Dr. Dobb's Journal - October 2008 - (Page 52)

d10NG_p4db 8/14/08 3:11 PM Page 52 State of the Art by Adelene Ng Indexing and Searching Image Files Using Lucene.NET along with open-source libraries Adelene Ng is a senior staff software engineer with Motorola. She holds a Ph.D. in Computer Science from the University of London. Adelene can be contacted at ng_a@hotmail.com. Lucene is a high-performance, full-featured text retrieval library. Originally written in Java, it has since been ported to C++, C#, Perl, and Python. In this article, I show how Lucene.NET can be used to index and search image files captured by digital cameras. What makes this possible is that digital photos embed the camera settings and scene information as metadata. The specification for this metadata is the Exchangeable Image File Format (www.exif.org). Examples of stored information include shutter speed, exposure settings, date and time, focal length, metering mode, and whether the flash was fired. Here I show how the EXIF information can be extracted from the images through some user-specified criteria. These user-specified search criteria are then used as an index to search your image library. To keep the example simple, I limited the EXIF search criteria to date range and user comments fields. All images that satisfy the search criteria are displayed as thumbnails. ImageSearcher The ImageSearcher utility I present here was developed in C# using Visual Studio 2008. (The complete source code for ImageSearcher is available online; see “Resource Center,” page 5.) It also makes use of a number of opensource libraries and components such as Lucene.NET 2.0 (incubator.apache.org/lucene.net), NLog 1.0 (www .nlog-project.org), and ExifExtractor (www.codeproject .com/KB/graphics/exifextractor.aspx). Although a number of open-source search libraries such as DotLucene.net (www.dotlucene.net) and NLucene (sourceforge.net/project/showfiles.php? group_id=57306) are available, the search library I selected was Lucene.NET because the DotLucene.NET project has been closed since May 2007 and NLucene has not been updated since 2002. 52 Dr. Dobb’s Journal l www.ddj.com l October 2008 In addition to Lucene, I use the NLog logging library, which has a programming interface similar to Apache log4net (logging.apache.org/log4net). I use NLog to write diagnostic messages to a file for logging and tracing purposes. To extract EXIF information, I use the ExifExtractor library. Although .NET already has utilities to extract EXIF information, it returns raw data and tags. More processing would be required for this to be used in this application. For example, if I wanted to extract shutter speed information, I would need to know the tag number, extract the tag, and then convert the data from ASCII to a number. ExifExtractor abstracts all these steps. To display the thumbnail images that have been returned by the search engine, I make use of Marc Lievin’s Image Thumbnail Viewer (www.codeproject.com/KB/cs/thumbnaildotnet2.aspx). http://www.exif.org http://logging.apache.org/log4net http://www.nlog-project.org http://incubator.apache.org/lucene.net http://www.nlog-project.org http://www.codeproject.com/KB/graphics/exifextractor.aspx http://www.codeproject.com/KB/graphics/exifextractor.aspx http://DotLucene.NET http://DotLucene.net http://sourceforge.net/project/showfiles.php?group_id=57306 http://sourceforge.net/project/showfiles.php?group_id=57306 http://www.codeproject.com/KB/cs/thumbnaildotnet2.aspx http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - October 2008

Dr. Dobb's Journal - October 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Developer’s Notebook Is Your Next Language COBOL? Conversations Safe Coding Practices Code Signing in Adobe AIR OpenID Single Sign-On The Book Cipher Algorithm Indexing and Searching Image files Extending Continuous Integration Into ALM The Agile Edge Effective Concurrency Swaine’s Flames

Dr. Dobb's Journal - October 2008

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