows an example of a specific electrical configuration of these circuits. The CPU 3 outputs a window signal WIND1 for controlling the gate circuit 16 and a reset signal HLRST1 for resetting the integration circuit 17. The timing of these signals WIND and HLRST will be described later.

The color signals R output from GCA9, G and B are added by Y _L synthesizing circuit 15, a relatively low frequency luminance signal Y _L (hereinafter referred to simply as the luminance signal Y _L) is generated. The luminance signal Y _L passes through the gate circuit 16 during a required horizontal scanning period while the window signal WIND1 is being supplied. The integration circuit 17 outputs a reset signal HLRS.
T1 is reset when given, integrating the luminance signal Y _L for inputting the subsequent gate circuit 16. Integrator 17
Is amplified by the amplifier circuit 18, and then the integration circuit 17
Immediately before is reset, it is input to an A / D converter 14 via a changeover switch 13, is converted into digital integrated data for photometry by the A / D converter 14, and is taken into the CPU 3.
The reference voltages V1 and V2 of the integrating circuit 17 and the amplifying circuit 18 give appropriate offsets to them.

In the photometry processing of this embodiment, an average photometry (hereinafter referred to as A) for measuring the average brightness in the visual field.
V photometry) and spot photometry (hereinafter, referred to as SP photometry) for measuring the brightness of the main subject in the field of view. This is particularly useful when the brightness of the background is different from the main subject in the field of view, and it is necessary to set appropriate exposure conditions accordingly.

In this embodiment, the integration by the integration circuit 17 and the A / D conversion operation and the addition processing by the A / D converter 14 are alternately performed every horizontal scanning period.

FIG. 4 shows an AV metering area and an SP metering area set in the photographing area 30 of the CCD 4.

The AV metering area is basically set over almost the entire photographing area. In this embodiment, the AV metering area is set to a period of 40 μs after a lapse of 16 μs from the fall of the horizontal synchronization signal HD (at the start of the horizontal scanning period) in the horizontal direction, and the 35th horizontal scanning is performed in the vertical direction. 246th from the line
It is set between the horizontal scanning lines.

The SP metering area is set as a small area at an arbitrary position in the photographing area 30. In this embodiment, the SP metering area is set at the center of the photographing area 30, and the horizontal direction is the 87th horizontal scanning line during the period of 15 μs after 28.5 μs from the fall of the horizontal synchronization signal HD. From 194
It is set between the horizontal scanning lines.

A memory associated with the CPU 3 is provided with a photometry area and a distance measurement area. The AV metering area data area and SP metering area data
There is an area.

When the AV metering area is SP in the vertical scanning direction
In a range not overlapping with the photometry area, integration is performed every other horizontal scanning line in the AV photometry area. In the range where the AV metering area and the SP metering area overlap in the vertical scanning direction, integration is performed alternately on the horizontal scanning line for the AV metering area and on the horizontal scanning line for the SP metering area. It is. The above integration is performed every other horizontal scanning line for A / D conversion, reset integration of the integration circuit, and data addition processing.

As shown in FIG. 5, between the 34th horizontal scanning line and the 86th horizontal scanning line,
16 μs from the fall of the horizontal synchronization signal HD to the gate circuit 16
Later, a window signal WIND1 having a pulse width of 40 μs is applied. Then, the integral of the luminance signal Y _L by the integral circuit 17, the next A / D conversion of the integrated signal in the horizontal scanning period, the reset and AV photometric area of the memory of the integrator circuit 17 of the horizontal scanning period the integration operation is performed The addition of the integral data to the data area is alternately repeated every horizontal scanning period (photometry in the AV photometry area).

Between the 87th horizontal scanning line and the 194th horizontal scanning line, the gate circuit 16 supplies a pulse width rising 28.5 μs after the falling of the horizontal synchronizing signal HD.
The window signal WIND1 of 15 μs and the horizontal synchronization signal H
A window signal WIND1 having a pulse width of 40 μs and rising 16 μs after the fall of D is alternately applied.

Window signal WIND with pulse width of 15 μs
1 when the integral of the applied luminance signal Y _L is performed in the integrating circuit 17, the next A / D conversion of the integrated signal in the horizontal scanning period of the horizontal scanning period integration operation is performed, the reset of the integrating circuit 17, The integration data is added to the SP photometry area data area of the memory (photometry in the SP photometry area). In addition, a window signal WIND having a pulse width of 40 μs
1 when the integral of the applied luminance signal Y _L is performed in the integrating circuit 17, the next A / D conversion of the integrated signal in the horizontal scanning period of the horizontal scanning period integration operation is performed, the reset of the integrating circuit 17, The integration data is added to the AV photometry area data area of the memory (photometry in the AV photometry area).

In the period from the 195th horizontal scanning line to the 246th horizontal scanning line, the pulse width is 40 μs, similarly to the above-mentioned period from the 34th horizontal scanning line to the 86th horizontal scanning line. Window signal WIND1
The integral of the luminance signal Y _L based on the processing of integrated data obtained by the integration is performed repeatedly alternately every horizontal scanning period (metering AV metering area).

The CPU 3 adds the integral data for one horizontal scanning line obtained based on the window signal WIND1 having a pulse width of 40 μs in the AV photometry area data area over one field period by a procedure described later, and the AV photometry value EV Calculate _AV .

Further, the CPU 3 sets the AV photometric value EV _AV
Is calculated separately from the window signal W having a pulse width of 15 μs.
The SP photometric value EV _SP is calculated by adding the integral data for one horizontal scanning line obtained based on IND1 in the SP photometric area data area over one field period by a procedure described later.

FIG. 6 shows the overall operation of the AV metering process and the SP metering process performed by the CPU 3.

When starting the photometric processing, the CPU 3 initializes the exposure conditions based on the photometric data obtained from the photometric sensor 26 as described above, and controls the iris and the electronic shutter so that the initial exposure conditions are realized. At least one of them is controlled (step 50). Without performing the preliminary photometry, the exposure condition statistically most likely as the initial exposure condition, for example, the exposure amount Ev = 10 (aperture F4,
A shutter speed of 1/60 second, or an aperture of F2.8 and a shutter speed of 1/125 second) may be set.

In the horizontal scanning period in the AV photometry area (step 51), a window signal WIND1 for the AV photometry area is output, and the integration circuit 17 performs the integration operation during the pulse width (step 52). . After the window signal WIND1 falls, the A / D converter 14 is driven to perform A / D conversion of the integration signal of the integration circuit 17 to obtain integrated data.

Next, it is determined whether or not the obtained integral data is within a predetermined range (step 53). This is to determine whether the obtained integrated data can be used as a photometric value for one horizontal line. If the layer portions in the horizontal scanning line a metering object, such as the luminance signal Y _L is saturated, the integral data is not suitable for use as a photometric value. Upper limit of the predetermined range, the dynamic range of the CCD 4, taking into account the gain or the like of GCA9 and amplifying circuit 18 is determined enough to eliminate the integration data based on the luminance signal Y _L are saturated. On the other hand, the horizontal scanning line subjected to photometry has a very dark portion, and the luminance signal Y
_{Even when L} is almost due to a noise component, it is not appropriate to use the integrated data as a photometric value.
Therefore, the lower limit of the predetermined range is set at a level at which the integrated data in which the noise component is dominant is excluded.

If the obtained integrated data is a value within a predetermined range, the integrated data is added to the value of the AV photometry area data area of the memory (step 54), and if it is still within the photometry area. The process returns to step 52 (step 55). If the integral data is out of the predetermined range, the line number counter is incremented by one (step 57), and the integral data addition processing is not performed. That is, the integrated data is not used as a photometric value. The line number counter counts the number of horizontal lines in which the integrated data is outside a predetermined range. If the value of the line number counter is within the predetermined value (step 58), the process returns to step 52 via step 55.

SP in the vertical direction in the AV metering area
The above operation is repeated for two horizontal scanning periods as one cycle for a portion not overlapping with the photometry area. The obtained integral data is added to the AV photometry area data area.

In a portion where the AV metering area and the SP metering area overlap in the vertical direction, the window signal WIND1 for the AV metering and the window signal WIND1 for the SP metering are alternately output, and the luminance is similarly increased. integration of the signal Y _L, the integration signal of the a / D conversion, integration data whether the check is within a predetermined range is performed. A
The integral data obtained by integration over the pulse width of the window signal WIND1 for V photometry is added to the AV photometry area data area, and the integrated data obtained by integration over the pulse width of the window signal WIND1 for SP photometry is It is added to the SP metering area data area. The line number counter for counting the number of lines determined to be NO in the determination in step 53 is also set to the AV light metering area and S
The number of lines determined to be NO is provided for each of the P photometry areas, and the number of lines determined as NO is separately counted in both photometry areas.
The predetermined number of lines for the determination in step 58 is also AV
Different values may be set for the photometry area and the SP photometry area.

When the user goes out of the range of the AV metering area (step
55), by using each addition value of the integrated data in the AV photometry area and the SP photometry area obtained so far,
The AV metering value EV _{AV in the AV} metering area and the SP metering value EV _{SP in the} SP metering area are calculated (step 5).
6). The calculation of the AV photometric value EV _AV and the SP photometric value EV _SP is performed by dividing the sum of the integrated data in each photometric area by the number of lines added as the integrated data, thereby averaging the integrated value per horizontal scanning line. Includes operations for finding values and operations for multiplying average values by appropriate constants. The number of lines added as the integration data is obtained by subtracting the value of the corresponding line number counter from half of the horizontal scanning lines in each photometric area.

The CPU 3 determines exposure conditions such as the aperture, shutter speed, and whether or not strobe light is emitted, based on the obtained photometric values EV _AV and EV _SP .

If the value of the line number counter for counting the number of horizontal lines in which the integrated data is out of the predetermined range exceeds the predetermined number (step 58), the CPU 3 changes the exposure condition (step 59). After clearing the photometry area of the memory, the photometry process from step 51 is repeated at the start of the next frame. The judgment in step 58 is A
The measurement may be performed only for the V photometry area, or may be performed for both the AV photometry area and the SP photometry area.

When changing the exposure condition, if the amount of integrated data in each horizontal line exceeds the above-mentioned predetermined range, the exposure amount is made smaller than the initially set exposure amount, and vice versa. It is preferable to change the exposure amount by one step (for example, ± 2 Ev) so as to increase the exposure amount. If the initial exposure is not too far from the actual brightness of the field of view (especially if you have pre-metered as described above)
By repeating the photometry process shown in FIG. 6 once or twice (one to two frame periods), an appropriate exposure amount will be obtained.

In any case, the process of determining whether an appropriate photometric value has been obtained will be referred to again in the description of FIG.

FIG. 7 shows the A obtained by the photometric processing.
9 is a flowchart showing a processing procedure performed by a CPU 3 to set an exposure condition based on a V photometric value EV _AV and an SP photometric value EV _SP .

The CPU 3 takes the difference ΔEV = EV _SP −EV _AV between the SP photometric value EV _SP and the AV photometric value EV _AV (step
60) Next, whether the difference ΔEV between the photometric values is equal to or greater than zero,
It is determined whether it is between zero and -0.5 EV, between -0.5 EV and -2 EV, or less than -2 EV (steps 61 and 63).

When it is determined that the photometric difference ΔEV is 0 ≦ ΔEV, that is, when it is determined that the main subject at the center is bright and the background is dark, the CPU 3 determines the SP photometric value EEV.
Set exposure conditions based on V _SP (step 6
2). If the exposure condition is set based on the AV metering value EV _AV , the main subject will be darkly photographed, and it is best that the main subject that the photographer wants to photograph most is appropriately exposed.

When it is determined that −0.5 EV ≦ ΔEV <0, that is, when it is determined that the luminance difference between the main subject and the background is small, the CPU 3 determines the exposure condition based on the AV photometric value EV _AV . Settings are made (step 64). This is because if the exposure condition is determined based on the AV photometry value EV _AV , it can be considered that both the main subject and the background are properly exposed. If it is determined that −2 EV <ΔEV <−0.5 EV,
That is, when it is determined that the luminance difference between the bright and the main object and the background towards the background is relatively large, CPU 3 performs the setting of the exposure conditions based on the value of the EV _AV -1 EV (step 65). That is, in this case, exposure correction (backlight correction) is performed so that the background is slightly dark because the background is bright.

When it is determined that .DELTA.EV.ltoreq.-2EV, that is, when it is determined that the main subject is darker than the background and the luminance difference is extremely large, it is necessary to light the strobe to brighten the main subject. Since there is, the CPU 3 performs daytime synchro photography. That is, the preparation for flash emission and the exposure conditions for flash emission are set (step
66). In this case, the main subject cannot be properly exposed even by the backlight correction described above, and it is determined that the correction by the strobe light emission is appropriate.

Next, focusing control will be described.

Referring again to FIG. 1, the output signal of gain control and blanking circuit 12 is
To enter. Gate circuit 19 is controlled by window signal WIND2 provided from CPU3. gain·
The output signal of the control and blanking circuit 12 passes through the gate circuit 19 during the required horizontal scanning period while the window signal WIND2 is being applied, and the BPF 20
To enter.

The BPF 20 extracts a high-frequency component necessary for focusing control from the input signal, and the output signal of the BPF 20 is input to the detection circuit 21. The high-frequency component signal output from the BPF 20 is detected by a detection circuit 21, integrated by an integration circuit 22, and amplified by an amplification circuit 23. After the change-over switch 13 selects the input terminal S3, the A / A The digital signal is input to a D converter 14 and converted into digital data for focusing control by the A / D converter 14.
It is taken into PU3.

The digital data given from the A / D converter 14 is integrated data obtained by integration over a horizontal scanning period of a distance measuring area set in the photographing area, which will be described later. The data for distance measurement is calculated by adding data over the vertical scanning period of the distance measurement area, and focusing control is performed based on the data. Details will be described later.

In general, when the image is out of focus and the image is blurred, the high frequency component contained in the video signal obtained from the CCD by photographing is small. When the image comes into focus, the high frequency component of the video signal increases, and the high frequency component included in the video signal at the position where the focus is correctly focused is maximized. In this embodiment, the focusing control is performed based on such a fact.
F20 is about 1.5 to extract high frequency components of video signal.
A pass band of 2.5 MHz is set.

On the other hand, in this embodiment, as shown in FIG.
They are arranged in a repetition of GB. Assuming that the read clock frequency of the CCD 4 is 13.5 MHz, a video signal obtained from a light receiving element (photodiode) provided with a green (G) filter includes a repetition frequency component of 6.8 MHz, a red (R) and a blue (B). ) Contains a 3.4 MHz repetition frequency component.

The video signal input to the BPF 20 through the gate circuit 19 is composed of the color signal components converted into the color filter array shown in FIG. Inside,
In addition to the frequency components representing the subject image, repetitive frequency components (3.4 MHz and 6.8 MHz) resulting from the above-described color filter arrangement are included.

The repetition frequency component caused by the color filter arrangement depends on the difference in the light transmittance between the R, G, and B color filters, that is, the difference in the sensitivity ratio between the color filters, and the loss of the white balance. Increase or decrease. For example, assuming that the light transmittances of the respective color filters are all the same and that the white balance is perfectly balanced, and if a pure white subject is photographed, there will be almost no repetition frequency components caused by the color filter arrangement. .

The GCA 9 corrects the fluctuation of the level of the video signal based on the difference in the light transmittance of the color filter and adjusts the white balance in order to remove as much as possible the repetition frequency component caused by the color filter arrangement. belongs to.

That is, referring to FIG. 2 again, when performing the color filter sensitivity ratio correction, the gains G _r2 , G _g2 , G _b2 of the amplifiers 92r, 92g, 92b for white balance adjustment are set to appropriate predetermined gains ( For example, the gain G _{g1 of the} amplifier 91g is fixed and the level of the other color signals R and B with respect to the G signal at a certain color temperature (usually about 5500 K) is set to the amplifier 91r. , 91b
_Is adjusted by changing the gains _Gr1 and _Gb1 . Once adjusted, these gains _Gr1 , _Gg1 , _Gb1 are fixed. As is well known, white balance adjustment is performed based on the detection signal of the color sensor at least by the amplifier 92.
This is performed by controlling the gains G _r2 and G _b2 of r and 92b. This means that the gain _Gr2 increases as the color temperature increases,
The gain G _b2 low, low gain G _r2 the color temperature decreases, carried out by increasing the gain G _b2. The gains G _g1 and G _g2 of the G signal amplifiers 91g and 92g may be fixed.

FIGS. 9 and 10 show the pass band of the BPF 20,
And a repetition frequency component (center frequency f _G = 6.8 MHz) caused by the G color filter array and a repetition frequency component (center frequency f _G ) caused by the R or B color filter array
_{(R / B} = 3.4 MHz) and the spectrum of the luminance signal of the video signal representing the subject image.

FIG. 9 shows a case where neither the color filter sensitivity ratio correction nor the white balance adjustment is performed. Part of the repetition frequency components (indicated by hatching) caused by the color filter arrangement, particularly the R and B color filter arrangements, enter the pass band of the BPF 20. Therefore, in this case, the video signal that has passed through the BPF 20 contains considerable repetition frequency components due to the color filter arrangement.

FIG. 10 shows a case where both the color filter sensitivity ratio correction and the white balance adjustment are performed. B
The repetition frequency components due to the color filters entering the pass band of the PF 20 are considerably reduced. Therefore, in this case, most of the video signals passing through the BPF 20 may be considered to represent the subject image. Good focusing processing that is not disturbed by the repetition frequency components caused by the color filter arrangement can be expected.

The minimum function of the GCA 9 is to correct the color filter sensitivity ratio, thereby considerably reducing the interference due to the repetition frequency components caused by the color filter arrangement. Preferably, GCA 9 achieves both color filter sensitivity ratio correction and white balance correction. This assures better focus control.

FIG. 11 shows a distance measuring area set in the photographing area 30 of the CCD. This distance measurement area is set at the center of the imaging area 30 where the probability that the main subject exists is high. In this embodiment, the horizontal direction is set as an area smaller than the SP photometric area shown in FIG. Of course, it is needless to say that the distance measurement area can be set to an arbitrary size in an arbitrary place in the photographing area 30.

As shown in FIG. 12, during the B field period, the 87th horizontal sync signal HD falls 31
window signal WI having a pulse width of 10 μs after elapse of μs
ND2 is supplied to the gate circuit 19, and as described above, while the window signal WIND2 is supplied, the gate circuit 19 allows the output signal of the circuit 12 to pass. The high-frequency component signal extracted by the BPF 20 passes through the detection circuit 21 and is integrated by the integration circuit.
It is given to 22 and integrated. The integrated output signal of the integrating circuit 22 is converted into digital data by the A / D converter 14 in the next horizontal scanning period via the amplifying circuit 23 and the changeover switch 13 and supplied to the CPU 3. The integration circuit 22 is A
After the / D conversion processing, it is reset by the reset signal HLRST2. The CPU 3 adds the digital data to the preceding data in the distance measuring area of the memory (the data is cleared in the first case and is therefore zero) and stored. The ranging area is cleared in synchronization with the 86th horizontal synchronization signal HD or at the start of the B field.

As described above, 1 in the ranging area
The detection of the high-frequency component signal by the BPF 20, detection and integration of the high-frequency component signal, A / D conversion of the integrated signal, and addition of the integral data in the horizontal scanning period are alternately performed in each horizontal scanning line. It is performed repeatedly. This repetition is performed until the 194th horizontal scanning period, that is, over the entire range of the ranging area.

Therefore, at the time when the scanning within the ranging area is completed, the BP is not stored in the ranging area of the memory.
This means that the added data for distance measurement indicating the integral value of the high frequency signal passing through F20 over the entire distance measurement region is stored.

As described above, the approximate distance to the subject is measured in the preliminary distance measurement using the distance measurement sensor 27. Based on the preliminary distance measurement data, the imaging lens 24 is positioned slightly in front of the in-focus position (referred to as an initial position).
Is fed out.

The integration operation of the high frequency component of the video signal output from the CCD 4 over the distance measurement area is performed by
This is performed at least six times (that is, in the B field period of each frame period over six frame periods) while moving forward by μm. First at the above initial position (extending amount of the imaging lens 24 = 0 μm), first addition data for distance measurement is obtained. In the next frame period, second distance measurement addition data is obtained at a position where the imaging lens 24 is extended by 10 μm from the initial position (imaging lens extension amount = 10 μm). Similarly, the third to sixth additional data for distance measurement are obtained while extending the imaging lens 24 by 10 μm.
The addition data at the six positions thus obtained is stored in a predetermined area of the memory as shown in FIG.

FIG. 14 is a graph showing the distance measurement addition data at the six positions shown in FIG. Imaging lens 24
The initial position is slightly before the true focus position. From this position, the imaging lens 24 is extended by 10 μm at a time, and distance measurement addition data is obtained at each position. The integrated value of the high-frequency signal included in the video signal becomes maximum at the true focus position. Imaging lens 24
Is a very small distance at 10μm.
The error is extremely small even if the position where the added data for distance measurement indicates the maximum value is regarded as the true focus position. Therefore, high-precision focusing can be achieved by positioning the imaging lens 24 at a position where the distance measurement addition data indicates the maximum value.

The above-described photometry processing and the distance measurement addition data collection processing for focusing control are performed alternately for each field. However, the distance measurement addition data obtained before the exposure condition is set is invalidated, and only the distance measurement addition data obtained after the exposure condition is set is made valid. This is because the value of the obtained additional data for distance measurement differs depending on the exposure conditions, so that accurate exposure data for distance measurement cannot be obtained unless the exposure conditions are properly set.

FIG. 15 shows the overall procedure of exposure control and focusing control based on preliminary photometry and preliminary distance measurement processing and subsequent preliminary photographing.

First, the CPU 3 performs preliminary photometry based on the photometric signal of the photometric sensor 26 and preparatory ranging based on the ranging signal from the ranging sensor 27 (step 70). The initial setting of the exposure condition is performed based on the preliminary photometry (step 71), and the imaging lens 24 is extended to the initial position based on the preliminary distance measurement (step 72).

Next, the changeover switch 13 is connected to the input terminal S2 (step 73). As a result, photometry and calculation of photometric values are performed in the A-field period according to the procedure shown in FIG. 6 (steps 74 and 75). This corresponds to the processing of steps 51 to 56 in FIG.

It is determined whether the photometric value thus obtained is appropriate (step 76). This judgment is shown in FIG.
Step 58 is included. In addition to the determination in step 58, it is also preferably determined whether the photometric value is within the range corresponding to the exposure condition set in step 71.

If it is determined that the obtained photometric value is appropriate, an exposure condition (aperture value, shutter speed) is set based on the photometric value, and the aperture value of the aperture is set to satisfy the exposure condition. And the shutter speed are set (step
80). This corresponds to the processing shown in FIG.

Subsequently, the changeover switch 13 is switched to the input terminal S3 side (step 81). When the reading of the video signal of the B field is started, the integration of the video signal and the A / A of the integrated signal are applied to the horizontal scanning lines in the ranging area as described above.
The addition of the D-converted and A / D-converted integrated data is performed over the entire ranging area (steps 82 and 83).

As described above, the added data for distance measurement is collected while extending the imaging lens 24 by 10 μm for each frame (B field). A counter is provided to count the number of times the imaging lens 24 is extended.

When the addition data is obtained for the distance measurement area, the counter is incremented (step 84), and the imaging lens 24 is extended by 10 μm (step 85). The obtained addition data is stored in the memory area shown in FIG.

The processing of steps 73 to 76 and 80 to 85 is repeated for each frame. When the value of the counter exceeds 5 (step 86), the distance measurement addition data for the six times in the area shown in FIG. And the maximum is found (step
87). Then, the imaging lens 24 is displaced to a position corresponding to the maximum distance measurement addition data, and is positioned there.
In the example shown in FIG. 13, the imaging lens 24 is positioned at a position extended by 30 μm from the initial position.

As described above, when photometry and distance measurement are completed and exposure conditions are set and focusing is performed, the changeover switch 13
Is switched to the input terminal S1, and the operation shifts to the main shooting.

If it is determined in step 76 that the photometric value is in an inappropriate range, the exposure condition is changed (step 77). This corresponds to step 59 in FIG. 6. When the photometric value is a large value, the exposure amount is reduced, and when the photometry value is the opposite, the exposure amount is increased.

Next, all the distance measurement addition data obtained so far in the memory area shown in FIG. 13 is cleared (step 78), the counter is further cleared, and the imaging lens is cleared.
24 is returned to the initial position (step 79). This is to prevent the addition data for distance measurement obtained in a state where an appropriate exposure condition is not set from being used for focusing control. Thereafter, the flow returns to step 74, and photometry is performed again in synchronization with the scanning of the A field.

As described above, photometry and distance measurement are performed alternately for each field. The reason why the photometry processing is performed in parallel during the distance measurement processing is that the
For example, if the exposure condition changes due to the subject moving or changing, zooming up or down, or suddenly becoming brighter by the sun, the previously stored values were stored in steps 78 and 79. This is because the added data and the counter are cleared and the distance measurement is performed again.

In the above embodiment, since the light transmittance of the color filter provided in the CCD 4 varies, this variation is corrected by the GCA 9. If a CCD provided with a so-called compensation filter having no variation for each color is used as the color filter, the color filter variation correction by GCA becomes unnecessary. The GCA 9 need only perform white balance adjustment.

[Brief description of the drawings]

FIG. 1 shows a digital still image according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the video camera.

FIG. 2 is a circuit diagram showing a specific example of a variable gain amplifier circuit.

FIG. 3 is a circuit diagram showing a more specific electrical configuration of a circuit portion necessary for photometry in the digital still video camera of FIG. 1;

FIG. 4 is a diagram illustrating a photometry area set in an imaging area.

FIG. 5 is a time chart showing a photometric process.

FIG. 6 is a flowchart illustrating a procedure of photometric processing by a CPU.

FIG. 7 is a flowchart illustrating a procedure for setting exposure conditions by a CPU;

FIG. 8 is a diagram showing an arrangement of color filters of a CCD.

FIG. 9 is a graph showing a pass band of a BPF when the color filter sensitivity ratio correction and the white balance correction are not performed, a repetition frequency due to an arrangement of color filters, and a spectrum of a luminance signal in a video signal.

FIG. 10 is a graph showing a pass band of a BPF when a color filter sensitivity ratio correction and a white balance correction are performed, and a repetition frequency and a spectrum of a luminance signal due to an arrangement of color filters.

FIG. 11 is a diagram showing a distance measurement area set in a shooting area.

FIG. 12 is a time chart showing a distance measuring process.

FIG. 13 is a diagram illustrating a storage area of distance measurement addition data.

FIG. 14 is a graph showing distance measurement addition data for focusing.

FIG. 15 is a flowchart illustrating a procedure of exposure control and focus control processing by a CPU.

[Explanation of symbols]

3 CPU 4 CCD (solid-state electronic image sensing device) 8 color separation circuit 9 GCA (amplifier circuit) 11 Clamp and resampling circuit 13 change-over switch 14 A / D converter 15 Y _L synthesizing circuit 16 gate circuit 17 integrating circuit 18 amplifier circuit 19 Gate circuit 20 Band-pass filter 21 Detection circuit 22 Integrator circuit 23 Amplifier circuit 24 Imaging lens 25 Imaging lens drive 26 Photometric sensor 27 Distance sensor

Continuation of front page (72) Inventor Minoru Arai 3-1-146 Izumi, Asaka-shi, Saitama Fuji Photo Film Co., Ltd. (56) References JP-A-1-164176 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 5/232 G02B 7/28 G03B 7/091 H04N 5/235-5/243

Claims (4)

(57) [Claims] 1. A method according to claim 1, wherein the signal is output from the solid-state electronic image sensor at a frame period.
One of the two-field video signals
Luminance signal component extracted from the video signal of the other field
Is integrated over the photometric region to obtain a photometric value,
Distance measurement taken from the video signal of the other field
By integrating the high frequency components for
Obtain the integral value for focusing control, and calculate the exposure
Based on the condition that the light quantity has been adjusted,
In a video camera that adjusts the in-focus position, an image is captured based on distance measurement data obtained from the distance measurement sensor for predictive distance measurement and the distance measurement sensor.
Position the lens at the initial position that is biased in one direction from the in-focus position
The initial positioning means, and the imaging lens
Move by a predetermined distance in the frame cycle in the direction opposite to one direction
While integrating the high-frequency component into multiple fields.
For each field.
Place the imaging lens at a position corresponding to the maximum value of the integration value.
A video camera equipped with a focus control means for positioning . 2. The exposure amount during the integration operation of the high frequency component is
When the exposure is changed, the high frequency
Integrate the minute and adjust the focus position of the imaging lens.
A means for controlling the focusing control means.
Video camera as described. 3. Output from the solid-state electronic image pickup device at a frame period.
One of the two-field video signals
Luminance signal component extracted from the video signal of the other field
Is integrated over the photometric region to obtain a photometric value,
Distance measurement taken from the video signal of the other field
By integrating the high frequency components for
Obtain the integral value for focusing control, and calculate the exposure
Based on the condition that the light quantity has been adjusted,
In a video camera that adjusts the focus position by using a distance measurement sensor, preliminary distance measurement is performed, and shooting is performed based on the distance measurement data obtained by the preliminary distance measurement.
Initial position at a position offset to the in-focus position or et way an image lens
And the integral of the high-frequency component is defined as
Moves in the opposite direction a predetermined distance at a time
Is performed for each field, and the maximum integrated value obtained for multiple
A focusing method for a video camera, wherein the imaging lens is positioned at a corresponding position . 4. The method according to claim 1 , wherein the exposure amount during the integration operation of the high frequency component is reduced.
When the exposure is changed, the high frequency
Integrate the minute and adjust the focus position of the imaging lens.
A method for focusing a video camera according to claim 3.