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Xử lý hình ảnh kỹ thuật số P10

IMAGE ENHANCEMENT Image enhancement processes consist of a collection of techniques that seek to improve the visual appearance of an image or to convert the image to a form better suited for analysis by a human or a machine. In an image enhancement system, there is no conscious effort to improve the fidelity of a reproduced image with regard to some ideal form of the image, as is done in image restoration. | 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 10 IMAGE ENHANCEMENT Image enhancement processes consist of a collection of techniques that seek to improve the visual appearance of an image or to convert the image to a form better suited for analysis by a human or a machine. In an image enhancement system there is no conscious effort to improve the fidelity of a reproduced image with regard to some ideal form of the image as is done in image restoration. Actually there is some evidence to indicate that often a distorted image for example an image with amplitude overshoot and undershoot about its object edges is more subjectively pleasing than a perfectly reproduced original. For image analysis purposes the definition of image enhancement stops short of information extraction. As an example an image enhancement system might emphasize the edge outline of objects in an image by high-frequency filtering. This edge-enhanced image would then serve as an input to a machine that would trace the outline of the edges and perhaps make measurements of the shape and size of the outline. In this application the image enhancement processor would emphasize salient features of the original image and simplify the processing task of a data-extraction machine. There is no general unifying theory of image enhancement at present because there is no general standard of image quality that can serve as a design criterion for an image enhancement processor. Consideration is given here to a variety of techniques that have proved useful for human observation improvement and image analysis. 10.1. CONTRAST MANIPULATION One of the most common defects of photographic or electronic images is poor contrast resulting from a reduced and perhaps nonlinear image amplitude range. Image 243 244 IMAGE ENHANCEMENT OUTPUT a Continuous image contrast enhancement b Quantized image contrast .