| Summary: | 碩士 === 國立中山大學 === 資訊工程學系研究所 === 99 === Light scattering and color shift are two major sources of distortion for underwater
photography. Light scattering is caused by light incident on objects reflected and
deflected multiple times by particles present in the water before reaching the camera.
This in turn lowers the visibility and contrast of the image captured. Color shift
corresponds to the varying degrees of attenuation encountered by light traveling in the
water with different wavelengths, rendering ambient underwater environments
dominated by bluish tone.
This paper proposes a novel approach to enhance underwater images by a
dehazing algorithm with wavelength compensation. Once the depth map, i.e., distances
between the objects and the camera, is estimated by dark channel prior, the light
intensities of foreground and background are compared to determine whether an
artificial light source is employed during image capturing process. After compensating
the effect of artifical light, the haze phenomenon from light scattering is removed by the
dehazing algorithm. Next, estimation of the image scene depth according to the residual
energy ratios of different wavelengths in the background is performed. Based on the
amount of attenuation corresponding to each light wavelength, color shift compensation
is conducted to restore color balance. A Super-Rsolution image can offer more details
that must be important and necessary in low resolution underwater image. In this paper
combine Gradient-Base Super Resolution and Iterative Back-Projection (IBP) to
propose Cocktail Super Resolution algorithm, with the bilateral filter to remove the
chessboard effect and ringing effect along image edges, and improve the image quality.
The underwater videos with diversified resolution downloaded from the Youtube
website are processed by employing WCID, histogram equalization, and a traditional
dehazing algorithm, respectively. Test results demonstrate that videos with significantly
enhanced visibility and superior color fidelity are obtained by the WCID proposed.
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