1、附 录 附录 A 外文资料 The research of digital image processing technique Introduction Interest in digital image processing methods stems from two principal application areas: improvement of pictorial information for human interpretation； and processing of image data for storage, transmission, and representa
2、tion for autonomous machine perception. This chapter has several objectives: (1)to define the scope ofthe field that we call image processing； (2)to give a historical perspective of the origins of this field； (3)to give an idea of the state of the art in image processing by examining some of the pri
3、ncipal area in which it is applied； (4)to discuss briefly the principal approaches used in digital image processing； (5)to give an overview of the components contained in a typic 叭 general-purpose image processing system； and (6) to provide direction to the books and other literature where image pro
4、cessing work normally is reporter. What Is Digital Image Processing? An image may be defined as a two-dimensional function,f(x,y)， where x and y are spatial (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. W
5、hen x, y, and digital image. Tire field of digital image processing refers to processing digital images by means of a digital computer. Note that a digital image is composed of a finite number of elements, each of which has a particular location and value. These elements are referred to as picture e
6、lements, 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 th
7、e visual band of the electromagnetic (E11)spectrum, imaging machines cover almost the entire EM spectrum, ranging from gamma to radio waves. They can operate on images generated by sources that human are not accustomed to associating with image. these include ultrasound, electron microscopy, and com
8、puter-generated images. Thus, digital image processing encompasses 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 computer vision, start ,sometimes a distinction is made by
9、 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 computing tire average intensity of an image (which yields a single n
10、umber) would not be considered an image processing operation. On the other hand, there are fields such as computer vision whose ultimate goal is to use computer toemulate human vision, including learning and being able to make inferences and take actions based on visual inputs. This area itself is a
11、 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
12、in between image processing and computer vision. There are no clear-cut boundaries in the continuum from image processing at one end to computer vision at the other. However， one useful paradigm is to consider three types of computerized processes is this continuum: how-， mid-, and high-ever process
13、es. low-level processes involve primitive operation such as image preprocessing to reduce noise, contrast enhancement, and image sharpening. A low-level process is characterized by the fact that both its input and output are images.mid-level processing on images involves tasks such as segmentation (
14、partitioning an image into regions or objects), description of those objects to reduce them to a form suitable for computer processing, and classification (recognition) of individual object.amid-level process is characterized by the fact that its inputs generally are images,but its output is attribu
15、tes extracted from those images (e. g., edges contours, and the identity of individual object). Finally, higher-level 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 associate
16、d with vision. Based on the preceding comments, 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 encompasses processes whose inputs and
17、outputs are images and, in addition,encompasses 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 are
18、a containing the text. Preprocessing that images, extracting (segmenting) the individual characters, describing the characters in a form suitable for computer processing, and recognizing those individual characters are in the scope of what we call digital image processing in this book. Making sense
19、of the content of the page may be viewed as being in the domain of image analysis and even computer vision,depending on the level of complexity implied by the statement making cense. As will become evident shortly, digital image processing, as we have defined it, is used successfully in a broad rang
20、 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 Processing One of the first applications of digital images was in the newspaper industry, when picture
21、sfirst sent by submarine cable between London and NewYork.Introduction 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 hours.Specialized printing equipment coded picture
22、s for cable transmission and then recondstruced on a telegragh printer fitted with typefaces simulating a halftone pattern. The idea of computer 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
23、 the foundation of what we call computer today. However, the basisfor what we call a modem digital computer 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 ideas are the foundation of a central processing unit (CPU), which is at the heart of computer today. Starting with von Neumann, there were a series of advances that led to computers powerful enough to be used for digital image processing. Briefly, these advances may
