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