movie adaptions vs book/comic versions

       I have always found it interesting when a book/comic is being turned into a movie and the changes they make. I become curious as to what will be put in/left out in the movie, compared to the books. One example of this is in the new Venom movie. The changes that were made really changes up the actual story in the comics. In the comics, the story of Venom starts off with Spider man first putting on the suite, not Eddy Brock. Also the story takes place in New York, but in the movie they are in San Francisco, California. There are a bunch of other details that I could list, but I feel like that may spoil the film so I won't mention them. Another example is the lack of details or explanation of events in the movies. One example of this is the Harry Potter franchise. In the books, there is so much more detail and information on the characters and events happening compared to the movies, were sometimes they gloss over some of this information. I feel this is probably due to time constants and the budget of the movies, still it is very interesting as to what they chose to leave out.