CN106292128A - A kind of formation method based on polarization extinction - Google Patents

Abstract

The invention discloses a kind of formation method based on polarization extinction, the i.e. front at camera lens and arrange a polaroid being perpendicular to camera optical axis, polaroid can uniformly rotate before camera lens；When polaroid uniform rotation, camera is continuously shot, and obtains the polarization image under different polarization angle；Take camera the first two field picture of obtaining of shooting as reference picture, constantly make extinction state differentiation with reference picture by shoot the image got after camera every time, obtain final delustring image, i.e. 180 ° of width delustring images obtained of polaroid rotation.It is high that the present invention has picture contrast, and the details of target clearly waits remarkable advantage, more conducively human eye or other scopes to the observation of object and detection, and principle is simple, and effect is obvious.

Description

Imaging method based on polarization extinction

Technical Field

The invention belongs to the technical field of imaging, and particularly relates to an imaging method based on polarization extinction.

Background

Due to too strong light reflected by the target or specular reflection on the surface of the target, the captured image may appear bright white, which may interfere with the observation or detection of the target by human eyes or other observation devices. In this case, therefore, some front-end devices are required to eliminate the strong light without affecting the target object detection information, so as to facilitate the human eyes or other observation devices to observe or detect the target object. In response to this situation, various systems for eliminating the strong light have been devised, and a common system is to add an attenuation sheet between the observation device and the target object to reduce the light intensity. However, the overall light intensity of the image obtained by such a system becomes low, the contrast ratio is reduced, and the resolution of the target details is also reduced.

Yet another technique is a polarization extinction system, utilizingThe mechanism of extinction by the polarizer is shown in fig. 1: when the light source satisfies Brewster's angle theta_BWhen the light is incident, the reflected light is completely linearly polarized light, the azimuth angle of the analyzer is adjusted, and when the polarization azimuth angle is vertical to the polarization direction of the reflected light, the reflected light can not pass through the polaroid completely due to the light blocking effect of the polaroid, so that the extinction purpose is achieved; when the light source is incident at a Brewster angle, the reflected light is partially polarized light, only part of the reflected light can be eliminated by adjusting the azimuth angle of the analyzer, and the influence of strong light on target detection can be effectively weakened as long as the incident angle is close to the Brewster angle.

The extinction system has a wide application range, and the extinction methods generally used by the system mainly include feedback extinction, optical extinction and the like. The feedback extinction is adjusted by using a circuit feedback signal, thereby achieving the purpose of eliminating strong light. Document 1(ZHANGJ H, LIU L G, ZHU H N, et al. the High resolution polarization modeling measuring System with magnetic-optical modulator [ J ]. Journal of electronics-laser.2001, 12 (10): 1041-1042.) discloses a method for modulating polarized light by using a novel magnetic modulator and a driving circuit, which has the advantages of rapidness and real-time performance, and has the disadvantages of High requirements on the light rotating material and complex System design; the optical extinction utilizes the property of light to eliminate strong light, and has simple principle, wide applicability and obvious effect. Document 2(CN103345099A) discloses an imaging method based on polarized light extinction, which includes steps of shooting polarized images at several angles, defining a 3 × 3 pixel window for each polarized image, comparing data in the window with a preset threshold, and obtaining a final extinction image after image fusion. Document 3(CN102998667A) discloses a wave water surface solar flare stripping method based on polarization remote sensing detection, which utilizes a polarization imaging detector based on a liquid crystal phase variable retarder to perform wave water surface polarization imaging detection to obtain a polarization intensity image, further calculate a polarization degree image and a polarization angle image, and calculate and obtain a target object under a separated solar flare background based on time series analysis and image fusion technology.

Disclosure of Invention

The invention aims to provide an imaging method based on polarization extinction, which can well eliminate strong light interference and is beneficial to human eyes or other observation equipment to observe and detect a target.

The technical solution for realizing the purpose of the invention is as follows: an imaging method based on polarization extinction is realized by the following steps:

step 1, arranging a polaroid perpendicular to an optical axis of a camera in front of the camera lens, wherein the polaroid can rotate at a constant speed in front of the camera lens;

step 2, when the polaroid rotates at a constant speed, continuously shooting by a camera to obtain polarization images under different polarization angles;

and 3, taking the first frame image shot by the camera as a reference image, and continuously judging the extinction state of the image shot by the camera each time with the reference image to obtain a final extinction image, namely an extinction image obtained by rotating the polaroid by 180 degrees.

Compared with the prior art, the invention has the following remarkable advantages: (1) compared with the existing method of extinction by using an attenuator, the method has the remarkable advantages of high image contrast, clear details of the target and the like, is more beneficial to the observation and detection of human eyes or other observation equipment on the target, and has simple principle and obvious effect. (2) The polarizer rotates at a constant speed, so that the camera can continuously shoot, and can acquire polarization images with different polarization angles, not only polarization images with a plurality of angles, such as 0 degrees, 60 degrees, 120 degrees, or 0 degrees, 45 degrees, 90 degrees and 135 degrees. (3) And each half turn of the polaroid is performed, an extinction image can be obtained by using an extinction judgment method, and the method is efficient and quick. (4) The applicability is strong, and the method can be applied to various occasions needing strong light interference elimination. For example, for the lake surface in the glistening Pond, observe underwater objects; identifying the license plate number of the vehicle head under the strong light irradiation; observing surface information of an object subjected to mirror reflection; the method is used for taking aerial photos of water surfaces affected by solar flares, surveying ships or water surface floaters and the like.

The present invention is described in further detail below with reference to the attached drawing figures.

Drawings

FIG. 1 is a schematic diagram of polarization extinction.

FIG. 2 is a flow chart of the polarization extinction-based imaging method of the present invention.

Fig. 3(a) is an image before extinction of the license plate number by strong light irradiation, and fig. 3(b) is an image after extinction by the present invention.

Fig. 4(a) is an image before the water surface is dull-lighted by solar flare, and fig. 4(b) is an image after the dull-lighting by the present invention.

Fig. 5(a) is an image before extinction of a museum exhibition relic, and fig. 5(b) is an image after extinction by the present invention.

Fig. 6(a) is an image before extinction of the simulated aerial water surface float, and fig. 6(b) is an image after extinction by the present invention.

Detailed Description

With reference to fig. 2, the imaging method based on polarization extinction of the present invention includes the following steps:

step 1, arranging a polaroid perpendicular to an optical axis of a camera in front of a camera lens, fixing the polaroid at the center of a gear, fixing the gear on a bracket, and driving the gear by using a stepping motorThe polarizer rotates at a constant speed, so that the polarizer in front of the camera lens is driven to rotate at a constant speed. The camera is a black-and-white CCD camera with visible light band and frame frequency of f_pAnd frames per second, the obtained image is an M-N gray image, fp is more than or equal to 10, and M, N is the width and the height of the image and the unit is a pixel. The stepping motor drives the gear inlaid with the polaroid to rotate at a constant speed, and the camera can acquire a polarization image with any polarization angle instead of only polarization images with a plurality of special angles, such as commonly used polarization images with the angles of 0 degree, 60 degrees, 120 degrees or 0 degree, 45 degrees, 90 degrees and 135 degrees. If the frame rate of the camera is 15 frames/second, the captured image is a gray scale image of 640 × 480, and fig. 3(a) is an image before extinction of the license plate under strong light.

And 2, continuously shooting by a camera while the polaroid rotates at a constant speed to obtain polarization images under different polarization angles. The polarizing angle changes from 0 degree to 180 degree at uniform speed every half turn of the polarizing film, if the rotating speed of the stepping motor (namely the rotating speed of the polarizing film) is set to be 180 degrees every second, namely the rotating speed of the polarizing film is set to be half turn every second, the polarizing film rotates 180 degrees/f every time_pThe camera takes an image, wherein f_pIs the frame rate of the camera. If the rotating speed of the motor is set to be 180 degrees/second, namely the rotating speed of the polaroid is 180 degrees/second, the camera continuously shoots while the polaroid rotates at a constant speed, and polarized images under different polarization angles are obtained. And when the polarizing plate rotates for half a turn, the polarization angle changes from 0 degrees to 180 degrees at a constant speed, and then the camera shoots an image when the polarizing plate rotates for every 180 degrees/15 degrees, namely 12 degrees, wherein 15 is the frame frequency of the camera. Increasing the frame rate of the camera or slowing the rotation speed of the stepping motor can control the polarizer to take more polarization images per 1 degree of rotation of the camera. The angle θ through which the polarization of an image captured by the camera is rotated can be expressed by the following formula:

$\mathrm{\θ}=\frac{{\mathrm{\θ}}_v}{f_p}$

wherein, theta_vThe angle through which the polarizer is rotated per second,f_pθ is the angle through which the polarization of each image taken by the camera is rotated, at the frame rate of the camera used. The smaller theta represents that more polarization images are shot by the camera every half turn of the polarizing plate, and the final extinction image is more accurate.

And 3, taking the first frame image shot by the camera as a reference image, and continuously judging the extinction state of the image shot by the camera each time with the reference image to obtain a final extinction image, namely an extinction image obtained by rotating the polaroid by 180 degrees. The extinction state distinguishing method comprises the following implementation processes:

comparing the gray value of each pixel point position of a new frame of image acquired by a camera with the gray value of the pixel point position corresponding to the reference image, taking the smaller gray value as the new gray value of the pixel point position in the reference image, and when the gray value of each pixel point position of the reference image does not change any more, the reference image at the moment is the final extinction image, wherein the extinction state discrimination formula is as follows:

$W_{{\mathrm{\θ}}_1}(i,j)=I_{{\mathrm{\θ}}_1}(i,j)$

$W_{{\mathrm{\θ}}_2}(i,j)=\min (I_{{\mathrm{\θ}}_2}(i,j),W_{{\mathrm{\θ}}_1}(i,j))$

$W_{{\mathrm{\θ}}_3}(i,j)=\min (I_{{\mathrm{\θ}}_3}(i,j),W_{{\mathrm{\θ}}_2}(i,j))$

·

·

·

·

·

·

$W_{{\mathrm{\θ}}_{n-1}}(i,j)=\min (I_{{\mathrm{\θ}}_{n-1}}(i,j),W_{{\mathrm{\θ}}_{n-2}}(i,j))$

$W_{{\mathrm{\θ}}_n}(i,j)=\min (I_{{\mathrm{\θ}}_n}(i,j),W_{{\mathrm{\θ}}_{n-1}}(i,j))$

wherein,representing the first frame of image acquired by the camera, the corresponding polarizer angle being theta₁(i, j) represents the pixel point of the ith row and the jth column,the gray value of the pixel point of the ith row and the jth column in the first frame image acquired by the camera is represented,obtaining the gray value of the ith row and jth column pixel point in the reference image from the first frame image acquired by the camera;second frame image acquired for cameraGray value of ith row and jth column pixel pointAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageThird frame image acquired for cameraGray value of ith row and jth column pixel pointAndafter the comparison, the process is carried out,taking the smaller of the two as a new gray value of the pixel point position in the reference imageImage of the n-1 frame acquired for the cameraGray value of ith row and jth column pixel pointAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageThe gray value of the ith row and jth column pixel point in the nth frame image acquired by the camera along with the uniform rotation of the polaroid is shown,is composed ofAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageIf it isI.e. the reference picture is no longer changed, thenThe resulting matte image.

The extinction effect comparison graphs of other sets of scene experiments performed by the invention are respectively shown in fig. 3(a), fig. 3(b), fig. 4(a), fig. 4(b), fig. 5(a), fig. 5(b), fig. 6(a) and fig. 6(b), and it can be seen from the graphs that the image after extinction is obviously compared with the image before extinction, the extinction effect is obvious, the target is clear, and the strong light interference is effectively eliminated.

Claims (4)

1. An imaging method based on polarization extinction is characterized by comprising the following implementation steps:

step 1, arranging a polaroid perpendicular to an optical axis of a camera in front of the camera lens, wherein the polaroid can rotate at a constant speed in front of the camera lens;

step 2, when the polaroid rotates at a constant speed, continuously shooting by a camera to obtain polarization images under different polarization angles;

and 3, taking the first frame image shot by the camera as a reference image, and continuously judging the extinction state of the image shot by the camera each time with the reference image to obtain a final extinction image, namely an extinction image obtained by rotating the polaroid by 180 degrees.

2. The method of claim 1, wherein in step 1, the CCD camera is a black and white CCD camera with a frame rate of f_pFrame/second, the image obtained is taken as a M x N gray scale image, f_pAnd the unit of M, N is equal to or more than 10, and the width and the height of the image are pixels.

3. A method of polarization extinction-based imaging according to claim 1, wherein in step 2, the polarization angle is varied at a constant rate from 0 ° to 180 ° for each half turn of the polarizer, and if the polarizer is set to rotate 180 ° per second, i.e., half turn per second, the polarizer rotates 180 °/f for each turn of the polarizer_pThe camera takes an image, wherein f_pIs the frame rate of the camera; the angle θ through which the polarization of an image captured by the camera is rotated is expressed by the following formula:

$\mathrm{\θ}=\frac{{\mathrm{\θ}}_v}{f_p}$

wherein, theta_vAngle of rotation per second of polarizer, f_pθ is the angle through which the polarization of each image taken by the camera is rotated, at the frame rate of the camera used.

4. A polarization extinction-based imaging method according to claim 1, wherein in step 3, the extinction state determination method is implemented as follows:

comparing the gray value of each pixel point position of a new frame of image acquired by a camera with the gray value of the pixel point position corresponding to the reference image, taking the smaller gray value as the new gray value of the pixel point position in the reference image, and when the gray value of each pixel point position of the reference image does not change any more, the reference image at the moment is the final extinction image, wherein the extinction state discrimination formula is as follows:

$\begin{array}{c}{W}_{{\mathrm{\θ}}_1}(i,j)=I_{{\mathrm{\θ}}_1}(i,j)\\ W_{{\mathrm{\θ}}_2}(i,j)=\min (I_{{\mathrm{\θ}}_2}(i,j),W_{{\mathrm{\θ}}_1}(i,j))\\ W_{{\mathrm{\θ}}_3}(i,j)=\min (I_{{\mathrm{\θ}}_3}(i,j),W_{{\mathrm{\θ}}_2}(i,j))\\ \·\\ \·\\ \·\\ \·\\ \·\\ \·\\ W_{{\mathrm{\θ}}_{n-1}}(i,j)=\min (I_{{\mathrm{\θ}}_{n-1}}(i,j),W_{{\mathrm{\θ}}_{n-2}}(i,j))\\ W_{{\mathrm{\θ}}_n}(i,j)=\min (I_{{\mathrm{\θ}}_n}(i,j),W_{{\mathrm{\θ}}_{n-1}}(i,j))\end{array}$

wherein,representing the first frame of image acquired by the camera, the corresponding polarizer angle being theta₁(i, j) represents the pixel point of the ith row and the jth column,the gray value of the pixel point of the ith row and the jth column in the first frame image acquired by the camera is represented,obtaining the gray value of the ith row and jth column pixel point in the reference image from the first frame image acquired by the camera;second frame image acquired for cameraGray value of ith row and jth column pixel pointAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageThird frame image acquired for cameraGray value of ith row and jth column pixel pointAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageImage of the n-1 frame acquired for the cameraGray value of ith row and jth column pixel pointAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageThe gray value of the ith row and jth column pixel point in the nth frame image acquired by the camera along with the uniform rotation of the polaroid is shown,is composed ofAndafter comparison, the smaller of the two is taken as a new gray value of the pixel point position in the reference imageIf it isI.e. the reference picture is no longer changed, thenThe resulting matte image.