Scaffolding for a processing pixel sorter

pixelsort.pde

import java.util.Collections;

Sorter sorter;
PImage photo;

void setup() {
  photo = loadImage("Foto3.JPG");
  sorter = new Sorter();
  sorter.init(photo);
  photo = sorter.image();
  size(photo.width, photo.height);
}

void draw() {
  image(photo, 0, 0);
}

class Sorter {
  int _width = 0;
  int _height = 0;  
  ArrayList<Node> _items = new ArrayList<Node>();

  void init(PImage p) {
    _width = p.width;
    _height = p.height;
    p.loadPixels();
    for (int y = 0; y < _height ; y++) {   
      for (int x = 0; x < _width ; x++) { 
        Node n = new Node();
        int index = (_width * y)+x;
        n.index = index;
        n.originalColor = p.pixels[index];
        _items.add(n);
      } 
    }
  }
  
  PImage image() {
        Collections.sort(_items);
        PImage returnImg = createImage(_width, _height, ARGB);
        returnImg.loadPixels();
        for (int y = 0; y < _height ; y++) {   
            for (int x = 0; x < _width ; x++) { 
                int index = (_width * y)+x;
                Node n = _items.get(index);
                returnImg.pixels[index] = n.originalColor;
            }
        }
        returnImg.updatePixels();
        return returnImg;
  }
}

class Node implements Comparable {
  int index = 0;
  color originalColor;
  
  float getValue() {
    return (red(originalColor) + green(originalColor) + blue(originalColor))/3.0;
  }
  
  public int compareTo(Object o) {
    Node n = (Node) o;
    float i1 = getValue();
    float i2 = n.getValue();
    return i1 == i2 ? 0 : (i1 > i2 ? 1 : -1);
  }
}