Okay, having listened to the writer commentary (screenwriter and novelist, a great combo), some adaptation notes:
- The novel was sparse, but much more dialogue heavy than the screenplay... and the final cut was even sparser than the screenplay. So both the screenwriter and the director/editor realised how much of the throughline could be told by performance.
- Dialogue for the screen works differently from dialogue in a book. The key word in script dialogue has to come at the end - lines/speeches have to end with a bang. In a book the key word (or concept) can be at the beginning, middle or end.
- The novel can build a pivotal event or relationship subtly over many minor incidents. The screenplay has to jump right to it and dramatise the situation more overtly. Two examples: Griet's attempted rape scene by the patron and the scene where Firth's character starts talking to Griet about painting technique in front of his wife, a transgression demonstrating how far their relationship has progressed.
- There is much more scope for backstory and subplot in a novel. The screenplay has to concentrate on the main plot and deal with the "now" more so than the "then".