JP2007336433A - Method of eliminating or reducing image defect in digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a user of a camera to remove dust in the camera that causes an image defect or perform an image correction effectively as needed. <P>SOLUTION: In the method for eliminating or reducing an image defect caused by dust deposited on the inside in a digital camera including an image sensing element, a light scattering plate is attached onto a front face of a photographing lens, then image data are captured in a first diaphragm state and presence/absence of an image defect is decided in the image data. If there is an image defect, image data are further captured in a second diaphragm state and both the image data are compared to perform either dust removing operation or image correction data creation. The first diaphragm state is near minimum diaphragm and the second diaphragm state is near open diaphragm. If changes in a density and a size of the image defect are more than fixed levels in image data near the open diaphragm, deposited dust is removed by vibrating an optical cover of the image sensing element and if the changes are less than or equal with the fixed levels, image correction data are generated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for eliminating or reducing image defects caused by dust adhering to the inside of a digital camera.

  In recent years, digital cameras (hereinafter simply referred to as “cameras”) that acquire images electrically with an image sensor have become widespread in place of cameras using silver halide films.

  Such a camera uses an image sensor such as CMOS or CCD, but if dust adheres to the vicinity of the surface of the image sensor, its shadow is projected into the image, resulting in an unsightly image defect. In particular, an interchangeable lens camera such as a single-lens reflex camera has a strong demand for countermeasures against defects because dust tends to enter the camera due to its mechanism.

  The dust that becomes a problem here adheres to the inside of the camera, mainly in the vicinity of the image sensor, and on the surface of an optical cover glass or optical low-pass filter (hereinafter referred to as OLPF) that is located within a few millimeters from the surface of the image sensor. To do.

  Two methods have been devised broadly to eliminate and reduce such image defects.

  (1) Remove dust with a physical force such as ultrasonic vibration.

  (2) Using image data of dust to correct image defects.

  As a method for removing dust with the physical force of (1), as disclosed in, for example, Patent Document 1 below, a glass plate (optical cover) that is an optical element on the front surface of an imaging element module is used with a piezoelectric body or the like. A technique for removing dust by vibrating is put into practical use. This method can effectively remove dust generated after the assembly of the camera as compared with a method of blowing dust with a blower or the like.

  Regarding the image correction of (2), for example, Patent Document 2 below discloses a method for correcting a captured image of a normal subject by capturing a white reference subject, storing dust addresses and data, and the like.

Patent Document 3 below discloses a method of extracting a dust image from a normal photographed image and correcting the image based on the data.
JP 2002-204379 A (Olympus) JP 2002-209147 A (Fuji Photo Film) JP 2005-301524 A (Olympus)

  However, image defects cannot be completely eliminated by only one of the above methods. That is, even if the dust removal operation is performed by vibrating the optical cover in the method (1), if the dust adheres to a surface other than the cover, it cannot be removed and there is no effect. In this case, image defects are not eliminated. In the method of correcting an image based on the shooting data of the method (2), it is difficult for a general user to prepare a reference subject at hand, or a past image is not necessarily shot under appropriate conditions. Because it is not always. Further, for example, it is necessary not to remove dust attached to the optical cover, but to sequentially perform image correction.

  The present invention has been made to solve the above inconveniences, and an object of the present invention is to determine the presence or absence of dust adhering to the inside of the camera and perform either dust removal or image correction. Is to provide.

In order to solve the above problems, a method for eliminating or reducing an image defect in a digital camera of the present invention is a method for eliminating or reducing an image defect caused by dust adhering to an inside of a digital camera having an image sensor.
After the light diffusing plate is attached to the front surface of the photographing lens, image data is acquired in the first aperture state, the presence or absence of an image defect is determined in the image data, and if the image defect exists, the second aperture Image data is acquired in a state, and either the dust removal operation or creation of image correction data is performed by comparing the two image data.

  According to the present invention, the user of the camera can remove dust inside the camera that causes an image defect or perform image correction as needed and effectively.

  The main point of the embodiment of the present invention is that when the camera user sets the “dust removal mode” and operates a predetermined switch after attaching the light diffusion plate to the front frame of the photographing lens, the following series of operations is performed. A program is executed to remove dust and correct image defects as necessary.

  That is, continuous shooting is performed by setting the aperture of the photographic lens to two types of a first aperture state and a second aperture state, and first, the presence or absence of dust is determined using image data captured in the first aperture state. If there is an image defect due to dust, whether the image data in the first aperture state and the second aperture state are compared, and dust is removed by vibration of the optical cover or the like, or image correction data is generated. Is determined.

  Embodiments 1 and 2 will be described below with reference to the drawings, with regard to respective steps constituting a method for eliminating or reducing image defects in a digital camera of the present invention.

[Embodiment 1]
1 is a flowchart of a method for eliminating or reducing image defects according to Embodiment 1 of the present invention, FIG. 2 is a schematic diagram showing a cross-sectional structure of a camera, (a) is a small aperture, (b) is an open aperture, (c ) Shows each state of vibration of the optical cover. FIGS. 3A and 3B are enlarged views of the vicinity of the image sensor showing how dust images are formed. FIG. 3A shows a state of a small stop and FIG.
(A) and (b) may be in any aperture state as long as it can be determined whether or not dust 5 is attached on the optical cover 4 based on the difference between the image sensor outputs photographed in each state. However, it is most preferable to set a small aperture (including a minimum aperture) and an open aperture that have the most difference in the aperture state.

  4A and 4B are diagrams for explaining the output of the image sensor in the image data, and FIG. 4A is a graph showing the output signal of the normalized image sensor of the first embodiment in one direction. This is compared with (b) showing the image sensor surface in the second embodiment.

  In the flowchart of FIG. 1, the inverted trapezoidal symbol represents an operation intended by the camera user.

  A description will be given along the flowchart of FIG.

  First, in order to identify an image defect due to dust, it is desirable that the entire screen of the image sensor is illuminated with uniform illuminance. In general, it is common to prepare and shoot a “reference subject” such as a uniformly illuminated white panel or a flat light source. However, it is not practical for ordinary camera users to prepare them.

  As shown in FIG. 2, if the milky white light diffusing plate 6 is disposed immediately in front of the photographing lens 2 and the amount of extension of the lens is adjusted so that the subject is near infinity, the image sensor 1 can be illuminated relatively uniformly. Is possible.

  By molding the lens protection cap with milky white translucent plastic, the “reference subject” can always be carried as the light diffusing plate 6 without further attention of the camera user. The light diffusing plate 6 can also be used for color temperature discrimination and white balance adjustment of the photographing light source.

(start)
The camera user who performs dust removal first covers the photographing lens 2 with the light diffusing plate 6 that is the milky white lens cap, and places it in an environment with appropriate brightness, and then selects the start of the dust removal mode. After that, the operation is automatic or semi-automatic based on the camera's built-in program.

(Calculation of shutter speed)
By covering the light diffusing plate 6, the diffused light 61 can be irradiated on the front surface of the image sensor 1.

  In this state, since the autofocus mechanism generally does not work, the extension of the taking lens 2 is fixed at a predetermined position, preferably at infinity. As a result, even if the light diffusing plate 6 has scratches, scratches, uneven illumination, or the like, no image is formed on the focal plane of the image sensor 1 and the influence on the image is reduced. Next, the amount of light transmitted through the diaphragm 3 is measured with an exposure meter (not shown) built in the camera. When the aperture 3 is changed from the minimum aperture (maximum F number) to the open aperture (minimum F number), the amount of light received by the image sensor 1 (the product of the illuminance on the element surface and the exposure time by a shutter not shown) is appropriate. Must be within the output range. For this purpose, the shutter speed, the gain of the image sensor output signal amplifier (not shown), and the like are calculated. If these are beyond the controllable range, a warning is displayed to the camera user to stop the operation so that the lens is placed under an appropriate brightness.

(Small aperture shooting)
Photographing is performed with the minimum aperture of the photographing lens 2 or a small aperture 3a in the vicinity thereof. The image data at this time is stored and analyzed, and it is determined whether or not there is an image defect of a predetermined value or more due to dust 5. In FIG. 3A, the small-aperture shooting data A is shown as image data A, and the criterion for determining the image defect is the density and size of the image defect, that is, the image sensor output (relative value normalized by the maximum value). It can be defined by the “depth” and “spread” of the drop, and combinations thereof. In the graph representing the output signal of the normalized image sensor in FIG. 4A in one direction, the image defect is shown as 1c. The reason for normalization is that the amount of light varies depending on the degree of aperture opening.

  Although it is desirable that both the density and the size of the image defect are small, it is practically desirable to determine the threshold value based on whether or not the image defect can be visually determined when the image is printed to a predetermined size. More strictly, it is necessary to define not only two values of density and size, but also a combination of both.

  If there is no image defect equal to or larger than the specified value in the entire aperture in the small-aperture shooting data A, there is no need for dust removal, so a message is displayed as necessary and the mode is terminated.

(Open shooting)
If there is an image defect exceeding the allowable value in the small-aperture shooting data A, then the aperture is opened to the wide aperture 3b or the vicinity thereof to obtain data. In FIG. 3 (b), the open aperture photographing data B is shown as image data B, and the density and size of the image defect are the “depth” of the decrease in the image sensor output (relative value normalized by the maximum value). Indicated by “spread”.

(Data difference calculation)
When the dust 5 is away from the image sensor in the optical axis direction, that is, when it adheres to the optical cover 4 (cover glass or OLPF), the image defect, that is, the shadow of the dust 5 varies depending on the aperture value.

  When the aperture is opened as shown in FIG. 3B, the “depth” of the image sensor drop is shallow and the “spread” becomes large. That is, the dust 5 has a certain distance d from the focal plane of the image sensor 1, and the sharpness of the shadow of the dust 5 projected on the focal plane of the image sensor 1 decreases as the diaphragm 3 is opened. Based on the small-aperture shooting data A, a difference C (= B−A) of the image sensor output from the wide-aperture shooting data B is calculated. FIG. 4A illustrates this state in only one direction of the image sensor output. This is compared with FIG. 4B of the second embodiment described later.

(Dust removal operation)
When the difference data C obtained in this way has a value greater than or equal to a predetermined value, that is, when the shape of the image defect changes depending on the aperture value, there is a high possibility that dust 5 has adhered to the optical cover 4. At this time, as shown in FIG. 2 (c), the high-frequency voltage is applied to the piezoelectric element 41 attached to the optical cover 4 by the high-frequency voltage source 43 to cause vibration, and dust adhered to the surface of the optical cover 4. 5 is removed. Reference numeral 42 denotes a packing that does not hinder the vibration of the optical cover 4 and maintains an airtight structure with the image sensor 1.

(Compensation data creation and storage)
On the other hand, when C is equal to or less than a predetermined value, it is estimated that the dust 5 is not on the surface of the optical cover 4 and is in close contact with the image sensor 1, for example, the image sensor 1. That is, the difference between the small aperture and the wide aperture image sensor output does not exceed the specified value. The dust 5 adheres to the surface of the image sensor 1 that is the focal plane, and the shadow of the dust 5 opens the aperture 3. This is because the sharpness does not decrease. In this case, since dust removal cannot be expected even if the optical cover 4 is vibrated, image correction data using the data A to C is created and stored. Based on this correction data, the image is corrected by a known method.

  The correction data should change depending on the aperture value at which the image is actually captured. However, if the reference data A and the variation C due to the aperture are stored, the correction data corresponding to the actually captured aperture can be obtained. Can be generated. Therefore, it is not necessary to store correction data corresponding to the aperture value.

  FIG. 5 shows a flowchart of a modification of the first embodiment.

  After the camera performs the dust removal operation, the camera subsequently performs full aperture photography again to determine whether the target dust has been removed. The re-shooting at the wide aperture is performed, and the shooting data B ′ at this time is stored. Difference calculation (C ′ = B′−A) is performed, and if there is a difference greater than the specified value, it is determined that dust is not removed, and a warning is displayed to the camera user. The content of the warning includes prompting the user to manually clean or bringing the user into the manufacturer for cleaning.

[Embodiment 2]
Next, Embodiment 2 of the present invention will be described.

  FIG. 4B is a diagram illustrating the imaging element surface according to the second embodiment.

  As shown in FIG. 4B, the entire screen of the image sensor 1 is divided into predetermined sections k (k = 1, 2, 3,...) In advance and the addresses of the sections are determined. The size of the partition can be determined as needed, but it is practical that one partition includes about tens of thousands of pixels 1a and divides the entire screen into tens to thousands of partitions. is there.

  After acquiring the small-aperture shooting data A as in the first embodiment, the presence / absence of a defect is determined for each section. An image defect extending over a plurality of pixels is shown as 1c.

  In this way, a more practical setting can be made such that a specific section, for example, a plurality of sections p (indicated by bold lines) in the vicinity of the screen center, has a strict defect judgment standard and a loose screen periphery.

  This determination is performed for each section over the entire screen, and when there is an image defect in the nth section (k = n), only the section data An is stored in small-aperture shooting (the number of sections is not limited to one). Absent).

  In open aperture photography, data Bn is acquired for the nth section and the difference calculation Cn = Bn−An is performed, so that the calculation speed can be improved and the memory can be used efficiently.

The flowchart of the image defect elimination or reduction method in Embodiment 1 of the present invention. Schematic diagram showing the cross-sectional structure of the camera, (a) is a small aperture, (b) is an open aperture, (c) is a diagram showing each state of vibration of the optical cover An enlarged view of the vicinity of the image sensor showing a dust image being formed, (a) is a small aperture, and (b) is an open aperture state. The figure for demonstrating the image pick-up element output in image data, (a) is the graph which represented the output signal of the image pick-up element normalized of Embodiment 1 in one direction, (b) shows the image pick-up element surface in Embodiment 2. Figure The flowchart which shows the modification of Embodiment 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Imaging device 1a ... Pixel, 1c ... Image defect 2 ... Shooting lens 3 ... Diaphragm 3a ... Small aperture, 3b ... Open aperture 4 ... Optical cover 41 ... Piezoelectric element 42 ... Packing 5 ... Dust 6 ... Light diffusion plate (milky white lens) cap)
61 ... Diffuse light

Claims (9)

A method for eliminating or reducing image defects caused by dust adhering to the inside of a digital camera having an image sensor,
After the light diffusing plate is attached to the front surface of the photographing lens, image data is acquired in the first aperture state, the presence or absence of an image defect is determined in the image data, and if the image defect exists, the second aperture A method for eliminating or reducing an image defect in a digital camera, wherein image data is acquired in a state, and either the dust removal operation or the creation of image correction data is performed by comparing the two image data.   2. The method of eliminating or reducing an image defect in a digital camera according to claim 1, wherein the first aperture state is in the vicinity of a minimum aperture, and the second aperture state is in the vicinity of an open aperture.   3. The method for eliminating or reducing image defects in a digital camera according to claim 1, wherein after the light diffusing plate is attached to the front surface of the photographing lens, the program is built in the camera.   3. The dust removal operation is performed when the image data in the vicinity of the open aperture is compared with the image data in the vicinity of the minimum aperture and the change in density and size of the image defect is greater than or equal to a certain level. To eliminate or reduce image defects in digital cameras.   5. The method of eliminating or reducing image defects in a digital camera according to claim 4, wherein in the dust removal operation, dust attached to the image pickup device is shaken to remove the attached dust.   After performing the dust removal operation, image data is acquired again in the vicinity of the open aperture, and the image data in the vicinity of the open aperture is compared with the image data in the vicinity of the minimum aperture. 5. The method of eliminating or reducing an image defect in a digital camera according to claim 4, wherein a dust warning is displayed when a predetermined value is exceeded.   3. The image correction data is generated when the image data in the vicinity of the open aperture is compared with the image data in the vicinity of the minimum aperture and the change in density and size of the image defect is below a certain level. A method for eliminating or reducing image defects in the digital camera described in 1.   3. The elimination or reduction of image defects in a digital camera according to claim 1, wherein the pixels of the image sensor are divided into predetermined numbers in advance and the presence or absence of image defects is determined for each of the sections. Method.   9. The method for eliminating or reducing image defects in a digital camera according to claim 8, wherein the determination criteria for the presence or absence of image defects differ for each of the sections.

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