Journalistic news coverage plays an essential role for providing an audience with a diverse, multifaceted perspective upon public affairs. However, in the scholarly debate, most measures of viewpoint diversity do not distinguish between statements raising commensurable interpretations, and contributions that construct different meaning in a consequential sense. We provide an operationalization of viewpoint diversity that builds upon a tradition of identifying distinct interpretations through framing analysis. Going beyond frame diversity, we then distinguish between equivalent, complementary and competing, diverse interpretations: we consider as commensurable those frames that derive from the same 'interpretative repertoire', a notion borrowed from discourse studies. We propose a strategy for operationalization and the measurement of viewpoint diversity. Our focus on meaningfully different interpretations contributes to advancing research into journalism, political opinion formation, audience elaboration, and other important fields of study.