JP6602159B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method thereof.

  In an imaging apparatus, a phenomenon (vignetting) in which incident light on an imaging surface of an imaging element is reduced by a lens member and a diaphragm may occur, and a difference occurs in the amount of reduction in incident light depending on the image height position. . As a result, a difference in incident light amount occurs concentrically with respect to the center of the optical axis on the image signal. The process of correcting the luminance unevenness due to the difference in the amount of incident light and correcting the entire image so that the average brightness is uniform is called shading correction. Patent Document 1 discloses an imaging apparatus that corrects a decrease in peripheral light amount based on a zoom position of a lens, an imaging distance, and an aperture value.

JP 2006-270919 A

  In the imaging device disclosed in Patent Document 1, the shape formed by the diaphragm blades is not considered. When the aperture shape of the aperture is circular, the lens member is also circular, so that the size of the exit pupil or the amount of incident light beam at the same image height can be regarded as the same. However, when the aperture shape of the stop is not circular, the shape of the exit pupil may be different even at the same image height, so that the amount of decrease in the amount of incident light changes even at the same image height.

  An object of the present invention is to provide an imaging apparatus that performs appropriate shading correction according to the shape of the stop.

  An image pickup apparatus according to an embodiment of the present invention includes an image pickup element that receives subject light from an image pickup optical system having a stop member and photoelectrically converts it into an image signal, an image height of a target pixel of the image signal, and the stop member Calculation means for calculating a correction coefficient according to the shape of the diaphragm member used for correcting shading generated in the image signal based on the optical information of the imaging optical system including the shape information of Correction means for correcting the shading based on the correction coefficient.

  According to the imaging apparatus of the present invention, it is possible to execute appropriate shading correction according to the shape of the diaphragm.

1 is a diagram illustrating a configuration of an imaging apparatus according to a first embodiment. It is a flowchart explaining the example of a shading correction process. It is a figure explaining the image signal obtained from the image sensor. It is a figure explaining the direction when the exit pupil is seen from the pixel on the same image height. It is a figure which shows the shape of the exit pupil when it sees from the position of two attention pixels. It is a figure which shows the shading correction coefficient in the same image height. It is a figure which shows the elliptic function with which the shading correction coefficient was approximated. It is a figure explaining the rotation according to F value of the opening shape of an aperture member. 6 is a diagram illustrating a configuration of Example 2. FIG. It is a flowchart explaining the example of a shading correction process. It is a figure which shows the periodic function expressing a shading correction coefficient. It is a figure which shows the shading correction coefficient for 1 period corresponding to (phi).

Example 1
FIG. 1 is a diagram illustrating a configuration of the imaging apparatus according to the first embodiment.
The imaging apparatus according to the first exemplary embodiment includes an imaging optical system 101, an imaging element 102, a control unit 103, a coordinate conversion unit 104, a coefficient calculation unit 105, a database 106, and a shading correction unit 107.

  The imaging optical system 101 forms an image of subject light. The imaging optical system 101 includes a focus lens for focusing on a subject and its control mechanism, a zoom lens for changing the focal length, its control mechanism, and a diaphragm member for adjusting the amount of incident light. The diaphragm member has a plurality of blade members. The imaging element 102 receives subject light from the imaging optical system 101, photoelectrically converts it into an electrical signal, and outputs it as an image signal. The control unit 103 controls the entire imaging apparatus. The coordinate conversion unit 104 converts the coordinates of the image signal obtained from the image sensor 102, and calculates the image height r and the deflection angle θ of the pixel of interest with the optical axis center of the imaging optical system 101 as the origin. The declination angle θ is an angle between a straight line connecting the target pixel and the optical center of the imaging optical system and a predetermined straight line passing through the target pixel. The coefficient calculation unit 105 calculates a shading correction coefficient c. The shading correction coefficient is a correction coefficient used for correcting shading appearing on the image signal. Specifically, the coefficient calculation unit 105 determines the shape of the diaphragm member based on at least the image height r and the deflection angle θ of the target pixel of the image signal and the optical information of the imaging optical system 101 including the shape information of the diaphragm member. A shading correction coefficient c according to the above is calculated.

  The database 106 stores parameters used for calculating the shading correction coefficient c. The database 106 is provided, for example, in a ROM (Read Only Memory). The shading correction unit 107 corrects shading that appears on the image signal output from the image sensor 102 based on the shading correction coefficient c calculated by the coefficient calculation unit 105.

FIG. 2 is a flowchart illustrating an example of shading correction processing by the imaging apparatus according to the first embodiment.
In step S <b> 201, the coordinate conversion unit 104 calculates the image height r and the deflection angle θ with the optical axis center as the origin from the coordinate position of the target pixel of the image signal output from the image sensor 102.

FIG. 3 is a diagram illustrating an image signal obtained from the image sensor.
Reference numeral 301 denotes an imaging plane on the image sensor 102. In FIG. 3, the horizontal axis is defined as the X axis and the vertical axis is defined as the Y axis. Further, it is assumed that the intersection of the X axis and the Y axis is the coordinate origin and coincides with the optical axis center of the imaging optical system 101. Reference numeral 302 denotes the position of the pixel of interest.

偏角θは、以下の式２で表現される。

したがって、結像面上の同一像高ｒの経路は、結像面３０１に示すように、光軸中心を原点に円を描く。 Assuming that the coordinates of the pixel of interest are (x, y), the image height r is expressed by Equation 1 below.

The declination θ is expressed by Equation 2 below.

Therefore, the path of the same image height r on the imaging plane draws a circle with the optical axis center as the origin, as shown in the imaging plane 301.

  Returning to the description of FIG. In step S <b> 202, the coefficient calculation unit 105 acquires optical information of the imaging optical system 101 from the control unit 103. The optical information includes the aperture value (F value) of the imaging optical system 101, the shape information N of the aperture member included in the imaging optical system 101, and the focal length information f of the imaging optical system 101.

  Next, in S203, the coefficient calculation unit 105 acquires parameters used for calculation of the shading correction coefficient c from the database 106 serving as a storage unit based on the image height r, the deflection angle θ, and the optical information of the pixel of interest. . In this example, the coefficient calculation unit 105 refers to the major axis and minor axis of an ellipse that are parameters of an elliptic function indicating one period of the periodic function expressing the shading correction coefficient c.

FIG. 4 is a diagram illustrating the direction when viewing the exit pupil from pixels on the same image height.
In FIG. 4, the direction in which the exit pupil is viewed from the positions of the two target pixels 401 and 402 on the same image height r on the imaging plane 301 is indicated by arrows.

FIG. 5 is a diagram showing the shape of the exit pupil when viewed from the positions of two pixels of interest.
In this example, the shape of the exit pupil when viewed from the positions of the target pixels 401 and 402 in FIG. 4 is shown. Reference numeral 501 denotes the shape of the rear frame of a lens that is one of the optical members included in the imaging optical system 101. Reference numerals 503 and 504 respectively indicate the shapes of the exit pupils when viewed from the target pixels 401 and 402 in FIG. When the diaphragm member included in the imaging optical system 101 is narrowed to some extent, the shape of the exit pupil is the shape of the diaphragm.

  At the pixel position that is not on the center of the optical axis, the center of the lens rear frame 501 does not coincide with the center of the exit pupils 503 and 504. When the center of the rear lens frame 501 is fixed and the positional relationship of the exit pupil viewed from the pixels on the path 303 having the same image height r is illustrated, the center of the exit pupil draws the path 502. When the diaphragm is configured by a finite number of blade members (in the case of FIG. 5, five blade members), the amount of the exit pupil hidden by the rear lens frame 501 (the amount of vignetting) is the same image height r. It will change.

  At the exit pupil 503, the amount of vignetting is maximized, and at the exit pupil 506, the amount of vignetting is minimized. When integration using a polygon and a circle is performed on the path 502, the amount of vignetting periodically changes depending on the center position of the exit pupil.

FIG. 6 is a diagram showing shading correction coefficients at the same image height.
FIG. 6 shows the shading coefficient c when the declination angle θ is changed from 0 to 2π at the same image height r. In FIG. 6, a periodic change in the amount of vignetting is depicted as a change in the shading correction coefficient c that corrects this change.

  When approximating the shape of the finite number of stops as an N-gon, the shading correction coefficient c becomes a periodic function having an N-period periodicity while the declination θ changes from 0 to 2π. In the first embodiment, the database 106 holds parameters used for calculating the shading correction coefficient c for one period indicated by 604 in FIG. 6 in association with the image height r. In the first embodiment, one period of the periodic function expressing the shading correction coefficient c is approximated by a simple function called an elliptic function.

ａは、楕円の長径である。ｂは、楕円の短径である。φは、楕円関数の偏角である。 FIG. 7 is a diagram illustrating an elliptic function in which a shading correction coefficient for one cycle is approximated.
An elliptic function 701 indicates one period of the shading correction coefficient c at the same image height r. The elliptic function 701 is expressed by Equation 3 below.

a is the major axis of the ellipse. b is the minor axis of the ellipse. φ is the argument of the elliptic function.

φ’は、楕円関数の初期位相である。φ’は、レンズ後枠と絞りとの位置関係で決まる。 Since the deflection angle θ on the image plane 301 is divided into N periods and one period is expressed by an elliptic function, the relationship between φ and θ is expressed by the following Expression 4.

φ ′ is the initial phase of the elliptic function. φ ′ is determined by the positional relationship between the lens rear frame and the stop.

  Further, since the amount of vignetting of the exit pupil due to the rear lens frame 501 varies depending on the image height r, as shown by 601, 602, and 603 in FIG. It has a periodic characteristic according to r. Therefore, in the elliptic function shown in FIG. 7, the major axis a and the minor axis b, which are parameters of the elliptic function, change as indicated by 701, 702, and 703. Therefore, the database 106 may store parameters a and b corresponding to the image height.

  Further, when the size of the aperture changes, the shading correction coefficient c changes. Therefore, the database 106 may further store parameters a and b in association with the F value. In addition, there may be a plurality of focal length information f of the imaging optical system 101, and the position of the exit pupil may change according to the focal length information f. Therefore, the database 106 may further store parameters a and b according to the focal length information f. In addition, if the characteristics can be regarded as substantially the same, the table may be shared.

  That is, in S203 of FIG. 2, the coefficient calculation unit 105 acquires a parameter corresponding to the image height r of the target pixel of the image signal among the parameters stored in the database 106. The coefficient calculation unit 105 may acquire parameters corresponding to the image height r and the F value. In addition, the coefficient calculation unit 105 may acquire parameters corresponding to the image height r and the focal length information f. In addition, the coefficient calculation unit 105 may acquire parameters corresponding to the image height r, the F value, and the focal length information f.

In S204 of FIG. 2, the coefficient calculation unit 105 calculates a shading correction coefficient c. When the deflection angle of the pixel of interest is θ, the coefficient calculation unit 105 calculates φ from the shape N of the diaphragm and the initial phase φ ′ using Equation 4. 704 in FIG. 7 is a point indicating a shading correction coefficient at a certain φ. The coefficient calculation unit 105 calculates an elliptic function p using Equation 3 based on the parameters a and b and φ acquired in S203. Then, the coefficient calculation unit 105 calculates a shading correction coefficient c using the following equation 5 based on the calculated p.

  In step S <b> 205, the shading correction unit 107 performs shading correction on the image signal obtained from the image sensor 102 using the shading correction coefficient c calculated by the coefficient calculation unit 105. In step S206, the control unit 103 advances the coordinates (x, y) to process the next pixel. In step S207, the control unit 103 determines whether all pixels have been processed. If there is a pixel that has not been processed, the process returns to S201. If all pixels have been processed, the process ends.

FIG. 8 is a diagram for explaining the rotation of the aperture shape of the diaphragm member included in the imaging optical system according to the F value.
Reference numeral 801 denotes an opening shape formed by a diaphragm member at a certain F value. Assume that the aperture shape of the aperture member rotates around the aperture center according to the F value, that is, the state of the aperture member. When the F value changes, the aperture shape rotates about the aperture center 802 as an axis. The rotation of the aperture shape corresponds to a shift in the relative positional relationship between the deflection angle θ defined on the imaging plane 301 in FIG. 3 and the aperture shape. Therefore, the coefficient calculation unit 105 shifts the characteristic of the shading correction coefficient 601 shown in FIG. 6 in the θ direction with the rotation of the aperture shape of the diaphragm member according to the F value. That is, the coefficient calculation unit 105 adjusts φ ′ corresponding to the rotation angle of the aperture shape of the aperture for one period of the periodic function expressing the shading correction coefficient.

  The imaging apparatus according to the first embodiment described above calculates a shading correction coefficient by approximating a decrease in the amount of incident light due to the aperture shape of the aperture member with a periodic function for pixels located at the same image height. . Therefore, shading correction can be performed with a small amount of data with high accuracy.

(Example 2)
FIG. 9 is a diagram illustrating the configuration of the second embodiment.
The camera system shown in FIG. 9 includes a lens unit 901 and a camera unit 902. The camera unit 902 functions as the imaging device of the second embodiment, and the lens unit 901 can be attached and detached. Of the processing units shown in FIG. 9, descriptions of processing units denoted by the same reference numerals as those in FIG. 1 are omitted.

  The lens unit 901 is a lens device that includes the imaging optical system 101, a lens control unit 903, a database 904, and a lens IF (Interface) 905. The lens control unit 903 controls the entire lens unit 901. The lens control unit 903 executes control of the imaging optical system 101 and control with the camera unit 902 via the lens IF 905. The database 904 stores shading correction coefficients in association with the optical information of the imaging optical system 101. The database 904 is, for example, a ROM. The lens control unit 903 transmits a shading correction coefficient corresponding to predetermined optical information among the shading correction coefficients in the database 904 to the camera unit 902.

  The camera unit 902 includes an image sensor 102, a coordinate conversion unit 104, a coefficient calculation unit 105, a shading correction unit 107, a camera control unit 906, a camera IF 907, and a storage unit 908.

  The camera control unit 906 controls the entire camera unit 902. The camera control unit 906 performs control with the lens unit 901 via the camera IF 907. The storage unit 908 stores the shading correction coefficient transmitted from the lens unit 901 in association with the image height r and the angle φ. As shown in Equation 4, the angle φ is determined according to the shape of the diaphragm member.

FIG. 10 is a flowchart illustrating an example of shading correction processing by the imaging apparatus according to the second embodiment.
In step S1001, the camera control unit 906 requests the lens unit 901 to transmit data in the database 904, that is, a shading correction coefficient. In step S <b> 1002, the lens control unit 903 acquires a shading correction coefficient corresponding to the F value and the focal length information f included in the optical information of the imaging optical system 101 from the database 904 via the lens IF 905. The lens control unit 903 transmits the acquired shading correction coefficient to the camera IF 907. The lens control unit 903 also transmits the aperture member shape information N and the initial phase φ ′ determined by the positional relationship between the lens rear frame and the aperture to the camera IF 907.

FIG. 11 is a diagram illustrating a periodic function expressing a shading correction coefficient corresponding to the image height r.
Reference numeral 1101 denotes a shading correction coefficient when the horizontal axis is the deflection angle θ of the pixel of interest and the vertical axis is the shading correction coefficient c. This shading correction coefficient has periodicity in the period of the shape information N of the diaphragm member included in the imaging optical system 101 as in the first embodiment. Therefore, in the present embodiment, the shading correction coefficient c at the same image height r is not stored in the database 904 for all the deviation angles θ from 0 to 2π, but for one cycle indicated by 1102 in FIG. Remember. Further, the storage unit 908 stores the shading correction coefficient c for one period in association with φ.

FIG. 12 is a diagram showing shading correction coefficients for one period corresponding to φ.
1201 is a shading correction coefficient at the same image height r. The storage unit 908 may store a shading correction coefficient table shown in FIG. 12 for each image height r. The shading correction coefficient varies depending on the F value and the focal length, but both are uniquely determined when the state of the imaging optical system 101 is determined. Therefore, in S1002 of FIG. 10, the lens unit 901 transmits a shading correction coefficient corresponding to the optical information among the shading correction coefficients stored in the database 904. The camera unit 902 stores the received shading correction coefficient in association with φ.

  S1003 in FIG. 10 is the same as S201 in FIG. Subsequently, in S1004, the coefficient calculation unit 105 refers to the storage unit 908. The coefficient calculation unit 105 calculates φ using Equation 4 based on the deflection angle θ of the pixel of interest, the shape information N of the aperture member, and the initial phase φ ′ determined by the positional relationship between the lens rear frame and the aperture. Then, the coefficient calculation unit 105 acquires a shading correction coefficient c corresponding to the image height r and φ among the shading correction coefficients recorded in the storage unit 908 as a shading correction coefficient used for shading correction.

  As shown in FIG. 12, when the shading correction coefficient is stored discretely, the shading coefficient c corresponding to the calculated φ may not exist. In that case, a shading correction coefficient used for shading correction may be calculated by linear interpolation which is a conventionally known interpolation process. Steps S1005 to S1007 in FIG. 10 are the same as steps S204 to S207 in FIG.

  Unlike the first embodiment, the imaging apparatus according to the second embodiment stores the shading correction coefficient itself in association with φ instead of the elliptic function parameter, and corresponds to φ calculated according to the aperture shape of the diaphragm member. The shading correction is executed using the shading correction coefficient. Therefore, even when it is difficult to approximate the decrease in the amount of incident light due to the aperture shape of the aperture member with a simple periodic function, it is possible to realize shading correction with high accuracy with a small number of data.

  When approximation by a simple periodic function is established as in the first embodiment, the amount of data to be stored is small, but the periodic function must be expressed by superimposing a plurality of sine waves or cosine waves. In this case, the number of parameters becomes enormous. In such a case, as in the second embodiment, shading correction can be realized by creating a database of the shading correction coefficient c and preparing it in a discrete manner.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

103 Control Unit 104 Coordinate Conversion Unit 105 Coefficient Calculation Unit

Claims (15)

An image sensor that receives subject light from an imaging optical system having an aperture member and photoelectrically converts it into an image signal; and
The diaphragm used for correcting shading generated in the image signal based on at least the image height and the deflection angle of the target pixel of the image signal and the optical information of the imaging optical system including the shape information of the diaphragm member Calculating means for calculating a correction coefficient according to the shape of the member;
An imaging apparatus comprising: correction means for correcting the shading based on the calculated correction coefficient. The calculation means calculates the correction coefficient based on an image height and a declination of a target pixel of the image signal, shape information of the diaphragm member, and an initial phase of a function expressing the correction coefficient. The imaging apparatus according to claim 1, wherein the imaging apparatus is characterized. The correction coefficient is represented by a periodic function having a period according to the shape information of the diaphragm member,
Storage means for storing a parameter of a function indicating one period of the correction coefficient;
The imaging apparatus according to claim 1, wherein the calculation unit calculates the correction coefficient using a parameter stored in the storage unit. The function indicating one period of the correction coefficient is an elliptic function,
The imaging apparatus according to claim 3, wherein the parameters are a major axis and a minor axis of an ellipse indicated by the elliptic function. The storage means stores at least the major axis and minor axis of the ellipse in association with the image height of the image signal,
The calculating means includes
Of the major axis and minor axis of the ellipse stored in the storage means, obtain the major axis and minor axis corresponding to the image height of the pixel of interest of the image signal,
Based on the deflection angle of the target pixel of the image signal, the shape information of the diaphragm member, and the initial phase of the periodic function expressing the correction coefficient, the deflection angle of the elliptic function is calculated,
Based on the acquired major axis and minor axis and the calculated declination, an elliptic function is calculated,
The imaging apparatus according to claim 4, wherein the correction coefficient is calculated based on the calculated elliptic function. The optical information further includes an aperture value of the imaging optical system,
The major axis and minor axis of the ellipse stored in the storage means are further associated with the aperture value,
The imaging apparatus according to claim 5, wherein the calculation unit acquires a major axis and a minor axis corresponding to the aperture value among the major axis and the minor axis of the ellipse stored in the storage unit. The optical information further includes focal length information of the imaging optical system,
The major axis and minor axis of the ellipse stored in the storage means are further associated with the focal length information,
The said calculating means acquires the major axis and minor axis corresponding to the said focal distance information among the major axis and minor axis of the said ellipse memorize | stored in the said memory | storage means. The Claim 5 or Claim 6 characterized by the above-mentioned. The imaging device described. The calculating means adjusts a phase of a periodic function expressing the correction coefficient when an aperture shape formed by the aperture member rotates around the aperture center of the aperture member according to a state of the aperture member; The imaging apparatus according to claim 3, wherein An imaging device in which a lens device can be attached and detached,
The lens device is
An imaging optical system having a diaphragm member;
Transmission means for transmitting a correction coefficient corresponding to the optical information of the imaging optical system to the imaging device,
The imaging device
An image sensor that receives subject light from the imaging optical system and photoelectrically converts it into an image signal;
Storage means for storing the correction coefficient transmitted from the lens device in association with the image height of the image signal and an angle determined according to the shape of the diaphragm member;
An angle is calculated based on the deflection angle of the target pixel of the image signal, the shape information of the diaphragm member, and the initial phase of the periodic function expressing the correction coefficient, and the target of the image signal is calculated from the storage unit. Calculating means for obtaining a correction coefficient corresponding to the image height of the pixel and the calculated angle;
An imaging apparatus comprising: correction means for correcting shading based on the acquired correction coefficient. When the correction coefficient corresponding to the calculated angle is not stored in the storage unit, the calculation unit is used for correcting the shading by interpolation processing based on the correction coefficient stored in the storage unit. The image pickup apparatus according to claim 9, wherein a correction coefficient to be calculated is calculated. The calculating means adjusts the phase of a periodic function expressing the correction coefficient when an aperture formed by the aperture member rotates at the aperture center of the aperture member according to a state of the aperture member. The imaging device according to claim 9 or 10, wherein the imaging device is characterized. The imaging device according to claim 1, wherein the diaphragm member includes a plurality of blade members. The imaging apparatus according to any one of claims 1 to 12, wherein the image height is a distance of the image signal from an optical center of the imaging optical system. The declination angle is an angle between a straight line connecting the target pixel and the optical center of the imaging optical system and a predetermined straight line passing through the target pixel. Imaging device. A method for controlling an imaging apparatus including an imaging element that receives subject light from an imaging optical system having an aperture member and photoelectrically converts the subject light into an image signal,
The diaphragm used for correcting shading generated in the image signal based on at least the image height and the deflection angle of the target pixel of the image signal and the optical information of the imaging optical system including the shape information of the diaphragm member A calculation step of calculating a correction coefficient according to the shape of the member;
And a correction step of correcting the shading based on the calculated correction coefficient.

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