I'm not sure I understood what you are wanting, but if you are after making the black and the gray more black I might suggest....going to image>mode>lab color, then filter>sharpen>unsharp mask, move the sliders around to make the black in your picture more prominent, when you raise the sliders (the top two) it will have more of an effect on the parts of your image that are black or have a black tint. Don't forget to change back to RGB to continue working.