POINT AND SPATIAL IMAGE RESTORATION TECHNIQUES A common defect in imaging systems is unwanted nonlinearities in the sensor and display systems. Post processing correction of sensor signals and pre-processing correction of display signals can reduce such degradations substantially (1). Such point restoration processing is usually relatively simple to implement. One of the most common image restoration tasks is that of spatial image restoration to compensate for image blur and to diminish noise effects. References 2 to 6 contain surveys of spatial image restoration methods. . | 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 12 POINT AND SPATIAL IMAGE RESTORATION TECHNIQUES A common defect in imaging systems is unwanted nonlinearities in the sensor and display systems. Post processing correction of sensor signals and pre-processing correction of display signals can reduce such degradations substantially 1 . Such point restoration processing is usually relatively simple to implement. One of the most common image restoration tasks is that of spatial image restoration to compensate for image blur and to diminish noise effects. References 2 to 6 contain surveys of spatial image restoration methods. . SENSOR AND DISPLAY POINT NONLINEARITY CORRECTION This section considers methods for compensation of point nonlinearities of sensors and displays. . Sensor Point Nonlinearity Correction In imaging systems in which the source degradation can be separated into cascaded spatial and point effects it is often possible directly to compensate for the point degradation 7 . Consider a physical imaging system that produces an observed image field FO x y according to the separable model FO x y OQ OD C x y X 319 320 POINT AND SPATIAL IMAGE RESTORATION TECHNIQUES FIGURE . Point luminance correction for an image sensor. where C x y X is the spectral energy distribution of the input light field Oq represents the point amplitude response of the sensor and Od denotes the spatial and wavelength responses. Sensor luminance correction can then be accomplished by passing the observed image through a correction system with a point restoration operator Or ideally chosen such that Or Oq 1 For continuous images in optical form it may be difficult to implement a desired point restoration operator if the operator is nonlinear. Compensation for images in analog electrical form can be accomplished with a nonlinear amplifier while digital
