Inspired by Michal, I tried this sketch effect once again. Previously I discovered it may look better if the picture is first turned invert (negative) before adding the effect, and then turned back positive again. What do you think? Which one is better? I'm not going to tell you which one is treated with invert. I just like to hear some comment first. Just try not to let the different amount of contrast bother you, and concentrate on line structure.