To determine where values change when light moves over an uneven surface by using a range of values to paint the different values in a realistic, monochromatic self-portrait;
To effectively communicate an image that looks like you through careful examination of the values and structure of your face.
reflection
Clean lines are important so the painting looks uniform and neat. Without a nice neat line the painting can look lumpy and off centered and will look nothing like the original photo. You also need a gray scale that fits with the value in the photo or the painting will look off.