Slider background image

Hello everyone, I’m having trouble drawing slider with background images.
Actually it works fine but the slider interface is above the png images.
My code is very easy, I’ve got 10 sliders on the same big image and I’m moving the image depending on the slider value:

g.drawImage(knobs, 200, 200, 150, 150, x , 0, 150, 150, false);

I was thinking about a transparency parameter or opacity but I can’t get it working.

Any idea?