Focus position detection apparatus, image pickup apparatus, and focus position detection method

Abstract

A focus position detection apparatus, an image pickup apparatus, and a focus position detection method are provided. To improve focus detection accuracy of an object having a large number of high-frequency components. An image plane phase difference pixel processor (115) as a focus position detection device performs an estimation process that estimates a plurality of estimated pixels (ZA'and ZB ') arranged between a plurality of phase difference pixels (ZA and ZB) on the basis of data of two image pixels (Gr) included in a row adjacent to a row in which the plurality of phase difference pixels (ZA and ZB) are arranged, and arranged in the same column as a corresponding phase difference pixel of the plurality of phase difference pixels ZA and ZB in a pixel array of the image sensor (102). Further, a ratio of a graph C, which is an average value of characteristics of pixel data along two rows including two image pixels Gr, to a graph A + B, which is a sum of characteristics of pixel data of phase difference pixels ZA and ZB, is determined by pre-adjustment, and the ratio is used as a correction rate F in an estimation process.

Description

Technical Field

[0001] The present invention relates to a focus position detection device, an image pickup device, and a focus position detection method. Background Art

[0002] As an automatic focus detection method for an image pickup device, image plane phase difference autofocus (AF) is known, in which phase difference AF is performed therein using a signal obtained from an image sensor. In an image sensor for performing image plane phase difference AF, in addition to image pixels for obtaining image data, phase difference pixels A and B are arranged at predetermined positions. Phase difference pixels A are partially shielded so as to receive a portion of the light flux passing through the pupil area of ​​the imaging lens, and phase difference pixels B are partially shielded so as to form a pair with phase difference pixels A. Then, the phase difference between the pixel data sequence of phase difference pixels A and the pixel data sequence of phase difference pixels B is calculated to perform focus detection.

[0003] Patent document 1 describes a method for performing refocusing focus detection with high precision using signals from discretely arranged phase difference pixels. In refocusing focus detection, the pixel data sequences of phase difference pixels A and B are added to each pixel to generate an additional data sequence. Then, the relative positions of the pixel data sequences of phase difference pixels A and B are gradually shifted in the column direction to generate similar additional data sequences in stages. Finally, a contrast evaluation value is calculated for each additional data sequence to estimate the contrast peak position, thereby performing focus detection. In this case, when performing focus detection, the configuration of Patent Document 1 increases the apparent density of the phase difference pixel data sequence by estimating the phase difference pixel data between the discretely arranged phase difference pixels, thereby improving focus detection accuracy.

[0004] For an object having a large number of complex patterns (ie, an object having a large number of high-frequency components), it is desirable to improve focus detection accuracy. Patent Document 1 does not describe such a viewpoint, and therefore, it appears that there is room for improvement in such a related art configuration.

[0005] The present disclosure relates to improving focus detection accuracy for an object having a large amount of high-frequency components.

[0006] Related technical literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Unexamined Patent Application No. 2016-038414 Summary of the Invention

[0009] According to at least one aspect of the present disclosure, a focus position detection device is provided for detecting a focus position based on signal values ​​from pixels of an image sensor. The image sensor includes image pixels, and a pair of first and second phase-difference pixels. The image pixels receive a subject image via a photographing lens group and photoelectrically convert the subject image. The pair of first and second phase-difference pixels respectively receive light fluxes passing through a pair of pupil regions of the photographing lens group and photoelectrically convert the light fluxes. The focus position detection device includes:

[0010] An estimator, configured to perform the following estimation process:

[0011] estimating a plurality of first estimated phase difference pixels arranged between a plurality of first phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of first estimated phase difference pixels are estimated being respectively included in rows adjacent to a row in which a plurality of pairs of the first phase difference pixels and the second phase difference pixels are arranged, and being arranged in the same column as corresponding second phase difference pixels among a plurality of second phase difference pixels in a pixel array of the image sensor, and

[0012] estimating a plurality of second estimated phase difference pixels arranged between the plurality of second phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of second estimated phase difference pixels are estimated being respectively included in rows adjacent to the rows in which the plurality of pairs of first phase difference pixels and second phase difference pixels are arranged, and being arranged in the same column as corresponding first phase difference pixels among the plurality of first phase difference pixels in the pixel array of the image sensor; and

[0013] a focus detector configured to detect a phase difference using a data sequence of the first phase difference pixels to which the plurality of first estimated phase difference pixels estimated by the estimator are added and a data sequence of the second phase difference pixels to which the plurality of second estimated phase difference pixels are added, and calculate an amount of defocus from a position in which the image is in focus;

[0014] The estimator determines, through pre-adjustment, a ratio of an average value of characteristics of pixel data along two rows including the two image pixels to a sum of characteristics of pixel data of the plurality of first phase difference pixels and characteristics of pixel data of the plurality of second phase difference pixels, and uses the ratio as a correction factor in the estimation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a perspective view showing an example of the external appearance of a digital camera as an example of the image pickup apparatus according to the embodiment;

[0016] Figure 2 is a functional block diagram illustrating an example of a digital camera;

[0017] Figure 3 is a diagram showing an example of arrangement of image pixels and phase difference pixels in an image sensor;

[0018] Figure 4 is a diagram showing an example of an object having a large amount of high-frequency components;

[0019] Figure 5 is shown by having Figure 4 FIG. 1 is a diagram showing an example of a focus position detection result in an in-focus state by a related art autofocus method for an object having a large amount of high-frequency components; FIG.

[0020] Figure 6 is a schematic diagram illustrating a method of estimating phase difference pixel data between phase difference pixels;

[0021] 7A to 7C are diagrams each showing an example of phase difference pixel data and image pixel data of a certain row when uniform light is exposed to the image sensor through the photographing lens;

[0022] Figure 8 is a diagram showing an example of a focus position detection result using a pixel data sequence of phase difference pixels after estimation by the phase difference pixel estimation method of the present embodiment;

[0023] Figure 9 is a flow chart illustrating an example of a pre-adjustment process; and

[0024] Figure 10 is a flowchart illustrating an example of an imaging plane phase difference detection process. DETAILED DESCRIPTION

[0025] Hereinafter, the embodiments will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components as much as possible in the drawings, and redundant descriptions will be omitted.

[0026] <Configuration Example of Digital Camera>

[0027] Figure 1 is a perspective view showing an example of the external appearance of a digital camera 1 as an example of the image pickup apparatus according to the embodiment.

[0028] like Figure 1 As shown, the digital camera 1 includes a main body 4 having a generally rectangular parallelepiped shape. A photographing lens group 2 is attached to a front surface 4A of the main body 4 of the digital camera 1. The photographing lens group 2 is generally composed of two components. The first is a zoom lens group 6 (see FIG. 1 ) that performs magnification of an object. Figure 2), and the second is a focus lens group 7 that adjusts the focus of the object (see Figure 2 ). Aperture shutter 103 (see Figure 2 ) and image sensor 102 (see Figure 2 ) is arranged behind the taking lens group 2.

[0029] The release button 3 is provided on the upper surface 4B of the main body 4 of the digital camera 1, which enables the user to recognize the half-pressed state and the fully pressed state. The half-pressed state serves as an auto focus (hereinafter referred to as AF) start trigger, and the fully pressed state serves as a shooting start trigger. On the back surface 4C of the main body 4 of the digital camera 1, an image display 114 (see FIG. 114 ) for displaying a monitoring screen and the like is provided. Figure 2 ) and the operation button group 116 (see Figure 2 ). The rear surface 4C is a surface whose normal direction is opposite to that of the front surface 4A, and is Figure 1 surface on the back side of the .

[0030] Figure 2 is a functional block diagram showing an example of the digital camera 1 . Figure 2 Schematically shows the Figure 1 The digital camera 1 is shown in FIG. 1 , and the front surface 4A of the main body 4 is shown facing the left side in the figure, the rear surface 4C is shown facing the right side in the figure, and the upper surface 4B is shown facing the upper side in the figure. The taking lens group 2 attached to the front surface 4A of the main body 4 is provided Figure 1 on the left side of the main body 4.

[0031] The photographing lens group 2 is attached to the front surface 4A of the main body 4 of the digital camera 1 and is formed of a zoom lens group 6 for performing magnification and a focus lens group 7 for performing focus adjustment. The light receiving surface of the image sensor 102 is arranged within the photographing lens group 2 via an aperture shutter 103. Data obtained from the image sensor 102 is sent to an image processor 107 and an image plane phase difference pixel processor 115.

[0032] Image processor 107 performs image processing, and the processed image data is stored in image memory 108. Image display circuit 109 is connected to the data path of image memory 108. Microprocessor 110 causes image display 114 to display an image via image display circuit 109, and writes and reads images to and from memory card 118 via card interface 117. Image plane phase difference pixel processor 115 calculates the phase difference based on the phase difference pixel data to obtain the amount of defocus. Image plane phase difference pixel processor 115 corresponds to the focus position detection device according to this embodiment.

[0033] The microprocessor 110 is connected to an image sensor control circuit 111 for controlling the image sensor 102. The microprocessor 110 is connected to the lens drive mechanism 104 and the encoder 105 to control the drive of the zoom lens group 6 and the focus lens group 7. The microprocessor 110 is connected to the aperture shutter 103 to control the exposure amount and exposure time. The release button 3 arranged on the upper surface 4B of the main body 4 of the digital camera 1 and the operation button group 116 arranged on the rear surface 4C are also connected to the microprocessor 110 to obtain information about the user's button operations.

[0034] <Image Sensor Pixel Configuration Example>

[0035] Figure 3 is a diagram showing an example of the arrangement of the image pixels 203 and the phase difference pixels ZA and ZB in the image sensor 102. Figure 3 , the horizontal arrangement in the figure is represented as a “row”, and the vertical arrangement is represented as a “column”. Figure 3 8 columns x 6 rows of pixels are representatively shown. A color filter is provided on each pixel.

[0036] The pixel group 201 is a unit of the image pixel 203 and includes four pixels of 2 columns×2 rows. Among the four pixels, the pixel R is provided with a red filter, the pixels Gr and Gb are provided with a green filter, and the pixel B is provided with a blue filter. Figure 3 In the example of , the pixel R is arranged at the upper left of the pixel group 201, the pixel Gr is arranged at the upper right, the pixel Gb is arranged at the lower left, and the pixel B is arranged at the lower right.

[0037] Image pixels 203 are configured by repeatedly arranging pixel groups 201 in the column direction and the row direction. This is the basic pixel configuration of image pixels 203, and this arrangement is generally called a "Bayer arrangement."

[0038] exist Figure 3 In the example of , the phase difference pixels are arranged in the fourth row 202 from the top, and the number "3" is assigned to the fourth row 202 in the Bayer arrangement. Figure 3 As shown, in row 202, phase difference pixels ZA (first phase difference pixels) and phase difference pixels ZB (second phase difference pixels) are alternately arranged along the column direction in the portion that originally belonged to pixel B in image pixel 203. The color filters on phase difference pixels ZA and ZB are green, not blue.

[0039] The light receiving area of ​​the phase difference pixel ZA is the left half of the pixel, and the right half of the same pixel is in a light-shielded state. The phase difference pixel ZA receives the luminous flux that has passed through the pupil portion area on the left side of the imaging lens (as viewed from the imaging surface). In the phase difference pixel ZB, the left and right halves of the paired pixels are arranged in an opposite manner. That is, the light receiving area of ​​the phase difference pixel ZB is the right half of the pixel, and the left half of the same pixel is in a light-shielded state. The phase difference pixel ZB receives the luminous flux that has passed through the right pupil portion area of ​​the imaging lens (when viewed from the imaging surface).

[0040] <Related Technology Focus Position Detection Issues>

[0041] The image plane phase difference pixel processor 115 is based on the Figure 3 The image sensor 102 of the illustrated pixel configuration receives data from phase difference pixels ZA and ZB to calculate the phase difference to obtain the amount of defocus. Note that in the related art configuration of autofocus using image plane phase difference, there is room for improvement in the focus detection accuracy of objects with a large amount of high-frequency components.

[0042] Figure 4 is a diagram showing an example of an object 601 having a large amount of high frequency components. Figure 4 In FIG, as an object 601, an object in which the left half of the screen is black in the x direction (horizontal direction in the figure) and the right half of the screen is white is shown. Figure 4 , an AF (auto focus) area 602 is indicated by a dotted rectangle at the center of the screen.

[0043] Figure 4 The object 601 shown in FIG is a stepping diagram in which the color changes from black to white at the center of the screen along the x direction of the screen. Figure 3 The illustrated configuration of the image sensor 102 shows that the object is a representative example of a high-frequency object pattern in the column direction of the phase difference pixels ZA and ZB, that is, an “object having a large amount of high-frequency components”.

[0044] Figure 5 is shown by having Figure 4 FIG. 1 is a diagram showing an example of a focus position detection result in an in-focus state using a related art autofocus method for an object 601 having a large amount of high-frequency components. Figure 5 The vertical axis represents the distance measurement result (defocus amount) (μm). Figure 5 The horizontal axis indicates the object position, which means that the object 601 is Figure 4 The position of the phase difference pixel column direction (x direction). Figure 5The distance measurement results in φ represent the results when the image sensor 102 is shifted in the x-direction by a unit finer than one pixel of the image sensor 102 .

[0045] The distance measurement result is in-focus and therefore ideally 0 (μm) at any object position. However, Figure 5 In the results of the related art method shown, a large distance measurement error occurs depending on the position of the object. Figure 5 In the example of , a distance measurement error exceeding 200 μm occurs. This error occurs because the data sequence of the phase difference pixels is sparse and the edge pattern of the object 601 is not correctly represented by the data sequence of the phase difference pixels ZA and ZB.

[0046] In order to solve this problem in the related art configuration, according to the present embodiment, correction is performed so as to make the data sequence of the phase difference pixels dense by estimating the phase difference pixel data between the phase difference pixels ZA and ZB.

[0047] <Phase Difference Pixel Estimation Method>

[0048] Figure 6 : is a schematic diagram showing a method of estimating phase difference pixel data between phase difference pixels ZA and ZB. Figure 6 Shown include Figure 3 The three rows of image pixels 203 are in the row 202. As described above, the row 202 includes the phase difference pixels ZA and ZB.

[0049] In this case, the row i and column j where pixel Z is arranged are denoted by Z i,j The pixel data sequence of the phase difference pixel ZA before estimation is {ZA 3,1 、ZA 3,5 , ...}, and the pixel data sequence of the phase difference pixel ZB before estimation is {ZB 3,3 、ZB 3,7 , ...}, each of which is a sequence of four pixels.

[0050] In this embodiment, the phase difference pixel data between the phase difference pixels ZA and ZB is estimated so that such a phase difference pixel data sequence becomes dense. Specifically, as described above, since the light receiving area of ​​the phase difference pixel ZA is the left half of the pixel, and the right half of the same pixel is in a light shielding state, as shown in FIG. Figure 6As shown, the estimated pixel ZB' (second estimated phase difference pixel) of the phase difference pixel ZB is estimated under the assumption that the estimated pixel ZB' is arranged in the right half area of ​​the same pixel where the phase difference pixel ZA is arranged. Similarly, as described above, since the light receiving area of ​​the phase difference pixel ZB is the right half of the pixel, and the left half of the same pixel is in a light shielding state, as shown in FIG. Figure 6 As shown, therefore, under the assumption that the estimated pixel ZA′ is arranged in the left half region of the same pixel where the phase difference pixel ZB is arranged, the estimated pixel ZA′ (first estimated phase difference pixel) of the phase difference pixel ZA is estimated.

[0051] Through this estimation process, the estimated pixel sequence of the phase difference pixel ZA is {ZA 3,1 ,ZA' 3,3 ,ZA 3,5 ,ZA' 3,7 ,...}, and the estimated pixel sequence of the phase difference pixel ZB is {ZB' 3,1 ,ZB 3,3 ,ZB' 3,5 ,ZB 3,7 ,...}, each of which is a dense sequence of two pixels.

[0052] The estimated pixel ZA′ of the phase difference pixel ZA can be calculated using the following equation (1).

[0053] [Equation (1)]

[0054]

[0055] The estimated pixel ZB′ of the phase difference pixel ZB can be calculated using the following equation (2).

[0056] [Equation (2)]

[0057]

[0058] By not using the phase difference pixel column direction ( Figure 4 In the case of adjacent pixel data shifted in the horizontal direction (in the horizontal direction), estimation is performed using adjacent pixel data on the same column as the estimated pixel, and estimation can be performed with relatively high accuracy even for high-frequency object patterns in the phase difference pixel column direction (i.e., "objects with a large amount of high-frequency components").

[0059] Furthermore, by performing correction using the correction factor F adjusted and ensured in advance, adverse effects of manufacturing variations, light flux vignetting, and lens aberrations can be absorbed, thereby performing estimation with high accuracy.

[0060] Will refer to 7A to 7C Describe the necessity of the correction factor F in the estimation process. 7A to 7C 1 and 2 are diagrams each showing an example of phase difference pixel data and image pixel data of a certain row when the image sensor 102 is exposed to uniform light through the imaging lens. Here, "a certain row" is a row including phase difference pixels ZA and ZB, for example, as shown in FIG. Figure 3 Line 202 is shown. Figure 7A 、 Figure 7B and Figure 7C The horizontal axis of each of indicates the column number of each pixel in a certain row of the image sensor. The horizontal axis is equivalent to the x-axis of the image sensor 102, and the center of the horizontal axis corresponds to the center of the image sensor.

[0061] Figure 7A Graphs A and B showing the characteristics of phase difference pixel data (ZA and ZB) and graph C showing the characteristics of image pixel data (average value of upper Gr and lower Gr) are shown. Figure 7A The vertical axis represents the data value of each pixel. Figure 7A In FIG. 1 , graph A is indicated by a solid line, graph B is indicated by a dotted line, and graph C is indicated by a thick solid line. Here, the “average value of upper Gr and lower Gr” is, for example, Figure 3 The average value of data of two pixels Gr shown is arranged in upper and lower rows of the row including the phase difference pixels ZA and ZB, and is arranged in the same column as the corresponding phase difference pixels of the phase difference pixels ZA and ZB.

[0062] like Figure 7A As shown, characteristic C of the image pixel data (the average value of upper Gr and lower Gr) tends to be maximum at the center of the image sensor 102 and decreases toward the ends of the image sensor 102. Characteristic A of the phase difference pixel data (ZA) tends to be high on the left side of the image sensor 102 and low on the right side. Characteristic B of the phase difference pixel data (ZB) tends to be high on the right side of the image sensor 102 and low on the left side. These characteristics are caused by the influence of general shading processing (edge ​​darkening).

[0063] Figure 7B Graph A+B shows the total value of the characteristics of the phase difference pixel data (ZA) and the characteristics of the phase difference pixel data (ZB). Figure 7A As shown, Figure 7B The vertical axis also indicates the data value of each pixel. Figure 7B Also shown with Figure 7A Graph C shows the characteristics of the same image pixel data (average value of upper Gr and lower Gr).

[0064] like Figure 7BAs shown in FIG. 1 , the characteristic A+B of the phase difference pixel data (ZA+ZB) has a tendency that the value is maximum at the center of the image sensor 102 and decreases toward the ends of the image sensor 102. The tendency of the characteristic A+B is similar to the tendency of the characteristic C of the image pixel data, but the data value itself does not match the data value of the characteristic C. As described above, Figure 3 As shown, the light receiving area of ​​each phase difference pixel ZA and ZB is substantially half of the light receiving area of ​​each image pixel 203. Therefore, the sum of the characteristic A of the phase difference pixel data (ZA) and the characteristic B of the phase difference pixel data (ZB) is expected to be approximately equal to the image pixel data C. Therefore, when the characteristic A of the phase difference pixel data (ZA) and the characteristic B of the phase difference pixel data (ZB) are added, the expected data is substantially equivalent to the image pixel data C. However, in practice, it is not always possible to obtain an ideal value because the light receiving area cannot be exactly half, there are manufacturing variations, vignetting of light flux, lens aberrations, etc. This leads to obtaining the following Figure 7B The differences in the data values ​​are shown.

[0065] Figure 7C Graph D shows the ratio (ratio F) of characteristic C (average value of upper Gr and lower Gr) of image pixel data to characteristic A+B (ZA+ZB) of total phase difference pixel data. Figure 7C The vertical axis represents the ratio F of each pixel.

[0066] like Figure 7C As shown, the ratio F tends to have substantially the same value along the x-direction of the image sensor 102. In this example, the ratio F is approximately 0.67, which is quite large. That is, unless the ratio F is considered as the correction factor F, a large estimation error will occur. Therefore, in this embodiment, as in the above equations (1) and (2), the estimation accuracy is improved by multiplying the correction factor F when calculating the estimated pixels ZA' and ZB' of the phase difference pixels ZA and ZB.

[0067] Strictly speaking, the ratio F (=correction factor F) varies slightly depending on the pixel position. Figure 7C In the example shown in FIG, the ratio F is slightly higher at the center of the image sensor 102 and slightly lower at the periphery of the image sensor 102. The ratio F varies even when the rows in which the phase difference pixels ZA and ZB are arranged are changed, and the ratio F also varies even when the focus position is changed. Therefore, it is necessary to determine the ratio F (=correction factor F) for each condition and position.

[0068] Figure 8 : is a diagram showing an example of a focus position detection result using a pixel data sequence of phase difference pixels ZA and ZB after estimation by the phase difference pixel estimation method according to the present embodiment. Figure 8 The outline and Figure 5The profiles of the comparative examples shown are the same.

[0069] like Figure 8 As shown, when estimating phase difference pixel data, Figure 5 The large distance measurement error generated in the comparative example is reduced. This is because the edge pattern of the object 601 can be expressed relatively accurately by accurately estimating the gaps in each phase difference pixel data sequence. Therefore, by performing autofocus using the pixel data sequence of phase difference pixels ZA and ZB after estimation using the phase difference pixel estimation method according to this embodiment, even for an object pattern with high frequencies in the phase difference pixel column direction, that is, an "object with a large high-frequency component," it is possible to estimate with relatively high accuracy.

[0070] Figure 9 is a flowchart illustrating an example of a pre-adjustment process. Figure 9 Each step in the flowchart is performed in, for example, an adjustment process immediately after the digital camera 1 is assembled at the factory.

[0071] In step S700, the digital camera 1 is fixed in front of a uniform light object, and the entire image sensor 102 is set to receive uniform light. In this case, the brightness of the object, exposure time and exposure sensitivity are set so that the pixel data is not saturated.

[0072] In step S701 , the microprocessor 110 moves the focus lens group 7 and the zoom lens group 6 to any desired initial positions via the lens driving mechanism 104 .

[0073] In step S702, the image sensor control circuit 111 acquires the data of all phase difference pixels ZA and ZB and the image pixel data near the phase difference pixels ZA and ZB. Figure 3 and Figure 6 Here, with respect to the row of phase difference pixels ZA and ZB, “image pixel data near phase difference pixels ZA and ZB” is two pixels Gr, one of which is arranged in a row with a row number smaller than 1 (in the row with a row number smaller than 1). Figure 3 In the example of ), another pixel Gr is arranged in a row with a row number greater by 1 (in Figure 3 In the example of FIG, the phase difference pixels ZA and ZB are arranged in the same column number as the corresponding phase difference pixels ZA and ZB. The data obtained in this step is output to the image plane phase difference pixel processor 115.

[0074] In step S703, the image plane phase difference pixel processor 115 calculates the ratio F (=correction factor F) of each of the phase difference pixels ZA and ZB acquired in step S702. The ratio F on the phase difference pixel ZA can be calculated using the following equation (3). Figure 3 As shown, due to Figure 3 Since there is no data of the phase difference pixel ZB on the phase difference pixel ZA shown, the average value of the data of two phase difference pixels ZB located on both sides of the phase difference pixel ZA in the same row is used.

[0075] [Equation (3)]

[0076]

[0077] The ratio F on the phase difference pixel ZB can also be calculated using the following equation (4).

[0078] [Equation (4)]

[0079]

[0080] In step S704, the image plane phase difference pixel processor 115 stores the ratio F obtained for each of the phase difference pixels ZA and ZB calculated in step S703 in the adjustment value memory in the digital camera 1. At this time, since a large amount of memory is required if coefficients are stored for each of the phase difference pixels ZA and ZB, an approximate curve can be obtained when the horizontal axis represents the positions of the phase difference pixels ZA and ZB and the vertical axis represents the ratio F, and only the coefficients of the approximate curve can be stored to save memory.

[0081] In step S705, if it is necessary to calculate the ratio F at another lens position and store it in the adjustment value memory (Yes in S705), the process proceeds to step S706, where the microprocessor 110 moves the focus lens group 7 and the zoom lens group 6 to the next lens position via the lens drive mechanism 104, and then repeats the process in step S702 and subsequent steps. In this case, if this process is repeated for all lens positions, it would require a very long time and a large capacity of the adjustment value memory. Therefore, it is possible to focus only on representative lens positions, and to obtain the ratio F of the lens positions between the representative lens positions through interpolation calculation.

[0082] When the calculation process of the ratio F is completed at all predetermined lens positions in step S705 (No in S705 ), the control flow ends.

[0083] Figure 10 is a flowchart illustrating an example of an imaging plane phase difference detection process. Figure 10 Each step in the flowchart is performed when photographing a subject with the digital camera 1. Figure 10 The process of the flowchart corresponds to the focus position detection method according to the embodiment.

[0084] In step S800 , the photographing lens group 2 of the digital camera 1 is directed toward the object to be measured, and a pattern of the target object is exposed to the phase difference pixels ZA and ZB of the image sensor 102 .

[0085] In step S801, the image plane phase difference pixel processor 115 acquires the data of the phase difference pixels ZA and ZB in step S800 and the image pixel data near the phase difference pixels ZA and ZB from the image sensor 102. At this time, since pixel data outside the AF area 602 where distance measurement is not performed is unnecessary, it is more efficient to limit the pixel data to only the pixel data within the AF area 602.

[0086] In step S802, the image plane phase difference pixel processor 115 (estimator) estimates estimated pixels ZA' and ZB' between the phase difference pixels ZA and ZB. Figure 6 As described above, the estimated pixels ZA' and ZB' are calculated using equations (1) and (2) above.

[0087] In step S803, the image plane phase difference pixel processor 115 (focus detector) uses the pixel data sequence (ZA, ZA', ZA, ZA', ...) of the phase difference pixel ZA whose data amount has been doubled after the estimation process in step S802 and the pixel data sequence (ZB, ZB', ZB, ZB', ...) of the phase difference pixel ZB whose data amount has also been doubled to perform phase difference detection and calculate the defocus (defocus amount). The phase difference detection method is a very common method, so its description will be omitted. However, in short, the offset between the two data sequences is obtained by scanning the correlation value and sub-pixel estimation. Then, the defocus is obtained by multiplying the offset between the two data sequences by a coefficient determined by the lens optical system. When the process of step S803 is completed, the control flow is terminated.

[0088] As reference Figure 6 and Figure 10As described in step S802 in , the image plane phase difference pixel processor 115 serving as the focus position detection device according to the present embodiment performs an estimation process of estimating a plurality of estimated pixels ZA' arranged between a plurality of phase difference pixels ZA based on data of two image pixels Gr, the two image pixels Gr on which the plurality of estimated pixels ZA' are based are respectively included in rows adjacent to the rows in which the plurality of phase difference pixels ZA and the plurality of phase difference pixels ZB are arranged, and are arranged in the same column as the corresponding phase difference pixels ZB among the plurality of phase difference pixels ZB; and estimating a plurality of estimated pixels ZB' arranged between a plurality of phase difference pixels ZB based on data of the two image pixels Gr, the two image pixels Gr on which the plurality of estimated pixels ZB' are based are respectively included in rows adjacent to the rows in which the plurality of phase difference pixels ZA and the plurality of phase difference pixels ZB are arranged, and are arranged in the same column as the corresponding phase difference pixels ZA among the plurality of phase difference pixels ZA in the pixel array of the image sensor 102. By pre-adjustment, the average value ( Figure 7B The sum of the characteristics of the pixel data of the phase difference pixels ZA and ZB ( Figure 7B The ratio of the curves in Figure 1(A+B) is calculated and used as the correction factor F in the estimation process.

[0089] With this configuration, for example, even in the case of an object having a large amount of high-frequency components, such as Figure 4 Even for the object 601 shown, accurate estimation of estimated pixels ZA' and ZB' can be performed. Furthermore, by using the correction factor F during the estimation process, relatively accurate phase difference estimation is possible even when the light receiving area of ​​the phase difference pixel is not exactly half, when there are manufacturing variations, when there is luminous flux vignetting, or when there are lens aberrations. Consequently, focus detection accuracy can be improved for objects with a large amount of high-frequency components.

[0090] According to at least one embodiment of the present disclosure, it is possible to improve focus detection accuracy for an object having a large amount of high-frequency components.

[0091] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Those skilled in the art can appropriately modify these specific examples, and such modifications are also included in the scope of the present disclosure, as long as they have the characteristics of the present disclosure. The elements and their arrangements, conditions, shapes, etc. included in the above specific examples are not limited to those described above and can be appropriately changed. As long as there is no technical contradiction, the elements of the above specific examples can be appropriately combined.

[0092] Explanation of symbols

[0093] 1: Digital camera (image pickup device)

[0094] 115: Image plane phase difference pixel processor (focus position detection device, estimator, focus detector)

[0095] ZA: Phase difference pixel (first phase difference pixel)

[0096] ZB: Phase difference pixel (second phase difference pixel)

[0097] ZA': estimated pixel (first estimated phase difference pixel)

[0098] ZB': estimated pixel (second estimated phase difference pixel)

[0099] F: Correction rate image plane phase difference pixel processor

Claims

1. A focus position detection device for detecting a focus position based on signal values ​​from pixels of an image sensor, the image sensor comprising image pixels and a pair of first and second phase difference pixels, the image pixels receiving a subject image via a photographing lens group and photoelectrically converting the subject image, the pair of first and second phase difference pixels respectively receiving light fluxes passing through a pair of pupil regions of the photographing lens group and photoelectrically converting the light fluxes, the focus position detection device comprising: An estimator configured to perform an estimation process of estimating: estimating a plurality of first estimated phase difference pixels arranged between a plurality of first phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of first estimated phase difference pixels are estimated being respectively included in rows adjacent to a row in which a plurality of pairs of the first phase difference pixels and the second phase difference pixels are arranged, and being arranged in the same column as corresponding second phase difference pixels among a plurality of second phase difference pixels in a pixel array of the image sensor, and estimating a plurality of second estimated phase difference pixels arranged between the plurality of second phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of second estimated phase difference pixels are estimated being respectively included in rows adjacent to the rows in which the plurality of pairs of first phase difference pixels and second phase difference pixels are arranged, and being arranged in the same column as corresponding first phase difference pixels among the plurality of first phase difference pixels in the pixel array of the image sensor; as well as a focus detector configured to detect a phase difference using a data sequence of the first phase difference pixels to which the plurality of first estimated phase difference pixels estimated by the estimator are added and a data sequence of the second phase difference pixels to which the plurality of second estimated phase difference pixels are added, and calculate an amount of defocus from a position in which the image is in focus; The estimator determines, through pre-adjustment, a ratio of an average value of characteristics of pixel data along two rows including the two image pixels to a sum of characteristics of pixel data of the plurality of first phase difference pixels and characteristics of pixel data of the plurality of second phase difference pixels, and uses the ratio as a correction factor in the estimation process.

2. An image pickup device comprising: The focus position detection device according to claim 1.

3. A focus position detection method for detecting a focus position based on a signal value from a pixel of an image sensor, the image sensor comprising an image pixel and a pair of first and second phase difference pixels, the image pixel receiving a subject image via a photographing lens group and photoelectrically converting the subject image, the pair of first and second phase difference pixels respectively receiving a light flux passing through a pair of pupil regions of the photographing lens group and photoelectrically converting the light flux, the focus position detection method comprising: The estimation step performs the estimation process of the following estimates: estimating a plurality of first estimated phase difference pixels arranged between a plurality of first phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of first estimated phase difference pixels are estimated being respectively included in rows adjacent to a row in which a plurality of pairs of the first phase difference pixels and the second phase difference pixels are arranged, and being arranged in the same column as corresponding second phase difference pixels among the plurality of second phase difference pixels, and estimating a plurality of second estimated phase difference pixels arranged between the plurality of second phase difference pixels based on data of two image pixels, the two image pixels based on which the plurality of second estimated phase difference pixels are estimated being respectively included in rows adjacent to the rows in which the plurality of pairs of first phase difference pixels and second phase difference pixels are arranged, and being arranged in the same column as corresponding first phase difference pixels among the plurality of first phase difference pixels; as well as a focus detection step of detecting a phase difference using a data sequence of the first phase difference pixels to which the plurality of first estimated phase difference pixels are added and a data sequence of the second phase difference pixels to which the plurality of second estimated phase difference pixels are added, and calculating a defocus amount to a position in which the image is in focus; The estimating step includes determining, by pre-adjustment, a ratio of an average value of characteristics of pixel data along two rows including the two image pixels to a sum of characteristics of pixel data of the plurality of first phase difference pixels and characteristics of pixel data of the plurality of second phase difference pixels, and using the ratio as a correction factor in the estimating process.

Images