histograma pixel por pixel

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

public class ejemplo_neg3 implements PlugInFilter
{
ImagePlus imp;

public int setup(String arg, ImagePlus imp)
{
this.imp = imp;
return DOES_ALL;
}

public void run(ImageProcessor ip)
{

int w=ip.getWidth();
int n=ip.getHeight();
for(int i=0;i {
for(int j=0;j {
int p=ip.getPixel(i,j);
p=(int)(p*0.5+1.5);
ip.putPixel(i,j,255-p);
}
ip.setPixel(i,j,255+p);

}
}

}