JP6463207B2 - Imaging apparatus, control method therefor, program, and storage medium - Google Patents

Description

  The present invention relates to an imaging apparatus that performs focus detection using a contrast detection method.

  2. Description of the Related Art Conventionally, in an imaging apparatus having an imaging element such as a digital camera, a contrast detection method is known as an autofocus method for automatically performing focus adjustment. In the contrast detection method, scanning is performed in one direction of a designated focus detection range from an image signal of a subject image formed on an image sensor, a high-frequency signal component is extracted, and a contrast value is calculated. Then, the sum of the contrast values within the focus detection range is used as the contrast evaluation value. By sequentially calculating such a contrast evaluation value while changing the defocus state accompanying the focus movement, it is determined that the focus position where the contrast evaluation value is the maximum is the state where the sharpness of the image is the highest, and the in-focus state is obtained. Position.

  In addition, recent digital cameras have functions corresponding to various shooting scenes. As one of them, models equipped with a shooting scene mode such as a starry sky shooting mode for shooting a celestial body are also becoming popular.

  Since the starry sky has an object distance of infinity, it is usually sufficient to shoot with the focus position of the photographic optical system set to the infinity position. Japanese Patent Application Laid-Open No. 2004-133830 proposes setting a specific imaging condition for setting the focal position to infinity when such starry sky imaging is performed.

  However, since shooting of the starry sky is performed outdoors at night, for example, when the imaging device is taken out of a warm room to a cold outdoor, a rapid temperature change may occur in the imaging device. In such a case, due to the temperature change, the lens barrel of the photographing optical system expands and contracts, and the focus position at infinity changes. Further, in continuous starry sky photography, since the exposure time becomes long, the temperature of the lens barrel of the photographing optical system changes with time due to heat generated by driving the image sensor. In order to prevent this, Patent Document 2 proposes a focus position correction method in which a thermometer is arranged in the imaging apparatus and focus position correction to infinity is performed based on the temperature information.

  However, it is usually desirable to obtain an accurate in-focus position with a focus detection device, and it is also desired to perform focus detection for starry sky photography to achieve a highly accurate in-focus state. When a general user who is not an astronomical photographer shoots the starry sky, take the image pickup device indoors or outdoors in a different temperature environment and start shooting immediately without waiting for the lens barrel temperature to stabilize. There are many cases. In this case, even if the focus position correction is performed in a state where the lens barrel is fluidly deformed due to a temperature change, an accurate infinity state is not obtained. For this reason, it is desirable to perform focus adjustment using a contrast detection method in a state as close as possible to the actual photographing even when photographing a starry sky.

JP-A-4-15629 Japanese Patent No. 4043250

  When performing contrast detection focus control on low brightness star images, long exposure is required to obtain a contrast evaluation value that has a mountain shape with respect to changes in the defocus amount. . However, flying objects such as high-intensity airplanes, meteors, and artificial satellites may pass through the focus detection range during long exposure. In addition, when the weather is not good, stars may be covered with clouds or the cloud shape may be deformed during long exposure. If the flying object in the defocus state crosses the focus detection range during the focus detection operation of the star image, if the brightness of the flying object is high, it is recognized as a subject having high contrast. That is, a maximum value (partial peak) occurs in the contrast evaluation value in a focus state different from the in-focus position.

  If a cloud is generated in the focus detection area, a conflict occurs between the contrast evaluation value acquired by the star image and the contrast evaluation value acquired by the outline of the cloud. In particular, since the outline of the cloud has an outline component in a blurred state (gradation state), the contrast evaluation value fluctuates due to a slight change in the outline of the cloud. Therefore, there is a high possibility that the shape of the contrast evaluation value becomes a waved shape such as noise, which causes a problem that the in-focus position cannot be determined.

  The present invention has been made in view of the above-described problems, and its purpose is caused by a suddenly high-intensity flying object or cloud that is generated suddenly when performing contrast detection focus detection on the starry sky. This is to prevent misfocus detection.

  An imaging apparatus according to the present invention is an imaging apparatus that performs focus detection by a contrast detection method in the vicinity of a focus position at infinity with respect to the starry sky, and includes an imaging unit that captures a subject image and a screen of the imaging unit. While the setting means for setting a plurality of focus detection ranges and the focus lens of the photographing optical system are moved in the direction of changing the focus position, an image is picked up by the image pickup means at the position of each focus lens, The calculation means for calculating the contrast evaluation value of the image corresponding to the position of the focus lens for each focus detection range, and the relationship between the position of the focus lens and the contrast evaluation value for each of the plurality of focus detection ranges Based on the shape of the curve, a maximum value of the contrast evaluation value is obtained, and it is determined whether or not the curve has a plurality of maximum values. And a focus detection range in which the curve is detected by the determination unit to detect a plurality of maximum values, the contrast evaluation value of the focus detection range is not used for focus detection, and the curve has a plurality of maximum values. Focus detection means for performing focus detection using a contrast evaluation value of a focus detection range having no value.

  According to the present invention, it is possible to prevent erroneous focus detection caused by a suddenly generated high-intensity flying object or cloud when performing contrast detection focus detection on the starry sky.

1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention. An illustration of the starry sky with flying objects. The figure which showed the contrast evaluation value shape in each focus detection range in FIG. An illustration of the starry sky with clouds. The figure which showed the contrast evaluation value shape in each focus detection range in FIG. FIG. 6 is a diagram for explaining determination of a plurality of maximum values in a focus detection range in which a cloud is applied in the contrast evaluation value of FIG. 5. The figure which showed the example which calculates | requires local maximum value by adding contrast evaluation value. The figure which showed the example which calculates | requires the average of the focus position in each focus detection range. The flowchart of operation | movement from a focus detection to focusing. The flowchart which shows the 1st multiple maximum value detection method. The flowchart which shows the 2nd multiple maximum value detection method.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, an imaging apparatus 100 is a digital camera in which an imaging apparatus main body having an imaging element and a photographing optical system are integrated. The imaging apparatus 100 includes a contrast detection type focus detection apparatus, and performs known hill-climbing focus detection. The contrast evaluation value in the following description is the integral amount of the contrast value generated from the edge component of the subject image when the subject image is scanned in a certain direction within the set focus detection range.

  In FIG. 1, reference numeral 101 denotes a photographing optical system. A glow stop 102 adjusts the light amount at the time of shooting by adjusting the aperture diameter, and also functions as an exposure time adjustment shutter at the time of still image shooting. Reference numeral 103 denotes a focus lens group that performs focus adjustment by movement in the optical axis direction. Reference numeral 104 denotes an image sensor that is configured by a C-MOS sensor or a CCD and acquires an image signal by photoelectric conversion. An image signal extraction unit 105 extracts an image signal from a photoelectric conversion signal of the image sensor 104.

  The photometry unit 106 performs photometric evaluation of an image area designated from the signal extracted by the image signal extraction unit 105. The exposure amount determination unit 107 calculates an appropriate exposure amount for photographing from the result of photometry by the photometry unit 106. Then, the gain adjustment unit 108 adjusts the intensity of the output signal of the image sensor so that the captured image is in an appropriate exposure state. At the same time, the aperture control unit 109 controls the aperture diameter of the iris diaphragm 102. Then, the above process is repeated so that the optimal exposure amount is obtained with respect to the change in the photoelectric conversion signal from the image sensor 104 again, and feedback control is performed. After the optimum exposure amount condition is determined, a recording image for storage is generated by the recording image generation unit 110 and is recorded on a recording medium such as a flash memory or a hard disk by the image recording unit 111.

  Next, the procedure from focus detection to focusing operation will be described. First, for the image signal obtained by the image signal extraction unit 105, the focus detection range determination unit 112 determines a focus detection range in which focus detection is performed. The focus detection range may be automatically determined according to an algorithm incorporated in the imaging apparatus, or may be manually designated by the photographer. Note that the following description will be made assuming that a specific divided region is set as the focus detection range when the starry sky focus is detected in the present embodiment.

  After the focus detection range is determined, the contrast evaluation value calculation unit 113 calculates the contrast evaluation value for the set focus detection range. At this time, if the specified number of changes in contrast evaluation values due to scanning of the focus lens group 103 have been obtained, it is determined that information on the contrast evaluation values for performing in-focus determination has been prepared. Then, the contrast evaluation value shape determination unit 114 determines a focus position at which the maximum shape of the change shape of the contrast evaluation value is obtained, and a plurality of maximum values are used for the change shape of the contrast evaluation value using the multiple maximum value detection method. Detect if it does not exist. The reason why the multiple maximum value detection method is necessary and the contents thereof will be described later.

  When a focus position at which the contrast evaluation value becomes a maximum value is searched, the focus position determination unit 115 performs an interpolation calculation of the contrast evaluation value obtained at each focus position to obtain an accurate contrast evaluation value. Calculate the maximum value. After searching for the focus position corresponding to this maximum value, the focus drive setting unit 116 obtains the focus drive amount for focusing, and the focus drive unit 121 drives the focus lens group 103 to bring it into focus.

  On the other hand, when a clear maximum value is not found in the change shape of the contrast evaluation value, the operation for determining the focus position by the focus position determination unit 115 is not performed. Here, as a method for discriminating a clear maximum value, for example, there is a method in which a threshold value is provided for a difference value between the maximum value and the minimum value of the contrast evaluation value and the determination result is used. Then, the focus drive setting unit 116 determines whether to continue focus drive according to the current focus state and perform contrast evaluation value calculation, or to shift to a state of searching for an object by driving the entire focus area.

  Next, the focusing operation when the shooting mode selection unit 118 selects the shooting mode of the starry sky in the present embodiment will be described. First, when the shooting mode selection unit 118 selects a starry sky shooting mode, the exposure method selection unit 117 determines an optimal exposure method for focus detection in the starry sky.

  Based on the exposure condition obtained by the exposure method selection unit 117, the exposure amount determination unit 107 controls the gain adjustment unit 108 and the aperture / shutter control unit 109. Here, the gain adjustment unit 108 adjusts the gain amount so that noise is not generated in the image signal due to an excessive increase in gain and the focusing accuracy on the starry sky is not affected. Then, the aperture / shutter control unit 109 sets the iris diaphragm 102 to the open state and adjusts the shutter open time so that the exposure time is such that focus detection can be performed on the star image.

  When photographing the starry sky, the scanning width of the focus lens for performing the hill-climbing contrast detection may be set around the focus position near infinity. However, as described above, when a temperature change occurs in the lens barrel of the photographic optical system, the relative position of the photographic lens group changes due to expansion and contraction of the lens barrel, and a focus change occurs. Therefore, the lens barrel temperature is acquired by the lens barrel temperature acquisition unit 119 (thermometer) installed in the lens barrel, and the object distance is corrected to infinity by the infinite focus position correction unit 120 based on the temperature information. Get information. Then, the correction information is sent to the focus drive setting unit 116, and the focus lens scanning range is determined so that the corrected infinity position is the center of the focus lens scanning range. Then, using the determined focus scanning range, an operation of acquiring a contrast evaluation value in a preset focus detection range is performed.

  Next, the contrast evaluation value shape determining unit 114 determines the shape of the contrast evaluation value change with respect to the acquired position change of the focus lens 103, and the focus position determining unit 115 determines the effective focus detection range. select. Details of this will be described later. By using the result of the contrast evaluation value in the effective focus detection range by the above operation, it is possible to perform an accurate focusing operation to the starry sky.

  Next, a description will be given of determination when the obtained contrast evaluation value is used and when it is not used in a plurality of focus detection ranges set in advance.

  FIG. 2 is a diagram illustrating the state of the subject when the focus detection operation is performed on the starry sky using the contrast detection method. Here, a high-intensity light source is provided in the screen while a contrast evaluation image is acquired by performing a long-second exposure at each focus position while changing the focus position to perform focus detection by contrast detection. It shows the situation that the airplane (aircraft) that passed through.

  In FIG. 2, the cross shape indicated by ST represents a star image. F1 to F9 indicate a set focus detection range, PL indicates an airplane, and L indicates a trajectory of an airplane wing light when the airplane passes through the screen. Specifically, while the contrast evaluation value is being acquired, the airplane passes through the focus detection range indicated by F2, F3, and F6, and the trajectory of the wing lamp is reflected.

  FIG. 3 shows a graph of a change shape of the contrast evaluation value corresponding to each of the focus detection ranges F1 to F9 in the focus detection state of FIG. Here, the vertical axis of the graph of FIG. 3 indicates the contrast evaluation value, and the horizontal axis of the graph indicates the focus position when the focus lens group 103 is scanned to acquire the contrast evaluation value.

  Here, in FIG. 2, it is assumed that the starry sky is in the best focus state when the focus lens is at the fourth focus position on the horizontal axis of the graph of FIG. When the focus lens is at the sixth focus position on the horizontal axis of the graph of FIG. 3, it is assumed that the airplane passes through the focus detection ranges of F2, F3, and F6 during the exposure operation.

  Continuing the description of the shape of the contrast evaluation value in FIG. 3, the focus detection ranges F1, F4, F5, and F7 to F9 in which only the star image ST exists in each focus detection range F1 to F9 are 4 on the horizontal axis of the graph. The contrast evaluation value is a maximum value at the second focus position. Therefore, it is possible to accurately detect the in-focus position on the star image. However, in the focus detection ranges F2, F3, and F6 through which the airplane has passed when the focus lens is at the sixth focus position out of focus, the wing lamp having a higher brightness than the star image is a linear locus. An image is recorded. Therefore, despite the fact that this wing light is an out-of-focus image, the contrast evaluation value is increased due to the large difference in luminance between the edge component and the background. That is, the contrast evaluation value of an image having a wing lamp locus in a blurred state is higher than the contrast evaluation value of an image in which the star image is in focus.

  In the focus detection ranges F2, F3, and F6 in which the airplane wing light trajectory is acquired as an image signal, the contrast evaluation value has a maximum value at the sixth or near sixth focus position. A state of being out of focus is erroneously determined as an in-focus state. That is, if the final focus position on the starry sky is determined using the contrast evaluation values and focus position determination results in all focus detection ranges, the focus accuracy may be reduced.

  In order to avoid this problem, it is detected whether or not the change shape of the contrast evaluation value with respect to the focus position change in each set focus detection range has a plurality of maximum values using a plurality of maximum value detection method. For the focus detection range having a plurality of maximum values, the contrast evaluation value result in the focus detection range is not used for in-focus position detection because it causes erroneous focus detection. Then, using the contrast evaluation value in the remaining focus detection range, a focus position that is in a focused state with respect to the starry sky is searched for, and is set as a final focus position for performing starry sky photographing.

  As described above, it is possible to prevent an in-focus phenomenon due to sudden intrusion of a high-intensity flying object during the focus detection operation of the contrast detection method. The method for detecting a plurality of maximum values from the change shape of the contrast evaluation value as described above will be referred to as a first plurality of maximum value detection method. In addition to airplanes, meteors, artificial satellites, and the like are conceivable as flying objects that pass through the screen during exposure and interfere with focusing on the star image.

  Next, in performing the focusing operation on the starry sky, clouds other than flying objects can be considered as factors that disturb the change shape of the contrast evaluation value. Most of the cloud shapes have a contoured shape with blurred edge components. Therefore, even if the defocus is increased, the contrast evaluation value for the cloud has a large blurring state because the blur component due to the change in defocus and the blur component of the contour shape originally possessed by the cloud are mixed. The change hardly occurs and the change in the contrast evaluation value becomes dull. Therefore, even if a change in the defocus amount is given when performing contrast detection, it is difficult to form a mountain shape in which the change shape of the contrast evaluation value has a clear maximum value.

  In addition, when the cloud shape changes while acquiring the contrast evaluation value, the contour image characteristics of the cloud change, and the change of the edge component causes disturbance in the change shape of the contrast evaluation value. There is also. In particular, in the state where thin clouds are applied to the entire screen, the contrast state of the starry sky changes over time, so the change shape of the contrast evaluation value becomes a shape close to the noise component, and multiple maximal waves It may also have a value.

  In such a state, if a plurality of maximum values are detected by the first method for detecting a plurality of maximum values described above, a detection result that there are a plurality of maximum values in all focus detection ranges is obtained. Therefore, as a result, the contrast evaluation values in the entire focus detection range are not used, and the focus detection operation cannot be performed on the starry sky.

  Therefore, in the focus detection range where the contrast evaluation value obtained by the star image and the contrast evaluation value obtained by the outline of the cloud are mixed, the second multiple maximum is different from the first multiple maximum detection method. A value detection method is used. Thus, the contrast evaluation value obtained from the outline of the cloud is not used, and the in-focus position is obtained only from the contrast evaluation value result obtained from the star image.

  FIG. 4 shows a state where a cloud is applied to a part of the focus detection range at the time of detecting the focus on the starry sky. Further, it is assumed that the cloud shape is deformed during exposure for focus detection. Similarly to FIG. 2, ST indicates a star image, and F1 to F9 indicate divided focus detection ranges. CL represents a cloud, and the state of FIG. 4 shows a state in which the cloud CL has entered the focus detection ranges F5, F6, F8, and F9.

  5 shows the change shape C of the contrast evaluation value corresponding to each of the focus detection ranges F1 to F9 set in FIG. 4, similarly to the relationship between FIG. 2 and FIG. P1 and P2 indicate the true in-focus position P1 of the starry sky and the false maximum position P2 caused by clouds, although the details will be described later. Here, as in FIG. 3, the vertical axis indicates the contrast evaluation value, and the horizontal axis indicates the focus position where the focus lens is scanned. In addition, it is assumed that the focus position 4 is the best in-focus state with respect to the star image ST.

  The focus detection ranges F1 to F4 and F7 are focus detection ranges in a state where no cloud has entered, and a change in the contrast evaluation value of only the star image ST existing in the focus detection range is detected. The change shape of the mountain-shaped contrast evaluation value is acquired.

  On the other hand, since the cloud has entered the focus detection ranges F5, F6, F8, and F9, as described above, the contrast evaluation value is acquired for the edge component having the cloud blur shape, and the contrast evaluation value is clear. It does not become a mountain shape.

  Among them, in the focus detection range F5, there is a star image that is not covered with a cloud, and therefore, the contrast evaluation value shape takes the maximum value P1 at the focus position 4 in the focused state with respect to the star image. However, when the star image is out of focus and the defocus amount increases, the star image becomes blurred and the contrast evaluation value decreases. On the other hand, when the cloud has a large amount of edge components due to time-series deformation, the influence of the contrast evaluation value caused by the cloud increases. Therefore, at the focus position of P2 in FIG. 5 different from the in-focus position of the star image, a maximum value of the second contrast evaluation value is generated due to a cloud different from P1.

  In particular, in a state where a cloud is applied to the entire surface of the screen and a star image is clouded or detached, such as in a lightly cloudy state, the contrast evaluation in which all focus detection ranges have a plurality of maximum values such as F5 described above. There is a high possibility that the value changes. Therefore, simply not using the contrast evaluation value of the focus detection range where multiple maxima are detected is effective for a starry sky in a clear sky state, but when applied to a starry sky where clouds are generated, There is a high possibility that the contrast evaluation value in the focus detection range will not be used.

  Therefore, it is desirable that the focus detection ranges F6, F8, and F9 are not used for in-focus position detection as a low-reliability contrast evaluation value, but a star image that is not completely covered with a cloud like the focus detection range F5 is included. It is desirable to use the contrast evaluation value for detecting the in-focus position.

  For this purpose, it is assumed that in the state where the star image exists, the contrast evaluation value in the vicinity of the in-focus state of the star image generates a value larger than the contrast evaluation value by the clouds in the same focus detection range. Even if there are multiple maximum values in the contrast evaluation value change shape, it is assumed that the maximum value is obtained in the contrast evaluation value change shape by the contrast component of the star image. It is desirable to determine the focal position.

  As a method for this, in this embodiment, when there are a plurality of maximum values, the upper value of the contrast evaluation value is extracted. Then, it is determined whether or not there is a contrast evaluation value that has not been extracted at the upper level among the extracted upper-level contrast evaluation values. If there is a contrast evaluation value that has not been extracted at the upper level among the extracted upper-level contrast evaluation values, it is determined that there are multiple maximum values.

  Next, a method for performing the above determination will be described with reference to FIG. FIG. 6 shows in detail the change characteristics of the contrast evaluation values in the focus detection ranges F5, F6, F8, and F9 into which the cloud has entered in FIG. Hereinafter, a method for determining the presence / absence of a plurality of maximum values in each focus detection range according to the second plurality of maximum values detection method will be described.

  First, in FIG. 6, it is assumed that the upper value of the contrast evaluation value is extracted up to the fourth position among all seven focus positions, and the above-mentioned multiple maximum value determination is performed. Note that the number of upper values may be changed depending on the amount of change in the defocus amount due to the focus movement width, or if the starry sky state can be detected in advance. In FIG. 6, the contrast evaluation values obtained at the respective focus positions are indicated by circular markers, and the numerical values indicated on the markers indicate the ranks up to the fourth highest contrast evaluation value.

  When the presence / absence determination of a plurality of maximum values is performed according to the above method, the focus detection range F5 is in a state where the focus positions at the first to fourth ranks of the contrast evaluation value are adjacent. In this state, the second multiple maximum value detection method determines that there are no multiple maximum values. The contrast evaluation value in this focus detection range is used. On the other hand, the focus detection ranges F6, F8, and F9 are in a state in which the contrast evaluation value of the fifth or lower rank is inserted between the first to fourth focus positions of the contrast evaluation value. Therefore, in the second multiple maximum value detection method, it is determined that there are multiple maximum values in each focus detection range. Therefore, the contrast evaluation value in this focus detection range is not used as a focus evaluation target.

  In order to obtain the in-focus position in the focus detection range F5 in FIG. 6, the maximum value of the contrast evaluation value may be simply set as the in-focus position, but the maximum value may be obtained by polynomial approximation interpolation. In addition, a method of obtaining the position of the center of gravity of the contrast evaluation value such that the position indicated by G in the figure is the in-focus position may be employed. In this case, a slight shift occurs with respect to the fourth focus position, which is the true focus position of the star image, but a position having almost no problem is determined as the focus position. By using the method as described above, it is possible to focus on the star image with high accuracy even in a state where the starry sky is clouded.

  As described above, regarding the focus detection of the contrast detection method for the starry sky, a plurality of maximum values are detected from the contrast evaluation values in the individual focus detection ranges, and it is determined whether or not the contrast evaluation values in the focus detection range are used from the results. Two types of multiple maximum value detection methods have been described. Here, when two types of multiple maximum value detection methods are actually used, it is necessary to use the two types depending on the state of the starry sky. For that purpose, it is good to first measure the starry sky and estimate the starry sky. Note that the focus state at the time of photometry may be set to a preset focus position at which the imaging apparatus is set to infinity.

  When estimating the starry sky using photometric values, the following can be considered. For example, in a starry sky where there is a cloud against a clear sky, there are many white components of the cloud, so the brightness value of the entire sky tends to increase. Accordingly, a predetermined photometric threshold value is set, and if the photometric value is equal to or greater than the threshold value, it can be determined that a cloud exists in the focus detection area where the photometry is performed.

  Therefore, when the photometric value is smaller than the threshold value, the starry sky in the focus detection range is in a clear sky state, and it is determined that there are no elements other than the flying object in the multiple maximum values generated in the contrast evaluation value. Select multiple local maximum detection method. On the other hand, if the photometric value is larger than the threshold value, it is determined that the starry sky is clouded, and the second multiple maximum value detection method described above is selected.

  As described above, it is possible to perform focusing with high accuracy by selecting an optimum multiple maximum value detection method for the starry sky state. The area for photometry may be the entire shooting screen, but it is more diverse if it is performed for each of the plurality of areas corresponding to the focus detection range and the multiple maximum value detection method is selected for each focus detection range. Focus detection corresponding to the condition of a starry sky can be performed.

  Next, a focus position acquisition method for finally obtaining a focus position in the entire focus detection range using the acquired contrast evaluation value in each focus detection range will be described.

  As a first method, the contrast evaluation value of the adopted focus detection range is added for each set focus position to generate a new contrast evaluation value shape change, and the newly obtained contrast A focus position where the maximum value is obtained from the evaluation value is searched, and that position is set as the final focus position.

  FIG. 7A shows a new contrast evaluation value obtained by adding the contrast evaluation values of the focus detection ranges F1, F4, F5, and F7 to F9 determined to be effective in the starry sky in the state shown in FIG. is there. FIG. 7B shows a new contrast evaluation value by adding the contrast evaluation values of the focus detection ranges F1 to F5 and F7 determined to be effective in the starry sky in the state shown in FIG.

  P in both figures indicates a focus position where the contrast evaluation value is a maximum value, and a contrast evaluation value determined to have a plurality of maximum values is not used. Thereby, the change shape of the contrast evaluation value becomes a smooth mountain shape, and the focus position at the local maximum position is brought into a focused state, so that the starry sky can be focused with high accuracy.

  In addition, the second method is a method of performing high-precision focusing on the starry sky by averaging the in-focus positions in the respective focus detection ranges.

  FIG. 8A shows an average of the focused focus positions in the focus detection ranges F1, F4, F5, and F7 to F9 in which the contrast evaluation values shown in FIG. It is the figure which showed the calculation made into a focus position. Similarly, FIG. 8B shows an average focus position in the focus detection ranges F1 to F5 and F7 determined to be effective in the starry sky in the state shown in FIG. It is the figure which showed the calculation made into a focal position. By setting the new focus position obtained by the above averaging to the final in-focus state, it is possible to focus on the starry sky with high accuracy.

  By using the method described above, it is possible to perform precise focus adjustment on the starry sky.

  Next, with respect to the imaging apparatus 100 of FIG. 1, the flow of processing when the shooting mode selection unit 118 selects the starry sky shooting mode will be described with reference to FIG. 9. Here, the flowchart of FIG. 9 shows a method for detecting a plurality of maximum values of contrast evaluation values in a plurality of preset focus detection ranges by performing photometry for each focus detection range, and according to the obtained photometry results. It is assumed that the method is changed.

  In FIG. 9, first, in step S1, focus detection ranges are sequentially selected from the set multiple focus detection ranges. In step S2, photometry processing is performed for the selected focus detection range, and in step S3, the obtained photometric value is compared with a preset threshold value. If the photometric value is equal to or greater than the threshold value, a flag for applying the second multiple maximum value detection method later is set in the selected focus detection range in step S5. On the other hand, if the acquired photometric value is less than the threshold value, in step S4, a flag is set for applying the first multiple maximum value detection method later to the selected focus detection range. The processes in steps S1 to S5 are repeated for all focus detection ranges.

  Through the above processing, a processing method designation flag indicating whether to perform the first or second multiple maximum value detection method later for all the focus detection ranges that have been set is set. In step S6, the focus movement operation and the contrast evaluation value acquisition operation set for the starry sky shooting mode are performed to acquire the contrast evaluation value information for each focus detection range.

  Thereafter, in step S7, the multiple maximum value detection method is changed in each focus detection range depending on whether the flag performs the first multiple maximum value detection method or the second multiple maximum value detection method. To do. The first multiple maximum value detection method and the second multiple maximum value detection method will be described using individual flowcharts.

  FIG. 10 is a flowchart regarding the first multiple maximum value detection method. When the first multiple maximum value detection method is started, first, in step S31, the contrast evaluation value information obtained in step S6 of FIG. 9 is acquired. In step S32, the change shape of the contrast evaluation value from the focus start position to the end position where the focus lens is moved is scanned to count how many maximum values exist in the evaluation value.

  In step S33, when only one maximum value is counted by the above counting process, it is determined that the change shape of the contrast evaluation value is a single mountain shape and does not have a plurality of maximum values. Then, in order to proceed with the process of accurately obtaining the in-focus position in the selected focus detection range, in step S34, the process of obtaining the focus position where the contrast evaluation value is the maximum value is performed by interpolation processing or the like. The focus position is acquired from the focus position information in step S35, and the first multiple maximum value detection method is terminated. Note that steps S34 and S35 may be omitted when a method of adding the contrast evaluation values and searching for the maximum value of the contrast evaluation value shape is used in post-processing.

  Returning to the description, if it is determined in step S33 that there are a plurality of local maximum values from the count in step S32, in step S36, processing is performed that does not use the contrast evaluation value of the currently set focus detection range. The first multiple maximum value detection method is terminated.

  Next, in step S7 of FIG. 9, the second multiple maximum value detection method is performed for the focus detection range in which the flag for performing the second multiple maximum value detection method is set. The flow of processing in the second multiple maximum value detection method will be described using the flowchart of FIG.

  In FIG. 11, when performing the second multiple maximum value detection method, the constant N is an integer of 2 or more less than the set focus position number (the number of points for obtaining the contrast evaluation value), and the multiple maximum of the contrast evaluation value. It is assumed that a constant for changing the value detection condition is set in advance.

  In step S41, the contrast evaluation value information obtained in step S6 in FIG. 9 is acquired as in step S31 in FIG. Next, in step S42, the acquired contrast evaluation values are sorted in descending order (in descending order). In step S43, the top N ranks of the contrast evaluation values sorted in step S42 are acquired. Here, N is a constant set in advance as described above.

  Next, in step S44, it is determined whether or not each focus position of the top N contrast evaluation values is in an adjacent state. The adjacent state referred to here is a state in which the focus positions of the contrast evaluation values other than the acquired top N positions do not interrupt between the top N positions as described in FIG.

  If it is determined in step S44 that the upper N-th focus position is in the adjacent state, it is determined that the change shape of the contrast evaluation value in the set focus detection range is not a plurality of maximum values, and the subsequent steps Continue processing. Then, in steps S45 and S46, as in steps S34 and S35 of FIG. 10, the focus position where the focus position at which the contrast evaluation value becomes the maximum value is accurately obtained by interpolation processing or the like is acquired, and the process ends. Note that steps S45 and S46 may also be omitted when using a method of searching for a maximum value by adding contrast evaluation values as described above in post-processing.

  Returning to the description, if it is determined in step S44 that the contrast evaluation value shape has a plurality of maximum values, processing in which the contrast evaluation value of the currently set focus detection range is not used in step S47. To end the second multiple maximum value detection method.

  The above is the detailed description of the first multiple maximum value detection method and the second multiple maximum value detection method.

  Returning to FIG. 9, in step S8, it is determined whether or not the contrast evaluation values of all focus detection ranges are not used in the process of step S7. Here, when the contrast evaluation values in the entire focus detection range are not used, focus detection cannot be performed using the contrast detection method. Therefore, the focus lens is moved to a preset infinity position, and a series of operations are performed. Finish the process of focusing on the starry sky.

  On the other hand, if there is a focus detection range in which the contrast evaluation value is valid, in step S9, the contrast evaluation value in each focus detection range determined to be valid is added for each focus position. If necessary, in step S10, an accurate focus position at which the contrast evaluation value becomes a maximum value is obtained by interpolation processing or the like, and the focus position is set as the final focus position. Then, the focus lens is moved to the obtained focus position, and the focusing process to the starry sky is ended.

  As described above, when the starry sky shooting mode is selected, the focusing operation to the starry sky is performed by the above processing flow.

  As described above, according to the present invention, when the contrast detection method is focused on the starry sky, the contrast of the focus detection range in which flying objects and clouds are present and noise is generated in the contrast evaluation value The evaluation value is not used. Thereby, it is possible to perform a focusing operation with high accuracy to the starry sky.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  The present invention is effective for an image pickup apparatus including a focus detection apparatus using a contrast detection method such as a digital camera.

100: imaging device 101: photographing optical system 102: iris diaphragm 103: focus lens group

Claims (12)

An imaging apparatus that performs focus detection by a contrast detection method in the vicinity of a focus position at infinity with respect to the starry sky,
Imaging means for capturing a subject image;
Setting means for setting a plurality of focus detection ranges in the screen of the imaging means;
While moving the focus lens of the photographic optical system in the direction of changing the focus position, the image is picked up by the imaging means at the position of each focus lens, and the focus lens position is set for each of the plurality of focus detection ranges. Calculating means for calculating a contrast evaluation value of the corresponding image;
For each of the plurality of focus detection ranges, a maximum value of the contrast evaluation value is obtained based on a curve shape representing a relationship between the position of the focus lens and the contrast evaluation value, and whether the curve has a plurality of maximum values. Determining means for determining whether or not;
For the focus detection range in which the curve is detected by the determining means to have a plurality of maximum values, the contrast evaluation value of the focus detection range is not used for focus detection, and the focus does not have a plurality of maximum values. Focus detection means for performing focus detection using the contrast evaluation value of the detection range;
An imaging apparatus comprising:   The imaging apparatus according to claim 1, wherein the calculation unit moves the focus lens around a focus position near infinity.   The determination means switches between a first determination method and a second determination method that are different in criteria for determining whether or not the curve has a plurality of maximum values according to the starry sky state. The imaging apparatus according to claim 1 or 2.   The imaging apparatus according to claim 3, wherein the first determination method determines that the curve has a plurality of maximum values when the curve simply has a plurality of maximum values.   In the second determination method, the positions of the focus lenses in which the magnitude of the contrast evaluation value is the value up to the top N (N is a predetermined integer equal to or greater than 2) are not adjacent to each other in the curve. In this case, it is determined that the curve has a plurality of maximum values.   The determination means uses the first determination method when the photometric value of the starry sky is less than a predetermined threshold, and the second determination when the photometric value of the starry sky is equal to or greater than the predetermined threshold. 6. The imaging apparatus according to claim 3, wherein a method is used.   7. The method according to claim 3, wherein the first determination method is used when a flying object passes through the starry sky, and the second determination method is used when a cloud exists in the starry sky. The imaging device according to any one of the above.   The focus detection unit adds the contrast evaluation values of the focus detection range in which the curve is determined not to have a plurality of maximum values by the determination unit, and matches the position of the focus lens where the added contrast evaluation value is maximum. The imaging apparatus according to claim 1, wherein the imaging apparatus is determined to be a focal position.   The focus detection unit calculates a focus position at which a contrast evaluation value is maximized from a contrast evaluation value of a focus detection range in which the determination unit determines that the curve does not have a plurality of maximum values, and calculates the calculated focus position. The imaging apparatus according to claim 1, wherein an average of the positions is determined as a focus position. A method for controlling an imaging apparatus having an imaging means for imaging a subject image and performing focus detection by a contrast detection method in the vicinity of a focus position at infinity with respect to the starry sky,
A setting step of setting a plurality of focus detection ranges in the screen of the imaging means;
While moving the focus lens of the photographic optical system in the direction of changing the focus position, the image is picked up by the imaging means at the position of each focus lens, and the focus lens position is set for each of the plurality of focus detection ranges. A calculation step of calculating a contrast evaluation value of the corresponding image;
For each of the plurality of focus detection ranges, a maximum value of the contrast evaluation value is obtained based on a curve shape representing a relationship between the position of the focus lens and the contrast evaluation value, and whether the curve has a plurality of maximum values. A determination step of determining whether or not,
For the focus detection range in which it is detected in the determination step that the curve has a plurality of maximum values, the contrast evaluation value of the focus detection range is not used for focus detection, and the focus does not have a plurality of maximum values. A focus detection step of performing focus detection using the contrast evaluation value of the detection range;
A method for controlling an imaging apparatus, comprising:   The program for making a computer perform each process of the control method of Claim 10.   A computer-readable storage medium storing a program for causing a computer to execute each step of the control method according to claim 10.