Comics is a medium used to express ideas through images, often combined with text or other visual information. Frequently, comics takes the form of sequences of panels of images. Often textual devices such as speech balloons, captions, and onomatopoeia indicate dialogue, narration, sound effects, or other information. The size and arrangement of panels contribute to narrative pacing. Cartooning and similar forms of illustration are the most common image-making means in comics; fumetti is a form which uses photographic images. Common forms include comic strips, editorial and gag cartoons, and comic books. Since the late 20th century, bound volumes such as graphic novels, comic albums, and tankobon have become increasingly common, while online webcomics have proliferated in the 21st century with the advent of the internet. The history of comics has followed different paths in different cultures. Scholars have posited a pre-history as far back as the Lascaux cave paintings in France. By the mid-20th century, comics flourished, particularly in the United States, western Europe (especially France and Belgium), and Japan. The history of European comics is often traced to Rodolphe Topffer's cartoon strips of the 1830s, but the medium truly became popular in the 1930s following the success of strips and books such as The Adventures of Tintin. American comics emerged as a mass medium in the early 20th century with the advent of newspaper comic strips; magazine-style comic books followed in the 1930s, in which the superhero genre became prominent after Superman appeared in 1938. Histories of Japanese comics and cartooning (manga) propose origins as early as the 12th century. Modern comic strips emerged in Japan in the early 20th century, and the output of comics magazines and books rapidly expanded in the post-World War II era (1945–) with the popularity of cartoonists such as Osamu Tezuka (Astro Boy, et al.). Comics has had a lowbrow reputation for much of its history, but towards the end of the 20th century began to find greater acceptance with the public and academics. The term comics is used as a singular noun when it refers to the medium, but becomes plural when referring to particular instances, such as individual strips or comic books. Though the term derives from the humorous (comic) work that predominated in early American newspaper comic strips, it has become standard for non-humorous works too. In English, it is common to refer to the comics of different cultures by the terms used in their original languages, such as manga for Japanese comics, or bandes dessinees for French-language comics. There is no consensus amongst theorists and historians on a definition of comics; some emphasize the combination of images and text, some sequentiality or other image relations, and others historical aspects, such as mass reproduction or the use of recurring characters. The increasing cross-pollination of concepts from different comics cultures and eras has only made definition more difficult.