![]() The reason for increased research in this area is that the process of taking images underwater is very difficult. Underwater image processing has received tremendous attention in the past few years. The difference between L f and L b is also the luminance of the artificial light source that is to say, the luminance of the artificial light source. Higher mean luminance in the foreground of an image than in the background indicates the existence of an artificial light source. In an underwater image without artificial lighting, the background directly transmits natural light without reflecting off of objects and is therefore the brighter part of the image. The existence of artificial lighting can be determined by the difference between the mean luminance of the foreground and the background, L f and L b. If an artificial light source L is employed during image capturing process, the luminance contributed by L must be deducted first to avoid over-compensation for the stages followed, as illustrated in Fig. Artificial light sources are often supplemented to avoid insufficient lighting commonly encountered in underwater photographic environment, as shown in Fig. Color balance is restored for the whole image, rather than just the top portion of the frame. 7, the color shift suffered at the lower part of the image is greatly reduced. įigure 8 demonstrates the result of fine-tuning the amount of wavelength compensation by deriving the water depth of every image pixel. The background of the image is natural light that travels directly to the camera without reflecting off objects therefore using the background for estimation allows underwater depths to be calculated more. During depth estimation in the depth range R, the foreground and background must first be separated to prevent the colors of the objects in the image from interfering with the estimation. As light transmits through the depth range R, the different underwater depths induce differences in color cast at the top and bottom of the image, thereby necessitating varied energy compensation that corresponds to the underwater depth of each point to rectify color cast. The depth range of the image covers the photographic scene from depth D to D+R, as shown in Figure 2. Thus, depth estimation for each point in the image is necessary to achieve corresponding energy compensation at the various depths. However, the depth of the top and bottom of the image are not the same using depth D for energy compensation of the entire image results in some color cast remaining at the bottom of the image. is the underwater image after haze removal and calibration of color cast, as shown J ˆ in Figure 7.
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