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Underwater Color Image Enhancement Using Wavelength Compensation and Dehazing

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The paper describes underwater image enhancement methods. While capturing under-water images, the quality of the image is degraded by absorption and scattering of light. Such problems should be addressed in order to analyse the underwater images effectively. In this paper we propose histogram equalisation and contrast stretching algorithm to enhance the underwater image quality. In both the cases WCID- Wavelength compensation and image dehazing algorithm is used. Using this techniques both scattering and absorption effects are eliminated.
Keywords:Image enhancement, histogram equalization, contrast stretching, WCID.
Analysis of underwater image is challenging due to the effects of scattering and absorption of light in underwater environment. These effects are addressed using technique such as image enhancement, histogram equalisation, etc. Contrast enhancement is the process of adjusting contrast and brightness of images or the process of removing undesired characteristics of image. Histogram equalisation is the process of graphical representation of number of pixels in the captured image. Today, several researches are carried out for processing and analysing of underwater images to improve underwater image quality. In aquatic environment scattering and absorption of light degrades the quality of the captured underwater image since contrast reduction and non-uniform colour cast takes place under water. KashifIqbal proposed unsupervised colour correction method (UCM) as preprocessing stage of underwater image enhancement. In underwater situations, one colour dominates the image due to scattering and absorption. In order to improve the quality of the underwater image an approach based on slide stretching is proposed. This includes contrast stretching of RGB algorithm and saturation and intensity stretching of HSI.
Segmentation of underwater image without losing object details, becomes difficult since clarity of underwater image is poor. So image segmentation approach has been developed in which contrast limited adaptive histogram equalization method is first used to enhance the image quality. Then segmentation of objects is performed using histogram underwater situations contrast and resolutions are low which leads to poor visibility making object identification Difficult. To find better contrast enhancement technique Balvant Singh compares contrast limited adaptive equalization method with contrast stretching and histogram equalization method using mean square error and SNR as parameters. Cosmin Ancuti proposed a strategy for underwater video and image enhancement. Using fusion principles input and weight measures are derived only from degraded version of the underwater image. In underwater images contrast varies across the scene and scene depth which disables proper operation of standard computer vision algorithms. An experiment with real underwater images with different degrees of turbidity shows that underwater scenes are reconstructed more accurately using physically-based light propagation model than by using standard stereo algorithms alone.[1] Since quality of underwater image is poor, success rate of scale-invariant feature transform (SIFT) image registration reduces while capturing underwater image. Pulung nurtantio andono proposed pre-processing of image based on the Contrast Limited Adaptive Histogram image Equalization (CLAHE) algorithm. He assumes that Rayleigh scattering dominates the distribution of pixel intensity values of recorded image. The underwater ultrasonic image includes speckle noise. Reduction of speckle noise and enhancement of image contrast has to be performed at the same time. For this purpose anisotropic diffusion model based on wavelet transform is proposed. This model provides improved speckle reduction and image enhancement. The clarity of underwater photoelectric image is reduced due to light scattering and absorption. Shuai Fang proposed single image enhancement based on image fusion strategy. He used the images to which white balance and global contrast enhancement is performed as inputs and computed weight sum of the inputs for each pixel. This improved the image enhancement.


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