JP4320843B2 - Autofocus method, apparatus and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an autofocus method, apparatus, and storage medium, and more particularly to an autofocus method, apparatus, and storage medium for calculating a focus from contrast information in a part of a subject signal obtained by an image sensor.
[0002]
[Prior art]
The focus lens is moved to extract and integrate a high-frequency component corresponding to the contrast of the video output signal obtained from the image sensor (CCD etc.), and the focus lens position where the AF evaluation value as the integration result is maximized is focused. Has already been put to practical use.
[0003]
In this autofocus control system, a hill-climbing servo system that always drives the focus device in a direction in which the AF evaluation value increases, and the AF evaluation value is obtained by temporarily scanning the entire driving range of the focus, and temporarily stored, A method for obtaining a focus position after analyzing AF evaluation values for the entire area is known. The former hill-climbing servo method gradually moves to the in-focus position, so it is very effective for video cameras that continuously capture subject images and output them as movies, but it can be focused instantaneously according to the shooting command. It is not suitable for a still camera etc.
[0004]
As a technique for adjusting the focus at high speed and with high accuracy, as disclosed in Japanese Patent Laid-Open No. 63-98615, there is known a method of scanning with a fine pitch in accordance with the result of scanning the entire area.
[0005]
[Problems to be solved by the invention]
However, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-98615, if the result is insufficient according to the result of scanning the entire area, it is necessary to scan at a finer pitch than during the entire area scan. The fine pitch scan has a drawback that it takes a long time for the focusing process.
[0006]
The present invention has been made in view of such circumstances, and an object thereof is to provide an autofocus method, apparatus, and storage medium for a camera that can quickly and accurately derive a focal point.
[0007]
[Means for solving the problems]
In order to achieve the above object, the invention according to claim 1 is configured such that the focus position is moved at an interval of not less than the focal depth of the photographing optical system and not more than twice the focal depth, and photoelectric conversion is performed by the imaging device for each focus position. A first search step for calculating a focus evaluation value based on an image signal indicating a captured subject image, and whether an appropriate in-focus position can be obtained using the evaluation value obtained by the first search If it is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the first search and the evaluation value obtained by the first search, the focus position at the time of the first search is approximately The focus position is moved at an intermediate position and at the same interval, and the focus evaluation value is calculated based on the image signal indicating the subject image photoelectrically converted by the image sensor for each focus position. If it is determined that a proper in-focus position can be obtained using the second search step, and the evaluation value obtained by the first search, based on the evaluation value obtained by the first search. Determining the in-focus position, moving the focus to the in-focus position, and determining that an appropriate in-focus position cannot be obtained using the evaluation value obtained by the first search. And a step of obtaining a focus position based on the evaluation value obtained by the second search or the evaluation values obtained by the first search and the second search, and moving the focus to the focus position. Yes.
[0008]
According to the present invention, based on the image signal indicating the subject image photoelectrically converted by the imaging device at each focus position, the focus position is moved at an interval greater than or equal to the focal depth of the imaging optical system and less than twice the focal depth. Performing a first search for calculating a focus evaluation value; determining whether or not an appropriate in-focus position can be obtained using the evaluation value obtained by the first search; If it is determined that it is impossible to obtain an appropriate in-focus position using each evaluation value obtained by the first search, the focus position is set at approximately the middle position of the focus position at the time of the first search and at the same interval. Performing a second search for calculating a focus evaluation value based on an image signal indicating a subject image photoelectrically converted by the imaging device for each focus position. If it is determined that an appropriate in-focus position can be obtained using the evaluation value obtained by the first search, the in-focus position is obtained based on the evaluation value obtained by the first search. When it is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the step of moving the focus to the focal position and the first search, the evaluation value obtained by the second search Alternatively, the step of obtaining the in-focus position based on the evaluation values obtained by the first search and the second search and moving the focus to the in-focus position is included. It can be derived.
[0009]
In order to achieve the above object, according to a ninth aspect of the present invention, there is provided a first search for moving a focus position at an interval greater than or equal to a focal depth of a photographing optical system and less than or equal to twice the focal depth, and at the time of the first search. Search means for performing at least a first search of a second search for moving the focus position at substantially the same position and at the same interval, and at least a first of the first and second searches. Evaluation value calculation means for calculating an evaluation value of focus based on an image signal indicating a subject image photoelectrically converted by the image sensor at each focus position at the time of the search, and an evaluation value obtained by the first search It is possible to determine the proper in-focus position by using the judging means for determining whether or not the proper in-focus position can be obtained and the evaluation value obtained by the first search. If it is determined, it is determined that it is impossible to obtain the in-focus position based on the evaluation value obtained by the first search, and to obtain the proper in-focus position using the evaluation value obtained by the first search. Then, an in-focus position calculating means for obtaining an in-focus position based on the evaluation value obtained by the second search, or the evaluation values obtained by the first search and the second search, and the in-focus position calculating means And a focus moving means for moving the focus to the in-focus position obtained by (1).
[0010]
According to the present invention, the first search that moves the focus position at an interval that is greater than or equal to the focal depth of the imaging optical system and less than or equal to twice the focal depth is substantially the same as the focus position at the time of the first search. Search means for performing at least a first search of a second search for moving the focus position at intervals, and an image sensor for each focus position during at least the first search of the first and second searches. It is possible to obtain an appropriate in-focus position using the evaluation value calculation means for calculating the focus evaluation value based on the image signal indicating the subject image photoelectrically converted by the evaluation value and the evaluation value obtained by the first search. If it is determined that it is possible to determine an appropriate in-focus position using the determination means for determining whether or not the evaluation value obtained by the first search is used, the first search If it is determined that the in-focus position is obtained based on the evaluation value obtained in this way, and it is impossible to obtain the proper in-focus position using the evaluation value obtained in the first search, the second search Focus position calculation means for obtaining a focus position based on the obtained evaluation value or evaluation values obtained by the first search and the second search, and focusing on the focus position obtained by the focus position calculation means. Since the focus moving means for moving is provided, the focal point can be derived quickly and with high accuracy.
[0011]
In order to achieve the object, the invention described in claim 18 is characterized in that a storage medium stores an autofocus program provided with the autofocus method according to any one of claims 1 to 8. Yes.
According to the present invention, since the storage medium stores the autofocus program provided with the autofocus method according to any one of claims 1 to 8, the storage medium automatically detects the digital camera or other device. It is possible to transfer a focus program.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of an autofocus (hereinafter abbreviated as AF) method, apparatus, and storage medium according to the present invention will be described in detail below with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an embodiment of a digital camera to which an autofocus method, apparatus and storage medium according to the present invention are applied.
[0013]
The optical system of the digital camera 8 includes a photographing lens 10 that can adjust the focus, a diaphragm 12 that adjusts the amount of light, and a solid-state imaging device (CCD) 14 that converts an image into an electrical signal. An imaging signal obtained by the CCD 14 is obtained as a digital R, G, B signal via a signal processing circuit 18 and an A / D converter 20. The signal processing circuit 18 and the A / D converter 20 are driven in synchronism with a timing signal applied from a timing generation circuit (not shown).
[0014]
The R, G, B signals output from the A / D converter 20 are temporarily stored in the buffer memory 24 and simultaneously transmitted to the high frequency component extraction circuit 26 connected to the other. The high frequency component extraction circuit 26 performs a process of selecting a component having a large contrast in order to determine the focus when performing autofocus. Further, the acquired contrast data is output to the focus area integration circuit 28 as data of the focus area 46 as shown in FIG.
[0015]
In the focus area integration circuit 28, the contrasts in the focus area 46 are summed and averaged and output to the CPU 34.
Note that the CPU 34 extracts the luminance component in the image from the obtained digital signal value of the image, integrates it for a predetermined area, etc. to obtain the luminance level of the subject, and obtains the luminance level of the subject obtained here. Equipped with a TTLAE function that calculates the exposure power (shooting aperture and shutter speed) required for shooting.
[0016]
Further, the CPU 34 is provided with a RAM that is a readable / writable storage means and a ROM that is a storage means in which programs and constants for controlling the operation of the CPU 34 are stored.
The digital camera 8 is provided with a release button 36, and the CPU 34 has a switch signal line S1 for detecting that the release button 36 has been pressed, and is released when half-pressed, and the release button 36 is fully pressed. The signal line S2 that can detect the closed state of the contact is connected only in the case of.
[0017]
Connected to the CPU 34 are a compression processing circuit 38 that performs data compression processing in order to store captured image data in a small capacity, and a recording medium 40 that records or reads out shooting data or a program of an autofocus method. Has been. The CPU 34 is connected to a motor driving circuit 42 (focus moving means) for controlling the motor for adjusting the focus (focus) of the lens 10 and the opening degree of the diaphragm 12. And the amount of light reaching the CCD can be adjusted.
[0018]
As described above, since peripheral devices are connected to the CPU 34, the CPU 34 includes search means for searching for a focus position, determination means for determining whether or not an appropriate in-focus position can be obtained, It can also function as a calculation means for calculating the focal position.
The AF method of the digital camera 8 configured as described above will be described.
[0019]
Initially, the focus of the lens 10 stands by at the farthest distance shooting position, and the diaphragm 12 is set to the open position. An image to be photographed is formed on a light receiving surface of a solid-state imaging device (CCD) 14 through a photographing lens 10 and a diaphragm 12. The subject image is converted into a signal charge of an amount corresponding to the amount of incident light by each sensor in the CCD. The charge signal accumulated in this way is transferred to the signal processing circuit 18, where the R, G, B signals for each pixel are sampled and held, added to the A / D converter 20, and digital R, G , Converted into a B signal and output.
[0020]
The R, G, and B signals output from the A / D converter 20 are temporarily stored in the buffer memory 24, and at the same time, the other is transmitted to the high frequency component extraction circuit 26 to determine the focus when autofocusing is performed. Used to do.
FIG. 2 shows the relationship between the AF integration area and the focus area in one frame of the captured image.
[0021]
The focus area 46 is a range having a 4 × 4 = 16 AF integration area 44 at the center of the captured image 43, and is a portion where a photographer is most likely to have a subject that the focus is desired to focus on. is there.
The high frequency component extraction circuit 26 divides the image data for each AF integration area 44 in which a plurality of pixels are collected using a G signal with high luminance, and the difference in luminance between adjacent pixels in this AF integration area is used as contrast. calculate. In this embodiment, the contrast is calculated using the G signal, but the present invention is not limited to this, and the object of the present invention can be achieved even when at least one of R, G, and B is used. . Further, the acquired contrast data is collected as focus area 46 data and output to the focus area integration circuit 28 (evaluation value calculation means and high frequency integration means).
[0022]
In the focus area integration circuit 28, the contrasts in the focus area are summed and averaged and output to the CPU 34 as an AF evaluation value. In this way, the AF evaluation value Σ1 at the “far” position where the first focus shown in FIG. When the first AF evaluation value is detected, the CPU 34 next outputs a command for moving the lens 10 one step along the optical axis to the “near” side of the focus with respect to the motor drive circuit 42. At this time, if one step is set to about twice the width of the subject depth that varies depending on how the aperture 12 is narrowed down, the number of AF evaluation value detection points can be reduced. Can do. Thereafter, AF evaluation values Σ2, Σ3, Σ4... Σ7 are obtained in the same manner, and an AF search is performed.
[0023]
FIG. 3 shows an example of the AF search detection result of the captured image 43 in FIG.
In FIG. 3, from the characteristics of the subject of the captured image 43, the maximum value is shown at the focus distance of Σ4 among Σn (n = 1, 2, 3,..., 7) which is the AF evaluation value of the focus area 46. The peak is clear. Here, among the AF evaluation values of Σn, the maximum value Σ4 is set as ΣMAX, and the AF evaluation value when a predetermined amount is defocused is set as ΣDEF. The autofocus procedure will be described below using the flowchart shown in FIG.
[0024]
FIG. 4 is a diagram showing a flowchart of an embodiment of the autofocus method according to the present invention.
According to the figure, the auto-focus (AF) procedure is as follows. When the auto-focus routine is started in step S100 (hereinafter abbreviated as S100), the CPU 34 in S102 “drives Focus to the START position”. A command for driving the focus of the lens 10 to the START position is output to the motor drive circuit 42. When the focus reaches the start position, the AF evaluation value of Σ1 is detected.
[0025]
In S104 “forward rotation SKIP SEARCH”, AF evaluation value data up to Σp is sampled and stored in the storage means in the CPU 34 while sequentially changing the focus position in steps of the focus position within about twice the focal depth of the optical system. To do.
In S106 “normal rotation (a) & (b)?”, The conditions of (a) & (b) shown in FIG. 5 are determined. The forward rotation skip search corresponds to a first search operation that detects AF evaluation values from Σ1 to Σ7 (Σp) in steps in the + X-axis direction shown in FIG. Further, the reverse skip search corresponds to a second search operation for detecting AF evaluation values from Σ8 to Σ13 (Σm) in steps in the −X axis direction shown in FIG.
[0026]
The determinations (a) and (b) are the following determinations.
[0027]
[Expression 1]
(A) (ΣMAX) − (ΣDEF) ≧ (A) (1)
[0028]
[Expression 2]
(A)> (ΣMAX) − (ΣDEF) ≧ (B) (2)
[0029]
[Equation 3]
(B)> (ΣMAX) − (ΣDEF) (3)
A: Threshold value at which the peak position of the AF evaluation value can be determined as the in-focus position
B: Threshold value at which it can be determined that the in-focus position is in the vicinity of the peak position of the AF evaluation value
[0030]
[Expression 4]
(B) Σ1, Σ2, Σ3,..., Σ (MAX-1-C) <Σ (MAX-1)
C: Constant (4)
[0031]
[Equation 5]
Σ (MAX + 1 + C),..., Σn−1, Σn <Σ (MAX + 1)
... (5)
In the determination of (a), it is determined whether or not the detected AF evaluation value curve has a clear peak. The criterion for this determination is the difference between the peak value of the AF evaluation value and the AF evaluation value at a position defocused by a predetermined amount. The value of this difference is a predetermined first threshold A or The magnitude relationship with the second threshold B is compared. The magnitude relationship between the first threshold value (A) and the second threshold value (B) is as follows.
[0032]
[Formula 6]
(A)> (B) (6)
The determination formula (1) of (a) compares the difference between the peak value of the AF evaluation value and the AF evaluation value at a position defocused by a predetermined amount with a predetermined threshold (A). The case where the formula (1) is satisfied is a case where other judgment is unnecessary because the peak of the AF evaluation value is clear.
[0033]
Expression (2) compares the difference between the peak value of the AF evaluation value and the AF evaluation value at a position defocused by a predetermined amount, and a predetermined threshold (A) and a predetermined threshold (B). When the expression (2) holds, the AF evaluation value peak is ambiguous, but it is determined that an in-focus position exists in the vicinity.
Expression (3) compares the difference between the peak value of the AF evaluation value and the AF evaluation value at a position defocused by a predetermined amount with a predetermined threshold (B), and Expression (3) is established. The case is a case where the peak of the AF evaluation value is unclear, and it is necessary to detect the AF evaluation value by the reverse search (second search) again.
[0034]
The determination formula (4) in (b) exceeds the predetermined range with respect to the AF evaluation value at the peak position + 1 (near direction) than the AF evaluation value at the focus position adjacent to the peak position of the AF evaluation value (close). ) Side, there is no large AF evaluation value.
The determination formula (5) exceeds a predetermined range (far) with respect to the AF evaluation value at the peak position-1 (far direction) than the AF evaluation value at the focus position adjacent to the peak position of the AF evaluation value. On the other hand, the condition is that there is no large AF evaluation value. In this determination, the AF evaluation value (slightly blurred) at the focus position adjacent to the peak position of the AF evaluation value (substantially determined as the in-focus position) and the AF evaluation value at the position defocused by a predetermined amount (obviously blurred If the detected AF evaluation value includes a lot of information other than the contrast, or the subject may have different distances in the detection area. If the detection area is sufficiently small, the former case is overwhelmingly large.
[0035]
In S106 shown in FIG. 4, it is determined whether or not the above equations (1), (4), and (5) hold. If all of the equations (1), (4), and (5) are satisfied, the process proceeds to S110 “focus position = interpolation calculation” (AF evaluation value−Focus position) with a second-order parabolic equation. Then, the process of obtaining the inflection point of the parabola (Focus position at which the AF evaluation value is maximum) from the representative three AF evaluation values and the Focus position is performed.
[0036]
Instead of the above interpolation calculation, the inflection point and the maximum value may be obtained by applying a quadratic or higher order function from the point sequence of the AF evaluation values, or a multi-order curve may be obtained using a method such as the least square method. Even if approximated, the object of the present invention is achieved.
If at least one of the expressions (1), (4), and (5) is not satisfied in S106, the process proceeds to S108 "Condition a?" And the determination shown in FIG. 5 is performed.
[0037]
FIG. 5 shows the result of determination based on the conditions (a) and (b) in S106 and S108 and the branch destination steps. According to the figure, as described above, when all of the expressions (1), (4), and (5) hold, the process branches to S110.
If equation (1) holds but at least one of equations (4) and (5) does not hold, the process branches to S112 “reverse search range = entire area”.
[0038]
If Expression (2) holds, the process branches to S112 regardless of the results of Expression (4) and Expression (5).
If Expression (3) holds, the process branches to S114 “reverse search range = adjacent two points” regardless of the results of Expression (4) and Expression (5).
In S112 “reverse search range = entire area”, as shown in FIG. 3, the focus position (Σ8, Σ9,...) Between the forward skip detection points from the “near” focus position toward the “far” focus position. , Σm), a flag for detecting the AF evaluation value is set.
[0039]
In S114 “reverse search range = two adjacent points”, in the example shown in FIG. 3, the forward skip is performed on both sides of the maximum AF evaluation value Σ4 from the “near” focus position to the “far” focus position. A flag for detecting AF evaluation values at two focus positions (Σ10, Σ11) in the middle of the detection points is set, and the process proceeds to S115.
In S115 “Reverse SKIP SEARCH”, a reverse skip search is performed in accordance with the detection program in S114, and the process proceeds to S110.
[0040]
In S116 “Reverse SKIP SEARCH”, a reverse skip search is performed in accordance with the detection program in S112.
In S118 “reverse rotation (a) & (b)?”, The determination of the conditions of (a) & (b) shown in FIG. 5 is performed on the data at the time of reverse rotation (AF evaluation value data at the time of the second search). Yes. If all of the expressions (1), (4), and (5) hold in S118, the process branches to S110 “focus position = interpolation calculation”, and the expressions (1), (4), and (5) If at least one of (5) does not hold, the process proceeds to S120 “c?”.
[0041]
In S120 “c?”, It is determined whether or not the peak positions of the AF evaluation values obtained during the forward search and reverse search are adjacent to each other within a predetermined focus pitch. Assuming that the predetermined focus pitch is FP, the formula indicating the determination in S120 is as follows.
[0042]
[Expression 7]
(ΣMAX focus position during forward rotation) − (ΣMAX focus position during reverse rotation)
≦ FP (7)
The meaning of the above judgment is that when the AF evaluation value is not sufficiently large, it is difficult to separate the contrast information and noise in the AF evaluation value, but the peak of the AF evaluation value detected by the forward search / reverse search is difficult. If the positions exist at substantially the same position, it is determined that the AF evaluation value indicating the peak position contains sufficient contrast information.
[0043]
If the above equation (7) holds in S120, the process branches to S122 “focus position calculation 1”, and the focus position is calculated as shown in the following equation (8). Then, the focus position data at the time of shooting is stored in the RAM of the CPU 34. In addition, the focus position is displayed on the viewfinder and the display unit.
[0044]
[Equation 8]
In-focus position = ((ΣMAX focus position during forward rotation) +
(ΣMAX focus position during reverse rotation)) / 2 (8)
When the step width during forward search / reverse search is within twice the depth of focus and the peak positions of AF evaluation values during forward search / reverse search are adjacent, the in-focus position determined by equation (8) is the depth of focus. Fits within. Note that the depth of focus changes depending on the amount of the aperture, and when a zoom lens is used, it varies depending on the zoom ratio. Therefore, the search step width is changed according to the state of each lens and optical system. It is possible to perform an efficient AF search in a short time.
[0045]
FIG. 6 shows the relationship between the search step width and the depth of focus.
According to the figure, the permissible circle of confusion is Φ, the minimum circle of confusion for forward search is ΦCW, the minimum circle of confusion for reverse search is ΦCCW, the step width of forward / reverse search is the depth of focus × 2, search step width If SP is SP and the AF evaluation value is detected in the middle of the forward search step during reverse search, the following equation (9) is established.
[0046]
[Equation 9]
ΦCW + ΦCCW = Φ × 2 (9)
Therefore, it is below the allowable circle of confusion at the middle position between forward and reverse.
If the above formula (7) is not satisfied in the determination in S120, the focus position cannot be determined and the process proceeds to S124 “focal position = Pern position”, and the distance to the subject is set as the lens characteristic. In addition, data for photographing with pan focus while being fixed at a predetermined focus position such as 2 (m) is stored in the RAM of the CPU 34. In addition, a display indicating that the focus position cannot be determined is displayed on the finder or the display unit.
[0047]
When the processing is completed in steps S110, S124, and S122, the CPU 34 obtains the focus position obtained as described above in the motor drive circuit 42 and stored in the RAM of the CPU 34 in S126 “drive focus to the focus position”. Outputs a command to focus on. Then, the motor drive circuit 42 drives the focus motor of the lens 10 to adjust the focus to the designated focus position. Then, in S128 “END”, the processing of this “AF” is terminated.
[0048]
When the focus is in focus, a display indicating that the focus is achieved is displayed on the viewfinder and the display unit. When the release button 36 is fully pressed and S2 is turned "ON", the CPU 34 outputs a command for driving the diaphragm 12 to the finally determined diaphragm value to the motor control circuit 42, and the decision is made. A charge accumulation time is controlled by an electronic shutter so as to obtain a shutter speed, and a captured image is captured.
[0049]
The photographic data stored in the buffer memory 24 is transferred to the compression processing circuit 38, compressed as required by a command from the CPU 34, and stored in the recording medium 40.
FIG. 7 shows a receiving means and a receiving method for receiving a program having an autofocus method according to the present invention from an external storage medium.
[0050]
According to the figure, the digital camera 8 is connected to a personal computer 190 having storage means, information processing means, and communication means by a connection line 192, and is bidirectional or from the personal computer 190 toward the digital camera 8. It is configured to be able to pass data. Note that the communication connection line 192 may be connected to a plurality of electric wires, or may be a communication method using light or radio waves as a medium.
[0051]
With the apparatus configured as shown in the figure, both devices are connected at S200 “Connect to storage medium or personal computer”, and at the next S202 “AF. Program download”, the digital camera 8 is connected to the auto according to the present invention. A program having a focusing method is received from the personal computer 190 and stored. In step S204 “execute”, the digital camera 8 switches between the received autofocus method and the conventional autofocus method according to an operation instruction from the operator, and controls autofocus.
[0052]
Instead of transmitting and executing the autofocus program, the PC 190 may output control signals to the digital camera 8 at any time to directly control the autofocus of the digital camera 8.
As described above, the software for realizing the function is downloaded to a device such as a digital camera or a CPU (microcomputer) in the system, and control is performed according to the program stored in the system or device. Various autofocus methods prepared after the purchase of the camera 8 can be used with the digital camera 8. When downloading the program, it may be a program for controlling the entire apparatus such as the digital camera 8 including the autofocus method according to the present invention, or only the program for the autofocus method portion according to the present invention is downloaded. May be.
[0053]
FIG. 8 shows an external storage medium storing a program having an autofocus method according to the present invention, and a digital camera.
According to the figure, the digital camera 8 is configured to be connectable to an external storage medium 194 storing a program provided with the autofocus method according to the present invention.
[0054]
With the apparatus configured as shown in the figure, both devices are connected in S210 “Storage medium connection”, and in the next S212 “AF program download”, the digital camera 8 performs the autofocus method according to the present invention. Download and run the provided program. Then, the autofocus method is controlled by switching the autofocus method according to the operation instruction of the operator.
[0055]
By downloading a program having an autofocus method from an external storage medium as described above, various autofocus methods prepared after purchasing the digital camera 8 can be used in the digital camera 8.
[0056]
【The invention's effect】
As described above, according to the autofocus method of the present invention, the focus position is moved at an interval of not less than the focal depth of the photographing optical system and not more than twice the focal depth, and photoelectric conversion is performed by the imaging device for each focus position. A first search step for calculating a focus evaluation value based on an image signal indicating a captured subject image, and whether an appropriate in-focus position can be obtained using the evaluation value obtained by the first search If it is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the first search and the evaluation value obtained by the first search, the focus position at the time of the first search is approximately The focus position is moved at the same interval at the intermediate position, and the focus is based on the image signal indicating the subject image photoelectrically converted by the image sensor at each focus position. When it is determined that a proper in-focus position can be obtained using the second search for calculating the evaluation value and the evaluation value obtained by the first search, the first search is performed. It is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the step of obtaining the in-focus position based on the evaluation value and moving the focus to the in-focus position and the first search. A focus position is obtained based on the evaluation value obtained by the second search or the evaluation values obtained by the first search and the second search, and the focus is moved to the focus position. As a result, the focal point can be derived quickly and with high accuracy.
[0057]
According to the autofocus device of the present invention, the first search for moving the focus position at an interval that is greater than or equal to the focal depth of the photographing optical system and less than or equal to twice the focal depth, and the focus position at the time of the first search A search means for performing at least a first search of a second search for moving a focus position at substantially the same position and at the same interval, and at least during the first search of the first and second searches An evaluation value calculating means for calculating an evaluation value of the focus based on an image signal indicating a subject image photoelectrically converted by the imaging device for each focus position, and an appropriate combination using the evaluation value obtained by the first search. It is possible to obtain an appropriate in-focus position by using a judging means for judging whether or not the in-focus position can be obtained and the evaluation value obtained by the first search. If it is determined, it is determined that it is impossible to obtain the in-focus position based on the evaluation value obtained by the first search, and to obtain the proper in-focus position using the evaluation value obtained by the first search. Then, an in-focus position calculating unit that obtains an in-focus position based on the evaluation value obtained by the second search, or the evaluation value obtained by the first search and the second search, and the in-focus position calculating unit Since the focus moving means for moving the focus to the in-focus position obtained by (1) is provided, the in-focus point can be derived quickly and with high accuracy.
[0058]
Further, according to the autofocus storage medium according to the present invention, since the storage medium stores the autofocus program provided with the autofocus method according to the present invention, the autofocus program according to the present invention is stored from the storage medium. The program can be transferred to a device such as a digital camera.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a digital camera to which an autofocus method according to the present invention is applied.
FIG. 2 is a diagram showing a relationship between an AF integration area and a focus area in a captured image frame.
FIG. 3 is a diagram showing an example of a detection result of AF search of the captured image shown in FIG. 2;
FIG. 4 is a flowchart showing an embodiment of autofocus of a digital camera according to the present invention.
FIG. 5 is a truth table showing a result of determination based on the conditions (a) and (b) in S106 and S108 shown in FIG. 4 and a branch destination.
FIG. 6 is a diagram showing the relationship between the search step width and the depth of focus.
FIG. 7 is a diagram showing a receiving means and a receiving method for receiving a program having an autofocus method according to the present invention from an external storage medium.
FIG. 8 is a diagram showing an external storage medium storing a program having an autofocus method according to the present invention and a digital camera.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 8 ... Digital camera, 10 ... Lens, 14 ... CCD (solid-state image sensor), 26 ... High frequency component extraction circuit, 28 ... Focus area integration circuit, 34 ... CPU, 42 ... Motor drive circuit, 190 ... Personal computer, 194 ... Storage medium

Claims (18)

The focus position is moved at an interval that is greater than or equal to the focal depth of the photographic optical system and less than or equal to twice the focal depth, and the focus evaluation value is calculated based on the image signal indicating the subject image photoelectrically converted by the image sensor for each focus position. Performing a first search to:
Determining whether it is possible to obtain an appropriate in-focus position using the evaluation value obtained by the first search; and
If it is determined that it is impossible to obtain an appropriate in-focus position using each evaluation value obtained by the first search, the focus is set at approximately the middle position of the focus position at the time of the first search and at the same interval. Performing a second search for moving the position and calculating a focus evaluation value based on an image signal indicating a subject image photoelectrically converted by the imaging device for each focus position;
When it is determined that an appropriate in-focus position can be obtained using the evaluation value obtained by the first search, the in-focus position is obtained based on the evaluation value obtained by the first search. Moving the focus to a position;
If it is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the first search, the evaluation value obtained by the second search, or the first search and the second search Obtaining a focus position based on the evaluation value obtained by the search, and moving the focus to the focus position;
Including an autofocus method. 2. The autofocus method according to claim 1, wherein the step of calculating the focus evaluation value includes the step of calculating an evaluation value by integrating high-frequency components included in the image signal. 3. The autofocus method according to claim 1, wherein the first search direction is opposite to the second search direction. 4. The autofocus method according to claim 1, wherein the second search is a search of the entire area or only one part. In determining whether it is possible to obtain an appropriate in-focus position using the evaluation value obtained by each search,
The difference between the evaluation value at the position defocused by a predetermined amount from the focus position at which the evaluation value becomes the maximum value and the maximum value of the evaluation value are obtained, and the evaluation of the position at which the maximum value of the evaluation value is defocused by the predetermined amount A step of determining whether or not the difference from the value is equal to or greater than a threshold that can be determined as the in-focus position, or
A function is obtained from the focus position where the evaluation value is the maximum value and the evaluation values at a total of three or more positions including at least two positions defocused by a predetermined amount. The autofocus method according to any one of claims 1 to 4, further comprising a step of determining whether or not the threshold is greater than or equal to a threshold that can be determined as a focal position. In determining whether it is possible to obtain an appropriate in-focus position using the evaluation value obtained by each search,
An evaluation value indicating a value larger than the evaluation value at the position defocused by the first predetermined amount from the focus position at which the evaluation value is the maximum value is further second than the position defocused by the first predetermined amount. 6. The autofocus method according to claim 1, further comprising a step of determining whether or not the lens exists outside a position defocused by a predetermined amount. In the calculation for obtaining the in-focus position based on the evaluation value obtained by the first or second search,
A function is obtained from the focus position where the evaluation value is the maximum value and the evaluation values at a total of three or more positions of at least two positions defocused by a predetermined amount,
Find the inflection point where the function shows the maximum value,
The autofocus method according to claim 1, further comprising a step of determining an inflection point indicating the maximum value as an in-focus position. Determining whether it is possible to obtain an appropriate in-focus position using the evaluation value obtained by the second search;
When it is determined that it is impossible to obtain an appropriate in-focus position using each evaluation value obtained by the second search, a predetermined predetermined focus position is set as the in-focus position, and the in-focus position Step to move the focus to
The autofocus method according to claim 1, further comprising: The first search that moves the focus position at an interval that is greater than the focal depth of the photographic optical system and less than twice the depth of focus, and the focus position is moved at approximately the same position as the focus position during the first search. Search means for performing at least a first search of the second search to be performed;
Evaluation value calculation means for calculating a focus evaluation value based on an image signal indicating a subject image photoelectrically converted by the imaging device for each focus position during at least the first search of the first and second searches; ,
Determination means for determining whether or not an appropriate in-focus position can be obtained using the evaluation value obtained by the first search;
When it is determined that an appropriate in-focus position can be obtained using the evaluation value obtained by the first search, the in-focus position is obtained based on the evaluation value obtained by the first search. If it is determined that it is impossible to obtain an appropriate in-focus position using the evaluation value obtained by the above search, the evaluation value obtained by the second search or the first search and the second search are obtained. A focus position calculating means for obtaining a focus position based on the evaluated value;
A focus moving means for moving the focus to the in-focus position obtained by the in-focus position calculating means;
An autofocus device characterized by comprising: 10. The autofocus device according to claim 9, wherein the focus evaluation value calculation means includes high frequency integration means for calculating an evaluation value by integrating high frequency components included in the image signal. The autofocus device according to claim 9 or 10, wherein the search means moves the focus in the reverse direction between the first search direction and the second search direction. The autofocus device according to any one of claims 9 to 11, wherein the second search means searches the entire area or only one part. Judgment means for determining whether it is possible to obtain an appropriate in-focus position using the calculated evaluation value,
The difference between the evaluation value at the position defocused by a predetermined amount from the focus position at which the evaluation value becomes the maximum value and the maximum value of the evaluation value are obtained, and the evaluation of the position at which the maximum value of the evaluation value is defocused by the predetermined amount A determination means for determining whether or not the difference from the value is equal to or greater than a threshold that can be determined as the in-focus position, or
A function is obtained from the focus position at which the evaluation value becomes the maximum value and the evaluation values at a total of three or more positions including at least two positions defocused by a predetermined amount, and the slope of the function at the position defocused by the predetermined amount is combined. The autofocus device according to any one of claims 9 to 12, further comprising a determination unit configured to determine whether or not a threshold that can be determined as a focal position is greater than or equal to. Judgment means for determining whether it is possible to obtain an appropriate in-focus position using the calculated evaluation value,
An evaluation value indicating a value larger than the evaluation value at the position defocused by the first predetermined amount from the focus position at which the evaluation value is the maximum value is further second than the position defocused by the first predetermined amount. 14. The autofocus device according to claim 9, further comprising a determination unit configured to determine whether or not the lens exists outside a position defocused by a predetermined amount. The calculating means for obtaining the in-focus position based on the evaluation value obtained by the first or second search,
A calculation means for obtaining a function from a focus position where the evaluation value is a maximum value and evaluation values at a total of at least two positions defocused by a predetermined amount;
A calculating means for obtaining an inflection point at which the function exhibits a maximum value;
A calculation means for determining an inflection point indicating the maximum value as an in-focus position;
The autofocus device according to any one of claims 9 to 14, further comprising: Determination means for determining whether or not an appropriate in-focus position can be obtained using the evaluation value obtained by the second search;
When it is determined that it is impossible to obtain an appropriate in-focus position using each evaluation value obtained by the second search, a predetermined predetermined focus position is set as the in-focus position, and the in-focus position Focus moving means for moving the focus to
The autofocus device according to claim 9, further comprising: 17. A receiving means for receiving an autofocus program comprising the autofocus method according to any one of claims 1 to 8 from an external storage medium. The autofocus device described in 1. A storage medium storing an autofocus program comprising the autofocus method according to any one of claims 1 to 8.

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