JP2003107330A - Camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a camera capable of performing a more accurate operation by reducing noise influence of an image pickup element, etc. SOLUTION: Imaging with a CCD 103 is performed with a shutter 102 closed, that is, in a light shielded state. Focus evaluation value operating parts 1125A and 1125B calculate a focus evaluation value based on an imaging signal in a focus detection area at that time, the focus evaluation value or reference variation at restarting is corrected by using the focus evaluation value as a noise level of a focus evaluation value. At restarting, whether or not restarting is needed is decided by using a corrected focus evaluation value and an uncorrected reference variation or an uncorrected focus evaluation value and corrected reference variation. The width 2Δb of a range is also corrected with the noise level even about a release allowable range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera that performs a focusing operation by a contrast method using an image pickup signal of an image pickup device.

[0002]

2. Description of the Related Art Conventionally, as one of AF methods for cameras, there is one called a contrast method. With this method,
An image of a subject is picked up by an image pickup device such as a CCD, and a focus position is determined using an image pickup signal in the focus area. Image signals in the area are passed through a bandpass filter (BPF),
A component in a predetermined spatial frequency band is extracted. Then, by integrating those absolute values within the area, the focus evaluation value for performing the focusing operation is obtained. The focus evaluation value represents the magnitude of contrast, and the highest focus is at the peak of the focus evaluation value.

That is, the peak position is the in-focus position. When searching for this peak, a conventionally known hill-climbing focusing operation is performed to find the peak.
By the way, AF is always activated regardless of the half-press of the release button.
In the continuous AF mode in which the operation is performed, the hill-climbing focus operation is restarted at predetermined time intervals so that the subject is always in focus.

[0004]

However, the output signal from the image sensor includes a signal such as dark current that is not related to the image information, and the focus evaluation value calculated based on the output signal is noisy. As influential. In particular, when the contrast of the subject is low, the influence of noise becomes relatively large, and there is a possibility that stable focusing operation cannot be performed.

An object of the present invention is to provide a camera that performs a camera operation such as a focusing operation based on a focus evaluation value calculated from an image pickup signal of an image pickup element, by reducing the influence of noise of the image pickup element and the like to achieve a more accurate operation. It is to provide a camera capable of performing an operation.

[0006]

The camera according to the present invention comprises:
An image pickup element for picking up a subject image through a taking lens, an evaluation value calculation means for calculating a focus evaluation value based on an image pickup signal output from the image pickup element, and noise included in the focus evaluation value calculated by the evaluation value calculation means. The noise level calculation means for calculating the level and the determination means for determining the necessity of the camera operation based on the focus evaluation value, the noise level and the predetermined reference focus evaluation value are provided to achieve the above-mentioned object.
Further, a plurality of filter circuits that pass different predetermined spatial frequency bands of the image pickup signal output from the image pickup device are provided, and the image pickup is performed based on the signal that the evaluation value calculation means passes through any one of the plurality of filter circuits. The focus evaluation value of the lens may be calculated, and the noise level calculation means may calculate the noise level for each filter circuit. The noise level is calculated each time the camera power is turned on, or before or after the shooting operation. The noise level is calculated with the shutter closed. A camera according to the present invention includes an image pickup device for picking up a subject image through a taking lens, an evaluation value calculation means for calculating a focus evaluation value based on an image pickup signal output from the image pickup device, and a focus evaluation value noise peculiar to the image pickup device. The above-described object is achieved by including a storage unit in which levels are stored in advance and a determination unit that determines whether or not a camera operation is necessary based on a focus evaluation value, a focus evaluation value noise level, and a predetermined reference focus evaluation value. . Also in this case, a plurality of filter circuits that pass different predetermined spatial frequency bands of the image pickup signal output from the image pickup device are provided, and the evaluation value calculation means is based on the signal that has passed through any one of the plurality of filter circuits. The focus evaluation value of the photographing lens may be calculated, and the noise level calculation means may calculate the noise level for each filter circuit. Further, focus evaluation value correction means for correcting the focus evaluation value based on the noise level is provided, and it is determined whether or not the camera operation is required based on the reference focus evaluation value and the focus evaluation value corrected by the focus evaluation value correction means. You may do it. Further, a reference value correction means for correcting the reference focus evaluation value based on the noise level is provided, and the necessity of camera operation is determined based on the focus evaluation value and the reference focus evaluation value corrected by the reference value correction means. You can Furthermore, the determination means may determine whether or not the release operation is possible, or whether or not the focusing operation of the photographing lens is necessary. When determining whether or not the focusing operation is necessary, a focusing operation unit that performs the focusing operation of the photographing lens based on the focus evaluation value, and a focusing operation unit when the determination unit determines that the focusing operation is necessary And a focusing operation control means for performing the focusing operation according to.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a functional block diagram of an AF (autofocus) digital camera according to an embodiment of the present invention. Reference numeral 101 denotes an interchangeable photographic lens, and the photographic lens 101 includes a ROM (not shown) in which lens information regarding the open F value and the like is stored. Shooting lens 101
When is attached to the lens mount (not shown) of the camera body, the lens information is read by the detector 121 on the body side and stored in the storage unit 1123. The shooting lens 1
A zoom lens 01 has a focusing lens for adjusting the focal position and a variable magnification lens for changing the focal length. The taking lens 101 is the driver 11
Driven by 3. That is, the driver 113 includes a zoom drive mechanism of a zoom lens and a drive circuit thereof, and a focus drive mechanism of a focusing lens and a drive circuit thereof, and each is controlled by the CPU 112.

The taking lens 101 forms a subject image on the image pickup surface of the image pickup element 103. The image pickup element 103 is a photoelectric conversion image pickup element that outputs an electric signal according to the light intensity of the subject image formed on the image pickup surface, and a CCD type or MOS type solid state image pickup element is used. The image sensor 103 is driven by a driver 115 that controls the timing of signal extraction. A diaphragm 102 is provided between the taking lens 101 and the image sensor 103. The diaphragm 102 is driven by a driver 114 including a diaphragm driving mechanism and a driving circuit therefor. An image pickup signal from the solid-state image pickup device 103 is input to an analog signal processing circuit 104, and in the analog signal processing circuit 104, correlated double sampling processing (CD
Processing such as S processing) is performed. Analog signal processing circuit 1
The image pickup signal processed in 04 is converted from an analog signal to a digital signal by the A / D converter 135.

The A / D converted signal is subjected to various image processing such as contour compensation and gamma correction in the digital signal processing circuit 106. The digital signal processing circuit 106 includes signal processing circuits such as a gain control circuit, an AE integration circuit, a luminance signal generation circuit, and a color difference signal generation circuit. The buffer memory 105 is a frame memory that can store data for a plurality of frames captured by the image sensor 103, and the A / D converted signal is temporarily stored in the buffer memory 105. In the digital signal processing circuit 106, the data stored in the buffer memory 105 is read and each processing described above is performed, and the processed data is stored in the buffer memory 106 again.

The CPU 112 is a digital signal processing circuit 10.
6 and drivers 113 to 115, etc., and performs sequence control of camera operation. The AE calculation unit 1121 of the CPU 112 performs automatic exposure calculation based on the image signal from the image sensor 103, and the AWB calculation unit 1122 calculates the white balance adjustment coefficient. The two types of bandpass filters (BPF) 1124A and 1124B are
A high frequency component in a band corresponding to each characteristic is extracted based on the image pickup signal in the focus detection area provided in the image pickup area. When a plurality of focus detection areas are set, the signals in each area are sequentially read, and the extraction processing for each area is performed by a bandpass filter (BPF) 1124.
A, 1124B. In the following, a case where there is one focus detection area will be described as an example.

The outputs of the BPFs 1124A and 1124B are input to the evaluation value calculation units 1125A and 1125B, respectively, and the focus evaluation values are calculated by integrating the absolute values of the high frequency components in the evaluation value calculation units 1125A and 1125B. The AF calculation unit 1126 performs AF calculation by the contrast method based on these focus evaluation values. C
The PU 112 adjusts the focusing lens position of the taking lens 101 using the calculation result of the AF calculation unit 1126,
Focus operation is performed. The operation unit 116 connected to the CPU 112 includes a power switch 1161 for turning on / off the power of the camera, a full-press switch 1162 for turning on / off in conjunction with a release button, and a half-press switch 11.
63, setting button 116 for selecting a shooting mode, etc.
4 are provided. The shooting modes set by the setting button 1164 include a normal shooting mode, a distant view shooting mode, a portrait shooting mode, a sports shooting mode, a close-up shooting mode, and a night view shooting mode, which will be described later. When you operate these switches and buttons, the signal corresponding to the operation is sent to the CPU.
It is input to 112.

Reference numeral 119 is a battery, the voltage of which is detected by the voltage detector 120. 118 is the shutter 11
7 is a driver for driving 7. Also, the AF auxiliary light 12
2 illuminates the subject at low brightness. The CPU 112 has a storage unit 1123 for storing various data and a timer 1127. The timer 1127 is generally called a half-press timer, and starts counting when the half-press operation of the release button is released and after the first focusing after the power is turned on as described later.

The image data, which has been subjected to various kinds of processing by the digital signal processing circuit 106, is temporarily stored in the buffer memory 105 and then recorded on the external storage medium 111 such as a memory card via the recording / reproducing signal processing circuit 110. It When recording image data in the storage medium 111, data compression is generally performed in a predetermined compression format, for example, the JPEG method. The recording / reproduction signal processing circuit 110 performs data compression when recording image data on the external recording medium 111 and data decompression processing when reading compressed image data from the storage medium 111. The recording / reproducing signal processing circuit 110 also includes an interface for performing data communication with the storage medium 111.

The monitor 109 is a liquid crystal display device for displaying a picked-up subject image, and is also used for reproducing and displaying image data recorded in the storage medium 111. When displaying an image on the monitor 109, the image data stored in the buffer memory 105 is read, and the D / A converter 108 converts the digital image data into an analog video signal. Then, an image is displayed on the monitor 109 using the analog video signal.

There are two modes of displaying the subject image captured by the image sensor 103 on the monitor 109. One is the display form when the release operation is not performed,
This is a display form called a through image in which subject images repeatedly captured by the image sensor 103 are sequentially updated and displayed. The other is a display form called a freeze image in which the subject image captured by the image sensor 103 is displayed for a predetermined time after the release operation of the camera.

In the contrast method, focusing is performed by utilizing the fact that there is a correlation between the degree of blurring of an image and the contrast, and the contrast of the image becomes maximum when the image is in focus. The size of the contrast can be evaluated by the size of the high frequency component of the image pickup signal. That is, BPF
A high-frequency component of the image pickup signal is extracted by 1124A and 1124B, and the focus evaluation value is obtained by integrating the absolute value of the high-frequency component by the evaluation value calculation units 1125A and 1125B. The focus evaluation value becomes the maximum value when the focus is achieved and the contrast becomes maximum. As described above, the AF calculation unit 112
6 performs AF calculation based on this focus evaluation value. CPU
Reference numeral 112 adjusts the focusing lens position of the taking lens 101 using the calculation result of the AF calculation unit 1126 to perform a focusing operation.

<< Description of Operation >> Next, the operation of the camera will be described with reference to the flowcharts of FIGS. When the power switch 1161 of FIG. 1 is turned on, the process of the flow shown in FIG. 2 is started. In step S100, CCD1
The noise included in the image pickup signal 03 is measured. 9 and 10 show specific examples of the processing performed in step S100. FIG. 9 is a first example, and after closing the shutter 117 of FIG. 1 in step S1001, image pickup is performed in step S1002. At this time, the subject light is blocked by the shutter 117 and does not enter the CCD 103, but the CCD 103 outputs a minute noise signal due to dark current or the like. Then, the focus evaluation value based on the signal output from the CCD 103 is calculated, and the calculation result is stored in the storage unit 1123. This is the noise level Δ
Call S. Then, in step S1003, the shutter 117 is opened.

The second example shown in FIG. 10 shows a case where the noise level is measured when the camera is adjusted. In step S1101, the shutter 117 is opened. Step S
The image is captured at 1102, and the focus evaluation value (noise level) is calculated. The calculated noise level is stored in the storage unit 1123. Then, in step S1103, the shutter 117 is closed.

The focus evaluation value calculated in step S1103 described above can be said to be a noise level for the focus evaluation value. A curve L0 in FIG. 11 shows the focus evaluation value for each lens position of the focusing lens, and the calculated focus evaluation value includes the noise level ΔS. In the following, a value obtained by subtracting the noise level ΔS from the calculated focus evaluation value is adopted as the actual focus evaluation value. As described above, by removing the noise level from the focus evaluation value, more accurate focusing operation can be performed.

Returning to FIG. 2, in step S101, C
The image pickup signal is read from the CD 103, and the A / D converter 135 performs A / D conversion of the image pickup signal. Further, the digital signal processing circuit 106 takes in the buffer memory 105, and AE calculation is performed. Step S1
In 02, it is determined whether or not the subject brightness calculated by the AE calculation unit 1121 is below a predetermined level. That is, it is determined whether the brightness is low. If the subject brightness is determined to be equal to or lower than the predetermined level in step S102, step S103
If it is determined that the subject brightness is higher than the predetermined level, the process proceeds to step S108.

When the process proceeds from step S102 to step S103, it is determined in step S103 whether the gain setting is the upper limit value. The gain here is a product of the A / D output in the digital signal processing circuit 106. If it is determined in step S103 that the gain setting is not the upper limit value, the process proceeds to step S104 and the gain setting is increased by one step. For example, when the ISO sensitivity is set to 100, the sensitivity is increased by one step and the sensitivity is set to 200. Then, from step S104 to step 10
Returning to step 2, it is determined whether the subject brightness after the gain setting change is below a predetermined level. On the other hand, if it is determined in step S103 that the gain setting is the upper limit value, that is, if it is determined that the ISO sensitivity is at the final stage (for example, 800), the AF auxiliary light 12 is determined in step S106.
Turn on 2. It should be noted that the lighting of the auxiliary light is continued until the focusing operation is completed.

In the following step S106, the CCD 103
It is determined whether or not the frame rate setting of the image pickup signal output from is the lower limit value. If it is determined to be the lower limit value in step S106, the process proceeds to step S108, and if it is determined that it is not the lower limit value, the process proceeds to step S107. When the process proceeds to step S107, the frame rate is reduced by one step in step S107, and then the process returns to step S102. That is, since the subject brightness is low, step S10
At 7, the frame rate is lowered to lengthen the storage time of the CCD 103. Similar to the gain setting, a plurality of settings are prepared in advance for the frame rate setting. In step S108, the absolute position of the focusing lens is detected by a photo coupler or the like to determine the reference position of the lens.

In the camera according to the present embodiment, the AF operation is performed only when the half-push switch 1163 is half-pushed, and once the focus is achieved, the focus state is maintained until the half-push is released. (S-AF),
It has a continuous AF mode (C-AF) in which an AF operation is always performed regardless of half-pressing. Switching between these modes is performed by operating the setting button 1164 in FIG. In step S109, it is determined whether the camera setting is C-AF or S-AF, and if it is determined to be S-AF, the process proceeds to step S110. In step S110, it is determined whether or not the button is half-pressed. If it is not determined to be half-pressed, the process returns to step S109, and if it is determined to be half-pressed, step S1.
Proceed to 11. On the other hand, if it is determined to be C-AF in step S109, the process proceeds to step S111. Continued Step S11
If the focusing lens is moved to the initial position in step 1, the process proceeds to step S112 in FIG. The end position on the infinity side or the end position on the closest side is selected as the initial position.

Steps S112 to S1 in FIG.
In the processes up to 15, sampling of focus evaluation values over the entire lens position is performed. First, in step S112, the movement of the focusing lens of the taking lens 101 is started. In the present embodiment, the lens position is moved from the infinity side end position to the close end side end position. Step S
In 113, the BP regarding the image pickup signal in the focus detection area
The evaluation value calculation unit 1125A performs the in-area integration by the signal processed by F1124A, and the evaluation value calculation unit 1125B performs the in-area integration by the signal processed by BPF1124B. The results are stored in the storage unit 1123 as a pair with the lens position at the time of sampling. Step S1
At 14, it is determined whether or not the lens position has become the closest end position. If it is determined in step S114 that it is the closest end position, the process proceeds to step S115 to stop lens driving. On the other hand, when it is determined in step S114 that the position is not the closest end position, the process returns to step S113, and the focus evaluation value is calculated and stored again. Therefore, from step S112
By the processing of S115, the focus evaluation value is stored in the storage unit 1123 for each sample position between the closest end ← → the infinite end of the focusing lens.

In step S116, a predetermined weighting process is performed on each calculated focus evaluation value. 12,
13 is a diagram showing an example of weighting. FIG. 12 is a diagram showing a weighting curve, in which the horizontal axis represents the lens position and the vertical axis represents the weight. The origin side of the horizontal axis is the infinity side, and the positive direction of the horizontal axis is the close side. The weighting curve in FIG. 12 is related to the AF mode in which the subject at the extreme end on the closest side is prioritized. The weight at the extreme end position on the closest side is set to 1, and the weight becomes smaller toward the infinity side. There is.

The weighting shown in FIG. 12 is applied to the curve L1 in FIG.
When the focus evaluation value as shown by (1) is performed, the focus evaluation value is corrected to the curve L2. Since the focus evaluation value is discrete data, the curves L1 and L2 are estimated by interpolation. Both the curves L1 and L2 have two peaks, and the focus evaluation value of the peak P2 on the infinity side of the curve L1 is larger than that of the peak P1 on the close side. On the other hand, in the focus evaluation value curve L2 after weighting, the peak P11 on the closest side
The focus evaluation value of is larger than the infinity side peak P12. Therefore, when the lens position having the maximum focus evaluation value is selected as the in-focus position, the peak P11 on the closest side is selected. As described above, the weighting curve of FIG. 12 is suitable for close-up photography such as portrait photography and close-up photography.

The weighting curve of FIG. 14 shows another example, which is the weighting curve in the distant view photographing mode. The weighting curve changes stepwise with the lens position x1 as a boundary, and the weight on the infinity side is smaller than the weight on the infinity side with respect to the lens position x1. Furthermore, FIG.
Reference numeral 5 denotes a weighting curve in the flash photography mode using the flash device, which is opposite to the distant view photography mode and has a larger weight on the near side at the lens position x2. The lens position x2 depends on the guide number of the flash device, and is set according to the reaching distance of the illumination light.

Returning to FIG. 3, in step S117, BP
It is determined whether or not the focus evaluation value A when F1124A is used is larger than the lower limit value at which focusing operation is possible. Step S
If it is determined in 117 that it is larger than the lower limit value, step S1
If it is determined that the value is equal to or less than the lower limit value, the process proceeds to step S121. Steps S117 to S12
If the process proceeds to 1, the BPF is set in step S121.
It is determined whether or not the focus evaluation value B when 1124B is used is larger than the lower limit value at which focusing operation is possible. BPF112
4B is different from the BPF 1124A in the setting of the center frequency, the bandwidth, and the like. If it is determined in step S121 that it is larger than the lower limit, the process proceeds to step S118,
If it is determined that the value is equal to or less than the lower limit value, the process proceeds to step S122. In step S122, since the focus evaluation values A and B are both lower than or equal to the lower limit values, it is determined that the subject has low contrast, and the focusing lens is moved to a predetermined lens position.

Step S117 or step S121
If the process proceeds from step S118 to step S118, the closest peak is selected based on the focus evaluation value A or B that exceeds the lower limit value. For example, when the evaluation value is the curve L2 in FIG. 13, the lens position of the peak P11 is selected as the closest peak. In step S119, step S118
Move the focusing lens to the closest peak lens position selected in. After moving the lens, step S120
Then, the focus evaluation value after the lens movement is obtained, and it is reconfirmed that the focus state is achieved.

Next, in step S123 of FIG. 4, it is determined whether the AF mode setting of the camera is C-AF or S-AF. If it is determined to be C-AF in step S123, the process proceeds to step S130 in FIG. 5, and if it is determined to be S-AF, the process proceeds to step S124. First, the case of S-AF, that is, the case of proceeding from step S123 to step S124 will be described. In step S124, AF locking is performed at the in-focus position confirmed in step S120.

If AF locking is performed in step S124, a flag representing the release permission state is set in subsequent step S125. In step S126, it is determined whether or not the half-push switch 1163 is turned on. If the half-push state is maintained and YES is determined, the process proceeds to step S127, and if the half-push state is released and NO is determined, step S126 is performed. Proceed to S129. Steps S126 to S1
If the process proceeds to 27, it is determined in step S127 whether the full-press switch 1162 is on. If YES is determined in the step S127, the process proceeds to a step S128, the photographing operation is performed, and then the process returns to the step S123.
On the other hand, when the process proceeds from step S126 to step S129, it is determined in step S129 whether the AF mode setting is C-AF or S-AF. If it is determined to be C-AF in step S129, the process returns to step S123 and S-
If it is determined to be AF, the process returns to step S109 in FIG.

Next, a case where the camera is set to C-AF and the process proceeds from step S123 to step S130 of FIG. 5 will be described. In step S130, the timer 1127 of FIG. 1 starts counting. Next, in step S131, driving of the focusing lens is stopped. In step S132, it is determined whether the halfway press switch 1163 is turned on. If it is determined in step S132 that the push switch 1163 is turned on, the process proceeds to step S133, and if it is determined that the halfway press switch 1163 is not half pressed, the process proceeds to step S138.

When the process proceeds from step S132 to step S138 while the half-push switch 1163 remains off, the restart time interval and the reference change amount of the focus evaluation value at the time of restart are determined in step S138. Set according to shooting conditions. The conditions include those shown in (a) to (h) below, but the basic idea is to set the time interval and the reference in the condition that it is not necessary to frequently perform AF operation after restarting. Set a large amount of change.
As a result, it is possible to reduce battery consumption due to frequent restarts. As for the settings of (a) to (h), all of them may be adopted, or they may be arbitrarily selected and set.

(A) Shooting mode For example, in the distant view shooting mode and the person shooting mode where there is little or no movement of the subject, the peak position of the focus evaluation value changes very little, so the time interval and the reference change amount are set to the normal shooting mode. Set larger than. On the other hand, in sports shooting mode in which the subject moves quickly, the peak position of the focus evaluation value is likely to change significantly, so the time interval and reference change amount should be set smaller than in normal shooting mode, and restarting frequently occurs. To be seen. Further, in the close-up mode and the night view shooting mode, the time interval and the reference change amount are set to be larger than those in the normal shooting mode.

(B) Aperture value of the aperture 102 As the aperture diameter becomes smaller, that is, as the aperture value increases, the depth of field increases. Therefore, the larger the aperture value, the larger the time interval and the reference change amount are set. (c) Subject Brightness The smaller the subject brightness, the larger the time interval and the reference change amount are set. For example, when the subject brightness becomes smaller than a predetermined value, the time interval and the reference change amount are set to be large.

(D) Number of Recording Pixels When picking up an image pickup signal from the CCD 103, there are a case where the signals of all the pixels are taken out for image processing and a case where the pixels are thinned out and taken out. The number of recording pixels when the pixels are thinned out is smaller than the number of full-size pixels of the CCD 103. For example, the number of full-size pixels is 2048 x 1
If it is 536, the number of recorded pixels is reduced to 1 by thinning out.
024 x 768 (XGA size) or 640 x 48
It can be set to 0 (VGA size). Therefore, when the number of recording pixels with low definition is small, the time interval and the reference change amount are set to be large. In addition to the number of recorded pixels, the time interval and the reference change amount may be set according to the compression rate. For example, when the compression rate is high, the time interval and the reference change amount are set to be larger than when the compression rate is low.

(E) Battery voltage The lower the battery voltage, the larger the time interval and the reference change amount are set. For example, when the battery voltage becomes lower than a predetermined value, the time interval and the reference change amount are set large to suppress the battery consumption.

(F) Opening F value of the taking lens 101 When the zooming operation of the taking lens 101 is performed, the opening F value changes accordingly. Therefore, the larger the opening F value, the larger the time interval and the reference change amount are set. In case of single focus lens,
Since the open F value is different for each lens, the time interval and the reference change amount are changed according to the F value of the mounted lens. The same applies to a lens-integrated camera.

(G) Lens Focal Length The longer the focal length of the lens, the shorter the time interval. (h) The elapsed time measured by the timer 1127 is set to be larger as the elapsed time becomes longer.

The case where the time interval and the restart level are set according to the elapsed time of the timer 1127 will be described below as an example. FIG. 16 is a diagram showing the relationship between the elapsed time and the restart time interval. For example, when the elapsed time is less than 30 seconds, the time interval is set to 1 second, and when the elapsed time is 30 seconds or more and less than 60 seconds, the time interval is set to 2 seconds. Similarly, each time the elapsed time increases by 30 seconds, the time interval increases by 1 second. That is, the frequency of restarts decreases as the elapsed time increases. Further, FIG. 17 is a diagram showing a relationship between the elapsed time and the evaluation value change amount. The reference change amount Δa2 after the elapsed time t1 is set to be larger than the reference change amount Δa1 when the elapsed time is less than t1. Therefore, it is more difficult to restart after the elapsed time t1. As shown in FIG. 18, the reference change amount Δa (= Δa1, Δa2) is set to Δa = K1 · y with respect to the in-focus peak value y. K1 is a constant such that K1 <1.

Next, in step S139, it is determined whether or not restarting is necessary. An example of this determination method is shown in FIGS. In the example shown in FIG. 6, whether or not the restart is necessary is determined by whether or not the restart time interval Δt shown in FIG. 16 has elapsed. If it is determined in step S139 that Δt has not elapsed, the process returns to step S131, and if it is determined that Δt has elapsed, the process proceeds to step S140. In the example shown in FIG. 7, step S139 of FIG.
91 and step S1392. The focus evaluation value is constantly calculated based on the signal output from the CCD 103. In step S1391, the constantly calculated focus evaluation value is the reference change amount with respect to the focus evaluation value peak stored in the storage unit 1123. It is determined whether or not the change is Δa or more.

FIG. 19 is a diagram showing the change over time of the focus evaluation value, where the vertical axis is the focus evaluation value and the horizontal axis is the time. The lens is moved to the peak position of the focus evaluation value, and the lens drive is stopped at time t2. When the subject moves after time t2, the focus evaluation value changes like L21 and L22. If it is determined in step S1391 in FIG. 7 that the focus evaluation value has changed by the reference change amount Δa or more, the process proceeds to step S140 in FIG. 5, and if it is determined that the change is smaller than the reference change amount Δa, the process proceeds to step S1392. move on. In step S1392, it is determined whether or not the restart time interval Δt has passed, and if it is determined that it has passed, step S140.
If it is determined that the time has not passed, the process proceeds to step S13.
Return to 1.

FIG. 8 is a diagram showing a third example of the determination method, and step S139 consists of two processes of step S1393 and step S1394. Step S
In 1393, it is determined whether or not the restart time interval Δt has elapsed. If it is determined that it has elapsed, the process proceeds to step S1394, and if it is determined that it has not elapsed, step S131.
Return to. In step S1394, it is determined whether or not the current focus evaluation value has changed by the reference change amount Δa or more with respect to the focus evaluation value peak stored in the storage unit 1123. If it is determined in step S1394 that the change amount is equal to or greater than the reference change amount Δa, the process proceeds to step S140, and if it is determined that there is no change, the process returns to step S131. In the case of the example shown in FIG. 8, even if the restart time interval Δt has elapsed, restart is not performed unless the focus evaluation value changes by the reference change amount Δa or more. Therefore, as compared with the control method in which the restart is performed at each restart time interval Δt as in the case of FIG. 6, useless restart is reduced and battery consumption can be reduced. The reference change amount Δa used in steps S1391 and S139 is Δa1 until the elapsed time of the timer 1127 reaches t1 as shown in FIG. 17, and changes to Δa2 when the elapsed time reaches t1.

If it is determined in step S139 that a restart is necessary and the process proceeds to step S140, step S14
At 0, a well-known hill climbing focus operation is executed. Figure 20
FIG. 4 is a diagram for explaining the concept of a hill-climbing focusing operation, and L3 shows a focus evaluation value curve that will be obtained for a subject. x3 is the lens position at the start of hill climbing, and the focus evaluation value at that time is y3. When you start the focusing operation,
For example, the lens is moved to the close side to calculate the focus evaluation value.
The focus evaluation value may or may not be weighted by the lens position. In the case of FIG. 20, the obtained focus evaluation value is larger than the focus evaluation value at the lens position x3, so it is determined that the focus position P is on the close side. As described above, when the lens is moved in the direction in which the focus evaluation value increases, the focus evaluation value decreases when the lens passes the focus position P. At this point, the maximum value among the calculated focus evaluation values is y4, so the lens position P at that time is estimated to be the in-focus position, and the lens is moved to the position where the focus evaluation value is y4. .

In a succeeding step S141, it is determined whether or not the in-focus position is found and the in-focus is achieved. Step S
Since the in-focus position is not necessarily found by the hill-climbing operation of 140, if it is determined that the in-focus cannot be achieved, the process proceeds to step S142 to move the focusing lens to a predetermined position, and then returns to step S131. On the other hand, if in-focus is determined in step S141, step S
Return to 131. The focus evaluation value data obtained during the hill climbing focus operation is stored in the storage unit 1123 separately from the data at the time of whole-area sampling stored in step S113. The data obtained and stored by the hill climbing focusing operation is replaced with new data every time the hill climbing focusing operation is performed.

On the other hand, steps S132 to S1
If the process proceeds to 33, it is determined in step S133 whether the focus evaluation value is within the release permission range. FIG.
As shown in, the release permission range refers to a range from y−Δb to y + Δb with respect to the peak value y. Δb is Δb =
K2 · y is set. K2 is a constant such that K2 ≦ K1. Note that y−Δa or less and y + with respect to the peak value y.
The range of Δa or more is the range of the focus evaluation position where the later-described restart is performed.

If it is determined in step S133 that the focus evaluation value is within the release permission range, the process returns to step S124 in FIG. 4, and if it is determined that the focus evaluation value is outside the release permission range, step S13.
4, the same hill climbing operation as in step S140 described above is performed. In step S135, step S141
Similarly to the above, it is determined whether or not the focus can be achieved by the hill climbing operation. If it is determined to be in focus in step S135, the process proceeds to step S124 in FIG. 4, and if it is determined that the focus is not achieved, the process proceeds to step S136 to move the lens to a predetermined position. Then, it progresses to step S124 of FIG.

In the above-described embodiment, the restart is performed when the focus evaluation value deviates from the range of the predetermined width 2Δa around the evaluation value peak y as shown in FIG. This is because AF is restarted when the composition is changed by panning the camera. However, in the direction in which the evaluation value is not large, the restart may be made only when the evaluation value becomes smaller than the level of y-Δa. The same applies to the release permission range, and the y-Δb level may be set as the release permission level, and the release may be permitted when the focus evaluation value is equal to or higher than the level.

As described above, in the present embodiment, the noise level due to the influence of the dark current or the like is calculated at the focus evaluation value stage, and the noise level is subtracted from the focus evaluation value based on the image pickup signal of the CCD 1123 for focusing operation. It was used as the focus evaluation value at that time. As a result, stable focusing operation can be performed even for a subject with low contrast.

Although the noise level is measured when the power is turned on in the above-mentioned embodiment, it may be measured before or after the photographing. Also, the noise level is measured at the time of adjustment after the camera is assembled, and the measured value is stored in the storage unit 1.
You may make it memorize | store in 123. In this case, the noise level is read from the storage unit 1123 when the focus evaluation value is calculated, and the one obtained by subtracting the noise level from the focus evaluation value is used for the focusing operation. Further, instead of correcting the focus evaluation value with the noise level as described above, the predetermined width 2Δa and the width Δb of the release permission range, which are the restart conditions, may be corrected with the noise level. That is, Δa
-(Noise level) and Δb- (noise level).

In the above-described embodiments, the interchangeable lens type digital camera has been described as an example, but a lens integrated type digital camera may be used. Further, the taking lens is not limited to the zoom lens, and may be a single focus lens. Furthermore, the present invention can be applied to a silver salt film camera as long as the subject is imaged by the image sensor and AF is performed by the contrast method.

In the correspondence between the embodiments described above and the elements in the claims, the driver 113 for driving the AF calculation unit 1126 and the taking lens 101 is a focusing operation means, and the CPU 112 is a noise level calculation means, a focusing operation. The operation control unit, the focus evaluation value correction unit, the reference value correction unit, and the noise calculation control unit are connected to the bandpass filter 1124.
A and 1124B are filter circuits each having a reference change amount Δa (Δ
a1 and Δa2) respectively constitute reference focus evaluation values.

[0053]

As described above, according to the present invention, the noise level of the focus evaluation value generated by the dark current of the image sensor or the like is calculated, and the camera is calculated based on the noise level, the focus evaluation value and the reference focus evaluation value. Since the necessity of the operation is determined, the influence of the noise level on the determination can be removed, and more appropriate determination can be performed. For example, when it is determined whether or not the focusing operation is necessary, a more stable focusing operation can be performed.

[Brief description of drawings]

FIG. 1 is a functional block diagram of an AF digital camera according to the present invention.

FIG. 2 is a flowchart showing the operation of the camera.

FIG. 3 is a flowchart showing a process following the flowchart of FIG.

FIG. 4 is a flowchart showing a process following the flowchart of FIG.

5 is a flowchart showing a series of processing when it is determined to be C-AF in step S125 of FIG.

FIG. 6 is a diagram showing a first example of a specific process of step S139.

FIG. 7 is a diagram showing a second example of a specific process of step S139.

FIG. 8 is a diagram showing a third example of a specific process of step S139.

9 is a flowchart showing a first example of noise measurement in step S100 shown in FIG.

10 is a flowchart showing a second example of noise measurement in step S100 shown in FIG.

FIG. 11: Focus evaluation value curve L0 and noise level Δ
It is a figure which shows S.

FIG. 12 is a diagram showing a first example of a weighting curve.

FIG. 13 is a diagram showing focus evaluation value curves before and after weighting processing.

FIG. 14 is a diagram showing a weighting curve in the distant view shooting mode.

FIG. 15 is a diagram showing a weighting curve in the flash photography mode.

FIG. 16 is a diagram showing a relationship between an elapsed time and a restart time interval.

FIG. 17 is a diagram showing a relationship between an elapsed time and an evaluation value change amount.

FIG. 18 is a diagram illustrating a release permission range.

FIG. 19 is a diagram showing a change over time in a focus evaluation value.

FIG. 20 is a diagram illustrating the concept of a mountain climbing focusing operation.

[Explanation of symbols]

101 shooting lens 102 aperture 103 CCD 104 Analog signal processing circuit 106 digital signal processing circuit 112 CPU 113-115, 118 driver 116 Operation part 119 battery 120 Voltage detector 135 A / D converter 1161 power switch 1162 full-press switch 1163 Half-press switch 1164 Setting button 1123 storage unit 1124A, 1124B bandpass filter 1125A, 1125B Evaluation value calculation unit 1126 AF calculation unit 1127 timer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideomi Hibino             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon (72) Inventor Toshiaki Maeda             Marunouchi 3 2-3 No. 3 shares, Chiyoda-ku, Tokyo             Ceremony Company Nikon (72) Inventor Masaru Ota             Tokyo Stock Exchange 1-325, Futaba 1-32             Company Nikon technical workshop F-term (reference) 2H011 AA03 BA31 BB03 DA00                 2H051 AA08 BA47 EA28                 5C022 AA13 AB03 AB12 AB15 AB20                       AB29 AB30 AB40 AB67 AC03                       AC32 AC42 AC54 AC73 AC74

Claims (11)

[Claims] 1. An image pickup device for picking up a subject image through a taking lens, an evaluation value calculation means for calculating a focus evaluation value based on an image pickup signal output from the image pickup device, and an evaluation value calculation means for calculating the focus evaluation value. A noise level calculation unit that calculates a noise level included in the focus evaluation value, and a determination unit that determines whether or not a camera operation is necessary based on the focus evaluation value, the noise level, and a predetermined reference focus evaluation value. A camera characterized by that. 2. An image pickup device for picking up a subject image through a taking lens, a plurality of filter circuits that pass different predetermined spatial frequency bands of image pickup signals output from the image pickup device, and one of the plurality of filter circuits. Evaluation value calculation means for calculating a focus evaluation value of the photographing lens based on a signal passing through one; noise level calculation means for calculating a noise level included in the focus evaluation value for each filter circuit; A camera, comprising: a determination unit that determines whether or not a camera operation is required based on an evaluation value, the noise level, and a predetermined reference focus evaluation value. 3. The camera according to claim 1, wherein the noise level calculation means calculates the noise level every time the camera power is turned on. 4. The camera according to claim 1, wherein the noise level calculating means calculates the noise level either before or after a shooting operation. 5. The camera according to claim 1, wherein a shutter that shields the image pickup device from the photographing lens, and noise that causes the noise level calculation unit to calculate a noise level by closing the shutter. A camera comprising an arithmetic control unit. 6. An image pickup device for picking up a subject image through a taking lens, an evaluation value calculation means for calculating a focus evaluation value based on an image pickup signal output from the image pickup device, and a focus evaluation value specific to the image pickup device. A noise level is stored in advance; and a determination unit that determines whether or not a camera operation is necessary based on the focus evaluation value, the focus evaluation value noise level, and a predetermined reference focus evaluation value. A camera to do. 7. An image pickup device for picking up a subject image through a taking lens, a plurality of filter circuits that pass different predetermined spatial frequency bands of image pickup signals output from the image pickup device, and one of the plurality of filter circuits. Evaluation value calculation means for calculating a focus evaluation value representing a focus adjustment state of the photographing lens based on a signal passing through one, and focus evaluation value noise level unique to a combination of the image sensor and each filter circuit And a determination unit that determines whether or not a camera operation is necessary based on the focus evaluation value, the focus evaluation value noise level, and a predetermined reference focus evaluation value. . 8. The camera according to claim 1, further comprising a focus evaluation value correction unit that corrects the focus evaluation value based on the noise level, and the determination unit includes the reference focus evaluation value. And a camera for determining whether or not a camera operation is necessary based on the focus evaluation value corrected by the focus evaluation value correction means. 9. The camera according to claim 1, further comprising a reference value correction unit that corrects the reference focus evaluation value based on the noise level, the determination unit including the focus evaluation value and the focus evaluation value. A camera, characterized in that the necessity of camera operation is determined based on a reference focus evaluation value corrected by the reference value correction means. 10. The camera according to claim 1, wherein the determination unit determines whether or not a release operation is possible. 11. The camera according to claim 1, wherein the determination unit determines whether or not a focusing operation of the photographing lens is necessary, and the determination unit determines the focus evaluation value based on the focus evaluation value. Focusing operation means for performing the focusing operation of the photographing lens, and focusing operation control means for causing the focusing operation means to perform the focusing operation when the determination means determines that the focusing operation is necessary. A camera characterized by that.