General Elements of Film Adaptation
       genre

drama
Some of the first movie adaptations were plays recorded on film.  Most of these early adaptations of dramatic works rely on a static camera to record actors performances, similar to a parent recording an elementary school play.  As filmmaking has evolved and come to rely on advanced editing and cinematography techniques, the chasm between drama and film widens, and the differences become more evident.  Film lacks the immediacy of drama; there is no spontaneous interaction between the actors and the audience.  On the other hand, drama does not have the temporal and spatial flexibility of film.  That means that moving through time and highlighting or eclipsing objects or people is not as easy on stage.  Despite these discrepancies, plays still tend to lend themselves well to adaptation for the cinema because they have abundant dialogue and are already designed for performance.  Furthermore, they have straightforward narrative plots with the necessary Aristotelian components of rising action, climax, and falling action.   Examples include His Girl Friday and Rosencrantz and Guildenstern Are Dead. 

short story
Although short fiction is not designed expressly for performance, its distilled narrative format facilitates ready adaptation to the silver screen.  In the introduction to Stories Into Film, an anthology of short stories that have been adapted into films, Alfred Hitchcock is quoted as saying, "You see, the nearest art form to the motion picutre is, I think, the short story.  It's the only form when you ask the audience to sit down and read it in one sitting."  In short stories, the characters aren't as developed and the plot isn't as complex as a longer story.  Thus, filmmakers have to make fewer decisions about what to change or eliminate.  In fact, when adapting from this genre, filmmakers often have to supplement the information in the source text.  Since short stories are not typically written exclusively as dialogue, adapting them involves making choices about the point of view which has considerable effect on interpretation of a work.  Examples of this genre include Rear Window and 2001: A Space Odyssey.

novel
Adapting the novel is a complicated undertaking.  Just as they do when adapting short fiction, filmmakers often have to alter the original point of view in order to translate the work from a written to a visual format.  Because characters are more developed than in the short story and the plot is complex and layered, these elements may have to be altered from the author's original vision in order to be shaped into a cinematic format.  Filmmakers must choose whether to depict all of the characters and subplots.  Also, when these are eliminated, other adjustments must be made to sustain the text as a whole.  Examples of novel adaptation include: One Flew Over the Cuckoo's Nest, The Color Purple, Lolita, and Kiss of the Spider Woman.