Tips for optimising Performance: 


PImage bg;

void setup() {
  size(640, 360);

  bg = loadImage("image.jpg");
  bg.resize(width,height); // we rescale the image once here, instead of in the draw loop
}

void draw() {
  image(bg, 0, 0);
  // this is much faster than image.(bg, 0,0, width, height) which would rescales the graphics every frame
}