What is the difference between digital diplomacy and public diplomacy?

Public diplomacy only covers one aspect of digital diplomacy related to the use of TOOLS for diplomacy including Twitter, Facebook and other social media. Other aspects of digital diplomacy include new TOPICS on diplomatic agenda and changing geopolitical or geo-economic ENVIRONMENT. However, digital diplomacy may sometimes be seen as just public diplomacy because of high media visibility of the use of Twitter and Facebook in international politics.