JP2016138998A - Imaging device and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which, when light in towns enters into a range-finder region, users desiring to focus stars might have concern that correct focusing of the stars cannot be made, and the users are tend to make a pose of an imaging device intentionally changed to prevent townscapes in a horizontal area of an angle of view from entering into the range finder region as much as possible, and as a result, the angle of view is not an originally intended angle of view.SOLUTION: When an infinity distance mode is set, the imaging device of the present invention is configured to change at least one of a position of a focus detection area and the number of areas of the focus detection area on the basis of a size of a tilt of an imaging optical system.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a focus adjustment technique for focusing on a point light source such as a star in the night sky. The present invention relates to an imaging apparatus applied to a digital still camera, a digital video camera, and the like.

  In recent years, imaging devices such as cameras and videos have high pixels, and even a slight focus shift becomes conspicuous, and there is a demand for more accurate focusing.

  This request is the same for stars in the night sky. Focusing on a point where the area of the high-intensity signal is strictly minimized, assuming the star as a point light source.

  In shooting a starry sky, the star to be shot is limited to a subject located at almost infinity, and the exposure has a setting unique to the starry sky. Therefore, a mode independent of other scene modes exists. (Starry sky mode)

  Normally, the focus position at which a subject located at almost infinity is in focus is a position uniquely determined in focus adjustment performed for each individual imaging apparatus.

  However, there may be a case where the image is out of focus during photographing due to a temperature difference or an attitude difference of the image pickup apparatus when photographing the night sky in actuality.

  For this reason, it is often necessary to focus even during shooting of a star whose distance to the imaging device hardly changes during shooting.

  In the shooting of the starry sky, the city light can be regarded as a point light source in the same way as the star. The focus position differs with light.

  As mentioned earlier, there is a need for more accurate focusing even in the starry sky mode, so it is necessary to correct even a slight focus difference between stars and city lights.

  As one means for performing focusing, there is a contrast AF method in which automatic focus adjustment is performed using an AF evaluation value obtained by extracting a specific frequency component by filter processing on a luminance signal obtained from an image sensor.

  In general, there is a problem that the accuracy of the AF evaluation value decreases under low illumination such as a night sky star. (Patent Document 1)

  In addition, since city lights often have higher luminance than star lights, when stars and city lights coexist in the same distance measurement area, the luminance signal is saturated and AF evaluation values cannot be acquired correctly. There is a case.

  As a result, a position that is not originally in focus may be erroneously determined as the focus position.

  On the other hand, there is a technique for enlarging a distance measurement area for a subject with a high priority selected according to a posture as means for increasing the focusing accuracy regardless of the posture of the imaging apparatus. (Patent Document 2)

JP 2013-250533 A JP 2012-128021 A

  A user who wants to focus on a star may have a concern that focusing on the star cannot be performed accurately when the city light enters the distance measurement area.

  For this reason, there is a tendency to intentionally change the attitude of the imaging device so that the streets near the horizontal of the angle of view do not enter the ranging area as much as possible.

  As a result, there was a problem that the angle of view was not intended.

  Therefore, in the imaging apparatus of the present invention, an imaging element that receives the light beam that has passed through the imaging optical system, an area setting unit that sets a plurality of focus detection areas on the imaging surface of the imaging element, and each of the plurality of focus detection areas Calculation means for calculating a focus evaluation value, focus adjustment means for performing focus adjustment based on the focus evaluation value, and mode setting means for setting an infinite distance mode for acquiring a focus evaluation value of a point light source subject corresponding to an infinite distance And an inclination detection means for detecting the inclination of the imaging optical system, and when the infinite distance mode is set, the position of the focus detection area and the position of the focus detection area based on the magnitude of the inclination of the imaging optical system. And changing means for changing at least one of the number of areas.

  According to the present invention, it is possible to focus on a star in the night sky with high accuracy by appropriately changing the position and number of distance measurement areas in accordance with the attitude of the imaging apparatus.

Block diagram of an imaging device that is a digital camera A diagram showing the relationship between the angle of view at the time of shooting and the AF evaluation value A diagram showing the relationship between the angle of view at the time of shooting and the AF evaluation value A diagram showing the relationship between the angle of view at the time of shooting and the AF evaluation value A diagram showing the relationship between the angle of view at the time of shooting and the AF evaluation value A diagram showing the relationship between the angle of view at the time of shooting and the AF evaluation value Flow chart for focusing on the starry sky Flow chart for focusing on the starry sky

  The present invention will be described below through embodiments of the invention.

  FIG. 1 is a block diagram illustrating a configuration example of a digital camera 100 as an example of an imaging apparatus according to an embodiment of the present invention.

  The lens barrel 101 drives a lens while holding a lens group therein.

  The zoom lens 102 optically changes the angle of view by adjusting the focal length.

  The focus lens 103 adjusts the focus position.

  The aperture and shutter 104 are used for exposure control that adjusts the amount of light.

  The light beam that has passed through the lens barrel 101, which is an imaging optical system, is received by the imaging element 105 using a CCD (charge coupled device), a CMOS (complementary metal oxide semiconductor), or the like, and converted from an optical signal to an electrical signal. Converted.

  The electrical signal is input to the image processing circuit 106, subjected to pixel interpolation processing, color conversion processing, and the like, and then sent to the internal memory 107 as image data.

  The display unit 108 displays shooting information and the like together with the shot image data.

  The operation unit 113 is a user interface for performing various menu operations and mode switching operations.

  The power supply unit 114 supplies power to the entire system according to the application.

  The storage memory 115 stores various data such as parameters.

  Next, the drive unit of the lens barrel 101 will be described.

  The exposure control unit 117 controls the aperture and shutter by calculating an exposure control value (aperture value and shutter speed) based on the luminance information obtained by the luminance signal calculation unit 122.

  Thereby, automatic exposure (AE) control is performed.

  The luminance signal calculation unit 122 calculates the electrical signal output from the image sensor 105 as the luminance of the subject.

  The evaluation value calculation unit 121 extracts a specific frequency component from the luminance signal calculated by the luminance signal calculation unit 122 and then calculates the evaluation value.

  The focus control unit 118 refers to an evaluation value that is a calculation result of the evaluation value calculation unit 121 according to the position of the focus lens 103 as a focus adjustment unit, and thereby a focus lens on which the light beam is focused on the surface of the image sensor 105. Control the position.

  Thereby, automatic focusing (AF) control is performed.

  The zoom lens driving unit 119 controls the zoom lens position in accordance with a zoom operation instruction from the operation unit 113.

  The inclination detection unit 112 detects acceleration applied to the imaging apparatus.

  By periodically monitoring the change in acceleration, the speed of the change, that is, the change speed of the posture of the imaging apparatus can also be detected.

  The posture determination unit 120 uses the output of the tilt detection unit 112 to calculate the vertical angle (elevation angle and depression angle) of the imaging apparatus and the time taken to change from the original posture to the posture, and the slow posture change or the fast posture Determine if it is a change.

  The range-finding frame control unit 123 controls the position, number, and shape of the focus detection areas set in the imaging plane of the image sensor 105 according to the posture of the imaging device and the change speed thereof by the posture determination unit 120.

  The ranging frame control unit 123 is an area setting unit that sets a plurality of focus detection areas on the imaging surface of the imaging element.

  The system control unit 116 functions as a calculation unit that calculates a focus evaluation value for each of a plurality of focus detection areas.

  The system control unit 116 is configured by a calculation device such as a CPU (Central Processing Unit) and performs various control programs stored in the internal memory 107 according to user operations, such as AE control, AF control, zoom control, and the like. Run the program to do.

  FIG. 2 illustrates the arrangement of distance measurement frames (focus detection frames) when photographing the starry sky, and the AF evaluation value in each distance measurement frame.

  In FIG. 2A, there is city light at the bottom of the angle of view, and a starry sky is present at the top including the center.

  If the user wants to focus on the starry sky, the arrangement shown in FIG. 2A may cause the lower part to be in focus on the city light due to the effect of the city light.

  FIG. 2B is a graph showing the relationship between the focus position and the AF evaluation value in each distance measurement frame.

  The focus lens is driven between infinity and close, and the higher the evaluation value, the higher the sharpness of the image.

  Clear peaks (peaks) appear in the upper left, upper, upper right, and center frames where only stars exist.

  No peak appears in the left and lower left frames where there is no light source including stars.

  The right, lower, and lower right frames where city lights are mixed tend to saturate when the amount of light is too strong. Even if they are not saturated, stars equivalent to infinity and finite city lights are mixed.

  Since the peak cannot be detected in the saturated lower right frame, there is no reliability for determining the focus position in focus.

  For the right and lower frames where a star equivalent to infinity and light from a finite city are mixed, the peak shape may be gentle, or two peaks may be formed, indicating the focus position where the focus is highly accurate There are times when you can't.

  Therefore, a peak with high reliability is detected in the upper left frame, the upper frame, the upper right frame, and the center frame, but in other frames, the reliability is low or no peak is detected in the first place.

  If the night sky has few stars, it is difficult to detect many reliable peaks.

  FIG. 3 is a little different from the desired angle of view, but illustrates the arrangement of the distance measurement frames and the AF evaluation value in each distance measurement frame when shooting the starry sky with the angle of view changed to the elevation angle. .

  Compared to FIG. 2A, FIG. 3A prevents the city light from entering the lower part of the angle of view.

  Compared with FIG. 2B, FIG. 3B can detect a highly reliable peak in each frame.

  FIG. 4 shows an example in which the position and number of distance measuring frames are changed without changing the angle of view in FIG. 2, that is, without changing the angle of view of the imaging apparatus to the elevation angle.

  FIG. 4A shows a state in which, as compared with FIG. 2A, the entire range-finding frame is shifted upward without changing the angle of view, and the lower part of the range-finding frame is subdivided.

  By subdividing the lower part of the distance measurement frame, it is possible to increase the possibility of separating the light from the stars and the city, and to increase the number of frames having highly reliable peaks.

  Compared with FIG. 2B, FIG. 4B can detect a highly reliable peak in the lower frame.

  FIG. 5 illustrates the arrangement of the distance measurement frames when photographing the starry sky near the zenith and the AF evaluation value in each distance measurement frame.

  FIG. 5A shows an angle of view near the zenith and is not affected by street light. Therefore, the entire frame is arranged in the center, and the number of frames is reduced as compared with the horizontal vicinity.

  When the size per frame is increased, the influence of noise is reduced when the AF evaluation value is acquired, so that the peak detection accuracy can be increased.

  Further, there is an advantage that the optical performance is better at the center of the angle of view than the end of the angle of view, such as less influence of aberration.

  FIG. 5B is a graph showing the relationship between the focus position in each distance measurement frame and the AF evaluation value with respect to FIG.

  FIG. 6 shows an example of a case where a flying object crosses during focusing.

  FIG. 6A is an image when exposure is performed at a predetermined focus position, and the trajectory of the flying object is reflected in the right frame.

  In focusing on the starry sky, since the AF evaluation value is detected under low illumination, the exposure time at each predetermined focus position tends to be long.

  Then, the peak position appears when the flying object is inside the frame, and the peak position disappears when the flying object is outside the frame. Therefore, there is a possibility that the peak does not always coincide with the star peak and the peak is erroneously detected.

  FIG. 6B is a graph showing the relationship between the focus position in each distance measurement frame and the AF evaluation value with respect to FIG. 6A, and the peak position in the right frame is deviated from the actual star position.

  Embodiments of the present invention will be described below with reference to FIGS.

  Step S701 is the start of starry sky focusing.

  Step S702 is a movement to the default position.

  Here, the default position corresponds to a focus position corresponding to infinity by adjustment when the starry sky is not focused once after the imaging apparatus is activated.

  An infinite distance mode for acquiring a focus evaluation value of a point light source subject corresponding to an infinite distance is set by the mode setting means.

  If the starry sky is focused even once, the previous position is set as the default position.

  In step S703, the inclination detection unit 112 detects the acceleration applied to the imaging apparatus, and the attitude determination unit 120 uses the detection result to determine the vertical angle (elevation angle and depression angle) of the imaging apparatus and the speed of the attitude change. judge.

  Step S704 is distance measurement frame control, and details are shown in FIG.

  Step S801 is the start of ranging frame control.

  In steps S802 and S803, the angle and the angle change speed used when determined in step S703 are acquired.

  In step S804, it is determined whether the angle change speed is faster or slower than a predetermined speed.

  That is, when the infinite distance mode is set, at least one of the position of the focus detection area and the number of areas of the focus detection area is changed based on the magnitude of the inclination of the imaging optical system.

  If the angle of view is determined by changing the angle of the imaging device at a slow speed, the angle of view can already be fine-tuned because there is a light source other than a star such as city lights in the lower frame with respect to the angle of view once determined There is sex.

  In this case, it is not necessary to change the position and number of the distance measurement frames from the initial position.

  If the change in angular velocity is greater than or equal to the predetermined velocity, the angle of view may not be finely adjusted.

  At that time, the process proceeds to a process of changing the position and number of the distance measurement frames.

  In step S805, the angle is compared with the zenith threshold angle to determine whether the posture of the imaging device is near the zenith.

  Step S806 is a case where the posture is near the zenith, and since the lower part of the distance measurement frame is not affected by the city light as shown in FIG. By arranging and reorganizing the frames, the number of frames is reduced compared to the initial value.

  When the size of each frame is increased, the influence of noise is reduced when acquiring the AF evaluation value (focus evaluation value), and thus there is an advantage that the detection accuracy of the peak position of the AF evaluation value is increased.

  In step S807, when the posture is not near the zenith, the angle is compared with the horizontal threshold angle to determine whether the posture of the imaging apparatus is near the horizontal.

  Step S808 is a case where the posture is near horizontal, and the lower part of the distance measurement frame may be affected by the city light as shown in FIG. By shifting in the direction and subdividing the lower ranging frame, the number of frames increases compared to the initial value.

  Step S809 is a case where the posture is an intermediate angle that is neither near the horizon nor near the zenith, and the positions of all the ranging frames are arranged in the center, and the combined, deformed and subdivided frames are released and defaulted. Return to the state.

  That is, when the magnitude of the tilt of the imaging optical system is smaller than a predetermined value, the positions on the imaging plane of the entire plurality of focus detection regions are compared with the angle of view compared to the case where the magnitude of the tilt of the imaging optical system is equal to or greater than the predetermined value. It is shifted to the upper side.

  Also, when the magnitude of the tilt of the imaging optical system is smaller than a predetermined value, the number of focus detection areas located below the angle of view is increased compared to the case where the magnitude of the tilt of the imaging optical system is greater than or equal to a predetermined value. ing.

  In addition, when the inclination of the imaging optical system is greater than or equal to a predetermined value, the positions on the imaging surface of the entire plurality of focus detection regions are compared with the angle of view compared to when the inclination of the imaging optical system is smaller than the predetermined value. It is shifted to the center part side.

  In addition, when the inclination of the imaging optical system is greater than or equal to a predetermined value, the number of focus detection areas is reduced compared to when the inclination of the imaging optical system is smaller than a predetermined value.

  In step S810, it is determined whether or not the angle has changed since the previous focusing was performed.

  In step S811, when the posture has not changed from the previous time, the AF evaluation value acquired at the time of the previous focusing is acquired.

  In step S812, it is determined whether or not there is a range-finding frame having a plurality of different peak positions for the acquired AF evaluation value.

  If there are multiple different peak positions in the starry sky, it is possible that the flying object entered and exited the frame on the way.

  In that case, the flying object flying in the night sky is likely to follow the same air route.

  Step S813 intends to increase even one frame capable of detecting a star by subdividing the target ranging frame.

  Step S814 is the end of the distance measurement frame control.

  Step S705 is photometry processing.

  In step S706, exposure setting is performed using the result of photometry in step S705.

  When the star is focused, the peak of the AF evaluation value is prevented from being crushed by intentionally underexposure to avoid saturation of luminance.

  In step S707, driving of the image sensor 105 is set for starry sky focusing.

  When AF is performed when not in the starry sky mode, the processing load is reduced by thinning out. However, since the proportion of stars in all pixels is very small, it is necessary to drive in all pixels.

  Step S708 is a movement to the start position of a process (scan) for driving the focus lens in a predetermined distance measurement range and acquiring AF evaluation values at predetermined intervals.

  When the starry sky mode is set after the imaging apparatus is activated, the focus lens moves to a position where the adjusted object at infinity is in focus.

  Considering the temperature difference and attitude difference during adjustment and starry sky photography, assuming a range that is out of focus in advance, the end of the range is set as the scan start position.

  Step S709 is an AF evaluation value acquisition loop start.

  In step S710, the focus is moved at predetermined intervals within the scan range.

  In step S711, an AF evaluation value is acquired at each focus position.

  Step S712 is the end of the AF evaluation value acquisition loop.

  In step S713, the reliability of the acquired AF evaluation value for each distance measurement frame is determined.

  As shown in FIG. 5B, when the peak of the evaluation value appears in all the ranging frames and the focus position with respect to the peak indicates the same position, it is determined that the reliability is high, and all the ranging frames are displayed. The average of the evaluation values at is calculated and the focus position in focus is determined.

  As shown in FIG. 5 (b), there is no problem if the reliability is high in all frames, but there may be no stars in the distance measurement frame, or reliability is lost due to the light of the city. There is also a case.

  Therefore, if a predetermined number of highly reliable ranging frames are provided, it is determined that the reliability has been ensured as a whole.

  If the reliability determination is OK, step S714 moves to the calculated peak focus position.

  When the reliability determination is NG, the position is moved to an infinite position that has been adjusted in advance.

  Step S701 is the end of starry sky focusing.

  That is, in the infinite distance mode, when there are a plurality of focus evaluation value peaks, the number of focus detection areas where the peaks exist is increased when the inclination of the imaging optical system does not change.

  As described above, the image pickup apparatus has been described as an example. However, the present invention is not limited to the image pickup apparatus, and the present invention can be applied to a portable device having the image pickup apparatus.

Claims (9)

  An image sensor that receives a light beam that has passed through an imaging optical system, an area setting unit that sets a plurality of focus detection areas on the imaging surface of the image sensor, and a calculation unit that calculates a focus evaluation value for each of the plurality of focus detection areas A focus adjusting means for performing focus adjustment based on the focus evaluation value, a mode setting means for setting an infinite distance mode for acquiring a focus evaluation value of a point light source subject corresponding to an infinite distance, and an inclination of the imaging optical system. Change in which at least one of the position of the focus detection area and the number of areas of the focus detection area is changed based on the magnitude of the inclination of the imaging optical system when the inclination detection means to detect and the infinite distance mode are set And an imaging device.   The changing means is configured to reduce the tilt of the imaging optical system when the tilt of the imaging optical system is smaller than a predetermined value, compared with a case where the tilt of the imaging optical system is greater than or equal to a predetermined value. The imaging apparatus according to claim 1, wherein the position on the imaging surface is shifted to the upper side of the angle of view.   The changing unit is configured to detect a focus detection area located below the angle of view when the magnitude of the tilt of the imaging optical system is smaller than a predetermined value, compared to when the magnitude of the tilt of the imaging optical system is equal to or greater than a predetermined value. The imaging apparatus according to claim 1, wherein the number of areas is increased.   The changing means is configured to reduce the inclination of the imaging optical system to a predetermined value or more when the inclination of the imaging optical system is smaller than a predetermined value. The imaging apparatus according to claim 1, wherein the position on the imaging surface is shifted toward the center of the angle of view.   The changing means may determine the number of the plurality of focus detection areas when the magnitude of the tilt of the imaging optical system is greater than or equal to a predetermined value compared to when the magnitude of the tilt of the imaging optical system is smaller than a predetermined value. The imaging apparatus according to claim 1, wherein the number is reduced.   In the infinite distance mode, the changing unit increases the number of focus detection areas where the peaks exist when there is a plurality of peaks of the focus evaluation value and the inclination of the imaging optical system does not change. The imaging device according to any one of claims 1 to 5.   2. The change means changes at least one of the position of the focus detection area and the number of areas of the focus detection area based on a speed at which the magnitude of the tilt of the imaging optical system is changed. The imaging device according to any one of Items 6 to 6.   When the speed at which the magnitude of the tilt of the imaging optical system is changed is greater than a predetermined value, the changing means determines the position of the focus detection area and the focus detection area based on the magnitude of the tilt of the imaging optical system. The imaging apparatus according to claim 1, wherein at least one of the number of areas is changed.   An area setting step for setting a plurality of focus detection areas on an imaging surface of an image sensor that receives a light beam that has passed through the imaging optical system; a calculation process for calculating a focus evaluation value for each of the plurality of focus detection areas; and the focus evaluation. A focus adjustment step of performing focus adjustment based on the value, a mode setting step of setting an infinite distance mode for acquiring a focus evaluation value of a point light source subject corresponding to an infinite distance, and an inclination detection step of detecting the inclination of the imaging optical system And a changing step of changing at least one of the position of the focus detection area and the number of areas of the focus detection area based on the inclination of the imaging optical system when the infinite distance mode is set. An imaging method characterized by the above.

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