int [] xd = {
    0,1,1,1,0,-1,-1,-1,0}; //neighbors’ x index cw (top)
  int [] yd = {
    1,1,0,-1,-1,-1,0,1,1}; //neighbors’ y index cw (top)
  PImage MyImage = loadImage("stockholm.jpg"); //load an image
  size(MyImage.width,MyImage.height); //size to match the image
  image(MyImage, 0,0); //display the image
  int [][] MyCopy = new int[width][height]; // array equal to image
  for(int x=1; x<width-1; x++) //for all pixels (except border)
    for(int y=1; y<height-1; y++){
      int b=0;
      int a=0;
      for(int i=0; i<8; i++){
        if(brightness(get(x+xd[i],y+yd[i]))<128) //case 1
          b++;
        if(brightness(get(x+xd[i],y+yd[i]))<128 &&
          brightness(get(x+xd[i+1],y+yd[i+1]))>128) //case 2
          a++;
      }
      if((b>=2 && b<=6) || a==1 )
        MyCopy[x][y]=1; //mark these ones as edges
      else
        MyCopy[x][y]=0;
    }
  for(int x=1; x<width-1; x++) //go through all pixels
    for(int y=1; y<height-1; y++){
      if(MyCopy[x][y]==1) //if they are marked
        set(x,y,color(0,0,0)); //paint them black
      else
        set(x,y,color(255,255,255)); //else white
    }
  save("MyImage.jpg"); //save just incase