Image Restoration What is image restoration? Image restoration is the improvement of an image using objective criteria and prior knowledge as to what the image should look like. What is the difference between image enhancement and image restoration? In image enhancement we try to improve the image usingsubjective criteria, while in image restoration we are trying to reverse a specific damage suffered by the image, using objective criteria. Why may an image require restoration? | Image Processing The Fundamentals. Maria Petrou and Panagiota Bosdogianni Copyright 1999 John Wiley Sons Ltd Print ISBN 0-471-99883-4 Electronic ISBN 0-470-84190-7 Chapter 6 Image Restoration What is image restoration Image restoration is the improvement of an image using objective criteria and prior knowledge as to what the image should look like. What is the difference between image enhancement and image restoration In image enhancement we try to improve the image using subjective criteria while in image restoration we are trying to reverse a specific damage suffered by the image using objective criteria. Why may an image require restoration An image may be degraded because the grey values of individual pixels may be altered or it may be distorted because the position of individual pixels may be shifted away from their correct position. The second case is the subject of geometric restoration Geometric restoration is also called image registration because it helps in finding corresponding points between two images of the same region taken from different viewing angles. Image registration is very important in remote sensing when aerial photographs have to be registered against the map or two aerial photographs of the same region have to be registered with each other. How may geometric distortion arise Geometric distortion may arise because of the lens or because of the irregular movement of the sensor during image capture. In the former case the distortion looks regular like those shown in Figure . The latter case arises for example when an aeroplane photographs the surface of the Earth with a line scan camera. As the aeroplane wobbles the captured image may be inhomogeneously distorted with pixels displaced by as much as 4 5 interpixel distances away from their true positions. 194 Image Processing The Fundamentals a Original b Pincushion distortion c Barrel distortion Figure Examples of geometric distortions caused by the lens. Figure In this figure the
