JP5871462B2 - Focus detection apparatus and control method thereof - Google Patents

Description

  The present invention relates to a focus detection apparatus and a control method thereof, and more particularly to a focus detection apparatus that performs automatic focus detection and a control method thereof.

  Currently, general imaging devices such as a still camera and a video camera have an automatic focus detection (AF) function. In addition, a contrast detection method and a phase difference detection method are widely used as automatic focus detection methods. Of these, the phase difference detection method detects the distance (or defocus amount) to the subject using the principle of triangulation from the phase difference of signals obtained from a pair of line sensors. By controlling the position of the focus lens included in the imaging lens based on the detection result, the imaging lens can be focused on the subject.

  As a specific configuration for realizing the phase difference detection method, a so-called TTL method in which light incident on an imaging lens is received by a line sensor, and a so-called external measurement in which light incident on a path other than the imaging lens is received by a line sensor. Two types of AF methods are known. The former can detect the defocus amount based on the phase difference of the output signal of the line sensor, and the latter can detect the subject distance.

JP-A-10-122855

On the other hand, the phase difference between signals obtained by the pair of line sensors included in the external measurement AF sensor is larger as the distance from the subject is closer, and is smaller as the distance is farther. This means that the signal interval corresponding to the same subject image among the image signals obtained by the line sensor decreases as the distance from the subject decreases. Even in the case of the TTL method, the same problem occurs because the phase shift of the image signal becomes large at the time of large defocus.

  Comparing image signals that contain many signal sections corresponding to different subject images and detecting the phase difference will reduce the phase difference detection accuracy, so an appropriate signal section is selected according to the distance to the subject. Therefore, it is necessary to detect the phase difference. However, there has been no proposal for performing such phase difference detection.

  The focusing accuracy of the phase difference detection method depends on the quality of the signal obtained from the line sensor, but since the optical system and the line sensor that generate a pair of signals are separate, the signal varies in their characteristics. Affected by. Specifically, there are differences in characteristics of line sensors (for example, sensitivity of pixels) and differences in characteristics of optical systems (for example, lenses) that form an image. Further, it may happen that only one of the pair of signals is affected by factors other than manufacturing errors.

In order to increase the focusing accuracy of the phase difference detection method, it is necessary to reduce the error of the detected phase difference even when the quality is different between a pair of signals. Therefore, proposals for correcting the obtained image signal have been made. In Patent Document 1, there are proposals for correcting noise of an image signal due to stray light based on an average value of the image signal and correcting noise due to stray light having a gradient.
However, there has been no proposal in the past regarding how to correct an image signal when controlling a section of an image signal used for phase difference detection according to the subject distance.

  As described above, an object of the present invention is to realize a highly accurate automatic focus detection even when the phase difference of an image signal is large in a phase difference detection type focus detection apparatus and its control method.

In order to achieve the above object, a focus detection device according to the present invention is a focus detection device that detects a subject distance or a defocus amount by detecting a phase difference between a pair of image signals obtained from a pair of sensors. A differential means for differentiating a pair of image signals to generate a pair of differential image signals, a first detection means for detecting a phase difference between the pair of differential image signals, and a phase difference detected by the first detection means Using the extraction means for extracting the section corresponding to the same subject from the pair of image signals, and the offset between the pair of image signals using the signal of the section extracted by the extraction means from the pair of image signals, and using a calculation means for calculating a correction value of the order to correct the difference in gain, a pair of image signals different offset and gain corrected using the correction value, to detect the object distance or the defocus amount Pair for And having second detection means for detecting a phase difference between an image signal.

  With such a configuration, according to the present invention, in the focus detection apparatus of the phase difference detection method and the control method therefor, it is possible to realize accurate automatic focus detection even when the phase difference of the image signal becomes large. it can.

1 is a block diagram illustrating a configuration example of a video camera as an example of an imaging apparatus to which a focus detection apparatus according to an embodiment of the present invention is applicable. The figure which shows the structural example of the external measurement AF sensor unit of FIG. (A) is an example of subject brightness, (b) is an example of an ideal image signal obtained by the external measurement AF unit 130 from the subject brightness of (a), and (c) is outside the subject brightness of (a). FIG. 6 is a diagram illustrating an example of an actual image signal obtained by the AF unit 130. 6 is a flowchart for explaining focus detection processing in the video camera according to the embodiment of the present invention. 5 is a flowchart for explaining details of a correction amount calculation process in S407 of FIG. (A) is an example of an image signal, (b) is a figure which shows an example of the differential signal of the image signal of (a), respectively. The figure which shows the relationship between the simple phase difference Wn calculated by S406, and a differential image signal. The figure which shows the relationship between the image signal and the area used for calculation of a correction value, and the relationship between an image signal and the 1st correction amount in embodiment of this invention. The figure which shows the relationship between the image signal and 2nd correction amount in the 1st Embodiment of this invention. The figure which shows the relationship of the image signal before and behind correction | amendment in the 1st Embodiment of this invention. The figure for demonstrating the effect of the 1st Embodiment of this invention. Flowchart of correction amount calculation in the second embodiment The flowchart for demonstrating the detail of the correction amount calculation process in the 2nd Embodiment of this invention. The flowchart for demonstrating the detail of the correction amount calculation process in the 3rd Embodiment of this invention.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration example of a digital video camera 10 as an example of an imaging apparatus to which an external measurement AF type focus detection apparatus according to an embodiment of the present invention is applied.

The lens unit 100 constitutes an imaging optical system, and a fixed lens 101, a variable power lens 102, a diaphragm 103, a fixed lens 104, and a focus lens 105 are arranged in this order from the subject side (light side). These individual lenses are shown as one lens in the figure, but may be composed of a plurality of lenses.
The position encoder 108 detects the magnification of the zoom lens 102, the size of the diaphragm 103 (aperture value), and the position of the focus lens 105.

  The zoom lens 102 is driven in the optical axis direction by a zoom motor (ZM) 106, and the focus lens 105 is driven in the optical axis direction by a focus motor (FM) 107. The zoom motor 106 and the focus motor 107 operate by receiving drive signals from the zoom drive circuit 120 and the focus drive circuit 121, respectively.

  The image sensor 109 is, for example, a CCD image sensor or a CMOS image sensor. The image sensor 109 converts a subject image within the imaging range formed by light incident on the lens unit 100 into an electrical signal for each pixel by a plurality of photoelectric conversion elements. The signal processing circuit 119 performs various signal processing such as A / D conversion processing, amplification processing, white balance processing, color interpolation processing, and gamma correction processing on the electrical signal output from the image sensor 109 to obtain a predetermined format. Generate image data. The image data is output to the display device 114 or recorded on a recording medium 115 such as a semiconductor memory, an optical disk, or a hard disk.

  The operation switch group 111 includes a power switch, a switch for starting and stopping a recording operation and a reproduction operation, a switch for selecting an operation mode, a zoom switch for changing the zoom magnification (view angle) of the lens unit 100, and the like. It has been. When the power switch is operated, a part of the program stored in the nonvolatile memory 113 is loaded into the RAM 112, and the CPU 110 executes the program loaded into the RAM 112, thereby controlling the operation of each part of the video camera. . The video camera according to the present embodiment, in addition to the external measurement AF, performs contrast detection for focus detection by searching for a position where the contrast of image data of a part of the image (focus detection area) captured by the image sensor 109 reaches a peak. Is possible. In contrast AF, the focus position is determined by so-called hill-climbing control that searches for a focus peak that maximizes contrast while repeatedly performing imaging and contrast detection from image data in the focus detection area while moving the focus lens in small increments. Search is performed.

  The digital video camera 10 is provided with an external AF sensor unit 130 having a focus detection optical system arranged so that the optical axis does not overlap with the lens unit 100 (imaging optical system). The external measurement AF sensor unit 130 has a pair of imaging lenses 131 (focus detection optical system) whose optical axes are parallel and a pair of line sensors 132. The line sensor 132 includes a plurality of light receiving elements (pixels) arranged in a line, and details thereof will be described later with reference to FIG. Subject light is incident on the line sensor 132 through the imaging lens 131 having a fixed focal length f (that is, without passing through the lens unit 100 which is an imaging optical system). The subject image is photoelectrically converted by the line sensor 132 and then converted into digital data by an A / D converter (not shown). Using a pair of digital data obtained from a pair of line sensors constituting the line sensor 132 and a known method, the CPU 110 calculates a subject distance, a correlation amount, a reliability, and the like. Based on these calculation results, the CPU 110 gives a position where the focus lens 105 is to be moved to the focus drive circuit 121 and controls the position of the focus lens 105 to realize external measurement AF.

Next, a configuration example of the external measurement AF sensor unit 130 will be described with reference to FIG.
In FIG. 2A, a subject 201 is a subject that performs focus detection among subjects included in the shooting range (field of view). The imaging lens 131 has a configuration in which first and second imaging lenses 202A and 202B having parallel optical axes are integrally formed. The line sensor 132 includes first and second line sensors 203A and 203B.

  The object scene image by the first imaging lens 202A is the first line sensor 203A that is one of the pair of line sensors, and the object scene image by the second imaging lens 202B is the other of the pair of line sensors. Each is detected by the second line sensor 203B. The first and second line sensors 203A and 203B photoelectrically convert each object scene image and output an electric signal corresponding to the luminance of the object scene image. The electrical signal output from the first line sensor 203A is referred to as an A image signal, and the electrical signal output from the second line sensor 203B is referred to as a B image signal.

  The first and second imaging lenses 202A and 202B and the first and second line sensors 203A and 203B are disposed apart from each other by a predetermined base line length B, respectively. Therefore, the subject distance L can be measured based on the principle of triangulation using the A and B image signals obtained from the first and second line sensors 203A and 203B.

  FIG. 2B shows the first line sensor 203A in more detail. The first line sensor 203A has a configuration in which 40 rectangular pixels are adjacently arranged at a pixel pitch p. The first line sensor 203A further includes a digital circuit (not shown) for controlling charge accumulation, and when the amount of accumulated charge in one pixel reaches a predetermined value, the accumulation operation of other pixels is stopped. It is configured. In addition, the CPU 110 can set which of the 40 pixels performs charge accumulation. This setting method is not particularly limited, but 40-bit data in which “1” is associated with valid pixels and “0” is associated with invalid pixels is used, and each bit is an input 40 The validity / invalidity of each pixel can be controlled by using one logic gate. Note that the configuration of the second line sensor 203B is the same as that of the first line sensor 203A, and a description thereof will be omitted. In the following description, the pixels 1 to 40 of the first line sensor 203A are referred to as SA1 to SA40, and the pixels 1 to 40 of the second line sensor 203B are referred to as SB1 to SB40.

FIG. 3A shows an example of the subject brightness, and FIG. 3B shows an example of the A image signal and the B image signal obtained by the external measurement AF sensor unit 130 from the subject brightness of FIG.
FIG. 3A shows the subject brightness 301 of a short-distance subject, the field of view of the first line sensor 203A (A image field of view), and the field of view of the second line sensor 203B (B image field of view). . FIG. 3B shows an ideal A image signal 301A and B image signal 301B with respect to the subject brightness shown in FIG.

  Here, for the purpose of explanation, it is assumed that the subject distance is known, and the signals in the common visual field section completely match when the A image signal 301A and the B image signal 301B are shifted by 20.1 pixels (that is, the phase difference = 20.1 pixel equivalent). That is, in the example of FIG. 3, the signal interval corresponding to the subject image common to the A image signal 301A and the B image signal 301B is about 20 pixels, and the remaining about 20 pixels correspond to different subject images. It is an image signal. Actually, it is necessary to calculate the phase difference (corresponding to 20.1 pixels) between the A image signal 301A and the B image signal 301B by correlation calculation.

  The A image signal 301A and the B image signal 301B shown in FIG. 3B are ideal signals. Since there are various fluctuation factors in the process until the subject image is formed on the line sensor, such an ideal image signal cannot actually be obtained. For example, aberrations of the first and second imaging lenses 202A and 202B that form a subject image on a line sensor, dust and dirt adhering to the lenses, sensitivity differences between pixels included in the line sensors 203A and 203B, and offset differences The influence of the gain difference affects the image signal. In the following description, as shown in FIG. 3C, it is assumed that an A image signal 301A ′ and an ideal B image signal 301B with slightly lowered sensitivity are obtained.

Next, the focus detection operation by the external measurement AF sensor unit 130 in this embodiment will be described with reference to the flowchart of FIG.
When a focus detection start instruction is generated, for example, by a specific button operation included in the operation switch group 111 in S401, the CPU 110 instructs the external measurement AF sensor unit 130 to start accumulation in S402. When the accumulated charge amount (voltage) in any of the pixels of the line sensors 203A and 203B reaches a predetermined value, the charge accumulation operation of all the pixels is automatically terminated by the control circuit of the external measurement AF sensor unit 130.

  In S403, the CPU 110 performs A / D conversion on the charge amount of each pixel amplified by an amplifier (not shown) included in the line sensors 203A and 203B, thereby obtaining an A image signal and a B image signal corresponding to the subject luminance. . Here, the CPU 110 reads the charges accumulated in SA1 to SA40 of the first line sensor 203A and SB1 to SB40 of the second line sensor 203B to obtain an A image signal and a B image signal. The obtained image signal is shown in FIG. FIG. 6A is the same as FIG.

  In S404, the CPU 110 affects the influence of static factors on the image signal, such as the aberration of the first and second imaging lenses 202A and 202B, and the sensitivity difference between the pixels of the first and second line sensors 203A and 203B. In order to remove the image signal, the image signal is corrected with a correction value prepared for each pixel in advance.

In S405, the CPU 110 generates a differential signal in the pixel direction of the corrected image signal obtained in S404. Here, the differential signal in the pixel direction is a signal obtained by interpolating a pixel at an intermediate position between two adjacent pixels. For example, in the case of an A image signal, SA1.5 is added by calculation between SA1 and SA2. Since the differential signal can be obtained by various methods, it is not limited to a specific method. For example, as a differential operation for calculating SA2.5 from four pixel values of SA1 to SA4,
SA2.5 = 2 × SA1 + SA2-SA3-2 × SA4
Can be used. This arithmetic expression includes a calculation as a low-pass filter in addition to the differentiation. FIG. 6B shows a differential A image signal 601A and a differential B image signal 601B obtained by applying this arithmetic expression to the image signal of FIG. By this calculation, it is possible to eliminate the influence of the offset between the image signals that occurs when, for example, the sensitivity of only the A image signal is low due to some external factor.

  In S406, the CPU 110 as the first detection unit calculates the phase difference (deviation amount) Wn between the differential A image signal 601A and the differential B image signal 601B obtained in S405. Here, it suffices if the phase difference Wn can be calculated with half the accuracy of a pixel unit, and in this example, it is sufficient if a shift amount equivalent to 20 pixels is obtained. When calculating the phase difference for actually determining the focus lens position, the amount of deviation is calculated with the accuracy of further increasing the resolution and finely interpolating between one pixel, but here the correction value of the image signal is calculated. This is a phase difference for detecting an interval to be performed, and therefore, an accuracy of about ½ pixel is sufficient. Therefore, the phase difference obtained in S406 is referred to as simple phase difference Wn.

  FIG. 7 shows the relationship between the simplified phase difference Wn obtained in S405 and the differential image signal. The differential A image signal 601A obtained in S405 is plotted with a white circle, and the differential B image signal 601B is plotted with a black triangle. The signal 701 plots a signal obtained by shifting the differential B image signal 601B by 20 pixels in the process of calculating the simple phase difference Wn in S406 as a white triangle. As can be seen from FIG. 7, when the differential B image signal is shifted by 20 pixels, there is a range that roughly matches the differential A image signal 601 </ b> A and a range that does not match.

In S407, the CPU 110 performs a correction amount calculation process. The correction amount calculation process will be described in detail with reference to the flowchart of FIG.
In S502, the CPU 110 extracts a section corresponding to the same subject from the original A image signal 301A ′ and the B image signal 301B. Specifically, the CPU 110 uses the image signal corrected in S405 to obtain pixel data in a common section corresponding to the same subject image among all sections of the A image signal 301A ′ and the B image signal 301B in S406. Extracted based on the simple phase difference Wn.

  As described above, in this example, since the simple phase difference Wn = 20 pixels is obtained in S406, the B image signal 301B is data of SB1 to SB20, and the A image signal 301A ′ is data of the common section of SA21 to SA40. Respectively. In FIG. 8, sections extracted in S502 of the A image signal 301A ′ and the B image signal 301B are indicated by frames 806 and 807, respectively.

  In step S503, the CPU 110 starts searching for a flat point from the beginning of the extraction interval of the A image signal 301A ′ and the B image signal 301B (the one with the smaller pixel number). Here, the flat point means a point where the signal changes gently. Specifically, the CPU 110 determines whether the difference in value from the immediately preceding or immediately following pixel data is within a predetermined threshold range (condition 1), or an inflection point exists between the immediately preceding pixel data (condition 2). Are sequentially searched in the sections of SA21 to SA40 and SB1 to SB20 as flat points. Here, the nth detected flat point is referred to as the nth flat point.

In the example of FIG. 8, since the pixel data 801 of the A image signal 301A ′ satisfies the above-described condition 2 and the pixel data 802 satisfies the condition 1, it is detected as a flat point. Similarly, pixel data 803 and 804 are detected as flat points in the B image signal 301B.
As a result of the flat point search, when no flat point can be detected in the A image signal 301A ′ (S504, Y) and when only one flat point can be detected (S506, Y), the correction amount cannot be calculated. The process ends (S511).

In this embodiment, as shown in FIG. 8, it is assumed that the first flat point (pixel data 801) and the second flat point (pixel data 802) are detected in the A image signal 301A ′.
In S507, the CPU 110 checks whether the B image signal 301B has detected the flat points corresponding to the first flat point and the second flat point of the detected A image signal 301A ′. In the present embodiment, as shown in FIG. 8, in the B image signal 301B, the first flat point (pixel data 803) and the second flat point corresponding to the first flat point and the second flat point of the A image signal 301A ′. It is assumed that a point (pixel data 804) has been detected. If the flat points corresponding to the first and second flat points of the A image signal 301A ′ are not detected in the B image signal 301B (S507, Y), the process ends abnormally as a case where the correction amount cannot be calculated ( S511).

  Here, the “corresponding flat point” may be, for example, a flat point detected at substantially the same position in the extraction section. Furthermore, it may be added as a requirement that conditions satisfying as a flat point (for example, the above-described condition 1 and condition 2) are common.

  As shown in FIG. 8, when a flat point corresponding to the first and second flat points of the A image signal 301A ′ is detected in the B image signal 301B (S507, N), the CPU 110 performs the first correction in S508. The amount (offset correction amount) is calculated. Specifically, as shown in FIG. 8, the CPU 110 performs A image signals 301 </ b> A ′ and B for a low-value flat point (here, the second flat point) among the detected first and second flat points. The difference between the image signals 301B is calculated as the first correction amount.

  In S509, the CPU 110 calculates the second correction amount using the first correction amount calculated in S508. Specifically, the CPU 110 calculates the ratio (Y1 / Y2) of Y1 and Y2 shown in FIG. 9 as the second correction amount. More specifically, the CPU 110 adds or subtracts an offset equal to the first correction amount to one of the A image signal 301A ′ and the B image signal 301B to correct the second flat point value to be equal. Here, it is assumed that the A image signal 301A ″ is obtained by adding the first correction amount to the A image signal 301A.

  Then, the CPU 110 obtains the difference Y1, Y2 between the value of the second flat point and the value of the first flat point in the A image signal 301A ″ and the B image signal 301B in which the values of the second flat points 802, 804 are aligned, The ratio Y1 / Y2 is calculated as the second correction amount (gain correction amount), and Y2 / Y1 may be calculated as the second correction amount, where Y1 <Y2, so that the A image signal 301A ′ Assuming that Y2 / Y1 is calculated as the second correction amount, the CPU 110 normally ends the correction amount calculation process assuming that the correction amount is correctly calculated (S510).

  Returning to FIG. 4, if the correction amount calculation process in S <b> 407 has ended abnormally in S <b> 408 (S <b> 408, N), the CPU 110 shifts the process to S <b> 410 to perform correlation calculation without performing image correction in S <b> 409. On the other hand, when the correction amount calculation process is normally completed, the CPU 110 corrects the image signal again in S409.

  The correction of the image signal in S409 is different from the correction performed in S404 in order to remove the influence on static image signals due to static factors such as sensor sensitivity variations and lens aberrations that are known in advance. This is correction for removing the influence on the image signal due to external factors.

  The CPU 110 applies the first correction amount to all the sections for one of the A image signal 301A ′ and the B image signal 301B, and offsets so that the values of the second flat points coincide as shown in FIG. Make corrections. Here, since the A image signal 301A ′ having a slightly low sensitivity is detected as described above, offset correction is performed by adding the first correction amount to the A image signal 301A ′ to obtain the A image signal 301A ″. Further, the CPU 110 performs gain correction by applying Y2 / Y1 calculated as the second correction amount to each pixel data constituting the A image signal 301A ″ after the offset correction, so that the first flat point is corrected. An A image signal 301A ′ ″ whose value substantially coincides with the B image signal 301B is obtained. FIG. 10 shows the A and B image signals before and after correction. After correcting the image signal in this way, the CPU 110 as the second detection unit calculates a (high-precision) phase difference for focus detection in S410.

  The calculation of the phase difference in S410 can be executed using any method for detecting the phase difference between signals, but for example, the Min method (and method) can be used. In the Min method, when the B image signal is shifted and superimposed on the A image signal, the difference value at the corresponding position of the A image signal and the B image signal is integrated in the pixel direction, and the area of the portion where the image signals do not overlap is calculated. This is a method for calculating and calculating the phase difference that minimizes the area. As described above, the detection of the phase difference (deviation amount) in S410 is performed with higher resolution than when calculating the simple phase difference Wn, for example, in units of 0.1 pixel.

  When the calculation of the phase difference is finished in S410, one focus detection sequence is finished. Until the focus detection end instruction is detected in the next S411, the CPU 110 returns the process to S402 and repeats the focus detection sequence. If a focus detection end instruction is detected in S411, the CPU 110 ends the focus detection process.

  The influence of the correction of the image signal according to the present embodiment on the focus detection accuracy will be described with reference to FIG. In the example described in the present embodiment, the phase difference to be calculated is equivalent to 20.1 pixels (pitch). However, when a noise component such as an offset or a gain difference is mixed in only one image signal, the accuracy of the phase difference detection is almost the pixel unit as in the range shown in (a) unless the image signal is corrected. descend. This is because if a noise component is mixed in only one image signal, the interval of the image signal to be used for the correlation calculation cannot be detected correctly, and as a result, the correlation calculation is performed by comparing the values of different pixel positions between the image signals. This is because the peak of the correlation calculation result becomes unclear. On the other hand, by using the differential image waveform as in the present embodiment, the section of the image signal used for the correlation calculation can be detected in a state where the influence of the noise component is eliminated. Therefore, correlation calculation can be performed in a state where the degree of coincidence of the pixel positions between the image signals is high, and the peak of the correlation calculation result becomes clear, for example, the phase difference is detected with accuracy within the range shown in (b). it can.

  As described above, in this embodiment, the correction values for performing the offset and gain correction of the image signal are not calculated using all the sections of the image signal, and the section corresponding to the same subject (the section having a common field of view). ) To calculate. Therefore, for example, even when an image signal with a large phase difference is obtained for a short-distance subject using an external measurement AF sensor, the influence of the image signal corresponding to a different subject can be greatly suppressed, and the accuracy is high. Focus detection can be realized.

  Furthermore, by determining the interval of the image signal used to calculate the correction value based on the phase difference of the differentiated image signal, the influence of the noise component is affected even when the noise component is mixed in only one image signal. Therefore, it is possible to extract an appropriate section without receiving a correction and obtain a highly accurate correction amount. As a result, focus detection accuracy can be improved.

(Second Embodiment)
Next, another example of the correction amount calculation process described with reference to FIG. 5 in the first embodiment will be described. Since other processes may be the same as those in the first embodiment, description thereof is omitted.
FIG. 12 is a flowchart for explaining the correction amount calculation processing according to the present embodiment. First, in S1202, the CPU 110 extracts a section corresponding to the same subject from the original A image signal 301A ′ and the B image signal 301B as in S502.

In S1203, the CPU 110 detects the maximum value and the minimum value of the extraction interval SA21 to SA40 of the A image signal 301A ′ as Amin and Amax, respectively. In S1204, the CPU 110 detects the maximum value and the minimum value of the extraction interval SB1 to SB20 of the B image signal 301B as Bmin and Bmax, respectively.
In S1205, the CPU 110 calculates Bmin−Amin as the first correction amount, and calculates (Bmax−Bmin) / (Amax−Amin) as the second correction amount in S1206.

(Third embodiment)
Next, still another example of the correction amount calculation process described with reference to FIG. 5 in the first embodiment will be described. Since other processes may be the same as those in the first embodiment, description thereof is omitted.
FIG. 13 is a flowchart for explaining the correction amount calculation processing according to the present embodiment. First, in S1302, the CPU 110 extracts a section corresponding to the same subject from the original A image signal 301A ′ and the B image signal 301B, as in S502.

In S1303, the CPU 110 detects the average value and the minimum value of the extraction interval SA21 to SA40 of the A image signal 301A ′ as Aave and Amin, respectively. In S1304, the CPU 110 detects the average value and the minimum value of the extraction interval SB1 to SB20 of the B image signal 301B as Bave and Bmin, respectively.
In S1305, the CPU 110 calculates Bmin-Amin as the first correction amount, and in S1306 calculates (Bave-Bmin) / (Aave-Amin) as the second correction amount.
The maximum value may be used instead of the minimum value. In this case, the second correction amount is (Bmax−Bave) / (Amax−Aave).

  According to the second and third embodiments, the same effect as that of the first embodiment can be obtained.

(Other embodiments)
In the above-described embodiment, the differential image signal may be used for calculating the phase difference for focus detection in S410. Thereby, detection with higher accuracy becomes possible. The differentiation process here may be made stronger (higher order) than the differentiation process in S405. The above embodiment has been described on the premise of the external measurement AF method for detecting the subject distance among the phase difference detection AF methods. However, the TTL method for detecting the defocus amount is used as well as a pair of sensors other than the line sensor. The present invention can be similarly applied to a method for obtaining an image signal. As a system that does not use a line sensor, for example, there is a system that detects a phase difference of image signals obtained from a plurality of phase difference detection pixels provided in an image sensor.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (10)

A focus detection device that detects a subject distance or a defocus amount by detecting a phase difference between a pair of image signals obtained from a pair of sensors,
Differentiating means for differentiating the pair of image signals and generating a pair of differential image signals;
First detection means for detecting a phase difference between the pair of differential image signals;
Extraction means for extracting a section corresponding to the same subject from the pair of image signals using the phase difference detected by the first detection means;
A calculating means for calculating the extraction means with the signal of the extracted interval, the correction value of the order to correct the difference between the offset and gain between the pair of image signals of the pair of image signals,
A phase difference between the pair of image signals for detecting the subject distance or the defocus amount is detected using the pair of image signals in which the difference between the offset and the gain is corrected using the correction value. And a focus detection device. Said calculation means, said extracting means detects a pair of flat points in each of the extracted interval, the value of one pair of flat points detected by the section of the pair of image signals of said pair of image signals, The focus detection apparatus according to claim 1, wherein a correction value for adjusting a value of a pair of flat points detected in the other section of the pair of image signals is calculated. Said calculation means, said extracting means detects a maximum value and a minimum value in each of the extracted interval, the maximum value and the minimum value detected by one the section of said pair of image signals of said pair of image signals, The focus detection apparatus according to claim 1, wherein a correction value for adjusting the maximum value and the minimum value detected in the other section of the pair of image signals is calculated. Said calculation means in each of the section the extraction means of said pair of image signals is extracted, the average and maximum values, or to detect the average value and the minimum value, whereas the section of said pair of image signals The detected average value and maximum value, or the average value and minimum value, and the correction value for matching the average value and maximum value detected in the other section of the pair of image signals, or the average value and minimum value. The focus detection apparatus according to claim 1, wherein: The correction value includes a first correction value for correcting a difference in offset between the pair of image signals and a second correction value for correcting a gain difference between the pair of image signals. ,
  The calculating means detects a pair of feature points from each of the sections of the pair of image signals, calculates the first correction value based on one value of the pair of feature points, and The focus detection apparatus according to claim 1, wherein the second correction value is calculated based on the value of the pair of feature points corrected by a correction value. The focus detection apparatus according to claim 5, wherein the feature points are a pair of flat points, a maximum value and a minimum value, an average value and a maximum value, or an average value and a minimum value. Focus detecting apparatus according to any one of claims 1 to 6, characterized in that to detect a phase difference with high resolution the second detecting means than the first detecting means. The said 2nd detection means detects the said phase difference using a pair of image signal differentiated higher-order than the said differential image signal, The any one of Claim 1 thru | or 7 characterized by the above-mentioned. The focus detection apparatus described in 1. Said pair of sensor focus detection apparatus according to any one of claims 1 to 8, characterized in that a plurality of phase difference detection pixels provided in the image pickup device. A method for controlling a focus detection apparatus that detects a subject distance or a defocus amount by detecting a phase difference between a pair of image signals obtained from a pair of sensors,
Differentiating means for differentiating the pair of image signals and generating a pair of differential image signals;
A first detection step in which a first detection means detects a phase difference between the pair of differential image signals;
An extracting step in which an extracting unit extracts a section corresponding to the same subject from the pair of image signals using the phase difference detected by the first detecting unit;
Calculation step calculating means, by using the period signal extracted by the extraction step of the pair of image signals, calculates a correction value of the order to correct the difference between the offset and gain between the pair of image signals When,
The pair of image signals for detecting the subject distance or the defocus amount using the pair of image signals in which the difference between the offset and the gain is corrected using the correction value. And a second detection step of detecting a phase difference between the focus detection apparatus and the focus detection apparatus.

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