JP6838894B2 - Focus control device, its control method and program - Google Patents

Description

The present invention relates to a focus adjustment device that adjusts the focus by a phase difference detection method using an output signal from an image sensor, a control method thereof, and a program thereof.

Some image pickup devices such as digital cameras perform autofocus of a phase difference detection method in which focus detection and focus adjustment are performed by detecting the phase difference of a pair of parallax image signals. In particular, the focus detection method of the phase difference detection method using the output signal from the image sensor that captures the subject image is called the imaging surface phase difference detection method.

As a technique relating to an image pickup apparatus that employs a phase difference detection method, Patent Document 1 describes a defocus amount calculated in the past based on an evaluation value based on contrast information of an image signal for the purpose of improving focus detection accuracy. When it is determined that the above is taken into consideration, a configuration is disclosed in which the final defocus amount is calculated based on a plurality of defocus amounts including the defocus amount calculated in the past.

Japanese Unexamined Patent Publication No. 2016-57546

In the phase difference detection method including the imaging surface phase difference detection method, for example, when shooting a low-brightness condition such as a night view or a room or when shooting a low-contrast subject such as a human face, the comparison is made when shooting a high-brightness or high-contrast subject. As a result, the obtained image signal becomes smaller, which may reduce the focusing accuracy.
However, Patent Document 1 does not mention processing adapted to the brightness condition and the contrast condition, and when the focusing control is performed with reference to the time of high brightness or the time of shooting a high contrast subject, the condition of low brightness or low When shooting a contrast subject, there may be a case where suitable focusing control cannot be performed and the focusing accuracy is lowered. On the other hand, if focusing control is performed based on low-brightness conditions or when shooting a low-contrast subject, suitable focusing control cannot be performed when shooting a high-brightness or high-contrast subject, and the focusing accuracy deteriorates. Can exist.

The present invention has been made in view of the above points, and an object of the present invention is to reduce a decrease in focusing accuracy due to a brightness condition or a contrast of a subject (referred to as a contrast condition).

The focus adjustment device of the present invention is a focus adjustment device that adjusts the focus by a phase difference detection method using an output signal from an image pickup element that captures a subject image, and is a subject image generated from the output signal of the image pickup element. The generation means for generating the focus detection information using a pair of image signals having a phase difference according to the focal state of the above, and the standard deviation of the focus detection information generated by the generation means for the amount of correlation change of the pair of image signals. A second calculation means for calculating the reliability of the focus detection information using the first calculation means calculated using the method and the standard deviation of the focus detection information calculated by the first calculation means and its threshold value are used to calculate the reliability evaluation value. comprising a calculation unit, a second calculation means, based on at least one of luminance conditions and contrast conditions, by changing the threshold value, the reliability evaluation value so as to reduce the focusing condition It is characterized in that the calculation condition of is changed.

According to the present invention, it is possible to reduce a decrease in focusing accuracy due to brightness conditions and contrast conditions.

It is a block diagram which shows the structure of the interchangeable lens type camera which concerns on embodiment. It is a figure for demonstrating the pixel structure of an image sensor. It is a flowchart which shows the shooting process by the interchangeable lens type camera which concerns on embodiment. It is a flowchart which shows the detail of the automatic focus detection processing in FIG. It is a flowchart which shows the detail of the frame addition determination operation in FIG. It is a characteristic diagram which shows an example of the relationship between the blur and the amount of correlation change. It is a characteristic diagram which shows the example of the relationship between the imaging sensitivity and the threshold value of the standard deviation of the defocus amount. It is a characteristic diagram which shows the example of the relationship between the amplitude of an image signal, and the threshold value of the standard deviation of the defocus amount. It is a characteristic figure which shows the example of the relationship between the contrast evaluation value and the threshold value of the standard deviation of the defocus amount. It is a characteristic diagram which shows an example of the relationship between the sharpness evaluation value, and the threshold value of the evaluation value which shows the degree of blurring of an image.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration of an interchangeable lens camera (hereinafter, simply referred to as a camera) according to the embodiment. The camera according to the embodiment is an example of an image pickup device equipped with a focus adjustment device to which the present invention is applied, and performs focus adjustment by an imaging surface phase difference detection method using an output signal from an image pickup device that images a subject image. ..
The camera includes a lens unit 10 and a camera body 20. When the lens unit 10 is attached to the camera body 20, the lens control unit 106 that controls the operation of the lens unit 10 and the camera control unit 212 that controls the operation of the entire camera can communicate with each other.

The configuration of the lens unit 10 will be described. The lens unit 10 includes a fixed lens 101, an aperture 102, a focus lens 103, an aperture drive unit 104, a focus lens drive unit 105, a lens control unit 106, and a lens operation unit 107.
The photographing optical system is composed of the fixed lens 101, the aperture 102, and the focus lens 103. The diaphragm 102 is driven by the diaphragm drive unit 104 and controls the amount of light incident on the image sensor 201 of the camera body 20. The focus lens 103 is driven by the focus lens driving unit 105, and adjusts the focus to form an image on the image sensor 201, which will be described later. The aperture drive unit 104 and the focus lens drive unit 105 are controlled by the lens control unit 106 to determine the aperture amount of the aperture 102 and the position of the focus lens 103. When the lens operation unit 107 performs a user operation, the lens control unit 106 controls according to the user operation. The lens control unit 106 controls the aperture drive unit 104 and the focus lens drive unit 105 according to the control command / control information received from the camera control unit 212, and also transmits the lens control information to the camera control unit 212.

Next, the configuration of the camera body 20 will be described. The camera body 20 is configured to be able to acquire an imaging signal from a luminous flux that has passed through the photographing optical system of the lens unit 10. The camera body 20 includes an image sensor 201, a CDS / AGC / AD converter 202, an image input controller 203, and an AF (autofocus adjustment) signal processing unit 204. Further, the camera body 20 includes a display control unit 205, a display unit 206, a recording medium control unit 207, a recording medium 208, an SDRAM 209, a ROM 210, and a flash ROM 211. Further, the camera body 20 includes a camera control unit 212 having an AF control unit 213, a camera operation unit 214, a timing generator 215, and a bus 216.

The image sensor 201 is composed of a CCD or a CMOS sensor, and a light beam that has passed through the photographing optical system of the lens unit 10 is imaged on the light receiving surface thereof, and is converted into a signal charge according to the amount of incident light by a photodiode. The signal charge accumulated in each photodiode is sequentially read out as a voltage signal corresponding to the signal charge based on the drive pulse given from the timing generator 215 according to the command of the camera control unit 212.
As shown in FIG. 2B, the image sensor 201 holds two photodiodes in one pixel in order to adjust the focus by the imaging surface phase difference detection method. FIG. 2A shows a pixel configuration when the imaging surface phase difference detection method is not adopted, and FIG. 2B shows a pixel configuration when the imaging surface phase difference detection method is adopted. By separating the luminous flux with a microlens and forming an image with two photodiodes of each pixel, an imaging signal and an image signal for AF (hereinafter, referred to as an AF signal) can be taken out. The sum of the signals of the two photodiodes (A + B image signal) becomes the imaging signal. Further, the signals of the individual photodiodes (A image signal and B image signal) become AF signals, respectively, and the pair of AF signals have a phase difference according to the focal state of the subject image.

The CDS / AGC / AD converter 202 performs correlated double sampling for removing reset noise, gain adjustment, and signal digitization for the image pickup signal and a pair of AF signals read out from the image sensor 201. Do. The CDS / AGC / AD converter 202 outputs an image pickup signal to the image input controller 203 and a pair of AF signals to the AF signal processing unit 204, respectively.
The image input controller 203 stores the image pickup signal output from the CDS / AGC / AD converter 202 in the SDRAM 209. The image signal stored in the SDRAM 209 is displayed on the display unit 206 by the display control unit 205 via the bus 216, and in the mode of recording the image pickup signal, the recording medium control unit 207 displays the image signal on the recording medium 208. Recorded.
The ROM 210 stores a control program executed by the camera control unit 212 and various data required for control.
The flash ROM 211 stores various setting information and the like related to the operation of the camera such as user setting information.

The AF signal processing unit 204 performs a correlation calculation on a pair of AF signals output from the CDS / AGC / AD converter 202, and performs an image shift amount and various information (two-image matching degree, contrast information, saturation information, scratches). Information etc.) is calculated. The AF signal processing unit 204 outputs the calculated image shift amount and various information to the camera control unit 212.

The camera control unit 212 controls by exchanging information with each unit of the camera. In addition, various camera functions operated by the user such as power ON / OFF, setting change, start of recording, start of AF control, confirmation of recorded image, etc. are executed according to the input from the camera operation unit 214. .. In addition, it communicates with the lens control unit 106 of the lens unit 10, sends control commands and control information of the lens, and acquires information on the lens unit 10 side.
Further, the AF control unit 213 of the camera control unit 212 performs focusing control on the subject, although the details will be described later. The AF control unit 213 notifies the AF signal processing unit 204 of a change in the setting for calculating these based on the image shift amount and various information acquired from the AF signal processing unit 204. For example, when the amount of image shift is large, the area for performing the correlation calculation is set wide, or the type of the bandpass filter is changed according to the contrast information.
The camera operation unit 214 includes operation units such as a shutter button, a mode changeover switch, an electronic dial, and a power switch.

In the present embodiment, the image pickup signal and the pair of AF signals are taken out from the image pickup element 201, but the present invention is not limited to this method. Considering the load of the image sensor 201, for example, an image pickup signal and one AF signal are taken out from the image sensor, and the difference between the image pickup signal and the AF signal is taken to generate another AF signal. May be good.

The shooting process by the camera according to the embodiment will be described with reference to FIG. The flowchart of FIG. 3 is realized, for example, by the camera control unit 212 executing the program stored in the ROM 210.
In step S1, the camera control unit 212 determines whether or not the first switch (SW1) is in the ON state. SW1 is turned on during the operation of the shutter button (for example, half-pressed), and in response to this, the camera control unit 212 instructs the start of the automatic focus detection process. When SW1 is in the ON state, the process proceeds to step S2, and when SW1 is in the OFF state, the determination process in step S1 is repeated.
In step S2, the camera control unit 212 performs the automatic focus detection process. The details of the automatic focus detection process will be described later using the flowchart of FIG.

In step S3, the camera control unit 212 acquires the defocus amount, which is the focus detection information generated in step S2, and determines whether or not the defocus amount is within the focusing range. Whether or not it is within the focusing range is determined by using the reliability evaluation value Rel relating to the reliability of the defocus amount described later. The details of this determination will be described together with the explanation of the reliability of the defocus amount. If it is within the focusing range, the process proceeds to step S5, and if it is out of the focusing range, the process proceeds to step S4.
In step S4, the camera control unit 212 transmits a drive command for the focus lens 103 to the lens control unit 106 of the lens unit 10 in order to control the drive of the focus lens 103 based on the defocus amount generated in step S2. After that, the process returns to step S2.

In step S5, the camera control unit 212 determines whether or not the second switch (SW2) is in the ON state. SW2 is turned on when the operation of the shutter button is completed (for example, fully pressed), and in response to this, the camera control unit 212 instructs the start of a series of processes such as shooting preparation processing and recording processing. If SW2 is in the on state, the process proceeds to step S6, and if SW2 is in the off state, the process proceeds to step S7.
In step S6, the camera control unit 212 performs a shooting preparation process, performs a recording process of the image data captured in the next step S8, and then ends the shooting process.
In step S7, the camera control unit 212 determines whether or not SW1 is in the ON state. When SW1 is in the ON state, the process returns to step S5, and when SW1 is in the OFF state, the shooting process ends.

The details of the automatic focus detection process in step S2 of FIG. 3 will be described with reference to FIG. The flowchart of FIG. 4 is executed under the control of the AF control unit 213 of the camera control unit 212.
In step S21, the AF control unit 213 performs the focus detection calculation.
Specifically, the AF control unit 213 instructs the AF signal processing unit 204 to perform a correlation calculation on the pair of AF signals acquired from the image sensor 201. Then, the AF control unit 213 calculates and generates the defocus amount based on the image shift amount, which is the shift amount at which the correlation amount received from the AF signal processing unit 204 becomes the minimum value. At this time, the correlation calculation is performed using three types of filters (for low frequency band, medium frequency band, and high frequency band) having different frequency bands, and the low frequency band and medium frequency are obtained by the correlation calculation using each filter. Generates three types of defocus amount, one for the region and one for the high frequency. The low-frequency, mid-frequency, and high-frequency filters relatively indicate the frequency band to be extracted, and the absolute value of the frequency band to be extracted is not particularly limited.
Further, the AF control unit 213 instructs the AF signal processing unit 204 to calculate the correlation amount of the pair of AF signals for each shift amount. Then, the AF control unit 213 generates a waveform of the correlation amount for each shift amount received from the AF signal processing unit 204.

In step S22, the AF control unit 213 calculates the amount of correlation change between the two images.
FIG. 6 is a characteristic diagram showing an example of the amount of correlation change when the focus lens 103 is driven from the state where the degree of blurring is large to the vicinity of focusing in the focus adjustment by the imaging surface phase difference detection method. The horizontal axis represents the degree of blurring of the subject, and the vertical axis represents the amount of correlation change MAXDER. The amount of correlation change MAXDER can be calculated by the equation (1). K in equation (1) is an integer variable for specifying the position. At this time, in the same manner as in step S21, three types of correlation change amounts MAXDER for low frequencies, mid frequencies, and high frequencies are calculated. As shown in FIG. 6, in the focus adjustment by the imaging surface phase difference detection method, it can be seen that the correlation change amount MAXDER increases from the state where the degree of blurring is large to the vicinity of the focal point.
MAXDER (k) = (COR [k-3] -COR [k-1])
-(COR [k-2] -COR [k]) ... (1)

In step S23, the AF control unit 213 calculates the standard deviation Defocus3σ of the defocus amount by using the correlation change amount MAXDER calculated in step S22. The standard deviation Defocus3σ of the defocus amount can be calculated by the equation (2). K in the equation (2) is a conversion coefficient for converting the image shift amount into a defocus amount, and A and B are conversion coefficients for converting the correlation change amount MAXDER to the standard deviation of the image shift amount. By substituting the three types of correlation change quantities MAXDER for low frequencies, mid frequencies, and high frequencies calculated in step S22, the standard deviation Defocus3σ of the three types of defocus quantities is calculated.
Defocus3σ = K × (A × MAXDER ^ B) ・ ・ ・ (2)

In step S24, the AF control unit 213 sets a threshold value of the standard deviation Defocus3σ of the defocus amount based on the luminance condition and the contrast condition.
In the next step S25, the reliability evaluation value regarding the reliability of the defocus amount is calculated, and at that time, the threshold value of the standard deviation of the defocus amount set in step S24 is used. The reliability evaluation value is calculated stepwise (in this embodiment, four steps of reliability evaluation values Rel3 to Rel0, which will be described later) by using the threshold value of the standard deviation of the defocus amount. At this time, the focusing condition can be changed according to the brightness condition and the contrast condition by changing the threshold value based on the brightness condition and the contrast condition, that is, changing the calculation condition of the reliability evaluation value. In the present embodiment, the focusing condition is relaxed by increasing the threshold value of the standard deviation of the defocus amount under the low brightness condition or the low contrast condition (including the low brightness and low contrast condition). As a result, it is possible to reduce the case where a shooting scene that may be originally determined to be in focus is determined to be out of focus, and it is possible to reduce a decrease in focusing accuracy due to brightness conditions and contrast conditions. ..

The setting of the threshold value of the standard deviation of the defocus amount in step S24 will be described.
Regarding the brightness condition, as shown in FIG. 7, the threshold value Defocus3σLMN of the standard deviation of the defocus amount is acquired based on the shooting sensitivity in the shooting scene. In FIG. 7, when the shooting sensitivity is SV1, the threshold value of the standard deviation of the defocus amount is Th1, when it is SV2, it is Th2, when it is SV3, it is Th3, and when it is SV1 or more and less than SV2, the threshold value of the standard deviation of the defocus amount is set. The relational expression is set so that the higher the sensitivity between Th1 and Th2, the larger the threshold value. Similarly, when SV2 or more and less than SV3, the relational expression is set so that the threshold value of the standard deviation of the defocus amount becomes larger as the sensitivity is higher between Th2 and Th3.
When shooting under low brightness conditions, there is often a correlation between brightness and shooting sensitivity in order to increase the shooting sensitivity and optimize the exposure, but when the shooting sensitivity increases, noise increases and the defocus amount is standard. The deviation Defocus3σ becomes large. Therefore, as shown in FIG. 7, by increasing the threshold value Defocus3σLMN as the imaging sensitivity (Sv1 <Sv2 <Sv3) increases, the reliability evaluation value indicating that the imaging sensitivity is the highest even when the imaging sensitivity is high. Make it easy to obtain. As a result, the focusing condition is relaxed, so that it becomes easier to focus even during high-sensitivity shooting. Here, the threshold value Defocus3σLMN is calculated for the threshold value used to calculate the reliability evaluation value (Rel3 in the present embodiment) indicating the highest reliability in order to relax the focusing condition. The details of the reliability evaluation values in ascending order will be described later.
Further, it is preferable that the threshold values Th2 and Th3 shown in FIG. 7 are variable based on the amplitude PB of the image signal, which is the luminance evaluation value, as shown in FIG. The amplitude PB is the difference between the maximum value and the minimum value of the image signal, and the value changes according to the subject brightness, and the value becomes smaller when the subject brightness is low. Therefore, as shown in FIG. 8A, the threshold value is increased (Th2_1) when the amplitude is PB1 or less, and the threshold value is decreased (Th2_1) when the amplitude is PB2 (> PB1) or more. Then, in the regions of PB1 to PB2, the smaller the amplitude PB, the larger the threshold value Defocus3σLMN. The same applies to FIG. 8 (b). The brightness evaluation value is not limited to the amplitude PB of the image signal, and may be the maximum value of the image signal, the minimum value of the image signal, or the subject brightness.
Further, for example, the threshold value Defocus3σLMN when the photographing sensitivity is high (Sv3) may be changed according to the F value (aperture value).

Regarding the contrast condition, as shown in FIG. 9, the threshold value Defocus3σCNT of the standard deviation of the defocus amount is acquired based on the contrast evaluation value PB / Peak represented by the ratio of the amplitude PB to the maximum value Peak of the image signal. When the contrast evaluation value PB / Peak becomes small, the subject contrast decreases. Therefore, as shown in FIG. 9, the threshold value is increased (Th5) when the contrast evaluation value is PB / Peak1 or less, and the threshold value is decreased (Th4) when the contrast evaluation value is PB / Peak2 (> PB / Peak1) or more. Then, in the regions of PB / Peak1 to PB / Peak2, the smaller the contrast evaluation value PB / Peak, the larger the threshold value Defocus3σCNT. As a result, the reliability evaluation value (Rel3 in the present embodiment) indicating the highest reliability is easily obtained, the focusing condition is relaxed, and focusing is facilitated. Here, the threshold value Defocus3σCNT is calculated for the threshold value used to calculate the reliability evaluation value indicating the highest reliability in order to relax the focusing condition. The details of the reliability evaluation values in ascending order will be described later.

The magnitudes of the threshold value Defocus3σLMN and the threshold value Defocus3σCNT obtained in this manner are compared, and the larger one is set as the threshold value Def3σTH3 of the standard deviation of the defocus amount.

In step S25, the AF control unit 213 calculates a reliability evaluation value Rel indicating the reliability of the defocus amount. The reliability evaluation value Rel is determined in four stages of reliability evaluation value Rel3, reliability evaluation value Rel2, reliability evaluation value Rel1, and reliability evaluation value Rel0 in descending order of reliability, and is calculated by the formula (3). Can be done. Def3σTH3, Def3σTH2, and Def3σTH1 of the formula (3) are threshold values of the standard deviation of the defocus amount, and the threshold value Def3σTH3 used to calculate the reliability evaluation value indicating the highest reliability among them is acquired in step S24. , It is set. The maximum value of the threshold value Defocus3σLMN (Th3 in this embodiment) and the maximum value of the threshold value Defocus3σCNT (Th5 in this embodiment) are set to be smaller than Def3σTH2.
Rel = Rel3 if (Defocus3σ ≦ Def3σTH3)
Rel2 if (Def3σTH3 <Defocus3σ≤Def3σTH2)
Rel1 if (Def3σTH2 <Defocus3σ≤Def3σTH1)
Rel0 if (Def3σTH1 ≦ Defocus3σ) ... (3)

The reliability evaluation value Rel3 has a meaning that the defocus amount is highly reliable and may be focused, and is a condition capable of focusing. Further, the reliability evaluation value Rel2 has a meaning that focusing may be performed only at the time of frame addition processing of the defocus amount described later, and is a condition capable of focusing. On the other hand, the reliability evaluation value Rel1 means that the directions of the defocus amount are in the same direction, and the reliability evaluation value Rel0 means that the reliability as the defocus amount is the lowest. It becomes. However, in the present embodiment, in the focusing determination in step S3, only when the reliability of at least one of the high-frequency defocus amount and the mid-frequency defocus amount is Rel3 or when the frame addition process is performed in Rel2. Judged as being in focus range. That is, when the reliability of the high-frequency defocus amount and the mid-frequency defocus amount is Rel1 or less, or when the frame addition process is not performed in Rel2, the reliability of the low-frequency defocus amount does not matter. It is determined that the focus is not in the focus range, and the process proceeds to step S4. In other words, in the present embodiment, the reliability of the low frequency defocus amount is not used for the focusing determination in step S3. This is because the accuracy of the defocus amount in the vicinity of the focus of the defocus amount for the low range is lower than that of the defocus amount for the high range and the mid range.
Using the formula (3), the reliability evaluation values for each of the three types of defocus amounts for the low frequency range, the mid frequency range, and the high frequency band generated in step S21 are calculated.

In step S26, the AF control unit 213 partially of the three types of defocus amounts for low frequencies, mid frequencies, and high frequencies generated in step S21 based on the reliability evaluation value calculated in step S25. Select the amount of defocus for. For example, among the three types of defocus amounts for low frequency, mid frequency, and high frequency, one defocus amount having the highest reliability evaluation value is selected.

In step S27, the AF control unit 213 performs a frame addition determination calculation. The details of the frame addition determination operation will be described later using the flowchart of FIG.

In step S28, the AF control unit 213 determines whether or not to perform frame addition based on the determination result obtained in step S27. When performing frame addition, the process proceeds to step S29, and when frame addition is not performed, this process ends.

In step S29, the AF control unit 213 controls to add and average the defocus amount calculated in the current frame and the defocus amount calculated in the frames for the past m frames. As a result, the final defocus amount obtained by adding the defocus amount calculated in the past to the defocus amount calculated in the current frame is set as the final defocus amount, and the final defocus amount is within the focusing range in step S3 of FIG. In that case, it is determined that the subject is in focus. After that, this process ends.

The details of the frame addition determination operation in step S27 of FIG. 4 will be described with reference to FIG.
In step S271, the AF control unit 213 determines whether or not the defocus amount selected in step S26 is the defocus amount for low frequencies. If the low-frequency defocus amount is selected, the process proceeds to step S279, and if the low-frequency defocus amount is not selected, the process proceeds to step S272. In the present embodiment, the frame addition is not uniformly performed on the defocus amount calculated in the filter frequency band for low frequencies. This is because, as described above, the low-frequency defocus amount is not used for the focusing determination in step S3, and there is no need to add frames.

In step S272, the AF control unit 213 determines whether or not the reliability evaluation value Rel of the defocus amount selected in step S25 is the reliability evaluation value Rel2. As described above, the reliability evaluation value Rel2 has the meaning that it may be focused only during the frame addition processing of the defocus amount. If the determination is true, the process proceeds to step S273, and if the determination is false, the process proceeds to step S279.

In step S273, the AF control unit 213 determines whether or not the defocus amount selected in step S26 is the defocus amount for high frequencies. If the high frequency defocus amount is selected, the process proceeds to step S278, and if the high frequency defocus amount is not selected, the process proceeds to step S274. In the present embodiment, the defocus amount calculated in the filter frequency band for high frequencies and to which the reliability evaluation value Rel2 is given is uniformly frame-added. This is because the high-frequency defocus amount has a higher accuracy of the defocus amount near the in-focus range than the mid-range defocus amount, so it is possible to focus by adding frames regardless of the DFD and sharpness evaluation values. Because it can be. In this way, in the high frequency defocus amount, by performing frame addition regardless of the DFD and the sharpness evaluation value, it is possible to increase the probability that the focus range is determined in step S3.
Then, in the present embodiment, whether or not to perform frame addition in step S274 or later with the defocus amount calculated in the filter frequency band for the mid range and given the reliability evaluation value Rel2 as the determination target. I am trying to judge whether or not.

In step S274, the AF control unit 213 uses the image signal evaluation value calculated from the image signal as an evaluation value DFD representing the degree of blurring of the image and a sharpness evaluation value represented by the ratio of the sharpness Sharpness of the image to the amplitude PB. Calculate the Sharpness / PB.

The evaluation value DFD representing the degree of blurring of the image can be calculated by the equation (4). K in the equation (4) is an integer variable for specifying the position, and A [k] and B [k] are signal values of the A image signal and the B image signal at the position k, respectively.
DFD
= Σ (A [k] + B [k]) ² / ((Σ (A [k]) ² + Σ (B [k]) ² ) / 2)
... (4)

Further, the sharpness of the image Sharpness can be calculated by the equation (5). K in the equation (5) is an integer variable for specifying the position, and S [k] is the image pickup signal (A + B image signal) at the position k.
Is the signal value of.
Sharpness
= Σ (S [k + 1] -S [k]) ² / Σ (S [k + 1] -S [k]) ... (5)

In step S275, the AF control unit 213 determines whether the evaluation value DFD representing the degree of image blur calculated in step S274 is equal to or greater than the threshold value (hereinafter referred to as DFD threshold value) DFD_PARAM_TH, or the sharpness evaluation value calculated in step S274. It is determined whether or not Sharpness / PB is equal to or higher than a predetermined threshold value SHARPNESS_TO_PB_TH. If the determination is true, it is determined that the focus lens position is in the vicinity of focusing, and the process proceeds to step S278 as a condition capable of focusing. If the determination is false, the process proceeds to step S276.

In step S276, the AF control unit 213 changes the DFD threshold value based on the sharpness evaluation value Sharpness / PB in order to relax the focusing condition under the low contrast condition or the low brightness condition. Since the sharpness evaluation value Sharpness / PB becomes small under low contrast conditions or low brightness conditions, this change is made so that the DFD threshold value also becomes small when the sharpness evaluation value is small. In the present embodiment, as shown in FIG. 10, the DFD threshold value is small when the sharpness evaluation value is Sharpness / PB1 or less, and the DFD threshold value is large when the sharpness evaluation value is Sharpness / PB2 (> Sharpness / PB1) or more. Then, in the region of Sharpness / PB1 to Sharpness / PB2, the smaller the sharpness evaluation value Sharpness / PB, the smaller the DFD threshold value.
Further, the DFD threshold value may be made variable according to the shooting sensitivity, and the higher the shooting sensitivity, the smaller the DFD threshold value may be. Further, the DFD threshold value may be updated based on the sharpness evaluation value only when the photographing sensitivity is equal to or higher than the threshold value. In that case, a step for determining whether or not the shooting sensitivity is equal to or higher than the shooting sensitivity threshold value is inserted between steps S275 and S276, and if the shooting sensitivity is equal to or higher than the threshold value, the process proceeds to step S276, and if the shooting sensitivity is lower than the threshold value, the process proceeds to step S279. You can do it like this. By updating the DFD threshold value based on the sharpness evaluation value in this way, it is possible to appropriately change the focusing condition when shooting a low-contrast subject under low-luminance conditions.

In step S277, the AF control unit 213 changes the determination condition from step S275 to determine whether or not to perform frame addition. Here, whether or not the evaluation value DFD representing the degree of image blur calculated in step S274 is equal to or greater than the DFD threshold value changed in step S276, or whether the contrast evaluation value PB / Peak is equal to or less than the predetermined threshold value PB_TO_PEAK. Is determined. The threshold value PB_TO_PEAK is a threshold value for determining whether or not the subject has high contrast. If the determination is true, it is determined that the focus lens position is in the vicinity of focusing, and the process proceeds to step S278 as a condition capable of focusing. If the determination is false, the process proceeds to step S279.

In step S278, the AF control unit 213 sets a flag for the frame addition determination calculation in order to perform frame addition of the defocus amount, and ends this process.
In step S279, the AF control unit 213 ends this process without setting a flag for the frame addition determination calculation because the frame addition of the defocus amount is not performed.

As described above, by relaxing the focusing conditions when shooting a low-brightness condition or a low-contrast subject, it is less likely that a shooting scene that may be determined to be in focus will be determined to be out of focus. You will be able to correctly determine the in-focus state. As a result, it is possible to reduce the number of shooting scenes that are out of focus, prevent the harmful effect of focusing the image while it is out of focus, and increase the number of shooting scenes that can be focused accurately.

Although the present invention has been described above with the embodiments, the above-described embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention is interpreted in a limited manner by these. It must not be. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features. For example, in the above embodiment, in step S24, the standard deviation of the defocus amount is changed based on the luminance condition and the contrast condition, but it may be changed based only on the luminance condition or only based on the contrast condition. You may.
(Other embodiments)
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.

10: Lens unit 20: Camera body 106: Lens control unit 201: Image sensor 204: AF signal processing unit 210: ROM
212: Camera control unit 213: AF control unit

Claims (20)

A focus adjustment device that adjusts the focus by a phase difference detection method using an output signal from an image sensor that captures a subject image.
A generation means for generating focus detection information using a pair of image signals generated from the output signal of the image sensor and having a phase difference according to the focal state of the subject image.
A first calculation means for calculating the standard deviation of the focus detection information generated by the generation means using the amount of correlation change of a pair of image signals, and
A second calculation means for calculating a reliability evaluation value regarding the reliability of the focus detection information using the standard deviation of the focus detection information calculated by the first calculation means and the threshold value thereof is provided.
The second calculation means changes the threshold value based on at least one of the brightness condition and the contrast condition, and changes the calculation condition of the reliability evaluation value so as to relax the focusing condition. A focus adjustment device characterized by. It said second calculation means, focusing device according to claim 1, wherein the calculating stepwise the reliability evaluation value by using the threshold value. The focus adjusting device according to claim 1 or 2 , wherein there are a plurality of the threshold values, and the threshold value used for calculating the reliability evaluation value indicating the highest reliability among them is changed. The focus adjusting device according to any one of claims 1 to 3 , wherein the second calculation means changes the calculation conditions based on the luminance evaluation value. The focus adjusting device according to claim 4 , wherein the luminance evaluation value is represented by at least one of the amplitude of the image signal, the maximum value of the image signal, the minimum value of the image signal, and the subject luminance. The second calculation means changes the threshold value based on the luminance evaluation value, and changes the threshold value.
The luminance evaluation value is represented by the amplitude of the image signal.
The focus adjusting device according to any one of claims 1 to 3, wherein in a predetermined region, the smaller the luminance evaluation value is, the larger the threshold value is. The focus adjusting device according to any one of claims 1 to 6 , wherein the second calculation means changes the calculation conditions based on the contrast evaluation value. The focus adjusting device according to claim 7 , wherein the contrast evaluation value is represented by a value of the amplitude of the image signal with respect to the maximum value of the image signal. The second calculation means changes the threshold value based on the contrast evaluation value, and changes the threshold value.
The contrast evaluation value is represented by a value of the amplitude of the image signal with respect to the maximum value of the image signal.
The focus adjusting device according to any one of claims 1 to 3, wherein the threshold value is increased as the contrast evaluation value is smaller in a predetermined region. The focus adjusting device according to any one of claims 1 to 9 , wherein the second calculation means changes the calculation conditions based on the photographing sensitivity. The generation means generates the focus detection information for each of a plurality of filter frequency bands, and generates the focus detection information.
The focus according to any one of claims 1 to 10 , further comprising a selection means for selecting a part of the focus detection information for each filter frequency band based on the reliability evaluation value. Adjustment device. Whether or not to add the focus detection information calculated in the past to the focus detection information generated by the generation means is at least one of the reliability evaluation value and the image signal evaluation value calculated from the image signal. The focus adjusting device according to any one of claims 1 to 11 , further comprising a determination means for determining based on one of the two. The focus adjusting device according to claim 12 , wherein the image signal evaluation value is at least one of a sharpness evaluation value, an evaluation value representing the degree of blurring of an image, and a contrast evaluation value. The determination means is characterized in that the determination condition is made variable by changing the combination of the sharpness evaluation value used as the image signal evaluation value, the evaluation value indicating the degree of blurring of the image, and the contrast evaluation value. 13. The focus adjusting device according to 13. The focus adjusting device according to claim 13 or 14 , wherein the sharpness evaluation value is represented by the ratio of the sharpness of the image to the amplitude of the image signal. The focus adjusting device according to any one of claims 13 to 15 , wherein the determination means changes a threshold value of an evaluation value representing the degree of blurring of the image based on the sharpness evaluation value. The focus adjusting device according to any one of claims 13 to 16 , wherein the determination means changes a threshold value of an evaluation value representing the degree of blurring of the image based on the photographing sensitivity. The determination means refers to the focus detection information generated in a predetermined filter frequency band.
The focus adjusting device according to any one of claims 12 to 17 , wherein the determination is made based on the reliability evaluation value and the image signal evaluation value calculated from the image signal. It is a control method of a focus adjustment device that adjusts the focus by a phase difference detection method using an output signal from an image sensor that captures a subject image.
A generation step of generating focus detection information using a pair of image signals generated from the output signal of the image sensor and having a phase difference according to the focal state of the subject image.
The first calculation step of calculating the standard deviation of the focus detection information generated in the generation step using the amount of correlation change of the pair of image signals, and
It has a second calculation step of calculating a reliability evaluation value regarding the reliability of the focus detection information using the standard deviation of the focus detection information calculated in the first calculation step and its threshold value .
In the second calculation step, the threshold value is changed based on at least one of the brightness condition and the contrast condition, and the calculation condition of the reliability evaluation value is changed so as to relax the focusing condition. A method of controlling a focus adjuster, which comprises. This is a program for adjusting the focus by a phase difference detection method using an output signal from an image sensor that captures a subject image.
A generation means for generating focus detection information using a pair of image signals generated from the output signal of the image sensor and having a phase difference according to the focal state of the subject image.
A first calculation means for calculating the standard deviation of the focus detection information generated by the generation means using the amount of correlation change of a pair of image signals, and
The computer is made to function as a second calculation means for calculating the reliability evaluation value regarding the reliability of the focus detection information by using the standard deviation of the focus detection information calculated by the first calculation means and the threshold value thereof.
The second calculation means changes the threshold value based on at least one of the brightness condition and the contrast condition, and changes the calculation condition of the reliability evaluation value so as to relax the focusing condition. A program featuring.

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