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摘要:
为了全面且针对性地研究水下湍流成像的退化因素, 同时优化相应图像恢复算法, 搭建了一个可控湍流条件和重复使用的水下成像实验系统, 利用循环水泵控制实验水箱中湍流的强度, 气泡发生器制造微气泡, 图像传感器获取不同条件下的正弦条纹目标板的成像结果。研究了流速场、程辐射和流体介质对水下成像的影响, 结合图像复原和超分辨率重建技术, 比较了基于三种退化因素的调制传递函数(MTF)的差异和适用性。结果表明, 湍流流速场在低空间频率段造成MTF快速下降, 程辐射和流体介质则会导致高空间频率的调制对比度减小; 在水下湍流退化图像恢复中, 湍流流速场的MTF适合图像复原, 程辐射和流体介质的MTF适合图像重建。
Abstract:In order to comprehensively and objectively study the degenerate factors of underwater turbulent imaging and optimize the corresponding image restoration algorithms, a reusable submarine imaging experiment system with a controllable turbulent flow condition is established. The circulating water pump is used to control the intensity of turbulence in the laboratory tank.The bubble generator is used to generate micro bubbles. The image sensor is used to obtain the images of sinusoidal stripe target plates under different conditions. The effect of turbulent flow field, path radiation and fluid media on submarine imaging in turbulent flow were studied, and the differences and applicability of modulation transfer functions (MTFs) of three degradation factors are compared by combining image restoration and super-resolution reconstruction. The experimental results show that the turbulent flow field causes MTF declines of the low spatial frequency, and the path radiation and fluid media lead to the decrease of modulation contrast of the high spatial frequency. In the restoration of the underwater turbulent degraded image, the MTF of the turbulent flow field is suitable for image restoration, and the MTFs of the path radiation and fluid media are suitable for image reconstruction.
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Overview: At present, the related researches of underwater turbulence mainly include three major categories. The first category is the theoretical calculation based on turbulent structure function and scattering properties. The second category is to use the refractive index power spectra to construct experimental systems for indoor or outdoor experimental measurements and analysis. The third category is the simulation testing based on the PIV system. The existing three categories of research methods have different emphases, and few literatures compare them.
In order to comprehensively and objectively study the degenerate factors of underwater turbulent imaging and optimize the corresponding image restoration algorithms, a reusable submarine imaging experiment system with a turbulent flow controllable condition is established. The circulating water pump is used to provide water force, and the water valve is used to control the turbulent flow field in the laboratory tank. The bubble generator is used to generate micro bubbles, and the bubbles is used as tracer particles. Image sensor is used to obtain the images of sinusoidal stripe target plates under different conditions. In order to reduce the experimental error, the experiment is conducted in a dark environment.
Through indoor and outdoor field experiments, the effect of turbulent flow field, path radiation and fluid media on submarine imaging in turbulent flow are studied. The modulation transfer function (MTF) of the underwater turbulence degradation is correspondingly extracted and analyzed for the three models. The adaptation performance and advantages of the three MTFs are compared and analyzed by using several typical image processing algorithms in turbulent image restoration and super-resolution reconstruction. The objective evaluation criteria such as information capacity (IC), blur metric (BM), and gray mean grads (GMG) are used to compare the objective effect of image processing. The experimental results show that the turbulent flow field, path radiation and fluid media affect the underwater imaging process in turbulent water. The turbulent flow field is the main factor that causes the degradation of underwater imaging in the low spatial frequency. The path radiation and fluid media are the main causes of image degradation. In the restoration of the underwater turbulent degraded image, the MTF of the turbulent flow field is suitable for the image restoration, and the MTFs of the path radiation and turbulent fluid media are suitable for the image super-resolution reconstruction. Compared with other methods of the same class, the information capacity and the gray mean grads value are larger and the blur metric value is smaller.
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图 4 基于不同MTF的盲复原图像。(a)不同空间频率的图像；(b)基于FMTF-motion的盲复原图像；(c)基于FMTF-path的盲复原图像；(d)基于FMTF-tur的盲复原图像
Figure 4. Blind restoration images of different MTFs. (a) Images of different spatial frequencies; (b) Blind restoration images of FMTF-motion; (c) Blind restoration images of FMTF-path; (d) Blind restoration images of FMTF-tur
图 5 水下湍流条纹图像的复原结果。(a)水下湍流条纹图像；(b)基于FMTF-motion的LS方法；(c)基于FMTF-path的LS方法；(d)基于FMTF-tur的LS方法；(e)基于FMTF-motion的BD方法；(f)基于FMTF-path的BD方法；(g)基于FMTF-tur的BD方法
Figure 5. Reconstruction results of underwater turbulence stripe images. (a) Stripe image of underwater turbulence; (b) LS method of FMTF-motion; (c) LS method of FMTF-path; (d) LS method of FMTF-tur; (e) BD method of FMTF-motion; (f) BD method of FMTF-path; (g) BD method of FMTF-tur
图 6 水下湍流条纹图像的超分辨率重建结果。(a)水下湍流条纹图像；(b)基于FMTF-motion的POCS方法；(c)基于FMTF-path的POCS方法；(d)基于FMTF-tur的POCS方法；(e)基于FMTF-motion的L1-TV方法；(f)基于FMTF-path的L1-TV方法；(g)基于FMTF-tur的L1-TV方法
Figure 6. Super resolution results of underwater turbulence stripe images. (a) Stripe image of underwater turbulence; (b) POCS method of FMTF-motion; (c) POCS method of FMTF-path; (d) POCS method of FMTF-tur; (e) L1-TV method of FMTF-motion; (f) L1-TV method of FMTF-path; (g) L1-TV method of FMTF-tur
图 7 海洋鱼群图像的复原结果。(a)海洋鱼群图像；(b)基于FMTF-motion的LS方法；(c)基于FMTF-path的LS方法；(d)基于FMTF-tur的LS方法；(e)基于FMTF-motion的BD方法；(f)基于FMTF-path的BD方法；(g)基于FMTF-tur的BD方法
Figure 7. Reconstruction results of sea fishes images. (a) Sea fishes image; (b) LS method of FMTF-motion; (c) LS method of FMTF-path; (d) LS method of FMTF-tur; (e) BD method of FMTF-motion; (f) BD method of FMTF-path; (g) BD method of FMTF-tur
图 8 海洋鱼群图像的超分辨率重建结果。(a)海洋鱼群图像；(b)基于FMTF-motion的POCS方法；(c)基于FMTF-path的POCS方法；(d)基于FMTF-tur的POCS方法；(e)基于FMTF-motion的L1-TV方法；(f)基于FMTF-path的L1-TV方法；(g)基于FMTF-tur的L1-TV方法
Figure 8. Super resolution results of sea fishes images. (a) Sea fishes image; (b) POCS method of FMTF-motion; (c) POCS method of FMTF-path; (d) POCS method of FMTF-tur; (e) L1-TV method of FMTF-motion; (f) L1-TV method of FMTF-path; (g) L1-TV method of FMTF-tur
表 1 不同调制对比度盲复原图像的GMG
Table 1. GMG of the blind restoration images of different MTFs
Spatial frequency of images/(lp/mm) FMTF-motion FMTF‐path FMTF‐tur 2 11360881 1189020 1189020 3 1615101 1102973 1102973 5 1267690 1557851 1557851 16 7047165 7226900 7226900 
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表 3 超分辨率重建条纹图像的客观评价
Table 3. Objective evaluations of stripe images in super-resolution reconstruction
Item FMTF-motion+
POCS
(Fig. 6(b))FMTF-path+
POCS
(Fig. 6(c))FMTF-tur+
POCS
(Fig. 6(d))FMTF-motion+
L1-TV
(Fig. 6(e))FMTF-path+
L1-TV
(Fig. 6(f))FMTF-tur+
L1-TV
(Fig. 6(g))IC 6.3721 9.6147 9.7786 7.4589 6.6690 9.1354 BM 0.1111 0.0368 0.0113 0.1071 0.0886 0.0136 GMG 1146400000 3400668600 62597149 1767000000 6601191 5136100000
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表 5 超分辨率重建鱼群图像的客观评价
Table 5. Objective evaluations of sea fishes images in super-resolution reconstruction
Item FMTF-motion+
POCS
(Fig. 8(b))FMTF-path+
POCS
(Fig. 8(c))FMTF-tur+
POCS
(Fig. 8(d))FMTF-motion+
L1-TV
(Fig. 8(e))FMTF-path+
L1-TV
(Fig. 8(f))FMTF-tur+
L1-TV
(Fig. 8(g))IC 4.9063 6.4578 6.5512 7.5888 5.3496 9.3000 BM 0.2119 0.1730 0.0821 0.1091 0.0873 0.0241 GMG 49262650 60496856 59643527 449843653 142110023 867582194
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