Sfumato is a painting method that softens the transition between colours by simulating an area beyond what the human eye is focusing on, often known as the out-of-focus plane. It is one of the Renaissance's canonical painting styles. Based on his expertise in optics and human perception, as well as his experiments with the camera obscura, Leonardo da Vinci was the most notable practitioner of sfumato. He pioneered it and used it in several of his works, including the Virgin of the Rocks and his renowned Mona Lisa painting. He described sfumato as "without lines or borders, like smoke."