Overview of grayscale image colorization techniques

Colorization is the process of adding color information to grayscale images. This operation may be performed in various ways. The colorization may be automatic, without the user’s effort, however, the semi-automatic methods are usually more flexible and useful. In this chapter, we start with a literature overview, where we enumerate and shortly characterize numerous state-of-the-art methods. Then, we present the details of one fully automatic and three semi-automatic techniques. We also show exemplary algorithms outcomes for several colorization applications such as medicine or astronomy. Finally, we present the methodology of assessing the results of the colorization algorithms. We describe the three most important quality measures and we evaluate their usefulness.