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 visualeffect of these images. The traditional image enhancement methods can be devided into spacedomain and frequency domain methods. The histogram equalization is the most popular wayof the former one; while the methods based on frequency often uses flourier transform andwavelet 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-illuminationimage, the improved histogram equalization algorithm of image enhancement based on darkarea removement is introduced. With this algorithm, we can segment out several dark areasfrom a low-illumination image by setting an upper limit of the dark area’s gray-level, thenprocess the left image use the improved histogram equalization algorithm. This algorithm canreduce the impact of the dark background to the useful details, it is proved to be efficient forlow-illumination images. Then we present a low-illumination image enhancing method baseon combination of the coefficients from the wavelet transform. In this algorithm, we use spacedomain method and frequency domain method to process the low frequency and highfrequency information separately. It is proved that the method can avoid visual image detailsloss caused by the amalgamation of low frequency gray-scale and reduce noise for highfrequency information. Using this method also can save exposure time.There is a significantresult in the image enhancing process.