JP2007081724A - Imaging apparatus and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow proper achromatization on brightness after shading correction. <P>SOLUTION: A different achromatization is executed in a region which is subjected to brightness shading correction and other region, based on brightness value of pixels and shading correction amount. So achromatic setting at low brightness and high brightness parts is optimized when performing brightness shading correction. The problem of disappearing of color which a subject should bear due to brightness shading correction is prevented to occur. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  Conventionally, a method has been disclosed in which scene discrimination is performed in shooting with a digital camera, and the amount of shading correction is increased in a character scene, and saturation suppression processing is also performed (see, for example, Patent Document 1). However, the technique described in Patent Document 1 performs saturation suppression processing according to the shading correction amount, and does not perform different saturation suppression processing according to the luminance value of the captured image.

JP 2004-88408 A

A problem in the prior art will be described with reference to FIG.
FIG. 5A shows an example of a photographed image with extreme luminance shading, and the periphery of the image is darkened by luminance shading. The subject is a colored fruit, but the color of the luminance shading portion has disappeared due to the achromatic processing at low luminance. It should be noted that the achromatic processing of the low luminance and high luminance portions is processing originally performed to suppress color noise, color bending, and the like.

  FIG. 5B is a diagram illustrating an example in which luminance shading correction is performed as it is with respect to FIG. Conventionally, as shown in FIG. 5 (a), only the brightness is increased by shading correction while leaving the portion that has been subjected to the achromatization processing at low brightness, so that the fruit that should originally be colored There was a problem that some colors disappeared.

  In view of the above-described problems, an object of the present invention is to make it possible to perform an appropriate achromatic process on the luminance after shading correction.

  An imaging apparatus according to the present invention includes an imaging unit that converts imaging light of a subject into an electrical signal and outputs a captured image, a correction unit that corrects shading of the luminance of the captured image, and a region in which the shading correction is performed by the correction unit. And an area other than the above-described area, the image forming apparatus includes an achromatic unit that performs different achromatic processing based on a luminance value of a corresponding pixel of the captured image.

  An imaging apparatus control method according to the present invention includes: an imaging process for converting imaging light of an object into an electrical signal and outputting a captured image; a correction process for correcting the luminance of the captured image; and a region for performing the shading correction. And an achromatic process for performing different achromatic processing based on the luminance value of the corresponding pixel of the photographed image in other areas.

  A computer program according to the present invention is a computer program that causes a computer to execute a control method of an imaging apparatus having a correction process for correcting shading of the brightness of a captured image, and includes the area for performing shading correction and the other areas. It is characterized by causing a computer to execute a control method of an imaging apparatus that performs different achromatic processing based on the luminance value of a corresponding pixel of a captured image.

  The recording medium of the present invention records the computer program described above.

  According to the present invention, since the different achromatic processing is performed based on the luminance value of the corresponding pixel in the region where the luminance shading correction is performed and the other region, the color difference signal of the image peripheral portion is generated by the luminance shading correction. It is possible to prevent disappearance and perform appropriate achromatic processing.

(First embodiment)
First, the configuration and shading correction operation of the imaging apparatus according to the present embodiment will be described with reference to FIGS.
FIG. 1 is a diagram illustrating a configuration of a solid-state imaging device according to the present embodiment.
As shown in FIG. 1, the imaging apparatus according to the present embodiment includes an optical system 101 that forms incident light on a solid-state imaging device, and an optical system control unit that controls exposure, zoom, focus, and the like of the optical system. 102, a solid-state image sensor 103 that converts the formed optical image into an electrical signal, and an imaging system control unit 104 that supplies a voltage and a pulse for driving the solid-state image sensor.

  In addition, an analog signal processing unit 105 that performs processing such as clamping and gaining on the output of the solid-state imaging device, an analog / digital (A / D) conversion unit 106 that performs digital conversion on the analog signal, and A / D conversion A digital signal processing unit 107 that generates an output image from a digital signal, an internal storage unit 108 that temporarily stores image data when an output image is generated by the digital signal processing unit, and finally the generated image data An interface (I / F) unit 109 with an external storage device for saving is configured.

FIG. 2 is a diagram illustrating a configuration of a portion that generates image data among the portions that constitute the digital signal processing unit 107 in FIG. 1.
The image data generation unit of the present embodiment stores a color conversion circuit 201 that generates and separates a luminance signal Y and color difference signals Cr and Cb from an A / D converted input image RGB, and a correction coefficient used for luminance shading correction. The color correction circuit 202 includes a color processing circuit 203 that performs white balance, high-brightness, and low-brightness color reduction processing on the color difference signal.

  In addition, a C gamma circuit 204 that converts color-processed image data so as to match the characteristics of the monitor, a shading correction circuit 205 that performs shading correction on the luminance signal using the correction table, and filtering the luminance signal. The image processing apparatus includes an edge emphasis circuit 206 that performs edge emphasis, a Y gamma circuit 207 that performs gamma processing on the luminance signal, and the like. The luminance signal and the color signal are combined and output as a Y Cr Cb signal.

  Thereafter, the image data is stored in an external storage device or the like in JPEG format or the like by an image output circuit (not shown).

FIG. 3 is a diagram illustrating an operation of luminance shading correction.
Generally, an image taken through an optical system (lens) has a phenomenon in which the amount of light decreases as the distance from the optical axis center to the peripheral portion increases. The decrease in the amount of peripheral light is greater as the F value is smaller. Moreover, it appears larger as the wide angle side. In an imaging device that uses a solid-state imaging device such as a CCD or CMOS, it is possible to electrically perform a correction operation to reduce the amount of light at the periphery of each pixel. The shading correction can be performed by multiplying by.

  FIG. 3 is a characteristic diagram showing luminance shading. In FIG. 3, the horizontal axis indicates the image height, and the luminance decreases as the image height increases from the on-axis (image center) to 100% of the image height (image corners). By multiplying this by a shading correction coefficient α for each pixel, the luminance can be increased to the position of the dotted line in the characteristic diagram.

This is expressed as follows.
Luminance Luminance after shading correction of each pixel Y '= Y * α
The correction can be made up to the position of the dotted line in the characteristic diagram, but the correction may be stopped halfway.

Next, the operation of the achromatic processing in the present invention will be described using the characteristic diagram of FIG.
FIG. 4 is a characteristic diagram showing the amount of achromaticity (color suppression) at each luminance, with the horizontal axis representing the luminance of the corresponding pixel in the captured image and the vertical axis representing the color difference. It can be seen that achromaticity is performed on the low luminance side and the high luminance side with the change points YL and YH as boundaries.

First, in FIG. 4A, a pixel 1 (luminance Y1) in the low luminance part and a pixel 2 (luminance Y2) in the high luminance part are shown as an example for the sake of explanation.
It is assumed that the luminance Y1 and Y2 are changed to luminance Y1 ′ (= Y1 * α, α is the luminance shading correction amount in the pixel 1) and Y2 ′ (= Y2 * α) by performing luminance shading correction. At that time, if the changing point of the achromatic color is not moved, the color difference signal of the pixel 1 becomes Cr (Cb) * 1/2 even though the luminance level is corrected to Y1 ′ and Y2 ′, respectively. The color difference signal of 2 is Cr (Cb) * 1.

  Therefore, FIG. 4B shows an achromatic amount for making the achromatic level in the pixels 1 and 2 appropriate. The characteristic indicated by the dotted line is equivalent to that shown in FIG. 4A, and the characteristic indicated by the solid line is a characteristic indicating the achromatic amount at each luminance according to the present embodiment.

  By setting the achromatic change points on the low luminance side and the high luminance side to YL / α and YH / α, respectively, the output luminance value of the pixel 1 is Y1 ′ and the output color difference value is Cr (Cb) * 1. Further, in the pixel 2, the output luminance value is Y2 ′ and the output color difference value is Cr (Cb) * 1/2, and a desired achromatic setting can be obtained.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.
FIG. 6 is a diagram showing a detailed configuration of a part that generates image data among the respective parts constituting the digital signal processing unit 107 in FIG.

  Also in the present embodiment, the basic configuration is almost the same as that of the first embodiment (FIG. 2) described above, except that the luminance value that is referred to during the achromatic processing is the luminance after shading correction. Different. As a result, the same achromatic processing as that in the first embodiment can be performed.

(Another embodiment according to the present invention)
Each unit constituting the imaging apparatus and each step of the imaging apparatus control 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.

  In addition, the present invention can be implemented as a system, apparatus, method, program, storage medium, or the like, and can be applied to a system composed of a plurality of devices. Moreover, you may apply to the apparatus which consists of one apparatus.

  In the present invention, a software program for realizing the functions of the above-described embodiments is supplied directly or remotely to a system or apparatus, and a computer of the system or apparatus reads out and executes the supplied program code. It includes the case where it is achieved also by doing.

  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.

  As a recording medium for supplying the program, for example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, 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, a client computer browser is used to connect to an Internet homepage, and the computer program itself of the present invention or a compressed file including an automatic installation function is downloaded from the homepage to a recording medium such as a hard disk. Can also be supplied.

  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.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer based on the instructions of the program is used for the actual processing. The functions of the above-described embodiment can be realized by performing some or all of the processes.

  Furthermore, after the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion board or The CPU or the like provided in the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

It is a block diagram of the imaging device in 1st Embodiment. It is a figure explaining a part of structure of the digital signal processing part in 1st Embodiment. It is a figure explaining luminance shading correction. It is a figure explaining the achromatic process in this invention. It is a figure explaining the subject of the prior art about an achromatic process. It is a figure explaining a part of structure of the digital signal processing part in 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Optical system 102 Optical system control part 103 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 (interface) part 201 Color conversion circuit 202 Correction Table 203 Color processing (color removal)
204 C Gamma Circuit 205 Shading Correction Circuit 206 Outline Enhancement Circuit 207 Y Gamma Operation Circuit

Claims (10)

Imaging means for converting imaging light of a subject into an electrical signal and outputting a captured image;
Correction means for correcting the shading of the brightness of the captured image;
An imaging apparatus comprising: an achromatic unit that performs different achromatic processing based on a luminance value of a corresponding pixel in an area where the shading correction is performed by the correcting unit and an area other than the area.   2. The achromatic means performs different achromatic processing in a region where the shading correction is performed and a region other than that based on a luminance value and a shading correction amount of a corresponding pixel of the captured image. The imaging device described in 1.   The imaging apparatus according to claim 1, wherein the achromatic unit performs the achromatic process using a luminance value after luminance shading correction.   4. The achromatic means changes a change point at which the low luminance part and high luminance part of the photographed image are subjected to an achromatic process from a luminance change point in the shading correction. The imaging apparatus according to item 1. An imaging step of converting the imaging light of the subject into an electrical signal and outputting a captured image;
A correction step for correcting shading of the brightness of the captured image;
A control method for an image pickup apparatus, comprising: an achromatic process for performing different achromatic processing based on a luminance value of a corresponding pixel of the captured image in an area where the shading correction is performed and other areas.   The imaging according to claim 5, wherein the achromatic step performs different achromatic processing based on a luminance value and a shading correction amount of a corresponding pixel in the region where the shading correction is performed and the other region. Control method of the device.   The method for controlling an imaging apparatus according to claim 5, wherein the achromatic step performs the achromatic processing using a luminance value after luminance shading correction.   8. The achromatic process includes changing a change point at which a low luminance part and a high luminance part of the photographed image are subjected to an achromatic process from a luminance change point in the shading correction. 2. A method for controlling an imaging apparatus according to item 1. A computer program for causing a computer to execute a control method of an imaging apparatus having a correction process for correcting shading of luminance of a captured image,
A computer program that causes a computer to execute a control method of an imaging apparatus that performs different achromatic processing based on a luminance value of a corresponding pixel of the captured image in an area where shading correction is performed and other areas.   10. A computer-readable recording medium on which the computer program according to claim 9 is recorded.

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