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| 作者：希赛网 来源：希赛网 http://www.csai.cn 2006年11月1日 |
DIGITAL IMAGE FILE FORMATS Why do we need so many different types of image file formats？The short answer is that there are many different types of images and applications with varying requirements[1]．A more complete answer（which we will not go into here）also considers market share，proprietary information，and a lack of coordination within the imaging industry．However，some standard file formats have been developed，and the ones presented here are widely available．Many other image types can be readily converted to one of the types presented here by easily available image conversion software．
% L" c0 y% v, p A field related to computer imaging is that of computer graphics．Computer graphics is a specialized field within the computer science realm that refers to the reproduction of visual data through the use of the computer．This includes the creation of computer images for display or print，and the process of generating and manipulating any images（real or artificial）for output to a monitor，printer，camera，or any other device that will provide us with an image．Computer graphics can be considered a part of computer imaging，insofar as many of the same tools the graphics artist uses may be used by the computer imaging specialist[2]．
! F2 R A! N; h p7 H+ Z In computer graphics，types of image data are divided into two primary categories：bitmap and vector．Bitmap images（also called raster images）can be represented by our image model I（r，c），where we have pixel data and the corresponding brightness values stored in some file format．Vector images refer to methods of representing lines，curves，and shapes by storing only the key points．These key points are sufficient to define the shapes，and the process of turning these into an image is called rendering．After the image has been rendered，it can be thought of as being in bitmap format，where each pixel has specific values associated with it．8 y5 f! U3 k, ^) L9 m$ B
Most of the types of file formats discussed fall into the category of bitmap images，although some are compressed，so that the I（r，c）values are not directly available until the file is decompressed．In general，these types of images contain both header information and the raw pixel data．The header must contain information regarding：（1）the number of rows（height），（2）the number of columns（width），（3）the number of bands，（4）the number of bits per pixel，and（5）the file type．Additionally，with some of the more complex file formats，the header may contain information about the type of compression used and any other necessary parameters to create the image．% l9 b* O! Z) M- f
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