JP2003241071A - Imaging device and automatic focusing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately focus at any time, without being influenced by an environment. <P>SOLUTION: The device is provided with a CPU 22 for moving a photographic lens 12 by the drive of a motor 11, obtaining the focused object image, calculating the focusing estimation value for estimating the focusing state, and then, judging whether or not the focal position of the photographic lens is appropriate based on whether or not a difference between the photographic lens position where the maximum value is obtained out of a series of focusing estimation values and the photographic lens position where the minimum value is obtained is above a prescribed value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as a digital camera having a contrast type automatic focusing function and an automatic focusing method performed by the imaging device.

[0002]

2. Description of the Related Art In recent years, with the spread of personal computers, a digital still camera (hereinafter referred to as "digital camera") that records an image in a digital data state on a memory card enclosing a non-volatile semiconductor memory instead of a silver salt film. (Referred to as) is widely spread.

In this type of digital camera, almost all models have an automatic focusing function, and many of them adopt the contrast method. In this contrast type automatic focusing, a CCD (Charge C
Image data of the area where automatic focusing is performed is taken out from an image sensor such as an open device (charge coupled device), and high-pass filtering is performed only in the horizontal direction or in both the horizontal and vertical directions to extract high frequency components of the spatial frequency. The sum of the absolute values is used as an AF (automatic focusing) evaluation value.

Since the above-mentioned AF evaluation value becomes maximum when the focusing lens for performing the focusing operation is at the accurate focusing position, the AF is performed while moving the focusing lens for each field for obtaining image data for one screen. By comparing the evaluation values, a predetermined focus range is scanned, and finally the focus lens is moved to a position where the maximum value is obtained, and a series of automatic focusing operations are completed.

In actual operation, the shutter time lag must be set until the automatic focusing operation is started after the shutter button of the camera is half-pressed and the shooting operation is not immediately started when the shutter button is fully pressed. Therefore, in order to shorten the time required to obtain the in-focus state, stop scanning at the time when the maximum AF evaluation value is determined, and place the focus lens at the position where the maximum evaluation value will be reached. Will be moved.

There are various methods for determining the maximum value of the AF evaluation value, but as the position of the focus lens moves, A
In many cases, the fact that the AF evaluation value changes from increasing to decreasing is used before and after the position where the maximum F evaluation value is obtained.

FIG. 8 exemplifies the process of the change of the AF evaluation value generally obtained with the movement of the position of the focus lens. The change of the AF evaluation value becomes small around the original focus position P. AF at the focus position P
It can be seen that the evaluation value has changed from increasing to decreasing.

Therefore, by detecting the peak position of the AF evaluation value in this way, it is possible to obtain accurate focusing relatively easily.

[0009]

However, when the image pickup device is driven to process the image data captured in each field to measure the AF evaluation value, that is, the strength of the contrast, the correct focus position is obtained. , When the noise component randomly included in each field is large, when the environment is such that flicker (flickering of the image) occurs depending on the type of light source, or when some object instantaneously crosses the front of the subject, etc. Then, the AF evaluation value may change greatly in field units.

In such a case, when the AF evaluation values are compared while moving the focus lens, it is erroneously recognized whether the peak of the AF evaluation value has passed due to the blurring of the AF evaluation value obtained for each field. In addition, since a noise component may be added, the maximum or minimum value of the AF evaluation value may be obtained at the position of the focus lens far from the position predicted from the distribution of the AF evaluation value. It not only takes a long time to obtain, but also becomes a factor that deteriorates the accuracy of automatic focusing.

The present invention has been made in view of the above situation, and an object thereof is an image pickup apparatus capable of always obtaining an accurate focus regardless of the environment and its automatic focus. To provide a method.

[0012]

The invention according to claim 1 is
An image pickup unit for picking up and outputting a subject image, a lens driving unit for sequentially driving the photographing lens, and a photographing lens sequentially driven by the lens driving unit are made incident on the image pickup unit and sequentially outputted from the image pickup unit. When the maximum value is obtained in the series of focus evaluation values sequentially obtained by the evaluation value calculation means for sequentially calculating the focus evaluation value for evaluating the focus state based on the subject image Focus determination means for determining whether or not the focus position of the photographing lens is appropriate by determining whether or not the difference between the photographing lens position and the photographing lens position when the minimum value is obtained is greater than or equal to a predetermined value. And is provided.

With this structure, the focus evaluation is performed only when the photographing lens position when the maximum focus evaluation value is obtained and the photographing lens position when the minimum focus evaluation value is obtained are sufficiently separated from each other. Since the lens position when the maximum value is obtained is determined to be the in-focus position, the probability of making an incorrect in-focus determination for a subject with low contrast can be reduced to obtain accurate in-focus. It will be possible.

According to a second aspect of the present invention, in the first aspect of the present invention, the focus determination means determines whether or not there is a large difference between the maximum value and the minimum value of the focus evaluation values. It is characterized in that it comprises means for judging whether or not the in-focus position of the taking lens is suitable by judging whether or not.

With such a configuration, in addition to the operation of the invention described in claim 1, if there is no large difference between the maximum value and the minimum value of the focus evaluation value, it is determined that focus is impossible. Therefore, the probability of making an incorrect focus determination can be further reduced.

According to a third aspect of the present invention, the image pickup is performed via an image pickup means for picking up and outputting a subject image, a lens driving means for sequentially driving the photographing lenses, and a photographing lens sequentially driven by the lens driving means. Evaluation value calculation means for sequentially calculating a focus evaluation value for evaluating a focus state based on a subject image incident on the means and sequentially output from the image pickup means, and a series of in-focus points sequentially obtained by the evaluation value calculation means. It is determined whether or not the focus evaluation value at the lens position at which the maximum value or the minimum value is obtained from the evaluation value and the lens position that is apart from the photographing lens position by a predetermined value or more is significantly different from the maximum value or the minimum value. Thus, a focus determination means for determining the suitability of the focus position of the photographing lens is provided.

With this structure, the photographing lens position when the maximum focus evaluation value is obtained and the photographing lens position when the minimum focus evaluation value is obtained are sufficiently separated from each other, and the maximum or minimum value is obtained. When it is possible to determine that the contrast is sufficient considering other values, the lens position when the maximum focus evaluation value is obtained is determined to be the in-focus position. It is possible to obtain an accurate focus by reducing the probability of making an incorrect focus determination.

According to a fourth aspect of the present invention, an image pickup process for picking up and outputting a subject image, a lens driving process for sequentially driving the photographing lens, and a photographing lens sequentially driven in the lens driving process are used for the image pickup. An evaluation value calculation step that sequentially calculates a focus evaluation value that evaluates the focus state based on the subject image that is sequentially output in the step, and the maximum value among the series of focus evaluation values that are sequentially obtained in this evaluation value calculation step. Judgment is made as to whether the focus position of the photographing lens is appropriate or not by judging whether or not the difference between the photographing lens position when the above is obtained and the photographing lens position when the minimum value is obtained is not less than a predetermined value. And a focus determination step to perform.

According to such a method, the focus evaluation is performed only when the photographing lens position when the maximum focusing evaluation value is obtained and the photographing lens position when the minimum focusing evaluation value is obtained are sufficiently separated from each other. Since the lens position when the maximum value is obtained is determined to be the in-focus position, the probability of making an incorrect in-focus determination for a subject with low contrast is reduced to obtain accurate in-focus. Is possible.

According to a fifth aspect of the present invention, an image pickup step for picking up and outputting a subject image, a lens driving step for sequentially driving the photographing lenses, and the image pickup through the photographing lenses sequentially driven in the lens driving step. An evaluation value calculation step that sequentially calculates a focus evaluation value that evaluates the focus state based on the subject image that is sequentially output in the step, and the maximum value among the series of focus evaluation values that are sequentially obtained in this evaluation value calculation step. Alternatively, by determining whether or not the focus evaluation value of the lens position which is apart from the photographing lens position when the minimum value is obtained and the predetermined value or more is greatly different from the maximum value or the minimum value, And a focus determination step of determining the suitability of the focus position.

With this method, the taking lens position when the maximum focus evaluation value is obtained and the taking lens position when the minimum focus value is obtained are sufficiently separated from each other, and the maximum or minimum value is obtained. When it is possible to determine that the contrast is sufficient considering other values, the lens position when the maximum focus evaluation value is obtained is determined to be the in-focus position. It is possible to obtain a correct focus by reducing the probability of making an incorrect focus determination.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment in which the present invention is applied to a digital camera having a contrast type automatic focusing function will be described below with reference to the drawings. .

FIG. 1 shows the circuit configuration thereof, and 10 is a digital camera. The digital camera 10 can be set by switching between a recording mode and a reproduction mode. In the monitoring mode of the recording mode, the focus lens 12 whose focus position is moved by driving the motor 11 is moved.
The CCD 13 which is an image pickup element disposed behind the photographing optical axis of the lens optical system including the timing generator (TG) 1
4. The scanning is driven by the vertical driver 15 and the photoelectric conversion output corresponding to the optical image formed at a constant cycle is output for one screen.

This photoelectric conversion output is appropriately adjusted in gain for each of the RGB primary color components in the state of an analog value signal, and then sample-held by a sample-hold circuit (S / H) 16 to obtain an A / D converter 17. Is converted into digital data by the color process circuit 18, and the color process circuit 18 performs color process processing including pixel interpolation processing to generate a digital value luminance signal Y and color difference signals Cb and Cr, and DMA (Dir
ect Memory Access) controller 19
Is output to.

The DMA controller 19 has a luminance signal Y and color difference signals Cb and C output from the color process circuit 18.
Similarly, r is once written in the buffer inside the DMA controller 19 using the composite synchronizing signal, the memory write enable signal, and the clock signal from the color process circuit 18, and is DMA-transferred to the DRAM 21 via the DRAM interface (I / F) 20. Do.

The CPU 22 controls the D of the luminance and color difference signals.
After the completion of the DMA transfer to the RAM 21, the luminance and color difference signals are sent to the DRAM 2 via the DRAM interface 20.
Read from 1 and VR via VRAM controller 23
Write to AM24.

The digital video encoder 25 outputs the luminance and color difference signals to the VRAM controller 23 through the VRAM controller 23.
It periodically reads from the RAM 24, generates a video signal based on these data, and outputs it to the display unit 26.

The display unit 26 is composed of, for example, a color liquid crystal display panel with a backlight and a drive circuit for the same.
It is disposed on the back side of the digital camera 10 and is in an EVF (Electronic View Fi) in the recording mode.
nder: electronic viewfinder), and displays an image based on the image information fetched from the VRAM controller 23 at that time by performing a display based on the video signal from the digital video encoder 25. Become.

Then, in the state where the image at that time is displayed as the monitor image in real time on the display unit 26 in this way, the shutters in the plurality of keys constituting the key input unit 27 are recorded at the timing when recording and saving are desired. When the key is operated, a trigger signal is generated.

In response to this trigger signal, the CPU 22 stops the path from the CCD 13 to the DRAM 21 immediately after the completion of the DMA transfer of the luminance and color difference signals for one screen captured from the CCD 13 at that time to the DRAM 21. ,
Transition to the state of record preservation.

In this state of record storage, the CPU 22
The luminance and color difference signals for one frame written in the RAM 21 are passed through the DRAM interface 20 to Y, C
Each component of b and Cr is read out in a unit called a basic block of vertical 8 pixels × horizontal 8 pixels, written in a JPEG circuit 28, and ADCT (Ad
adaptive Discrete Cosine Tr
data is compressed by a process such as Huffman coding which is an entropy coding method, and the obtained code data is read from the JPEG circuit 28 as a data file of one image, and the storage medium of the digital camera 10 Is written in the flash memory 29, which is a non-volatile memory, which is detachably attached.

Then, with the compression processing of the luminance and color difference signals for one frame and the completion of writing all the compressed data to the flash memory 29, the CPU 22 again causes the CCD 13 to operate.
To the DRAM 21 again.

At this time, the CPU 22 also creates image data in which the number of constituent pixels of the original image data is greatly thinned, and the created image data is associated with the original image data as a preview image also called a thumbnail image and is associated with the flash memory. 29.

The key input section 27 has a recording (REC) mode and a reproducing (PL) mode in addition to the shutter key described above.
AY) recording / re-mode switching key for switching between modes, "menu" key for displaying various menu items, cursor keys for selecting up / down / left / right directions for selecting images and modes, and specifying menu selection items It is composed of an "Enter" key or the like for determining the content, and a signal associated with the key operation is directly sent to the CPU 22.

It is assumed that the shutter key is operated by two-step pressing operation, and the AE (automatic exposure) and AF (automatic focusing) operations are performed in the first-step pressing operation, that is, the so-called "half-press" state. It is assumed that the value is executed and the value is locked, and further, the image capturing operation based on each value of the above AE and AF is executed in the state of the pressing operation in the second stage, so-called "full pressing".

In the reproduction mode, the CPU 22 makes CC
The path from D13 to the DRAM 21 is stopped, and the CPU 22 reads out the code data for one specific frame from the flash memory 29 and writes it in the JPEG circuit 28 in response to the operation of the image selection key of the key input unit 27, and the JPEG circuit 2
The luminance and color difference signals for one frame are expanded and stored in the VRAM 24 via the VRAM controller 23 in a basic block unit of vertical 8 pixels × horizontal 8 pixels obtained by performing decompression processing in 8.

Then, the digital video encoder 25
Generates a video signal based on the luminance and color difference signals for one frame which are expanded and stored in the VRAM 24, and the display unit 2
Display with 6.

Next, the operation of the above embodiment will be described. FIG. 2 shows a case where automatic focusing is performed in response to a half-press operation of the shutter key from the monitoring state in the recording mode,
It mainly illustrates the processing contents by the CPU 22.

In the figure, at the beginning of the process, first, the drive position of the focus lens 12 at that time is acquired from the motor 11 (step A01), and the CCD 13 at that time is obtained.
The contrast value of the image data captured by the
It is calculated and obtained from the contents stored in No. 21, and is held as it is as the focus evaluation value (step A02).

Then, only when the acquired focus evaluation value is larger than the maximum value or smaller than the minimum focus evaluation value acquired so far, this is newly set as the maximum value or the minimum value at that time. The update is set together with the lens position (step A03).

At the same time, when the update setting is actually performed, the ratio "minimum value / maximum value" between the maximum value and the minimum value of the focus evaluation value and the focus when the maximum value is obtained. The absolute value of the difference between the drive position of the lens 12 and the drive position of the focus lens 12 when the minimum value is obtained is calculated and held at the same time.

Further, an increase / decrease pattern consisting of the focus evaluation value acquired in step A02 and a series of focus evaluation values acquired before that is analyzed and updated and set (step A0).
4).

Next, it is determined whether or not the end point of the moving range of the focus lens 12 has been reached (step A0).
5). If it is determined that the end point has not been reached, whether or not the peak (maximum value) of the focus evaluation value has been passed through the increase / decrease pattern of the focus evaluation value updated and set in step A04 is continuously determined, for example, twice. Then, it is determined whether or not the focus evaluation value has decreased twice in a row after the focus evaluation value has increased (step A10).

If it is determined that the peak has not passed, whether or not there is a turning-back condition for switching the moving direction of the focus lens 12 according to the increase / decrease pattern of the same focus evaluation value, for example, the focus evaluation value is determined. It is judged whether or not it has decreased four times in a row (step A11).

If it is determined that the conditions for folding back are not satisfied, the motor 11 is moved again by one step without changing the driving direction of the focus lens 12 (step A14), and then the processing from step A01 is performed. Repeat.

When it is determined in step A11 that the increase / decrease pattern of the focus evaluation value is the return condition, the return end condition is determined depending on whether or not the drive direction of the focus lens 12 has already been turned back. It is determined whether or not (step A12).

If it is determined that the return end condition is not satisfied, the direction in which the focus lens 12 is driven by the motor 11 is switched to the opposite direction, and the motor 11 is moved by one step (step A13). The processing from step A01 is repeated.

If it is determined in step A05 that the end point of the moving range of the focus lens 12 has been reached, or if it is determined in step A10 that the peak focus evaluation value has passed, the above steps are performed. Depending on whether the ratio “minimum value / maximum value” of the maximum value and the minimum value in the series of focus evaluation values obtained up to that time calculated in A03 is less than or equal to a preset reference value, It is determined whether the focus evaluation values are distributed over a sufficiently wide range (step A06).

Here, when it is determined that the ratio of the maximum value to the minimum value in the focus evaluation values is less than or equal to a preset reference value, and therefore the focus evaluation values are distributed over a sufficiently wide range, Then, the focus lens 1 when the maximum focus evaluation value calculated in step A03 is obtained
Depending on whether or not the absolute value of the difference between the drive position of 2 and the drive position of the focus lens 12 when the minimum focus evaluation value is obtained is also a preset reference value or more,
It is determined whether or not the maximum focus evaluation value is at a sufficiently reliable and accurate focus position (step A).
07).

FIG. 3 shows an example of the change characteristic of the focus evaluation value accompanying the driving of the focus lens, and each focus is changed along the ideal change characteristic I of the focus evaluation value shown by the broken line. It represents a state in which the evaluation values are distributed with an appropriate error.

When such a focus evaluation value distribution is obtained, the ratio "minimum value / maximum value" between the maximum value and the minimum value in the focus evaluation values determined in step A06 is set in advance. The focus lens 12 when it becomes smaller than the reference value and the maximum focus evaluation value is obtained as shown in FIG.
The absolute value ΔL of the difference between the driving position of the focus lens 12 and the driving position of the focus lens 12 when the minimum focus evaluation value is obtained is larger than a preset reference value.

Therefore, in step A07, this point is determined, and the motor 11 causes the focus lens 1 to move.
2 is moved to the drive position when the maximum focus evaluation value is obtained (step A08), and the automatic focus processing according to FIG. 2 is completed.

In step A06, it is determined that the ratio "minimum value / maximum value" of the maximum value and the minimum value in the series of focus evaluation values obtained up to that time is larger than the preset reference value. Or the difference between the drive position of the focus lens 12 when the maximum focus evaluation value is obtained in step A07 and the drive position of the focus lens 12 when the minimum focus evaluation value is obtained. If it is determined that the absolute value is smaller than the preset reference value, or if it is determined that the return end condition is satisfied in step A12, it is determined that accurate focusing cannot be obtained, and it is dealt with. The focus lens 12 is moved by the motor 11 to the lens position, for example, the hyperfocal position (step A09), and the automatic focusing process according to FIG. 2 is completed.

FIG. 4 shows an example of the change characteristic of the focus evaluation value due to the driving of the focus lens, which is distributed without obtaining the proper change characteristic of the focus evaluation value. Is represented.

When such a focus evaluation value distribution is obtained, the ratio "minimum value / maximum value" between the maximum value and the minimum value in the focus evaluation values determined in step A06 is temporarily set in advance. Even if it becomes smaller than the reference value, as shown in the figure,
The absolute value ΔL of the difference between the drive position of the focus lens 12 when the maximum focus evaluation value is obtained and the drive position of the focus lens 12 when the minimum focus evaluation value is obtained is preset. It does not exceed the standard value.

Therefore, in step A07, this point is determined, and the flow advances to step A09 to focus by the motor 11 so as to reach the hyperfocal position indicated by II in the figure, assuming that accurate focusing cannot be obtained. The lens 12 is moved.

As described above, the drive position of the focus lens 12 when the maximum focus evaluation value calculated from the contrast is obtained and the drive position of the focus lens 12 when the minimum value is obtained are sufficiently separated. When the maximum focus evaluation value is obtained, the lens position is determined to be the focus position, so the probability of making an incorrect focus determination for a subject with low contrast is reduced, and It is possible to obtain a proper focus.

Further, in particular, prior to the determination at the step A07, the ratio between the maximum value and the minimum value of the focus evaluation value is compared with the reference value at the step A06, so that the step A0 is performed.
It is determined whether or not to make the determination of 7. By preliminarily determining the conditions in which accurate focusing cannot be obtained in this way, the time required for automatic focusing can be shortened as a result.

(Second Embodiment) A second embodiment in which the present invention is applied to a digital camera having a contrast type automatic focusing function will be described below with reference to the drawings.

The circuit configuration is shown in FIG.
Since they are basically the same as those shown in FIG. 3, the same parts are designated by the same reference numerals, and the illustration and description thereof will be omitted.

Next, the operation of the above embodiment will be described. FIG. 5 shows a case where automatic focusing is performed in response to a half-press operation of the shutter key from the monitoring state in the recording mode.
It mainly illustrates the processing contents by the CPU 22.

In the figure, at the beginning of the process, first, the drive position of the focus lens 12 at that time is acquired from the motor 11 (step B01), and at that time, the CCD 13
The contrast value of the image data captured by the
It is calculated and obtained from the contents stored in No. 21, and is held as it is as the focus evaluation value (step B02).

Next, only when the acquired focus evaluation value is larger than the maximum focus evaluation value acquired so far, this is newly set as the maximum value and updated with the lens position at that time (step B03). .

At the same time, 10 pieces of data from the smallest focus evaluation value acquired so far are updated and set as the minimum value candidate together with their rank and lens position (step B04).

Furthermore, an increase / decrease pattern consisting of the focus evaluation value acquired in step B02 and a series of focus evaluation values acquired before that is analyzed and updated and set (step B0).
5).

Next, it is determined whether or not the end point of the moving range of the focus lens 12 has been reached (step B0).
6). If it is determined that the end point has not been reached, then whether or not the peak (maximum value) of the focus evaluation value has been passed through the increase / decrease pattern of the focus evaluation value updated and set in step B05 is continuously determined, for example, twice. Then, after the focus evaluation value has increased, it is determined whether or not the focus evaluation value has decreased twice consecutively (step B13).

When it is determined that the peak has not passed, whether or not there is a turnback condition for switching the moving direction of the focus lens 12 according to the increase / decrease pattern of the same focus evaluation value, for example, the focus evaluation value is It is judged whether or not it has decreased four times in a row (step B14).

If it is determined that the conditions for folding back are not satisfied, the motor 11 is moved again by one step without changing the driving direction of the focus lens 12 (step B17), and then the processing from step B01 is performed. Repeat.

When it is determined in step B14 that the increase / decrease pattern of the focus evaluation value is the return condition, the return end condition is determined by whether or not the drive direction of the focus lens 12 has already been turned back. It is determined whether or not (step B15).

If it is determined that the conditions for ending the loopback are not satisfied, the driving direction of the focus lens 12 by the motor 11 is switched to the opposite direction, and is moved by one step (step B16). The processing from step B01 is repeated.

If it is determined in step B06 that the end point of the moving range of the focus lens 12 has been reached, or if it is determined in step B13 that the peak focus evaluation value has passed, the above steps are performed. After confirming that the minimum value candidate in the focus evaluation values updated and set in B04 still exists (step B07), the one with the smallest focus evaluation value among them is updated and set in step B03. A ratio "minimum value / maximum value" between the maximum value and the minimum value is calculated from the same maximum value, and the focus evaluation value is in a sufficiently wide range depending on whether the value is less than or equal to a preset reference value. It is determined whether or not it is distributed over (step B08).

Here, if it is determined that the ratio of the maximum value to the minimum value in the focus evaluation values is less than or equal to a preset reference value, and therefore the focus evaluation values are distributed over a sufficiently wide range, Next, the absolute value of the difference between the drive position of the focus lens 12 when the maximum focus evaluation value is obtained and the drive position of the focus lens 12 when the minimum focus evaluation value is obtained is calculated. , Whether or not the value is greater than or equal to a preset reference value, whether or not the maximum value of the focus evaluation value is at a sufficiently reliable and accurate focus position. It is determined (step B09).

If the absolute value of the lens position difference is smaller than the reference value, it is determined that the minimum value of the focus evaluation values adopted in the inspection includes a large error, and the result is the same. The minimum value candidate of the focus evaluation value is deleted, and the remaining minimum value candidates are updated and set so as to be moved up (step B11), and the processing from step B07 is repeatedly executed.

If it is determined in step B09 that the absolute value of the lens position difference is greater than or equal to the reference value,
The focus lens 12 is moved by the motor 11 to the drive position when the maximum focus evaluation value is obtained (step B10), and the automatic focus processing according to FIG. 5 is completed.

When it is determined in step B07 that the minimum value candidate in the focus evaluation value no longer exists, or in step B08, the ratio of the maximum value to the minimum value in the focus evaluation value "minimum value / minimum value / When it is determined that the “maximum value” is larger than the preset reference value, or the above step B1
If it is judged that the condition is the end condition for loopback in 5,
Assuming that accurate focusing cannot be obtained, the focus lens 12 is moved by the motor 11 so as to reach a lens position corresponding to that, for example, a hyperfocal position (step B1).
2) Then, the automatic focusing processing according to FIG. 5 is completed.

FIG. 6 shows an example of the change characteristic of the focus evaluation value with the driving of the focus lens. Except for a part, the change of the ideal focus evaluation value shown by the broken line as a whole. This shows a state in which the focus evaluation values are distributed with an appropriate error along the characteristic III.

When a series of such focus evaluation value distributions are obtained, the maximum value d5 of the focus evaluation values is updated and set in step B03, while the value is set as the minimum value candidate in step B04. In ascending order of d4, d1, d1
Data of 10 focusing evaluation values such as 1, d2, d9, d12, ...

FIG. 7 shows the flow of processing contents for each of the minimum value candidates. The smallest focus evaluation value d4 among these minimum value candidates is first selected as the minimum value candidate in step B07, In B08, it is determined that the ratio with the maximum value is smaller than the reference value, but the following step B
At 09, it is determined that the corresponding lens position difference ΔL has not reached the reference value, and at step B11 the difference is deleted and the ranks of other candidates are advanced.

The next minimum value candidate d1 is selected in step B07, and it is determined in step B08 that the ratio to the maximum value is smaller than the reference value, and then the following step B0.
At 9, it is determined that the corresponding lens position difference ΔL is greater than or equal to the reference value.

Therefore, the minimum value candidate d1 is judged as the correct minimum focus evaluation value, and in step B10, the focus lens is driven by the motor 11 based on the maximum focus evaluation value d5. The drive positions of 12 are controlled to move.

According to the first embodiment, the difference between the lens position of the focus lens 12 where the maximum focus evaluation value is obtained and the same lens position where the minimum focus evaluation value is obtained is not sufficiently separated. When it is judged, it is not known which of the maximum value and the minimum value is incorrect data.Therefore, if at least the maximum value is incorrect data, there is no choice but to process it as if proper focus cannot be obtained. When only the minimum value is incorrect data, it is determined that an error occurs even though the maximum value is correct data, and proper focusing cannot be obtained.

On the other hand, in the second embodiment, a focus evaluation value that is judged to be sufficient in contrast is taken into consideration by taking into consideration other values that are substantially the same but other than the minimum value. Since the focus is determined, even if the minimum value of the focus evaluation value is incorrect, if the maximum value is correct data, an appropriate focus can be obtained without causing an error. Therefore, the possibility of obtaining accurate focus can be increased.

In the second embodiment, the lens position at which the minimum value candidate and the maximum value are obtained after determining whether the ratio of the sequentially selected minimum value candidate and maximum value is less than or equal to the reference value. Whether or not the in-focus position is appropriate is determined by determining whether or not the difference is greater than or equal to the reference value (steps B07 to B
09, B11), first, the focus evaluation value of the lens position that is more than the reference value away from the lens position where the maximum value is obtained is extracted, and it is determined whether the ratio between the focus evaluation value and the maximum value is the reference value or less. The appropriateness of the in-focus position may be determined by the determination.

In the second embodiment, the minimum focus evaluation value candidate is changed. However, the minimum focus evaluation value may be correct and the maximum focus evaluation value may not be correct. In this case, by changing the maximum value candidate instead of the minimum focus evaluation value, the possibility of obtaining accurate focus can be further increased. In this case, as a result, a lens position is obtained at a lens position at which the minimum value is obtained and at a lens position separated by a reference value or more, and a ratio between the minimum value and the reference value is equal to or less than the reference value (maximum value candidate). The position is determined as the focus lens position.

Further, in each of the first and second embodiments described above, the present invention is applied to a digital still camera. However, the present invention is not limited to this, and a passive method including a contrast method is also used. It is needless to say that the present invention can be applied to, for example, a camera unit provided in a mobile phone or a personal computer, a video tape recorder with a built-in camera, or the like as long as it is an image pickup apparatus that performs the automatic focusing operation of the system. is there.

In addition, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the invention.

Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiments, at least one of the problems described in the section of the problem to be solved by the invention can be solved, and it is described in the section of the effect of the invention. When at least one of the effects described above is obtained, a configuration in which this constituent element is deleted can be extracted as an invention.

[0088]

According to the first aspect of the present invention, when the taking lens position when the maximum focusing evaluation value is obtained and the taking lens position when the minimum focusing value is obtained are sufficiently separated from each other. Only when the maximum focus evaluation value is obtained, the lens position is determined to be the focus position, so the probability of making an incorrect focus determination for a subject with low contrast is reduced, and accurate focus is achieved. Can be obtained.

According to the invention of claim 2, in addition to the effect of the invention of claim 1, if there is no large difference between the maximum value and the minimum value of the focus evaluation value, it becomes impossible to focus. Since the determination is made, the probability of making an incorrect focus determination can be further reduced.

According to the third aspect of the invention, the taking lens position when the maximum focus evaluation value is obtained and the taking lens position when the minimum focus value is obtained are sufficiently separated from each other and the maximum value is obtained. Alternatively, if it is possible to determine that the contrast is sufficient considering the values other than the minimum value, the lens position when the maximum focus evaluation value is obtained is determined to be the in-focus position. On the other hand, it is possible to reduce the probability of making an incorrect focus determination and obtain accurate focus.

According to the fourth aspect of the present invention, only when the taking lens position when the maximum focus evaluation value is obtained and the taking lens position when the minimum focus value is obtained are sufficiently separated from each other. Since the lens position when the maximum focus evaluation value is obtained is determined to be the in-focus position, the probability of making an incorrect focus determination for a subject with low contrast is reduced, and accurate focus is obtained. It becomes possible.

According to the fifth aspect of the present invention, the taking lens position when the maximum focus evaluation value is obtained and the taking lens position when the minimum focus value is obtained are sufficiently separated from each other and the maximum value is obtained. Alternatively, if it is possible to determine that the contrast is sufficient considering the values other than the minimum value, the lens position when the maximum focus evaluation value is obtained is determined to be the in-focus position. On the other hand, it is possible to obtain a correct focus by reducing the probability of making an incorrect focus determination.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a digital still camera according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the processing contents during automatic focusing according to the same embodiment.

FIG. 3 is a view exemplifying a change characteristic of a focus evaluation value associated with driving of the focus lens according to the same embodiment.

FIG. 4 is a view exemplifying a change characteristic of a focus evaluation value along with driving of the focus lens according to the same embodiment.

FIG. 5 is a flowchart showing the processing contents during automatic focusing in the digital still camera according to the second embodiment of the present invention.

FIG. 6 is a view exemplifying a change characteristic of a focus evaluation value associated with driving of the focus lens according to the same embodiment.

FIG. 7 is a diagram showing a flow of processing contents for each minimum value candidate according to the embodiment.

FIG. 8 is a diagram exemplifying a change characteristic of a focus evaluation value (contrast) associated with driving of a general focus lens.

[Explanation of symbols]

10 ... Digital camera 11 ... Motor 12 ... Focus lens 13 ... CCD 14 ... Timing generator (TG) 15 ... Vertical driver 16 ... Sample hold circuit (S / H) 17 ... A / D converter 18 ... Color process circuit 19 ... DMA controller 20 ... DRAM interface (I / F) 21 ... DRAM 22 ... CPU 23 ... VRAM controller 24 ... VRAM 25 ... Digital video encoder 26 ... Display 27 ... Key input section 28 ... JPEG circuit 29 ... Flash memory

Claims (5)

[Claims] 1. An image pickup means for picking up and outputting a subject image, a lens driving means for sequentially driving a photographing lens, and a photographing lens which is sequentially driven by the lens driving means and is incident on the image pickup means. Evaluation value calculation means for sequentially calculating a focus evaluation value for evaluating the focus state based on the subject image sequentially output from the means, and the maximum value among the series of focus evaluation values sequentially obtained by the evaluation value calculation means. Judgment is made as to whether the focus position of the photographing lens is appropriate or not by judging whether or not the difference between the photographing lens position when the above is obtained and the photographing lens position when the minimum value is obtained is not less than a predetermined value. An image pickup device comprising: 2. The focus determining means determines whether or not the focus position of the taking lens is appropriate by determining whether or not there is a large difference between the maximum value and the minimum value of the focus evaluation values. The image pickup apparatus according to claim 1, further comprising: a unit that determines whether or not the image is inappropriate. 3. An image pickup means for picking up and outputting a subject image, a lens driving means for sequentially driving a photographing lens, and a photographing lens which is sequentially driven by the lens driving means and is incident on the image pickup means. Evaluation value calculation means for sequentially calculating a focus evaluation value for evaluating the focus state based on the subject image sequentially output from the means, and the maximum value among the series of focus evaluation values sequentially obtained by the evaluation value calculation means. Alternatively, by determining whether or not the focus evaluation value of the lens position which is apart from the photographing lens position when the minimum value is obtained and the predetermined value or more is greatly different from the maximum value or the minimum value, An image pickup apparatus comprising: a focus determination unit that determines whether or not a focus position is appropriate. 4. An image pickup step of picking up and outputting a subject image, a lens drive step of sequentially driving a photographing lens, and a sequential output in the image pickup step via a photographing lens sequentially driven in this lens driving step. An evaluation value calculation step for sequentially calculating a focus evaluation value for evaluating a focus state based on a subject image, and a maximum value among the series of focus evaluation values sequentially obtained in this evaluation value calculation step A focus determination step of determining whether the focus position of the photographing lens is appropriate by determining whether or not the difference between the photographing lens position and the photographing lens position when the minimum value is obtained is equal to or more than a predetermined value. An automatic focusing method for an image pickup apparatus, comprising: 5. An image pickup step of picking up and outputting a subject image, a lens driving step of sequentially driving a photographing lens, and a sequential output in the image pickup step via a photographing lens sequentially driven in this lens driving step. An evaluation value calculation step for sequentially calculating a focus evaluation value for evaluating the focus state based on the subject image, and a maximum value or a minimum value in the series of focus evaluation values sequentially obtained in this evaluation value calculation step are obtained. Whether the focusing position of the taking lens is appropriate or not by determining whether or not the focusing evaluation value of the lens position which is separated from the taking lens position by a predetermined value or more is greatly different from the maximum value or the minimum value. An automatic focusing method for an image pickup apparatus, comprising: