The Study Of Image Enhancement Algorithm Based On Wavelet Transform

With the development of the society the internet and computers are used widely in the people's everyday life. The transmit of images visions vides and so on have brought so many pleasures, at the same time the demand of such documents becomes more and more strongly. But the quality of images may decrease because during the course of gaining and transmitting images they are interfered with by all kinds of causes. The paper is about how to deal with these images to suffice for the practice, so now what we must do is to deal with the enhancement of images.The image enhancement is an important part of digital image processing. There are many methods of image enhancement, Image enhancement techniques can. be divided into two broad categories:Spatial domain methods, which operate directly on pixels, and frequency domain methods, which operate on the Fourier transform of an image. There are many spatial domain methods, such as:grey scale manipulation, histogram equalization, neighborhood averaging, median filtering, and image sharpening and so on. Image enhancement in the frequency domain is straightforward. We simply compute the Fourier transform of the image to be enhanced, multiply the result by a filter (rather than convolve in the spatial domain), and take the inverse transform to produce the enhanced image. The idea of blurring an image by reducing its high frequency components or sharpening an image by increasing the magnitude of its high frequency components is intuitively easy to understand. The main frequency domain enhancement methods are:low pass filtering, high pass filtering and homomorphic filtering. Frequency domain enhancement is often more efficient to implement these operations as convolutions by small spatial filters in the spatial domain.But the traditional methods will enhancement the image with block effect; this is not satisfied human viewer. The technology of wavelet analysis has special advantages to deal with images it can withdraw characters of signals in many directions and in freely scale. The technology can separated noises from signals in different scales. In this paper we discussed how the property of the wavelet basis affects the process of image denoising. This paper mainly studied image enhancement based on wavelet transform, the follows are the main work.In the first, this paper has deeply discussed the present situation of the method of image denoising and image enhancement. Wavelet filtration technology is widely used because the way of its calculation is simple. After deeply researching the selection on threshold function and threshold in wavelet filtration technology in theory, the paper adopts a developing threshold function and threshold.Secondly, mainly focus on image enhancement based on wavelet transform, for the image transformed, considering several methods such as different wavelet base selection and different variable parameters with different results. The experimental and calculation results show that the enhancement algorithm and evaluation criteria are effectual.