Three inventors came up with the Tri-Ergon sound-on-film system in 1918. From 1922 to 1926, they tried to introduce the process to film production, and UFA showed an interest, but, possibly due to financial difficulties, never made a sound film.[10] In the period immediately following World War I, the film industry boomed, helped by the 1920s German inflation. This enabled film makers to borrow money in Papiermark which would be vastly devalued by the time it had to be repaid. Nevertheless, film budgets were tight and the need to save money was a contributing factor to the rise of German Expressionism, as was the desire to move forward and embrace the future that swept most of Europe at the time. Expressionist movies relied heavily on symbolism and artistic imagery rather than stark realism to tell their stories. Given the grim mood in post-WWI Germany, it was not surprising that these films focused heavily on crime and horror. The film usually credited with sparking the popularity of expressionism is Robert Wiene's The Cabinet of Dr. Caligari (1920). It painted a picture on the cinema screen with non-realistic sets built with exaggerated geometry, images painted on the floors and walls to represent objects (and often light and shadow), and a story involving the dark hallucinations of an insane man. An exaggerated acting style and unnatural costume design are other trademarks of this movement. Other notable works of Expressionism are Friedrich Wilhelm Murnau's Nosferatu (1922), and Carl Boese and Paul Wegener's The Golem: How He Came Into the World (1920). The Expressionist movement died down during the mid-1920s, but it continued to influence world cinema for years afterward. Its influence is particularly noticeable in American horror films and film noir, and the works of European directors as diverse as Jean Cocteau and Ingmar Bergman.