Unless perhaps you're talking about something like Andy Warhol's Empire, filmmaking is very rarely a solitary endeavor (actually I think even that was a two man job). Typically it requires the minimum involvement of a small cast and crew, and more often than not additional producers, backers, film processors and so on, each by virtue of mere presence altering the final product in their own particular way. Sadly, despite consistent failures, Hollywood attempts again and again to create a formula that will translate the novel to the screen, and it is a consistent trend of the ambitious film crew to mangle the work of authors. Even in the most favorable of situations, a team of filmmaking virtuosos collaborating on a cinematic version of, oh I don't know, Pynchon's Gravity's Rainbow (but seriously, try to imagine that as a film), are unlikely to crack the outer shell intense private vision behind the novel itself. The art of writing a novel, a good novel, is internal. It is a matter dealing with the thoughts, ideals, obsessions and base complexities of a particular individual, the author. The camera, as astounding an invention as it may be, cannot replicate these particulars. Being that it is neither eye nor imagination, but a mechanical abstraction of the eye directed by the imagination of not one, but a team of people, further tangles the matter. The novel is not duplicated by whirring cogs or digital vidcap, and neither is its contemporary, the graphic novel.
Following the recent tragic disassembly of stories by comic authors Alan Moore and Stan Lee (although Stan Lee endorses this) I found this excerpt of Dan Clowes' 1997 essay Modern Cartoonist: The Naked Truth quite appropriate (penned pre crappy Ghost World movie):
They [comics] are in a sense the ultimate domain of the artist who seeks to wield absolute control over his imagery. Novels are the work of one individual but they require visual collaboration on the part of the reader. Film is by its nature a collaborative endeavor. The filmmaker's vision, filtered through "reality," is more accessible to a general audience but in most cases less a precise, pre-conceived vision than one based on compromise and serendipity. Comics offer the creator a chance to control the specifics of his own world in both abstract and literal terms. As such, the best comics are usually done by a single creator, often an obsessive-compulsive type who spends hours fixing things and making tiny background details "just right." Nabokov (whose favorite artist was Saul Steinberg) has a good line: "There is nothing I loath more than a group activity, that communal bath where the hairy and slippery mix in multiplication of mediocrity." At its highest level of achievement, comics allow the creator to transmit vivid images from one specific imagination to another individual who may react as passively or actively as he sees fit, without an editor or panel of executives tweaking it to make it more "audience friendly."
And so my dissent has been expressed. Meanwhile Hollywood unbuckles, preparing to drop another Cleveland steamer on my childhood.
Recommended reading:
The entire Tintin series.