Underwater images mainly suffer from the problem of poor color contrast and poor visibility. These problems occurred due to the scattering of light and refraction of light while entering from rarer to denser medium. Scattering causes the blurring of light and reduces the color contrast. These effects of water on underwater images are only not due the nature water but also because of the organisms and other material present in the water. Image enhancement is the process of improving the quality of the input image so that it would be easily understood by viewers in the future. Image enhancement improves the information content of the image and alters the visual impact of the image on the observer. Image enhancement intensifies the features of images. It accentuates the image features like edges, contrast to build display of photographs more useful for examination and study. Active range of the chosen features of images is amplified by enhancement so that they can be detected simply. Many techniques and methods are established by researchers to solve the problem of underwater image enhancement. In this work different underwater image enhancing techniques have been studied. Keywords: Homomorphic Filtering, Histogram Equalization, Bilateral filtering, Contrast Stretching, CLAHE I. INTRODUCTIONFrom last few years, underwater image processing area has received a great attention of researchers to explore the mysterious underwater world. Underwater surveys have numerous scientific applications in the field of archaeology, geology and biology, involving tasks such as ancient shipwreck prospection, environmental damage assessment etc. To capture a clear underwater image has a crucial importance in oceanic engineering [1]. Clear underwater images have a great importance in scientific operations like taking a census of sea population, include the discovery of objects in liquids or the image analysis needed to identify targets submerged in a liquid. There have also been studied that attempted to identify targets suspended in a solution. These studies could be useful for defense applications. For capturing a clear visible underwater image, water must be a limpid or clear, but naturally all the water is turbid with particles such as sand, planktonsor , minerals. As outdoor images are distorted because of particles present in the air, like that underwater images also get distorted because of particles present in the water. Underwater Images becomes more and more hazy or less visible as water depth increases. Generally underwater images get distorted because of two reasons. One is light scattering effect and second is color change effect. Therefore, the processing of underwater image captured is necessary because the quality of underwater images affect and these image leads due to low contrast, poor visibility conditions (absorption of natural light), non uniform lighting and little color variations, pepper noise and blur effect in the underwater images because of all these reasons number of methods are existing to cure...