【正文】 eporter.What Is Digital Image Processing?An image may be defined as a twodimensional function,f(x,y)，where x and y arespatial (plane) coordinates, and the amplitude of fat any pair of coordinates (x,y) is called the intensity or gray level of the image at that point. When x, y, and digital image. Tire field of digital image processing refers to processing digital images by means of a digital puter. Note that a digital image is posed of a finite number of elements, each of which has a particular location and value. These elements are referred to as picture elements, image elements, pels, and pixels. Pixel is the term most widely used to denote the elements of a digital image.Vision is the most advanced of our senses, so it is not surprising that images play the single most important role in human perception. However, unlike human who are limited to the visual band of the electromagic (E11)spectrum, imaging machines cover almost the entire EM spectrum, ranging from gamma to radio waves. They can operate on images 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)論文21generated by sources that human are not accustomed to associating with image. these include ultrasound, electron microscopy, and putergenerated images. Thus, digital image processing enpasses a wide and varied field of application.There is no general agreement among authors regarding where image processing stops and other related areas, such as image analysis and puter vision, start ,sometimes a distinction is made by defining image processing as a discipline in which both the input and output of a process are images. We believe this to be a limiting and somewhat artificial boundary. For example, under this definition, even the trivial task of puting tire average intensity of an image (which yields a single number) would not be considered an image processing operation. On the other hand, there are fields such as puter vision whose ultimate goal is to use puter toemulate human vision, including learning and being able to make inferences and take actions based on visual inputs. This area itself is a branch of artificial intelligence (AI) whose objective is to emulate human intelligence. This field of AI is in its earliest stages of infancy in terms of development, with progress having been much slower than originally anticipated. The area of image analysis (also called image understanding) is in between image processing and puter vision.There are no clearcut boundaries in the continuum from image processing at one end to puter vision at the other. However，one useful paradigm is to consider three types of puterized processes is this continuum: how，mid, and highever processes. lowlevel processes involve primitive operation such as image preprocessing to reduce noise, contrast enhancement, and image sharpening. A lowlevel process is characterized by the fact that both its input and output are processing on images involves tasks such as segmentation (partitioning an image into regions or objects), description of those objects to reduce them to a form suitable for puter processing, and classification (recognition) of individual process is characterized by the fact that its inputs generally are images,but its output is attributes extracted from those images (e. g., edges contours, and the identity of individual object). Finally, higherlevel processing involves making senseof an ensemble of recognized objects, as in image analysis, and, at the far end of the continuum, performing the cognitive function normally associated with vision. Based on the preceding ments, we see that a logical place of overlap between image processing and image analysis is the area of recognition of individual regions or objects in an image. Thus, what we call in this book digital image processing enpasses 石家莊鐵道大學(xué)四方學(xué)院畢業(yè)論文22processes whose inputs and outputs are images and, in addition,enpasses processes that extract attributes from images,up to and including the recognition of individual objects. As a simple illustration to clarify these concepts, consider the area of automated analysis of text. The processes of acquiring an image of the area containing the text. Preprocessing that images, extracting (segmenting) the individual characters, describing the characters in a form suitable for puter processing, and recognizing those individual characters are in the scope of what we call digital image processing in this book. Making sense of the content of the page may be viewed as being in the domain of image analysis and even puter vision,depending on the level of plexity implied by the statement making cense. As will bee evident shortly, digital image processing, as we have defined it, is used successfully in a broad rang of areas of exceptional social and economic value. The concepts developed in the following chapters are the foundation for the methods used in those application areas.The Origins of Digital Image ProcessingOne of the first applications of digital images was in the newspaper industry, when pictures~first sent by submarine cable between London and of the Bartlane cable picture transmission system in the early 1920s reduced the time required to transport a picture across the Atlantic from more than a week to less than three printing equipment coded pictures for cable transmission and then recondstruced on a telegragh printer fitted with typefaces simulating a halftone pattern.The idea of puter goes back to the invention of the abacus in Asia Mintor,more than 5000 years ago. More recently, there were developments in the past two centuries that are the foundation of what we call puter today. However, the basisfor what we call a modem digital puter dates back to only the 1940s with theintroduction by John von Neumann of two key concepts: (1) a memory to hold a stored program and data, and (2)conditional branching. There two i