title: org.im4java.core.CommandException: magick: no images found for operation
body: <p>I am trying to compare two images located under my OS machine. 
  I have ImageMagick running on my os machine.
  and I am using this method:</p>
  
  <pre><code>public boolean compareImages (String expectedScreenShot, String capturedScreenShot, String pdiffCompare) {
    ProcessStarter.setGlobalSearchPath("/usr/local/bin/");
    CompareCmd compare = new CompareCmd();
    // For metric-output
    IMOperation cmpOp = new IMOperation();
    // Set the compare metric
    cmpOp.metric("AE");
    // Add the expected image
    cmpOp.addImage(expectedScreenShot);
    // Add the current image
    cmpOp.addImage(capturedScreenShot);
    // This stores the difference
    cmpOp.addImage(pdiffCompare);
    try {
       // Do the compare
       compare.run(cmpOp);
       compare.getErrorText();
       return true;
    }
    catch (Exception ex) {
       return false;
    }
     }
  </code></pre>
  
  <p>I'm using im4java:1.4.0, but when I run <code>compare.run(cmpOp);</code> I am receiving this exception:</p>
  
  <blockquote>
    <p>org.im4java.core.CommandException: org.im4java.core.CommandException:
    magick: no images found for operation `-metric' at CLI arg 1 @
    error/operation.c/CLIOption/5225.</p>
  </blockquote>
  
  <p>Any help would be appreciated.</p>