Processing gif from frames

import gifAnimation.*; // https://extrapixel.github.io/gif-animation/

GifMaker gifExport;
int start = 25;
int   end = 42;
int frame;

void setup() {
  size(1419, 925, P2D);

  frameRate(15);
  frame = start;

  gifExport = new GifMaker(this, "expand.gif");
  //gifExport.setRepeat(1); // make it an "endless" animation
  //gifExport.setTransparent(255, 255, 255); // make black the transparent color. every black pixel in the animation will be transparent
}

void draw() {
  background(255);
  if (frame <= end ) {
    PImage img;
    String frameString = String.format("%05d", frame); //5 leading zeros, change to zeros in your animation
    img = loadImage("GifFrames/Frames"+frameString+".png");
      image(img, 0, 0);

  gifExport.setDelay(1);
  gifExport.addFrame();

   frame ++;
  }  else {

  gifExport.finish();
  println("gif saved");
  exit();
  }
}