JP6884582B2 - Imaging device, imaging method and imaging program - Google Patents

Description

The present invention relates to an image pickup apparatus that performs focus adjustment control (AF).

In the AF method, an image shift amount, which is a shift amount of a pair of image signals obtained by photoelectric conversion of a pair of subject images formed by two light fluxes passing through different regions of the exit pupils of an imaging optical system. There is a phase difference detection method (phase difference AF) that calculates the amount of defocus from. In this phase difference AF, the drive amount of the focus lens calculated from the defocus amount is calculated, and the focus lens is driven by the drive amount to obtain the in-focus state. The in-focus state is determined when the defocus amount after driving the focus lens is within a predetermined range (hereinafter, referred to as an in-focus determination width).

Such phase-difference AF is started in response to a half-press operation of the release button of the image pickup apparatus. Normally, by performing imaging (exposure) in response to the release button being fully pressed after the in-focus state is obtained by AF, a sufficiently focused still image can be obtained. However, the release button may be fully pressed at once without being stopped in the half-pressed operation state. In such a case, there are a process of performing imaging after the end of AF and a process of starting imaging regardless of whether or not it is in focus. Patent Document 1 discloses an imaging device that supports quick shooting with practically acceptable focusing accuracy by changing the focusing determination width according to whether or not the release button is fully pressed at once. ing.

If the focus lens is not obtained even though the focus lens is driven by AF, AF is performed again. In Patent Document 2, when the defocus amount does not fall within the focusing determination width and hunting occurs in which the focus lens continues to move even after several AFs, imaging is performed by changing the focusing determination width. An imaging device that prevents a delay in the timing of the above is disclosed.

Japanese Unexamined Patent Publication No. 2010-197601 Japanese Unexamined Patent Publication No. 2013-061537

The focus determination width is a parameter that is directly related to the accuracy of AF and the time required for AF. For example, if the focusing determination width is small, the time required for AF increases because the number of times AF is repeated without obtaining the focusing state is increased, but the accuracy of AF is improved.

However, even if the focus determination width is reduced, the AF accuracy does not necessarily improve due to various factors such as the limit of the actual drive accuracy of the focus lens and the detection variation of the defocus amount due to the variation of the subject. It can be a factor that unnecessarily slows down the AF speed. On the other hand, the AF speed is desired to be high within a range in which a practically acceptable focusing accuracy can be obtained so as not to miss a shutter chance.

The present invention provides an image pickup apparatus capable of shortening the time until an in-focus state is obtained by AF while improving the accuracy of AF regardless of the subject.

The imaging apparatus as one aspect of the present invention includes a defocus detecting means for detecting the defocus amount of the imaging optical system and a control means for performing focus adjustment control so that the defocus amount is within the focusing determination range. .. Then, the control means acquires information indicating the degree of variation in the defocus amount by using the signal obtained by photoelectric conversion of the subject image formed by the imaging optical system, and the first type having a relatively large degree of variation. In the case of, the focus determination range is made smaller than in the second case where the degree of variation is relatively small .

Further, the focus adjustment control method as another aspect of the present invention includes a step of detecting the defocus amount of the imaging optical system and a step of performing focus adjustment control so that the defocus amount is within the focusing determination range. Has. Then, in the focus adjustment control, information indicating the degree of variation in the defocus amount is acquired using the signal obtained by photoelectric conversion of the subject image formed by the imaging optical system, and the degree of variation is relatively large. The case of 1 is characterized in that the focusing determination range is made smaller than that of the second case where the degree of variation is relatively small.

A focus adjustment control program, which is a computer program for causing a computer of an imaging device to execute a process according to the focus adjustment control method, also constitutes another aspect of the present invention.

According to the present invention, the focusing determination range is appropriately changed according to the degree of variation in the defocus amount depending on the subject, so that the focusing state can be maintained regardless of the subject while performing focus adjustment control with good accuracy. The time to obtain can be shortened.

The block diagram which shows the structure of the image pickup apparatus which is the Example of this invention. The figure which shows the pixel composition of the image pickup device in an Example. The flowchart which shows the operation about the image pickup in an Example. The flowchart which shows the AF processing in an Example. The flowchart which shows the focus detection processing in an Example. The figure which shows the AF area used in the said focus detection process. The figure which shows the image signal obtained from the said AF area. The figure which shows the relationship between the shift amount and the correlation amount of the image signal. The figure which shows the relationship between the shift amount of the image signal and the correlation change amount. The flowchart which shows the reliability evaluation process in an Example. The figure which shows the conventional focusing determination width. The figure which shows the focusing determination width in an Example. The graph which shows the relationship between maxder and the standard deviation of the image displacement amount in an Example. The flowchart which shows the focusing determination width calculation process in an Example. The figure which shows the evaluation value which can be output from a filter in an Example.

Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a digital camera main body (hereinafter referred to as a camera main body) 200 and an interchangeable lens unit 100 as an imaging device according to an embodiment of the present invention. The interchangeable lens unit 100 is detachably attached (replaceable) to the camera body 200 via a mount portion (not shown) having an electrical contact unit 106.

In the interchangeable lens unit 100, 101 is an image pickup lens including a zoom mechanism, and 102 is an aperture shutter for controlling the amount of light. Reference numeral 103 denotes a focus lens that moves in the optical axis direction to adjust the focus. The image pickup optical system is composed of the image pickup lens 101, the aperture shutter 102, and the focus lens 103. Reference numeral 104 denotes a focus motor for driving the focus lens, and reference numeral 105 denotes a lens controller for controlling the operation of the interchangeable lens unit 100 such as driving the focus motor 104.

In the camera body 200, 201 is an image pickup element that photoelectrically converts a subject image formed by the image pickup optical system, and 202 is an A / D conversion unit that converts an analog electric signal output from the image pickup element 201 into a digital signal. .. Reference numeral 203 is an image processing unit, and 204 is an AF signal processing unit. Reference numeral 205 denotes a format conversion unit, and 206 is a memory such as a random access memory (hereinafter referred to as DRAM), as a high-speed buffer for temporary storage of image data, and as a working memory for compression / decompression processing of image data. used. Reference numeral 207 is an image recording unit including a recording medium such as a memory card and its interface. Reference numeral 208 denotes a timing generator, and 209 is a system control unit that controls operations of the camera body 200 such as AF processing (focus adjustment control) and imaging processing (imaging control).

Reference numeral 210 denotes a communication unit that communicates between the camera body 200 (system control unit 209) and the interchangeable lens unit 100 (lens controller 105). Reference numeral 211 is an AE processing unit, and reference numeral 212 denotes an image display memory (hereinafter referred to as VRAM). Reference numeral 213 is an image display unit, which is an image display unit that displays various information related to imaging, in addition to a live view image acquired before imaging and a still image captured by imaging. Reference numeral 215 is a mode switch operated by the user to select an imaging mode. The imaging mode includes a macro mode, a sports mode, and the like.

Reference numeral 216 is a main switch operated by the user to turn on the power to the camera body 200 and the interchangeable lens unit 100 that receives power from the camera body 200. Reference numeral 217 is a first switch (hereinafter referred to as SW1). SW1 (217) is turned on in response to a half-press operation as the first operation of the release button, which is an operation member (not shown) by the user, and prepares for imaging such as AF (autofocus adjustment) and AE (autoexposure). A signal instructing the system control unit 209 to execute the process is output. Reference numeral 218 is a second switch (hereinafter referred to as SW2). The SW2 (218) is turned on in response to a full-press operation of the release button as a second operation by the user, and outputs a signal instructing the system control unit 209 to execute the imaging process. Reference numeral 214 denotes an operation unit including various switches and dials operated by a user other than the mode switch 215, the main switch 216, SW1 (217) and SW2 (218). The operation unit 214 includes a menu switch for making various settings at the time of imaging and image reproduction, an imaging / reproduction mode switch for switching between an imaging mode and a reproduction mode, and the like.

The image sensor 201 described above is composed of a CCD sensor, a CMOS sensor, or the like, and photoelectrically converts the light (subject image) imaged on the image pickup surface by a photodiode included in each of the plurality of pixels. Each photodiode of the image sensor 201 accumulates an electric charge according to the amount of photoelectrically converted light. The electric charge accumulated in each photodiode is sequentially read out based on the drive pulse given from the timing generator 208 in response to the command of the system control unit 209, and is output as an analog electric signal.

Each pixel of the image sensor 201 used in this embodiment is composed of two (pair) photodiodes A and B and one microlens provided for the pair of photodiodes A and B. The pair of photodiodes A and B photoelectrically convert a pair of optical images formed by light fluxes from different regions (AF pupils) of the exit pupils of the imaging optical system via one microlens. A pair of AF signals, A signal and B signal, are output from the pair of photodiodes A and B. Further, an imaging pixel signal (A + B signal) can be obtained by adding the outputs of the pair of photodiodes A and B, and an imaging signal can be obtained by adding the imaging pixel signals in all the pixels.

By adding a plurality of A signals and a plurality of B signals output from a plurality of pixels in a direction orthogonal to the pupil division direction, AF by the imaging surface phase difference detection method (hereinafter referred to as imaging surface phase difference AF) can be obtained. The pair of phase difference image signals used is obtained. The AF signal processing unit 204 performs a correlation calculation on the pair of phase difference image signals, calculates an image shift amount which is a phase difference between the pair of phase difference image signals, and further captures an image of the subject from the image shift amount. Calculate the defocus amount (and defocus direction) of the optical system.

FIG. 2A shows a pixel configuration that does not correspond to the imaging surface phase-difference AF, and FIG. 2B shows a pixel configuration that corresponds to the imaging surface phase-difference AF. In each figure, the Bayer arrangement is used, where R indicates a red color filter, B indicates a blue color filter, and Gr and Gb indicate a green color filter. In the pixel configuration corresponding to the imaging surface phase difference AF shown in FIG. 2 (b), within the pixel corresponding to one pixel (enclosed by a solid line) in the pixel configuration not compatible with the imaging surface phase AF shown in FIG. 2 (a). Two photodiodes (with small A and B) divided into two in the horizontal direction in the figure are provided. The pixel division method shown in FIG. 2B is merely an example, and may be divided in the vertical direction of the figure or divided into two in the horizontal and vertical directions (four divisions in total). Further, a plurality of types of pixels divided by different division methods may be included in the same image pickup device.

The image pickup signal and the pair of phase difference image signals as analog electric signals read from the image pickup element 201 are input to the A / D conversion unit 202. The A / D converter 202 performs correlated double sampling for removing reset noise, gain adjustment, and digitization of an analog electric signal. The A / D conversion unit 202 outputs the image pickup signal to the image processing unit 203 and the pair of phase difference image signals to the AF signal processing unit 204, respectively.

The AF signal processing unit 204 performs a correlation calculation on the pair of phase difference image signals output from the A / D conversion unit 202 to perform image shift amount and reliability information (two-image matching degree, two-image steepness, contrast information, etc.). Calculate saturation information, scratch information, etc.). Further, the AF signal processing unit 204 calculates the defocus amount from the calculated image shift amount, and outputs the defocus amount and reliability information to the system control unit 209. The details of the correlation calculation will be described later with reference to FIGS. 6 to 9. The defocus detection means is configured by the image sensor 201 and the AF signal processing unit 204.

Next, the processing performed by the system control unit 209 as the control means in the camera body 200 of this embodiment will be described. First, the entire process related to imaging executed by the system control unit 209 will be described with reference to the flowchart of FIG. The system control unit 209 composed of a computer including a CPU and the like executes this process according to an imaging program which is a computer program. In the following description, "S" means a step.

First, in S301, the system control unit 209 causes the AE processing unit 211 to perform AE processing on the output from the image processing unit 203, and proceeds to S302.

In S302, the system control unit 209 checks the state of SW1 (217), and if it is ON, proceeds to S303, otherwise proceeds to S301.

In S303, the system control unit 209 performs AF processing described later together with the AF signal processing unit 204, and the focus lens is set so that the defocus amount of the imaging optical system is within the focusing determination width (within the focusing determination range) described later. Controls the drive of 103. Then proceed to S304.

In S304, the system control unit 209 checks the state of SW1 (217), and if it is ON, proceeds to S305, otherwise proceeds to S301.

In S305, the system control unit 209 checks the state of SW2 (218), and if it is ON, proceeds to S306, and if not, proceeds to S304.

In S306, the system control unit 209 performs an imaging process, and then returns to S301.

The AF process (focus adjustment control method) executed by the system control unit 209 together with the AF signal processing unit 204 in S303 described above will be described with reference to the flowchart of FIG. The system control unit 209 and the AF signal processing unit 204 execute this processing according to the focus adjustment control program which is a part of the above-mentioned imaging program.

First, in S401, the system control unit 209 initializes the AF process.

Next, in S402, the system control unit 209 causes the AF signal processing unit 204 to perform focus detection processing, and acquires the defocus amount and reliability information calculated by the AF signal processing unit 204. Then, the process proceeds to S403. The focus detection process is performed for each frame (hereinafter referred to as an image pickup frame) in which the image pickup pixel signal and the AF signal are read out from the image pickup element 201. The details of the focus detection process will be described later.

In S403, the system control unit 209 determines whether or not the reliability indicated by the reliability information acquired in S402 is higher than the preset "reliability threshold value 2", and if so, proceeds to S404, and so on. If not, proceed to S413. The "reliability threshold value 2" is a threshold value indicating that the accuracy of the defocus amount cannot be guaranteed when the reliability is less than the reliability threshold value 2, but the focus position direction of the subject can be guaranteed.

In S404, the system control unit 209 determines whether or not the defocus amount acquired in S402 (hereinafter referred to as the detected defocus amount) is smaller than the preset focusing determination width “Def amount threshold value 2”. .. When the detected defocus amount is Def amount threshold value 2 or less, the focus position is within the second focus determination range. If the detected defocus amount is smaller than the Def amount threshold value 2, the process proceeds to S405, and if not, the process proceeds to S412. In the "Def amount threshold value 2", if the detected defocus amount is equal to or less than the Def amount threshold value 2, the focus lens 103 is driven a predetermined number of times (for example, three times) according to the detected defocus amount to cause a second focusing. It is a threshold value indicating that a state is obtained. The second focusing state is a state in which the subject enters the depth of focus of the imaging optical system and the subject is in focus with high accuracy. The Def amount threshold value 2 is set to, for example, a value 5 times the depth of focus.

In S405, the system control unit 209 determines whether or not the focus lens 103 is in the stopped state, and if so, proceeds to S406, and if not, proceeds to S410.

In S406, the system control unit 209 determines whether or not the reliability indicated in the reliability information acquired in S402 is higher than the preset "reliability threshold value 1", and if so, proceeds to S407, and so on. If not, proceed to S410. The "reliability threshold value 1" is a threshold value indicating that the variation in the detected defocus amount is within a predetermined range (for example, within the depth of focus) when the reliability is the reliability threshold value 1 or more.

In S407, the system control unit 209 determines whether or not the detected defocus amount is smaller than the preset focusing determination width "Def amount threshold value 1", and if so, proceeds to S408, otherwise. Then proceed to S409. When the detected defocus amount is smaller than the Def amount threshold value 1, the focus position is in the first focusing determination range. The “Def amount threshold value 1” is a threshold value indicating that the first focusing state is obtained when the detected defocus amount is 1 or less of the Def amount threshold value, and takes a value smaller than the Def amount threshold value 2. The first in-focus state means a state in which the detected defocus amount is smaller than that in the second in-focus state, and practically acceptable focusing accuracy is obtained.

As described above, in this embodiment, "Def amount threshold value 1" and "Def amount threshold value 2" are used as the Def amount threshold value which is the value at the end of the focusing determination width. Further, in this embodiment, as will be described later with reference to FIG. 14, a plurality of “Def amount threshold values 1”, which are the first focusing determination widths, are set according to the magnitude (variation degree) of the variation in the detected defocus amount. It is changed between the focusing determination widths (1 to 4) of.

In S408, the system control unit 209 determines that the imaging optical system is in the focused state and ends this process.

On the other hand, in S409, the system control unit 209 calculates the drive amount of the focus lens 103 (hereinafter referred to as the focus drive amount) from the detected defocus amount, and transmits a focus command including the focus drive amount to the lens controller 105. The lens controller 105 controls the drive of the focus motor 104 so that the focus lens 103 is driven by the focus drive amount included in the focus command. After this, the system control unit 209 returns to S402.

By performing the above-mentioned processes S405 to S409, when the reliability acquired in S402 is higher than the "reliability threshold value 1", the defocus amount is calculated (detected) again with the focus lens 103 stopped. can do.

In S410, the system control unit 209 calculates a focus drive amount (hereinafter, referred to as a partial focus drive amount) with respect to a predetermined ratio of the detected defocus amount, and transmits a focus command including the partial focus drive amount to the lens controller 105. .. The predetermined ratio will be described later. The lens controller 105 controls the drive of the focus motor 104 so that the focus lens 103 is driven by the partial focus drive amount included in the focus command.

Next, in S411, the system control unit 209 instructs the lens controller 105 to stop the focus lens 103, and returns to S402.

Further, in S412, the system control unit 209 calculates a partial focus drive amount with respect to a predetermined ratio of the defocus amount acquired in S402, and sends a focus command including the partial focus drive amount to the lens controller 105, similarly to S410. Send. The lens controller 105 controls the drive of the focus motor 104 so that the focus lens 103 is driven by the partial focus drive amount included in the focus command. Then, the system control unit 209 returns to S402.

The "predetermined ratio" referred to in S410 and S421 is a ratio in which the driving amount of the focus lens 103 is smaller than the detected defocus amount, for example, 80%. Further, the drive speed of the focus lens 103 in S410 and S421 is set to be slower than the drive speed at which the drive of the focus lens 103 for the partial focus drive amount is completed by the time the focus detection process in the next imaging frame is completed. To. This makes it possible to prevent the focus lens 103 from passing through a position (focusing position) where a focusing state can be obtained with respect to the subject when the detected defocus amount is incorrect. Further, when returning from S412 to S402, the next focus detection process can be performed (that is, overlap AF control is performed) while driving the focus lens 103 without stopping it.

In S413, the system control unit 209 determines whether or not the out-of-focus condition is satisfied, and if so, proceeds to S414, and if not, proceeds to S415. The out-of-focus condition is a condition for determining that there is no subject to be focused on. For example, it is a condition that the driving of the focus lens 103 in the entire movable range is completed, that is, the focus lens 103 detects both the far side and the near side movable ends and returns to the initial position.

Then, in S414, the system control unit 209 determines that the imaging optical system is out of focus and ends this process.

In S415, the system control unit 209 determines whether or not the focus lens 103 has reached the movable end on the far side or the near side, and if so, proceeds to S416, and if not, proceeds to S417.

In S416, the system control unit 209 reverses the driving direction of the focus lens 103 and returns to S402.

In S417, the system control unit 209 drives the focus lens 103 in a predetermined direction and returns to S402. The driving speed of the focus lens 103 here is set to be the fastest in the range of the driving speed that does not pass the in-focus position when the defocus amount can be detected, for example.

Next, the focus detection process executed by the system control unit 209 and the AF signal processing unit 204 in the above-mentioned S402 will be described with reference to the flowchart of FIG. First, in S501, the system control unit 209 sets a focus detection region (hereinafter, referred to as AF region) in a range selected by the user or selected according to a predetermined algorithm in the imaging surface of the image sensor 201, and proceeds to S502. ..

In S502, the AF signal processing unit 204 acquires AF signals (A signal and B signal) from the pixels included in the AF region set in S501 of the image pickup surface of the image pickup element 201, and proceeds to S503.

In S503, the AF signal processing unit 204 vertically performs row addition averaging processing on the AF signal acquired in S502 to generate a pair of phase difference image signals. This vertical row addition averaging process can reduce the influence of noise on a pair of phase difference image signals.

In S504, the AF signal processing unit 204 performs one of a plurality of types of filter processing for extracting signal components in a predetermined frequency band from the pair of phase difference image signals generated by the vertical row addition averaging processing in S503. Proceed to S505.

In S505, the AF signal processing unit 204 calculates the correlation amount of the pair of phase difference image signals that have undergone the filtering process in S504, and proceeds to S506.

In S506, the AF signal processing unit 204 calculates the amount of correlation change from the amount of correlation calculated in S505, and proceeds to S507.

In S507, the AF signal processing unit 204 calculates the amount of image shift from the amount of correlation change calculated in S505, and proceeds to S508.

In S508, the AF signal processing unit 204 evaluates the reliability of the image shift amount calculated in S507, and proceeds to S509.

In S509, the AF signal processing unit 204 converts the image shift amount into a defocus amount and outputs the detected defocus amount to the system control unit 209. Then, the process proceeds to S510.

In S510, the AF signal processing unit 204 determines whether or not all of the plurality of types of filter processing in S504 has been completed, and if so, proceeds to S511, and if not, proceeds to S504. As a plurality of types of filter processing in S504, the AF signal processing unit 204 processes, for example, a pair of phase difference image signals generated by vertical row addition averaging by a bandpass filter having a plurality of frequency bands having different bands. In the horizontal direction.

The AF signal processing unit 204 determines in S510 whether or not the series of processing of S504 to S509 has been performed for all of the plurality of frequency bands, and if so, proceeds to S511, and if not, returns to S504. ..

In S511, at least one of a plurality of detection defocus amounts corresponding to each of the plurality of frequency bands calculated by the series of processes of S504 to S509 is selected to end the focus detection process.

Next, the focus detection process described with reference to FIG. 5 will be described in detail. FIG. 6 shows an example of the AF region 602 on the pixel array 601 of the image sensor 201 in the focus detection process. The shift regions 603 on both sides of the AF region 602 are regions necessary for the correlation calculation. Therefore, the area 604, which is the combination of the AF area 602 and the shift area 603, is a pixel area required for the correlation calculation. In the figure, p, q, s, and t represent the coordinates in the horizontal direction (x-axis direction), p and q represent the x-coordinates of the start point and the end point of the pixel area 704, respectively, and s and t represent the AF area, respectively. The x-coordinates of the start point and the end point of 602 are shown.

FIG. 7A shows an example of a pair of phase difference image signals acquired from a plurality of pixels included in the AF region 602 shown in FIG. The solid line indicates one phase difference image signal 701, which is referred to as an A image signal below. Further, the broken line indicates the other phase difference image signal 702, which is referred to as a B image signal below. 7 (a) shows the A image and B image signals 701 and 702 before the shift, and FIGS. 7 (b) and 7 (c) show the A image and B image signals 701 and 702, respectively, of FIG. 7 (a). It shows a state of shifting from the position in the plus direction and the minus direction. When calculating the amount of correlation between the A image and the B image signals 701 and 702, both the A image and the B image signals 701 and 702 are shifted by 1 bit in the direction of the arrow.

Next, a method of calculating the correlation amount will be described. First, as shown in FIGS. 7 (b) and 7 (c), the A image and the B image signals 701 and 702 are shifted by 1 bit each, and the sum of the absolute values of the differences between the A image and the B image signals 701 and 702 is summed. Is calculated. Let i be the shift amount, ps be the maximum shift amount in the minus direction, qt be the maximum shift amount in the plus direction, x be the start coordinate of the AF area 602, and y be the end coordinate of the AF area 602. .. At this time, the correlation amount COR can be calculated by the following equation (1).

FIG. 8A shows an example of the relationship between the shift amount and the correlation amount COR. The horizontal axis shows the shift amount, and the vertical axis shows the correlation amount COR. Among the 802,803 near the extreme values in the correlation amount 801 that changes with the shift amount, the degree of coincidence between the A image and the B image signals 701 and 702 is the highest in the shift amount corresponding to the smaller correlation amount.

Next, a method of calculating the amount of correlation change will be described. The difference in the correlation amount every other shift in the waveform of the correlation amount 801 shown in FIG. 8A is calculated as the correlation change amount. Assuming that the shift amount is i, the maximum shift amount in the minus direction is ps, and the maximum shift amount in the plus direction is qt, the correlation change amount ΔCOR can be calculated by the following equation (2).

FIG. 9A shows an example of the relationship between the shift amount and the correlation change amount ΔCOR. The horizontal axis shows the shift amount, and the vertical axis shows the correlation change amount ΔCOR. The correlation change amount 901 that changes with the shift amount changes from plus to minus in the portion of 902 and 903. The state in which the amount of correlation change is 0 is called zero cross, and the degree of coincidence between the A image and B image signals 701 and 702 is the highest. Therefore, the shift amount that gives zero cross is the image shift amount.

FIG. 9B shows an enlarged portion shown by 902 in FIG. 9A. 904 is a part of the correlation change amount 901. A method of calculating the image shift amount PRD will be described with reference to FIG. 9B.

The shift amount (k-1 + α) that gives a zero cross is divided into an integer part β (= k-1) and a decimal part α. The fractional part α can be calculated by the following equation (3) from the similarity relationship between the triangle ABC and the triangle ADE in the figure.

The integer part β can be calculated from FIG. 9B by the following equation (4).
β = k-1 (4)
Then, the image shift amount PRD can be calculated from the sum of α and β (α + β).
When there are a plurality of zero crosses of the correlation change amount ΔCOR as shown in FIG. 9A, the one having a larger change in the correlation change amount ΔCOR in the vicinity thereof is defined as the first zero cross. This steepness is an index showing the ease of performing AF, and the larger the value, the easier it is to perform accurate AF. The steepness maxder can be calculated by the following equation (5).

As described above, in this embodiment, when there are a plurality of zero crosses of the correlation change amount, the first zero cross is determined by the steepness thereof, and the shift amount that gives the first zero cross is defined as the image shift amount.

Next, the reliability evaluation process performed by the AF signal processing unit 204 in S508 will be described with reference to the flowchart of FIG. In S1001, the AF signal processing unit 204 normalizes the maxder according to the imaging conditions (sensor gain, read-out line addition number, etc.) and subject conditions (contrast, etc.). The reason for normalizing maxder is to improve the accuracy of reliability.

Next, in S1002, the AF signal processing unit 204 determines whether or not the detected defocus amount is larger than the predetermined defocus amount threshold value. When the detected defocus amount is larger than the defocus amount threshold value, the AF signal processing unit 204 proceeds to S1003 and sets the reliability to 0. When the detected defocus amount is equal to or less than the defocus amount threshold value, the process proceeds to S1004, and it is determined whether or not the maxder normalized in S1001 is equal to or less than the normalized maxder threshold value.

When the normalized maxder is equal to or less than the normalized maxder threshold value, the AF signal processing unit 204 proceeds to S1003, sets the reliability to 0, and ends this process. A reliability of 0 indicates that the reliability of the detected defocus amount is extremely low.

In this embodiment, the defocus amount threshold value and the maxder threshold value are set for each filter. The defocus amount threshold is set according to the defocus amount detection capability of each filter (the limit distance at which focus can be detected from the viewpoint of the total shift amount). Further, the normalized maxder becomes small in a scene where the reliability is likely to be mistaken, such as when the brightness is low or when the focus detection process is performed for a low contrast subject. Therefore, by setting the normalized maxder threshold value, it is possible to prevent an erroneous output of reliability.

The AF signal processing unit 204, which determines in S1004 that the normalized maxder is larger than the normalized maxder threshold, proceeds to S1005 and estimates the standard deviation of the image shift amount based on the normalized maxder. As shown in FIG. 13, since there is a negative correlation between the normalized maxder and the standard deviation of the image shift amount, the standard deviation of the image shift amount can be estimated from the normalized maxder.

Next, in S1006, the AF signal processing unit 204 multiplies the standard deviation of the image shift amount by a predetermined conversion coefficient to calculate the standard deviation of the detected defocus amount. The conversion coefficient used here is the same as the conversion coefficient used when calculating the detection defocus amount from the image shift amount, the aperture value of the aperture 102, the exit pupil distance of the imaging optical system, the individual information of the image sensor 201, and the conversion coefficient. It is a value determined by the coordinates of the AF region on the image pickup surface. As described above, the standard deviation as information indicating the degree of variation in the detected defocus amount is obtained from the image shift amount, that is, the shift amount of the pair of phase difference image signals obtained by photoelectric conversion of the subject image.

Further, the standard deviation of the detected defocus amount is also normalized by dividing by the aperture value F and the permissible circle of confusion δ. When evaluating the reliability (that is, the standard deviation of the detected defocus amount) based on the maxder, it is necessary to set the threshold value for the number of the above conversion coefficients. Therefore, in this embodiment, a more desired threshold value can be set without holding a large amount of threshold data in the ROM 137. Further, since it is normalized by the aperture value F, it is possible to set the threshold value regardless of the state of the aperture 102.

In the following S1400, the AF signal processing unit 204 sets the focusing determination width. The focusing determination width setting process in this step will be described later.

Next, in S1007 and thereafter, the AF signal processing unit 204 evaluates the reliability of the detected defocus amount according to the standard deviation of the detected defocus amount. In this embodiment, the threshold value of the standard deviation of the detected defocus amount is set in three stages (THRESHOLD1, THRESHOLD2, THRESHOLD3). THRESHOLD1, THRESHOLD2 and THRESHOLD3
THRESHOLD3 <THRESHOLD2 <THRESHOLD1
Has a relationship. Further, the reliability N (N = 0 to 3) means that the smaller the number, the lower the reliability.

First, if the standard deviation of the detected defocus amount is larger than THRESHOLD1 in S1007, the AF signal processing unit 204 proceeds to S1003 and determines that the reliability of the detected defocus amount is 0. Further, in S1008, when the standard deviation of the detected defocus amount is THRESHOLD1 or less and larger than THRESSHOLD2, the AF signal processing unit 204 proceeds to S1009 and determines the reliability as reliability 1.

Further, in S1010, when the standard deviation of the detected defocus amount is THRESHOLD2 or less and larger than THRESSHOLD3, the AF signal processing unit 204 proceeds to S1011 and determines the reliability as reliability 2. When the standard deviation of the detected defocus amount is THRESHOLD 3 or less, the AF signal processing unit 204 proceeds to S1012 and determines the reliability as the reliability 3.

The above is the basic process for evaluating the reliability, but the reliability evaluation method may be changed for each of the roles of the three types of filters. FIG. 15 shows the reliability that can be output from each filter. The condition marked with ◯ means the reliability that can be output, and the condition marked with × means the reliability that is not output. Since the low-frequency filter has low accuracy, it does not output reliability 3, which means that it can be focused. Further, in the high frequency filter, the total shift amount is small and the focus cannot be detected for the subject at the time of large blur, so the reliability 1 is not output. By processing in this way, the possibility of outputting an erroneous reliability can be reduced.

In the imaging surface phase difference AF, the difference between the frequency band of the bandpass filter and the frequency band of the subject and the effect of vignetting of the AF pupil due to the lens frame holding the lens constituting the imaging optical system change according to the amount of defocus. To do. Therefore, in the imaging surface phase difference AF, the detected defocus amount may deviate from the proportional relationship (linearity) with respect to the actual defocus amount of the focus lens 103. This deviation of the detected defocus amount is likely to occur especially when the detected defocus amount is large, and changes according to the spatial frequency of the subject and the detected defocus amount. It is difficult to make corrections.

On the other hand, considering the time required for the AF process and the operation quality in the AF process, it is desirable to minimize (eliminate) the reversal of the drive direction of the focus lens 103. Therefore, in this embodiment, as described above, in AF from a state where the defocus amount is large, the focus drive amount corresponding to the detected defocus amount is not set as it is, but is 1 or less with respect to the detected defocus amount. Multiply by the coefficient of to set the partial focus drive amount. As a result, it is possible to prevent the focus lens 103 from having to reverse the driving direction due to passing through the in-focus position, and to realize smooth AF.

However, as described above, the deviation of the detected defocus amount tends to occur when the defocus amount is large, and the linearity is maintained when the defocus amount is small. Under the condition that the linearity of the detected defocus amount is maintained, it is desirable to set the focus drive amount corresponding to the detected defocus amount as it is to realize faster AF.

In this embodiment, as the focus drive amount in one frame, the range of the detection defocus amount in which the focus drive amount corresponding to the detection defocus amount can be set is set as the first defocus range, and the detection defocus larger than that is set as the first defocus range. The range of quantity is defined as the second defocus range. If the detected defocus amount is within the first defocus range, even if the first focus determination range for determining whether or not the in-focus state is obtained is widened, the in-focus state (practically acceptable) The first in-focus state) is obtained. On the other hand, when the detected defocus amount is in the second defocus range, the focus lens 103 is driven until a highly accurate focusing state (second focusing state) is obtained by narrowing the focusing determination width. Is desirable.

Further, in this embodiment, in order to realize faster AF when the detected defocus amount is in the first defocus range, not only the focus drive amount in one frame but also the first focus determination width is used. The "Def amount threshold value 1" is also changed according to the subject.

Next, “Def amount threshold value 1” will be described with reference to FIGS. 11 (a) and 11 (b) and FIGS. 12 (a) and 12 (b). In this embodiment, by appropriately setting (changing) the focusing determination width, which is the "Def amount threshold value 1", according to the subject to be imaged (that is, the subject image), until the focusing state is obtained by the AF process. Reduce the time required for. In any of FIGS. 11 (a) and 11 (b) and 12 (a) and 12 (b), the defocus amount is within ± 1 Fδ as the focusing reference width as the practically acceptable focusing accuracy. ..

FIGS. 11A and 11B show a conventional method in which the focusing determination width (± 0.25Fδ) is constant regardless of the subject. FIG. 11A shows a first focus with the defocus detection variation when the subject has high contrast and the degree of variation in the detected defocus amount (hereinafter referred to as defocus detection variation) is ± 0.25 Fδ. The relationship with the judgment width is shown. Further, FIG. 11B shows the relationship between the defocus detection variation and the first focus determination width when the subject has a low contrast and the defocus detection variation is ± 0.75 Fδ.

The detection error of the defocus amount in the imaging surface phase difference AF includes an offset error caused by various factors such as the band shift as described above, a variation for each detection when the defocus amount is repeatedly detected, and the like. In the conventional method shown in FIG. 11A, even a high-contrast subject having a small defocus detection variation uses the same focusing determination width as a low-contrast subject having a large defocus detection variation. For this reason, the focusing state is determined more strictly than the above-mentioned practically acceptable focusing accuracy.

As described in S407 of FIG. 4, when the detected defocus amount is not within the focusing determination width (Def amount threshold value 1), the focus lens is driven again. It is desirable that the focus lens is driven in the vicinity of the in-focus state based on the detected defocus amount acquired in the frame in which the focus lens is stopped in order to ensure the detection accuracy of the defocus amount. Therefore, in order to detect the defocus amount, a frame for determining the stop of the focus lens, an imaging frame after the lens is stopped, and a frame for calculating the defocus amount from a pair of phase difference image signals obtained by the imaging frame. Etc. are required. During these plurality of frames, the focus lens cannot move, and the AF process for moving the focus lens to the in-focus position is delayed.

12 (a) and 12 (b) show the focusing determination width in this embodiment. In this embodiment, the defocus detection variation according to the subject, that is, the standard deviation of the detection defocus amount acquired in the focus detection process (S1006 in FIG. 5) is set as the “Def amount threshold value 1”. Set the focus judgment width.

FIG. 12A shows the relationship between the defocus detection variation and the in-focus determination width when the subject has high contrast and the defocus detection variation is ± 0.25 Fδ. Further, FIG. 12B shows the relationship between the defocus detection variation and the in-focus determination width when the subject has a low contrast and the defocus detection variation is ± 0.75 Fδ.

In FIG. 12A, the defocus detection variation is appropriately considered, and the focusing determination width (Def amount threshold value 1) is widened while ensuring the focusing accuracy that is practically allowed. As a result, the frequency with which the focus lens 103 is driven a plurality of times in the vicinity of the focused state is reduced.

The flowchart of FIG. 14 shows the focusing determination width setting process executed by the AF signal processing unit 204 in S1400 of FIG. In this embodiment, the focusing determination width is set stepwise as in the determination of reliability. In step S1401, the AF signal processing unit 204 reads the standard deviation of the detected defocus amount calculated in S1006.

Subsequently, in S1402, the AF signal processing unit 204 determines whether or not the standard deviation of the detected defocus amount is smaller than Def1_Th1, and if so, proceeds to S1403 and sets the focusing determination width (Def amount threshold value 1). Set the focus determination width to 1 for high-contrast subjects. When the standard deviation of the detected defocus amount is Def1_Th1 or more and smaller than Def1_Th2, the AF signal processing unit 204 proceeds to S1405 and sets the focusing determination width to the focusing determination width 2 for the medium contrast subject.

If the standard deviation of the detected defocus amount is Def1_Th2 or more and smaller than Def1_Th3, the AF signal processing unit 204 proceeds to S1407 and sets the focusing determination width to the focusing determination width 3 for a low-contrast subject. .. When the standard deviation of the detected defocus amount is Def1_Th3 or more, the AF signal processing unit 204 proceeds to S1408 and sets the focusing determination width to the focusing determination width 4 for an ultra-low contrast subject. Here, the magnitude relationship of the focusing determination width is shown below.

Focus judgment width 4 <Focus judgment width 3 <Focus judgment width 2 <Focus judgment width 1
As described above, in this embodiment, the higher the contrast of the subject and the smaller the defocus detection variation, the wider the focusing determination width is set. As a result, it is possible to shorten the time required for the AF process to obtain the focusing state while ensuring at least the practically acceptable focusing accuracy.

In the above embodiment, the case where the focusing determination width is changed stepwise has been described, but the focusing determination width is continuously changed according to the difference between the standard deviation of the detected defocus amount and the focusing reference width. You may do so.

Further, in the above embodiment, the standard deviation is used as the information indicating the degree of variation in the detected defocus amount, but information indicating other degrees of variation such as dispersion may be used. Further, in the above embodiment, the case where the degree of variation in the defocus amount is calculated by using a pair of phase difference image signals has been described, but the degree of variation is acquired by using another signal obtained by photoelectric conversion of the subject image. You may. For example, information indicating the contrast of the subject image may be generated from the image pickup signal generated by the output from the image sensor 201, and the degree of variation in the defocus amount may be estimated from the information indicating the level of the contrast.

Further, in the above embodiment, the case where AF is performed by driving the focus lens in the optical axis direction has been described, but the above embodiment can also be applied when AF is performed by driving the image sensor in the optical axis direction. ..

Further, in the above embodiment, a case where the focus determination width is changed according to the defocus detection variation in the AF process from the half-press operation (SW1 ON) to the full-press operation (SW2 ON) of the release button will be described. did. However, the focusing determination width may be changed according to the defocus detection variation only when a specific condition such that the half-press operation to the full-press operation of the release button is performed at once is satisfied. As a result, the quick shooting property required by the user can be ensured.
(Other Examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Each of the above-described examples is only a representative example, and various modifications and changes can be made to each of the examples in carrying out the present invention.

103 Focus lens 200 Digital camera body 201 Image sensor 204 AF signal processing unit 209 System control unit

Claims (7)

Defocus detection means for detecting the amount of defocus in the imaging optical system,
It has a control means for performing focus adjustment control so that the defocus amount is within the focus determination range.
The control means
Using the signal obtained by photoelectric conversion of the subject image formed by the imaging optical system, information indicating the degree of variation in the defocus amount is acquired.
The first case in which the degree of variation is relatively large is characterized in that the focusing determination range is made smaller than in the second case where the degree of variation is relatively small. The defocus detection means calculates the defocus amount from the image shift amount of the pair of phase difference image signals obtained by the phase difference detection method.
The imaging device according to claim 1, wherein the control means acquires information indicating the degree of variation using the image shift amount. The imaging device according to claim 1, wherein the control means acquires information indicating the degree of variation by using information on the contrast of the subject image obtained from the signal. The control means determines whether the defocus amount is within the first focus determination range, and then determines whether the defocus amount is within the second focus determination range narrower than the first focus determination range. ,
The imaging device according to any one of claims 1 to 3 , wherein the control means changes the second focusing determination range according to the degree of variation. The control means
The focus adjustment control is performed according to the first operation of the operating member, and the imaging control is performed according to the second operation of the operating member.
Any one of claims 1 to 4 , wherein when the second operation is performed before the focus adjustment control is completed, the focus determination range is changed according to the degree of variation. The imaging apparatus according to. Steps to detect the amount of defocus in the imaging optical system,
It has a step of performing focus adjustment control so that the defocus amount is within the focusing determination range.
In the focus adjustment control,
Using the signal obtained by photoelectric conversion of the subject image formed by the imaging optical system, information indicating the degree of variation in the defocus amount is acquired.
A focus adjustment control method characterized in that the first case where the degree of variation is relatively large is smaller than the second case where the degree of variation is relatively small. To the computer of the image pickup device
Processing to detect the amount of defocus in the imaging optical system and
A computer program that executes a process of performing focus adjustment control so that the defocus amount is within the focus determination range.
To the computer that performs the focus adjustment control,
Using the signal obtained by photoelectric conversion of the subject image formed by the imaging optical system, information indicating the degree of variation in the defocus amount is acquired.
A focus adjustment control program characterized in that the focus adjustment determination range is made smaller in the first case where the degree of variation is relatively large than in the second case where the degree of variation is relatively small.

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