JP2008206013A - Dust removal device, imaging apparatus, and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To support a dust-proof member near the vibration nodes occurring in the dust-proof member without considerably increasing the size of the dust-proof member with respect to an imaging element. <P>SOLUTION: The dust removal device is provided with the dust-proof member 31 which prevents adhesion of dust to the imaging element 4, a vibration generating means 32 which allows the dust-proof member 31 to vibrate and support members 34 which support the dust-proof member 31. The dust-proof member 31 is equipped with weights 33 for moving the positions 31a and 31b of the sections of vibration occurring in the dust-proof member 31 by the vibration generating member 32 toward the outer edges of the dust-proof member 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to dust-proofing of an image sensor provided in an imaging apparatus.

  Conventionally, in a single-lens reflex digital camera with interchangeable lenses, a dust-proof member is disposed between the image sensor and the photographic optical system, thereby preventing dust and dust from adhering to the image sensor. A device that removes dust and dirt adhering to a dust-proof member by vibrating is known (see Patent Document 1).

JP 2004-64555 A

In the camera disclosed in Patent Document 1, the dust-proof member is supported in the vicinity of the vibration node so as not to inhibit the vibration generated in the dust-proof member. However, the position of the vibration node when vibration occurs in the dustproof member is not necessarily near the outer edge of the dustproof member. Therefore, in order to prevent the imaging range of the image sensor and the support position of the dust-proof member from overlapping, the dust-proof member must be sufficiently large with respect to the size of the image sensor, which may increase the size of the camera. is there.
An object of the present invention is to provide a dust removal device, an imaging device, and a camera that can support a dustproof member in the vicinity of a vibration node generated in the dustproof member without increasing the size of the dustproof member.

A dust removing apparatus according to a first aspect of the present invention includes a dust-proof member that prevents dust from adhering to an image sensor, a vibration generating unit that generates vibration in the dust-proof member, and a support member that supports the dust-proof member. . In this dust removing apparatus, the dust-proof member is provided with a weight for moving the position of the vibration node generated in the dust-proof member by the vibration generating means in the direction of the outer edge of the dust-proof member.
According to a second aspect of the present invention, in the dust removing apparatus according to the first aspect, the weight is provided outside the support position where the support member supports the dustproof member.
According to a third aspect of the present invention, in the dust removal apparatus according to the first or second aspect, the support position at which the support member supports the dustproof member is located at the outer edge of the dustproof member among the vibration nodes generated in the dustproof member. It almost coincides with the position of the nearest node.
According to a fourth aspect of the present invention, in the dust removing device according to any one of the first to third aspects, the dust-proof member bends and vibrates in a vibration mode of a predetermined order by the vibration generating means.
According to a fifth aspect of the present invention, in the dust removing apparatus according to the fourth aspect, the dust-proof member has a substantially square shape, and the vibration generating means has a plurality of parallel parallel to any two outer edges facing the dust-proof member. A bending vibration having a node is performed.
According to a sixth aspect of the present invention, in the dust removing apparatus according to the fourth aspect, the dustproof member has a substantially circular shape, and the vibration generating means performs concentric bending vibration.
A seventh aspect of the present invention is the dust removing device according to any one of the first to sixth aspects, wherein the dust-proof member and the support member are used to form a space that substantially seals the image sensor.
According to an eighth aspect of the present invention, there is provided an image pickup apparatus that outputs an image pickup signal of a subject based on an incident light beam, a dustproof member that prevents dust from adhering to the image pickup element, and a vibration generating means that generates vibration in the dustproof member. And a support member that supports the dustproof member. In this imaging apparatus, the dustproof member is provided with a weight for moving the position of the vibration node generated in the dustproof member by the vibration generating means in the direction of the outer edge of the dustproof member.
A camera according to a ninth aspect of the invention includes the imaging apparatus according to the eighth aspect and a recording control unit that records a captured image of a subject on a recording medium based on an imaging signal.

  According to the present invention, it is possible to support the dustproof member in the vicinity of the vibration node generated in the dustproof member without enlarging the dustproof member with respect to the image sensor.

  FIG. 1 is a block diagram showing the configuration of a digital camera according to an embodiment of the present invention. This digital camera includes a camera body 100 and a photographic lens 200 attached to the camera body 100. The camera body 100 includes a CPU 1, an imaging device 2, a photometric device 5, a sequence device 6, a flash device 7, a power supply unit 8, a viewfinder display device 9, a display device 10, a controller 11, a memory card 12, an image processing unit 13, and a RAM 14. ROM 15 and operation member 16 are provided.

  The CPU 1 executes various processes and controls as described below in conjunction with other components. Various functions and operations are realized in the camera body 100 by the CPU 1 performing appropriate processing and control according to the operation state of the camera body 100.

  The imaging device 2 includes a dust removal device 3 and a CCD 4 that is an imaging device. The CCD 4 outputs an imaging signal based on the subject image formed by the light beam incident from the photographing lens 200. This imaging signal is converted into image data, and then output to the image processing unit 13 via the CPU 1. The dust removing device 3 is disposed between the photographing lens 200 and the CCD 4 so as to substantially seal the CCD 4 in order to prevent dust and dirt from adhering to the CCD 4. Note that dust and dust attached to the dust removing device 3 are removed by vibration generated in the dust removing device 3 as described later.

  The photometric device 5 measures the amount of incident light from the photographing lens 200, and obtains an appropriate exposure during photographing based on the measurement result. The appropriate exposure obtained by the photometric device 5 is output to the CPU 1 and used for controlling the sequence device 6 and the like. The sequence device 6 controls a series of mechanism operations at the time of shooting such as the operation of the quick return mirror and the operation of the shutter according to the control of the CPU 1. The flash device 7 is a flash device built in the camera body 100 and its operation is controlled by the CPU 1.

  The power supply unit 8 appropriately supplies necessary electric energy to each part of the camera body 100 and the photographing lens 200. The in-finder display device 9 is provided in the finder of the camera body 100 and displays various information according to the operating state of the camera body 100. For example, information such as shutter speed, aperture value, and auto focus area is displayed on the in-finder display device 9. Thereby, it is possible to notify the user of information necessary for shooting.

  The display device 10 displays various images under the control of the CPU 1. For example, a captured image captured by the camera body 100, a setting menu screen including various setting menu items for performing various settings on the camera body 100, and the like are displayed. For example, a liquid crystal display or the like is used for the display device 10, and the display device 10 is installed at a position where the user can easily see the camera body 100.

  Under the control of the CPU 1, the controller 11 executes a writing process when recording captured image data on the memory card 12 that is a recording medium and a reading process when reading captured image data recorded on the memory card 12. The memory card 12 is a general-purpose external recording medium that can be attached to and detached from the camera body 100, and image data captured by the camera body 100 is recorded by a writing process of the controller 11.

  The image processing unit 13 performs predetermined image processing on the captured image data output from the CCD 4. For example, the image processing unit 13 performs processing for adjusting the appearance of the captured image, processing for converting the format of the image data, and the like. The image data that has been subjected to image processing by the image processing unit 13 is recorded on the memory card 12 by the controller 11.

  The RAM 14 is used as a work area when the CPU 1 executes various processes and controls. The RAM 14 includes a VRAM used when displaying an image on the display device 10. The ROM 15 stores programs and data used when the CPU 1 executes various processes and controls. The operation member 16 includes various operation switches. Various processes and controls are executed in the CPU 1 in accordance with the operation content input by the user using the operation member 16.

  Next, details of the dust removing device 3 will be described with reference to the drawings. FIG. 2 is a plan view and a cross-sectional view of the dust-proof member 31, the vibration member 32, and the weight 33 that constitute the dust removing device 3. 2A is a plan view of the dust-proof member 31, the vibration member 32, and the weight 33 when viewed from the direction of the photographing lens 200 in the camera body 100. FIG. On the other hand, the cross-sectional view of (b) shows a cross section of the dust-proof member 31, the vibration member 32, and the weight 33 when cut along the center line AA in the plan view of (a). As shown in this figure, the dustproof member 31 has a substantially square shape. The pair of upper and lower vibrating members 32 and the pair of left and right weights 33 are respectively attached to the front side surface of the dust-proof member 31 (that is, the surface opposite to the side where the CCD 4 is present).

  The dustproof member 31 is used to prevent dust and dirt from adhering to the CCD 4 in FIG. 1 and is disposed so as to cover the CCD 4. The dust-proof member 31 is provided on the optical path of subject light incident on the CCD 4 via the photographing lens 200, and is composed of a transparent material such as glass.

  The vibration member 32 is composed of a piezoelectric element using piezoelectric ceramics or the like that generates a piezoelectric effect. As a material of this piezoelectric ceramic, for example, PZT (lead zirconate titanate) is known. When an electric signal is applied to the vibration member 32, the vibration member 32 is in a direction perpendicular to the optical axis of the photographing lens 200 (that is, a direction perpendicular to the imaging surface of the CCD 4), that is, FIG. In (a), the expansion and contraction motion is repeated periodically in the radial direction parallel to the paper surface.

  When the vibration member 32 extends in a direction perpendicular to the optical axis of the photographic lens 200, it will extend in the same direction on the front side of the dust-proof member 31, that is, the surface on which the vibration member 32 is attached, according to the movement. The power to be generated. Then, the dustproof member 31 is deformed so as to swell in the front side direction. The cross-sectional view of FIG. 2B shows the state at that time. On the other hand, when the vibration member 32 contracts in a direction perpendicular to the optical axis, a force for contracting in the same direction is generated on the front side of the dust-proof member 31 according to the movement. Then, contrary to what is shown in the sectional view of FIG. 2B, the dustproof member 31 is deformed so as to swell in the direction of the back side.

  In the dustproof member 31, the bending operation as described above is periodically repeated according to the expansion / contraction motion of the vibration member 32. As a result, bending vibration occurs in the dustproof member 31. By this bending vibration, dust and dust attached to the dust-proof member 31 can be removed.

  The broken lines indicated by reference numerals 31a and 31b in FIG. 2 indicate the positions of the nodes of the bending vibration generated in the dustproof member 31 as described above. The node 31a and the node 31b are parallel to the two outer edge portions facing left and right in the dustproof member 31. The dust-proof member 31 performs a bending motion having these nodes 31 a and 31 b by the vibration member 32.

  When attaching the dustproof member 31 so as to cover the CCD 4 in the camera body 100, the dustproof member 31 is supported in the vicinity of the nodes 31a and 31b so as not to inhibit the bending vibration as described above. There is a need. Therefore, the range in which the CCD 4 can be installed is the range shown in the shaded area in FIG. 2A inside the support point, that is, inside the nodes 31a and 31b.

  The weight 33 is provided in the dust-proof member 31 in order to move the position of the vibration node generated in the dust-proof member 31 by the vibration member 32 in the direction of the outer edge portion of the dust-proof member 31. As the material of the weight 33, for example, a metal having a specific gravity higher than that of the glass used for the dustproof member 31 can be used. Or you may integrate these by making the weight 33 and the dust-proof member 31 into the same material.

  In the case where the weight 33 is provided on the dust-proof member 31 and the case where the weight 33 is not provided, the position of the node of the vibration generated in the dust-proof member 31 changes as follows. FIG. 3 shows how the dust-proof member 31 bends and vibrates when the weight 33 is not provided. 3A is a plan view of the dust-proof member 31 and the vibration member 32 when viewed from the direction of the taking lens 200 in the camera body 100. FIG. On the other hand, the cross-sectional view of (b) shows a cross section of the dust-proof member 31 and the vibration member 32 when cut along the center line BB in the plan view of (a). In FIG. 3, the vibration nodes 31 a and 31 b are located more inside in the dust-proof member 31 than in FIG. 2. Therefore, it can be seen that the shaded area where the CCD 4 can be installed is narrower than in FIG.

  As described above, when the weight 33 is not provided on the dust-proof member 31, the position of the node of vibration generated in the dust-proof member 31 is located on the inner side as compared with the case where the weight 33 is provided on the dust-proof member 31. . That is, by providing the weight 33 on the dust-proof member 31, the position of the vibration node generated in the dust-proof member 31 is moved to the outer side, that is, toward the outer edge of the dust-proof member 31 as compared with the case where the weight 33 is not provided. be able to. As a result, the area where the CCD 4 can be installed can be expanded.

  FIG. 4 shows a plan view and a cross-sectional view of the imaging device 2 in which the dust removing device 3 having the dustproof member 31, the vibration member 32, and the weight 33 described above and the CCD 4 are installed. 4, a plan view of (a) shows a planar shape of the imaging device 2 when viewed from the direction of the photographing lens 200 in the camera body 100. FIG. The cross-sectional view of (b) shows a cross-section of the imaging device 2 when cut along the center line CC in the plan view of (a).

  The dust removing device 3 further includes a support member 34 and a sealing member 35 in addition to the dustproof member 31, the vibration member 32 and the weight 33. The support member 34 has a rectangular shape with a constant width, and is disposed on the substrate 41 on which the CCD 4 is disposed along the outer edge of the dust-proof member 31. The support member 34 supports the dustproof member 31.

  The sealing member 35 fixes the dust-proof member 31 on the support member 34 by sealing between the dust-proof member 31 and the support member 34. With such a support structure and a sealing structure, a space for substantially sealing the CCD 4 is formed between the substrate 41 and the dust removing device 3 using the dustproof member 31 and the support member 34.

  As shown in FIG. 4, the support position where the support member 34 supports the dust-proof member 31 is substantially coincident with the positions of the nodes 31a and 31b. Thereby, the dust-proof member 31 can be supported by the support member 34 so as not to inhibit the bending vibration generated in the dust-proof member 31. When the dustproof member 31 vibrates in a higher-order vibration mode, a greater number of vibration nodes may occur than shown in FIG. In that case, it is preferable that the dust-proof member 31 is supported by the support member 34 so as to substantially coincide with the position of the node closest to the outer edge of the dust-proof member 31 among those vibration nodes. In this way, similarly, the dust-proof member 31 can be supported by the support member 34 without hindering the bending vibration generated in the vibration member 31.

  The weight 33 is provided in a portion of the dust-proof member 31 outside the support position where the support member 34 supports the dust-proof member 31. That is, the weight 33 is located outside the imaging surface of the CCD 4. Therefore, the incident light beam from the photographing lens 200 is not blocked by the weight 33 and passes through the transparent dustproof member 31 and reaches the CCD 4. As a result, the subject image is formed on the CCD 4 without missing, and the image pickup signal is output from the CCD 4. Furthermore, by arranging the weight 33 in this way, the position of the vibration node generated in the dust-proof member 31 can be efficiently moved toward the outer edge of the dust-proof member 31.

  By the way, when the dust-proof member 31, the vibration member 32, and the weight 33 are considered as an integrated vibration body, the vibration body has a specific resonance frequency corresponding to the material, shape, and the like. For example, the material of the dust-proof member 31 is glass, and the size thereof is 40 mm in width (longitudinal direction), 28 mm in length (short direction), and 0.4 mm in thickness. The material of the vibration member 32 is PZT, and the size thereof is 10 mm in width (longitudinal direction), 3 mm in length (short direction), and 0.5 mm in thickness. The weight 33 is made of iron, and the shape thereof is 4 mm wide and 0.5 mm thick. When the resonance frequency at this time was calculated, a result of about 1 kHz was obtained. Further, when the positions of the nodes 31a and 31b at this time are calculated, when the weight 33 is provided on the dust-proof member 31, the weight 33 is positioned about 6 mm from the left and right ends of the dust-proof member 31, respectively. When not provided, the result that it was located in about 12 mm from the left and right ends of the dust-proof member 31 was obtained.

  When an AC electric signal having the same frequency as the resonance frequency as described above is applied to the vibration member 32, the vibration body bends and vibrates in a resonance state, so that the amplitude is maximized. Therefore, when removing dust and dirt adhering to the dustproof member 31 by vibration, it is preferable to apply an AC electrical signal having the same frequency as the resonance frequency to the vibration member 32 so that the effect is maximized. Note that the exact resonance frequency of the vibrating body may be unknown due to variations in dimensions, mass, etc. during manufacture, mounting errors, etc., so the AC electrical signal applied to the vibrating member 32 is changed within a predetermined range. Also good.

  In the embodiment described above, the dustproof member 31 has a substantially square shape, but the dustproof member 31 may have another shape. One example will be described with reference to FIG. FIG. 5 is a plan view and a cross-sectional view of a dust-proof member 31 having a substantially circular disk shape, and a vibrating member 32 and a weight 33 having a ring-like shape that matches the shape of the dust-proof member 31. In FIG. 5, the plan view of (a) shows the planar shape of the dust-proof member 31, the vibration member 32, and the weight 33 when viewed from the direction of the photographing lens 200 in the camera body 100. On the other hand, in the cross-sectional views of (b) and (c), cross sections of the dust-proof member 31, the vibration member 32, and the weight 33 when cut along the center line DD in the plan view of (a) are respectively shown. In the cross-sectional view of (b), a cross section when the dustproof member 31 is not vibrating is shown. Moreover, in the sectional view of (c), a vibration is generated in the dust-proof member 31 by the vibration member 32, and a cross-section when the dust-proof member 31 is deformed so as to swell in the front side direction is shown.

  In FIG. 5, the vibration member 32 is attached to the back side of the dust-proof member 31, and the weight 33 is attached to the front side of the dust-proof member 31. When an electric signal is applied to the vibration member 32, the vibration member 32 periodically repeats expansion and contraction in the direction perpendicular to the optical axis in accordance with the electric signal, as in FIG. The dustproof member 31 is deformed by the expansion and contraction motion, and performs concentric bending vibration. At this time, a circular vibration node is generated in the dust-proof member 31.

  Circular vibration nodes generated in the dust-proof member 31 are positioned as indicated by reference numerals 31a and 31b in the cross-sectional view of FIG. The position of the vibration node changes as follows depending on whether the weight 33 is provided on the dust-proof member 31 or not. FIG. 6 is a plan view and a cross-sectional view of the dust-proof member 31, the vibration member 32, and the weight 33 when the dust-proof member 31 is flexibly vibrated when the weight 33 is not provided. Similarly to FIG. 5, FIG. 6A is a plan view of the dust-proof member 31, the vibration member 32, and the weight 33 when viewed from the direction of the photographing lens 200 in the camera body 100. Yes. On the other hand, in the cross-sectional views of (b) and (c), cross sections of the dust-proof member 31, the vibration member 32, and the weight 33 when cut along the center line EE in the plan view of (a) are respectively shown. In the cross-sectional view of (b), a cross section when the dustproof member 31 is not vibrating is shown. Moreover, in the sectional view of (c), a vibration is generated in the dust-proof member 31 by the vibration member 32, and a cross-section when the dust-proof member 31 is deformed so as to swell in the front side direction is shown.

  When the diameter of the vibration node when the weight 33 is provided on the dustproof member 31 is R1, this diameter R1 is represented as the distance between the vibration nodes 31a-31b in the cross-sectional view of FIG. Similarly, when the diameter of the vibration node when the weight 33 is not provided on the dust-proof member 31 is R2, this diameter R2 is expressed as the distance between the vibration nodes 31a-31b in the cross-sectional view of FIG. Is done. From these sectional views, it can be seen that the diameter R1 of the vibration node when the weight 33 is provided on the dust-proof member 31 is larger than the diameter R2 when the weight 33 is not provided.

  As described above, by providing the weight 33 on the dust-proof member 31, the diameter of the circular vibration node generated in the dust-proof member 31 can be increased compared to the case where the weight 33 is not provided. Therefore, the position of the vibration node can be moved further outward, that is, in the direction of the outer edge of the dust-proof member 31. As a result, as in the case of FIG. 2, the area where the CCD 4 can be installed can be expanded.

According to the embodiment described above, the following operational effects are obtained.
(1) The dust-proof member 31 is provided with a weight 33 for moving the position of a vibration node generated in the dust-proof member 31 by the vibration member 32 in the direction of the outer edge of the dust-proof member 31. Since it did in this way, the dust-proof member 31 can be supported in the vicinity of the node of the vibration which arises in the dust-proof member 31 without making the dust-proof member 31 very large with respect to CCD4.

(2) The weight 33 is provided on the dust-proof member 31 outside the support position where the support member 34 supports the dust-proof member 31. Since this is done, it is possible to prevent the incident light beam from being blocked by the weight 33 and to form an image on the CCD 4 without missing the subject image. Furthermore, the position of the vibration node generated in the dustproof member 31 can be efficiently moved in the direction of the outer edge of the dustproof member 31.

(3) The support position at which the support member 34 supports the dust-proof member 31 is substantially coincident with the position of the node closest to the outer edge of the dust-proof member 31 among the vibration nodes generated in the dust-proof member 31. Since it did in this way, the dust-proof member 31 can be supported by the support member 34 so that the bending vibration produced in the dust-proof member 31 may not be inhibited.

(4) The dust-proof member 31 has a substantially square shape, and the vibration member 32 performs flexural vibration having a plurality of nodes parallel to any two outer edges facing each other in the dust-proof member 31. Alternatively, the dustproof member 31 has a substantially circular shape, and the vibration member 32 performs concentric bending vibration. Since it did in this way, the shape of the dust-proof member 31 can be determined according to the shape of CCD4. Furthermore, according to the shape of the dustproof member 31, the dustproof member 31 can be vibrated efficiently.

(5) The dust-proof member 31 and the support member 34 are used to form a space that substantially seals the CCD 4. Since this is done, it is possible to prevent dust and dirt from adhering to the CCD 4 when the photographing lens 200 is detached from the camera body 100.

  In the embodiment described above, the example in which the vibration generated in the dust-proof member 31 is the bending vibration of the primary mode has been described, but the present invention is not limited to this content. That is, the dust-proof member 31 can be bent and vibrated in an arbitrary order of vibration mode.

  In the embodiment described above, the digital camera having the image sensor has been described as an example. However, the present invention can also be applied to a digital video camera.

  The embodiment and various modifications described above are merely examples, and the present invention is not limited to these contents as long as the features of the invention are not impaired.

It is a block diagram which shows the structure of the digital camera by one Embodiment of this invention. It is the top view and sectional drawing of a dustproof member, a vibration member, and a weight which have a substantially square shape. It is the top view and sectional drawing of a dustproof member and a vibration member which have a substantially square shape in which a weight is not provided. It is the top view and sectional drawing of an imaging device with which a dust removal device and CCD were installed. It is the top view and sectional drawing of a dustproof member, a vibration member, and a weight which have a substantially circular shape. It is the top view and sectional drawing of a dustproof member and a vibration member which have a substantially circular shape where a weight is not provided.

Explanation of symbols

1: CPU 2: Imaging device 3: Dust removal device 4: CCD
5: Photometry device 6: Sequence device 7: Flash device 8: Power supply unit 9: Display device in viewfinder 10: Display device 11: Controller 12: Memory card 13: Image processing unit 14: RAM
15: ROM 16: Operation member 100: Camera body 200: Shooting lens

Claims (9)

A dust-proof member for preventing dust from adhering to the image sensor;
Vibration generating means for generating vibration in the dustproof member;
A support member for supporting the dust-proof member,
A dust removing device, wherein the dust-proof member is provided with a weight for moving the position of a vibration node generated in the dust-proof member by the vibration generating means in the direction of the outer edge of the dust-proof member. The dust removal apparatus according to claim 1,
The dust removing apparatus, wherein the weight is provided outside a support position where the support member supports the dustproof member. The dust removal apparatus according to claim 1 or 2,
The dust removal is characterized in that the support position at which the support member supports the dust-proof member substantially coincides with the position of the node closest to the outer edge of the dust-proof member among the vibration nodes generated in the dust-proof member. apparatus. In the dust removal apparatus as described in any one of Claims 1-3,
The dust removing apparatus, wherein the dust-proof member is flexibly vibrated in a vibration mode of a predetermined order by the vibration generating means. The dust removal apparatus according to claim 4,
The dust removing device has a substantially square shape, and the vibration generating means performs flexural vibration having a plurality of nodes parallel to any two outer edges facing each other in the dust preventing member. . The dust removal apparatus according to claim 4,
The dust removing apparatus, wherein the dust-proof member has a substantially circular shape, and the vibration generating means performs concentric bending vibration. In the dust removal apparatus as described in any one of Claims 1-6,
A dust removing device, wherein the dust-proof member and the support member are used to form a space that substantially seals the imaging device. An image sensor that outputs an imaging signal of a subject based on an incident light beam;
A dust-proof member for preventing dust from adhering to the image sensor;
Vibration generating means for generating vibration in the dustproof member;
A support member for supporting the dust-proof member,
The imaging apparatus, wherein the dust-proof member is provided with a weight for moving the position of a vibration node generated in the dust-proof member by the vibration generating means in the direction of the outer edge of the dust-proof member. An imaging device according to claim 8,
A camera comprising recording control means for recording a captured image of the subject on a recording medium based on the imaging signal.

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