CN111856770B - Polarization imaging device - Google Patents
Polarization imaging device Download PDFInfo
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- CN111856770B CN111856770B CN201910346396.8A CN201910346396A CN111856770B CN 111856770 B CN111856770 B CN 111856770B CN 201910346396 A CN201910346396 A CN 201910346396A CN 111856770 B CN111856770 B CN 111856770B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
- G02B27/288—Filters employing polarising elements, e.g. Lyot or Solc filters
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
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- G02B3/0037—Arrays characterized by the distribution or form of lenses
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/50—Constructional details
- H04N23/55—Optical parts specially adapted for electronic image sensors; Mounting thereof
Abstract
The invention provides a polarization imaging device, which comprises a lens and a focusing light field camera body with a micro lens array. The device is characterized by further comprising a four-quadrant polarization modulation array optical filter and an aperture inserting sheet, wherein the light through hole of the aperture is rectangular. The shape and the focal length of each micro lens unit in the micro lens array are the same; the micro lens units are sparsely arranged in a rectangular shape. The aperture insert is positioned at the position of the lens diaphragm, and one or more four-quadrant polarization modulation array filters are fixed on the aperture insert. By adjusting the aperture inserting sheet, any one of the four-quadrant polarization modulation array optical filters fixed on the aperture inserting sheet can be positioned on the optical axis of the lens, and the plane of the four-quadrant polarization modulation array optical filter is perpendicular to the optical axis of the lens. The invention has simple structure, small volume and convenient use, and can realize real-time and high-resolution linear polarization imaging or full polarization imaging.
Description
Technical Field
The invention relates to the technical field of image data generation and processing, in particular to a real-time high-resolution polarization imaging device, and particularly relates to a polarization imaging device capable of flexibly switching between a linear polarization imaging mode and a full polarization imaging mode.
Background
The imaging device used to obtain polarization information of the optical radiation of the object scene is called a polarization camera. The polarization properties of light are typically described precisely by the Stokes vector (S), which has four components, written as S ═ S0，S1，S2，S3]See, document 1: qu's basic theory of electromagnetism in advanced optics course-optics [ M]Beijing: scientific press, 2009, 42-43. When the polarization camera can only acquire the first three components (namely S) in the Stokes vector of the target light radiation0，S1And S2) When we call it a linear polarization camera, we call it a full polarization camera when the polarization camera can acquire all four components of the Stokes vector S of the target light radiation. The polarization camera can be further divided into a real-time polarization camera and a non-real-time polarization camera according to the difference of the real-time performance of the acquired images. In consideration of many practical application occasions, the shot objectThe real-time polarization camera is an important research direction for people because the real-time polarization camera is not static and results obtained by a non-real-time camera can generate 'artifacts' to obviously reduce the imaging effect.
In addition, although a full-polarization camera can obtain all polarization information of target light radiation, the accuracy and stability of the measurement result are generally worse than those of a linear polarization camera due to more unknown variables to be measured. If it is known in advance that the shooting scene does not inherently contain the circular polarization component S3The linear polarization camera is used, so that the cost is lower, and the measurement result precision is higher. This requires that: the polarization camera is preferably capable of flexibly switching between a "linear polarization imaging" mode and a "full polarization imaging" mode according to the actual application. There is currently only one type of real-time polarization camera that can have this potential: i.e. a polarization camera based on a light field imaging architecture.
Polarization cameras based on light field imaging structures are also classified into two categories, the first category being polarization cameras based on first generation light field imaging structures, see document 2: ren Ng, digital Light Field Photography [ D ]. San Francisco: Stanford University,2006, and document 3: the invention relates to a national patent application, in particular to a snapshot type compact noise immune light field imaging full-polarization spectrum detection device and a method, and the application number is as follows: 201710097593.1. the second category is polarization cameras based on Focused light field imaging structures (i.e., "Focused Plenoptic cameras"), see document 4: todor Georgiev, Andrew lumsdaine. focused Plenoptic Camera and Rendering [ J ]. Journal of Electronic Imaging,2010,19(2),021106, and document 5: todor Georgiev, Andrew Lumsdaine.methods and Apparatus for Rich Image Capture with Focused Plenoptic Cameras [ P ]. US Patent, US-8345144B1,2013. . The imaging result resolution of the first type of polarization camera is very low, limited by the principle of the first generation of light field imaging structure. Document 3 achieves full-polarization detection of targets, belonging to a full-polarization camera, but does not have the capability of flexibly switching between a "linear polarization imaging" mode and a "full-polarization imaging" mode.
Todor Georgiev et al have studied polarization cameras based on focused light field imaging structures and applied us patent in 2013, such polarization cameras belonging to the second category mentioned above. The system designed by Todor Georgiev suffers from the following drawbacks:
1) the polarization imaging function is single.
The polarization modulation element that Todor Georgiev places in the camera lens can only produce linearly polarized light. The structure only has the potential of linear polarization measurement, cannot realize full polarization measurement, and also does not have the capability of flexibly switching between a linear polarization imaging mode and a full polarization imaging mode.
2) Only one specific object plane can be imaged.
When the distance between the shot object and the imaging system deviates from the preset value, the mosaic effect of the image can occur, and the imaging quality is poor.
3) The resolution of the output polarized image is low.
The elements used by such imaging systems to perform polarization modulation of light are tiled by four small optical elements, the seams of which produce blurred projections in the image that interfere with imaging. To address this problem, Todor Georgiev adopts a method of reducing the secondary imaging magnification of the microlens unit below 1/5, which can significantly reduce the blurred projection area of the polarization modulation element seam on the image, but the output image resolution is still 1/30 of the original image resolution.
In summary, a polarization imaging device capable of simultaneously realizing small structure, real-time performance and high resolution is lacking under the prior art, and especially a polarization imaging device capable of flexibly switching between a "linear polarization imaging" mode and a "full polarization imaging" mode according to the requirement of an actual shooting scene is lacking.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at a shot target at any distance, the polarization imaging device with strong real-time performance and high resolution is provided, and the convenient switching between a linear polarization imaging mode and a full polarization imaging mode can be realized according to the polarization characteristic of the shot target.
The technical scheme of the invention is as follows:
a polarized imaging apparatus includes a lens, a focused light field camera body with a microlens array. It is characterized in that the preparation method is characterized in that,
the light through hole of the diaphragm is rectangular;
in addition, the device also comprises a four-quadrant polarization modulation array optical filter and an aperture insert;
wherein, in the microlens array, the shape and the focal length of each microlens unit are the same; the micro lens units are sparsely arranged in a rectangular shape; gaps between adjacent microlens units are light-tight;
if the distance between the plane where all the microlens units in the microlens array are located and the imaging surface of the lens is a, and the distance between the plane where all the microlens units in the microlens array are located and the imaging photosensitive surface of the focused light field camera body is b, then:
the four-quadrant polarization modulation array optical filter meets the following conditions:
assuming that a beam of light passes through the four-quadrant polarization modulation array optical filter along the direction opposite to the incident light of the imaging equipment, the polarization states of the emergent light of the four quadrants respectively correspond to four points on the Bojia sphere, and the four points are P1,P2,P3,P4. The following two requirements are simultaneously satisfied: first, P1,P2,P3,P4The four points are all positioned on the surface of the Bojia ball; second, P1,P2,P3,P4Four points not being coplanar, or P1,P2,P3,P4All located on the equator line of the Poincare sphere, but at most two points may coincide.
The aperture insert is positioned at the position of the lens diaphragm, and one or more four-quadrant polarization modulation array filters are fixed on the aperture insert. By adjusting the aperture inserting sheet, any one of the four-quadrant polarization modulation array optical filters fixed on the aperture inserting sheet can be positioned on the optical axis of the lens, and the plane of the four-quadrant polarization modulation array optical filter is perpendicular to the optical axis of the lens.
Further, the clear aperture of the rectangular aperture can be adjusted.
The invention has the advantages of
Aiming at the defects in the prior art, the invention provides a real-time polarization imaging device which has the following specific beneficial effects:
1) the device has simple structure, small volume and convenient use, and can realize real-time and high-resolution linear polarization imaging or full polarization imaging.
2) Due to the sparse arrangement design of the micro-lens units, the area of fuzzy projection generated by seams on the four-quadrant polarization modulation array filter in the image is reduced, and the resolution of the output image is improved.
3) Due to the rectangular aperture with the adjustable aperture, when the distance between a shot object and the imaging device is changed or the angle of an imaging field is changed by using the zoom lens, the device can obtain a high-definition polarization imaging result.
4) Due to the adjustable design of the aperture inserting sheet, different four-quadrant polarization modulation array optical filters are arranged on the inserting sheet, the linear polarization imaging mode and the full polarization imaging mode can be flexibly switched according to the polarization characteristic of the target radiation light of the actual shooting scene, and accordingly the aperture inserting sheet has strong environment target adaptability.
Drawings
FIG. 1 is a schematic diagram of the apparatus of the present invention;
FIG. 2 is a schematic view of a microlens array according to the present invention;
FIG. 3 is a schematic diagram of a microlens array according to the present invention;
FIG. 4 is a schematic diagram of an implementation of a rectangular aperture in accordance with the present invention;
FIG. 5 is a schematic diagram of five implementations of a four-quadrant polarization modulation array filter according to the present invention;
FIG. 6 is a diagram of a light beam passing through a four-quadrant polarization modulation array filter;
FIG. 7 is a schematic diagram showing the distribution of the polarization states of the four outgoing beams in FIG. 6 allowed on a Poincar sphere;
FIG. 8 is a schematic diagram of three implementations of an aperture insert according to the present invention;
fig. 9 is a schematic diagram of three implementations of a lens according to the present invention;
fig. 10 is a schematic diagram illustrating the principle of image mosaic effect.
Detailed Description
The device is realized on the basis of a focusing light field camera structure. The prior literature generally recognizes: "focused light field camera" refers to an imaging system that includes a lens, a microlens array, and an imaging photosensitive element. Among them, the Microlens Array, which is known by the english name of Microlens Array, is a flat plate-like optical element having many fine Microlens units arranged on the surface thereof. In the present invention, to distinguish from the above-described concept of "focused light field camera", we refer to a portion of the focused light field camera that does not include a lens as a "focused light field camera body".
Referring to fig. 1, the structural features of the known focused light field camera are as follows: a micro lens array 3 is arranged between the lens 1 and an imaging chip 9 of the focusing light field camera body 2, and the micro lens array 3 is positioned in front of or behind an imaging surface 8 of the lens 1, and is positioned behind in the figure. The microlens array 3 performs secondary imaging on the imaging surface 8 of the lens 1: when the microlens array 3 is positioned in front of the imaging surface 8, the imaging surface 8 is a virtual imaging surface; when the microlens array 3 is located behind the imaging surface 8, the imaging surface 8 is a real imaging surface. The imaging chip 9 is located behind the microlens array 3 (i.e. away from the lens 1) and is used for receiving the secondary imaging result of the microlens array 3.
As shown in fig. 1, compared with the existing focused light field camera, the present invention further includes a rectangular aperture 4, a four-quadrant polarization modulation array filter 5 and an aperture insert 6; the four-quadrant polarization modulation array optical filter 5 is fixed on the aperture insert sheet 6, and the aperture insert sheet 6 is positioned at the lens diaphragm.
Light radiation 7 emitted by a shot object enters the lens 1 along the direction indicated by an arrow in the figure, then sequentially passes through the rectangular aperture 4 and the four-quadrant polarization modulation array filter 5, is focused and imaged on an imaging surface 8, then further diverges and performs secondary imaging through the micro-lens array 3, and an imaging result falls on an imaging chip 9 in the focusing light field camera body 2 and is finally output in the form of an image. It should be noted that: the order of the light radiation 7 passing through the rectangular aperture 4 and the four-quadrant polarization modulation array filter 5 does not need to be specified, and the light radiation can also pass through the four-quadrant polarization modulation array filter 5 first and then pass through the rectangular aperture 4.
In fig. 1, the rectangular aperture 4 and the four-quadrant polarization modulation array filter 5 both need to be placed as close to the aperture surface of the lens 1 as possible, and the plane where the rectangular aperture 4 and the four-quadrant polarization modulation array filter 5 are located needs to be parallel to the aperture surface of the lens 1. For all lenses, incident light of a shot scene in any direction in the field of view of the lens needs to pass through a narrowest traffic critical path, the plane where the traffic critical path is located is the diaphragm surface of the lens, and the diaphragm surface of the lens is perpendicular to the optical axis of the lens. The invention can obtain the best imaging effect only if the rectangular aperture 4 and the four-quadrant polarization modulation array filter 5 are arranged close to the diaphragm surface of the lens 1 as much as possible.
Fig. 2 is a schematic diagram illustrating a sparse arrangement of microlenses in a rectangular shape according to the microlens array of the present invention. In order to realize three-dimensional imaging, the space utilization rate of a lens imaging surface needs to be improved in the existing focusing light field camera, the arrangement mode between the microlens units 10 in the microlens array is compact, that is, the adjacent microlens units 10 are in seamless connection, and meanwhile, the shapes and focal lengths of the microlens units 10 are usually different, and the different purposes are to improve the depth of field of imaging. The microlens units 10 provided by the present invention have the same shape and focal length, the arrangement of the microlens units 10 is sparse according to a rectangle, and the gaps between adjacent microlens units 10 are opaque. Fig. 2 shows the way in which the microlenses are sparsely arranged in a rectangular shape: the centers of the microlens units 10 are arranged at equal intervals in the horizontal direction, D in the drawing1The arrangement intervals along the vertical direction are also equal, and D is shown in the figure2，D1And D2Are larger than the diameter d of the microlens unit 10. In addition, to secure a region other than all the microlens regions on the surface of the microlens array where the microlens unit 10 is locatedThe area is opaque, and black chromium plating treatment or black light absorption velvet planting can be carried out on the area. Of course, D1And D2The values of (a) may be equal or unequal, as long as the arrangement manner between the microlens units 10 makes the blurred area of the seam of the four-quadrant polarization modulation array filter 5 on the imaging plane as small as possible.
Fig. 3 is a schematic structural diagram of a microlens array according to the present invention, in which the plane of all the microlens units 10 in the microlens array 3 is parallel to the plane of the imaging chip 9, and there is a gap between all the microlens units 10, and the gap area is covered by a black chrome film 11. On the other side of the microlens array 3 (i.e., the side without the microlens unit 10), an antireflection film 12 is coated for the purpose of suppressing light reflected from the black chrome film 11 in the microlens array 3 from entering the microlens unit 10 through secondary reflection, thereby avoiding the problem of image ghosting as much as possible.
Fig. 4 is a schematic diagram of an implementation of a rectangular aperture according to the present invention. The reason why the rectangular aperture is adopted in the present invention is: the point spread function of incident light after passing through the rectangular aperture is rectangular, and then the seamless close arrangement of all light beams can be realized only by the sparse arrangement microlens array according to the rectangle to the imaging plane, at the moment, the lost pixel on the imaging chip in the focusing light field camera body is the least, so that the imaging chip can be utilized fully, and the resolution of the finally output image is the highest. The through hole 13 in the middle of the rectangular diaphragm is rectangular, and as shown in fig. 4, the length of one right-angle side of the rectangular through hole 13 is C1The length of the other right-angle side is C2And C is1/C2＝D1/D2Or C1/C2＝D2/D1. In addition, the aperture of the through hole 13 of the rectangular diaphragm can be adjusted, and the length-width ratio of the rectangular through hole 13 needs to be ensured to be unchanged in the adjusting process. As shown in fig. 4, the aperture of the through hole 13 gradually decreases from left to right. Under the best use state, two right-angle sides of the rectangular through hole are respectively parallel to two right-angle sides of the camera photosensitive chip, the center of the through hole 13 of the rectangular aperture is always positioned on the optical axis of the lens, and the plane of the through hole 13 is verticalAt the optical axis of the lens. The aperture-adjustable rectangular aperture can be formed by mutually stacking two L-shaped sheets or 4I-shaped sheets, and the L-shaped or I-shaped sheets can simultaneously move towards or away from each other relative to the center of the optical axis.
Fig. 5 is a schematic diagram of five implementation manners of the four-quadrant polarization modulation array filter according to the present invention. Among them, fig. 5(a) can only realize the linear polarization imaging mode; fig. 5(B) to 5(E) realize the full-polarization imaging mode. Fig. 5(a) is a four-quadrant polarization modulation array filter simply composed of four-quadrant polarizers 15, in the drawing, the four-quadrant polarizers 15 are composed of four rectangular polarizers with the same size and material, different texture stripes of each quadrant represent different polarization directions, and the four polarizers are closely arranged to form a "field" shape. Fig. 5(B) to 5(E) show the case where the four-quadrant polarization modulation array filter is composed of a four-quadrant wave plate 14 and a four-quadrant polarizing plate 15 which are sequentially stacked. The four-quadrant wave plate 14 includes 1,2, 3, or 4 rectangular wave plates with the same size and material, for example, the four-quadrant wave plate 14 of fig. 5(B) includes 1 rectangular wave plate, the four-quadrant wave plate 14 of fig. 5(C) includes 2 rectangular wave plates, the four-quadrant wave plate 14 of fig. 5(D) includes 3 rectangular wave plates, the four-quadrant wave plate 14 of fig. 5(E) includes 4 rectangular wave plates, and the different areas of the rectangular wave plates in fig. 5(B) to 5(E) represent different retardation characteristics. If the total number of the rectangular wave plates is less than four, any one to three quadrants are left empty, as shown by the dotted lines in FIG. 5; the four-quadrant polarizing film 15 is composed of four rectangular polarizing films with the same size and material, different texture stripes of each quadrant represent different polarization directions, and the four polarizing films are closely arranged to form a field shape. The best implementation, whether it be the four-quadrant wave plate 14 or the four-quadrant polarizer 15, is made up of several square wave plates or square polarizers of the same material and size that are closely spliced together.
Fig. 6 shows a case where a beam of light passes through the four-quadrant polarizer 15 and the four-quadrant wave plate 14 in this order. The emergent light of each quadrant of the four-quadrant polarization modulation array optical filter is I1,I2,I3,I4. In which I1,I2,I3,I4Different gray scales on the light path represent different polarization states, and the polarization state of emergent light corresponds to four points P on the Poincar sphere1,P2,P3,P4The description is given. P is1,P2,P3,P4The allowed distribution pattern on the Ponga ball 16 is shown in FIG. 7: p is1,P2,P3,P4The surfaces of the Ponga ball 16 are required, which are either not coplanar, as shown in FIG. 7 (A); or may be located entirely on the equator 17 as shown in fig. 7(B), allowing a maximum of two points to coincide. If the polarization characteristic setting of the four-quadrant polarization modulation array filter satisfies P1,P2,P3,P4At least three of which are located on the equator 17 and do not coincide with each other, the device according to the invention can now perform the function of "linear polarization imaging", and otherwise perform the function of "full polarization imaging". The situation shown in fig. 6 is the result of light rays obtained through fig. 5(B) to 5 (E). When light passes through the four-quadrant polarization modulation array filter shown in fig. 5(a), the above constraint must be satisfied, so that the linear polarization imaging mode can be realized.
Fig. 8 is schematic diagrams of three implementation manners of the aperture insert according to the present invention, which are respectively: a replaceable diaphragm insert 6-1, a push-pull diaphragm insert 6-2 and a runner diaphragm insert 6-3. The shape and the size of the insert are different corresponding to each implementation mode, wherein only one four-quadrant polarization modulation array optical filter 5 is installed in the replaceable iris insert 6-1, and when the replaceable iris insert is used, the four-quadrant polarization modulation array optical filter 5 is replaced by replacing the replaceable iris insert 6-1 inserted into a lens, so that the function of switching between the two functions of a linear polarization imaging mode and a full polarization imaging mode is achieved. The push-pull type aperture inserting sheet 6-2 and the rotary wheel type aperture inserting sheet 6-3 are provided with two or more than two four-quadrant polarization modulation array optical filters 5, and the structural design of the push-pull type aperture inserting sheet and the rotary wheel type aperture inserting sheet ensures that any one four-quadrant polarization modulation array optical filter 5 can be easily adjusted to a proper position and can be kept fixed. The four-quadrant wave plate in the four-quadrant polarization modulation array filter 5 faces the side of the object to be shot, and the four-quadrant polarizing plate faces the side of the focusing light field camera body.
Fig. 9 is schematic diagrams of three implementation manners of the lens according to the present invention. The lens 1 in fig. 9(a) has a replaceable diaphragm insert 6-1. In the drawing, 18 is a locking knob of the replaceable diaphragm insert 6-1 for locking the replaceable diaphragm insert 6-1 to thereby lock the array filter 5 in a fixed position, and 19 is a lifting knob of the replaceable diaphragm insert 6-1 for easy insertion and removal from the side of the lens. In addition, in order to enhance the sealing performance of the lens, the bottom of the pull handle 19 is widened, and a rubber gasket is added to the contact area with the lens, thereby preventing dust from entering the inside of the lens. The reference numeral 20 denotes a rotary ring for adjusting the aperture of the rectangular aperture, and the aperture of the rectangular aperture can be adjusted by rotating the rotary ring 20. The lens 1 in fig. 9(B) has a push-pull type aperture insertion sheet 6-2, which is a schematic view from the rear of the lens viewed from the back incident light angle, and when the push-pull type aperture insertion sheet 6-2 is in use, the insertion depth of the push-pull type aperture insertion sheet in the lens is controlled by pushing and pulling, so as to realize the switching of the different four-quadrant polarization modulation array filters 5. Fig. 9(C) shows a lens 1 with a turret type aperture plate 6-3, which is a schematic view from the rear of the lens from the perspective of the incident light. The rotating shaft center of the rotating wheel type aperture inserting sheet 6-3 is fixed on the lens 1, when in use, the switching of different four-quadrant polarization modulation array optical filters 5 is realized by a rotating method, and the rotating mode can be manual or automatic electric control.
It should be noted that the aperture insert 6 may be a sheet made of a metal material or a carbon fiber material, the four-quadrant polarization modulation array filter 5 is tightly adhered by the four-quadrant polarizer 15 and the four-quadrant wave plate 14, or the four-quadrant polarization modulation array filter 5 only has the four-quadrant polarizer 15. When the four-quadrant polarization modulation array optical filter 5 is fixed on the aperture insert 6, the corresponding position part of the aperture insert 6 can be hollowed and then fixed in a way of being embedded into the groove. Of course, other means of attachment, such as adhesive attachment, are also possible.
The invention is mainly embodied in the following four aspects:
1) the target at any distance can be clearly imaged.
The Todor Georgiev places a square polarized light modulating optical element of fixed size in the camera lens, which makes the structure only image a specific plane of the object clearly. As shown in fig. 10, assuming that the clear dimension of the square light modulation optical element is set to image for a specific object plane, and the image of the scene object of the object plane on the camera imaging chip is as shown in fig. 10(a), in the figure, each microlens unit corresponds to a square imaging area (including 4 small blocks with different depths) in a shape of "tian", which is called a sub-image 21, and the adjacent sub-images 21 are closely arranged, which means that the space on the camera imaging plane is fully utilized and no pixel is wasted. However, when the distance between the shooting target and the camera deviates from the preset object plane, the imaging effect after the lens finishes focusing is as shown in fig. 10(B), and it can be seen that the size of the sub-image 21 corresponding to each microlens unit changes, resulting in a gap between the corresponding adjacent sub-images 21. The space on the imaging surface of the camera is not fully utilized, and the phenomenon is the image mosaic effect caused by mismatching of the clear aperture of the lens. Fig. 10(B) shows only the case where there is a gap in the sub-image 21, but aliasing may occur in the sub-image 21, which is determined depending on whether the shooting target is far from the set object plane or near. However, in both the far and near regions, the larger the deviation distance is, the more serious the image mosaic effect is, and the poorer the imaging quality is. In order to solve the problem, the lens aperture is made into a rectangle with an adjustable aperture in the device, so that for targets at any distance, the 'sub-images' corresponding to each micro lens can be closely arranged by adjusting the aperture of the rectangular aperture, the mosaic effect of the image is eliminated, and the imaging effect is finally obviously improved.
In the Todor Georgiev scheme, if a zoom lens is used, a certain degree of image mosaic effect is generally brought when the focal length is changed, so that the function of adjusting the aperture of the rectangular aperture can also improve the imaging effect when the field angle for imaging the target needs to be adjusted.
2) The convenient switching of the polarization measurement mode can be realized.
Although a full-polarization camera can obtain all polarization information of target light radiation, the accuracy and stability of the measurement result are generally worse than those of a linear polarization camera due to more unknown variables to be measured. If the shooting scene is known not to contain the circular polarization component, the linear polarization camera is used, so that the cost is lower, and the measurement result precision is higher. This requires that: the polarization camera is preferably capable of flexibly switching between a "linear polarization imaging" mode and a "full polarization imaging" mode depending on the application.
Due to the design of the flexibly adjustable aperture insert, the rapid switching between the linear polarization imaging mode and the full polarization imaging mode can be realized only by simply switching the type of the four-quadrant polarization modulation array filter carried on the aperture insert.
3) The imaging resolution is high.
In the Todor Georgiev device, the polarization modulating element disposed within the lens is tiled by multiple small optical elements, the seams of which produce blurred projections in the image, thereby interfering with the imaging. To address this problem, Todor Georgiev et al have adopted a method of reducing the magnification of the secondary imaging of the microlens unit below 1/5, which can limit the blurred projection area of the optical element seam on the image to a small range, but this significantly sacrifices the resolution of the output image. In the system of Todor Georgiev et al, the output image resolution is reduced to 1/30 the original image resolution.
Different from the method of Todor Georgiev, the method solves the problem by sparsely arranging the microlens units, and simultaneously controls the magnification of secondary imaging of the microlens units to be within the range of
To
In the meantime. Doing so better guarantees the resolution of the output image. Because: the resolution of the output image is approximately equal to the original image resolution of the imaging chip multiplied by the secondary imaging magnification of the micro-lens unit2Therefore, the maximum output resolution of the corresponding device of the present invention is about 1/4 of the original image resolution of the imaging chip, which is seen to be significantly better than that of the device of Todor Georgiev.
The sparse arrangement of the microlens units can overcome the problem of blurred projection in the image caused by the seams of optical elements in the lens, but also pay the cost of losing a part of incident light energy. In other words, the sparser the arrangement between the microlens units, the longer the imaging exposure time required by the apparatus of the present invention in the case where the subject scene luminance is constant. Experiments have shown that the horizontal spacing D between microlens elements is limited by light diffraction problems and limited subject scene brightness1Or vertical spacing D2All larger than the diameter d of the microlens unit, the invention can realize better imaging result. But by trade-off we get the best value range for the microlens cell diameter D to be less than min (D)1,D2) 2/3 while being greater than max (D)1,D2) 1/4 of (1).
Claims (3)
1. A polarization imaging apparatus includes a lens, a focused light field camera body with a microlens array; it is characterized in that the preparation method is characterized in that,
the light through hole of the diaphragm is rectangular;
in addition, the device also comprises a four-quadrant polarization modulation array optical filter and an aperture inserting sheet;
wherein, in the microlens array, the shape and the focal length of each microlens unit are the same; the micro lens units are sparsely arranged in a rectangular shape; gaps between adjacent microlens units are light-tight;
if the distance between the plane where all the microlens units in the microlens array are located and the imaging surface of the lens is a, and the distance between the plane where all the microlens units in the microlens array are located and the imaging photosensitive surface of the focusing light field camera body is b, then:
the four-quadrant polarization modulation array optical filter meets the following conditions:
assuming that a beam of light passes through the four-quadrant polarization modulation array optical filter along the direction opposite to the incident light of the imaging equipment, the polarization states of the four-quadrant emergent light respectively correspond to four points on a Pongar ball, and the four points are P1,P2,P3,P4(ii) a The following two requirements are simultaneously satisfied: first, P1,P2,P3,P4The four points are all positioned on the surface of the Bonga ball; second, P1,P2,P3,P4Four points not being coplanar, or P1,P2,P3,P4All are positioned on the equator line of the Poincare sphere, but at most two points can be superposed;
the aperture insert is positioned at the position of the lens diaphragm, and one or more four-quadrant polarization modulation array optical filters are fixed on the aperture insert; by adjusting the aperture insert, any four-quadrant polarization modulation array optical filter fixed on the aperture insert can be positioned on the optical axis of the lens, and the plane of the four-quadrant polarization modulation array optical filter is vertical to the optical axis of the lens; different four-quadrant polarization modulation array filters are used instead, so that the function of switching between the two functions of the linear polarization imaging mode and the full polarization imaging mode is achieved.
2. The polarization imaging apparatus of claim 1, wherein the clear aperture of the rectangular aperture of the polarization imaging apparatus is adjustable.
3. The polarization imaging apparatus of claim 1, wherein the microlens unit horizontal pitch D of the polarization imaging apparatus1Vertical distance D2And the diameter d of the microlens unit, each satisfying the following condition: (max (D)1,D2)×1/4)<d<(min(D1,D2)×2/3)。
Priority Applications (1)
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