The film Who Framed Roger Rabbit? was very loosely based on a 1981 novel entitled Who Censored Roger Rabbit?, written by sci-fi author Gary Wolf.
Who Censored Roger Rabbit? basically was born out of a mixture of Wolf's fascination with noir novels and 1940's era comic strips; he wanted to somehow merge the two worlds together. Thus, he created the concept of having comic strip characters exist in real life.
The book has a few similarities to the film: Eddie Valiant, Roger and Jessica Rabbit, and Baby Herman are all in the book, along with a few of their basic character traits (Eddie attempts to battle alcoholism, and Jessica is just as buxom as in the movie version). Also, the general premise of a murder of a bigwig in the world of the 'toons is retained. However, this is where the similarities stop.
The plot of the book actually revolves around the "murder" (see below) of Roger Rabbit, as well as one of the heads of a major art syndicate (vaguely like Marvin Acme from the film). Valiant is charged with the investigation of the murder of Roger Rabbit, who happens to be in the middle of a divorce from Jessica Rabbit at the time. The plot eventually rolls along to discover that a "judge" advocating censorship is behind most of the actions, i.e. the Judge Doom character.
Another major difference is the 'toons themselves. In the film, the 'toons act, move, and talk like real people, vocalizing their thoughts and emotions directly. In the book, however, the 'toons simply make word balloons that say in a text form what they're thinking or feeling. This concept rolls over into what the 'toons do for a living; in the film, they make movies, while in the book, they are merely photographed, and the photographs when lined up make a comic strip.
Issues Dealt With In The Novel
The movie very gently deals with much of the same issues dealt with in the novel, but the novel really digs into many of them.
Censorship: Rather than actually being murdered, 'toons are instead censored, which for them is much the same as murder. The "dip" used in the movie is what is used for censorship. The book obviously takes a huge anti-censorship stance as can be gathered from the direct comparison of censorship and murder.
Racism: The 'toons are treated as second class people throughout the book, but the humanoid toons are treated with much more compassion than the non-humanoid toons, called "barnyard" 'toons. This leads to a clear caste system in which characters lower in the caste system are treated poorly simply because of their external appearance. This also leads to much of the trouble between Jessica and Roger, as Jessica (due to her "humanoid" toon status and buxom appearance) is seen as nearly human (a major plot point of the book is an affair that Jessica supposedly has with a human), while Roger is clearly in the "barnyard" class.
Alcoholism: The thread of Eddie's alcoholism runs deep throughout the book, pushing a large number of the questionable decisions that Eddie makes in the early stages in the book, as opposed to just a scene or two in the film. The causes for his alcoholism are also addressed, and they run much deeper than just the death of his brother.
Pornography: Pornography is a rather substantial issue in the book, mostly in terms of how it relates to censorship. One of the primary characters is a producer of pornographic comic books who alternates between being massively sleazy and semi-heroic as a protector of freedom of expression, in much the same way as Larry Flynt.
From The Novel To The Film
The book was picked up by Disney for film release in late 1981; Disney went on to announce that the film was in "production" in late 1982. However, due to the difficulties of adapting a somewhat edgy book into the family film that Disney wanted, the film kept getting pushed back. Finally, in 1985, the decision was made to basically scrap the whole book, leaving only the faintest structure, and then to pull pieces from the book together in a family-friendly framework.
The result was a very good family film with just a touch of dealing with other issues, but without the topical nature of the source book.
The book is available from Ballantine Books; although it is not actively printed, it is still relatively easy to find. Much harder to find is the sequel, Who P-p-plugged Roger Rabbit?, in which a formula is found that allows 'toons to become humans and vice-versa.