Still high on the list of the world’s 100 best novels, Joseph Conrad’s haunting “Heart of Darkness” continues to fascinate, mystify, and attract adaptors. Although Francis Ford Coppola’s 1979 award-winning film “Apocalypse Now,” starring Marlon Brando is, arguably, the most imaginative of the lot—moving Conrad’s brooding and inscrutable Congo tale to Vietnam—the 1902 novella inspired earlier films (Boris Karloff as the charismatic Kurtz in 1958, John Malkovich in 1993). “Heart of Darkness” has also been turned into radio dramas, theatre pieces, even an opera. But a graphic novel, a comic book? Why not? as illustrator and cartoonist Peter Kuper might say. He had already taken on adaptations of Franz Kafka and Upton Sinclair, and, as he says in his introduction, which he calls “The Art of Darkness,” he read a lot about the book and showed his work to scholars. He even observes a three-part structure, following the first publication of the novella as a three-part magazine series in 1889.