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| author | robcast |
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| date | Mon, 12 Dec 2011 20:37:53 +0100 |
| parents | 8abbc40d0df5 |
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>digilib -- Digital Image Library</title> </head> <body> <table border="0" cellspacing="0" cellpadding="10"> <tr> <td bgcolor="#a0a0a0"> </td> <td> <img src="images/digilib-logo-big.png" align="left" /> <h1> <tt>digilib</tt> -- a versatile image viewing environment for the internet </h1> </td> </tr> <tr> <td bgcolor="#a0a0a0" valign="top" align="right"> <p> <b><a href="index.html">Info</a> </b> </p> <p> <b><a href="http://developer.berlios.de/projects/digilib/">Project</a> </b> </p> <p> <b><a href="http://developer.berlios.de/project/showfiles.php?group_id=251">Download</a> </b> </p> <p> <b><a href="docs.html">Docs</a></b> <br /> <a href="build-maven.html">Building</a> <br /> <a href="digilib-config.html">Configuring</a> <br /> <a href="http://developer.berlios.de/docman/?group_id=251">...more</a> </p> <p> <b><a href="tips.html">Tips</a> </b> </p> <p> <b><a href="http://hg.berlios.de/repos/digilib">Source</a> </b> </p> </td> <td> <p>Some tips for running digilib</p> <ul> <li> <a href="#vm_settings">Java VM settings for digilib</a> </li> <li> <a href="#prescaled_images">Prescaled images</a> </li> <li> <a href="#installing_jai">Installing JAI</a> </li> </ul> <h1 id="vm_settings">Java VM settings for digilib</h1> <p>The Java virtual machine (Java-VM) only uses a fixed amount of memory for its operations. When an operation needs more memory than available it aborts with an error ("out of memory error").</p> <p>digilib can need a lot of memory depending on the size and type of images. Since digilib runs as a servlet under Tomcat its in the same VM as the Tomcat server.</p> <p>The amount of memory Tomcat (version 5.0) uses is configured by creating a "setenv.sh" script with a line</p> <pre> CATALINA_OPTS="-Xmx512m" </pre> <p>in Tomcat's "bin" directory (giving 512MB in this case).</p> <p> You can check the amount of memory your digilib instance has available on the bottom of the web page /server/dlConfig.jsp in your digilib instance (e.g. <a href="http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp" class="external free" rel="nofollow">http://digilib.mpiwg-berlin.mpg.de/digitallibrary/server/dlConfig.jsp</a>). </p> <h1 id="prescaled_images">Prescaled images</h1> <p>You can provide any number of scaled-down versions of your images that digilib uses when a smaller version of an image is requested. Since less data has to be read and processed this can speed up digilib's performance quite a lot.</p> <p>The actual process is that the client requests a certain target size, digilib scans all available scaled-down versions of the same image, selects the smallest image that is larger than the requested size and scales it down to the requested size.</p> <p>The scaled-down versions of the image have to have the same file name as the original hi-res file. They can have a different type and extension (e.g. img002.jpg for img002.TIFF)</p> <p>The scaled down images have to be in the same subdirectory (the part that shows up in digilib's "fn" parameter) as the hi-res file. The first part of each directory tree is configured by the basedir-list parameter in digilib-config.xml.</p> <p>The sequence of directories in basedir-list is from hi-res to lo-res. Images must be present in the hires directory but they need not be present in all lower-res directories.</p> <p>e.g. if digilib-config.xml contains</p> <pre> <parameter name="basedir-list" value="/images:/scaled:/thumb" /> </pre> <p>and a user requests the image "books/book1/page0002" digilib looks for</p> <pre> /thumb/books/book1/page0002.* /scaled/books/book1/page002.* /images/books/book1/page002.* </pre> <p>and uses the first image that is bigger than or equal to the requested size.</p> <p> For batch-prescaling our images we use a script called "scale-o-mat" that uses a lot of freely available imaging libraries (ImageMagick, libtiff, netpbm) and is available in our public CVS <a href="http://itgroup.mpiwg-berlin.mpg.de/cgi-bin/cvsweb.cgi/scaleomat/" class="external autonumber" rel="nofollow">[1]</a>. The script is given a hi-res base directory, a destination base directory, a destination size and a starting directory. It then processes all files in the starting directory and all its subdirectories and creates scaled images in corresponding directories under the destination base directory. </p> <p>We currently use prescaled thumbnails of 100 pixels and images for browser display of 1500 pixels. Remember that the prescaled image has to be larger (or the same size) than the requested image size!</p> <p>There is another optimization in digilib: if the requested image is exactly the same size and type as the prescaled image then the prescaled image is sent unmodified to the client which is a lot faster. So it makes sense to produce thumbnails of exactly 90 pixels width when they are used in an HTML page where all images are 90 pixels wide.</p> <h1 id="installing_jai">Installing JAI</h1> <p> In theory you can install the <a href="http://java.sun.com/javase/technologies/desktop/media/jai/" class="external text" rel="nofollow">Java Advanced Imaging</a> and JAI-ImageIO JAR files <code>jai_core.jar, jai_codec.jar, jai_imageio.jar</code> (and native library files if available) in the <code>/WEB-INF/lib/</code> directory of the digilib web application. </p> <p>But there are classloader issues. Newer versions of Tomcat refuse to load the libraries and I found that in some cases digilib stopped reading TIFF files after a period of running.</p> <p> In these cases it helped to install the JAI files in Tomcats <code>lib/</code> directory or Jettys <code>lib/ext/</code> or globally in the local Java JDK installation (i.e. in the Java's /jre/lib/ext/ directory on linux). </p> <h1 id="mpiwg_setup">Sample setup</h1> <p>The current digilib setup at the MPIWG (as of December 2010):</p> <ul> <li> One frontend server running the lightweight web-multiplexer <a href="http://www.apsis.ch/pound/" class="external text" rel="nofollow">pound</a> on port 80 that distributes requests to three servers runnning digilib </li> <li> the three servers run digilib under <a href="http://www.eclipse.org/jetty/" class="external text" rel="nofollow">Jetty</a> on port 8080 without Apache <ul> <li>one server is the frontend server (Linux 32bit, Dual 2.4GHz Xeon, 2GB RAM)</li> <li>the other server is a separate, newer machine (Linux 64bit, Dual 1.8GHz Opteron, 2GB RAM)</li> <li>the third server is a separate, newer machine (Linux 32bit, Dual 2.8GHz Xeon, 4GB RAM)</li> </ul> </li> <li> the digilib instances (digilib 2.0b1 as of 12.12.2011) run on Jetty 8.0.4 on Java 1.6.0_26 with 1GB of <a href="#vm_settings">Java VM memory for digilib</a> (-Xmx1024m) with JAI (1.1.3) and JAI-ImageIO (1.1) <a href="#installing_jai">installed in the Jetty/lib/ext</a>(!) </li> <li>both digilib servers access all image files over NFS (over GBit Ethernet) from a central file server (Solaris 10, Sun Fire 240, multiple RAIDs on Fibrechannel)</li> </ul> </td> </tr> <tr> <td style="padding: 0px" align="left"> <a href="http://developer.berlios.de"> <img src="http://developer.berlios.de/bslogo.php?group_id=0&type=1" width="124" height="32" border="0" alt="BerliOS Logo" /> </a> </td> <td></td> </tr> </table> </body> </html>