Mathematical Morphology provides powerful tools for image processing, analysis and understanding. In this paper, we will work on how to apply these tools to analyze scores, that are image-like representations of Music. To do that, we will consider chroma rolls, a representation of scores similar to piano rolls that use chromas instead of pitches. Endowing this representation with a lattice structure, one can define Mathematical Morphology operators, and setting a group structure to the Time-Frequency plane allows us to use the notion of structuring element. We will show throughout some examples how this relates with the notion of pitch-class set and chord progressions, and we will analyze two Chopin's Nocturnes with this technique.