Coffee powder images were acquired by using an image acquisition cabinet (Immagini & Computer, Bareggio, Italy) equipped with a digital camera (EOS 550D, Canon, Milano, Italy). In particular, the digital camera was placed on an adjustable stand positioned 60 cm above a black cardboard base where the Petri dish containing the sample was placed. Light was provided by 4 100-W frosted photographic floodlights, in a position allowing minimum shadow and glare.