Shading for cel animation based on images is a recent research topic in computer-assisted animation. This paper proposes an image-based shading pipeline to give a 3D appearance to a 2D character by inspecting the hand-drawn image directly. The proposed method estimates normal vectors on the character's outline and interpolates them over the remaining image. The method does not limit the animator's creative process and requires minimal user intervention. The resulting shading pipeline can be easily applied to photorealistic and non-photorealistic 2D cel animation. In the proposed method, the animator can easily simulate environment reflections on the surface of 2D reflecting objects. As far as the authors are concerned, the proposed technique is the only one in the literature that is genuinely an image-based method for 2D animation.