Underwater image recovery considering polarization effects of objects

Abstract

In underwater imaging scenarios, the scattering media could cause severe image degradation due to the backscatter veiling as well as signal attenuation. In this paper, we consider the polarization effect of the object, and propose a method of retrieving the objects radiance based on estimating the polarized-difference image of the target signal. We show with a real-world experiment that by taking into account the polarized-difference image of the target signal additionally, the quality of the underwater image can be effectively enhanced, which is particularly effective in the cases where both the object radiance and the backscatter contribute to the polarization, such as underwater detection of the artifact objects.

Polarimetric image recovery method combining histogram stretching for underwater imaging

“…4(b) , the range of gray level of the intensity image is compressed into a narrow band. Here we introduce the measure of enhancement (EME) to quantify the image quality 25 , 26 as follows: where the image i ( x, y ) is divided into m × n blocks , and refer to the max- and min-value of the image in the block . In order to avoid being divided by zero, the parameter q is a small constant set to 0.0001 25 .…”

“…7(e) has only a slight improvement. This is because our method perform histogram stretching for the cross-linear image, which contains more useful information and has a larger space of enhancement by histogram stretching 5 , 25 . Therefore, the proper way of combining histogram stretching and polarimetric image recovery is critical for the performance of image recovery, which is the key point of our method.…”

“…In addition, to further verify the superiority and effectiveness of our method, we use various evaluation criterions to evaluate the quantify of the images in Fig. 7 , including local image contrast (IC) 24 , EME 25 , standard deviation 30 σ and blind-reference-less image spatial quality evaluator (BRISQUE) 31 . Higher value of EME, IC and σ indicates higher image quality, while lower value of BRISQUE indicate higher image quality.…”

“…The polarimetric recovery method is based on two orthogonal polarization images. However, previous polarimetric recovery methods directly process the original orthogonal polarization images 17 , 25 . Actually, although the polarizer can partially block the backscattering light, some unwanted scattering lights still exist in the orthogonal images, which results in the compression of gray level range of the intensity image 11 .…”

Absolute Measurement of the Refractive Index of Water by a Mode-Locked Laser at 518 nm

“…In terms of power attenuation, power-based measurements are negatively affected by extreme environments underwater. In short-path underwater measurements, optical waves, with a transmission window of between 480 nm and 540 nm, are an ideal candidate [ 7 , 8 , 9 ]. With excellent laser alignment and inherent high power, the underwater optical technique has shown itself to be highly effective in marine applications [ 10 ].…”