A sample plugin

We will start digging into this topic by analyzing the following plugin code. That will give us a nice starting point to introduce the different aspects for developing ImageJ plugins:

import ij.*;
import ij.process.*;
import ij.gui.*;
import java.awt.*;
import ij.plugin.*;
import ij.plugin.frame.*;

public class Test_Plugin implements PlugIn {
    public void run(String arg) {
        int width = 300;
   	     int height = 300;   	 
ImageProcessor ip = new ByteProcessor(width, height);
  ip.setColor(Color.black);
   	   ip.fill();
       for(int x = 0; x < width; x++) {
   	    for(int y = 0; y < height; y++) {
   	      if (x == y || (width - x) == y)
   	        ip.putPixel(x, y, 255);
   	     }
   	   }
   	   ImagePlus imp = new ImagePlus("Result image", ip);    
   	   imp.show();
    }
}

First things first: this is a plugin, and not a macro. To edit it, navigate to Plugins | New | Plugin. A sample skeleton will be opened and you just need to fill in the run(arg...