Under the copyright regime in the Hong Kong SAR, copyright subsists in:
Copyright protects the way that an idea is expressed.
Copyright does not protect the idea itself.
This is an important distinction.
Copyright protects a novel about time travel, but it does not protect the underlying subject matter of the novel.
Another author can therefore write about the same subject matter i.e. time travel without infringing the copyright in the first novel.
On the other hand, the copyright in the first novel is infringed if the way it is expressed is copied.
Copyright protects a photograph of a landscape, but it does not protect the underlying subject matter of the photograph.
Another photographer can therefore take photographs of the same landscape without infringing the copyright in the first photograph.
The copyright in the first photograph is infringed if the photograph is copied.