What are the image file formats and how to choose them?

The commonly used image file formats are as follows: 1 .BMP format BMP is the abbreviation of English Bitmap, which is the standard image file format in Windows operating system and can be supported by many Windows applications. With the popularity of Windows operating system and the development of rich Windows applications, BMP bitmap format is naturally widely used. This format is characterized by rich image information and almost no compression, but this leads to its inherent defect-occupying too much disk space. So BMP is popular on stand-alone computers at present. Second, GIF format GIF is the abbreviation of English graphic exchange format. As the name implies, this format is used to exchange pictures. Actually, it's the same. In 1980s, CompuServe, a famous online information service organization in the United States, developed this GIF image format for the limitation of network transmission bandwidth at that time. GIF format is characterized by high compression ratio and less disk space, so this image format has been widely used soon. At first, GIF was only used to store a single still image (called GIF87a). Later, with the development of technology, several still images can be stored at the same time to form a continuous animation, which became one of the few formats that supported 2D animation at that time (called GIF89a). In GIF89a, you can specify a transparent area to make the image have an extraordinary display effect and make GIF more beautiful. At present, a large number of color animation files used on the internet are mostly files in this format, also known as GIF89a format files. In addition, considering the actual situation in network transmission, the GIF image format also adds a gradual display mode, that is, in the process of image transmission, users can first see the general outline of the image, and then gradually see the details of the image as the transmission process continues, thus adapting to the user's viewing psychology of "from hazy to clear". At present, a large number of color animation files used on the Internet are mostly files in this format. However, GIF has a small disadvantage, that is, it can't store pictures with more than 256 colors. Nevertheless, this format is still widely used on the Internet, which is inseparable from the advantages of short GIF image files, fast download speed and animation composed of many image files of the same size. Third, JPEG format JPEG is also a common image format. It was developed by the Joint Photographic Expert Group and named "ISO10918-1". JPEG is just a common name. The extension of JPEG files is. Jpg or. Jpeg, its compression technology is very advanced. It uses lossy compression to remove redundant image and color data, and can display very rich and vivid images at the same time, in other words, it can get better image quality with the least disk space. At the same time, JPEG is a very flexible format, which has the function of adjusting the image quality, allowing you to compress this file with different compression ratios. For example, we can compress the BMP bitmap file of 1.37MB to 20.3KB at most. Of course, we can find a balance between image quality and file size. JPEG is widely used because of its excellent quality and performance, especially on the Internet and CD-ROM. At present, all kinds of browsers support JPEG as an image format. Because of its small file size and fast download speed, the web page can provide a large number of beautiful images in a short download time, and JPEG has naturally become the most popular image format on the network. Fourth, JPEG2000 format JPEG 2000 is also formulated by JPEG organization. Its official name is "ISO 15444". Compared with JPEG, it has a new generation of still image compression technology with higher compression rate and more new functions. As an upgraded version of JPEG, JPEG2000 has a compression ratio about 30% higher than JPEG. Unlike JPEG, JPEG2000 supports both lossy and lossless compression, while JPEG can only support lossy compression. Lossless compression is very useful for saving some important pictures. An extremely important feature of JPEG2000 is that it can realize progressive transmission, which is similar to the progressive display of GIF, that is, the outline of the image is transmitted first, and then the data is transmitted step by step, so as to continuously improve the image quality and make the image display from hazy to clear, instead of slowly displaying from top to bottom as JPEG does now. In addition, JPEG2000 also supports the so-called "region of interest" function. You can arbitrarily specify the compression quality of the region of interest in the image, or you can choose to decompress the specified part first. Compared with JPEG, JPEG 2000 has obvious advantages and backward compatibility, and it is just around the corner to replace the traditional JPEG format. JPEG2000 can be applied to the traditional JPEG market, such as scanners, digital cameras, and other emerging fields, such as network transmission and wireless communication. 5.TIFF format TIFF (tagged image file format) is an image format widely used in Mac. Developed jointly by Aldus and Microsoft, it was originally designed for cross-platform storage of scanned images. It is characterized by complex image format and much information stored. It is precisely because it stores a lot of subtle information of the image and the quality of the image is also improved, so it is very conducive to the reproduction of the original. There are two forms of this format: compressed and uncompressed, in which compressed can be stored as LZW lossless compression scheme. However, due to the complex structure and poor compatibility of TIFF format, sometimes your software may not correctly identify TIFF files (most software has solved this problem now). At present, it is also very convenient to transplant TIFF files on Mac and PC, so TIFF is now one of the most widely used image file formats on microcomputers. 6.PSD format This is a special format Photoshop document (PSD) of Adobe's famous image processing software Photoshop. PSD is actually a "draft" of graphic design in Photoshop, which contains samples of various designs such as layers, channels and masks, so that the final design can be modified when the file is opened next time. Among the various image formats supported by Photoshop, PSD has much faster access speed and more powerful functions than other formats. With the wider application of Photoshop, we have reason to believe that this format will gradually become popular. PNG format PNG (Portable Network Graphics) is a new network image format. At the end of 1994, because Unysis announced that GIF had a patented compression method, the author of GIF software was required to pay a certain fee, which prompted the birth of free png image format. PNG combines the advantages of GIF and JPG from the beginning, and intends to replace these two formats in one fell swoop. 1 996 65438+1October1was proposed by PNG to the international network alliance and was recommended and recognized. Most drawing software and browsers began to support PNG image browsing. Since then, the PNG image format has been full of vitality. PNG is the most undistorted format at present, which absorbs the advantages of GIF and JPG, has rich storage forms and has two color modes of GIF and JPG. Another feature of PNG is that it can compress image files to the limit of network transmission, but it can retain all information related to image quality, because PNG uses lossless compression to reduce file size, which is different from JPG sacrificing image quality for high compression rate. Its third feature is that the display speed is very fast. Downloading the image information of 1/64 can display a low-resolution preview image. Fourthly, PNG also supports the production of transparent images, which is very useful when making web images. We can set the image background to be transparent, and replace the transparent color with the color information of the webpage itself, so that the image and the webpage background can be harmoniously integrated. The disadvantage of PNG is that it does not support animation application effects. If it can be strengthened in this respect, it can completely replace GIF and JPEG. The default format of Macromedia's Fireworks software is PNG. Now, more and more software begin to support this format, and it is becoming more and more popular on the Internet. Eight, SWF format uses Flash, we can make an animation with the suffix SWF(Shockwave format). The animated images in this format can express rich multimedia forms with a relatively small volume. In image transmission, you don't have to wait until all files have been downloaded before you can watch them, but you can watch them while downloading them, so it is especially suitable for network transmission, especially when the transmission rate is not good, and you can get better results. Facts have also proved this point. SWF has been widely used in multimedia presentation and interactive design of web pages. In addition, SWF animation is made by vector technology, so no matter how many times the screen is enlarged, the screen will not be damaged. To sum up, the works in SWF format are favored by more and more web designers because of their high-definition image quality and compact size, and have become the mainstream of web animation and web picture design and production, and now they have become the de facto standard of network animation. Nine, SVG format SVG can be regarded as the hottest image file format at present. Its full English name is Scalable Vector Graphics, which means extensible vector graphics. It is based on XML (Extensible Markup Language) and developed by World Wide Web Consortium (W3C). Strictly speaking, it should be an open standard vector graphics language, which allows you to design exciting and high-resolution Web graphics pages. Users can draw images directly with codes, open SVG images with any word processing tools, and make the images interactive by modifying some codes, and they can be inserted into HTML at any time and viewed by browsers. It provides the advantages that GIF and JPEG, the popular formats on the Internet, do not have: you can enlarge the graphic display at will, but never at the expense of image quality; Text remains editable and searchable in SVG images; Generally speaking, SVG files are much smaller than JPEG and GIF files, so the download speed is very fast. It is believed that the development of SVG will provide a new image standard for the Web. Other non-mainstream image formats: 1, PCX format PCX format is a compressed format developed by ZSOFT when developing the image processing software Paintbrush, which takes up less disk space. Because this format has been around for a long time and has the ability of compression and full color, it is still popular now. 2.DXF format DXF (Autodesk Graphic Interchange Format) is a vector file format in AutoCAD. It stores files in ASCII code, which is very accurate in representing the size of graphics. Many softwares support input and output in DXF format. 3.WMF format WMF(Windows metafile format) is a common metafile format in Windows and belongs to vector file format. It has the characteristics of short file and modeling mode, and the whole graph is often spliced by various independent components, and its graph is often rough. 4.EMF format EMF(Enhanced Metafile) is a Windows 32-bit extended metafile format developed by Microsoft to make up for the shortage of using WMF. It also belongs to the vector file format, which aims to make the metafile more acceptable. 5.LIC(FLI/FLC) format Flic format was developed by Autodesk Company. FLIC is the collective name of FLC and FLI: FLI is an original animation file format based on 320×200 resolution, while FLC adopts more efficient data compression technology, so the compression ratio is higher than FLI, and the resolution is also improved a lot. 6.EPS format EPS(Encapsulated PostScript) is a format that PC users rarely see, while users of Apple Mac machines use it more. It is an ASCII file format described in PostScript language, which is mainly used for typesetting, printing and other output work. 7.TGA format TGA(Tagged Graphics) file is an image file format developed by American Truevision Company for its graphics card, which has been accepted by the international graphics and image community. TGA has a simple structure, belongs to the general format of graphics and image data, has great influence in the field of multimedia, and is the preferred format for converting computer-generated images into TV.