PImage img;
img = loadImage("sample.jpg");
size(800, 597);
imageMode(CENTER);
noFill();
background(255);
for( int i = 0; i < img.height; i++ ){
  
  beginShape();
  for( int j = 0; j < img.width; j++ ){
    color c = img.get(j,i);
    float gray = (red(c)+green(c)+blue(c))/3;
    stroke(0,0,0,100);
    vertex(j,i-gray/10.0);
  }
  endShape();
}