Proper-motion diagrams of stars in the field of view of NGC 1978 in four F814W magnitude intervals (left). The m_F814W vs. m_F555W − m_F814W CMD of stars in the left panels is plotted on the right. Stars within the red circles plotted in the left panels are considered probable cluster members and are colored black, whereas the most-evident field stars are represented with red crosses. The remaining stars are colored gray. See the text for details.