Research On Enhancement Algorithm For Low-illumination Image

Because of the shortage of light,there are many low-illumination images.Therefore,enhancement processing need be implemented to improve the quality and visual effect of these images.The traditional image enhancement methods can be divided into space domain and frequency domain methods.The histogram equalization is the most popular way of the former one;while the methods based on frequency often uses flourier transform and wavelet transform to enhance the images.This research discusses both of the two methods.Aiming at the darkness,low contrast and connected dark pixels of low-illumination image,the improved histogram equalization algorithm of image enhancement based on dark area removement is introduced.With this algorithm,we can segment out several dark areas from a low-illumination image by setting an upper limit of the dark area's gray-level,then process the left image use the improved histogram equalization algorithm.This algorithm can reduce the impact of the dark background to the useful details;it is proved to be efficient for low-illumination images.Then we present a low-illumination image enhancing method base on combination of the coefficients from the wavelet transform.In this algorithm,we use space domain method and frequency domain method to process the low frequency and high frequency information separately.It is proved that the method can avoid visual image details loss caused by the amalgamation of low frequency gray-scale and reduce noise for high frequency information.Using this method also can save exposure time.There is a significant result in the image enhancing process.