Image searching on the Web Qunyan Mao SIMS, UC Berkeley
Image on the Web • More images on the web • Format of image – GIF: Compu. Serve Graphics Interchange format, a dominant web format – JPEG: support “true color”, ideal for photographs – TIF: large file size, not well suited for web pages
Image format – BMP: such as desktop wallpaper image, not supported by any Web browser – PNG: Portable Network Graphics. An image format for the future.
Image indexing • Two methods used in indexing images – text-based – content-based
Text-based vs content based • Text-based : commonly used image indexing and searching method – descriptive text – controlled vocabulary • Drawbacks: – have to have descriptor along with the image to make it accessible – consistency: different type of textual data – human intervention
Text-based vs. . content based • Content-based indexing and searching – goal: provide algorithms that can automatically recognize the important features in an image without human intervention – search by color, shape, spatial relationship
Where to start • Search engine: – general search engine: Alta. Vista, Lycos, – image search engine: Web. SEEK • Specialized image database: – Museum, archive, and library digital image database
How search engine work • How does a Web search engine identify images and match to your criteria – look for graphic files: HTML tags: <img src> and <href>. Example: Alta. Vista – Look for caption: HTML tag<alt> – Look for title of Web page – Employ human intervention to catalog images
Search example: Giraffe • Alta. Vista • Lycos • Web. SEEK
Alta. Vista • Http: //image. altavista. com/cgi-bin/avncgi • Text-based indexing: file name and path name • (live search demo)
Lycos • Http: //lycospro. lycos. com • Text-based indexing: file name, path name and caption(<ALT> tag) • (live search demo)
Web. SEEK: • Http: //www. disney. ctr. columbia. edu/websee k • content-based image search engine • (live search demo)
Specialized image database • Museums, archive, and library digital image database – Fine arts museums of San Francisco http: //www. thinker. org/imagebase/index-2. html – California heritage collection http: //sunsite. berkeley. edu/Cal. Heritage/collecti on. html – National Museum of America Art
Problems in using search engines • Search result heavily relies on the how the webmaster name the image file and directory. • Even with the content -based search, there a lot unexpected results
Specialized image database • More likely use controlled vocabulary to describe the image • well organized comparing to the other images on the Web • have their own search tools or find aids
Before using the image • Available for viewing doesn’t mean available for reuse • Make sure you have right to use it
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