cx.smooth();
cx.notStroke();

thanks, that makes sense but i still see the stroke:

1. 
   PGraphics c1, c2, c3;
   
   void setup() {
   
     size(600, 600);
     smooth();
     noStroke();
     background(255);
   
     c1 = createGraphics(width, height, P2D);
     c2 = createGraphics(width, height, P2D);
     c3 = createGraphics(width, height, P2D);
   
     c1.beginDraw();
     c1.smooth();
     c1.noStroke();
     c1.fill(255, 0, 0);
     c1.ellipse (width/3, height/3, 2*width/3, 2*width/3);
     c1.endDraw();
   
     c2.beginDraw();
     c2.smooth();
     c2.noStroke();
     c2.fill(0, 255, 0);
     c2.ellipse (2*width/3, height/3, 2*width/3, 2*width/3);
     c2.endDraw();
   
     c3.beginDraw();
     c3.smooth();
     c3.noStroke();
     c3.fill(0, 0, 255);
     c3.ellipse (width/2, 2*height/3, 2*width/3, 2*width/3);
     c3.endDraw();
   
   
     image(c1, 0, 0);
     image(c2, 0, 0);
     image(c3, 0, 0);
    
   /* 
     fill(255, 0, 0);
     ellipse (width/3, height/3, 2*width/3, 2*width/3);
    
     fill(0, 255, 0);
     ellipse (2*width/3, height/3, 2*width/3, 2*width/3);
    
     fill(0, 0, 255);
     ellipse (width/2, 2*height/3, 2*width/3, 2*width/3);
   */
   
     blend(c1, 0, 0, width, height, 0, 0, width, height, ADD);
     blend(c2, 0, 0, width, height, 0, 0, width, height, ADD);
     blend(c3, 0, 0, width, height, 0, 0, width, height, ADD);
   }
   
   

  c1 = createGraphics(width, height, JAVA2D);
  c2 = createGraphics(width, height, JAVA2D);
  c3 = createGraphics(width, height, JAVA2D);

P2D will be abandoned in next version, it adds more issues than solutions...