1 Results of a stroke-based algorithm:(a) source photo,(b) painted version, and (c) final rendering. for these problems. Two main approaches to designing SBR algorithms exist. Greedy algorithms greedily place the strokes to match the target goals. Optimization algorithms iteratively place and then adjust stroke positions to minimize the objective function. A greedy algorithm produced Figure 1, and an optimization algorithm produced Figure 2. This is a somewhat unusual view of these algorithms. I have sacrificed chronological ordering in this tutorial in order to present algorithms in this way. Haeberli introduced both a semiautomatic greedy algorithm and an automatic optimization algorithm in a seminal paper. 4 The subsequent pen-and-ink algorithms developed together by Michael Salisbury, David Salesin, Georges Winkenbach, and others demonstrated the potential of highly automated SBR to create beautiful and expressive imagery. 5-8 Digital paint systems had previously automated some aspects of the stroke renderings, but didn’t automate any stroke placement choices. Although this tutorial focuses on the technical details of SBR algorithms, it’s important to remember that they’re useless without human control. Every aspect of the system (including the choice of stroke models, the setting of weight parameters, and the selection of input imagery) requires aesthetic decisions that only an artist, working toward some goal, can make. Ideally, a human artist using the system should have total control over the decisions made. For example, a user should be able to specify spatially varying styles to use, so that different rendering styles are used in different parts of the image, or to specify positions of individual strokes. However, one of the great advances in art in the age of digital machines is the ability to create complex systems of procedural art, where the artist doesn’t directly create the final work, but rather creates rules according to which final decisions are made (although simpler procedural works—such as those of John Cage—exist without computers). Hence, an artist might design the energy function, but not necessarily edit every individual image produced by the algorithm. In one possible scenario, the artwork’s creation might occur at a time after the artist’s involvement. The main goal of SBR algorithms is to provide procedural tools that automate parts of the image creation process, not to replace the artist.