(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`/,—\._
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`E4
`(19) World Intellectual Property Organization
`32"?»
`International Bureau
`arm)
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`(43) International Publication Date
`WO 2009/1 16652 A1
`24 September 2009 (24.09.2009)
`
`
`(10) International Publication Number
`
`(51)
`
`International Patent Classification:
`H04N 5/243 (2006.01)
`H04N 5/238 (2006.01)
`G033 15/05 (2006.01)
`H04N 5/335 (2006.01)
`H04N 5/225 (2006.01)
`H04N 9/04 (2006.01)
`H04N 5/232 (2006.01)
`H04N 9/07 (2006.01)
`
`(21)
`
`International Application Number:
`
`PCT/JP2009/055550
`
`(22)
`
`International Filing Date:
`
`13 March 2009 (13.03.2009)
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`(25)
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`(26)
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`(30)
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`(71)
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`(72)
`(75)
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`Filing Language:
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`Publication Language:
`
`English
`
`English
`
`Priority Data:
`2008-074460
`
`21 March 2008 (21.03.2008)
`
`JP
`
`Applicant flor all designated States except US): CANON
`KABUSHIKI KAISHA [JP/JP]; 30-2, Shimomaruko 3-
`ohome, Ohta—ku, Tokyo, 1468501 (JP).
`
`Inventors; and
`Inventors/Applicants (for US only): OHWA, Yasushi
`[JP/JP]; c/o CANON KABUSHH<I KAISHA, 30-2, Shi-
`momaruko 3—chome, Ohta—ku, Tokyo, 1468501 (JP).
`HOMMA, Yoshihiro [JP/JP]; c/o CANON KABUSHIKI
`KAISHA, 30—2, Shimomaruko 3—chome, Ohta—ku, Tokyo,
`1468501 (JP).
`
`(74) Agents: OKABE, Masao et al.; No. 602, Fuji Bldg, 2-3,
`Marunouchi 3—chome, Chiyoda—ku, Tokyo, 1000005 (JP).
`
`(81)
`
`Designated States (unless otherwise indicated, for every
`kind ofnatinnal protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ,
`CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ,
`EC, EE, EG, ES, FI, GB, GD, GE, GII, GM, GT, IIN,
`HR, HU, ID, IL, IN, IS, KE, KG, KM, KN, KP, KR, KZ,
`LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ,
`OM, PG, PH, PL, PT, RO, RS, RU, SC, SD, SE, SG, SK,
`SL, SM, ST, SV, SY, TJ, TM, TN, TR, TT, TZ, UA, UG,
`US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84)
`
`Designated States (unless otherwise indicated, for every
`kind ofregional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ,
`TM), European (AT, BE, BG, CH, CY, CZ, DE, DK, EE,
`ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV,
`MC, MK, MT, NL, NO, PL, PT, RO, SE, SI, SK, TR),
`OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML,
`MR, NE, SN, TD, TG).
`Published:
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`with international search report (Art. 21(3))
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`(54) Title: IMAGE PICKUP APPARATUS AND CONTROL METHOD THEREFOR
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`(57) Abstract: An image pickup apparatus arranged so that an optical image of an object obtained by emitting a flash is converted
`into an electric signal to obtain a first image regarding photographing of the object, the same optical image of the Object is con-
`verted into an electric signal to obtain a second image, a distance fi‘om the object is measured for each image area of the first im-
`age on the basis of the second image, and the first image is corrected on the basis of the distance from the object measured for
`each image area and light distribution characteristic data of a flash stored beforehand corresponding to the distance of the object.
`
`
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`W02009/116652A1|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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`WO 2009/116652
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`PCT/JPZOO9/055550
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`DESCRIPTION
`
`IMAGE PICKUP APPARATUS AND CONTROL METHOD THEREFOR
`
`TECHNICAL FIELD
`
`The present invention relates to an image pickup
`
`apparatus which picks up an image of an object by using
`
`a strobe, and a control method therefor.
`
`10
`
`BACKGROUND ART
`
`With an image pickup apparatus such as a digital
`
`camera, strobe photographing has been conventionally
`
`carried out, which irradiates an object with a flash by
`
`using a strobe which is so—called a flash unit,
`
`to
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`thereby photograph the object.
`
`In the strobe photographing, generally, because
`
`of strobe light distribution characteristics,
`
`a flash
`
`is not uniformly distributed onto the object.
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`Therefore,
`
`the object may look brighter at its center
`
`and darker at its periphery, or the object may look
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`brighter as it is nearer, and darker as it is farther
`
`because it is unreachable by the flash.
`
`Conventionally available techniques regarding
`
`strobe photographing are,
`
`for example, disclosed in
`
`Japanese Patent Application Laid—Open Nos. Hll—331575,
`
`2003—283922, and 2005—354167. Specifically, Japanese
`
`Patent Application Laid—Open No. H11—331575 discusses
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`an image processing technique of obtaining,
`
`in portrait
`
`photographing with a wall set as a background, a
`
`distance of a person as a main object from information
`
`of the object, and correcting brightness based on light
`
`distribution characteristics in strobe photographing.
`
`Japanese Patent Application Laid—Open No. 2003—283922
`
`discusses a technique of correcting an image based on
`
`light distribution characteristics including lens
`
`characteristics in strobe photographing.
`
`Japanese
`
`Patent Application Laid—Open No. 2005—354167 discusses
`
`a technique of correcting an image according to light
`
`distribution characteristics dependent on an object
`
`distance on the basis of pieces of distance measurement
`
`information of some places in strobe photographing.
`
`However,
`
`the conventional techniques discussed in
`
`Japanese Patent Laid—Open Nos. Hll—331575, 2003—283922,
`
`and 2005—354167 have had difficulties of removing local
`
`light distribution unevenness caused by the strobe
`
`(flash unit),
`
`from an image photographed by the strobe
`
`10
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`20
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`photographing.
`
`DISCLOSURE OF THE INVENTION
`
`To solve the problem,
`
`the present invention
`
`provides a technique of removing local light
`
`25
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`distribution unevenness caused by a flash unit,
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`from an
`
`image photographed by using the flash unit.
`
`According to an aspect of the present invention,
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`WO 2009/116652
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`PCT/JP2009/055550
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`an image pickup apparatus comprises a flash unit which
`
`emits a flash to an object; a first image obtaining
`
`unit which converts an optical image of the object
`
`formed by an optical unit into an electric signal to
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`obtain a first image regarding photographing of the
`
`object; a second image obtaining unit which cinverts
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`the optical image of the object into an electric signal
`
`to obtain a second image for measurement of distance
`
`distribution of the object; a distance measurement unit
`
`which measures a distance from the object for each
`
`image area of the first image on the basis of the
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`second image; a storing unit which stores light
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`distribution characteristic data regarding light
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`distribution characteristics of the flash unit; and a
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`correction unit which corrects the first image on the
`
`basis of the distance from the object measured by the
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`distance measurement unit for each image area and the
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`light distribution characteristic data corresponding to
`
`the distance of the object.
`
`According to another aspect of the present
`
`invention, a control method for an image pickup
`
`apparatus including a flash unit for emitting a flash
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`to an object and a storing unit for storing light
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`10
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`20
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`distribution characteristic data regarding light
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`25
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`distribution characteristics of the flash unit,
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`comprises: a first image obtaining step of converting
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`an optical image of the object formed by an optical
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`unit into an electric signal to obtain a first image
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`regarding photographing of the object; a second image
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`obtaining step of converting the optical image of the
`
`object into an electric signal to obtain a second image
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`for measurement of distance distribution of the object;
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`a distance measurement step of measuring a distance
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`from the object for each image area of the first image
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`on the basis of the second image; and a correction step
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`of correcting the first image on the basis of the
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`distance from the object measured in the distance
`
`measurement step for each image area and the light
`
`distribution characteristic data corresponding to the
`
`distance of the object.
`
`Further features of the present invention become
`
`apparent from the following description of an exemplary
`
`embodiment with reference to the attached drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG.
`
`1 is a block diagram illustrating an example
`
`of an internal configuration of a digital camera (image
`
`pickup apparatus) according to an embodiment of the
`
`present invention.
`
`FIG.
`
`2 is a flowchart illustrating an example of
`
`a processinngrocedure in a control method for the
`
`digital camera (image pickup apparatus) according to
`
`the embodiment of the present invention.
`
`FIGS. 3A,
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`3B and 3C are schematic diagrams each
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`illustrating an example of a basic pixel array of a
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`general image pickup element.
`
`FIGS.
`
`4A and 4B are schematic diagrams each
`
`illustrating an example of a basic pixel array of an
`
`image pickup element according to the embodiment of the
`
`present invention.
`
`FIGS.
`
`5A and 5B are schematic diagrams each
`
`illustrating an example of a pixel structure of an
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`image sensor
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`(color pixel) of the image pickup element
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`according to the embodiment of the present invention.
`
`FIGS.
`
`6A and 6B are schematic diagrams each
`
`illustrating an example of a pixel structure of the
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`image sensor
`
`(color pixel) of the image pickup element
`
`according to the embodiment of the present invention.
`
`FIG.
`
`7 is a schematic diagram illustrating an
`
`example of a pixel array of the image pickup element
`
`according to the embodiment of the present invention.
`
`FIGS.
`
`8A and 8B are schematic diagrams each
`
`illustrating an example of a pixel structure of a
`
`distance measurement pixel 81 illustrated in FIG. 7.
`
`FIGS.
`
`9A and 9B are schematic diagrams each
`
`illustrating an example of a pixel structure of a
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`distance measurement pixel 82 illustrated in FIG. 7.
`
`FIGS. 10A and 10B are conceptual diagrams of
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`detection of image deviation caused by an out—of—focus
`
`state of the image pickup element according to the
`
`embodiment of the present invention.
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`FIG. 11 is a schematic diagram illustrating a
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`modified example of a pixel array of the image pickup
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`element according to the embodiment of the present
`
`invention.
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`5
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`FIG. 12 is a schematic diagram illustrating a
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`modified example of a pixel array of the image pickup
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`element according to the embodiment of the present
`
`invention.
`
`FIG. 13 is a schematic diagram illustrating a
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`10
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`modified example of a pixel array of the image pickup
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`element according to the embodiment of the present
`
`invention.
`
`FIG. 14 is a conceptual diagram of focus
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`detection of the digital camera (image pickup
`
`15
`
`apparatus) according to the embodiment of the present
`
`invention.
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`FIG. 15 is a conceptual diagram of focus
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`detection of the digital camera (image pickup
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`apparatus) according to the embodiment of the present
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`20
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`invention.
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`FIG. 16 is a schematic diagram illustrating a
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`status of pixel signals read from row groups
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`respectively including the distance measurement pixels
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`81 and $2 of the image pickup element according to the
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`25
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`embodiment of the present invention.
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`FIGS. 17A and 17B are schematic diagrams each
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`illustrating an example of a pixel structure of a
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`distance measurement pixel of the image pickup element
`
`according to the embodiment of the present invention.
`
`FIGS. 18A and 18B are schematic diagrams
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`illustrating light—shielding layers in the distance
`
`measurement pixels 81 and 52 of the image pickup
`
`element according to the embodiment of the present
`
`invention.
`
`FIG. 19 is a schematic diagram illustrating an
`
`example of a pixel array of the image pickup element
`
`according to the embodiment of the present invention.
`
`FIGS. 20A and 20B are schematic diagrams each
`
`illustrating an example of a distance measurement pixel
`
`of the image pickup element according to the embodiment
`
`of the present invention.
`
`FIG. 21 is a schematic diagram illustrating a
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`status of strobe photographing of an object which uses
`
`the digital camera (image pickup apparatus) according
`
`to the embodiment of the present invention.
`
`FIG. 22 is a schematic diagram illustrating an
`
`example of a photographed image when the strobe
`
`photographing of the object illustrated in FIG. 21 is
`
`carried out.
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`FIG. 23 is a schematic diagram illustrating an
`
`example of object distance distribution in the strobe
`
`photographing of the object illustrated in FIG. 21.
`
`FIGS. 24A, 24B, 24C, 24D and 24E are schematic
`
`diagrams illustrating strobe light distribution
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`characteristics.
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`FIGS. 25A and 25B are schematic diagrams each
`
`illustrating an example of strobe light distribution
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`characteristics based on a zoom position.
`
`FIG. 26 is a schematic diagram illustrating an
`
`example of strobe light distribution characteristics.
`
`FIG. 27 is a schematic diagram illustrating an
`
`example of a correction gain in the case of the strobe
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`light distribution characteristics illustrated in FIG.
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`10
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`26.
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`FIG. 28 is a schematic diagram illustrating an
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`example of a photographed image when photographing of
`
`the object illustrated in FIG. 21 is carried out.
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`FIG. 29 is a schematic diagram illustrating an
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`example of object distance distribution of a horizontal
`
`image portion illustrated in FIG. 28.
`
`FIG. 30 is a schematic diagram illustrating an
`
`example of a correction gain in the horizontal image
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`portion illustrated in FIG. 28.
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`FIG. 31 is a schematic diagram illustrating an
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`example of a photographed image after correction
`
`processing performed for the photographed image
`
`illustrated in FIG. 22.
`
`FIG. 32 is a schematic diagram illustrating an
`
`example of a degree of in—focus when an iris aperture
`
`is wide.
`
`FIG. 33 is a schematic diagram illustrating an
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`example of a degree of in—focus when the iris aperture
`
`is narrow.
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`FIG. 34 is a schematic diagram illustrating an
`
`example of a degree of in—focus for the horizontal
`
`image portion illustrated in FIG. 28.
`
`FIG. 35 is a flowchart illustrating an example of
`
`a detailed processing procedure in image correction
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`processing of Step 86 illustrated in FIG. 2.
`
`FIG. 36 is a schematic diagram illustrating an
`
`example of object distance distribution in the
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`horizontal image portion illustrated in FIG. 28.
`
`FIG. 37 is a schematic diagram illustrating an
`
`example of a degree of in—focus in the horizontal image
`
`portion illustrated in FIG. 28.
`
`FIG. 38 is a schematic diagram illustrating an
`
`example of a menu setting screen regarding correction
`
`processing in strobe light distribution characteristics.
`
`FIG. 39 is a schematic diagram illustrating an
`
`example of a menu setting screen regarding the
`
`correction processing in the strobe light distribution
`
`characteristics.
`
`FIG. 40 is a flowchart illustrating an example of
`
`proceeding processing to the flowchart of FIG.
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`2 when
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`various settings are made on the menu setting screens
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`illustrated in FIGS. 38 and 39.
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`BEST MODE FOR CARRYING OUT THE INVENTION
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`10
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`A preferred embodiment of the present invention
`
`will now be described in detail in accordance with the
`
`accompanying drawings.
`
`An embodiment of the present invention is
`
`described below by way of an example where a digital
`
`camera is applied as an image pickup apparatus of the
`
`present invention.
`
`FIG.
`
`1 is a block diagram illustrating an example
`
`of an internal configuration of the digital camera
`
`(image pickup apparatus) according to the embodiment of
`
`the present invention.
`
`A digital camera 100 of this embodiment includes
`
`an iris 101, a photographing lens 102, an image pickup
`
`element 103, an A/D conversion unit 104, a development
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`processing unit 105, a pupil—divided image phase
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`difference distance measurement unit 106, a lens
`
`control unit 107, an exposure control unit 108, and an
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`iris control unit 109. The digital camera 100 of this
`
`embodiment further includes a strobe control unit 110,
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`a strobe 111, a strobe light distribution
`
`characteristic storing unit 112, a correction unit 113,
`
`an operation input unit 114, a compression processing
`
`unit 115, and an image data storing unit 116. The
`
`correction unit 113 includes a correction gain
`
`calculation unit 113a and a correction processing unit
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`113b.
`
`The iris 101 adjusts an amount of light to be
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`ll
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`guided into the digital camera 100, and its aperture
`
`diameter can be changed based on photographing
`
`conditions. This iris 101 is controlled by the iris
`
`control unit 109.
`
`The photographing lens 102 has a function of
`
`guiding an optical image of an object to the image
`
`pickup element 103, and includes one or a plurality of
`
`lenses including a focus lens. The photographing lens
`
`102 is controlled by the lens control unit 107.
`
`The image pickup element 103 includes pixels two—
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`dimensionally arranged on the same plane.
`
`In each
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`pixel,
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`the image pickup element 103 converts the
`
`optical image (object image) of the object guided by
`
`the photographing lens 102 into an electric signal
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`(image signal) of an analog signal to pick up an image
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`of the object. The image pickup element 103 includes,
`
`for example, a CCD sensor or a CMOS sensor.
`
`The A/D conversion unit 104 converts the image
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`signal of the analog signal output from the image
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`pickup element 103 into an image signal of a digital
`
`signal.
`
`The development processing unit 105 converts the
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`image signal output from the A/D conversion unit 104
`
`from an RGB signal into a YUV signal to perform
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`development processing.
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`The pupil—divided image phase difference distance
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`measurement unit 106 performs prOCessing of measuring a
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`12
`
`distance from the object for each image area of the
`
`photographed image based on a pixel signal from a
`
`distance measurement pixel disposed in the image pickup
`
`element 103. Specifically,
`
`the pupil—divided image
`
`phase difference distance measurement unit 106 extracts
`
`the pixel signal from the distance measurement pixel
`
`disposed in the image pickup element 103,
`
`from an
`
`output of the A/D conversion unit 104, and obtains
`
`object distance distribution of an image photographed
`
`within an angle of View based on pupil—divided images A
`
`and B.
`
`The lens control unit 107 controls a focus lens
`
`of the photographing lens 102 according to distance
`
`measurement information obtained by the pupil—divided
`
`image phase difference distance measurement unit 106.
`
`The exposure control unit 108 determines
`
`photographing conditions to enable photographing with
`
`appropriate exposure, based on the image signal output
`
`from the A/D conversion unit 104.
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`The iris control unit 109 controls the iris 101
`
`according to the photographing conditions (exposure
`
`conditions) determined by the exposure control unit 108.
`
`The strobe control unit 110 controls the strobe
`
`111 according to the photographing conditions (exposure
`
`25
`
`conditions) determined by the exposure control unit 108.
`
`The strobe 111 emits a flash to the object when
`
`necessary due to underexposure or the like under
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`13
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`control of the strobe control unit 110.
`
`The strobe light distribution characteristic
`
`storing unit 112 stores strobe light distribution
`
`characteristic data indicating light distribution
`
`characteristics of the strobe 111 characterized by room
`
`and focus positions of the photographing lens 102, an
`
`iris value of the iris 101, or an object distance.
`
`The correction unit 113 performs correction
`
`processing of the photographed image on the basis of a
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`10
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`distance of the object in each image area of the
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`photographed image measured by the pupil—divided image
`
`phase difference distance measurement unit 106, and the
`
`light distribution characteristic data stored in the
`
`strobe light distribution characteristic storing unit
`
`15
`
`112.
`
`The correction gain calculation unit 113a of the
`
`correction unit 113 calculates a gain when the
`
`photographed image data is corrected based on the zoom
`
`and focus positions of the photographing lens 102,
`
`the
`
`object distance distribution of the image photographed
`
`within the angle of View,
`
`in—focus conditions based on
`
`the iris value of the iris 101, and the strobe light
`
`distribution characteristic data.
`
`The correction processing unit 113b of the
`
`correction unit 113 performs correction processing of
`
`the photographed image data on the basis of the gain
`
`calculated by the correction gain calculation unit 113a.
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`The operation input unit 114 enters input
`
`information entered by a user to the correction unit
`
`113. For example,
`
`the operation input unit 114
`
`includes a display screen for displaying a menu setting
`
`screen, and enters input information to the correction
`
`unit 113 via the menu setting screen.
`
`The compression processing unit 115 performs
`
`processing of compressing the photographed image data
`
`corrected by the correction unit 113.
`
`The image data storing unit 116 stores the image
`
`data compressed by the compression processing unit 115.
`
`FIG.
`
`2 is a flowchart illustrating an example of
`
`a processing procedure of a control method for the
`
`digital camera (image pickup apparatus) according to
`
`the embodiment of the present invention. Specifically,
`
`FIG.
`
`2 mainly illustrates a processing procedure
`
`regarding image correction during strobe photographing.
`
`First,
`
`in Step 81,
`
`for example,
`
`the correction
`
`unit 113 determines whether to carry out strobe
`
`photographing, on the basis of input information
`
`entered from the operation input unit 114.
`
`If a result
`
`of the determination indicates that strobe
`
`photographing is not carried out
`
`(Sl/NO),
`
`the
`
`processing of the flowchart is finished.
`
`On the other hand, if a determination result of
`
`Step 81 indicates that strobe photographing is carried
`
`out
`
`(Sl/YES),
`
`the strobe 111 emits a flash to an object
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`
`to photograph the object by the photographing lens 102
`
`or the image pickup element 103. Thus, photographed
`
`image data of the object in the strobe photographing is
`
`obtained. Then,
`
`the process proceeds to Step 82.
`
`In Step 82,
`
`the lens control unit 107 detects a
`
`current zoom position of the photographing lens 102 and
`
`a current focus position (focus lens position) of the
`
`photographing lens 102. Then,
`
`the correction gain
`
`calculation unit 113a of the correction unit 113
`
`obtains zoom position information regarding the current
`
`zoom position of the photographing lens 102 and focus
`
`position information (focus lens position information)
`
`regarding the current focus position of the
`
`photographing lens 102 from the lens control unit 107.
`
`In Step 83,
`
`the exposure control unit 108 obtains,
`
`from the iris control unit 109, iris value information
`
`regarding a current iris value of the iris 101 detected
`
`by the iris control unit 109. The correction gain
`
`calculation unit 113a obtains the iris value
`
`information regarding the current iris value of the
`
`iris 101 from the exposure control unit 108.
`
`In Step S4,
`
`the correction gain calculation unit
`
`113a obtains object distance distribution information
`
`regarding the object distance distribution measured by
`
`the pupil—divided image phase difference distance
`
`measurement unit 106. The object distance distribution
`
`information obtained by the pupil—divided image phase
`
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`
`difference distance measurement unit 106 is described
`
`below.
`
`In Step 85,
`
`the correction gain calculation unit
`
`113a calculates an image correction gain on the basis
`
`5
`
`of different types of information obtained in Steps 82
`
`to S4 and the strobe light distribution characteristic
`
`data stored in the strobe light distribution
`
`characteristic storing unit 112. The strobe light
`
`distribution characteristic data and the method of
`
`10
`
`calculating the image correction gain by the correction
`
`gain calculation unit 113a are described below in
`
`detail.
`
`In Step S6,
`
`the correction processing unit 113b
`
`of the correction unit 113 performs processing of
`
`15
`
`correcting the photographed image data obtained by the
`
`strobe photographing of Step 81 by using the image
`
`correction gain calculated by the correction gain
`
`calculation unit 113a. The correction processing of
`
`the correction processing unit 113b is described below
`
`20
`
`in detail.
`
`Subsequently,
`
`the photographed image data
`
`corrected by the correction unit 113 is compressed by
`
`the compression processing unit 115 to be stored in the
`
`image data storing unit 116. Then,
`
`the processing of
`
`25
`
`the flowchart is finished.
`
`Steps S7 and 88 illustrated in FIG.
`
`2 enable
`
`insertion of determination processing as to whether to
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`proceed from Step 81 to Step 82 under conditions
`
`described later. Steps S7 to S9 illustrated in FIG.
`
`2
`
`are described below in detail referring to FIG. 40.
`
`Phase Difference AF by Distance Measurement Pixel
`
`Disposed In Image Pickup Element 103
`
`Next, auto—focus
`
`(phase difference AF) of a phase
`
`difference system according to this embodiment is
`
`described. First, referring to FIGS.
`
`3A to BC and FIGS.
`
`4A and 4B, a pixel array of the image pickup element
`
`103 that is a basis for phase difference AF is
`
`described.
`
`FIGS. 3A to 3C are schematic diagrams each
`
`illustrating an example of a basic pixel array of a
`
`general image pickup element.
`
`FIGS.
`
`4A and 4B are
`
`schematic diagrams each illustrating an example of a
`
`basic pixel array of the image pickup element 103
`
`according to the embodiment of the present invention.
`
`10
`
`15
`
`First,
`
`the basic pixel array of the general image
`
`pickup element illustrated in FIGS.
`
`3A to BC is
`
`20
`
`described. Each of FIGS.
`
`3A to BC illustrates a color
`
`array included in a basic unit portion of an area
`
`sensor where a basic unit is 2 pixels x 2 pixels.
`
`FIG.
`
`3A illustrates a so—called Bayer array, which is
`
`referred to as a pure color Bayer array below.
`
`FIG.
`
`3B
`
`25
`
`illustrates an example where the Bayer array is applied
`
`to a complementary color filter, which is referred to
`
`as a complementary color Bayer array below.
`
`FIG.
`
`3C
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`
`illustrates three complementary color filters with G,
`
`which is referred to as a complementary color array
`
`with G below.
`
`As a generally known basic pixel array,
`
`in
`
`5
`
`addition to the basic pixel arrays illustrated in FIGS.
`
`3A to 3C, for example,
`
`there is a complementary color
`
`checkered array of a unit of 2 pixels X
`
`4 pixels, which
`
`is often used as an image pickup element for a video
`
`movie camera. As another generally known basic pixel
`
`10
`
`array, for example,
`
`there is a complementary color
`
`checkered array of 2 pixels x
`
`8 pixels (refer to
`
`Japanese Patent Application Laid-Open No. HO9—46715).
`
`The color pixel arrays of 2 pixels x 4 pixels and 2
`
`pixels x
`
`8 pixels are more advantageous as area sensors
`
`15
`
`for processing moving images
`
`(videos performing
`
`interlace scanning). As a camera for processing still
`
`images,
`
`the array of 2 pixels x 2 pixels is more
`
`advantageous in that signal processing can be
`
`simplified and a high—quality image can be obtained.
`
`20
`
`The area sensor with 2 pixels x 2 pixels set as a basic
`
`unit is described below. However,
`
`this arrangement can
`
`be applied to the area sensors having color pixel
`
`arrays of 2 pixels x
`
`4 pixels and 2 pixels x
`
`8 pixels.
`
`Next, referring to FIGS.
`
`4A and 4B,
`
`the basic
`
`25
`
`pixel array of the image pickup element 103 of this
`
`embodiment is described.
`
`FIG.
`
`4A illustrates a pixel
`
`array in the case of a pure color Bayer array, while
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`
`FIG.
`
`4B illustrates a pixel array in the case of a
`
`complementary color Bayer array or a complementary
`
`color array with G.
`
`In FIGS. 4A and 4B, a portion "S" is a function
`
`sensor cell
`
`(distance measurement pixel) for reading
`
`photometry data regarding distance measurement for AF.
`
`In the image pickup element 103 of this embodiment,
`
`a
`
`distance measurement pixel equivalent to an AF sensor
`
`is included in the image pickup element 103 itself, and
`
`distance measurement for AF of the digital camera is
`
`carried out by reading a signal from the image pickup
`
`element 103. Through this arrangement,
`
`this embodiment
`
`enables highly accurate AF. There is no need to
`
`dispose any other AF sensors, and hence a compact and
`
`low—cost digital camera can be provided.
`
`Next, a pixel
`
`(distance measurement pixel) to
`
`detect photometry data for AF distance measurement and
`
`the image pickup element 103 including the distance
`
`measurement pixel according to this embodiment is
`
`10
`
`15
`
`20
`
`described.
`
`As an image pickup element for a digital still
`
`camera of a large number of pixels, mainly, an
`
`interline—type CCD or a full—frame type CCD is used.
`
`The interline—type CCD is often used for a low—cost
`
`25
`
`camera equal to or less than a 2/3—inch optical system,
`
`while the full—frame type CCD is often used for a high—
`
`cost camera equal to or more than a 1—inch optical
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`
`systemr A biggest difference between these types is
`
`that signal charges can be read even if a light enters
`
`the image pickup element in the case of the interline—
`
`type CCD while no signal charge can not be read unless
`
`a mechanical shutter disposed in the front of the image
`
`pickup element is closed in the case of the full—frame
`
`type CCD.
`
`The inventors of the present invention have
`
`offered a solution by proposing a improved full—frame
`
`type CCD of a structure which includes a storage unit
`
`for storing charges of a few lines between an image
`
`area of the full—frame type CCD and a horizontal CCD.
`
`The inventors of the present invention have offered a
`
`partial reading driving method for AF in an opened
`
`state of the mechanical shutter based on the improved
`
`full—frame type CCD. Additionally,
`
`the inventors of
`
`the present invention have offered a method of
`
`partially reading only a part of the image area
`
`necessary for AF, at high speed (high—speed clearing
`
`method for signal charges other than necessary portion)
`
`in the case of the interline—type CCD.
`
`Thus, both in the interline—type CCD and in the
`
`full—frame type CCD (improved type), signal charges of
`
`an area including the distance measurement pixel set in
`
`the image area can be read without opening/closing the
`
`mechanical shutter many times within a short period of
`
`time. An example of the embodiment using the improved
`
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`
`full—frame type CCD is described below. However,
`
`the
`
`example can be applied to the interline—type CCD.
`
`Before description of the distance measurement
`
`pixel,
`
`the image sensor
`
`(color pixel) of the image
`
`5
`
`pickup element 103 is described.
`
`FIGS. 5A and 5B are schematic diagrams each
`
`illustrating an example of a pixel structure of the
`
`image sensor
`
`(color pixel) of the image pickup element
`
`103 according to the embodiment of the present
`
`10
`
`invention.
`
`FIG.
`
`5A illustrates a structure of the
`
`pixel of the image sensor of the image pickup element
`
`103 when viewed from the top, while FIG. 5B illustrates
`
`a pixel structure of a section cut on the line I—I' of
`
`FIG.
`
`5A and its potential profile. Specifically, each
`
`15
`
`of FIGS. 5A and 5B mainly illustrates a photoelectric
`
`conversion unit in the pixel of the image sensor.
`
`In FIGS. 5A and SE, a clock gate electrode 201 is
`
`made of, for example,
`
`light—transparent polysilicon.
`
`A
`
`semiconductor layer surface under the clock gate
`
`20
`
`electrode 201 is a clock phase area. The clock phase
`
`area is divided into two areas by ion implantation.
`
`One is a clock barrier area 202, and the other area is
`
`a clock well area 203 formed by implanting ions so as
`
`to set higher potential than in the clock barrier area
`
`25
`
`202.
`
`A virtual gate 204 is for fixing channel
`
`pote