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IMAGE RESTORATION MODELS Image restoration may be viewed as an estimation process in which operations are performed on an observed or measured image field to estimate the ideal image field that would be observed if no image degradation were present in an imaging system. Mathematical models are described in this chapter for image degradation in general classes of imaging systems. These models are then utilized in subsequent chapters as a basis for the development of image restoration techniques. . | Digital Image Processing PIKS Inside Third Edition. William K. Pratt Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-37407-5 Hardback 0-471-22132-5 Electronic 11 IMAGE RESTORATION MODELS Image restoration may be viewed as an estimation process in which operations are performed on an observed or measured image field to estimate the ideal image field that would be observed if no image degradation were present in an imaging system. Mathematical models are described in this chapter for image degradation in general classes of imaging systems. These models are then utilized in subsequent chapters as a basis for the development of image restoration techniques. 11.1. GENERAL IMAGE RESTORATION MODELS In order effectively to design a digital image restoration system it is necessary quantitatively to characterize the image degradation effects of the physical imaging system the image digitizer and the image display. Basically the procedure is to model the image degradation effects and then perform operations to undo the model to obtain a restored image. It should be emphasized that accurate image modeling is often the key to effective image restoration. There are two basic approaches to the modeling of image degradation effects a priori modeling and a posteriori modeling. In the former case measurements are made on the physical imaging system digitizer and display to determine their response for an arbitrary image field. In some instances it will be possible to model the system response deterministically while in other situations it will only be possible to determine the system response in a stochastic sense. The a posteriori modeling approach is to develop the model for the image degradations based on measurements of a particular image to be restored. Basically these two approaches differ only in the manner in which information is gathered to describe the character of the image degradation. 297 298 IMAGE RESTORATION MODELS FIGURE 11.1-1. Digital image restoration model. .