java - I am making a multithreaded application to process an image yet the sequential version is faster, why? -

i having static bufferedimage in threads , letting each thread modify sections of image. processing extremely independent each pixel done separately, yet sequential version faster how fix that?

edit 1: here how code looks like

public static void main(string[] args) throws ioexception, interruptedexception {     long startime, endtime;     long time;     startime = system.currenttimemillis();     //also tried use nano      workingthread t1 = new workingthread("input.jpg");     workingthread t2 = new workingthread();     workingthread t3 = new workingthread();     workingthread t4 = new workingthread();      t1.start();     t2.start();     t3.start();     t4.start();      t1.join();     t2.join();     t3.join();     t4.join();      endtime = system.currenttimemillis();     time = endtime - startime;     system.out.println("the time consumed in miliseconds  " + time); }  public class workingthread extends thread {    public static bufferedimage img;   public static int p;   public int nb;   public static int width, height;    public workingthread(string file) throws ioexception {     file f = new file(file);     img = imageio.read(f);     width = img.getwidth();     height = img.getheight();     p = 1;     nb = 0; }    public workingthread() {     nb = p;     p++; }    public void run() {      int start=nb*height/p;     int end = (nb + 1) * height/p;     //the image split according y axis in case     for(y=start; y < end ; y++) {        for(x =0; x<width; x++) {             pixel = img.getrgb(x, y);             //processing             img.setrgb(x, y, pixel);         }   } } 

as comments have pointed out, flaw in benchmark the overhead of thread setup , teardown larger time takes execute code sequentially.

by inserting silly code takes lot of time, below:

//processing (int = 0; < 1000; i++) {     pixel = ((~pixel ^ pixel) | pixel) & pixel; } 

...inside for x/y loop , increasing max value of i, you'll see multithreaded version faster sequential one.

ps: used image 2500 x 3300 pixels.