I'd just do:

1. img = pg.get()

Complete example:

1. size(300,300);
2. PGraphics pg = createGraphics(300,300,P2D);
3. pg.beginDraw();
4. pg.background(128,255,0);
5. pg.ellipse( 150,150,100,100);
6. pg.endDraw();
7. PImage img = pg.get();
8. image(img,0,0);

BTW, why do you want to do that? A PGraphics is actually a PImage, with added stuff to allow drawing on it. You can use it whenever you need a PImage, even where a parameter specify it wants a PImage.

no idea :)

good point,

thanks both.