To install ImageJ, download the Mac OS X .tar.gz file and double-click on it to extract the "ImageJ (OS X)" folder. To run ImageJ, open this folder and double-click on the ImageJ icon.
Memory
To make more than 64MB of memory available to ImageJ, add a line similar to
to the ImageJ.app/Contents/Resources/MRJApp.properties file, where ImageJ.app is the directory (bundle) that the Finder displays as the ImageJ application. You can view the files and folders in the ImageJ bundle by control-clicking on the ImageJ application and selecting "Show Package Contents". Another way to make more memory available to ImageJ is by running from the command line and using the -mx option.com.apple.mrj.application.vm.options=-Xmx200M
Upgrades
To upgrade to the latest version of ImageJ, replace the ij.jar file in the ImageJ application with a newer one from http://rsb.info.nih.gov/ij/upgrade/. To do this, control-click on the ImageJ application, select "Show Package Contents", and then drag the newer ij.jar into the Contents/Resources/Java folder.
Known Problems
Or if you have a Mac OS 9 ImageJ folder, type:java -jar -mx256m ImageJ.app/Contents/Resources/Java/ij.jar (or java -mx256m -cp ImageJ.app/Contents/Resources/Java/ij.jar ij.ImageJ)
The -mx256m switch specifies that ImageJ will have available a maximum of 256MB of RAM.java -jar -mx256m ij.jar (or java -mx256m -cp ij.jar ij.ImageJ)
Here is a simple AppleScript that sends commands to Terminal to have it automatically launch ImageJ:
With OS X 10.1 or later, you can also run ImageJ by double-clicking on ij.jar.tell application "Terminal" run do script with command "cd /Applications/ImageJ java -jar -mx350m ./ImageJ.app/Contents/Resources/Java/IJ.jar" end tell