News Column

Patent Application Titled "Image Processing Apparatus, Image Pickup Apparatus and Image Processing Method" Published Online

August 8, 2014



By a News Reporter-Staff News Editor at Health & Medicine Week -- According to news reporting originating from Washington, D.C., by NewsRx journalists, a patent application by the inventor Itoh, Yoshinori (Shimotsuke-shi, JP), filed on January 13, 2014, was made available online on July 24, 2014 (see also Canon Kabushiki Kaisha).

The assignee for this patent application is Canon Kabushiki Kaisha.

Reporters obtained the following quote from the background information supplied by the inventors: "The present invention relates to an image processing technology to perform an image restoration process on an image generated by image capturing using a zoom lens.

"An image acquired by image capturing of an object by an image pickup apparatus such as a digital camera contains a blur component that is an image degradation component caused by spherical aberration, coma aberration, field curvature, astigmatism or the like of an image pickup optical system (hereinafter simply referred to as 'an optical system').

"Such a blur component is generated because a light flux emitted from one point of the object forms an image with some divergence on an image pickup plane; the light flux should normally converge at one point when there is no influence of aberration or diffraction.

"Such a blur component is optically expressed by a point spread function (PSF), which is different from a blur caused by defocus.

"Moreover, a color blur in a color image caused by longitudinal chromatic aberration, chromatic spherical aberration or chromatic coma aberration of the optical system can be said to be a difference between blurring degrees of respective wavelengths of light.

"In addition, horizontal color shift caused by chromatic aberration of magnification of the optical system can be said to be position shift or phase shift of color light components caused by differences of image capturing magnifications for the respective color light components.

"An optical transfer function (OTF) obtained by Fourier transform of the point spread function (PSF) is frequency component information of aberration, which is expressed by a complex number.

"An absolute value of the optical transfer function (OTF), that is, an amplitude component is called a modulation transfer function (MTF), and a phase component is called a phase transfer function (PTF).

"The MTF and the PTF are respectively a frequency characteristic of the amplitude component and a frequency characteristic of the phase component of image degradation caused by the aberration.

"The phase component is herein expressed as a phase angle by the following expression where Re(OTF) and Im(OTF) respectively represent a real part and an imaginary part of the OTF.

"Re (OTF) and Im (OTF) express the real part and imaginary part of OTF, respectively.

"PTF=tan.sup.-1(Im(OTF)/Re(OTF))

"Thus, since the optical transfer function (OTF) of the optical system degrades the amplitude component and the phase component of the image, respective points of the object in the degraded image are asymmetrically blurred like coma aberration.

"Moreover, the chromatic aberration of magnification is generated because an image pickup apparatus captures, according to its spectral characteristics, images of respective color components whose imaging positions are mutually shifted due to differences of imaging magnifications for respective light wavelengths.

"Therefore, not only the shift of the imaging positions among the color components is generated, but also shift of imaging positions among wavelengths in each color component, that is, the phase shift is generated, which causes image spread.

"Thus, although the chromatic aberration of magnification is strictly not a color shift as a mere parallel shift, this specification describes the color shift as being the same as the chromatic aberration of magnification.

"As a method for correcting the degradation of the amplitude component (MTF) and the degradation of the phase component (PTF) in the degraded image (input image), there is known one using information on the optical transfer function (OTF) of the optical system.

"This method is called 'image restoration' or 'image recovery', and a process to correct the degraded image (to reduce the blur component) by using the information of the optical transfer function (OTF) of the optical system is hereinafter referred to as 'an image restoration process' or simply as 'image restoration'. As a method of the image restoration, though described in detail below, there is known one which performs convolution of an image restoration filter in a real space on the input image; the image restoration filter has an inverse characteristic to that of the optical transfer function.

"Japanese translation of a PCT application publication No. 2005-509333 discloses an image processing method which holds filter coefficients to be used for correction of image degradation due to aberration of an image capturing optical system and performs the image restoration (image recovery) using the filter coefficients.

"This disclosed method performs the image restoration to allow the aberration of the image capturing optical system, which enables miniaturization of the image capturing optical system and increase of an aperture diameter thereof.

"In addition, the disclosed method corrects, by the image restoration, the image degradation generated due to increase of refractive indices of lens units constituting the image capturing optical system, which enables increase of magnification of a compact image capturing optical system.

"However, performing the image restoration on all images obtained in the entire magnification variation range of the image capturing optical system extremely increases a data amount of the filter coefficients.

"Moreover, the increase of the data amount of the filter coefficients decreases an image processing speed and increases manufacturing cost because of necessity of an image processing engine capable of performing high-speed computing.

"On the other hand, allowing an excessively large aberration makes it impossible to correct, by the image restoration, the degradation component due to the aberration and increases noise resulted from increase of a degree of the image restoration.

"Accordingly, even in the case of performing the image restoration, it is necessary to take into consideration an amount of the aberration of the image capturing optical system appropriate for the image restoration.

"For example, of various aberrations of the image capturing optical system, a large field curvature makes 'uneven blur' remarkable; the uneven blur is generated by asymmetry of resolution caused by tilting of an image plane on an image sensor due to manufacturing errors of lenses or tilting of the image sensor.

"Such uneven blur makes it difficult to perform good image restoration difficult.

"The image processing method disclosed in Japanese translation of a PCT application publication No. 2005-509333 does not take into consideration the aberration amount appropriate for the image restoration and further does not take into consideration the aberration amount appropriate for suppressing the data amount."

In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventor's summary information for this patent application: "The present invention provides an image processing apparatus, an image pickup apparatus, an image processing program and an image processing method each capable of fast performing good image restoration while achieving miniaturization of an image capturing optical system and increase of an aperture diameter thereof.

"The present invention provides as one aspect thereof an image processing apparatus including an image acquirer configured to acquire an input image produced by image capturing through a zoom lens whose magnification is variable, and a processor configured to perform an image restoration process using an image restoration filter produced on a basis of information on aberration of the zoom lens. The processor is configured to not perform the image restoration process on a central image area of the input image produced by the image capturing through the zoom lens set in a specific magnification state and to perform the image restoration process on a specific image area more outer than the central image area of that input image.

"The present invention provides as another aspect thereof an image pickup apparatus including an image capturer configured to perform image capturing using a zoom lens, and the above-described image processing apparatus.

"The present invention provides as still another aspect thereof a non-transitory storage medium storing an image processing program to cause a computer to perform a process on an input image produced by image capturing through a zoom lens whose magnification is variable. The process includes acquiring the input image, and performing an image restoration process using an image restoration filter produced on a basis of information on aberration of the zoom lens. The process does not perform the image restoration process on a central image area of the input image produced by the image capturing through the zoom lens set in a specific magnification state and performs the image restoration process on a specific image area more outer than the central image area of that input image.

"The present invention provides as yet still another aspect thereof an image processing method including acquiring an input image, and performing an image restoration process using an image restoration filter produced on a basis of information on aberration of the zoom lens. The method does not perform the image restoration process on a central image area of the input image produced by the image capturing through the zoom lens set in a specific magnification state and performs the image restoration process on a specific image area more outer than the central image area of that input image.

"Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

"FIGS. 1A to 1C are sectional views of a zoom lens used in an image pickup apparatus that is Embodiment 1 of the present invention.

"FIGS. 2A to 2C are sectional views of another zoom lens used in the image pickup apparatus of Embodiment 1.

"FIGS. 3A to 3C are sectional views of still another zoom lens used in the image pickup apparatus of Embodiment 1.

"FIGS. 4A and 4B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 1A to 1C at its wide-angle end.

"FIGS. 5A and 5B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 1A to 1C at its middle zoom position.

"FIGS. 6A and 6B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 1A to 1C at its telephoto end.

"FIGS. 7A and 7B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 2A to 2C at its wide-angle end.

"FIGS. 8A and 8B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 2A to 2C at its middle zoom position.

"FIGS. 9A and 9B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 2A to 2C at its telephoto end.

"FIGS. 10A and 10B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 3A to 3C at its wide-angle end.

"FIGS. 11A and 11B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 3A to 3C at its middle zoom position.

"FIGS. 12A and 12B respectively show longitudinal aberration charts and lateral aberration charts of the zoom lens shown in FIGS. 3A to 3C at its telephoto end.

"FIGS. 13A and 13B show an image restoration filter used in the image pickup apparatus of Embodiment 1.

"FIGS. 14A and 14B show correction of a point image by an image restoration process performed in the image pickup apparatus of Embodiment 1.

"FIGS. 15A and 15B show correction of an amplitude component and a phase component by the image restoration process.

"FIGS. 16A to 16C show examples of an area of an input image on which the image restoration process is performed in the image pickup apparatus of Embodiment 1.

"FIG. 17 shows a configuration of the image pickup apparatus of Embodiment 1.

"FIG. 18 is a flowchart showing image processing (including the image restoration process) performed in the image pickup apparatus of Embodiment 1.

"FIG. 19 shows a configuration of an image processing apparatus that is Embodiment 2 of the present invention."

For more information, see this patent application: Itoh, Yoshinori. Image Processing Apparatus, Image Pickup Apparatus and Image Processing Method. Filed January 13, 2014 and posted July 24, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3647&p=73&f=G&l=50&d=PG01&S1=20140717.PD.&OS=PD/20140717&RS=PD/20140717

Keywords for this news article include: Microtechnology, Canon Kabushiki Kaisha.

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Source: Health & Medicine Week


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