WO2012073727A1

WO2012073727A1 - Imaging device and focal position detection method

Info

Publication number: WO2012073727A1
Application number: PCT/JP2011/076721
Authority: WO
Inventors: 貴嗣青木
Original assignee: 富士フイルム株式会社
Priority date: 2010-11-30
Filing date: 2011-11-18
Publication date: 2012-06-07
Also published as: JP2014032214A

Abstract

The purpose of the present invention is to achieve high-speed and high-precision phase-difference autofocusing. Provided is an imaging device comprising: an imaging element with a first and a second phase difference detection pixel (x, y) that have been pupil-divided inside a phase difference detection area (40) arranged two dimensionally in a light-receiving surface; a focus lens positioned at the front of an optical path for the imaging element; and a control means that drive controls the focus lens to the focal position. The control means: divides the area (40) into a plurality of divided areas (I, II, III, IV); for each divided area, adds output signals for a plurality of pixels (x) lined up in a row in a direction perpendicular to the phase difference detection method in a divided area to a plurality of pixels (x) lined up in the phase difference detection direction in said divided area, for each pixel (x); and similarly adds output signals for pixels (y). The control means then calculates for each divided area the correlation between the pixel (x) signals added and the pixel (y) signals added to calculate an evaluation curve, performs a prescribed arithmetic processing on the evaluation curve calculated for each divided area, and finds an overall evaluation curve for the whole area. The control means finds the amount of defocus from this overall evaluation curve.

Description

Imaging apparatus and focus position detection method thereof

The present invention relates to an imaging apparatus that detects the distance to a subject and controls the focal position of a photographic lens, and an in-focus position detection method thereof.

The focus position detection method for detecting the distance to the main subject includes a contrast method and a phase difference AF method. The phase difference AF method is often used in single-lens reflex cameras because it can detect the in-focus position at a higher speed and with higher accuracy than the contrast method.

The phase difference AF method employed in the conventional single-lens reflex camera is, for example, as described in Patent Document 1 below, arranged separately on two right and left sides apart from a solid-state image sensor that captures a subject image. A phase difference detection line sensor is provided, and the distance to the main subject is detected based on the phase difference between the detection information of the first line sensor and the detection information of the second line sensor.

The phase difference AF method described in Patent Document 1 requires a line sensor for phase difference detection in addition to the solid-state imaging device, which increases the parts cost and manufacturing cost, and further increases the size of the apparatus. .

On the other hand, as described in Patent Document 2 below, a pixel in which a pixel for detecting a phase difference is provided on a light receiving surface of a solid-state imaging device has been proposed. By adopting a solid-state image sensor in which pixels for phase difference detection are formed as a solid-state image sensor that captures a subject image, an external phase difference detection sensor becomes unnecessary, and the cost can be reduced.

Japanese Unexamined Patent Publication No. 2010-8443 Japanese Laid-Open Patent Publication No. 2010-91991

However, the conventional technique described in Patent Document 2 is intended for single-lens reflex cameras, and is premised on mounting a large-area solid-state imaging device. In the phase difference detection pixel, as described in Patent Document 2, the light shielding film opening of each of a pair of adjacent pixels is made small, and the light shielding film opening position of one and the other is set to the phase difference detection direction (normal case). Is configured to detect the phase difference by shifting in the horizontal direction.

A large-format (large area) solid-state imaging device that can increase the light receiving area of each pixel can obtain phase difference information at high speed and high accuracy even if the light shielding film aperture is slightly reduced. However, the light receiving area of each pixel cannot be increased. For example, in a solid-state image sensor mounted on a compact camera or the like, the original light-shielding film aperture is small. If the information is acquired at high speed, there arises a problem that the accuracy of the phase difference information, that is, the focus position detection accuracy is lowered.

An object of the present invention is to provide an imaging apparatus capable of acquiring phase difference information and obtaining a focus position at high speed and with high accuracy even when applied to a solid-state image sensor having a small area, and a focus position detection method thereof. is there.

According to the imaging apparatus and the focus position detection method of the present invention, a first phase difference detection pixel and a second phase difference detection that are divided into pupils in a phase difference detection area provided on a light receiving surface that captures an image of a subject. An image sensor in which a pair of pixels is arranged two-dimensionally;
A focus lens that is placed in front of the optical path of the image sensor and forms a focused optical image of the subject on the light receiving surface;
A first distribution curve of the output signal from the first phase difference detection pixel with respect to one arrangement direction of the pair pixels, and a second distribution curve with respect to the one arrangement direction of the output signal from the second phase difference detection pixel. An in-focus position detection method of an imaging apparatus, comprising: a control unit that obtains a phase difference from the distribution curve of the first lens and controls the drive of the focus lens to the in-focus position based on the phase difference,
Dividing the phase difference detection area into a plurality of divided areas in a direction perpendicular to the phase difference detection direction;
For each of the divided areas, output signals from the plurality of first phase difference detection pixels arranged in a line in the perpendicular direction in the divided area are output to the plurality of first signals arranged in the one arrangement direction in the divided area. One phase difference detection pixel is added for each first phase difference detection pixel, and for each of the divided areas, a plurality of the second phase differences arranged in a row in the perpendicular direction in the divided area The output signal from the detection pixel is added to each of the plurality of second phase difference detection pixels arranged in the one arrangement direction in the divided area for each second phase difference detection pixel,
Correlation between a first addition signal obtained by adding the output signal of the first phase difference detection pixel and a second addition signal obtained by adding the output signal of the second phase difference detection pixel to the divided area. Is calculated for each of the first and second phase difference detection pixels to calculate a correlation calculation curve for each divided area,
Among the correlation calculation curves calculated for each of the divided areas, a comprehensive evaluation curve obtained by performing a predetermined calculation process on an arbitrary plurality of correlation calculation curves is obtained, and the focus lens is combined with the focus lens from the comprehensive evaluation curve. A defocus amount for driving and controlling the focal position is obtained.

According to the present invention, an evaluation curve (correlation calculation curve) is obtained for each divided area, and a predetermined calculation process is performed on the plurality of evaluation curves to obtain an overall evaluation curve (a plurality of areas). Since the defocus amount is calculated from the number of pixels, the number of added pixels is not increased and the pattern of the subject is not averaged. Even when a small solid-state image sensor is mounted, the phase difference AF can be performed at high speed and with high accuracy. Can be done.

It is a functional block block diagram of the imaging device which concerns on one Embodiment of this invention. It is explanatory drawing of the phase difference detection area provided on the light-receiving surface of the solid-state image sensor shown in FIG. It is a surface expansion schematic diagram in the dotted-line rectangular frame of FIG. It is a figure explaining the concept of the phase difference amount calculated | required by extracting only the phase difference detection pixel of FIG. 3, and its detection signal. It is explanatory drawing of the evaluation curve for every division area, and a total evaluation curve. It is reliability explanatory drawing of the evaluation curve for every division area. It is explanatory drawing of the majority decision example when the evaluation curve with respect to a different subject is calculated | required among the evaluation curves for every divided area. It is explanatory drawing when the number of the evaluation curves with respect to a different subject becomes the same number among the evaluation curves for every divided area. It is explanatory drawing of the phase difference detection pixel which makes a horizontal direction and a vertical direction a phase difference detection direction. It is explanatory drawing of the phase difference direction of FIG. It is a figure which shows the example of a division | segmentation of a phase difference detection area when using the phase difference detection pixel of FIG. It is a figure which shows an example of the evaluation curve of the horizontal direction calculated | required for every division area shown in FIG. 9, and a vertical direction.

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

FIG. 1 is a functional block diagram of a digital camera according to an embodiment of the present invention. The digital camera 10 of the present embodiment has a function of capturing a still image or a moving image of a subject and digitally processing a captured image signal in the camera 10, and includes a photographic lens 20 including a telephoto lens and a focus lens, and a photographic lens 20. The analog image data output from each pixel of the solid-state image sensor 21 and the solid-state image sensor 21 placed on the imaging surface of the solid-state image sensor 21 and the analog image data such as automatic gain adjustment (AGC) and correlated double sampling processing. From an analog signal processing unit 22 to be processed, an analog / digital conversion unit (A / D) 23 that converts analog image data output from the analog signal processing unit 22 into digital image data, and a system control unit (CPU) 29 described later The A / D 23, the analog signal processing unit 22, the solid-state imaging device 21, and the photographic lens 20 are driven and controlled by It includes a moving section 24, a flash 25 that emits light in response to an instruction from the CPU 29.

The digital camera 10 according to the present embodiment further includes a digital signal processing unit 26 that takes in digital image data output from the A / D 23 and performs interpolation processing, white balance correction, RGB / YC conversion processing, and the like. A compression / decompression processing unit 27 that compresses or reversely decompresses the image data, a display unit 28 that displays a menu or the like, and a through image or a captured image, and a system control unit that performs overall control of the entire digital camera A media interface (I / F) unit 31 that performs interface processing between the (CPU) 29, an internal memory 30 such as a frame memory, and a recording medium 32 that stores JPEG image data, and the like are connected to each other. And an operation unit 33 for inputting an instruction from the user to the system control unit 29. It is connected.

The system control unit 29 analyzes the captured image data (through image) output from the solid-state imaging device 21 in a moving image state and processed by the digital signal processing unit 26 using the subordinate digital signal processing unit 26 and the like as described later. To obtain an evaluation curve (correlation calculation curve) and detect the distance to the main subject. Then, the system control unit 29 controls the position of the focus lens placed in front of the optical path of the solid-state imaging device 21 in the photographic lens 20 via the driving unit 24, and the optical image focused on the subject is a solid-state imaging device. An image is formed on the light receiving surface 21.

The solid-state image pickup device 21 is a CMOS type in this embodiment, and an output signal of the solid-state image pickup device 21 is processed by an analog signal processing unit (AFE: analog front end) 22, and this AFE portion (correlated double sampling processing or A circuit for performing a clamp process, a signal amplifier circuit for performing gain control, and the like) are generally provided as a peripheral circuit on a solid-state imaging device chip. In addition, a horizontal scanning circuit, a vertical scanning circuit, a noise reduction circuit, a synchronization signal generation circuit, and the like are also formed as peripheral circuits around the light receiving unit on the chip of the solid-state imaging device 21, and the A / D in FIG. The conversion part 23 may also be formed. The solid-state imaging device 21 may be a CCD type, and the embodiments described below can be applied as they are.

FIG. 2 is an explanatory diagram of the light receiving surface of the solid-state image sensor 21. On the light receiving surface of the solid-state image sensor 21, a large number of pixels (light receiving elements: photodiodes) (not shown) are arranged in a two-dimensional array. In this embodiment, a plurality of pixels are arranged in a square lattice pattern. Note that the pixel array is not limited to a square lattice array, and may be a so-called honeycomb array in which even-numbered pixel rows are shifted by 1/2 pixel pitch with respect to odd-numbered pixel rows.

A rectangular phase difference detection area 40 is provided at an arbitrary partial region position on the light receiving surface, in the illustrated example, at the center position. In this example, only one phase difference detection area 40 is provided with respect to the light receiving surface. However, the phase difference detection area 40 may be provided at a plurality of locations so that AF can be performed anywhere on the imaging screen. The entire area of the light receiving surface may be used as a phase difference detection area.

In the present embodiment, the phase difference detection area 40 is divided into four in the vertical direction (up and down direction y) with respect to the phase difference detection direction (in this example, the left and right direction, that is, the x direction is the phase difference detection direction). For each of the divided areas I, II, III, and IV, a correlation calculation described later is performed. Note that the number of divisions is not limited to four, and may be six or seven, and can be divided into an arbitrary number.

FIG. 3 is a schematic enlarged surface view of a portion indicated by a dotted rectangular frame 41 in FIG. 2 in the phase difference detection area 40. A large number of pixels are arranged in a square lattice on the light receiving surface of the solid-state imaging device 21, and the same applies to the phase difference detection area 40.

In the illustrated example, each pixel is indicated by R (red), G (green), and B (blue). R, G, and B represent colors of the color filters stacked on each pixel, and the color filter array is a Bayer array in this example, but is not limited to the Bayer array, and other color filters such as stripes. An array may be used.

The pixel array and the color filter array in the phase difference detection area 40 are the same as the pixel array and the color filter array on the light receiving surface outside the phase difference detection area 40. Pixels of the same color adjacent to are designated as phase

difference detection pixels

1x and 1y. In the present embodiment, paired pixels for phase difference detection are provided at discrete and periodic positions in the area 40, in the illustrated example, at checkered positions.

In the illustrated example, the same color pixels are diagonally adjacent because the color filter array is a Bayer array, and in the case of a horizontal stripe array, the same color pixels are arranged in the horizontal direction. Will be adjacent to. Alternatively, instead of providing two pixels constituting a pair in the same color filter row in the horizontal stripe arrangement, each pixel constituting the pair may be provided separately in each filter row of the same color closest in the vertical direction. The same applies to the vertical stripe arrangement.

In the present embodiment, the phase

difference detection pixels

1x and 1y are provided in the most G filter mounted pixels among R, G, and B, and 8 pixels are arranged in the horizontal direction (x direction) and in the vertical direction (y direction). It is arranged so that every eight pixels and the entire checkered position. Accordingly, when viewed in the phase difference detection direction (left-right direction), the phase difference detection pixels 1x are arranged every four pixels.

FIG. 4 is a diagram schematically showing only the phase

difference detection pixels

1x and 1y of FIG. Similarly to Patent Document 2, the phase

difference detection pixels

1x and 1y constituting the paired pixels are formed such that the light

shielding film openings

2x and 2y are smaller than other pixels (pixels other than the phase difference detection pixels), and the pixel 1x The light shielding film opening 2x is eccentrically provided in the left direction, and the light shielding film opening 2y of the pixel 1y is eccentrically provided in the right direction (phase difference detection direction).

The curve X shown in the lower part of FIG. 4 is a graph in which the detection signal amounts of the phase difference detection pixels 1x arranged in a horizontal row are plotted, and the curve Y is a detection signal of the phase difference detection pixel 1y that forms a pair with these pixels 1x. It is the graph which plotted quantity.

The paired

pixels

1x and 1y are adjacent pixels and are very close to each other, and therefore are considered to receive light from the same subject. For this reason, it is considered that the curve X and the curve Y have the same shape, and the shift in the left-right direction (phase difference detection direction) is caused by the difference between the image seen by one pixel 1x of the paired pixel divided by the pupil and the other pixel 1y. This is the amount of phase difference from the image seen in.

By performing a correlation calculation between the curve X and the curve Y, the phase difference amount (lateral shift amount) can be obtained, and the distance to the subject can be calculated from the phase difference amount. A known method (for example, a method described in Patent Document 1 or a method described in Patent Document 2) may be adopted as a method for obtaining the evaluation value of the correlation amount between the curve X and the curve Y. For example, the integrated value of the absolute value of the difference between each point X (i) constituting the curve X and each point Y (i + j) constituting the curve Y is used as the evaluation value, and the j value giving the maximum evaluation value is expressed as the phase difference. The amount (lateral deviation).

However, when the light receiving area of each pixel is small, the amount of each signal is small and the ratio of noise is increased. Therefore, it is difficult to detect the phase difference with high accuracy even if correlation calculation is performed. Therefore, within the phase difference detection area 40 of FIG. 2, the detection signals of the pixels 1x at the same horizontal position are added by a plurality of pixels in the vertical direction, and the detection signals of the pixels 1y at the same horizontal position are added in the vertical direction. If only a plurality of pixels are added, the influence of noise can be reduced and the detection accuracy (AF accuracy) of the in-focus position can be improved.

However, it is not necessary to increase the number of pixel additions. As the number of pixel additions increases, the arrangement area of the phase difference detection pixels to be added to the pixels in the phase difference detection area 40 extends in the vertical direction (vertical direction). It will be. The subject pattern is usually different between a pattern imaged in the upper part of the phase difference detection area 40, a pattern imaged in the middle part, and a pattern imaged in the lower part. For this reason, if all these pixels are added, the pattern after subject pixel addition is averaged in the phase difference detection direction (left and right direction), resulting in a problem that the evaluation value for obtaining the phase difference is lowered. .

Therefore, in the present embodiment, as shown in FIG. 2, the phase difference detection area 40 is divided into four, the pixel addition range is limited to each divided area, and pixels are not added beyond the divided area. In other words, pixels are added to each divided area I, II, III, IV to obtain a divided area evaluation curve (correlation calculation curve), and each divided area evaluation curve is added to evaluate the entire evaluation curve of the phase difference detection area 40 ( Comprehensive evaluation curve).

FIG. 5 is a graph showing the respective evaluation curves I, II, III, IV for each divided area, and a total evaluation curve (evaluation curve for all areas) V obtained by summing up these four divided area evaluation curves. The divided area evaluation curve I is the same as the divided area I in FIG. 4 obtained by adding the detection signals of the phase difference detection pixels 1x in the divided area I in the vertical direction (for example, reference numeral 45 in FIG. 3). 4 is an evaluation curve obtained by correlation calculation with the curve Y in FIG. 4 obtained by adding the detection signals of the phase difference detection pixel 1y in the vertical direction (for example, reference numeral 46 in FIG. 3). In this example, the maximum evaluation value is obtained as the minimum value.

Similarly, the divided area evaluation curve II is an evaluation curve obtained in the divided area II, the divided area evaluation curve III is an evaluation curve obtained in the divided area III, and the divided area evaluation curve IV is obtained in the divided area IV. Evaluation curve.

The number of added pixels for obtaining each of these four divided area evaluation curves I, II, III, and IV is substantially divided with respect to the number of phase difference detection pixels 1x arranged in the vertical direction of the phase difference detection area 40. Since the number of areas is one-thousand, there is little possibility that the subject pattern is averaged, and the evaluation value can be calculated with high accuracy.

In this embodiment, a total evaluation curve V obtained by summing up these four divided area evaluation curves I, II, III, and IV is obtained, and further, a sub-pixel interpolation operation is performed from the total evaluation curve V, whereby a phase difference is obtained. The amount (defocus amount) is obtained. This makes it possible to calculate the phase difference with high accuracy while being resistant to noise and maintaining the evaluation value of each divided area of the subject, thereby improving the AF accuracy.

Since one unit of the horizontal axis of the graph of FIG. 5 is the pixel interval of the phase difference detection pixels of FIG. 3 (because of the checkered array of 8 pixel intervals, the interval is 4 pixels), the minimum of the comprehensive evaluation curve V Subpixel interpolation of the position that gives the true minimum value (maximum evaluation value), that is, the phase difference amount, taking into account the position of the value and the slope of the curve that extends to the right and the curve that extends to the left with respect to this minimum value. Calculate by calculation. As a result, the phase difference amount can be obtained for each pixel in FIG.

In the above-described embodiment, the four divided area evaluation curves I, II, III, and IV are summed to obtain the overall evaluation curve V, and the maximum evaluation value is obtained. However, when the correlation calculation is performed for each of the divided areas I, II, III, and IV, there may be a divided area where only a correlation calculation result with low reliability can be obtained.

For example, as shown in FIG. 6, when only the correlation curve (evaluation curve) II is viewed, the position of the horizontal axis that gives the maximum evaluation value (minimum value in this example) is not clear and unknown (for example, the presence of a plurality of points). Exists. In such a case, only the three correlation curves I, III, and IV with high reliability other than the low reliability correlation curve II are added to obtain a total comprehensive evaluation curve (correlation of the divided region I). Since the calculation curve is not used, V is a correlation calculation curve for a plurality of areas instead of the “all” area), and the overall evaluation curve V is subjected to sub-pixel interpolation processing, and the phase difference for adjusting the focus lens to the in-focus position. The amount, that is, the defocus amount is calculated. Thereby, it is possible to further improve the AF accuracy.

Whether or not the reliability is high is determined by quantifying the reliability and determining whether or not the reliability is higher than a predetermined threshold. For example, when there are a plurality of minimum values that have the same minimum evaluation value in a single divided area evaluation curve, it is determined that the reliability is low.

There may be a plurality of subjects with different shooting distances in the phase difference detection area 40 of FIG. Assume that subjects A and B exist. In such a case, for example, as shown in FIG. 7, in the divided areas I, II, and III, evaluation curves I, II, and III for calculating the maximum evaluation value for the subject A are calculated, and in the divided area IV, for the subject B. Thus, an evaluation curve IV for obtaining the maximum evaluation value is calculated. Unlike the case of FIG. 6, the evaluation curve IV of FIG. 7 is not necessarily low in reliability but high in reliability.

However, in such a case, if all the divided area evaluation curves I, II, III, and IV are summed up to obtain the overall evaluation curve V, there is a possibility that the in-focus position may be incorrect. Therefore, in such a case, a position on the horizontal axis that takes the maximum evaluation value of each evaluation curve I, II, III, IV (not a precise position, but a position that is considered to be within a certain range of some extent). The total evaluation curve V is obtained by adding the majority of the divided area evaluation curves I, II, and III. As a result, even when subjects with different shooting distances exist in the phase difference detection area (AF area), it is possible to prevent erroneous focusing.

In the description of FIG. 7, it is assumed that the majority of the four divided area evaluation curves is taken. However, since the number of divided areas is 4, there may be a case where the number is equal to 2 to 2. This case will be described with reference to FIG. In FIG. 8, there are two divided area evaluation curves I and III (the evaluation curve for the subject A) and two divided area evaluation curves II and IV (the evaluation curve for the subject B).

In such a case, when the total evaluation curve V is obtained by adding the four divided area evaluation curves I, II, III, and IV, the subject A is not focused and the subject B is not focused. turn into. Therefore, either subject A or subject B is selected. In the present embodiment, of the subjects A and B, the subject closer to the camera is determined as the main subject. That is, the subject on the side where the amount of positional deviation is small (see the horizontal axis in FIG. 5: the side close to the imaging device) is selected, and only the divided area evaluation curves I and III are added to obtain the total evaluation curve V, and the subpixel interpolation is performed. To calculate the phase difference amount.

As a result, even when there are subjects with different shooting distances in the AF area, it is possible to prevent erroneous focusing, and it is possible to preferentially focus on a close subject.

FIG. 9 is a diagram showing a pixel arrangement of phase difference detection pixels according to another embodiment of the present invention. In each of the embodiments described above, the phase

difference detection pixels

1x and 1y are provided with only the phase difference detection direction as the horizontal direction (x direction). However, in this embodiment, as shown in FIG. The phase difference detection direction is used, and the vertical direction (y direction) is also the second phase difference detection direction.

For this reason, as shown in FIG. 9, in this embodiment, among the four adjacent pixels A, B, C, and D in the square array, the upper left pixel A (corresponding to the phase difference detection pixel 1x) and the lower right pixel B ( The phase difference in the horizontal direction (x direction) is detected by the phase difference detection pixel 1y), and the phase difference in the vertical direction (y direction) is detected by the upper right pixel C and the lower left pixel D. That is, the small light shielding film opening of the pixel A is decentered to the left side, the small light shielding film opening of the pixel B is decentered to the right side, the small light shielding film opening of the pixel C is decentered upward, and the small light shielding film opening of the pixel D is It is eccentric to the side.

By arranging the set of the phase difference detection pixels A, B, C, and D shown in FIG. 9 at periodic and discrete positions in the phase difference detection area 40 of FIG. 10, the vertical and horizontal positions are arranged. Detect phase difference. In this case, the rectangular phase difference detection area 40 is divided into a mesh shape, and is divided into four areas I, II, III, and IV in the example shown in FIG. Each of the four divided areas is considered to have a high probability of obtaining the same evaluation curve in the vertical and horizontal directions within the same area.

FIG. 12 is a diagram illustrating an example in which a total of eight divided area evaluation curves, that is, a horizontal divided area evaluation curve and a vertical divided area evaluation curve are obtained in each of the four divided areas. From the divided area I, a horizontal divided area evaluation curve Ia and a vertical divided area evaluation curve Ib are obtained, and from the divided area II, a horizontal divided area evaluation curve IIa and a vertical divided area evaluation curve IIb are obtained. From the divided area III, a horizontal divided area evaluation curve IIIa and a vertical divided area evaluation curve IIIb are obtained, and from the divided area IV, the horizontal divided area evaluation curve IVa and the vertical divided area evaluation curve are obtained. IVb is obtained.

In the example of FIG. 12, since the reliability of the evaluation value of the divided area IV is small, a total of six divided area evaluation curves for the divided areas I, II, and III are added to obtain a total evaluation curve V, and the subpixels are obtained. Interpolation is performed to calculate a phase difference amount, that is, a defocus amount. In this way, since the in-focus position is obtained by detecting the phase difference in different directions, it is possible to further improve the AF accuracy.
Further, since the divided areas with low reliability are excluded and are not used for the AF calculation, the AF accuracy can be further improved.

As in the above-described embodiment, the imaging apparatus divides the phase difference detection area into a plurality of regions, obtains a divided area evaluation curve for each divided area, adds only the reliable divided area evaluation curve, and adds up the total. By obtaining a comprehensive evaluation curve and calculating a phase difference amount by interpolating the comprehensive evaluation curve with sub-pixels, it is possible to perform focusing control of the photographing lens. For this reason, even when a small-area image sensor is used, it is possible to obtain high-speed and high-precision AF performance comparable to that of a single-lens reflex camera.

In the above-described embodiment, the pupil-divided pair pixel constituting the phase difference detection pixel has been described by using an example in which the reduced light shielding film openings are shifted in opposite directions. The method of configuring is not limited to this, and for example, one microlens may be mounted on a pair of pixels to divide the pupil.

Further, in the above-described embodiment, when the required calculation process is performed on the correlation calculation curve for each area to obtain a total evaluation curve for all areas (or a plurality of areas), “addition and summation” is performed as the required calculation process. As described above, “average value” and “multiplication value” may also be obtained.

Furthermore, in the above-described embodiment, the example in which the pair pixels for detecting the phase difference are provided at discrete and periodic positions in the phase difference detection area has been described. However, the pixel need not necessarily be provided at the periodic and discrete positions. 4 may be random positions (even if the phase difference detection pixels provided in the same row are at random positions, the curves X and Y in FIG. 4 can be obtained), or all the pixels are used as phase difference detection pixels. That's fine.

The imaging apparatus and the focus position detection method thereof according to the embodiments described above include the first phase difference detection pixel and the second phase divided in the phase difference detection area provided on the light receiving surface that captures the image of the subject. An image sensor in which a pair of pixels composed of phase difference detection pixels are two-dimensionally arranged;
A focus lens that is placed in front of the optical path of the image sensor and forms a focused optical image of the subject on the light receiving surface;
A first distribution curve of the output signal from the first phase difference detection pixel with respect to one arrangement direction of the pair pixels, and a second distribution curve with respect to the one arrangement direction of the output signal from the second phase difference detection pixel. An in-focus position detection method of an imaging apparatus, comprising: a control unit that obtains a phase difference from the distribution curve of the first lens and controls the drive of the focus lens to the in-focus position based on the phase difference,
Dividing the phase difference detection area into a plurality of divided areas in a direction perpendicular to the phase difference detection direction;
For each of the divided areas, output signals from the plurality of first phase difference detection pixels arranged in a line in the perpendicular direction in the divided area are output to the plurality of first signals arranged in the one arrangement direction in the divided area. One phase difference detection pixel is added for each first phase difference detection pixel, and for each of the divided areas, a plurality of the second phase differences arranged in a row in the perpendicular direction in the divided area The output signal from the detection pixel is added to each of the plurality of second phase difference detection pixels arranged in the one arrangement direction in the divided area for each second phase difference detection pixel,
Correlation between a first addition signal obtained by adding the output signal of the first phase difference detection pixel and a second addition signal obtained by adding the output signal of the second phase difference detection pixel to the divided area. Is calculated for each of the first and second phase difference detection pixels to calculate a correlation calculation curve for each divided area,
Among the correlation calculation curves calculated for each of the divided areas, a comprehensive evaluation curve obtained by performing a predetermined calculation process on an arbitrary plurality of correlation calculation curves is obtained, and the focus lens is combined with the focus lens from the comprehensive evaluation curve. It is characterized in that a defocus amount for driving control to a focus position is obtained.

In the imaging apparatus and the focus position detection method according to the embodiment, when calculating the correlation calculation curves of the plurality of areas, the reliability of each correlation calculation curve for each divided area is evaluated, and the reliability is higher than a predetermined threshold. Only the correlation calculation curve for each divided area is subjected to the predetermined calculation process to obtain the comprehensive evaluation curve.

In addition, the imaging apparatus and the focus position detection method thereof according to the embodiment include an evaluation value represented as an absolute value of a difference between the first addition signal and the second addition signal in the correlation calculation curve for each divided area. The comprehensive evaluation curve is obtained by selectively using only the correlation calculation curve for each divided area where the position where the maximum value is within the same range and the reliability is higher than a predetermined threshold value.

In addition, the imaging apparatus and the focus position detection method of the embodiment take a majority decision of the position that gives the maximum evaluation value of the correlation calculation curve for each divided area, and only the correlation calculation curve for each divided area becomes a large number. The comprehensive evaluation curve is obtained by selectively using.

Further, in the imaging apparatus and the focus position detection method according to the embodiment, when a plurality of correlation calculation curves in which the position where the evaluation value is maximized are within the same range are obtained, the position where the evaluation value is maximized is determined. The correlation calculation curve having a smaller phase difference is selected.

In addition, in the imaging apparatus and the focus position detection method according to the embodiment, when a plurality of correlation calculation curves in which the position where the evaluation value is maximized are within the same range are obtained, among the plurality of divided areas, The correlation calculation curve is selected for a divided area including a subject whose evaluation value is maximum at a position closer to the image sensor.

In addition, in the imaging apparatus and the focus position detection method thereof according to the embodiment, in addition to the pair of pixels of the first phase difference detection pixel and the second phase difference detection pixel that detect the phase difference in the horizontal direction, A pair pixel of the first phase difference detection pixel and the second phase difference detection pixel for detecting a phase difference is provided in the phase difference detection area of the image sensor, and the phase difference detection area is formed in a plurality of mesh shapes. Dividing into divided areas, for each divided area, obtaining a correlation calculation curve for each of the divided areas in the horizontal direction and a correlation calculation curve for each of the divided areas in the vertical direction. The comprehensive evaluation curve is obtained based on the above.

In addition, among the correlation calculation curves for each of the divided areas, if the position where the evaluation value of the horizontal correlation calculation curve and the vertical correlation calculation curve in the same divided area is different from each other, The comprehensive evaluation curve is obtained from the correlation calculation curves of the remaining divided areas excluding the correlation calculation curves of the divided areas.

According to the embodiment described above, since pixel addition is performed for each divided area, the number of pixel additions is increased and the pattern of the subject is not averaged, and the pixel addition is highly accurate. The phase difference amount can be detected, and the phase difference AF can be realized at high speed and with high accuracy even with a small and small area solid-state imaging device.

Since the in-focus position detection method according to the present invention can obtain high-speed and high-precision AF performance, a digital camera, particularly a compact digital camera, a camera-equipped mobile phone, an electronic device with a camera, an imaging device for an endoscope, etc. It is useful to apply to.
This application is based on Japanese Patent Application No. 2010-267932 filed on Nov. 30, 2010, the contents of which are incorporated herein by reference.

1x, 1y Phase

difference detection pixels

2x, 2y Light shielding film opening 10 of phase difference detection pixels Imaging device 20 Shooting lens 21 Solid-state imaging device 24 Drive unit 26 Digital signal processing unit 29 System control unit 40 Phase difference detection areas I, II, III , IV Divided area

Claims

Imaging in which a pair of pixels composed of a first phase difference detection pixel and a second phase difference detection pixel divided into pupils are two-dimensionally arranged in a phase difference detection area provided on a light receiving surface for capturing an image of a subject. Elements,
A focus lens that is placed in front of the optical path of the image sensor and forms a focused optical image of the subject on the light receiving surface;
A first distribution curve of the output signal from the first phase difference detection pixel with respect to one arrangement direction of the pair pixels, and a second distribution curve with respect to the one arrangement direction of the output signal from the second phase difference detection pixel. And a control means for driving and controlling the focus lens to the in-focus position based on the phase difference.
The control means includes
Means for dividing the phase difference detection area into a plurality of divided areas in a direction perpendicular to the phase difference detection direction;
For each of the divided areas, output signals from the plurality of first phase difference detection pixels arranged in a line in the perpendicular direction in the divided area are output to the plurality of first signals arranged in the one arrangement direction in the divided area. One phase difference detection pixel is added for each first phase difference detection pixel, and for each of the divided areas, a plurality of the second phase differences arranged in a row in the perpendicular direction in the divided area Means for adding the output signal from the detection pixel for each of the second phase difference detection pixels to the plurality of second phase difference detection pixels arranged in the one arrangement direction in the divided area;
Correlation between a first addition signal obtained by adding the output signal of the first phase difference detection pixel and a second addition signal obtained by adding the output signal of the second phase difference detection pixel to the divided area. Calculating a correlation calculation curve for each divided area by calculating for each of the first and second phase difference detection pixels;
Among the correlation calculation curves calculated for each of the divided areas, a comprehensive evaluation curve obtained by performing a predetermined calculation process on an arbitrary plurality of correlation calculation curves is obtained, and the focus lens is combined with the focus lens from the comprehensive evaluation curve. An image pickup apparatus comprising: a unit that obtains a defocus amount for driving and controlling the focus position.
The imaging apparatus according to claim 1,
When calculating the correlation calculation curves of the plurality of areas, the reliability calculation of each correlation calculation curve for each of the divided areas is performed, and the predetermined calculation processing is performed only for the correlation calculation curves of each of the divided areas whose reliability is higher than a predetermined threshold. To obtain the overall evaluation curve.
The imaging apparatus according to claim 1,
Reliability in which the position where the evaluation value expressed as the absolute value of the difference between the first addition signal and the second addition signal is maximum is within the same range in the correlation calculation curve for each divided area. An imaging apparatus characterized in that the comprehensive evaluation curve is obtained by selectively using only a correlation calculation curve for each divided area having a threshold value higher than a predetermined threshold.
The imaging apparatus according to claim 3,
Taking a majority decision of the position that gives the maximum evaluation value of the correlation calculation curve for each divided area, and selectively obtaining only the correlation calculation curve for each of the divided areas to obtain the comprehensive evaluation curve An imaging device.
The imaging apparatus according to claim 3,
When a plurality of correlation calculation curves in which the position where the evaluation value is maximized is within the same range are obtained, the correlation calculation curve having a smaller phase difference at the position where the evaluation value is maximum is selected. An imaging device.
The imaging apparatus according to claim 3,
When a plurality of correlation calculation curves in which the position where the evaluation value is maximized are within the same range are obtained, the subject whose position where the evaluation value is maximum is closer to the imaging element among the plurality of divided areas. An image pickup apparatus comprising: selecting the correlation calculation curve in a divided area including:
The imaging apparatus according to claim 1,
In addition to the paired pixels of the first phase difference detection pixel and the second phase difference detection pixel that detect the phase difference in the horizontal direction, the first phase difference detection pixel that detects the phase difference in the vertical direction, A pair of second phase difference detection pixels is provided in the phase difference detection area of the image sensor, the phase difference detection area is divided into a plurality of divided areas in a mesh shape, and the horizontal direction is determined for each of the divided areas. An imaging apparatus that obtains a correlation calculation curve for each of the divided areas and a correlation calculation curve for each of the divided areas in the vertical direction, and obtains the comprehensive evaluation curve based on the correlation calculation curve of each of the divided areas.
The imaging apparatus according to claim 7,
Of the correlation calculation curves for each of the divided areas, when the positions where the evaluation values of the horizontal correlation calculation curve and the vertical correlation calculation curve in the same divided area are maximum are different from each other, the divided area An imaging device for obtaining the comprehensive evaluation curve from the correlation calculation curves of the remaining divided areas excluding the correlation calculation curve.
Imaging in which a pair of pixels composed of a first phase difference detection pixel and a second phase difference detection pixel divided into pupils are two-dimensionally arranged in a phase difference detection area provided on a light receiving surface for capturing an image of a subject. Elements,
A focus lens that is placed in front of the optical path of the image sensor and forms a focused optical image of the subject on the light receiving surface;
A first distribution curve of the output signal from the first phase difference detection pixel with respect to one arrangement direction of the pair pixels, and a second distribution curve with respect to the one arrangement direction of the output signal from the second phase difference detection pixel. An in-focus position detection method of an imaging apparatus, comprising: a control unit that obtains a phase difference from the distribution curve and controls the drive of the focus lens to the in-focus position based on the phase difference,
Dividing the phase difference detection area into a plurality of divided areas in a direction perpendicular to the phase difference detection direction;
For each of the divided areas, output signals from the plurality of first phase difference detection pixels arranged in a line in the perpendicular direction in the divided area are output to the plurality of first signals arranged in the one arrangement direction in the divided area. One phase difference detection pixel is added for each first phase difference detection pixel, and for each of the divided areas, a plurality of the second phase differences arranged in a row in the perpendicular direction in the divided area The output signal from the detection pixel is added to each of the plurality of second phase difference detection pixels arranged in the one arrangement direction in the divided area for each of the second phase difference detection pixels,
Correlation between a first addition signal obtained by adding the output signal of the first phase difference detection pixel and a second addition signal obtained by adding the output signal of the second phase difference detection pixel to the divided area. For each of the first and second phase difference detection pixels to calculate a correlation calculation curve for each divided area,
Among the correlation calculation curves calculated for each of the divided areas, a comprehensive evaluation curve obtained by performing a predetermined calculation process on an arbitrary plurality of correlation calculation curves is obtained, and the focus lens is combined with the focus lens from the comprehensive evaluation curve. An in-focus position detection method for an imaging apparatus, characterized in that a defocus amount for driving and controlling to a focus position is obtained.
An in-focus position detection method for an imaging apparatus according to claim 9,
When calculating the correlation calculation curves of the plurality of areas, the reliability calculation of each correlation calculation curve for each of the divided areas is performed, and the predetermined calculation processing is performed only for the correlation calculation curves of each of the divided areas whose reliability is higher than a predetermined threshold. The focus position detection method of the imaging device, wherein the comprehensive evaluation curve is obtained by applying
An in-focus position detection method for an imaging apparatus according to claim 9,
Reliability in which the position where the evaluation value expressed as the absolute value of the difference between the first addition signal and the second addition signal is maximum is within the same range in the correlation calculation curve for each divided area. An in-focus position detection method for an imaging apparatus, wherein the comprehensive evaluation curve is obtained by selectively using only a correlation calculation curve for each divided area having a threshold value higher than a predetermined threshold.
An in-focus position detection method for an imaging apparatus according to claim 11,
Taking a majority decision of the position that gives the maximum evaluation value of the correlation calculation curve for each divided area, and selectively obtaining only the correlation calculation curve for each of the divided areas to obtain the comprehensive evaluation curve A method for detecting a focus position of an imaging apparatus.
An in-focus position detection method for an imaging apparatus according to claim 11,
When a plurality of correlation calculation curves in which the position where the evaluation value is maximized is within the same range are obtained, the correlation calculation curve having a smaller phase difference at the position where the evaluation value is maximum is selected. An in-focus position detection method for an imaging apparatus.
An in-focus position detection method for an imaging apparatus according to claim 11,
When a plurality of correlation calculation curves in which the position where the evaluation value is maximized are within the same range are obtained, the subject whose position where the evaluation value is maximum is closer to the imaging element among the plurality of divided areas. A focus position detection method for an imaging apparatus, wherein the correlation calculation curve in a divided area including the image is selected.
An in-focus position detection method for an imaging apparatus according to claim 9,
In addition to the paired pixels of the first phase difference detection pixel and the second phase difference detection pixel that detect the phase difference in the horizontal direction, the first phase difference detection pixel and the first phase difference detection pixel that detect the phase difference in the vertical direction. A pair of phase difference detection pixels is provided in the phase difference detection area of the image sensor, the phase difference detection area is divided into a plurality of divided areas in a mesh shape, and the horizontal direction is divided into each divided area. An in-focus position detection method for an imaging apparatus that obtains a correlation calculation curve for each divided area and a correlation calculation curve for each divided area in the vertical direction, and obtains the comprehensive evaluation curve based on the correlation calculation curve for each divided area .
An in-focus position detection method for an imaging apparatus according to claim 15,
Of the correlation calculation curves for each of the divided areas, when the positions where the evaluation values of the horizontal correlation calculation curve and the vertical correlation calculation curve in the same divided area are maximum are different from each other, the divided area The focus position detection method of the imaging device which calculates | requires the said comprehensive evaluation curve from the correlation calculation curve for every remaining division area which excluded this correlation calculation curve.