How hard do you think to turn white background picture into black and create a dramatic effect?

What you need to do is just three steps;

1. Create an empty layer;
2. Go to Image->Apply Image
   change the Layer setting be “background” which means we would like to use background as our template;
   change Channel setting to be “green” and check the invert Checkbox beside;
   Usually, red channel got most bright color and blue channel have the darkest. So when you invert that, the red channel got darkest effect. You can choose whatever applies to our image to achieve the best. Here, we are using invert green channel. Now, we will get a black and white picture;
3. Third step, add color to that picture but still keep that black style; we just need to duplicate the background, put it on top of our black and white layer, and change its mode to be “color”. The color of our original picture is added on our new black background.