Lights and darks of a picture. The life of Giovanni Francesco Barbieri, "il Guercino" - the squinter.

Barbieri did not make a secret of the dysfunction of his eyes. In contrast, he showed his squinting eye distinctly in his famous self-portrait from ca. 1635. It can be assumed that "Il Guercino" was so detailed in studying light and shadow with his one eye that he could compensate for his amblyopic eye. By this, Barbieri could create pictures with an amazing degree of variations of light and shadow.