Removing The Speckle On The Image

The speckle is a common phenomenon. One kind speckle lies in the domain of the coherent wave. In this case the existence of the speckle is unavoidable, such as holography, coherent processing, coherent imaging, synthesized aperture radar, acoustic imaging, observing of the star and microwave etc. Another condition is incoherent, because of the asymmetry in the medium. For example the particle in the air, the defect on the surface of the object, such as the speckle on the leafage etc. In a word, we call the irregular speckle in the image as the imaging speckle.The existence of the imaging speckle not only effects the resolution of the image, but also makes the appearance of the image modulated by the speckle. It is very unfavorable for our observing. So people try to remove or weaken the speckle. In past, the research was concentrated on the coherent condition or using the coherent filtering to eliminate the speckle. The first reason is that the method that to eliminate the laser speckle is realized by scanning on the limited aperture in the imaging process to weak the speckle . The formation of the laser speckle is a result that the random distribution wave superposes , the operation above can change the statistic property of the wave, then we can mean the speckle , but for the speckle in the image , the forming course ended , the speckle has been on the image , In this condition the idea above should be studied further . The second reason is that the method of using the coherent filtering to eliminate the speckle has its limit. First, when the space frequency of the image and the space frequency of the speckle are high ,we can eliminate the speckle using a small filtering window (high-pass filtering or low-pass filtering ) ,while ,at the same time we will lost the high space frequency information and decrease the resolution of the image. The other condition is concentrated on restoring the image or removing the blur of the image. We will record the blur image because of the disturb of the atmosphere, misfocusing, the relative motion between the target and the recording medium . We can eliminate this kind speckle by compensating filtering (inverse filtering) on the frequency plane of the coherent system . But the effect cannot satisfy us by using any method above.Because the method to eliminate or weak the speckle that has solidified on the image has not been involved, while the speckle exists in all kinds of the conditions, it haspractical meaning to research the idea for removing the speckle on the image .This thesis concentrates its researching on this condition .In the 4F system , illuminating the image by the laser beam , scanning the frequency spectrum by moving the limited aperture in the plane of the frequency spectrum , we will get the recomposed image in the image plane . The speckle has been weakened or eliminated. The reason is that when the speckle waves of the image pass the aperture the weight factor is different in the different time , then the position of the speckle in the image plane is different in the different time . Then in the image plane the speckle of the original image has been averaged by integrating , but the image point has been superposed in a regular mode , the image has been reproduction .We analyze the method to eliminate or weak the laser speckle by moving the limited aperture to scan the field of the image plane or pupil plane , and get the express of the statistic property of the speckle that has been weakened . The autocorrelation function of the averaging by time and the probability- density function of the time-averaging intensity, these statistic property of the speckle that has been weakened only depend on the shape of the aperture and its moving mode . We also discuss the image processing by 4F system, and deduce the probability-density function of moving the limited aperture in the plane of the frequency to average the intensity of the speckle in the image plane . We expatiate the theory that to remove the speckle on the image by moving the limited aperture...