JP3453153B2 - 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 / automatic focusing control using a video signal obtained by preliminarily photographing an incident light image using a solid-state electronic image pickup device
(Including movie video cameras and still video cameras) and focusing methods thereof.

[0002]

2. Description of the Related Art Some video cameras have various automatic focusing functions (so-called AF functions), and among them, an optical image incident by a solid-state electronic image pickup device such as CCD is preliminarily photographed and There is one that performs focus control using the obtained video signal.

However, in a video camera which performs focus control using a video signal obtained from such a solid-state electronic image pickup device, conventionally, a video signal for focus control is obtained directly from the solid-state electronic image pickup device. Therefore, a dedicated circuit for preprocessing the video signal is required, which causes a problem that the video camera becomes large.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the size of a camera capable of performing focus control using a video signal obtained from a solid-state electronic image pickup device.

The present invention provides a video camera equipped with an image pickup optical system including a solid-state electronic image pickup device having an image pickup lens and a color filter for converting a light image incident through the image pickup lens into a video signal and outputting the image signal. A color separation circuit that color-separates a video signal output from an electronic image pickup device to output a plurality of color signals, and an output color of the color separation circuit due to a difference in light transmittance of color filters of the solid-state electronic image pickup device Based on the amplification circuit that corrects the variation in the signal level, the high frequency component extraction means that extracts the high frequency component for distance measurement from the output color signal of the amplification circuit, and the high frequency component extracted by the high frequency component extraction means, A focusing control unit that controls the focusing of the imaging lens is provided.

Further, in the focusing method according to the present invention, the light image incident through the image pickup lens is preliminarily photographed by the solid-state electronic image pickup device having a color filter, and a plurality of video signals obtained from the solid-state electronic image pickup device by the preliminarily photographing are obtained. The color signals are separated into color signals, the level variations of the color signals due to the difference in the light transmittance of the color filters of the solid-state electronic image pickup device are corrected, and the distance is measured from the color signals whose level variations are corrected. Is extracted, and focusing control of the imaging lens is performed based on the extracted high frequency component.

In the present invention, the color signal in which the level variation due to the variation of the light transmittance of the color filter of the solid-state electronic image pickup device is corrected is used for the focus control.

A color separation circuit and an amplifier circuit for performing signal processing on a video signal obtained from a solid-state electronic image pickup device are generally used in video cameras for signal-processing and recording the video signal obtained from the solid-state electronic image pickup device. It is equipped.

Therefore, the circuit for processing the video signal for focus control and the circuit for processing the video signal for recording can be shared. Therefore, it is not necessary to separately provide a dedicated circuit for processing the video signal for focus control, and the video camera can be downsized.

In the present invention, since the repeating frequency component generated in the video signal due to the variation of the light transmittance of the color filter provided in the solid-state electronic image pickup device is removed to some extent by the amplifier circuit, such a color Focusing control can be performed with high accuracy without being disturbed by the repetition frequency component based on the filter array.

In a preferred embodiment of the present invention,
Further white balance adjustment is performed by the amplifier circuit. By this white balance adjustment, it is possible to further reduce the adverse effects of the repetitive frequency components due to the color filter array, and it becomes possible to perform focusing control with higher accuracy.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 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 of a digital circuit of an embodiment of the present invention.
It is a block diagram which shows the electric constitution of a still camera.

The image pickup optical system includes an image pickup lens 24, a diaphragm (not shown), and a CCD 4 as a solid-state electronic image pickup device (image sensor). A mechanical shutter is provided if necessary, but generally the shutter function is achieved by an electronic shutter realized by the control of the CCD 4. The image pickup lens 24 forms an object image on the CCD 4, and the image pickup lens drive 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 range finding sensor 27 is provided for preliminary range finding. The photometric data and range finding data by these sensors 26 and 27 are stored in the CPU 3. Given. CPU3
Controls at least one of the aperture value and the shutter speed on the basis of 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 image pickup lens 24 near the in-focus position via the image pickup lens driving device 25 based on the distance measurement data from the distance measurement sensor 27.

After the rough exposure amount adjustment based on the preliminary photometry and the general focusing control based on the preliminary distance measurement, the preliminary photographing is performed. By this preliminary shooting CCD
The calculation of the photometric value, the precise exposure control, and the highly accurate focusing control are performed by using the video signal obtained from No. 4. These highly accurate exposure control and focusing control will be described in detail later.

A clock signal generation circuit (hereinafter referred to as CG) 1 includes a clock signal CLK, a horizontal transfer pulse H for driving the horizontal transfer path of the CCD 4, a substrate extraction pulse SUB for sweeping 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 emission.

The clock signal CLK is given to a synchronizing signal generating circuit (hereinafter referred to as SSG) 2, and the SSG2 generates a horizontal synchronizing signal HD and a vertical synchronizing signal VD based on this clock signal CLK and gives it to CG1.

The horizontal transfer pulse H is given to a CCD (solid-state electronic image pickup device) 4. Substrate extraction 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 are the CPU
Given to 3. A shutter enable signal TS indicating that the exposure condition has been set from the CPU 3 to the CG 1.
An electronic shutter control signal TS1 for starting exposure in EN and CCD 4 is applied.

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

The video signals of the A field and the B field representing the subject image output from the CCD 4 are passed through the correlated double sampling circuit (CDS) 7 to the color separation circuit 8
Given to three primary colors, G (green), R (red) and B
It is separated into (blue) color signals.

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

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

The clamp and resampling circuit 11 is
The three color signals R, G, B are clamped and re-converted into color sequential signals of GRGB ... Which match the color filter arrangement in the CCD 4. This color sequential signal is input to the gain control and blanking circuit 12. The gain control and blanking circuit 12 amplifies the color sequential signal to an appropriate level for recording and adds the blanking signal to it. The output signal of the gain control and blanking circuit 12 is given to the first input terminal S1 of the changeover switch 13.

Prior to the main photographing, precise photometric processing (exposure control) and focusing control are performed as described above. The photometric processing is carried out by utilizing the low frequency component of the video signal obtained from the CCD 4 by preliminary photography, and the focusing control is carried out by utilizing the high frequency component of the above video signal.

In order to take out the low frequency component of the video signal representing the image in the photometric area (described later) provided in the photographing area of the CCD 4 for the photometric processing, the Y _L synthesizing circuit 15,
A gate circuit 16, an integrating circuit 17, and an amplifying circuit 18 are provided. The output signal of the amplifier circuit 18 is the second signal of the changeover switch 13.
Input terminal S2.

On the other hand, for focusing control, in order to extract a high frequency component of a video signal representing an image in a distance measuring area (described later) provided in the photographing area of the CCD 4, a gate circuit is provided.
19, band pass filter (hereinafter referred to as 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 given to the third input terminal S3 of the changeover switch 13.

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

In the photometric processing and focusing control prior to the main photographing, the changeover switch 13 selects and outputs the input signal of either the input terminal S2 or S3. As will be described later, the changeover switch 13 is basically changed over between the input terminals S2 and S3 for each field. The photometry process is performed by selecting the input terminal S2 during the period of the A field (first field) that constitutes one frame, and the input terminal S3 is selected during the period of the B field (second field). Focus control is performed by. Since it is considered that the A field image and the B field image forming one frame represent the field images at almost the same time points, the B field image signal is converted to the A field image signal for photometric processing in this way. Each 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.

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

Of the photometric processing (and exposure control based on it) prior to the actual photographing and the focusing control, the photometric processing will be described first.

The photometric processing is performed by the Y _L combining circuit 15, as described above.
This is performed using the gate circuit 16, the integration circuit 17, and the amplification circuit 18. The Y _L synthesizing circuit 15 outputs the output color signal R of the GCA 9,
G and B are given.

An example of a specific electrical configuration of these circuits is shown in FIG. 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, G and B output from the GCA 9 are added by the Y _L synthesizing circuit 15 to generate a relatively low frequency luminance signal Y _L (hereinafter simply referred to as luminance signal Y _L ). The luminance signal Y _L passes through the gate circuit 16 while the window signal WIND1 is applied during the required horizontal scanning period. The integrator circuit 17 has a reset signal HLRS.
It is reset when T1 is given, and then the luminance signal Y _L input from the gate circuit 16 is integrated. Integrator circuit 17
The integrated signal of is amplified by the amplification circuit 18, and then the integration circuit 17
Immediately before being reset, the data is input to the A / D converter 14 via the change-over switch 13, converted into digital integrated data for photometry by the A / D converter 14 and taken into the CPU 3.
The reference voltage divisions V1 and V2 of the integrating circuit 17 and the amplifying circuit 18 give them an appropriate offset.

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

Further, 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 photometric area and an SP photometric area set in the photographing area 30 of the CCD 4.

The AV metering area is basically set over almost the entire shooting area. In this embodiment, the AV photometric area is set for a period of 40 μs after 16 μs has elapsed from the trailing edge of the horizontal synchronizing signal HD (at the start of the horizontal scanning period) in the horizontal direction, and the 35th horizontal scanning in the vertical direction. From line 246
It is set up to the second horizontal scan line.

The SP photometric area is set as a small area at an arbitrary position within 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 in the vertical direction during a period of 15 μs after 28.5 μs has elapsed from the fall of the horizontal synchronizing signal HD. From the 194th
It is set up to the second horizontal scan line.

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

The AV photometric area is SP in the vertical scanning direction.
In the range not overlapping the photometric area, integration is performed every other horizontal scanning line in the AV photometric area. In the range where the AV photometric area and the SP photometric area overlap in the vertical scanning direction, the integration is performed alternately on the horizontal scanning line for the AV photometric area and the integration on the horizontal scanning line for the SP photometric area. Be done. 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 scan line and the 86th horizontal scan line,
16 μs from the falling edge of the horizontal sync signal HD to the gate circuit 16
After that, a window signal WIND1 having a pulse width of 40 μs is applied. Then, the integration circuit 17 integrates the luminance signal Y _L , A / D-converts the integration signal in the horizontal scanning period subsequent to the horizontal scanning period in which this integration operation is performed, resets the integration circuit 17, and sets the AV photometric area of the memory. 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 has a pulse width rising 28.5 μs after the falling edge of the horizontal synchronizing signal HD.
Window signal WIND1 of 15 μs and horizontal sync signal H
A window signal WIND1 having a pulse width of 40 μs, which rises 16 μs after the fall of D, is alternately applied.

Window signal WIND with a pulse width of 15 μs
When 1 is given to the integration circuit 17 to integrate the luminance signal Y _L , A / D conversion of the integration signal, reset of the integration circuit 17 in the horizontal scanning period subsequent to the horizontal scanning period in which the integration operation is performed, The integrated data is added to the SP photometric area data area of the memory (photometry of the SP photometric area). In addition, a window signal WIND with a pulse width of 40 μs
When 1 is given to the integration circuit 17 to integrate the luminance signal Y _L , A / D conversion of the integration signal, reset of the integration circuit 17 in the horizontal scanning period subsequent to the horizontal scanning period in which the integration operation is performed, Integration data is added to the AV photometry area data area of the memory (photometry of the AV photometry area).

Between the 195th horizontal scanning line and the 246th horizontal scanning line, the pulse width of 40 μs is the same as the above-mentioned 34th horizontal scanning line to the 86th horizontal scanning line. Window signal WIND1
The integration of the luminance signal Y _L and the processing of the integrated data obtained by this integration are alternately repeated every horizontal scanning period (photometry in the AV photometry area).

The CPU 3 adds the integrated data for one horizontal scanning line obtained on the basis of the window signal WIND1 having a pulse width of 40 μs in the AV metering area data area for one field period by the procedure described later to obtain the AV metering value EV. Calculate _AV .

Further, the CPU 3 uses the AV photometric value EV _AV
Window signal W with a pulse width of 15 μs
The integrated data for one horizontal scanning line obtained based on IND1 is added in the SP metering area data area over one field period by the procedure described later to calculate the SP metering value EV _SP .

FIG. 6 shows the overall operation of the AV photometry processing and SP photometry processing performed by the CPU 3.

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

In the horizontal scanning period within the AV photometric area (step 51), the window signal WIND1 for the AV photometric area is output and the integrating circuit 17 is caused to perform an integrating 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 integrated signal of the integrating circuit 17 to obtain integrated data.

Next, it is judged whether or not the obtained integrated 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. When the luminance signal Y _L is saturated in the portion of the horizontal scanning line which is the object of photometry, the integrated data is not suitable for use as a photometric value. The upper limit of this predetermined range is determined in consideration of the dynamic range of the CCD 4, the gain of the GCA 9 and the amplifier circuit 18, and the like so that the integrated data based on the saturated luminance signal Y _L can be excluded. On the other hand, the portion of the horizontal scanning line that is the object of photometry is extremely dark, 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 value of the above-mentioned predetermined range is set to the level at which the integrated data in which the noise component is dominant is excluded.

If the obtained integrated data has 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. (Step 55) Return to Step 52. If the integrated data is out of the predetermined range, the line number counter is incremented by 1 (step 57) and the addition process of the integrated data 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 whose 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 through step 55.

SP in the vertical direction of the AV photometric area
For the portion that does not overlap the photometric area, the above operation is repeated with two horizontal scanning periods as one cycle. The obtained integrated data is added to the AV photometric area data area.

In the portion where the AV photometric area and the SP photometric area overlap in the vertical direction, the window signal WIND1 for AV photometry and the window signal WIND1 for SP photometry are alternately output, and the same luminance is obtained. Integration of the signal Y _L , A / D conversion of the integrated signal, and checking whether the integrated data is within a predetermined range are performed. A
The integrated data obtained by integration over the pulse width of the window signal WIND1 for V photometry is added to the AV photometric 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 photometric area data area. The line number counter that counts the number of lines determined to be NO in the determination in step 53 also has an AV metering area and S
The number of lines, which are provided for the P photometry areas and are determined to be NO, are separately counted in both photometry areas.
The predetermined number of lines for the judgment in step 58 is also AV.
Different values may be set for the photometric area and the SP photometric area.

When it goes out of the range of the AV metering area (step
55), using the respective added values of the integrated data in the AV and SP photometric areas obtained up to that time,
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 AV photometric value EV _AV and SP photometric value EV _SP are calculated by dividing the added value of the integrated data in each photometric area by the number of lines added as the integrated data, and averaging the integrated values per horizontal scanning line. Includes calculations for finding values and calculations for multiplying the average value by an appropriate constant. The number of lines added as the integrated data can be 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 the exposure conditions such as the aperture, the shutter speed, and the presence / absence of stroboscopic light emission based on the obtained photometric values EV _AV and EV _SP .

Further, when the value of the line number counter for counting the number of horizontal lines whose integrated data is outside the predetermined range exceeds the predetermined number (step 58), the CPU 3 changes the exposure condition (step 59). After clearing the photometric area of the memory, the photometric process from step 51 is repeated at the time of starting the next frame. The judgment in step 58 is A
It 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 conditions, if most of the integrated data for each horizontal line exceeds the above-mentioned predetermined range, the exposure amount is made smaller than the initially set exposure amount, and in the opposite case. It is advisable to change the exposure amount by one step (for example, ± 2 Ev) such that the exposure amount is increased. If the initial exposure is not too far from the actual brightness of the field of view (especially when pre-metering as described above),
An appropriate exposure amount may be obtained by repeating the photometric processing shown in FIG. 6 once or twice (one frame to two frame periods).

In any case, the process of determining whether or not an appropriate photometric value has been obtained will be touched upon again in the explanation of FIG.

FIG. 7 shows A obtained by the above photometric processing.
6 is a flowchart showing a processing procedure performed by a CPU 3 for setting an exposure condition based on a V photometry value EV _AV and an SP photometry value EV _SP .

The CPU 3 obtains a 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 of the photometric value is zero or more,
It is determined whether it is between zero and -0.5 EV, between -0.5 EV and -2 EV, or below -2 EV (steps 61 and 63).

When it is determined that the difference ΔEV in the photometric values is 0 ≦ ΔEV, that is, when the main subject in the central portion is bright and the background is dark, the CPU 3 determines the SP photometric value E.
Exposure conditions are set based on V _SP (step 6).
2). This is because if the exposure condition is set based on the AV photometric value EV _AV , the main subject will be photographed darkly, and it is best to properly expose the main subject that the photographer wants to photograph most.

When it is determined that -0.5 EV≤ΔEV <0, that is, when the luminance difference between the main subject and the background is small, the CPU 3 sets the exposure condition based on the AV photometric value EV _AV . Make settings (step 64). This is because if the exposure condition is set based on the AV photometric value EV _AV , it can be considered that both the main subject and the background are properly exposed. If -2EV <ΔEV <-0.5 EV is determined,
That is, when it is determined that the background is brighter and the brightness difference between the main subject and the background is relatively large, the CPU 3 sets the exposure condition based on the value of EV _AV -1EV (step 65). That is, in this case, since the background is bright, exposure correction (backlight correction) is performed so that the background becomes slightly dark.

When it is determined that ΔEV ≦ −2EV, that is, when the main subject is darker than the background and the difference in luminance is extremely large, it is necessary to make the main subject bright by emitting a strobe light. Therefore, the CPU 3 performs daytime synchronized photography. That is, the preparation for strobe emission and the exposure conditions for strobe emission are set (step
66). In this case, the main subject cannot be properly exposed even by the backlight correction as described above, and it is determined that the correction by the stroboscopic light emission is appropriate.

Next, focusing control will be described.

Referring again to FIG. 1, the output signal of the gain control and blanking circuit 12 is the gate circuit 19
To enter. The gate circuit 19 is controlled by the window signal WIND2 given from the CPU3. gain·
The output signal of the control and blanking circuit 12 passes through the gate circuit 19 and BPF20 during the period in which the window signal WIND2 is given in the required horizontal scanning period.
To enter.

The BPF 20 extracts a high frequency component required 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 the detection circuit 21, integrated by the integration circuit 22, and further amplified by the amplification circuit 23. Then, when the changeover switch 13 selects the input terminal S3, A / The data is input to the D converter 14, converted into digital data for focusing control by the A / D converter 14, and then converted into C
Captured by PU3.

The digital data supplied from the A / D converter 14 is integral data obtained by integration over a horizontal scanning period of a range-finding area, which will be described later, set in the photographing area, and the CPU 3 converts this integrated data. The data for distance measurement is calculated by adding up over the vertical scanning period of the distance measurement area, and focusing control is performed based on this data. Details will be described later.

Generally, when the image is out of focus and out of focus, the high frequency component contained in the image 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 contained in the video signal becomes maximum at the correctly focused position. In this embodiment, focusing control is performed based on such a fact, and the BP
F20 has about 1.5 to extract high frequency component of video signal.
A pass band of 2.5 MHz is set.

On the other hand, the color filter provided in the CCD 4 is GR in the horizontal direction in this embodiment, as shown in FIG.
It is arranged in GB repeats. Assuming that the read clock frequency of the CCD 4 is 13.5 MHz, the repetitive frequency components of 6.8 MHz are red (R) and blue (B) in the video signal obtained from the light receiving element (photodiode) provided with the green (G) filter. ), The repetition frequency component of 3.4 MHz is included.

Since 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. 8 in the clamp and resampling circuit 11, this video signal Some of the
In addition to the frequency components representing the subject image, the repetitive frequency components (3.4 MHz and 6.8 MHz) due to the color filter array described above are included.

The repetitive frequency component due to the color filter array 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 impaired white balance. And increase or decrease. For example, assuming that the light transmittances of the color filters are all the same and the white balance is perfectly balanced, if a pure white object is photographed, the repetitive frequency component due to the color filter array will be almost eliminated. .

The GCA 9 corrects the fluctuations in the level of the video signal due to the difference in the light transmittance of the color filters and adjusts the white balance in order to remove the repetitive frequency components due to the color filter array as much as possible. belongs to.

That is, referring again to FIG. 2, when the color filter sensitivity ratio correction is performed, the gains G _r2 , G _g2 , and G _b2 of the white balance adjustment amplifiers 92r, 92g, and 92b are set to appropriate predetermined gains ( For example, the gain G _{g1 of the} amplifier 91g is fixed, and the levels of the other color signals R and B with respect to the G signal at a certain color temperature (usually about 5500K) are set to the amplifier 91r. , 91b
Adjustment is performed by changing the gains G _r1 and G _b1 of. Once adjusted, these gains G _r1 , G _g1 and G _b1 are fixed. The white balance adjustment is based on the detection signal of the color sensor as is well known.
This is performed by controlling the gains G _r2 and G _b2 of r and 92b. This is because the gain G _r2 increases as the color temperature increases,
This is performed by lowering the gain G _b2 and lowering the gain G _r2 and increasing the gain G _b2 when the color temperature becomes lower. 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 the repetition frequency component (center frequency f _G = 6.8 MHz) resulting from the G color filter array, and the repetition frequency component resulting from the R or B color filter array (center frequency f
_{(R / B} = 3.4 MHz) and the luminance signal spectrum 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. A part (represented by hatching) of the repetitive frequency components due to the color filter array, particularly the R and B color filter arrays, enters the pass band of the BPF 20. Therefore, in this case, the video signal that has passed through the BPF 20 contains a considerable number of repeating frequency components due to the color filter array.

FIG. 10 shows a case where both the color filter sensitivity ratio correction and the white balance adjustment are performed. B
The repetitive frequency component due to the color filter entering the pass band of PF20 is considerably reduced. Therefore, in this case, it can be considered that most of the video signals that have passed through the BPF 20 represent a subject image. It is possible to expect good focusing processing that is not disturbed by the repetitive frequency components due to the color filter array.

The minimum function of the GCA 9 is to correct the color filter sensitivity ratio, which considerably reduces the interference by the repetitive frequency components due to the color filter array. Preferably GCA 9 achieves both color filter sensitivity ratio correction and white balance correction. This ensures a better focus control.

FIG. 11 shows a distance measuring area set in the photographing area 30 of the CCD. This distance measuring area is set at the center of the photographing area 30 where the main subject is highly likely to exist. 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 measuring area can be set to any location within the photographing area 30 and to any width.

As shown in FIG. 12, in the B field period, 31 from the falling edge of the 87th horizontal synchronizing signal HD.
Window signal WI with a pulse width of 10 μs after μs has elapsed
ND2 is applied to the gate circuit 19, and as described above, the gate circuit 19 allows the output signal of the circuit 12 to pass while the window signal WIND2 is applied. The high frequency component signal extracted by the BPF 20 passes through the detection circuit 21 and the integration circuit.
It is given to 22 and integrated. The integrated output signal of the integrating circuit 22 is passed through the amplifying circuit 23 and the change-over switch 13, converted into digital data by the A / D converter 14 in the next horizontal scanning period, and given to the CPU 3. The integrating circuit 22 is A
It is reset by the reset signal HLRST2 after the / D conversion process. The CPU 3 stores this digital data by adding it to the previous data in the distance measuring area of the memory (which is zero because it has been cleared in the first case). The distance measuring area is cleared in synchronization with the 86th horizontal synchronizing signal HD or at the start of the B field.

As described above, 1 within the distance measuring area
The detection of the high frequency component signal by the BPF 20, the detection and integration of the high frequency component signal, the A / D conversion of the integrated signal, and the addition of the integrated data in the horizontal scanning period are alternately performed for each horizontal scanning period on the horizontal scanning line of the book. It is repeated. Then, this repetition is performed until the 194th horizontal scanning period, that is, over the entire range-finding area.

Therefore, at the time when the scanning within the distance measuring area is completed, the BP is set in the distance measuring area of the memory.
The addition data for distance measurement representing the integrated value of the high-frequency signal that has passed through F20 over the entire distance measurement area is stored.

As described above, in the preliminary distance measurement using the distance measuring sensor 27, the approximate distance to the subject is measured. Based on this preliminary distance measurement data, the image pickup lens 24 is considered to be the in-focus position, which is a little before this position (called the initial position)
Is delivered to.

The integration operation of the high frequency component of the video signal output from the CCD 4 over the distance measuring area is performed by the image pickup lens 24 at 10
It is performed at least 6 times (that is, in the B field period of each frame period over 6 frame periods) while feeding forward by μm. At the above-mentioned initial position (extending amount of the imaging lens 24 = 0 μm), first addition data for distance measurement is obtained. In the next frame period, the second distance measurement addition data is obtained at a position where the imaging lens 24 is extended by 10 μm from the initial position (image pickup lens extension amount = 10 μm). Similarly, the third to sixth distance measurement addition data can be obtained while the imaging lens 24 is extended by 10 μm.
The 6-position addition data 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 of is just before the true focus position. The image pickup lens 24 is extended by 10 μm from this position, and the 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
The unit feeding amount of is 10 μm, which is a very small distance.
Even if the position where the addition data for distance measurement shows the maximum value is regarded as the true focus position, the error is extremely small. Therefore, highly accurate focusing can be achieved by positioning the imaging lens 24 at the position where the distance measurement addition data shows the maximum value.

The above-described photometric processing and distance measurement addition data collection processing for focusing control are alternately performed 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 valid. This is because the value of the additional data for distance measurement that is obtained differs depending on the exposure condition, so that accurate additional data for distance measurement cannot be obtained if the exposure condition is not set appropriately.

FIG. 15 shows an overall procedure of preliminary photometry, preliminary distance measurement processing, and exposure control and focusing control based on preliminary photographing performed thereafter.

The CPU 3 first performs preliminary photometry based on the photometry signal of the photometry sensor 26 and preliminary rangefinding based on the rangefinding signal from the rangefinding sensor 26 (step 70). The exposure conditions are initialized 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, in the A field period, the photometry and the calculation of the photometric value are performed in the procedure shown in FIG. 6 (steps 74 and 75). This corresponds to the processing of steps 51 to 56 in FIG.

It is judged whether or not the photometric value thus obtained is appropriate (step 76). This judgment is shown in FIG.
The determination of step 58 of 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.

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

Then, the changeover switch 13 is changed over 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 is performed on the horizontal scanning line in the distance measurement area as described above, and the A /
The addition of the D-converted and A / D-converted integral data is performed over the entire distance measuring area (steps 82 and 83).

As described above, the distance measurement addition data is collected while the imaging lens 24 is extended 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 image pickup lens 24 is extended by 10 μm (step 85). The obtained addition data is stored in the memory area shown in FIG.

When the processing of steps 73 to 76 and 80 to 85 is repeated for each frame and the value of the counter exceeds 5 (step 86), the addition data for distance measurement of 6 times in the area shown in FIG. To find the maximum value (step
87). Then, the imaging lens 24 is displaced to a position corresponding to the maximum addition data for distance measurement, and 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 the photometry and the distance measurement are completed and the exposure condition is set and the focusing is performed, the changeover switch 13
Is switched to the input terminal S1 and the actual photographing is started.

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, and the exposure amount is decreased when the photometric value is large, and is increased in the opposite case.

Next, all the distance measurement addition data obtained so far in the memory area shown in FIG. 13 are cleared (step 78), the counter is further cleared, and the imaging lens
24 is returned to the initial position (step 79). This is because the addition data for distance measurement obtained in the state where the proper exposure condition is not set is not used for focusing control. After that, the process 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 alternately performed for each field. The photometric processing is performed in parallel while the distance measurement processing is being performed.
If the exposure conditions change due to, for example, the subject moving or changing, zooming up or down, or sudden brightening due to sunlight, it was stored in steps 78 and 79 until then. This is because the added data and the counter are cleared and distance measurement is performed again.

[Brief description of drawings]

FIG. 1 is a block diagram of a digital still camera according to an embodiment of the present invention.
It is a block diagram which shows the electric constitution of a video camera.

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

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

FIG. 4 is a diagram showing a photometric area set within a shooting area.

FIG. 5 is a time chart showing photometric processing.

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

FIG. 7 is a flowchart showing a procedure of exposure condition setting processing by a CPU.

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

FIG. 9 is a graph showing a pass band of a BPF when color filter sensitivity ratio correction and 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 BPF pass band in the case of performing color filter sensitivity ratio correction and white balance correction, and a spectrum of a repetition frequency and a luminance signal due to an arrangement of color filters.

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

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

FIG. 13 is a diagram showing a storage area of added data for distance measurement.

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

FIG. 15 is a flowchart showing a procedure of processing of exposure control and focusing control by the CPU.

[Explanation of symbols]

3 CPU 4 CCD (solid-state electronic image sensor) 8 Color separation circuit 9 GCA (amplification circuit) 11 Clamp and resampling circuit 13 Changeover switch 14 A / D converter 15 Y _{L combination} circuit 16 Gate circuit 17 Integration circuit 18 Amplification circuit 19 Gate circuit 20 Band pass filter 21 Detection circuit 22 Integration circuit 23 Amplification circuit 24 Imaging lens 25 Imaging lens driving device 26 Photometric sensor 27 Distance measuring sensor 91r, 91g, 91b Color filter Sensitivity ratio correction variable gain amplifiers 92r, 92g, 92b White balance adjustment variable gain amplifier

Claims (8)

(57) [Claims] 1. A video camera having an imaging optical system including a solid-state electronic image pickup device having an image pickup lens and a color filter for converting a light image incident through the image pickup lens into a video signal and outputting the image signal. A color separation circuit for color-separating a video signal output from the device to output color signals of a plurality of colors; amplifier circuit for correcting variations in level, based on the high-frequency component extracted high-frequency component extracting means for extracting a high frequency component, and by the high frequency component extraction means for ranging from the output color signal of the amplifier circuit, the A video camera having a focusing control means for controlling the focusing of an imaging lens. 2. The video camera according to claim 1, wherein the amplifier circuit further adjusts the white balance of the color signals. 3. A distance measuring sensor for preliminary distance measurement, and an initial positioning means for positioning the image pickup lens at an initial position based on distance measuring data obtained from the distance measuring sensor. The listed video camera. 4. The high-frequency component extracting means extracts the high-frequency component from the output color signal for scanning a predetermined distance-measuring region within the photographing region, and the high-frequency component is extracted by the imaging lens. Further, the initial positioning means positions the image pickup lens at a position deviated from the in-focus position in the direction opposite to the one direction by further controlling the plurality of fields by moving the lens in one direction by a predetermined distance. The focusing control means calculates an integrated value of the high frequency signal obtained from the high frequency component extracting means in the distance measuring area, and the image is picked up at a position corresponding to the maximum value of the integrated value over a plurality of fields. The video camera according to claim 3, which positions a lens. 5. An optical image incident through an imaging lens is preliminarily photographed by a solid-state electronic image pickup device having a color filter, and by this preliminarily photographing, a video signal obtained from the solid-state electronic image pickup device is color-separated into color signals of a plurality of colors. The level variation of the color signal due to the difference in the light transmittance of the color filter of the solid-state electronic image sensor is corrected, and the high frequency component for distance measurement is extracted from the color signal corrected for the level variation. performs focusing control of the imaging lens based on the high frequency components issued extracted, focusing method for a video camera. 6. The focusing method for a video camera according to claim 3, further comprising white balance adjustment of the color signals of the color-separated plural colors. 7. Preliminary distance measurement is performed using a distance measurement sensor, and based on distance measurement data obtained by this preliminary distance measurement, the imaging lens is initially positioned at a position deviated in one direction from the in-focus position. The extraction of the high frequency components is performed over a plurality of fields while moving the imaging lens in the direction opposite to the one direction by a predetermined distance, and the high frequency components extracted in each field are integrated to obtain the maximum value of these integrated values. The video camera focusing method according to claim 5, wherein the imaging lens is positioned at a corresponding position. 8. The focusing method for a video camera according to claim 7, wherein the extraction of the high frequency component is performed from the color sequential signal for scanning a predetermined distance measuring area within the photographing area.