Depicting shape, materials and lighting: observation, formulation and implementation of artistic principles

The appearance of a scene results from complex interactions between the geometry, materials and lights that compose that scene. While Computer Graphics algorithms are now capable of simulating these interactions, it comes at the cost of tedious 3D modeling of a virtual scene, which only well-trained artists can do. In contrast, photographs allow the instantaneous capture of a scene, but shape, materials and lighting are difficult to manipulate directly in the image. Drawings can also suggest real or imaginary scenes with a few lines but creating convincing illustrations requires significant artistic skills.The goal of my research is to facilitate the creation and manipulation of shape, materials and lighting in drawings and photographs, for laymen and professional artists alike. This document first presents my work on computer-assisted drawing where I proposed algorithms to automate the depiction of materials in line drawings as well as to estimate a 3D model from design sketches. I also worked on user interfaces to assist beginners in learning traditional drawing techniques. Through the development of these projects I have formalized a general methodology to observe how artists work, deduce artistic principles from these observations, and implement these principles as algorithms. In the second part of this document I present my work on relighting multiple photographs of a scene, for which we first need to estimate the materials and lighting that compose that scene. The main novelty of our approach is to combine image analysis and lighting simulation in order to reason about the scene despite the lack of an accurate 3D model