I've tried:
Config.useFramebufferWithAlpha = true;
FrameBuffer fb = new FrameBuffer(getWidth(), getHeight(), FrameBuffer.SAMPLINGMODE_OGSS);
fb.clear(new Color(255,255,255,0));
world.renderScene(fb);
world.draw(fb);
fb.update();
BufferedImage result = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
fb.display(result.getGraphics());
Config.useFramebufferWithAlpha = false;
return result;
But the alpha value is only "1" or "0", so the edges don't appear smooth. Is there an easy way to fix this?