Hi, I created a design to use on a POS cardboard display. I'm having trouble printing a good clean copy. The image looks great on the computer screen but when printed, the black looks purple and there is spotting in the white background. I tried Staples and Office Max and the quality was very poor. My next step was to try a sign printing shop. This is not a big sign. It will fit on an 8.5"x11" piece of paper. I tried jpeg and pdf. Neither worked. What is the best way to get this printed so it looks clean and professional? Thanks in advance for your help.