JP2010004399A - Image capturing apparatus and image capturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a suitable image when the face exists in a peripheral part of an image. <P>SOLUTION: When generating an EVF image, a shading correction is strengthened in order to enhance reduction in the quantity of light in a terminal part of the image so as to easily detect the face in a face detection section 202. At the same time, when performing main photographing, it is determined whether the face is present in the end and when the face exists in the end, a state where the shading correction amount is large is maintained, but when the face does noe exist in the end, the shading correction amount is reduced in order to reduce noises. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, an imaging method, a program, and a recording medium, and more particularly to a technique suitable for use in performing shading correction.

  In general, in an image taken through an optical system (lens), a phenomenon occurs in which the amount of light decreases as the distance from the optical axis center to the peripheral portion increases. Such a decrease in the amount of light in the peripheral portion is larger as the F value is smaller, and is larger as the angle is widened. In an imaging apparatus using a solid-state imaging device such as a CCD or a CMOS, it is possible to perform shading correction that electrically corrects and calculates a light amount drop of each pixel in the peripheral portion. Specifically, for example, the shading correction can be performed by multiplying the photographed image by the reciprocal of the shading information under a certain photographing condition.

  However, if the shading correction is always performed, an increase in noise is caused in the peripheral portion of the image. Therefore, an imaging apparatus is disclosed that refers to luminance information and color information, for example, determines whether or not the scene is conspicuous in shading like the sky, and changes the shading correction amount according to the scene (for example, Patent Document 1).

JP 2007-27943 A

  However, in the technique described in Patent Document 1, the shading correction amount is increased in the case of a uniform screen where shading is conspicuous, such as in the sky, or when there is a high-frequency subject in the periphery. For this reason, for example, when there is a subject such as a face that does not like a decrease in the amount of peripheral light at the periphery of the image, such as a group photo, the shading correction cannot be sufficiently performed.

  In addition, the decrease in the amount of light in the peripheral portion becomes large, so that the peripheral portion of the image becomes dark or the contrast becomes low. Therefore, when face detection is performed on an image having a face in the periphery of the image, such as a group photo, the signal level for detecting a face such as a contour signal or a color difference signal may not be secured due to this influence.

  The present invention has been made in view of the above-described problems, and an object thereof is to obtain an appropriate image when a face exists in the peripheral portion of the image.

  An image pickup apparatus according to the present invention includes an image pickup unit that picks up a subject and generates an image signal, a face detection unit that performs face detection on the image signal generated by the image pickup unit, and an image generated by the image pickup unit. A correction unit that performs shading correction on the signal; and an instruction unit that issues an instruction to record an image signal generated by the imaging unit on a recording medium. The shading correction is performed with a correction amount necessary for detecting the face at the end of the image, and the correction amount is changed according to the detection result by the face detection unit for the image signal instructed by the instruction unit. It is characterized by that.

  The imaging method of the present invention includes an imaging process for imaging an object to generate an image signal, a face detection process for performing face detection on the image signal generated in the imaging process, and an image generated in the imaging process. A correction process for performing shading correction on the signal, and an instruction process for issuing an instruction to record the image signal generated in the imaging process on a recording medium. In the correction process, in the face detection process The shading correction is performed with the correction amount necessary for detecting the face at the edge of the screen, and the correction amount is changed according to the detection result in the face detection step for the image signal instructed in the instruction step. It is characterized by doing.

  The program of the present invention includes an imaging process for capturing an image of a subject to generate an image signal, a face detection process for performing face detection on the image signal generated in the imaging process, and an image signal generated in the imaging process. A correction process for performing shading correction on the image, and an instruction process for issuing an instruction to record the image signal generated in the imaging process on a recording medium. In the correction process, the face detection process is performed. The shading correction is performed with the correction amount necessary for detecting the face at the edge of the screen, and the correction amount is set according to the detection result in the face detection step for the image signal instructed in the instruction step. It is characterized by causing a computer to execute a change.

  The recording medium of the present invention is characterized by recording the program described above.

  According to the present invention, it is possible to secure a signal level for detecting a face. As a result, even when there is a subject such as a face that does not like a decrease in the amount of peripheral light at the edge of the screen, the shading correction can be strengthened, so that an appropriate image can be obtained.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, a configuration example of the imaging apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus according to the present embodiment.
In FIG. 1, an imaging apparatus 100 includes an optical system 101 that forms an image of incident light on a solid-state imaging device 103, and an optical system control unit 102 that controls exposure, zoom, focus, and the like of the optical system 101. ing.

  In addition, the solid-state imaging device 103 that converts the optical image that has been formed into an electrical signal, the imaging system control unit 104 that drives the solid-state imaging device 103, and the clamped and gained electrical signals that are output from the solid-state imaging device 103 And an analog signal processing unit 105 that performs such processing. Further, an analog / digital (A / D) conversion unit 106 that performs A / D conversion of an analog signal into a digital signal, and a digital signal processing unit 107 that generates image data from the A / D converted digital signal are provided. .

  Further, when the image data is generated by the digital signal processing unit 107, the image data is temporarily output to the internal storage unit 108 and the generated image data is output to the external storage device 112 for finally storing the image data. And an interface (I / F) unit 109. Furthermore, an image display unit 110 that functions as an electronic viewfinder that displays an image based on the generated image data, and a control unit 111 that controls each unit of the imaging apparatus 100 are provided.

Next, a general configuration for performing processing such as shading correction on a digital signal will be described with reference to FIG.
The A / D converted digital signal is input to the shading correction unit 301 as an RGB signal. The shading correction unit 301 performs shading correction on the RGB signal read from the solid-state image sensor using a shading correction amount set separately.

  The luminance processing unit 303 performs luminance processing such as contour enhancement, noise reduction, and gamma processing on the luminance signal output from the shading correction unit 301. On the other hand, the color processing unit 304 performs color conversion on the color signal output from the shading correction unit 301, color processing such as white balance, high-brightness, low-brightness color reduction, and gamma processing. To implement. Then, the signals output from the luminance processing unit 303 and the color processing unit 304 are combined by the adder 305 and output as a YCrCb signal.

FIG. 4 is a diagram showing a change in luminance with respect to image height.
In FIG. 4, the horizontal axis indicates the image height, and the brightness of an image taken through the optical system (lens) decreases as the image height increases from the axial (center of the image) to 100% of the image height (four corners of the image). ing. In the shading correction, the luminance at the end can be increased to the luminance at the center of the image by multiplying the shading correction coefficient for each pixel. When the luminance before the shading correction is Y and the shading correction coefficient is α, the luminance Y ′ after the shading correction is as follows.
Luminance Y ′ = Y * α after shading correction of each pixel

  Although it is possible to correct the luminance level to the center of the image, it is also possible to stop the correction halfway. In this embodiment, the shading correction amount is increased for the EVF image in order to prioritize the detection of any face on the screen without omission over the image quality. On the other hand, in the case of performing actual photographing, in consideration of an increase in noise, if a face is not detected at the edge of the screen, correction is stopped halfway.

Next, among the configurations of the digital signal processing unit 107 in FIG. 1, a configuration for generating image data will be described with reference to FIG. FIG. 2 is a block diagram illustrating a configuration example of the digital signal processing unit 107 according to the present embodiment.
In the digital signal processing unit 107 shown in FIG. 2, the A / D converted digital signal is input to the shading correction unit 201 as an RGB signal. The shading correction unit 201 performs shading correction on the RGB signals read from the solid-state image sensor 103 using a separately set shading correction amount.

  The face detection unit 202 detects the presence / absence of a face and the face coordinates in the input signal, and outputs the information to the shading correction unit 201. The luminance processing unit 203 performs luminance processing such as edge enhancement, noise reduction, and gamma processing on the luminance signal output from the shading correction unit 201. On the other hand, the color processing unit 204 performs color conversion on the color signal output from the shading correction unit 201, color processing such as white balance, high-brightness, low-brightness color reduction, and gamma processing. To implement. Then, the signals output from the luminance processing unit 203 and the color processing unit 204 are combined by the adder 205 and output as a YCrCb signal.

  Here, face detection by the face detection unit 202 will be described. Face detection includes a method of detecting from a luminance signal and a method of detecting from a color signal. In the method of detecting from the luminance signal, a plurality of columns are scanned in the vertical direction to detect the contour of the subject. When it is determined that the detected contour is a face contour, it is detected that there is a face. In the method of detecting from the color signal, the photographing screen is divided into a plurality of areas, and the skin color area is detected from the color difference signal. When it is determined that the face is detected by detecting the skin color area, the face is detected as being present. In this embodiment, either method may be used.

FIG. 5 is a flowchart illustrating an example of an imaging processing procedure in the present embodiment. 5 is performed under the control of the control unit 111.
First, processing for causing the image display unit 110 to display an EVF image is started when the imaging apparatus 100 is turned on.

  In step S501, the imaging system control unit 104 operates the solid-state imaging device 103 under EVF drive conditions. Next, in step S <b> 502, the shading correction unit 201 increases the shading correction amount in order to improve the light amount drop at the edge of the image so that the face detection unit 202 can easily detect the face. In step S503, shading correction is performed on the image signal output from the solid-state image sensor 103. In step S502, when the shading correction is strengthened, the shading correction amount is increased to such an extent that any face on the screen can be detected without omission.

  In step S504, the face detection unit 202 performs face detection on the image signal on which shading correction has been performed. In step S505, the digital signal processing unit 107 functions as a display control unit, generates an EVF image reflecting the face detection result, and displays the EVF image on the image display unit 110.

  Next, in step S506, it is determined whether or not a photographer has operated a shutter switch (not shown) to detect a trigger signal (hereinafter referred to as SW2) for actual photographing (recording processing). If the result of this determination is that SW2 has not been detected, processing proceeds to step S513. In step S513, it is determined whether there is an instruction to end the display of the EVF image. As a result of this determination, if there is an instruction to end, the process ends.

  On the other hand, if the result of determination in step S513 is that there is no instruction to end, processing returns to step S503. Then, the sequence from the shading correction in step S503 to the EVF display in step S505 is repeated until SW2 is detected.

  On the other hand, if SW2 is detected as a result of the determination in step S506, the process proceeds to step S507, where the control unit 111 functions as an instruction unit, and the process proceeds to the main imaging sequence. In step S507, the imaging system control unit 104 operates the solid-state imaging device 103 under the driving conditions for main imaging. Next, in step S508, the shading correction unit 201 determines whether or not a face exists at the end of the captured image (EVF image) based on the face detection result by the face detection unit 202. At this time, as a face detection result to be referred to, it is determined whether or not a face exists using an image of several frames acquired immediately before the main photographing.

  In addition, about the reference | standard used as an edge part, you may enable it to change a setting by a photographer. As shown in FIG. 4, the luminance decreases as the image height goes from the on-axis (image center) to 100% of the image height (image corners). In normal times, for example, a range exceeding 80% of the image height may be defined as an end, and the range defined as the end may be changed by the photographer.

  If the result of this determination is that a face is present at the edge of the photographed image, the shading correction unit 201 has a large shading correction amount in step S509 in order to avoid the face from becoming dark due to the effect of a decrease in the amount of light at the periphery. Keep in state. On the other hand, if the result of determination in step S508 is that there is no face at the edge of the captured image, the shading correction unit 201 decreases the shading correction amount in step S510 in order to avoid an increase in noise at the edge of the image. When the shading correction amount is determined, shading correction is performed on the image signal generated in the main photographing in step S511.

  Next, in step S 512, the digital signal processing unit 107 generates image data for actual shooting from the image signal subjected to the shading correction in step S 511, and records it in the external storage device 112 via the I / F unit 109. After recording, the process returns to step S501 again.

  In the present embodiment, if a face is detected at the edge of the image, the shading correction is kept strong, and if no face is detected at the edge of the image, the shading correction is weakened. On the other hand, the intensity of shading correction at the time of actual photographing may be increased as the face is at the end. In this case, the shading correction unit 201 does not determine whether or not a face is present at the end, and the shading correction unit 201 performs shading according to the coordinates based on the information about the coordinates of the face at the end as the face detection result. Adjust the correction amount. In addition, it is determined whether or not a face exists at the end, and when there is a face at the end, the shading correction amount corresponding to the coordinate is determined based on the information about the coordinates of the face at the end. You may make it adjust.

  As described above, according to this embodiment, since the shading correction is performed with the correction amount necessary for detecting the face at the edge of the screen, the signal level for detecting the face can be ensured. . As a result, even when there is a subject such as a face that does not like a decrease in the amount of peripheral light at the edge of the screen, the shading correction can be strengthened, so that an appropriate image can be obtained. Also, when no face is detected at the edge of the screen, the shading correction amount is reduced, so that an increase in noise at the edge of the image can be prevented.

(Other embodiments according to the present invention)
Each means constituting the image pickup apparatus and each step of the image pickup method in the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  Further, the present invention can be implemented as, for example, a system, apparatus, method, program, or recording medium. Specifically, the present invention may be applied to a system including a plurality of devices. The present invention may be applied to an apparatus composed of a single device.

  Note that the present invention includes a case where a software program for realizing the functions of the above-described embodiments (in the embodiment, a program corresponding to the flowchart shown in FIG. 5) is directly or remotely supplied to a system or apparatus. This includes the case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Examples of the recording medium for supplying the program include a flexible disk, a hard disk, an optical disk, and a magneto-optical disk. Further, there are MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, there is a method of connecting to a homepage on the Internet using a browser of a client computer. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  As another method, the program of the present invention is encrypted, stored in a recording medium such as a CD-ROM, distributed to users, and encrypted from a homepage via the Internet to users who have cleared predetermined conditions. Download the key information to be solved. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  As another method, the program read from the recording medium is first written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Then, based on the instructions of the program, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

It is a block diagram which shows the structural example of the imaging device which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the digital signal processing part which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the conventional digital signal processing part. It is a figure which shows the change of the brightness | luminance with respect to image height. It is a flowchart which shows an example of the imaging process procedure in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Imaging device 101 Optical system 102 Optical system control part 103 Solid-state image sensor 104 Imaging system control part 105 Analog signal processing part 106 A / D conversion part 107 Digital signal processing part 108 Internal storage part 109 I / F part 110 Image display part 111 Control unit 112 External storage device 201 Shading correction unit 202 Face detection unit 203 Luminance processing unit 204 Color processing unit 205 Adder

Claims (12)

Imaging means for imaging a subject and generating an image signal;
Face detection means for performing face detection on the image signal generated by the imaging means;
Correction means for performing shading correction on the image signal generated by the imaging means;
Instruction means for issuing an instruction to record the image signal generated by the imaging means on a recording medium;
The correction means performs shading correction with a correction amount necessary for the face detection means to detect a face at the edge of the screen, and the face detection means performs an image signal instructed by the instruction means. An imaging apparatus, wherein the correction amount is changed according to a detection result.   For the image signal instructed by the instruction means, the correction means sets the correction amount according to a detection result for the image signal generated immediately before instructed by the instruction means by the face detection means. The imaging apparatus according to claim 1, wherein the imaging apparatus is changed.   The correction unit reduces the correction amount of the image signal instructed by the instruction unit when the face detection unit does not detect a face at the end of the screen. Item 3. The imaging device according to Item 1 or 2.   For the image signal instructed by the instruction means, the correction means increases the correction amount as the face position detected by the face detection means is closer to the edge of the screen. The imaging device according to claim 1 or 2.   5. The imaging apparatus according to claim 1, further comprising a display control unit that displays an image based on the image signal subjected to shading correction by the correction unit on a display unit. An imaging step of imaging an object and generating an image signal;
A face detection step of performing face detection on the image signal generated in the imaging step;
A correction step of performing shading correction on the image signal generated in the imaging step;
An instruction step for issuing an instruction to record the image signal generated in the imaging step on a recording medium,
In the correction step, shading correction is performed with a correction amount necessary for detecting a face at an edge of the screen in the face detection step, and the face detection step is performed on the image signal instructed in the instruction step. An imaging method, wherein the correction amount is changed in accordance with a detection result in.   In the correction step, for the image signal instructed in the instruction step, the correction amount is determined according to a detection result for the image signal generated immediately before instructing in the instruction step in the face detection step. The imaging method according to claim 6, wherein:   In the correction step, for the image signal instructed in the instruction step, the correction amount is reduced when a face is not detected at the end of the screen in the face detection step. The imaging method according to claim 6 or 7.   In the correction step, for the image signal instructed in the instruction step, the correction amount is increased as the position of the face detected in the face detection step is the edge of the screen. The imaging method according to claim 6 or 7.   10. The imaging method according to claim 6, further comprising a display control step of displaying an image based on the image signal subjected to the shading correction in the correction step on a display unit. An imaging step of imaging an object and generating an image signal;
A face detection step of performing face detection on the image signal generated in the imaging step;
A correction step of performing shading correction on the image signal generated in the imaging step;
Causing the computer to execute an instruction step for issuing an instruction to record the image signal generated in the imaging step on a recording medium;
In the correction step, shading correction is performed with a correction amount necessary for detecting a face at an edge of the screen in the face detection step, and the face detection step is performed on the image signal instructed in the instruction step. A program that causes a computer to change the correction amount in accordance with a detection result in the program.   A computer-readable recording medium on which the program according to claim 11 is recorded.

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