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Chapter 1:
Image Stabilization
Image stabilization is the technique of improving image quality by actively removing the apparent motion of an object induced by vibration, tracking errors, and differential refraction in the atmosphere. It is the apparent motion of the object because usually the object itself is quite stable, yet in the imaging system the object appears to be moving. The result of using image stabilization is an image that is sharper and has higher contrast and resolution. In astronomical imaging, image stabilization is an important tool for removing the effects of the earth's atmosphere. Light from a distant star or other heavenly object travels through the vacuum of space and arrives at a space telescope having undergone very little in the way of physical changes. However, when that same light is propagated through a turbulent medium such as earth's atmosphere and reaches an earth-based telescope, the arriving light may have little more than its frequency in common with its transmitted form (Tyson 2000)! For centuries, astronomers have observed this effect as the blurry images seen through their telescopes; however, only recently have scientists begun to understand and develop techniques to compensate for this effect (Babcock 1953). The distorting effect of a turbulent medium on light passing through it imposes a limit on the performance of optical systems. As a result, there is significant demand for atmospheric compensation systems for use in astronomical, communications, and military systems. New applications are also being developed for industrial and medical purposes (Love 1999; Restaino and Teare 2000; Wittrock 2003). Image stabilization is arguably one of the most important advances in the science of imaging. The techniques and instrumentation used to correct for image motion are based on understanding the physical effects that degrade image quality. To this end, two important components of image motion can be identified as beam wander and image dancing, defined by Lawrence (2004) as angular deviation of the beam from the line-of-sight path, possibly causing the beam to miss the receiver; and fluctuations in the beam angle of arrival, causing the focus to move in the image plane, respectively.
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