Flemish painter, regarded as an early practitioner of plein-air painting. He was trained in his native city of Antwerp, and moved to Paris in the 1770s. About ten years later he relocated to Rome, where he spent the majority of his career. Although Denis was not an official student of French landscape painter Pierre-Henri de Valenciennes, he followed the elder and more famous artist's example. Denis's cloud studies probably predate Valenciennes' influential 1800 treatise on landscape, which emphasized direct observation from nature. Both men were among the first to produce oil-on-paper sketches outdoors, a practice that became increasingly popular in the 1800s. Denis was closely associated with the French picture dealer Jean-Baptiste Lebrun, as well as his more famous wife, the painter Elisabeth Vigée-Lebrun, with whom he spent time in Italy. He also enjoyed a close relationship with the head of the French academy in Rome. Denis's landscape practice consisted of painted and drawn studies from nature, as well as more highly finished landscape paintings. His sketches, like those of other landscape artists of his time, are more dynamic than his finished works. //