| Our country has 18,000 kilometers long coastline and 3,000,000 square kilometers sea national territory, so the studies on seas'rules, as well as seas-exploration are vital for our country's economy and military. The images'information is the basic and significant source for human to obtain information. However, the poor underwater condition results the underwater images with a too low-quality for the seas-exploration. From the perspective of digital images'processing, we did some research on the underwater images'pre-processing methods to improve their quality.We adopted the majority of existing images'pre-processing methods, and had ameliorated some of them to process the real underwater images. In the local measure enhancement method, we proposed a new enhancement method based on the local complexity, which was effective for the small size underwater images. Aiming at the brightness distributive characters of underwater images, we ameliorated the wavelet transformative enhancement, and proposed a new enhancement method which was based on the wavelet and nonlinear iteration. This new method will not only enhance the underwater images'effectively but also solve the problem of the underwater image's uneven brightness distribution.We could choose the prior method in the certain condition after comparative analyzing all those methods from both enhancement and de-noised parts. For the underwater images'enhancement, if the image's brightness is even, but for the whole it is dark, we should choose the homomorphic-filtering method(low-frequency gain is supposed to be bigger than 1) and enhancement method based on wavelet and nonlinear iteration. If the underwater image's brightness is uneven, we suggest choosing the enhancement method based on wavelet and nonlinear iteration. In the process of underwater images'de-noising, if it is pepper-and-salt noise, we'd better choose median filtering; if it is gaussian noise, we'd better choose BayesShrink de-noising method. |
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