Abstract: In NPR, a reasonable light and shade and coordination directly affect the effect of the last created menu. This paper discussed the methods of catching the tone of the object in Non-photorealistic rendering scene in double light source condition,and presented a method which can obtain hue information of the scene and objects based on small ball,this method supposes the surface of objects in scene is symmetrically covered with a layer of the same size balls, and two adjacent balls maintain a state of approximate tangent, by computing the ball's sheltered degree by other balls in double light source condition and the approximate mirror reflection information to confirm the hue information of the small ball in it's position. These hue informations can be used to control brushstroke's hue at the corresponding position in the process of painting,thereby ensures the rationality of the whole hue in the last created menu. This method can be applied to a variety of double light source non-photorcalistic rendering for obtaining light and shade information, and has simple structure,fast computation speed and facilitate the realization the adjustment of local information in scene. Simulation results show it is effective.

Key words: Non-photorealistic, Double light source, Hue information, Brushstroke