JP5274307B2 - Imaging device - Google Patents

Description

  The present invention relates to a technique for performing appropriate focus detection according to the state of a subject.

  A camera equipped with a focus adjustment device that detects the amount of focus deviation by receiving light from a subject incident through the photographing lens and automatically adjusts the focal position of the photographing lens according to the distance from the camera to the subject. It is popular. The following two methods are generally known as means for adjusting the focus. One is a contrast AF method (mountain climbing AF method, TV-AF method) in which focus detection is performed based on the contrast of an image signal captured through a photographing lens. The other is a phase difference AF method (pupil division method, autocorrelation method) that performs focus detection based on the amount of image shift by a plurality of focus detection light beams that have passed through different pupil regions of the photographing lens.

  By the way, in each of the above-described focus detection methods in which light from a subject is received and focus detection is performed, not only light from the subject but also light from the background is incident, so the amount of focus deviation detected is influenced by the background. Will receive. When the background contrast is lower than that of the subject, the influence of the background contributing to the detection of the focus shift amount is small, and the focus shift of the subject can be detected correctly. However, when there is a high-contrast background, the contribution of the background to the detection of the focus shift amount becomes large, and the focus shift amount of the subject may not be detected correctly. In other words, perspective conflicts may occur. When perspective conflicts occur, setting the photographic lens position based on the detected amount of focus deviation results in focusing between the subject and the high-contrast background. Will not focus correctly.

  As a method for solving such a problem, the following method has been proposed.

  In Patent Document 1, a line sensor for detecting a deviation amount is provided, and left and right images are formed on the line sensor from light transmitted through a photographing lens, and a video signal of a left image of the line sensor is divided into a plurality of pixel blocks. Then, a correlation calculation between each pixel block and the video signal of the right image is performed to detect a focus shift amount. Further, in the detection of the amount of focus deviation, the presence / absence of perspective conflict is checked, and in the case of perspective conflict, the pixel block is further divided into blocks having a smaller number of pixels, and correlation calculation is performed on each divided block to detect the amount of focus deviation. .

  In Patent Document 2, a high frequency component and a low frequency component are extracted from an output signal of an image sensor by a filter, and processing data obtained thereby is divided into blocks that are units of focus detection calculation. The defocus amount is calculated for each divided block, and the reliability of the defocus amount is determined. For each of the plurality of areas, if it is determined that at least one of the blocks included in the area is highly reliable, the area is determined to be focus-detectable.

Japanese Patent Laid-Open No. 08-248303 Japanese Patent Application Laid-Open No. 08-075997

  In Patent Document 1, the presence / absence of perspective conflict is determined based on the degree of mismatch between a pair of images. However, although the influence of contrast is taken into account when obtaining the degree of image mismatch, the periodicity of the image is not taken into consideration. For this reason, there is a possibility that focus detection may be performed based on an unreliable image shift amount, and it is difficult to say that high-precision focus detection can be performed. In addition to the image sensor, a line sensor for detecting the shift amount is provided, so that there are many error factors and it is difficult to perform high-precision focus detection. Specifically, there are many error factors such as the difference in the path of the optical system to the image sensor and the optical system to the line sensor, the manufacturing error of the mold members etc. constituting each optical system, and the error due to factors such as expansion due to temperature. .

  In Patent Document 2, since the reliability of the defocus amount is determined by using the defocus amount, if the defocus amount itself is originally unreliable, such as when the subject has periodicity, Without performing accurate focus detection, useless reliability determination calculation is performed. Also, if you want to perform focus detection on a perfectly periodic subject, either focus once on a subject that is about the same distance as the periodic subject, or manually set the photographic lens roughly in focus. The photographer will be forced to move to the vicinity.

  As described above, in the conventional focus detection method described above, there are cases where the distance conflict cannot be reduced depending on the subject, or the focus detection with high reliability cannot be performed.

  Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to enable appropriate focus detection according to the state of the subject.

In order to solve the above-described problems and achieve the object, an imaging apparatus according to the present invention performs first photoelectric conversion on a subject image formed by a photographing lens and outputs a first signal for image generation. A photoelectric conversion cell; and a second photoelectric conversion cell that divides a pupil region of the photographing lens and photoelectrically converts a subject image from the divided pupil region to output a second signal for phase difference detection. An imaging device having at least a first focus detection unit that receives at least the first signal and performs contrast-type focus detection and outputs a first evaluation value for focus adjustment; and receives the second signal. And a second focus detection means for performing phase difference type focus detection and outputting a second evaluation value for focus adjustment, and dividing the screen of the image sensor into a plurality of divided areas, and for each divided area the subject obtained from the first and second signals On the basis of the defocus amount of the amount and the imaging lens of the frequency band component and a high frequency band component, and evaluating means for evaluating the reliability of the focus detection of the second focus detection unit, based on the evaluation result by the evaluation means When the reliability is high, the first evaluation value is obtained when the photographing lens is driven using the second evaluation value and the defocus amount of the photographing lens falls within a predetermined value. And a control means for controlling to drive the photographic lens using the first evaluation value when the reliability is low. And

  According to the present invention, it is possible to detect an appropriate focus according to the state of the subject.

1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows pixel arrangement | positioning of the image pick-up element provided with the pixel for phase difference detection in one Embodiment. FIG. 3 is a structural diagram of a pixel for detecting a first phase of an image sensor in an embodiment. FIG. 6 is a structural diagram of a pixel for detecting a second phase of an image sensor in an embodiment. It is a figure which shows the concept of a focus detection in one Embodiment. It is a figure which shows the concept of a focus detection in one Embodiment. It is a figure which shows the shift | offset | difference of an image in one Embodiment. It is a figure explaining the relationship (example of imaging lens drive) between an imaging lens position and a contrast evaluation value in a contrast method in an embodiment. It is a figure which shows the detailed structure of a to-be-photographed object determination block in one Embodiment. It is a flowchart which shows the focus adjustment operation | movement in one Embodiment. It is a figure which shows the reliability determination conditions and determination result of a phase difference system in one Embodiment. The figure which shows shift | offset | difference of the image of the to-be-photographed object in one Embodiment It is a figure which shows the to-be-photographed object imaged on the image pick-up element in one Embodiment. It is a figure which shows a mode that the face frame was set smaller than the division area in one Embodiment. It is a figure which shows a mode that the face frame was set larger than the division area in one Embodiment. It is a figure which shows a mode that the face frame was set to the magnitude | size equivalent to a division area in one Embodiment. It is a figure which shows a mode that the area | region was subdivided so that the boundary of a face frame and a division area might fit in one Embodiment.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus according to an embodiment of the present invention.

  In FIG. 1, the subject luminous flux that has passed through the photographing lens 101 is formed as a subject image and enters the image sensor 102. The image sensor 102 is a charge accumulation type sensor in which phase difference detection pixels are discretely incorporated, and is constituted by a CMOS image sensor or a CCD image sensor. The image sensor 102 converts a subject light into a first signal for image generation and outputs the first photoelectric conversion cell, and a second photoelectric sensor that converts the light into a second signal for phase difference detection and outputs the second signal. It has a conversion cell. The A / D conversion unit 103 converts an electrical signal input from the image sensor 102 from an analog signal to a digital signal. Here, the first signal for image generation is a signal obtained by converting the signal output from the first photoelectric conversion cell (hereinafter referred to as an imaging pixel) by the A / D conversion unit 103. The second signal for phase difference detection is a signal obtained by converting the signal output from the second photoelectric conversion cell (hereinafter referred to as phase difference detection pixel) by the A / D conversion unit 103.

  The region instruction unit 120 instructs which divided region by adding a signal specific to the divided region to the signals for the entire screen input from the A / D conversion unit 103. The contrast focus detection block 112 receives the first signal for image generation and the second signal for phase difference detection, extracts the high-frequency component, and performs integration processing on the high-frequency component. Thereby, the in-focus state of the subject is determined, and the driving direction and driving amount of the photographing lens 101 are determined. In the present embodiment, the first signal and the second signal are input to the contrast focus detection block 112 (block for performing contrast-type first focus detection). However, only the first signal is input. You may extract and input.

  Reference numeral 104 denotes a high-pass filter (HPF) for extracting a high-frequency component of the subject, and the integration circuit 105 integrates the high-frequency component in the selected area and supplies the memory 122 with an address assigned to each divided area. Thus, the integration result for each divided region is written or read. Then, the integration result is output to the contrast evaluation unit 114. The memory 122 writes or reads the integration result for each divided area at a specified address. The peak hold circuit 106 detects and holds the peak value of the signal level from the input from the HPF 104 in the same contrast evaluation region simultaneously with the integration circuit 105. The contrast evaluation unit 114 reads the contrast evaluation value and the peak value from the integration circuit 105 and the peak hold circuit 106 for the region selected by the region instruction unit 120. Then, a first evaluation value indicating the driving amount and driving direction of the photographing lens 101 is calculated from the magnitude relationship of the contrast evaluation value with respect to the peak value. Further, the first evaluation value is output to the focus detection method switching unit 109. The specific operation of the contrast evaluation unit 114 will be described later.

  The phase difference focus detection block (block for performing phase difference type second focus detection) 115 extracts the second signal from the output signal of the area instruction unit 120 and calculates the defocus amount based on the second signal. This is a block for determining the driving direction and driving amount of the photographing lens 101 up to the focal position. The phase difference detection signal extraction unit 113 extracts the second signal from the output signal of the region instruction unit 120 and outputs the second signal to the defocus amount calculation unit 107. The defocus amount calculation unit 107 calculates the defocus amount from the second signal and writes the defocus amount for each divided region by giving the address assigned to each divided region to the memory 121, or Read. The defocus amount is output to the phase difference evaluation unit 111 and the scene evaluation unit 119. The memory 121 writes or reads the defocus amount for each divided area at a specified address. The phase difference evaluation unit 111 calculates the driving direction and driving amount of the photographing lens 101 until focusing is performed based on the defocus amount. The second evaluation value based on the calculation result is output to the focus detection method switching unit 109.

  The subject determination block 108 controls the focus detection by calculating the frequency band distribution of the subject from the first and second signals with reference to the cutoff frequency fp / 2 obtained from the frequency fp determined by the arrangement of the phase difference detection pixels. It is a block to do. The description of the frequency fp, the subject determination method, and the focus detection method selection conditions will be described later. The frequency calculation unit 117 separates the frequency calculated from the mixed signal of the first and second signals on the basis of the cut-off frequency fp / 2 obtained from the frequency fp into a low frequency band and a high frequency band, and integrates them. . This integration result is output to the frequency evaluation unit 118.

  The frequency evaluation unit 118 evaluates the ratio between the low frequency band component and the high frequency band component of the subject based on the integration result. In addition, whether or not the contrast can be detected for the low frequency band component and the high frequency band component is evaluated. The evaluation result for each divided region of the image sensor 102 is output to the scene evaluation unit 119.

  The scene evaluation unit 119 evaluates the captured image for each area based on the evaluation result for each divided area and the defocus amount for each divided area, and evaluates the reliability of phase difference detection for each divided area. Then, a control signal for selecting a focus detection method is generated from the reliability evaluation result and output to the focus detection method switching unit 109.

  In the present embodiment, the first and second signals are input to the subject determination block 108, but only the first signal may be extracted and input.

  The focus detection method switching unit 109 has a first evaluation value input from the contrast evaluation unit 114 and a second evaluation value input from the phase difference evaluation unit 111 based on the control signal input from the scene evaluation unit 119. Either is selected and output to the motor drive control unit 110. The motor drive control unit 110 generates a motor control signal for driving the motor based on the first evaluation value or the second evaluation value input from the focus detection method switching unit 109 and outputs the motor control signal to the motor 116. The motor 116 drives the photographic lens 101 according to the motor control signal (adjusts the focus).

  Next, the arrangement of the phase difference detection pixels of the image sensor 102 and the frequency fp determined thereby will be described with reference to FIG.

  FIG. 2 is an enlarged view of a part of the image sensor 102. In the figure, 201 (including other white pixels) is a normal imaging pixel, and 202 and 203 (including other hatched pixels) are phase difference detection pixels. The phase difference detection pixels have a pair configuration of two adjacent pixels, and are discretely arranged in the image sensor 102. In addition, the interval between the imaging pixels is d. In FIG. 2, the number of phase difference detection pixels is shown as a ratio of 2% of the total number of pixels for the sake of simplicity of explanation. Further, the interval between adjacent phase difference detection pixel pairs is described as 10 * d.

  When the phase difference detection pixels are arranged as shown in FIG. 2, the frequency determined by the arrangement of the imaging pixels of the imaging element 102 is 1 / d (= fs), so that the band satisfying the sampling theorem is 0 to 0. It can be expressed as fs / 2. Since the frequency determined by the arrangement of the phase difference detection pixel pairs is 1 / 10d (= fs / 10 = fp), the band that satisfies the sampling theorem can be expressed as 0 to fs / 20 (= fp / 2).

  FIG. 3 shows a detailed view of the phase difference detection pixel S1 (for example, 202 among the pair of phase difference detection pixels). This is in principle the same as the structure disclosed in Japanese Patent Laid-Open No. 2000-156823.

  FIG. 3A is a view of the phase difference detection pixel S1 as viewed from above, and FIG. 3B is a B-B ′ cross section of FIG. This pixel does not have a color filter layer, and a microlens 301 is formed on the top. Reference numeral 302 denotes a smooth layer for forming a plane for forming a microlens, and 303 denotes a light shielding film. An opening 303 a is formed in the light shielding film 303. Reference numeral 304 denotes a smooth layer and 305 denotes an insulating layer.

  FIG. 4 is a detailed view of the phase difference detection pixel S2 (of the paired phase difference detection pixels, for example, 203). An opening 303a is provided at the same distance from the pixel center in the opposite direction to the S1 pixel.

  Next, detection of image shift by the phase difference method will be described below.

  In the area sensor exceeding 1 million pixels, an approximate image is formed on the microlens in S1 and S2 in the arrangement of FIG. If the photographing lens 101 that connects an image to the image sensor 102 is in focus on the image sensor 102, the image signal from S1 and the image signal from S2 are the same. If the point to be focused is in front of or behind the image plane of the image sensor 102, a phase difference occurs between the image signal of S1 and the image signal of S2. Then, the phase shift direction is reversed between the case where the image formation point is before and the case where the image formation point is after.

  5 and 6 are conceptual diagrams of focus detection by the phase difference method. Here, for simplification of description, S1 and S2 are represented on the same plane. In the figure, the pair of S1 and S2 is covered with the same microlens, but the principle is the same even if S1 and S2 are covered with different microlenses.

  Light from a specific point of the subject is divided into a light beam (L1) incident on S1 through the pupil region for S1 and a light beam (L2) incident on S2 through the pupil region for S2. These two light beams are condensed at one point on the surface of the microlens as shown in FIG. 5 when the camera is in focus. The same image is exposed on S1 and S2. Thereby, the image signal read from S1 and the image signal read from S2 are the same.

On the other hand, when the camera is not in focus, L1 and L2 intersect at a position different from the microlens surface as shown in FIG. Assume that the distance between the microlens surface and the intersection of two light beams, that is, the defocus amount is x. Further, the amount of deviation between the S1 image and the S2 image generated at this time is n pixels, the sensor pitch is d, the distance between the centers of gravity of the two pupils is Daf, and the distance from the principal point of the photographing lens to the focal point is Suppose u. At this time, the defocus amount x is
x = n × d × u / Daf (1)
Is required. Furthermore, since u is considered to be approximately equal to the focal length f of the taking lens,
x = n × d × f / Daf (2)
Find it in

  FIG. 7 shows the state of the image signal read from S1 on the image sensor 102 and the state of the image signal read from S2. An image shift n × d occurs between the image signal read from S1 and the image signal read from S2. If the amount of deviation between the two image signals is obtained, the defocus amount x is obtained therefrom, and the photographing lens 101 is further moved by x, autofocus can be achieved.

  By the way, in order to generate the image shift as described above, it is necessary to separate the light beams L1 and L2 passing through two different pupils among the light incident on the lens. In the method of this embodiment, pupil division is performed by generating a focus detection cell having a pupil division function on the image sensor 102. As a result, one of the images formed on the sensor by the light beams from the two pupil positions that are symmetric about the optical axis is photoelectrically converted by S1, the other is photoelectrically converted by S2, and the pupil positions are different. Two images are obtained.

  When focus detection is performed by the phase difference method, the first signal for image generation and the second signal for phase difference detection are used for phase difference detection from the image sensor 102 via the A / D converter 103 in FIG. The signal is input to the signal extraction unit 113. The phase difference detection signal extraction unit 113 extracts signals from the phase difference detection pixels S1 and S2. The phase difference detection signals S1 and S2 obtained in this way are output to the defocus amount calculation unit 107. The defocus amount calculation unit 107 generates an image by S1 and an image by S2 from the phase difference detection signal, and calculates the defocus amount of the image by calculating the correlation between the two images. Further, the calculated defocus amount is written in the memory 121. The defocus amount calculation unit 107 reads the defocus amount of a specific area from the memory 121 and then outputs it to the phase difference evaluation unit 111. The phase difference evaluation unit 111 outputs a second evaluation value for controlling the driving amount and driving direction of the photographing lens 101 based on the defocus amount of a specific area.

  Next, a specific operation of the contrast focus detection block 112 will be described. The contrast focus detection block 112 drives the photographing lens 101 in a direction in which the contrast evaluation value from the integration circuit 105 is larger than the read value from the peak hold circuit 106 for the region selected by the region instruction unit 120. The maximum value of the contrast evaluation value is searched. FIG. 8 shows an example of driving the photographing lens 101 according to the contrast evaluation value by the contrast evaluation unit 114 at this time. In FIG. 8, the horizontal axis indicates the number of drive pulses included in the motor control signal output from the motor drive control unit 110 to the motor 116, that is, the moving position of the photographing lens 101. The vertical axis represents the contrast evaluation value calculated from the first and second signals at each photographing lens position corresponding to the number of drive pulses.

  For example, when the photographing lens 101 is moved in the close direction from the infinity position by the contrast method, the contrast evaluation value from the integration circuit 105 is larger than the read value from the peak hold circuit 106 and approaches the in-focus position. Go. The contrast evaluation value shows a maximum value at the position where the subject is in focus. A control signal for driving in the current driving direction is output to the focus detection method switching unit 109. When the photographing lens 101 is further driven, the contrast evaluation value from the integration circuit 105 becomes smaller than the read value from the peak hold circuit 106. The in-focus position is detected by reversing these two evaluation values. Therefore, the contrast evaluation unit 114 controls the motor 116 to be driven via the motor drive control unit 110 while evaluating the magnitude relationship between the two evaluation values. As indicated by the arrow in FIG. 8, the contrast evaluation value once reaches the maximum value and passes through this, and the contrast evaluation value from the integration circuit 105 becomes smaller than the read value from the peak hold circuit 106. When the contrast evaluation value from the integration circuit 105 decreases by a predetermined value with respect to the read value from the peak hold circuit 106, it is determined that the taking lens 101 has passed the in-focus position. Therefore, a control signal for driving the photographing lens 101 in the reverse direction to a position where the contrast evaluation value becomes equal to the read value from the peak hold circuit 106 is output to the focus detection method switching unit 109. When the contrast evaluation value from the integration circuit 105 becomes equal to the read value from the peak hold circuit 106, a control signal for stopping the photographing lens 101 is output to the focus detection method switching unit 109.

  Next, evaluation contents performed by the frequency calculation unit 117 and the frequency evaluation unit 118 will be described with reference to FIG.

  Reference numeral 901 denotes a high-pass filter (HPF) having a cutoff frequency of fp / 2 (= fs / 20), and extracts high-frequency band components of the first and second signals received from the A / D conversion unit 103. Reference numeral 903 denotes an integration circuit for integrating the high frequency components extracted by the HPF 901. The calculation result H of the integration circuit 903 is a value indicating the amount of the high frequency band that the subject has.

  Reference numeral 902 denotes a low-pass filter (LPF) having a cutoff frequency of fp / 2, and extracts low-frequency band components of the first and second signals received from the A / D conversion unit 103. Reference numeral 904 denotes an integration circuit for integrating the low frequency components extracted by the LPF 902. The calculation result L of the integration circuit 904 is a value indicating the amount of the low frequency band that the subject has. The frequency fp determined by the arrangement of the phase difference detection pixels described above is a set value given from a CPU (not shown) or the like. This may be a fixed value or variable.

  The low frequency band evaluation unit 905 evaluates a low frequency band component of the subject by comparing the product kL obtained by multiplying L by a correction coefficient k for weighting and the band determination reference value A. Here, the band determination reference value A is a reference value for determining whether or not the contrast of the input subject can be detected. The value of A is determined by the sensitivity of the image sensor 102 and the like. The distribution evaluation unit 906 evaluates the frequency distribution of the subject by comparing the size of kL and H. The high frequency band evaluation unit 907 evaluates the high frequency band component of the subject by comparing H and A with each other.

  Evaluation results from the low frequency band evaluation unit 905, the distribution evaluation unit 906, and the high frequency band evaluation unit 907 are output to the scene evaluation unit 119 for the region selected by the region instruction unit 120.

  Next, subject determination and focus detection method determination performed by the scene evaluation unit 119 will be described with reference to FIGS. 9, 11, and 12.

  The scene evaluation unit 119 indicates the evaluation value of the low frequency band evaluation unit 905 indicating whether or not the contrast can be detected in the low frequency band of the subject input for each region, and indicates whether the high frequency band of the subject can be detected in the contrast. Based on the evaluation value of the high-frequency band evaluation unit 907 and the evaluation value of the distribution evaluation unit 906 indicating whether or not the focus detection by the phase difference method with high accuracy can be performed on the frequency distribution of the subject, the scene evaluation is performed for each region. The scene evaluation result is stored. Further, the focus detection method is determined from the scene evaluation result, and a control signal for selecting the focus detection method is output to the focus detection method switching unit 109. The scene evaluation and the scene evaluation result will be described later.

  In FIG. 9, a product kL obtained by multiplying L by k is used as an evaluation value for determination, but in this embodiment, a coefficient k = 1 is set to facilitate understanding.

  Next, conditions for determining the reliability of the phase difference method will be described with reference to FIG.

  FIG. 11A is a table showing conditions for classifying a subject by frequency distribution. It is classified into a to c according to the magnitude relationship of A, kL, and H.

  FIG. 11-2 shows the frequency distribution of the captured image represented by the first and second signals, with the horizontal axis representing the frequency and the vertical axis representing the output obtained by integrating the captured image with the integration circuits 903 and 904 (hereinafter referred to as “Power”). It is the figure shown on the done plane. A frequency distribution in which aliasing does not occur in sampling at the frequency fs is shown.

  A low frequency band component having a frequency of fp / 2 or lower is denoted by L (a region with a horizontal line), and a high frequency band component having a frequency of fp / 2 or higher is denoted by H (a region with a vertical line). Further, the hatched portion in FIG. 11-3 is a figure obtained by converting A shown in FIG. 9 into an area on the plane described above. The boundary line of this region is indicated by a broken line in FIGS. 11-2 to 11-9.

Hereinafter, subjects classified into ac shown in FIG. 11A will be described.
(1) Subjects classified as a in FIG. 11A Subjects classified as a in FIG. 11-1 are subjects having a higher frequency band component H than the reference value A and the low frequency band component kL. When the determination is a, it can be determined that the taking lens 101 is in the vicinity of the focal point. As examples of frequency characteristics indicated by the photographed image at this time, FIG. 11-4 shows a case where A <kL <H, and FIG. 11-6 shows a case where kL <A <H.
(2) Object classified as b in FIG. 11-1 As an example of the frequency characteristic with few high frequency band components determined as b, the case of A <H <kL is shown in FIG. 11-5, and H <A <kL. The case is shown in FIG. 11-7, and the case of H <kL <A is shown in FIG. 11-9. These are characterized in that the high frequency band component H is smaller than the low frequency band component kL.

When the classification of b in FIG.
(B1) Since the subject itself has few high-frequency band components, the high-frequency component H is calculated to be small even if the defocus amount is within a predetermined value. When the high frequency component H is calculated to be small (b3) It is determined that the high frequency component H is small, but the focus detection reliability by the phase difference method is low.

Since the subject classified into (b1) and (b2) has less high-frequency band component H than low-frequency band component L, it is considered that the influence of aliasing is small, so that focus detection by the phase difference method is possible. What is determined as (b1) is a subject whose defocus amount is calculated to be within a predetermined value. What is determined as (b2) is a subject for which a defocus amount greater than a predetermined value has been calculated. At this time, it can be determined that the position of the taking lens 101 is away from the in-focus position. (B3) is determined in the case of a subject for which focus detection by the phase difference method is difficult, and a subject having periodicity is applied. As an example, FIG. 12 shows a shift of an image of a subject having periodicity. With respect to the point P0 where the image of S1 is located, at the points P1, P2, P3, P4, P5,... Not uniquely determined.
(3) Subjects classified as c Subjects classified as c are low-illuminance and low-contrast subjects. This subject has a small power of the high frequency band component H and the low frequency band component kL. As an example of the frequency characteristics of the subject, FIG. 11-8 shows a case where kL <H <A, and FIG. 11-9 shows a case where H <kL <A. It is difficult to perform accurate focus detection on this subject at high speed. Therefore, the process at the time of out-of-focus described later is performed.

  The flow of the focus detection process performed by the focus detection apparatus described above will be described using the flowchart of FIG. 10 and FIGS. 13A to 13E.

FIG. 13A shows a subject imaged on the image sensor 102, and shows a landscape with trees in the background of a person. FIG. 13B shows a state in which the face frame is set smaller than the divided area. In the figure, a thick dotted line represents a boundary line between divided areas, and a thick solid line frame represents a face frame. In this case, since the tree imaged around the face frame is also included in the same divided area as the face frame, perspective conflict may occur in the divided area. Therefore, in this embodiment, the divided area is further divided. FIG. 13C shows a state in which the face frame is set larger than the divided area. In the figure, the outer thick solid line frame represents the face frame, and the thick dotted line represents the boundary line of the divided areas. In this case, the scene evaluation unit 119 performs scene evaluation and focus detection on the divided areas (18 areas in the figure) represented by the thick solid line included in the face frame. FIG. 13D shows a state in which the face frame is set to the same size as the divided area. In this case, if the position of the divided area does not match the position of the face frame, the background may enter the divided area as shown in FIG. 13D. When the focus detection is started as shown in FIG. 13E so that the position of the face frame matches the position of the face frame, in step S1001, the area of the image sensor 102 is divided with respect to the subject shown in FIG. 13A. In step S1002, the integration circuit 105 integrates the first signal for each divided region based on the signal from the image sensor 102, and then writes the integration result for each region to the memory 122. Further, the defocus amount calculation unit 107 calculates the defocus amount for each divided region based on the second signal and writes it to the memory 121. In addition, the scene evaluation unit 119 performs scene evaluation for each divided region and stores the scene evaluation result. The area designating unit 120 designates a divided area to be integrated. Thereafter, the process proceeds to step S1003.

  In step S1003, the face frame set by the face detection unit (not shown) is compared with the area of the region divided in step S1001. If it is determined that the face frame is larger than the divided area (divided area <face frame), the process proceeds to step S1007. If it is determined that the face frame is smaller than the divided area (divided area> face frame), the process advances to step S1006. If it is determined that the face frame and the divided area are approximately the same (divided area≈face frame), the process proceeds to step SS1004.

  In step S1004, the area is divided again so that the boundary of the area approaches the position of the face frame without changing the area of the divided area, and the process proceeds to step S1005. In step S1005, the integration circuit 105 integrates the first signal for each divided region based on the signal from the image sensor 102, and then writes the integration result for each region to the memory 122. Further, the defocus amount calculation unit 107 calculates the defocus amount for each divided region based on the second signal and writes it to the memory 121. In addition, the scene evaluation unit 119 performs scene evaluation for each divided region and stores the scene evaluation result. The area designating unit 120 designates a divided area to be integrated. Thereafter, the process proceeds to step S1007.

  In step S1006, the image is divided again so that the area of the divided region is further reduced, and then the process proceeds to step S1002.

  In step S1007, the scene evaluation result is read from the scene evaluation unit 119 for the divided areas included in the face frame. Among the scene evaluation results of all the divided areas included in the face frame, it is determined which determination results of a to c in FIG. 11A occupy a large number (hereinafter referred to as dominant). When a is dominant in the scene evaluation results of the divided areas included in the face frame, the focus detection is performed with higher accuracy in the phase difference detection pixel having the frequency fp with respect to the set face frame. It is difficult. Therefore, the process proceeds to step S1008 in order to perform focus detection by the contrast method for the divided area determined as a included in the face frame. If b is dominant in the scene evaluation results of the divided areas included in the face frame, the process proceeds to step S1009 to perform focus detection by the phase difference method. If c is dominant in the scene evaluation results of the divided areas included in the face frame, the process proceeds to step S1013 in order to perform the process when out of focus.

  In step S <b> 1008, focus detection is performed using a contrast method by driving the photographic lens 101 for a divided region in which the scene evaluation result is a among divided regions included in the face frame. Since the peak of the contrast evaluation value shown in FIG. 8 may be different in each divided region, the peak position is determined by, for example, majority of the divided regions.

  In step S <b> 1009, among the divided areas included in the face frame, the defocus amount of the divided area whose scene evaluation result is b is read from the memory 121. Thereafter, the process proceeds to step S1010.

  In step S1010, the scene evaluation unit 119 determines the focus state of the subject based on the defocus amount read from the memory 121. When it is determined that the focus detection reliability by the phase difference method is high, that is, when the image shift amount can be uniquely narrowed down, in order to perform subject determination based on the defocus amount, step S1011 is performed. Proceed to The subjects corresponding to this are the above (b1) and (b2). When it is determined that the reliability of focus detection by the phase difference method is low, that is, when the amount of image shift cannot be uniquely narrowed due to the periodicity of the subject, a step for performing focus detection by the contrast method The process proceeds to S1008. The subject corresponding to this is the above (b3).

  In step S1011, the focus state is determined by comparing the calculated defocus amount with a predetermined value. When the defocus amount is within the predetermined value, it is difficult to detect the phase difference focus with a higher accuracy than the current phase difference detection pixel arrangement interval, and the process advances to step S1008 to perform focus detection using the contrast method. Here, the subject (b1) is identified. When the defocus amount is larger than the predetermined value, the focus detection can be performed with high accuracy by the phase difference method, and the process proceeds to step S1012. This corresponds to the above (b2). The predetermined value depends on the frequency fp determined by the arrangement of the phase difference detection pixels.

  In step S1012, since there is a possibility that the defocus amount differs for each divided region, a representative value of the defocus amount is determined by obtaining a majority vote or an average based on the defocus amount for each divided region. The driving amount and driving direction of the photographing lens 101 are calculated from the determined defocus amount. At this time, the second evaluation value based on the calculation result is output to the focus detection method switching unit 109. The focus detection method switching unit 109 transmits the second evaluation value based on the driving amount and driving direction of the photographing lens to the motor drive control unit 110. The motor drive control unit 110 drives the photographing lens 101 by generating a motor control signal from the input evaluation value and supplying it to the motor 116. Thereafter, the process proceeds to step S1007.

  In step S1013, the focus detection of the subject for which focus detection is difficult is interrupted by stopping the imaging lens 101 at the current position. The motor drive control unit 110 outputs a control signal for stopping the motor 116. After processing, focus detection is terminated.

  With the above configuration, the following effects can be obtained with respect to the above-described conventional problems.

  For the focus detection device disclosed in Japanese Patent Laid-Open No. 08-248303, when evaluating the reliability of phase difference detection, for subjects that are not good at the phase difference method such as a subject with periodicity, etc. Since focus detection is performed using the contrast method, highly accurate focus detection is possible.

  For the focus detection device disclosed in Japanese Patent Application Laid-Open No. 08-075997, the reliability of the phase difference method is evaluated based on the signal from the imaging pixel, and therefore, useless reliability determination calculation is performed. There is nothing. In addition, since focus detection is performed on a subject with periodicity using a contrast method, high-precision focus detection can be performed.

  As described above, according to the present embodiment, by dividing the image sensor 102 into a plurality of regions, focus detection can be performed on the subject with higher accuracy, and erroneous focusing due to perspective conflict can be reduced.

Claims (2)

A first photoelectric conversion cell that photoelectrically converts an object image formed by the photographing lens and outputs a first signal for generating an image; and a pupil region of the photographing lens is divided, and the divided pupil region An image sensor having a second photoelectric conversion cell that photoelectrically converts the subject image of the subject and outputs a second signal for phase difference detection;
First focus detection means for receiving at least the first signal, performing focus detection by contrast method, and outputting a first evaluation value for focus adjustment;
Second focus detection means for receiving the second signal and performing phase difference type focus detection and outputting a second evaluation value for focus adjustment;
The screen of the image sensor is divided into a plurality of divided areas, and the amount of the low frequency band component and the high frequency band component of the subject obtained from the first signal and the second signal for each divided area, and the data of the photographing lens. Evaluation means for evaluating the reliability of focus detection of the second focus detection means based on the focus amount ;
Based on the evaluation result by the evaluation means, when the reliability is high, the defocus amount of the photographic lens is within a predetermined value after driving the photographic lens using the second evaluation value. Control to switch to a state in which the photographing lens is driven using the first evaluation value at a point in time, and to drive the photographing lens using the first evaluation value when the reliability is low Means ,
An imaging apparatus comprising:   The evaluation means further includes a face detection means for detecting the face of the subject, and compares the size of the divided area with the face frame set by the face detecting means. The face frame is more than the divided area. The imaging apparatus according to claim 1, wherein when the area is small, the divided area is subdivided into smaller areas.