Whilst most film makers strive to be original in there work, there is also a large and profitable market in creating films based on other media products. For example, there are several films adapted from...
Books
Books work as a great starting point for films as it provides the characters and story, so it makes it easier for film makers as now they can put their attention onto other aspects. Also, if a film is based on a book that has already been successful and found an audience, then it helps in terms of advertising as fans of the books will be excited to hear that it will now have a movie adaptation.It always prompt interest when a piece of literature in converted to film as it allows comparisons between the text and the screen. Comparisons can also be made between how the characters/setting/story are conveyed compared to our own visualisation when reading the original story.
However, while books have been converted to films for years and continue to be made, many argue that the film's never do the books justice and leave out important characters, plot points and details that made the original story so likable. One example of this is the Disney franchise and their adaptation of The Jungle Book, which recieved criticism for lacking Rudyard Kipling's original story and plot.
Also, it has become well-known in the film-industry that many authors will refuse to give the rights for their books to be changed into films. Authors such as Roald Dahl and Stephen King have publicly slated films based on their work and many fans will often share the opinion that the original book is better than the film. Yet, this does not stop audiences paying to see book-to-film adaptations in large amounts, regardless of the film's quality or how it compares to the original literature.
Some examples of films based on books include The Hobbit, Phyco, and The Lorax. (All the films listed share the same names with the book titles.)
Comics

Since comics are a similiar form to books, it makes sence that they too have been converted into film. This has lead to great success in terms of the superhero movie genre. Many classic superheros such as Superman, Spiderman and Captain America have found success both in their original comics but also when moved to the big screen. Due to the success of films such as The Avengers and Iron Man, which broke box office records, big-name film companies have paid millions to maintain the rights over comic book companies such as Marvel, owned by Disney, and DC, owned by Warner Bros. However, films based on comics are not limited to superheros, as children's comedies such as Garfield, Marmaduke and The Smurfs were all live-action adaptations of classic comic strips. Unlike books however, comics are told mainly through visuals - many of these visuals are used to influence the films artistic style. A new feature though is being able to hear the characters speak instead of text trapped in speech bubbles. Also, apposed to still images used in comics, motion can now be used and, in terms of superhero movies, this is much more benefitial for the action/fighting sequences.
Examples of films based on comic books include Batman, Dennis the Menace, and The Mask.
TV Shows
Television shows are possibly the easist to convert to film due to the similarities between the productuion process of creating a TV show and making a movie.While most film adaptation of TV shows will be created by the same cast and crew, there have been many that used a completely different set of actors and crew in there attempts to replict the original source material. While most TV episodes are 30 minutes long, the time frame is more than doubled for their film interpretations.
Examples of TV to film adaptations include Bewitched, 21 Jump Street, The Flintstones in Viva Rock Vegas, and Mr. Peabody and Sherman.
Video Games
Though possible the newest form of film adaptation listed, there are now many films in the production stage that are based on a video game. Since the great success of Disney's Wreck-It Ralph, a film based on the concept of video games and feature cameos from famous video game character, many film makers have jumped on the band wagon and decided to make video games into full length films.
In 2016 alone, film versions of Ratchet and Clank, World of Warcraft, and Angry Birds have all been scheduled for release.
Theatre Productions
Due to the success of broadway musicals and theatre productions, while many films are being converted into play, the opposite is also happening with many plays being made into movies. One of the biggest down sides to a musical being changed to film is the lack of audience, as this changes the atmosphere of the scene and what may work before a live theatre audience may not have the same effect on a cinema audience. Another disadvantage is that most theatre productions take just over 2 hours with an intermission half way through, while most films are 1 and a half hours and contain no breaks. Subsequently, large parts of the original version have to be removed in order to fill an alloted time.
Examples of theatre productions that have made the move to the big screen feature Into the Woods, The Sound of Music and Les Miserables.