Ever see a movie based on a book that drives you to pick up a copy of the book? Or vice versa--read a book that sends you to the theater adaptation? Chances are you may be disappointed by one or the other...unless you are an author. I was conflicted after seeing "The Girl on the Train" at a theater recently. The flashbacks and setting locales were confusing. While reading the novel would have helped clear things up, it would have removed the suspense and "who-done-it" conclusion.
Any author who has gone through the editing process with a professional editor is often cautioned every scene should drive the story forward. Rule exceptions that stands out with a "but" are mysteries that requires red herrings--like Girl on a Train--or historicals that call attention to actual history. A backstory that reveals character may also earn a pass for adding length to a novel that may or may not be cruicial to the story.
A screenwriter's job is to taper that novel length down to a fixed number of screen minutes. That may mean vaporizing characters, dialog, and even some plot lines until a viable outline of the novel remains to be adapted. Even some of the author's "little darlings" that remain may end up on a cutting room floor once the screen editor does his job. If you've read the book first, at least you can plug in missing links to the story, however.
One of my favorite movies, Gone With The Wind, was a very large and popular novel that became a very long and popular classic movie. But when I read the book, I noticed several characters had been eliminated in the movie. Scarlett had two other children by her previous husbands before she married Rhett, and commentary about Civil War battles was obliterated by the character-driven plot. I appreciated the history in the novel, but I loved the streamlined romantic movie version that still took four hours to tell.
I felt the same about other favorite movies, after reading the books, Raintree County and Pride and Prejudice. The screen version of The Last of the Mohicans was almost unrecognizable as a book adaption when the romanticized Daniel Day Lewis movie was released twenty years ago. However, To Kill a Mockingbird was entertaining in both of its venues.
Some fans of Diana Gabaldon's Outlander books have commented about some of the casting in the Starz TV series of Outlander. Wrong hair or eye color, a different twist in the plot? I've read all the Outlander books and think the small screen version has brought the books to life with uncanny accuracy. Diana wrote one of the screenplays herself, and has been concordant about any changes, remarking instead on the talented cast and scriptwriters in the lavish production. I wholeheartedly agree. Adapting a novel to the screen is a huge validation and compliment to any author. And reading the book--before or after you see the screen version--can be a DOUBLE TREAT, even with a preference. Which do you prefer?