Underwater active polarization imaging device based on liquid crystal phase delayer

Abstract

The invention discloses an underwater active polarization imaging device based on a liquid crystal phase retarder, which comprises a CCD (Charge Coupled Device) camera, an optical filter, a beam splitter prism, the liquid crystal phase retarder, a polarizer, a front lens and an annular active light source which are sequentially arranged on the same straight line, and the imaging device is arranged in front of a shot target at an object distance capable of clearly imaging; wherein the rotating table, the liquid crystal controllable phase delayer, the annular active light source and the CCD industrial camera are connected to a computer for control and image processing, and the underwater active polarization imaging device calculates a Stokes vector of a shot target by shooting a plurality of polarization images with different polarization angles and polarization states; according to the method, the image of the target object is acquired through the polarization information of the object, the influence of scattering absorption of underwater impurities can be eliminated, and an underwater high-definition image is presented through relative algorithm optimization.

Description

Technical Field

[0001] The invention relates to the technical field of liquid crystal polarization imaging measurement, and in particular to an underwater active polarization imaging device based on a liquid crystal phase retarder. Background Art

[0002] Underwater imaging technology is of great significance in the research of underwater environment detection, underwater military and many other fields. Due to the serious scattering effect of light waves caused by the tiny particles suspended in the water, chaotic media such as soluble organic matter and non-uniform factors such as bubbles, the background scattered light is superimposed on the target reflected light to form noise, which greatly reduces the image contrast and seriously loses the detail information. Underwater images taken by traditional visible light imaging technology have the problems of information loss and low contrast, which makes the scene produce a serious "curtain effect".

[0003] Polarization optical imaging is a new type of optical imaging technology. Polarization images can reflect many unique information that is difficult to observe in intensity images. Polarization optical descattering imaging is one of its important application directions. It is suitable for clear imaging in foggy atmospheric environments and turbid underwater environments. Compared with the atmospheric environment, the attenuation coefficient of the underwater environment is higher and the ambient lighting is weaker. Active illumination imaging can obtain clearer images. In recent years, there have been many studies using Stokes vector imaging. Stokes vectors use light wave intensity to describe the polarization state of light waves. All Stokes vector imaging can calculate the image polarization degree by measuring the polarization state at different angles multiple times.

[0004] At present, according to the characteristics of the detection object, polarization imaging systems are mainly divided into time-sharing type and simultaneous type. The simultaneous polarization imaging system requires multiple optical devices to work together, and the system structure is complex and the entire system is expensive. The time-sharing polarization imaging system has a simple system structure. Common time-sharing polarization detection mainly includes rotating wave plate type and liquid crystal phase retarder type. Among them, the liquid crystal phase retarder type time-sharing polarization system has a fast response speed, which can avoid the jitter caused by the rotating device, thereby improving the measurement accuracy. Therefore, it is of great significance to develop an underwater active polarization imaging device and method based on a liquid crystal phase retarder. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an underwater active polarization imaging device based on a liquid crystal phase retarder to solve the technical problem that traditional polarization imaging cannot be applied to environmental water bodies with different turbidity.

[0006] Technical solution: The underwater active polarization imaging device based on a liquid crystal phase retarder described in the present invention comprises: a CCD camera, a filter, a beam splitter, a liquid crystal phase retarder, a polarizer, a front lens, and an annular active light source. The CCD camera, the filter, the beam splitter, the liquid crystal phase retarder, the polarizer, the front lens, and the annular active light source are sequentially installed on the same straight line along the optical axis, and the imaging device is placed in front of the target object at an object distance where a clear image can be formed; wherein the rotating table, the liquid crystal controllable phase retarder, the annular active light source, and the CCD industrial camera are connected to a computer for control and image processing, and the underwater active polarization imaging device calculates the Stokes vector of the target by shooting multiple polarization images with different polarization angles and polarization states.

[0007] Furthermore, the CCD camera and the liquid crystal controllable phase retarder are controlled by computer software to take pictures and images, and the pixels of the camera are formed by combining the polarization of the polarizer and the liquid crystal.

[0008] Furthermore, the annular active light source includes an annular LED lamp combination array and an annular polarizer, the LED lamp combination array includes a plurality of LED lamps and a plurality of magnets, the annular polarizer includes an annular polarizer whose size matches the annular LED lamp and a plurality of magnets, and the polarization state of the light source is adjusted by adding or subtracting annular polarizers, wherein the liquid crystal phase retarder type time-sharing polarization system has a fast response speed.

[0009] Furthermore, the filter device includes a rotating stage and three-color narrow-pass filters of R, G, and B. The rotating stage can be controlled by computer software to an off-axis position to capture intensity images of the three-color channels.

[0010] Furthermore, the input voltage of the liquid crystal controllable phase retarder is adjusted to control the camera to record linear polarization images at four polarization angles of 0°, 45°, 90°, and 135°.

[0011] Furthermore, the Stokes vector of the photographed target is calculated using polarization images with different polarization angles and polarization states as follows: based on the images with different polarization states, the polarized light intensity in the direction corresponding to the angle of the linear polarizer in the imaging module is calculated; based on the polarized light intensity, four components of the Stocks vector are calculated; based on the four components of the Stocks vector and the original image without polarization, an enhanced image of the underwater target is obtained.

[0012] Furthermore, the four components of the Stocks vector are calculated according to the linearly polarized light intensity, and the formula is as follows:

[0013]

[0014] Among them, the four linear polarization images of 0°, 45°, 90°, and 135° are recorded as I0°, I45°, I90°, and I135°, where IR and IL represent the intensity values ​​of left-handed and right-handed circularly polarized light, respectively;

[0015] Furthermore, obtaining an enhanced image of an underwater target object includes the following steps:

[0016] (81) The degree of polarization DoP image is extracted according to the stock vector description, and the formula is as follows:

[0017]

[0018] Among them, the four linear polarization images at 0°, 45°, 90°, and 135° are denoted as I0°, I 45 °,I 90 ° and,I 135 °;

[0019] (82) Preprocessing the processed DoP image and intensity image is performed as follows: denoising the DoP image by a two-bit median filter algorithm, and processing the intensity image by a contrast-limited adaptive histogram equalization algorithm;

[0020] (83) The preprocessed DoP image and the preprocessed intensity image are fused by non-subsampled shearlet transform, as follows: The two images are decomposed into low-frequency subbands and high-frequency subbands by NSCT. and the low frequency subband of the DoP image Adopting adaptive fuzzy logic fusion algorithm:

[0021]

[0022] η2=1-η1

[0023]

[0024] (84) For the high frequency subband of the intensity image and the high frequency subband of the DoP image Adopt the fusion rule of taking the largest absolute value of pixels:

[0025]

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the image of the target object is acquired through the polarization information of the object, which can eliminate the influence of scattering and absorption of underwater impurities, and then present a high-definition underwater image through relative algorithm optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a schematic diagram of the structure of the device of the present invention;

[0028] Figure 2 It is a structural schematic diagram of the annular active light source of the present invention;

[0029] Figure 3 is a flow chart of the method of the present invention;

[0030] Figure 4 Flow chart of the Stokes vector acquisition process of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0032] like Figure 1 As shown, an embodiment of the present invention provides an underwater active polarization imaging device based on a liquid crystal phase retarder, comprising: a CCD camera, a filter, a beam splitter, a liquid crystal phase retarder, a polarizer, a front lens, and an annular active light source, wherein the CCD camera, the filter, the beam splitter, the liquid crystal phase retarder, the polarizer, the front lens, and the annular active light source are sequentially installed on the same straight line along the optical axis, and the imaging device is placed in front of the photographed target at an object distance where a clear image can be formed; wherein the rotating table, the liquid crystal controllable phase retarder, the annular active light source, and the CCD industrial camera are connected to a computer for control and image processing, and the underwater active polarization imaging device calculates the Stokes vector of the photographed target by photographing multiple polarization images with different polarization angles and polarization states.

[0033] The CCD camera and the liquid crystal controllable phase retarder are controlled by computer software to shoot and image, and the camera pixels are formed by combining polarizers and liquid crystal polarization. The annular active light source includes an annular LED light combination array and an annular polarizer, the LED light combination array includes a plurality of LED lights and a plurality of magnets, the annular polarizer includes an annular polarizer whose size matches the annular LED light and a plurality of magnets, and the polarization state of the light source is adjusted by adding or subtracting annular polarizers, wherein the liquid crystal phase retarder type time-sharing polarization system has a fast response speed.

[0034] The filter device includes a rotating stage and three-color narrow-pass filters of R, G, and B. The rotating stage can be controlled by computer software to an off-axis position to capture intensity images of the three-color channels. Adjust the input voltage of the liquid crystal controllable phase retarder to control the camera to record linear polarization images at four polarization angles of 0°, 45°, 90°, and 135°. The Stokes vector of the photographed target is calculated using polarization images of different polarization angles and polarization states as follows: According to the images of different polarization states, calculate the polarized light intensity in the direction corresponding to the angle of the linear polarizer in the imaging module; calculate the four components of the Stocks vector according to the polarized light intensity; obtain an enhanced image of the underwater target according to the four components of the Stocks vector and the unpolarized original image. The four components of the Stocks vector are calculated according to the linear polarized light intensity, and the formula is as follows:

[0035]

[0036] Among them, four linear polarization images at 0°, 45°, 90°, and 135° are recorded as I0°, I45°, I90°, and I135°, where IR and IL represent the intensity values ​​of left-handed and right-handed circularly polarized light, respectively; obtaining an enhanced image of an underwater target includes the following steps:

[0037] (81) The degree of polarization DoP image is extracted according to the stock vector description, and the formula is as follows:

[0038]

[0039] Among them, the four linear polarization images at 0°, 45°, 90°, and 135° are denoted as I0°, I 45 °,I 90 ° and,I 135 °;

[0040] (82) Preprocessing the processed DoP image and intensity image is performed as follows: denoising the DoP image by a two-bit median filter algorithm, and processing the intensity image by a contrast-limited adaptive histogram equalization algorithm;

[0041] (83) The preprocessed DoP image and the preprocessed intensity image are fused by non-subsampled shearlet transform, as follows: The two images are decomposed into low-frequency subbands and high-frequency subbands by NSCT. and the low frequency subband of the DoP image Adopting adaptive fuzzy logic fusion algorithm:

[0042]

[0043] η2=1-η1

[0044]

[0045] (84) For the high frequency subband of the intensity image and the high frequency subband of the DoP image Adopt the fusion rule of taking the largest absolute value of pixels:

[0046]

[0047] The embodiment of the present invention provides an underwater active polarization imaging method based on a liquid crystal phase retarder, comprising the following steps:

[0048] S1, CCD camera, filter, beam splitter, liquid crystal phase retarder, polarizer, front lens, annular active light source are installed in the same straight line along the optical axis, and the fast axis or slow axis of the liquid crystal controllable phase retarder is aligned with the horizontal direction, and the distance between the devices is adjusted to make the imaging field of view spacious and bright; firstly, according to the different turbidity levels of the water body, the best active light source mode is selected, and the computer switches the active light source to the corresponding light source intensity. When polarized light is needed as the active light source, the circular polarization is adsorbed on the annular active light source by a magnet.

[0049] S2. Place the object to be photographed in front of the lens, adjust the distance between the object and the lens, and align the focal length to make the image clear;

[0050] S3. Adjust the input voltage of the liquid crystal controllable phase retarder, control the camera to record linear polarization images at four polarization angles of 0°, 45°, 90°, and 135°, then control the rotating stage to rotate 120° three times by computer, rotate each narrow-pass filter to the optical axis position, and capture the intensity image of each channel.

[0051] S4, input the four linear polarization images of 0°, 45°, 90° and 135° obtained in step S3 into the Stokes vector matrix, and obtain the enhanced image of the underwater target according to the four components of the Stocks vector and the unpolarized light intensity image. Calculating the four components of the Stocks vector includes: assuming that the Stokes vector of the target is S, S = [S0, S1, S2, S3] T , let the four linear polarization images be denoted as I 0° ,I 45° ,I 90° and,I 135° , where I R ,I L Represent the intensity values ​​of left-handed and right-handed circularly polarized light respectively.

[0052]

[0053] Extract the degree of polarization DoP image based on the Stocks vector description.

[0054]

[0055] S5, preprocessing the degree of polarization DoP image and intensity image obtained in step S4, the processing process includes:

[0056] The DoP image is denoised by a two-bit median filter algorithm, and the R, G, and B channel intensity images are processed by three-channel color correction. The color correction algorithm independently compensates the red, blue, and green channel intensity images, and sets α, β, and γ as the compensation coefficients for the red, blue, and green channels, respectively.

[0057]

[0058] When the blue and green channels account for a large proportion, and The green channel of the image has a relatively high brightness, while the blue channel has a relatively low brightness. The image has a blue-green color cast. The compensation coefficients for each channel are as follows:

[0059]

[0060] g=0

[0061] When the green channel accounts for a large proportion, and The green channel of the image has a relatively high brightness, while the red and blue channels have similar brightness. The image has a green color cast. The compensation coefficients for each channel are as follows:

[0062]

[0063] g=0

[0064] When the blue channel accounts for a small proportion, and The green channel of the image has a higher relative brightness, and the red channel has a relative brightness far away from the blue channel. The image has a yellow color cast. The channel compensation coefficients are as follows:

[0065] α=0

[0066]

[0067] g=0

[0068] When the blue channel accounts for a large proportion, The blue channel of the image has a relatively high brightness, and the image has a blue color cast. The compensation coefficients of each channel are as follows:

[0069]

[0070] β=0

[0071]

[0072] The preprocessed R, G, and B three-channel intensity images are fused as R, G, and B channels into a light intensity image. The preprocessed DoP image and the Y channel of the preprocessed intensity image are fused by non-subsampled contourlet transform (NSCT). The processing process includes: first, the two images are decomposed into low-frequency subbands and high-frequency subbands by NSCT, and the low-frequency subband of the intensity image is and the low frequency subband of the DoP image Using the local Laplace energy fusion algorithm:

[0073]

[0074]

[0075] For the high frequency subband of the intensity image and the high frequency subband of the DoP image Adopt the fusion rule of Adaptive Gaussian Pulse Coupled Neural Network (AGPCNN):

[0076]

[0077] U0(i,j)=0

[0078] E0(i,j)=0

[0079] Θ n (i,j)=1

[0080] P0(i,j)=0

[0081]

[0082] Repeat the above steps to obtain underwater polarization-enhanced images under different light source states.

Claims

1. An underwater active polarization imaging device based on a liquid crystal phase retarder, characterized in that: include: A CCD camera, a filter, a beam splitter, a liquid crystal phase retarder, a polarizer, a front lens, and an annular active light source are arranged in sequence on the same straight line along an optical axis, and an imaging device is placed in front of a photographed target at an object distance where a clear image can be formed; wherein a rotating table, a liquid crystal controllable phase retarder, an annular active light source, and a CCD industrial camera are connected to a computer for control and image processing, and the underwater active polarization imaging device calculates the Stokes vector of the photographed target by photographing multiple polarization images with different polarization angles and polarization states.

2. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 1, characterized in that: The CCD camera and the liquid crystal controllable phase retarder are controlled by computer software to shoot images, and the pixels of the camera are formed in a manner of combining polarizing plates and liquid crystal polarization.

3. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 1, characterized in that: The annular active light source includes an annular LED lamp combination array and an annular polarizer, the LED lamp combination array includes a plurality of LED lamps and a plurality of magnets, the annular polarizer includes an annular polarizer whose size matches the annular LED lamp and a plurality of magnets, the polarization state of the light source is adjusted by adding or subtracting annular polarizers, wherein the liquid crystal phase retarder type time-sharing polarization system has a fast response speed.

4. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 1, characterized in that: The filter device comprises a rotating platform and three-color narrow-pass filters of R, G and B. The rotating platform can be controlled by computer software to an off-axis position to shoot intensity images of the three-color channels.

5. The underwater active polarization imaging device based on liquid crystal phase retarder according to claim 1, characterized in that: The input voltage of the liquid crystal controllable phase retarder is adjusted to control the camera to record linear polarization images at four polarization angles of 0°, 45°, 90°, and 135°.

6. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 1, characterized in that: The Stokes vector of the photographed target is calculated using polarization images with different polarization angles and polarization states as follows: according to the images with different polarization states, the polarized light intensity in the direction corresponding to the angle of the linear polarizer in the imaging module is calculated; according to the polarized light intensity, four components of the Stocks vector are calculated; according to the four components of the Stocks vector and the original image without polarization, an enhanced image of the underwater target is obtained.

7. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 6, characterized in that: The four components of the Stocks vector are calculated according to the linearly polarized light intensity, and the formula is as follows: Among them, the four linear polarization images of 0°, 45°, 90°, and 135° are recorded as I0°, I45°, I90°, and I135°, where IR and IL represent the intensity values ​​of left-handed and right-handed circularly polarized light, respectively.

8. The underwater active polarization imaging device based on a liquid crystal phase retarder according to claim 7, characterized in that: Obtaining an enhanced image of an underwater target includes the following steps: (81) The degree of polarization DoP image is extracted according to the stock vector description, and the formula is as follows: Among them, the four linear polarization images at 0°, 45°, 90°, and 135° are denoted as I0°, I 45 °,I 90 ° and,I 135 °; (82) Preprocessing the processed DoP image and intensity image is performed as follows: denoising the DoP image by a two-bit median filter algorithm, and processing the intensity image by a contrast-limited adaptive histogram equalization algorithm; (83) The preprocessed DoP image and the preprocessed intensity image are fused by non-subsampled shearlet transform, as follows: The two images are decomposed into low-frequency subbands and high-frequency subbands by NSCT. and the low frequency subband of the DoP image Adopting adaptive fuzzy logic fusion algorithm: η2=1-η1 (84) For the high frequency subband of the intensity image and the high frequency subband of the DoP image Adopt the fusion rule of taking the largest absolute value of pixels:

Images